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2021, Vol. 62, No. 11　Online: 15 November 2021

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Single-atomic Pt sites anchored on defective TiO2 nanosheets as a superior photocatalyst for hydrogen evolution Xiaolong Hu, Junying Song, Jingli Luo, Hao Zhang, Zhiming Sun, Chunquan Li, Shuilin Zheng, Qingxia Liu 2021, 62(11): 1-10.  DOI: 10.1016/j.jechem.2021.03.003 Abstract ( 6 )   PDF (11763KB) ( 2 )   Single-atomic site catalysts have drawn considerable attention because of their maximum atom-utilization efficiency and excellent catalytic activity. In this work, a highly active single-atomic Pt site photocatalyst was synthesized through employing defective TiO2 nanosheets as solid support for photocatalytic water splitting. It indicated that the surface oxygen vacancies on defective TiO2 nanosheets could effectively stabilize the single-atomic Pt sites through constructing a three-center Ti-Pt-Ti structure. The Ti-Pt-Ti structure can hold the stability of isolated single-atomic Pt sites and facilitate the separation and transfer of photoinduced charge carriers, thereby greatly improving the photocatalytic H2 evolution. Notably, our synthesized photocatalyst exhibited a remarkably enhanced H2 evolution performance, and the H2 production rate is up to 13460.7 μmol·h-1·g-1, which is up to around 29.0 and 4.7 times higher than those of TiO2 nanosheets and Pt nanoparticles-TiO2. In addition, a plausible enhanced reaction mechanism was also proposed combining with photo-electrochemical characterizations and density functional theory (DFT) calculation results. Ultimately, it is believed that this work highlights the benefits of a single-site catalyst and paves the way to rationally design the highly active and stable single-atomic site photocatalysts on metal oxide support.

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Solar-harvesting lead halide perovskite for artificial photosynthesis SunJe Lee, Gyu Yong Jang, Jung Kyu Kim, Jong Hyeok Park 2021, 62(11): 11-26.  DOI: 10.1016/j.jechem.2021.02.025 Abstract ( 4 )   PDF (4656KB) ( 3 )   Facing the upcoming energy and environmental crisis, artificial photosynthesis for producing various solar fuels (e.g., hydrogen or carbon products) via a solar-to-chemical energy conversion is receiving increasing attention; however, its low conversion efficiency is a challenge for commercialization. To resolve low-efficiency issues, lead halide perovskite (LHP) with outstanding optoelectronic properties compared to conventional semiconductors can be a promising approach to improve the solar-to-fuel conversion reactions and solar fuel production efficiency. The tunable energy band structure and charge transport properties of LHP have promoted their extensive use in the production of solar fuels. This study summarizes the recent advancements of LHP-mediated solar-to-fuel conversions, classified by their redox reactions, namely solar water splitting, hydrohalic acid splitting, and CO2 reduction. Advanced approaches for achieving high conversion efficiency and long-term durability are discussed, including the configuration of devices, the composition of LHP, and the protection strategy of LHP. Moreover, the reaction mechanisms of LHP-mediated solar-to-chemical energy conversions and obstacles for enhancing the conversion efficiency are discussed. Finally, we present the perspectives on the development of LHP-incorporated solar-to-fuel conversion systems, which might open a new era of energy harvesting and storage.

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Recent progress in solution assembly of 2D materials for wearable energy storage applications Dong Zhou, Liang Zhao, Bo Li 2021, 62(11): 27-42.  DOI: 10.1016/j.jechem.2021.03.002 Abstract ( 5 )   PDF (11145KB) ( 1 )   Wearable energy storage devices are desirable to boost the rapid development of flexible and stretchable electronics. Two-dimensional (2D) materials, e.g., graphene, transition metal dichalcogenides and oxides, and MXenes, have attracted intensive attention for flexible energy storage applications because of their ultrathin 2D structures, high surface-to-volume ratio, and unique physical/chemical properties. To achieve commercialization of 2D material-based wearable energy storage devices (2DM-WESDs), scalable and cost-efficient manufacturing is a critical challenge. Among existing manufacturing technologies, solution-based assembly strategies show strong potential to achieve low-cost and scalable production. A timely review of the recent progress in solution-based assembly strategies and the resultant 2DM-WESDs will be meaningful to guide the future development of 2DM-WESDs. In this review, first, a brief introduction of exfoliation and solution preparation of 2D material species from bulk materials is discussed. Then, the solution-based assembly strategies are summarized, and the advantages and disadvantages of each method are compared. After that, two major categories of 2DM-WESDs, supercapacitor and battery, are discussed, emphasizing their state-of-the-art energy storage performances and flexibilities. Finally, insights and perspectives on current challenges and future opportunities regarding the solution assembly of 2DM-WESDs are discussed.

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Enhanced mass transfer in three-dimensional single-atom nickel catalyst with open-pore structure for highly efficient CO2 electrolysis Pengbo Zhai, Xiaokang Gu, Yi Wei, Jinghan Zuo, Qian Chen, Wei Liu, Huaning Jiang, Xingguo Wang, Yongji Gong 2021, 62(11): 43-50.  DOI: 10.1016/j.jechem.2021.03.011 Abstract ( 5 )   PDF (4532KB) ( 2 )   Design of efficient catalysts for electrochemical reduction of carbon dioxide (CO2) with high selectivity and activity is of great challenge, but significant for managing the global carbon balance. Herein, a series of three-dimensional (3D) single-atom metals anchored on graphene networks (3D SAM-G) with open-pore structure were successfully mass-produced via a facile in-situ calcination technique assisted by NaCl template. As-obtained 3D SANi-G electrode delivers excellent CO Faradaic efficiency (FE) of >96% in the potential range of -0.6 to -0.9 V versus reversible hydrogen electrode (RHE) and a high current density of 66.27 mA cm-2 at -1.0 V versus RHE, outperforming most of the previously reported catalysts tested in H-type cells. Simulations indicate that enhanced mass transport within the 3D open-pore structure effectively increases the catalytically active sites, which in turn leads to simultaneous enhancement on selectivity and activity of 3D SANi-G toward CO2 electroreduction. The cost-effective synthesis approach together with the microstructure design concept inspires new insights for the development of efficient electrocatalysts.

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Main group metal elements for ambient-condition electrochemical nitrogen reduction Ying Sun, Yu Wang, Hui Li, Wei Zhang, Xi-Ming Song, Da-Ming Feng, Xiaodong Sun, Baohua Jia, Hui Mao, Tianyi Ma 2021, 62(11): 51-70.  DOI: 10.1016/j.jechem.2021.03.001 Abstract ( 5 )   PDF (19704KB) ( 1 )   Electrocatalytic N2 reduction under ambient-condition is considered to be the most appealing strategy to the conventional Haber-Bosch process for synthetic ammonia to alleviate greenhouse emissions and reduce environmental pollution, mainly powered by renewable energy. Recent years, rapid advances have been gained in this attractive research field, and numerous electrocatalysts have been exploited. However, its conversion efficiency is still far behind the requirement of industrial applications owing to the breakage of the N≡N triple bond, which is an energetically challenging kinetically complex multistep reaction and the strong competing reaction of hydrogen evolution reaction. Recently, main group metal-based catalysts have been demonstrated promising application prospect for ammonia production, significantly boosting their further application in this field. However, a comprehensive review of main group metal-based catalysts towards electrochemical ammonia production applications is still lacking. In this review, the fundamentals of N2 reduction, such as the reaction pathways, the reaction potential and the challenges of N2 reduction have been comprehensively discussed. And then, the role, mechanism, and effect of each main group element-based catalysts used for N2 reduction (Li, K, Al, Ga, Sn, Sb, Bi, and their compounds) are systematically summarized. Finally, several state-of-the-art strategies to promote their NRR catalytic performance, as well as the existing problems and prospects are put forward. This review is expected to guide the design and establishment of more efficient electrocatalytic N2 reduction systems based on main group metal elements in the future.

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Copper-comprising nanocrystals as well-defined electrocatalysts to advance electrochemical CO2 reduction Jianfeng Huang, Tianyi Yang, Ke Zhao, Shuangqun Chen, Qin Huang, Yu Han 2021, 62(11): 71-102.  DOI: 10.1016/j.jechem.2021.03.009 Abstract ( 5 )   PDF (38284KB) ( 1 )   In the continuous development of electrochemical CO2 reduction (ECR), Cu-based electrocatalysts have received great attention, due to their unique ability to produce high value-added multicarbon products. Of particular interest are various Cu-comprising nanocrystals, not only because they usually show better catalytic properties than bulk materials, but also because their well-defined structures and highly tunable compositions facilitate in-depth mechanistic studies. This review aims to summarize the latest developments of electrocatalysts for ECR, with a focus on systems using Cu-comprising nanocrystals. We first give a general introduction to the field of ECR, covering the significance of this process, reaction mechanisms, catalyst evaluation criteria, and electrolytic cell configurations. Next, we discuss Cu-comprising nanocrystals developed for ECR by categorizing them into four groups: monometallic copper, copper-containing bimetals/multimetals, copper compounds, and copper-metal oxide hybrids; among these groups, we choose representative examples for detailed discussion on the synthetic methods, structural and compositional reaction sensitivities, and catalyst evolution during ECR. In the last section, we outline the challenges in this field from the fundamental and applicative aspects, and give perspectives on the expansion of catalyst varieties, the identification and preservation of active sites, and the exploration of industrially relevant operations for these nanocrystals. We hope the insights provided in this review will inspire the design and development of next-generation catalysts for ECR.

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Recent progresses in dry gas polymeric filters Samaneh Bandeh Ali, Hamid Ghasemi, Reyhaneh Ahmadi, Ali Ghaffari 2021, 62(11): 103-119.  DOI: 10.1016/j.jechem.2021.03.008 Abstract ( 4 )   PDF (10992KB) ( 1 )   Filtration and membrane separation are popular methods in gas separation since they are cost and energy efficient. Despite to air filters, there are comparatively few studies on dry gas filters, particularly at industrial scale. In fact, major unsolved challenges such as high efficiency, low pressure drop, long-term stability, high-thermal and chemical stability and advanced physiochemical properties, are still remained. The aim of this review is to scrutinize the advanced scientific and technological practices (such as selection of appropriate polymeric materials and additives, nanotechnology, modification techniques and preparation methods) towards design and fabrication of an efficient filter media for solid particles removal from the natural gas flow. Recent progresses in solid particle separation mechanisms, modeling and simulation techniques and the effect of membrane fabrication methods on its performance, strategies for modification of filter media, current challenges and future perspective are discussed.

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An almost full reversible lithium-rich cathode: Revealing the mechanism of high initial coulombic efficiency Dong Luo, Jianming Fan, Zhuo Yao, Huixian Xie, Jiaxiang Cui, Yajun Yang, Xiaokai Ding, Jiapeng Ji, Shuxing Wu, Ming Ling, Chenyu Liu, Zhan Lin 2021, 62(11): 120-126.  DOI: 10.1016/j.jechem.2021.03.005 Abstract ( 5 )   PDF (3178KB) ( 2 )   Low initial Coulombic efficiency (ICE) is an important impediment to practical application of Li-rich layered oxides (LLOs), which is due to the irreversible oxygen release. It is generally considered that surface oxygen vacancies are conducive to the improvement of ICE of LLOs. To reveal the relation of oxygen vacancies and ICE, sample PLO (Li-Mn-Cr-O) and its treated product (TLO) are comprehensive investigated in this work. During the treated process, part of oxygen atoms return to original constructed vacancies. It makes oxygen vacancies in sample TLO much poorer than those in sample PLO, and induces the formation of Li-poor spinel-layered integrated structure. Electrochemical measurement indicates the ICE of sample PLO is only 80.8%, while sample TLO is almost full reversible with the ICE of ~97.1%. In term of high-energy X-ray diffraction, scanning transmission electron microscopy, X-ray photoelectron spectroscopy and synchrotron hard/soft X-ray absorption spectroscopy, we discover that the ICE is difficult to be improved significantly just by building oxygen vacancies. LLOs with high ICE not only have to construct suitable oxygen vacancies, but also require other components with Li-poor structure to stabilize oxygen. This work provides deep insight into the mechanism of high ICE, and will contribute to the design and development of LLOs for next-generation high-energy lithium-ion batteries.

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A hydrophilic poly(methyl vinyl ether-alt-maleic acid) polymer as a green, universal, and dual-functional binder for high-performance silicon anode and sulfur cathode Hao Chen, Zhenzhen Wu, Zhong Su, Luke Hencz, Su Chen, Cheng Yan, Shanqing Zhang 2021, 62(11): 127-135.  DOI: 10.1016/j.jechem.2021.03.015 Abstract ( 4 )   PDF (9922KB) ( 2 )   Binders could play crucial or even decisive roles in the fabrication of low-cost, stable and high-capacity electrodes. This is especially the case for the silicon (Si) anodes and sulfur (S) cathodes that undergo large volume change and active material loss in lithium-ion batteries during prolonged cycles. Herein, a hydrophilic polymer poly(methyl vinyl ether-alt-maleic acid) (PMVEMA) was explored as a dual-functional aqueous binder for the preparation of high-performance silicon anode and sulfur cathode. Benefiting from the dual functions of PMVEMA, i.e., the excellent dispersion ability and strong binding forces, the as-prepared electrodes exhibit improved capacity, rate capability and long-term cycling performance. In particular, the as-prepared Si electrode delivers a high initial discharge capacity of 1346.5 mAh g-1 at a high rate of 8.4 A/g and maintains 834.5 mAh g-1 after 300 cycles at 4.2 A/g, while the as-prepared S cathode exhibits enhanced cycling performance with high remaining discharge capacities of 663.4 mAh g-1 after 100 cycles at 0.2 C and 487.07 mAh g-1 after 300 cycles at 1 C, respectively. These encouraging results suggest that PMVEMA could be a universal binder to facilitate the green manufacture of both anode and cathode for high-capacity energy storage systems.

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Low temperature surface oxygen activation in crystalline MnO2 triggered by lattice confined Pd single atoms Xuemei Liao, Yonghui Zhao, Changwen Liu, Xiaopeng Li, Yu Sun, Kenichi Kato, Miho Yamauchi, Zheng Jiang 2021, 62(11): 136-144.  DOI: 10.1016/j.jechem.2021.03.012 Abstract ( 5 )   PDF (9165KB) ( 1 )   Tuning the coordination environment is the research axis of single atom catalysts (SACs). SACs are commonly stabilized by various defects from support. Here, we report a lattice confined Pd SAC using MnO2 as support. Compared with the Pd clusters anchored on the surface, the lattice confined Pd single atoms allows spontaneous exaction of surrounding lattice oxygen at room temperature when employed in CO oxidation. The MnO2 supported Pd SAC exhibited a high turnover frequency of 0.203 s-1 at low reaction temperature, which is higher than that of recently reported Pd SACs. Theoretical calculations also confirmed the confined monatomic Pd activate lattice oxygen with an ultralow energy barrier. Our results illustrate that the unique coordination environment of single atom provided by lattice confinement is promising to boost the activity of SACs.

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General synthesis of hollow mesoporous conducting polymers by dual-colloid interface co-assembly for high-energy-density micro-supercapacitors Jing Cui, Fei-Fei Xing, Hao Luo, Jie-Qiong Qin, Yan Li, Yonghui Zhong, Facai Wei, Jianwei Fu, Chengbin Jing, Jiangong Cheng, Zhong-Shuai Wu, Shaohua Liu 2021, 62(11): 145-152.  DOI: 10.1016/j.jechem.2021.03.016 Abstract ( 5 )   PDF (10012KB) ( 1 )   Rational design and precise regulation over the morphology, structure, and pore size of functional conducting mesoporous polymers with enriched active sites and shorten electron-ion transport pathway are extremely important for developing high-performance micro-supercapacitors (MSCs), but still remain a great challenge. Herein, a general dual-colloid interface co-assembly strategy is proposed to fabricate hollow mesoporous polypyrrole nano-bowls (mPPy-nbs) for high-energy-density solid-state planar MSCs. By simply adjusting the size of block copolymer micelles, the diameter of polystyrene nanospheres and the amount of pyrrole monomer, mesopore size of the shell, void and shell thickness of mPPy-nbs can be simultaneously controlled. Importantly, this strategy can be further utilized to synthesize other hollow mesoporous polymers, including poly(tris(4-aminophenyl)amine), poly(1,3,5-triaminobenzene) and their copolymers, demonstrative of excellent universality. The structurally optimized mPPy-nb exhibits high specific surface area of 122 m2 g-1and large capacitance of 225 F g-1 at 1 mV s-1. Furthermore, the MSCs assembled by mPPy-nbs deliver impressive volumetric capacitance of 90 F cm-3 and energy density of 2.0 mWh cm-3, superior to the most reported polymers-based MSCs. Also, the fabricated MSCs present excellent flexibility with almost no capacitance decay under varying bending states, and robust serial/parallel self-integration for boosting voltage and capacitance output. Therefore, this work will inspire the new design of mesoporous conducting polymer materials toward high-performance microscale supercapacitive devices.

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In-situ/operando techniques to identify active sites for thermochemical conversion of CO2 over heterogeneous catalysts Kai Feng, Yaning Wang, Man Guo, Jingpeng Zhang, Zhengwen Li, Tianyu Deng, Zhihe Zhang, Binhang Yan 2021, 62(11): 153-171.  DOI: 10.1016/j.jechem.2021.03.054 Abstract ( 11 )   PDF (8794KB) ( 8 )   The catalytic conversion of CO2 to fuels or chemicals is considered to be an effective pathway to mitigate the greenhouse effect. To develop new types of efficient and durable catalysts, it is critical to identify the catalytic active sites, surface intermediates, and reaction mechanisms to reveal the relationship between the active sites and catalytic performance. However, the structure of a heterogeneous catalyst usually dynamically changes during reaction, bringing a great challenge for the identification of catalytic active sites and reaction pathways. Therefore, in-situ/operando techniques have been employed to real-time monitor the dynamic evolution of the structure of active sites under actual reaction conditions to precisely build the structure-function relationship. Here, we review the recent progress in the application of various in-situ/operando techniques in identifying active sites for catalytic conversion of CO2 over heterogeneous catalysts. We systematically summarize the applications of various optical and X-ray spectroscopy techniques, including Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and X-ray absorption spectroscopy (XAS), in identifying active sites and determining reaction mechanisms of the CO2 thermochemical conversion with hydrogen and light alkanes over heterogeneous catalysts. Finally, we discuss challenges and opportunities for the development of in-situ characterization in the future to further enlarge the capability of these powerful techniques.

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Synthetic poly-dioxolane as universal solid electrolyte interphase for stable lithium metal anodes Tao Chen, Haiping Wu, Jing Wan, Mengxue Li, Yucheng Zhang, Lin Sun, Yuncong Liu, Lili Chen, Rui Wen, Chao Wang 2021, 62(11): 172-178.  DOI: 10.1016/j.jechem.2021.03.018 Abstract ( 12 )   PDF (4553KB) ( 6 )   Lithium (Li) metal is a promising anode for the next generation high-energy-density batteries. However, the growth of Li dendrites, low coulombic efficiency and dramatic volume change limit its development. Here, we report a new synthetic poly-dioxolane (PDOL) approach to constructing an artificial 'elastic' SEI to stabilize the Li/electrolyte interface and the Li deposition/dissolution behavior in a variety of electrolytes. By coating PDOL with optimized molecular weights and synthetic routes on Li metal anode, the 'elastic' SEI layer could be maintained on top of the Li metal anode to accommodate the Li deposition/dissolution. No dendrite formation was observed during the cycling process, and the interfacial side reactions were reduced significantly. Consequently, we successfully achieved 330 cycles with a CE of 98.4% in ether electrolytes and 90 cycles with a CE of 94.3% in carbonate electrolytes. Simultaneously, the Li-metal batteries with LiFePO4 as cathodes also exhibited improved cycling performance. This strategy could promote the development of dendrite-free metal anodes toward high-performance Li-metal batteries.

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A strongly interactive adatom/substrate interface for dendrite-free and high-rate Li metal anodes Shun Li, Zhendong Li, Liyuan Huai, Mingming Ma, Kailin Luo, Jiahe Chen, Deyu Wang, Zhe Peng 2021, 62(11): 179-190.  DOI: 10.1016/j.jechem.2021.03.023 Abstract ( 6 )   PDF (14231KB) ( 5 )   Lithium (Li) metal is considered as one of the most promising anode materials to build next-generation high-energy-density batteries. Nonetheless, dendritic Li deposition has dramatically hindered the practical applications of Li metal batteries (LMBs). Uniformizing Li deposition is a prerequisite to achieve safe and practical LMBs. Herein, an underpotential deposition (UPD) process is first proposed to alter the kinetic and uniformity of Li deposition morphology. Based on the strong interaction between the Li adatoms and manganese (Mn) based substrate, a competition between the UPD and bulk Li deposition is observed, on which the predominance of the UPD scenario tends to uniformize Li nucleation and deposition by the surface coverage of Li monolayers at potentials that are more positive than the Nernst potential of Li metal. Inspired by this process, an advanced hybrid Mn-graphene oxide structure is developed for Li protection, not only enabling dendrite-free Li anodes for high-capacity and -current density cycling, but also improving the interfacial kinetic of Li metal anodes at subzero temperatures, showing potential applicability in low temperature conditions.

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Controlling phase transfer of molybdenum carbides by various metals for highly efficient hydrogen production Xingtao Sun, Jiafeng Yu, Xin Tong, Meng Yang, Jixin Zhang, Jian Sun 2021, 62(11): 191-197.  DOI: 10.1016/j.jechem.2021.03.022 Abstract ( 4 )   PDF (3024KB) ( 4 )   The α phase Mo carbide has been widely investigated recently for its high activity in hydrogen production from water gas shift (WGS) reaction. However, high loading of noble metals as well as high economic and environmental cost derived from high-temperature ammonification and carbonization process will lead to high cost of hydrogen production. Thus, the efficient controlling of phase transfer is promising. Herein, metals (Au, Pt, Rh, Cu) with a wide range of loadings were impregnated on flame spray pyrolysis (FSP) made MoO3 to produce Mo carbides by one-step carbonization. A breakthrough high metal-normalized hydrogen production rate of 213 mmol H2·gmetal-1·s-1 was achieved on 0.025 wt% Rh/MoCx, which was much higher than Pt and Au based Mo carbides ever reported. The addition of trace Rh induced direct MoO3 transformation to high purity α-MoC1-x in one-step carbonization instead of two-steps ammonification and carbonization process. In comparison to Rh, the addition of Pt, Au and Cu tend to transfer MoO3 into β-Mo2C at the same conditions. Besides, the one with 2 wt% Rh exhibited high stability in WGS reaction even at high temperature (300 °C) due to its inhibition on carbides oxidation induced by H2O. We demonstrate that it is feasible to control phase transfer of Mo carbides even by trace amount of metals to simplify the production process of catalysts. The catalytic performance improved by Rh in aspects of both activity and stability provides a guide for producing more stable Mo carbides catalysts.

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Sulfur-modified nickel selenide as an efficient electrocatalyst for the oxygen evolution reaction Kai Wan, Jiangshui Luo, Xuan Zhang, Palaniappan Subramanian, Jan Fransaer 2021, 62(11): 198-203.  DOI: 10.1016/j.jechem.2021.03.013 Abstract ( 4 )   PDF (3080KB) ( 2 )   The sluggish four-electron transfer of the oxygen evolution reaction (OER) limits the performance of water electrolyzers. Hence, OER electrocatalysts based on earth-abundant elements are urgently needed. Heteroatom doping has been an efficient approach to boost the intrinsic OER activity of the active sites by modifying the electronic structure. Here, a simple anion substitution strategy is reported that increases the OER activity of nickel selenides via a one-step hydrothermal treatment of a metal-organic framework precursor. The resulting S-substituted Ni3Se4 nanoparticles display distortion of their crystal lattice. As expected, the sulfur substitution modifies the electronic structure of Ni3Se4 and leads to outstanding electrocatalytic activity. All the S-substituted Ni3Se4 catalysts exhibit higher OER activities than the original Ni3Se4. The optimized catalyst achieves a current density of 10 mA cm-2 at an overpotential of 275 mV with a Tafel slope of 64 mV dec-1 in 1.0 M KOH. In addition to its electrochemical activity, the S-Ni3Se4-2 catalyst also exhibits good stability with only a 7.5% increase in overpotential at 50 mA cm-2 after 100 hours. This work demonstrates one strategy to modify the electronic structure of transition metal compounds by anion regulation.

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Electronic structure engineering in organic thermoelectric materials Xiaojuan Dai, Qing Meng, Fengjiao Zhang, Ye Zou, Chong-an Di, Daoben Zhu 2021, 62(11): 204-219.  DOI: 10.1016/j.jechem.2021.03.020 Abstract ( 5 )   PDF (11400KB) ( 6 )   Electronic structures, which play a key role in determining electrical and optical properties of π-conjugated organic materials, have attracted tremendous interest. Efficient thermoelectric (TE) conversion of organic materials has rigorous requirements on electronic structures. Recently, the rational design and precise modulation of electronic structures have exhibited great potential in exploring state-of-the-art organic TE materials. This review focuses on the regulation of electronic structures of organic materials toward efficient TE conversion. First, we present the basic knowledge regarding electronic structures and the requirements for efficient TE conversion of organic materials, followed by a brief introduction of commonly used methods for electronic structure characterization. Next, we highlight the key strategies of electronic structure engineering for high-performance organic TE materials. Finally, an overview of the electronic structure engineering of organic TE materials, along with current challenges and future research directions, are provided.

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Research progress on construction and energy storage performance of MXene heterostructures Fanfan Liu, Sen Jin, Qixun Xia, Aiguo Zhou, Li-Zhen Fan 2021, 62(11): 220-242.  DOI: 10.1016/j.jechem.2021.03.017 Abstract ( 7 )   PDF (16309KB) ( 2 )   MXenes are a family of two-dimensional (2D) transition metal carbides, carbonitrides/nitrides with superior physical and chemical properties, which have attracted extensive attention since the discovery in 2011. The impressive electrochemical activity of MXene makes it one of the most potential electrode materials in rechargeable batteries and supercapacitors. However, single-component MXene electrodes are difficult to achieve high specific capacity, efficient ion/electron transport, and high stability compatibility in an electrochemical environment. Studies have shown that it is an effective method to introduce nanomaterials between MXene layers to construct heterostructures and to improve the electrochemical performance through the synergistic effect among the components in the heterostructures. The introduction of nanomaterials can effectively suppress the restacking of MXene nanosheets, shorten the diffusion path of ions and promote the electrolyte transport, which is beneficial to enhance the rate performance of MXene; moreover, the excellent mechanical flexibility of MXene can reduce the volume expansion of nanomaterials during charge/discharge, thereby effectively protecting the integrity of the electrode structure and improving the cycling stability. Therefore, in this review, combined with theoretical calculations, we summarize the recent advances of MXene heterostructures in terms of synthesis strategies and energy storage applications, including supercapacitors, metal-ions batteries (Li, Na, K, Mg, Zn, Al) and metal anode protection. Furthermore, potential challenges and application perspectives for MXene heterostructures are also outlined.

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A bilateral cyano molecule serving as an effective additive enables high-efficiency and stable perovskite solar cells Pengyun Liu, Huimin Xiang, Wei Wang, Ran Ran, Wei Zhou, Zongping Shao 2021, 62(11): 243-251.  DOI: 10.1016/j.jechem.2021.03.024 Abstract ( 6 )   PDF (8454KB) ( 4 )   The existence of defects in perovskite films is a major obstacle that prevents perovskite solar cells (PSCs) from high efficiency and long-term stability. A variety of additives have been introduced into perovskite films for reducing the number of defects. Lewis base-based additive engineering has been considered as an effective way to eliminate defects, especially the defects caused by the uncoordinated Pb2+. In this work, for the first time, a bilateral cyano molecule (succinonitrile, SN) which is a commonly used plasticizer in solid electrolyte of solid-state lithium batteries was selected as an additive to modify organic-inorganic hybrid perovskite films in PSCs. SN is featured with two cyano groups (-C≡N) distributing at both terminals of the carbon chain, providing two cross-linking points to interact with perovskites crystals via coordinating with uncoordinated Pb2+ and forming hydrogen bonds with -NH2 groups in perovskite. It was found that the addition of SN into perovskite precursor solution could effectively reduce defects, particularly inhibit the appearance of Pb0 and thus suppress trap-assisted nonradiative charge carrier recombination. As a result, the efficiency of CH3NH3PbI3(Cl) (MAPbI3(Cl))-based PSCs was improved from 18.4% to 20.3% with enhanced long-term stability at N2 and humid air atmosphere. This work provides a facile and effective strategy to enhance the PCE and stability of PSCs simultaneously, facilitating the commercialization of PSCs.

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Oxygen vacancies enriched nickel cobalt based nanoflower cathodes: Mechanism and application of the enhanced energy storage Jiahui Ye, Xingwu Zhai, Long Chen, Wen Guo, Tiantian Gu, Yulin Shi, Juan Hou, Fei Han, Yi Liu, Changchun Fan, Gang Wang, Shanglong Peng, Xuhong Guo 2021, 62(11): 252-261.  DOI: 10.1016/j.jechem.2021.03.030 Abstract ( 6 )   PDF (10051KB) ( 2 )   The rational design of oxygen vacancies and electronic microstructures of electrode materials for energy storage devices still remains a challenge. Herein, we synthesize nickel cobalt-based oxides nanoflower arrays assembled with nanowires grown on Ni foam via the hydrothermal process followed annealing process in air and argon atmospheres respectively. It is found that the annealing atmosphere has a vital influence on the oxygen vacancies and electronic microstructures of resulting NiCo2O4 (NCO-Air) and CoNiO2 (NCO-Ar) products, which NCO-Ar has more oxygen vacancies and larger specific surface area of 163.48 m2/g. The density functional theory calculation reveals that more oxygen vacancies can provide more electrons to adsorb -OH free anions resulting in superior electrochemical energy storage performance. Therefore, the assembled asymmetric supercapacitor of NCO-Ar//active carbon delivers an excellent energy density of 112.52 Wh/kg at a power density of 558.73 W/kg and the fabricated NCO-Ar//Zn battery presents the specific capacity of 180.20 mAh/g and energy density of 308.14 Wh/kg. The experimental measurement and theoretical calculation not only provide a facile strategy to construct flower-like mesoporous architectures with massive oxygen vacancies, but also demonstrate that NCO-Ar is an ideal electrode material for the next generation of energy storage devices.

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A review of fire-extinguishing agent on suppressing lithium-ion batteries fire Shuai Yuan, Chongye Chang, Shuaishuai Yan, Pan Zhou, Xinming Qian, Mengqi Yuan, Kai Liu 2021, 62(11): 262-280.  DOI: 10.1016/j.jechem.2021.03.031 Abstract ( 50 )   PDF (4452KB) ( 41 )   Safety issue of lithium-ion batteries (LIBs) such as fires and explosions is a significant challenge for their large scale applications. Considering the continuously increased battery energy density and wider large-scale battery pack applications, the possibility of LIBs fire significantly increases. Because of the fast burning and the easy re-ignition characteristics of LIBs, achieving an efficient and prompt LIBs fire suppression is critical for minimizing the fire hazards. Different from conventional fire hazards, the LIBs fire shows complicated and comprehensive characteristics, and an effective and suitable fire-extinguishing agent particularly designed for LIBs is highly desirable. Considerable efforts have been devoted to this topic, to the best of our knowledge, a comprehensive review on this regard is still rare. Moreover, in practice, a guidance for the design and selections of a proper fire-extinguishing agent for LIBs is urgently needed. Herein, the special mechanisms and characteristics for LIBs fire and the corresponding design principles for LIBs fire-extinguishing agent were introduced. It is revealed that a fire-extinguishing agent developed for LIBs fire will most likely need a high heat capacity, high wetting, low viscosity and low electrical conductivity. After a comprehensive comparison of these agents in terms of these performances, water-based fire-extinguishing agents show best. Several typical fire-extinguishing agents such as gaseous agents, dry powders, water-based and aerosol fire-extinguishing agents were then introduced, and their fire extinguishment mechanisms were presented. Finally, their effectiveness in suppressing the fire were summarized. Water-based fire-extinguishing agents possess high cooling capacity and excellent anti-reflash performance for the fire. We believe this review could shed light on developing an efficient fire-extinguishing agent particularly designed for LIBs.

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Cation-vacancy induced Li+ intercalation pseudocapacitance at atomically thin heterointerface for high capacity and high power lithium-ion batteries Ding Yuan, David Adekoya, Yuhai Dou, Yuhui Tian, Hao Chen, Zhenzhen Wu, Jiadong Qin, Linping Yu, Jian Zhang, Xianhu Liu, Shi Xue Dou, Shanqing Zhang 2021, 62(11): 281-288.  DOI: 10.1016/j.jechem.2021.03.045 Abstract ( 3 )   PDF (9616KB) ( 1 )   It is challenging to create cation vacancies in electrode materials for enhancing the performance of rechargeable lithium ion batteries (LIBs). Herein, we utilized a strong alkaline etching method to successfully create Co vacancies at the interface of atomically thin Co3-xO4/graphene@CNT heterostructure for high-energy/power lithium storage. The creation of Co-vacancies in the sample was confirmed by high-resolution scanning transmission electron microscope (HRSTEM), X-ray photoelectron spectroscopy (XPS) and electron energy loss near-edge structures (ELNES). The obtained Co3-xO4/graphene@CNT delivers an ultra-high capacity of 1688.2 mAh g-1 at 0.2 C, excellent rate capability of 83.7% capacity retention at 1 C, and an ultralong life up to 1500 cycles with a reversible capacity of 1066.3 mAh g-1. Reaction kinetic study suggests a significant contribution from pseudocapacitive storage induced by the Co-vacancies at the Co3-xO4/graphene@CNT interface. Density functional theory confirms that the Co-vacancies could dramatically enhance the Li adsorption and provide an additional pathway with a lower energy barrier for Li diffusion, which results in an intercalation pseudocapacitive behavior and high-capacity/rate energy storage.

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New insights into “dead lithium” during stripping in lithium metal batteries Xiao-Ru Chen, Chong Yan, Jun-Fan Ding, Hong-Jie Peng, Qiang Zhang 2021, 62(11): 289-294.  DOI: 10.1016/j.jechem.2021.03.048 Abstract ( 28 )   PDF (2617KB) ( 17 )   Lithium (Li) metal attributes to the promising anode but endures the low Columbic efficiency (CE) and safety issues from the inactive Li accumulation. The metallic Li which is isolated from the lithium anode (named dead Li0) consists the major component of the inactive Li. We systematically and meticulously investigated the formation and evaluation of dead Li0 during stripping process from electron transfer, the oxidation of Li0 to Li+ and the diffusion of Li+ through solid electrolyte interphase (SEI). The above-mentioned processes were regulated by adjusting the contact sites of electron channels, the dynamic rate of conversion from Li0 to Li+, and the structure as well as components of SEI. The design principles for achieving less dead Li0 and higher CE are proposed as a proof of concept in lithium metal batteries. This new insight sheds a comprehensive light on dead Li0 formation and guides the next-generation safe batteries for future application.

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Contribution to the understanding of the performance differences between commercial current collectors in Li-S batteries A. Benítez, F. Luna-Lama, A. Caballero, E. Rodríguez-Castellón, J. Morales 2021, 62(11): 295-306.  DOI: 10.1016/j.jechem.2021.03.014 Abstract ( 8 )   PDF (10130KB) ( 3 )   Lithium-sulfur batteries have been recognised as highly promising next-generation batteries, due to their low cost and high theoretical energy density. Despite numerous advances in this technology over the last decade, its commercialisation is still a challenge that has not yet been achieved. Many efforts have been made to improve the problems that these batteries present, mainly by investigating different cathode manufacturing strategies, testing novel Li anodes, new additives in the electrolytes, and modified separators or interlayers. However, the characteristics of the current collectors used in the preparation of the electrodes have been rarely addressed. Three commercial collectors are commonly used in basic research on Li-S batteries: Al foil, carbon coated Al foil (Al-C), and carbon paper (gas diffusion layer, GDL). In this work, a detailed study of the electrochemical response of these commercial collectors has been carried out. The tests were carried out on two S composites formed by carbons of a different natures, commercial carbon black and synthetic N-doped graphene. In addition, the S impregnation method was different, using either melt diffusion at 155 °C or ethylenediamine as S solvent, respectively. In both systems, the results were similar -the electrodes supported on GDL delivered higher specific capacities than those supported on Al and Al-C, with minimal differences between the two. Of the different collector properties examined to explain this behaviour, namely Al corrosion, electrical conductivities, surface-level composition, and surface texture, only the latter had a significant effect in the performance of GDL-based electrodes. SEM images revealed a rough and cracked surface formed by the agglomerated carbon particles that give rise to a complex pore system, predominantly consisting of macropores. All of these features are beneficial for a better anchoring of the active material on the collector surface, in addition to enhancing the wettability of the electrolyte and favouring reaction kinetics. In contrast, the Al-based collector possesses a very smooth and non-porous surface, detrimental to both the active material-substrate interface and the active material impregnation by the electrolyte.

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Improvement in potassium ion batteries electrodes: Recent developments and efficient approaches Syed Musab Ahmed, Guoquan Suo, Wei Alex Wang, Kai Xi, Saad Bin Iqbal 2021, 62(11): 307-337.  DOI: 10.1016/j.jechem.2021.03.032 Abstract ( 3 )   PDF (22366KB) ( 1 )   Demand for efficient and continuous application for high-grid energy storage systems involves the study towards novel battery technologies. Hence, considering the vast naturally available resources of potassium all over the world and its encouraging intercalation chemistries, it has recently enticed attention in electrochemical energy storage industry in the form of potassium ion batteries (PIBs). The major factor in this K+ based battery, is to develop efficient approaches to manufacture electrode substance to intercalate its big size potassium ions with considerable voltage, kinetics, charge/discharge capacity, capacity retention, cost, etc. This study contributes in the recent developments of anode and cathode materials for PIBs, including several electrode materials in regards to synthesis, structure, electrochemical performance, and K-storage mechanisms. Finally, the review contributes to provide helpful sources for the increasing number of scientists working in this industry regarding its critical issues and challenges and also to indicate the future direction of electrode materials in PIBs.

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State-of-the-art progress in the selective photo-oxidation of alcohols Zewen Shen, Yezi Hu, Bingfeng Li, Yingtong Zou, Shaojun Li, G. Wilma Busser, Xiangke Wang, Guixia Zhao, Martin Muhler 2021, 62(11): 338-350.  DOI: 10.1016/j.jechem.2021.03.033 Abstract ( 4 )   PDF (4220KB) ( 2 )   Photocatalytic oxidation of alcohols has received more and more attention in recent years following the numerous studies on the degradation of pollutants, hydrogen evolution, and CO2 reduction by photocatalysis. Instead of the total oxidation of organics in the degradation process, the photo-oxidation of alcohols aims at the selective conversion of alcohols to produce carbonyl/acid compounds. Promising results have been achieved in designing the catalysts and reaction system, as well as in the mechanistic investigations in the past few years. This review summarizes the state-of-the-art progress in the photo-oxidation of alcohols, including the development of photocatalysts and cocatalysts, reaction conditions including the solvent and the atmosphere, and the exploration of mechanisms with scavengers experiment, electron paramagnetic resonance (EPR) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The challenges and outlook for the further research in this field are also discussed.

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The nature of irreversible phase transformation propagation in nickel-rich layered cathode for lithium-ion batteries Feng Wu, Na Liu, Lai Chen, Ning Li, Jinyang Dong, Yun Lu, Guoqiang Tan, Mingzhe Xu, Duanyun Cao, Yafei Liu, Yanbin Chen, Yuefeng Su 2021, 62(11): 351-358.  DOI: 10.1016/j.jechem.2021.03.035 Abstract ( 8 )   PDF (12116KB) ( 8 )   Ni-rich layered cathode is regarded as one of the most promising candidates to achieve lithium-ion batteries (LIBs) with high energy density. However, due to the irreversible phase transformation (IPT) and its eventual propagation from surface to the bulk of the material, Ni-rich layered cathode typically suffers from severe capacity fading, structure failure, and thermal instability, which greatly hinders its mass adoption. Hence, achieving an in-depth understanding of the IPT propagation mechanism in Ni-rich layered cathode is crucial in addressing these issues. Herein, the triggering factor of IPT propagation in Ni-rich cathode is verified to be the initial surface disordered cation mixing domain covered by a thin rock-salt phase, instead of the rock-salt phase itself. According to the density functional theory (DFT) results, it is further illustrated that the metastable cation mixing domain possesses a lower Ni migration energy barrier, which facilitates the migration of Ni ions towards the Li slab, and thus driving the propagation of IPT from surface to the bulk of the material. This finding clarifies a prevailing debate regarding the surface impurity phases of Ni-rich cathode material and reveals the origin of IPT propagation, which implies the principle and its effectiveness of tuning the surface microstructure to address the structural and thermal instability issue of Ni-rich layered cathode materials.

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Triggering in-plane defect cluster on MoS2 for accelerated dinitrogen electroreduction to ammonia Wanru Liao, Ke Xie, Lijuan Liu, Xiuyun Wang, Yu Luo, Shijing Liang, Fujian Liu, Lilong Jiang 2021, 62(11): 359-366.  DOI: 10.1016/j.jechem.2021.03.043 Abstract ( 3 )   PDF (4469KB) ( 3 )   Electrochemical nitrogen reduction reaction (eNRR) is an alternative promising manner for sustainable N2 fixation with low-emission. The major challenge for developing an efficient electrocatalyst is the cleaving of the stable N≡N triple bonds. Herein, we design a new MoS2 with in-plane defect cluster through a bottom-up approach for the first time, where the defect cluster is composed of three adjacent S vacancies. The well-defined in-plane defect clusters could contribute to the strong chemical adsorption and activation towards inert nitrogen, achieving an excellent eNRR performance with an ammonia yield rate of 43.4 ± 3 μg h-1 mgcat.-1 and a Faradaic efficiency of 16.8 ± 2% at -0.3 V (vs. RHE). The performance is much higher than that of MoS2 with the edge defect. Isotopic labeling confirms that N atoms of produced NH4+ originate from N2. Furthermore, the in-plane defect clusters realized the alternate hydrogenation of nitrogen in a side-on way to synthesize ammonia. This work provides a prospecting strategy for fine-tuning in-plane defects in a catalyst, and also promotes the progress of eNRR.

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Degradation study on tin-and bismuth-based gas-diffusion electrodes during electrochemical CO2 reduction in highly alkaline media Fabian Bienen, Armin Löwe, Joachim Hildebrand, Sebastian Hertle, Dana Schonvogel, Dennis Kopljar, Norbert Wagner, Elias Klemm, Kaspar Andreas Friedrich 2021, 62(11): 367-376.  DOI: 10.1016/j.jechem.2021.03.050 Abstract ( 9 )   PDF (6218KB) ( 4 )   This work investigated the degradation of tin -based gas-diffusion electrodes (GDE) and also a promising Bi2O3 GDE in electrochemical CO2 reduction in highly alkaline media which has not been studied before. The contributions of the electrode wetting (or flooding, if excessively) and catalyst leaching on the degradation were analyzed. Therefore, electrochemical impedance spectroscopy was used to monitor the wetted surface area of the GDE in combination with post-mortem analysis of the penetration depth by visualizing the electrolyte's cation in the GDE cross-section. Furthermore, to reveal a possible degradation of the electrocatalyst, its distribution was mapped in the GDEs cross-section after operation while the catholyte was additionally analyzed via ICP-MS. The results clearly demonstrate that the SnO2 catalyst dissolves in the reaction zone inside the GDE and might be partially redeposited near the GDEs surface. Since the redeposition process occurs only partially a steady loss of catalyst was observed impeding a clear distinction of the two degradation phenomena. Nevertheless, the deterioration of the electrode performance measured as faraday efficiency (FE) of the parasitic hydrogen evolution reaction (HER) qualitatively correlates with the differential double layer capacitance (Cdl). A significant difference of the rate of increase for the hydrogen FE and Cdl can be ascribed to the superposition of both above-mentioned degradation mechanisms. The demonstrated instability of SnO2 contrasts with the behavior of Bi2O3 GDE which is stabilized during CO2 conversion by redeposition of the diluted dissolved species as metallic Bi which is active for the CO2 reduction reaction.

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Recent advances in catalytic systems for CO2 conversion to substitute natural gas (SNG): Perspective and challenges I. Hussain, A.A. Jalil, N.S. Hassan, M.Y.S. Hamid 2021, 62(11): 377-407.  DOI: 10.1016/j.jechem.2021.03.040 Abstract ( 11 )   PDF (29776KB) ( 9 )   It has been well established that carbon dioxide (CO2) is one of the main greenhouse gasses and a leading driver of climate change. The chemical conversion of CO2 to substitute natural gas (SNG) in the presence of renewable hydrogen is one of the most promising solutions by a well-known process called CO2 methanation. There have been comprehensive efforts in developing effective and efficient CO2 methanation catalytic systems. However, the choice of competitive and stable catalysts is still a monumental obstruction and a great challenge towards the commercialization and industrialization of CO2 methanation. It is necessary to emphasize the critical understandings of intrinsic and extrinsic interactions of catalyst components (active metal, support, promoter, etc.) for enhanced catalytic performance and stability during CO2 methanation. This study reviews the up-to-date developments on CO2 methanation catalysts and the optimal synergistic relationship between active metals, support, and promoters during the catalytic activity. The existing catalysts and their novel properties for enhanced CO2 methanation were elucidated using the state-of-the-art experimental and theoretical techniques. The selection of an appropriate synthesis method, catalytic activity for CO2 methanation, deactivation of the catalysts, and reaction mechanisms studies, have been explicitly compared and explained. Therefore, future efforts should be directed towards the sustainable developments of catalytic configurations for successful industrial applications of CO2 utilization to SNG using CO2 methanation.

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Boosting lithium batteries under harsh operating conditions by a resilient ionogel with liquid-like ionic conductivity Le Yu, Qing Liu, Libin Wang, Songtao Guo, Qiaomei Hu, Yaqian Li, Xiwei Lan, Zhifang Liu, Xianluo Hu 2021, 62(11): 408-414.  DOI: 10.1016/j.jechem.2021.03.042 Abstract ( 6 )   PDF (2539KB) ( 2 )   New chemistries are being developed to increase the capacity and power of rechargeable batteries. However, the risk of safety issues increases when high-energy batteries using highly active materials encounter harsh operating conditions. Here we report on the synthesis of a unique ionogel electrolyte for abuse-tolerant lithium batteries. A hierarchically architected silica/polymer scaffold is designed and fabricated through a facile soft chemistry route, which is competent to confine ionic liquids with superior uptake ability (92.4 wt%). The monolithic ionogel exhibits high conductivity and thermal/mechanical stability, featuring high-temperature elastic modulus and dendrite-free lithium cycling. The Li/LiFePO4 pouch cells achieve outstanding cyclability at different temperatures up to 150 °C, and can sustain cutting, crumpling, and even coupled thermal-mechanical abuses. Moreover, the solid-state lithium batteries with LiNi0.60Co0.20Mn0.20O2, LiNi0.80Co0.15Al0.05O2, and Li1.2Mn0.54Ni0.13Co0.13O2 cathodes demonstrate excellent cycle performances at 60 °C. These results indicate that the resilient and high-conductivity ionogel electrolyte is promising to realize high-performance lithium batteries with high energy density and safety.

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Self-template synthesis of hollow Fe-doped CoP prisms with enhanced oxygen evolution reaction activity Xueda Ding, Haitao Huang, Qiang Wan, Xu Guan, Yuanxing Fang, Sen Lin, Dongyang Chen, Zailai Xie 2021, 62(11): 415-422.  DOI: 10.1016/j.jechem.2021.04.001 Abstract ( 4 )   PDF (4456KB) ( 3 )   The development of efficient, durable and low cost electrocatalysts is crucial but extremely challenging for the oxygen evolution reaction (OER). Herein, we develop a self-template strategy to synthesize hollow Fe-doped CoP prisms (Fe-CoP) via ion exchange of cobalt acetate hydroxide with [Fe(CN)6]3- and phosphorization-induced transformation of CoFe-PBA (Co/Fe-containing prussian blue analogue) prisms in N2 atmosphere. The obtained Fe-CoP not only inherits the hollow prism-like morphology of CoFe-PBA, but also forms rich mesoporous channel. The Fe-CoP prisms exhibit extraordinary OER performances in 1.0 M KOH, with a low overpotential of 236 mV to deliver a current density of 10 mA cm-2 and a low Tafel slope of 32.9 mV dec-1. Moreover, the presented electrocatalyst shows good long-term operating durability and activity. The XPS and TEM analysis confirm that Fe-CoP has undergone surface reconstruction in the process of electrocatalytic OER, and the in situ formed oxides and oxyhydroxides are the real active species to boost OER. This work provides a promising pathway to the design and synthesis of efficient and robust electrocatalysts with hierarchical hollow structure for boosting OER.

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A thermoresponsive composite separator loaded with paraffin@SiO2 microparticles for safe and stable lithium batteries Hao Dong, Peican Wang, Shuaishuai Yan, Yingchun Xia, Baoguo Wang, Xiaolin Wang, Kai Liu 2021, 62(11): 423-430.  DOI: 10.1016/j.jechem.2021.03.046 Abstract ( 5 )   PDF (3373KB) ( 2 )   Lithium-ion batteries (LIBs)-related accidents have been reported for years and safety issues are stumbling blocks for the practical applications of lithium metal batteries (LMBs) with higher energy density. More effective strategies to shut down the battery at the early stage of thermal runaway with less side effects on the electrochemical performance are greatly desired. In this work, the core-shell structural paraffin@SiO2 microparticles were synthesized by in situ emulsion interfacial hydrolysis and polycondensation and the paraffin@SiO2-loaded separator (PSS) was prepared by a facile filtration method. The introduction of hydrophilic silica shells in paraffin@SiO2 enhanced the wettability of carbonate electrolyte with the composite separator and improved the processability of soft paraffin. As a result, when used in LMBs at room temperature, the cell with PSS inside had a more uniform deposition of lithium, a much lower overpotential and a more stable electrochemical performance than the cell with the blank separator or the conventional pure paraffin-loaded separator inside. More significantly, when a heating stimulation (i.e. 115 ℃) was subjected to the cell with PSS inside, the paraffin in the core of paraffin@SiO2 could be released, blocking the gaps between particles and the pores in the separator and efficiently stopping the transportation of Li+ between two electrodes, resulting in the thermally-induced shutdown of the cell below the melting temperature of PE (~135 ℃) in the Celgard2325 separator. The core-shell structure of paraffin@SiO2 enables the maintaining of each component's benefits while avoiding each one's drawbacks by elaborating microstructural design. Therefore, the conventional dilemma between the electrochemcial performance and safety of LMBs could be solved in the future.

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Magnesium hydride nanoparticles anchored on MXene sheets as high capacity anode for lithium-ion batteries Shulin Zhong, Shunlong Ju, Yifei Shao, Wei Chen, Tengfei Zhang, Yuqin Huang, Hongyu Zhang, Guanglin Xia, Xuebin Yu 2021, 62(11): 431-439.  DOI: 10.1016/j.jechem.2021.03.049 Abstract ( 2 )   PDF (13884KB) ( 2 )   Magnesium hydride, with high specific capacity, favorable voltage profile and low voltage hysteresis properties, is regarded as a promising anode for lithium storage. However, the rapid fading of capacity caused by huge volume change, low electron/ion conduction, and spontaneous agglomeration of active materials during cycling greatly limit its practical application in lithium-ion batteries. Herein, we report the synthesis of monodisperse MgH2 nanoparticles with an average particle size of <20 nm homogeneously anchored on Ti3C2 MXene sheets by bottom-up self-assembly strategy. The unique nanoarchitectures are able to efficiently enhance the lithium insertion/extraction kinetics, accelerate the electron/lithium ion transfer and buffer the strain of volume changes. More importantly, the formed F-Mg bounding between MgH2 and MXene could avoid the shedding of MgH2 nanoparticles to electrolyte during cycling, which significantly enhance the capacity, cyclability, and rate performance of magnesium hydride. Moreover, due to the high density of MXene and the synergistic effect between the MgH2 and MXene matrix, the MgH2/MXene composite with 60 wt% MgH2 delivers a superior volumetric capacity of 1092.9 mAh cm-3 at a current density of 2000 mA g-1 after 1000 cycles. These results highlight the great promising of MgH2/MXene composite for high performance lithium-ion batteries.

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Recycling valuable cobalt from spent lithium ion batteries for controllably designing a novel sea-urchin-like cobalt nitride-graphene hybrid catalyst: Towards efficient overall water splitting Tingting Liu, Sheng Cai, Genfu Zhao, Zhihui Gao, Shuming Liu, Huani Li, Lijuan Chen, Mian Li, Xiaofei Yang, Hong Guo 2021, 62(11): 440-450.  DOI: 10.1016/j.jechem.2021.03.052 Abstract ( 4 )   PDF (7828KB) ( 2 )   Along with the continuous consumption in lithium-ion batteries (LIBs), the price of cobalt is inevitably going up in recent years. Therefore, recycling valuable Co element from spent devices, and boosting its service efficiency are becoming two indispensable approaches to promote the utilization of Co in various energy conversion/storage devices. Herein, we realize the recovery of Co from spent LIBs and synthesize a three-dimensional (3D) sea-urchin-like cobalt nitride composite material (labeled as CoN-Gr-2), which is used as a bi-functional catalyst for water splitting. Benefiting from the intrinsic high conductivity, larger surface area and unique 3D sea-urchin-like architecture, CoN-Gr-2 shows an excellent electron transfer efficiency, highly exposed active sites as well as the superior mass transport capacity. The CoN-Gr-2 catalyst exhibits low overpotentials of 128.9 mV and 280 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), which are comparable to the commercial 20 wt% Pt/C and RuO2 catalysts. Moreover, when adopting CoN-Gr-2 as both anode and cathode materials for overall water splitting (in 1.0 M KOH electrolyte), the assembled cell achieves a current density of 10 mA cm-2 at 1.61 V, which almost close to that of Pt/C||RuO2 benchmark (1.60 V), demonstrating its superior water-splitting efficiency. Meanwhile, the CoN catalysts exhibit strong chemical interaction with the Gr support, suppressing the aggregation of CoN catalysts and maintains their high activity during HER and OER reactions. So, the cell exhibits a high current retention of 97.3% after 40 h. This work successfully develops an industrial chain from recycling Co wastes in spent energy devices to controllably designing 3D sea-urchin-like CoN-Gr with high water splitting efficiency. Therefore, it could further promote the efficient utilization of valuable Co element in various energy devices.

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Fully-inorganic strontium incorporated CsPbI2Br perovskite solar cells with promoted efficiency and stability Jyoti V. Patil, Sawanta S. Mali, Chang Kook Hong 2021, 62(11): 451-458.  DOI: 10.1016/j.jechem.2021.04.003 Abstract ( 6 )   PDF (10036KB) ( 1 )   In the present investigation, we fabricated strontium (Sr2+) incorporated CsPbI2Br-based inorganic perovskite solar cells in ambient conditions. The morphology, crystallinity, absorption, elemental composition and photoluminescence analysis of the bare CsPbI2Br and CsPb1-xSrxI2Br perovskite thin films were studied systematically to investigate the role of Sr2+ incorporation. It is observed that the surface morphology of the CsPbI2Br perovskite thin film has been improved by partial substitution of Pb2+ by Sr2+ which facilitates photoactive black phase-stabilization and defect passivation. The champion device having CsPb0.98Sr0.02I2Br composition exhibited a power conversion efficiency (PCE) of 16.61% which is much higher than the bare device (13.65%). Furthermore, our CsPb0.98Sr0.02I2Br-based devices maintain > 85% of its initial efficiency over 100 h in ambient conditions.

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Recent advances of Cu-based hole transport materials and their interface engineering concerning different processing methods in perovskite solar cells Tengling Ye, Xiaochen Sun, Xiaoru Zhang, Sue Hao 2021, 62(11): 459-476.  DOI: 10.1016/j.jechem.2021.04.002 Abstract ( 2 )   PDF (12708KB) ( 1 )   In recent years, perovskite solar cells (PSCs) have become a much charming photovoltaic technology and have triggered enormous studies worldwide, owing to their high efficiency, low cost and ease of preparation. The power conversion efficiency has rapidly increased by more than 6 times to the current 25.5% in the past decade. Hole transport materials (HTMs) are an indispensable part of PSCs, which great affect the efficiency, the cost and the stability of PSCs. Inorganic Cu-based p-type semiconductors are a kind of representative inorganic HTMs in PSCs due to their unique advantages of rich variety, low cost, excellent hole mobility, adjustable energy levels, good stability, low temperature and scalable processing ability. In this review, the research progress in new materials and the control of photoelectric properties of Cu-based inorganic HTMs were first summarized systematically. And then, concerning different processing methods, advances of the interface engineering of Cu-based hole transport layers (HTLs) in PSCs were detailly discussed. Finally, the challenges and future trends of Cu-based inorganic HTMs and their interface engineering in PSCs were analyzed.

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Circumventing chemo-mechanical failure of Sn foil battery anode by grain refinement and elaborate porosity design Shuibin Tu, Xin Ai, Xiancheng Wang, Siwei Gui, Zhao Cai, Renming Zhan, Yuchen Tan, Weiwei Liu, Hui Yang, Chenhui Li, Yongming Sun 2021, 62(11): 477-484.  DOI: 10.1016/j.jechem.2021.03.053 Abstract ( 10 )   PDF (9742KB) ( 9 )   Tin (Sn) metal foil is a promising anode for next-generation high-energy-density lithium-ion batteries (LIBs) due to its high capacity and easy processibility. However, the pristine Sn foil anode suffers nonuniform alloying/dealloying reaction with lithium (Li) and huge volume variation, leading to electrode pulverization and inferior electrochemical performance. Herein, we proposed that reduced grain size and elaborate porosity design of Sn foil can circumvent the nonuniform alloy reaction and buffer the volume change during the lithiation/delithiation cycling. Experimentally, we designed a three-dimensional interconnected porous Sn (3DIP-Sn) foil by a facile chemical alloying/dealloying approach, which showed improved electrochemical performance. The enhanced structure stability of the as-fabricated 3DIP-Sn foil was verified by chemo-mechanical simulations and experimental investigation. As expected, the 3DIP-Sn foil anode revealed a long cycle lifespan of 4400 h at 0.5 mA cm-2 and 1 mAh cm-2 in Sn||Li half cells. A 3DIP-Sn||LiFePO4 full cell with LiFePO4 loading of 7.1 mg cm-2 exhibited stable cycling for 500 cycles with 80% capacity retention at 70 mA g-1. Pairing with high-loading commercial LiNi0.6Co0.2Mn0.2O2 (NCM622, 18.4 mg cm-2) cathode, a 3DIP-Sn||NCM622 full cell delivered a high reversible capacity of 3.2 mAh cm-2. These results demonstrated the important role of regulating the uniform alloying/dealloying reaction and circumventing the localized strain/stress in improving the electrochemical performance of Sn foil anodes for advanced LIBs.

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Lithium bis(trifluoromethanesulfonyl)imide blended in polyurethane acrylate photocurable solid polymer electrolytes for lithium-ion batteries Cristian Mendes-Felipe, J.C. Barbosa, R. Gonçalves, D. Miranda, C.M. Costa, J.L. Vilas-Vilela, S. Lanceros-Mendez 2021, 62(11): 485-496.  DOI: 10.1016/j.jechem.2021.01.030 Abstract ( 4 )   PDF (3397KB) ( 2 )   The increased demand of electronic devices promotes the development of advanced and more efficient energy storage devices, such as batteries. Lithium-ion batteries (LIBs) are the most studied battery systems due to their high performance. Among the different battery components, the separator allows the control of lithium ion diffusion between the electrodes. To overcome some drawbacks of liquid electrolytes, including safety and environmental issues, solid polymer electrolytes (SPEs) are being developed. In this work, a UV photocurable polyurethane acrylate (PUA) resin has been blended with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) up to 30 wt% LiTFSI content to reach a maximum ionic conductivity of 0.0032 mS/cm at room temperature and 0.09 mS/cm at 100 °C. Those values allowed applying the developed materials as photocurable SPE in Swagelok type Li/C-LiFePO4 half-cells, reaching a battery discharge capacity value of 139 mAh.g-1 at C/30 rate. Those results, together with the theoretical studies of the discharge capacity at different C-rates and temperatures for batteries with LiTFSI/PUA SPE demonstrate the suitability of the developed photocurable SPE for LIB applications.

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Insight into the structure-capacity relationship in biomass derived carbon for high-performance sodium-ion batteries Jianguo Sun, Yao Sun, Jin An Sam Oh, Qilin Gu, Weidong Zheng, Minhao Goh, Kaiyang Zeng, Yuan Cheng, Li Lu 2021, 62(11): 497-504.  DOI: 10.1016/j.jechem.2021.04.009 Abstract ( 11 )   PDF (5195KB) ( 5 )   Carbonaceous materials are the most promising candidates as the anode for sodium-ion batteries (SIBs), however, they still suffer from low electric conductivity and sluggish sodium ion (Na+) reaction kinetics. Appropriate composition modulation using heteroatoms doping and structure optimization is highly desired. A basic empirical understanding of the structure-capacity relationship is also urgent in tackling the above problems. Herein, multi-functional nitrogen (N) doped carbon micro-rods with enlarged interlayer spacing are synthesized and investigated as the anode in SIBs, showing an ultra-stable capacity of 161.5 mAh g-1 at 2 A g-1 for over 5000 cycles. Experimental investigations and first-principle calculations indicate that the enlarged interlayer spacing can facilitate Na+ intercalation and N doping can guarantee the high electric conductivity and favorable electrochemical active sites. Additionally, pyridinic N is theoretically proved to be more effective to enhance Na+ adsorption than pyrrolic N due to the lower adsorption energy and stronger binding energy with Na+. Full SIBs show a high capacity and cyclability, making the biomass-derived carbon micro-rods to be a promising anode for practical SIBs applications.

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Perspective on the perovskite quantum dots for flexible photovoltaics Jiabei Yuan, Nopporn Rujisamphan, Wanli Ma, Jianyu Yuan, Youyong Li, Shuit-Tong Lee 2021, 62(11): 505-507.  DOI: 10.1016/j.jechem.2021.04.024 Abstract ( 6 )   PDF (4903KB) ( 2 )

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Defective TiO2-graphene heterostructures enabling in-situ electrocatalyst evolution for lithium-sulfur batteries Yanqi Feng, Hui Liu, Yi Liu, Fuwei Zhao, Junqi Li, Xuanmeng He 2021, 62(11): 508-515.  DOI: 10.1016/j.jechem.2021.04.008 Abstract ( 4 )   PDF (4074KB) ( 2 )   Lithium-sulfur (Li-S) batteries are considered as one of the promising next-generation energy storage systems because of their high energy density. While the low utilization of sulfur and sluggish reaction kinetics would lead to degradation of electrochemical performance and thus hinder the practical application of Li-S batteries. Herein, a double-shelled TiO2-graphene heterostructure (H-TiO2/rGO) with abundant oxygen vacancies (OVs) and highly exposed active plane as advanced host material in Li-S batteries is designed. This rational structure not only provides sufficient active sites and lower bandgap for lithium polysulfides (LiPSs), but also builds smooth adsorption-diffusion-conversion of LiPSs on catalyst, which greatly reduces interfacial energy barrier and promotes the utilization of sulfur through suppressing the devastating shuttling effect. Combining the synergetic merits of strong anchoring ability and catalyzing the of LiPSs, the electrode (S-TiO2/rGO-1) exhibits superior rate performance and long lifespan (1000 cycles at 1C, 0.023% capacity loss per cycle) with high columbic efficiency. This work paves an alternative way to establish smooth adsorption-diffusion-conversion of polysulfides on catalyst in Li-S batteries and provides a new sight to understand catalyst design in energy storage devices.

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MoS2 on topological insulator Bi2Te3 thin films: Activation of the basal plane for hydrogen reduction Guowei Li, Jue Huang, Qun Yang, Liguo Zhang, Qingge Mu, Yan Sun, Stuart Parkin, Kai Chang, Claudia Felser 2021, 62(11): 516-522.  DOI: 10.1016/j.jechem.2021.04.010 Abstract ( 5 )   PDF (3513KB) ( 3 )   2H-MoS2 is a well-studied and promising non-noble metal electrocatalyst for heterogeneous reactions, such as the hydrogen evolution reaction (HER). The performance is largely limited by the chemically inert basal plane, which is unfavorable for surface adsorption and reactions. Herein, we report a facile method to boost the HER activities of 2H-MoS2 by coupling with epitaxial Bi2Te3 topological insulator films. The as-obtained MoS2/ Bi2Te3/SrTiO3 catalyst exhibits prominent HER catalytic activities compared to that of pure MoS2 structures, with a 189 mV decrease in the overpotential required to reach a current density of 10 mA cm-2 and a low Tafel slope of 58 mV dec-1. Theoretical investigations suggest that the enhanced catalytic activity originates from the charge redistribution at the interface between the Bi2Te3topological insulator films and the MoS2 layer. The delocalized sp-derived topological surface states could denote electrons to the MoS2 layer and activate the basal plane for hydrogen adsorption. This study demonstrates the potential of manipulating topological surface states to design high-performance electrocatalysts.

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Decorating hole transport material with -CF3 groups for highly efficient and stable perovskite solar cells Bin Li, Yuan Cai, Xia Tian, Xiaozhong Liang, Da Li, Zheng Zhang, Sijing Wang, Kunpeng Guo, Zhike Liu 2021, 62(11): 523-531.  DOI: 10.1016/j.jechem.2021.04.017 Abstract ( 7 )   PDF (7165KB) ( 3 )   The hole transport material (HTM) plays an extremely important role to determine the power conversion efficiency (PCE) and the stability of perovskite solar cells (PSCs). Herein, we report an effective strategy to improve the performance of HTMs by introducing -CF3 groups via the rational decorative mode. Upon direct attachment or nonconjugated alkoxyl bridging of -CF3 groups on the terminal diphenylamines, the resulting molecular HTMs, i.e., 2,7-BCzA4CF3 and 2,7-BCzA4OCCF3, show distinct properties. Compared with 2,7-BCzA4CF3, the nonconjugated alkoxyl bridging -CF3 group-based 2,7-BCzA4OCCF3 exhibits better thermal stability, hydrophobicity, and a dramatically upgraded hole mobility by 135.7-fold of magnitude to 1.71 × 10-4 cm2 V-1 S-1. The PSCs with 2,7-BCzA4OCCF3 as HTM exhibit an PCE of up to 20.53% and excellent long-term stability, maintaining 92.57% of their performance for 30 days in air with humidity of 30% without encapsulation. This work provides beneficial guidelines for the design of new HTMs for efficient and stable PSCs.

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Gradually modulating the three parts of D-π-A type polymers for high-performance organic solar cells Jialing Zhou, Peiqing Cong, Lie Chen, Bao Zhang, Yanfang Geng, Ailing Tang, Erjun Zhou 2021, 62(11): 532-537.  DOI: 10.1016/j.jechem.2021.03.056 Abstract ( 7 )   PDF (5007KB) ( 3 )

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Phosphorus-doped lithium-and manganese-rich layered oxide cathode material for fast charging lithium-ion batteries Yuqiong Kang, Xingang Guo, Zhiwu Guo, Jiangang Li, Yunan Zhou, Zheng Liang, Cuiping Han, Xiangming He, Yun Zhao, Naser Tavajohi, Baohua Li 2021, 62(11): 538-545.  DOI: 10.1016/j.jechem.2021.04.026 Abstract ( 7 )   PDF (4100KB) ( 3 )   Owing to their high theoretical specific capacity and low cost, lithium-and manganese-rich layered oxide (LMR) cathode materials are receiving increasing attention for application in lithium-ion batteries. However, poor lithium ion and electron transport kinetics plus side effects of anion and cation redox reactions hamper power performance and stability of the LMRs. In this study, LMR Li1.2Mn0.6Ni0.2O2 was modified by phosphorus (P)-doping to increase Li+ conductivity in the bulk material. This was achieved by increasing the interlayer spacing of the lithium layer, electron transport and structural stability, resulting in improvement of the rate and safety performance. P5+ doping increased the distance between the (003) crystal planes from ~0.474 nm to 0.488 nm and enhanced the structural stability by forming strong covalent bonds with oxygen atoms, resulting in an improved rate performance (capacity retention from 38% to 50% at 0.05 C to 5 C) and thermal stability (50% heat release compared with pristine material). First-principles calculations showed the P-doping makes the transfer of excited electrons from the valence band to conduction band easier and P can form a strong covalent bond helping to stabilize material structure. Furthermore, the solid-state electrolyte modified P5+ doped LMR showed an improved cycle performance for up to 200 cycles with capacity retention of 90.5% and enhanced initial coulombic efficiency from 68.5% (pristine) or 81.7% (P-doped LMR) to 88.7%.

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Awakening the oxygen evolution activity of MoS2 by oxophilic-metal induced surface reorganization engineering Xueqin Mu, Yang Zhu, Xiangyao Gu, Shipeng Dai, Qixin Mao, Lintao Bao, Wenxuan Li, Suli Liu, Jianchun Bao, Shichun Mu 2021, 62(11): 546-551.  DOI: 10.1016/j.jechem.2021.04.019 Abstract ( 5 )   PDF (4410KB) ( 1 )   Although molybdenum disulfide (MoS2)-based materials are generally known as active electrocatalysts for the hydrogen evolution reaction (HER), the inert performance for the oxygen evolution reaction (OER) seriously limits their wide applications in alkaline electrolyzers due to there exists too strong metal-sulfur (M-S) bond in MoS2. Herein, by means of surface reorganization engineering of bimetal Al, Co-doped MoS2 (devoted as AlCo3-MoS2) through in situ substituting partial oxidation, we successfully significantly activate the OER activity of MoS2, which affords a considerably low overpotential of 323 mV at -30 mA cm-2, far lower than those of MoS2, Al-MoS2 and Co-MoS2 catalysts. Essentially, the AlCo3-MoS2 substrate produces lots of M-O (M=Al, Co and Mo) species with oxygen vacancies, which trigger the surface self-reconstruction of pre-catalysts and simultaneously boost the electrocatalytic OER activity. Moreover, benefiting from the moderate M-O species formed on the surface, the redistribution of surface electron states is induced, thus optimizing the adsorption of OH* and OOH* intermediates on metal oxyhydroxides and awakening the OER activity of MoS2.

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Earth-abundant magnetite with carbon coatings as reversible cathodes for stretchable zinc-ion batteries Zhao Wang, Yurou Wang, Guoqi Wang, Wei Wu, Jian Zhu 2021, 62(11): 552-562.  DOI: 10.1016/j.jechem.2021.04.012 Abstract ( 4 )   PDF (16136KB) ( 2 )   Earth-abundant magnetite (Fe3O4) as cathode materials in aqueous zinc-ion batteries (ZIBs) is limited by its very low capacity and poor cycling. Here, a combined strategy based on carbon coating and electrolyte optimization is adopted to improve the performance of Fe3O4. The Zn-Fe3O4@C batteries display specific capacities of 93 mAh g-1 and 81% capacity retention after 200 cycles. Such performance is attributed to the enhanced electrical conductivity and structural stability of Fe3O4@C nanocomposites with suppressed iron dissolution. Experimental analysis reveals that the charge storage is contributed by diffusion-limited redox reactions and surface-controlled pseudocapacitance. A stretchable Zn-Fe3O4@C battery is further fabricated, showing stable performance when it is bent or stretched. Fe3O4 is a promising cathode material for cost-effective, safe, sustainable and wearable energy supplies.

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C≡N-based carbazole-arylamine hole transporting materials for perovskite solar cells: Substitution position matters Zi'an Zhou, Xianfu Zhang, Rahim Ghadari, Xuepeng Liu, Wenjun Wang, Yong Ding, Molang Cai, Jia Hong Pan, Songyuan Dai 2021, 62(11): 563-571.  DOI: 10.1016/j.jechem.2021.04.021 Abstract ( 9 )   PDF (11267KB) ( 5 )   Hole transporting materials (HTMs) containing passivating groups for perovskite materials have attracted much attention for efficient and stable perovskite solar cells (PSCs). Among them, C≡N-based molecules have been proved as efficient HTMs. Herein, a series of novel C≡N functionalized carbazole-arylamine derivatives with variable C≡N substitution positions (para, meta, and ortho) on benzene-carbazole skeleton (on the adjacent benzene of carbazole) were synthesized (p-HTM, m-HTM and o-HTM). The experimental results exhibit that the substitution positions of the C≡N unit on HTMs have minor difference on the HOMO energy level and hydrophobicity. m-HTM has a relatively lower glass transition temperature compared with that of p-HTM and o-HTM. The functional theory calculations show that the C≡N located on meta position exposed very well, and the exposure direction is also the same with the methoxy. Upon applying these molecules as HTMs in PSCs, their device performance is found to sensitively depend on the substitution position of the C≡N unit on the molecule skeleton. The devices using m-HTM and o-HTM exhibit better performance than that of p-HTM. Moreover, m-HTM-based devices exhibit better light-soaking performance and long-term stability, which could be resulted from better interaction with the perovskite according to DFT results. Moreover, we further prepared a HTM with two C≡N units on the symmetrical meta position of molecular skeleton (2m-HTM). Interestingly, 2m-HTM-based devices exhibit relatively inferior performance compared with that of the m-HTM, which could be resulted from weak negative electrical character of C≡N unit on 2m-HTM. The results give some new insights for designing ideal HTM for efficient and stable PSCs.

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Aurivillius compound Bi5Ti3CrO15 as a visible-light-active photocatalyst for hydrogen production from water Zeming Gu, Jun Qian, Ran Wang, Meilin Lv, Xiaoxiang Xu, Chun Luo 2021, 62(11): 572-580.  DOI: 10.1016/j.jechem.2021.04.014 Abstract ( 5 )   PDF (6589KB) ( 2 )   Layered Aurivillius compound Bi5Ti3CrO15 has been synthesized by a hydrothermal method for the application as a photocatalyst to liberate hydrogen from water. Bi5Ti3CrO15 owns a narrow band gap (Eg ~2.46 eV) and shows stable photocatalytic activity under both full range (λ ≥250 nm) and visible light illumination (λ ≥420 nm). A short hydrothermal reaction time is critical to achieve high photocatalytic activity as defects such as Cr6+ and Bi5+ can be avoided. An AQE as high as 3.66% at 420 nm ± 20 nm has been recorded, warranting promising application in the field of solar energy conversions. DFT calculation reveals the important role of Cr3+cations for visible light sensitivity of Bi5Ti3CrO15.

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Manipulating selenium molecular configuration in N/O dual-doped porous carbon for high performance potassium-ion storage Dongjun Li, Lifeng Wang, Xiaolong Cheng, Yu Yao, Yu Jiang, Pengcheng Shi, Ying Wu, Xiaojun Wu, Cheng Ma, Yan Yu 2021, 62(11): 581-589.  DOI: 10.1016/j.jechem.2021.04.006 Abstract ( 4 )   PDF (5888KB) ( 2 )   Potassium-selenium (K-Se) batteries have attracted more and more attention because of their high theoretical specific capacity and natural abundance of K resources. However, dissolution of polyselenides, large volume expansion during cycling and low utilization of Se remain great challenges, leading to poor rate capability and cycle life. Herein, N/O dual-doped carbon nanofibers with interconnected micro/mesopores (MMCFs) are designed as hosts to manipulate Se molecular configuration for advanced flexible K-Se batteries. The micropores play a role in confining small Se molecule (Se2-3), which could inhibit the formation of polyselenides and work as physical barrier to stabilize the cycle performance. While the mesopores can confine long-chain Se (Se4-7), promising sufficient Se loading and contributing to higher discharge voltage of the whole Se@MMCFs composite. The N/O co-doping and the 3D interpenetrating nanostructure improve electrical conductivity and keep the structure integrity after cycling. The obtained Se2-3/Se4-7@MMCFs electrode exhibits an unprecedented cycle life (395 mA h g-1 at 1 A g-1 after 2000 cycles) and high specific energy density (400 Wh kg-1, nearly twice the specific energy density of the Se2-3@MMCFs). This study offers a rational design for the realization of a high energy density and long cycle life chalcogen cathode for energy storage.

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Enhanced chemical trapping and catalytic conversion of polysulfides by diatomite/MXene hybrid interlayer for stable Li-S batteries Zehui Fan, Chen Zhang, Wuxing Hua, Huan Li, Yan Jiao, Jingyi Xia, Chuan-Nan Geng, Rongwei Meng, Yingxin Liu, Quanjun Tang, Ziyang Lu, Tongxin Shang, Guowei Ling, Quan-HongYang 2021, 62(11): 590-598.  DOI: 10.1016/j.jechem.2021.04.038 Abstract ( 6 )   PDF (3866KB) ( 4 )   Lithium-Sulfur (Li-S) batteries with high theoretical energy density are promising energy storage systems in the next decades, while the lithium polysulfides (LiPSs) shuttling caused by the sluggish sulfur redox reaction severely lowers the practical performance. The use of interlayer between the cathode and separator has been widely investigated to physically or chemically block the LiPSs, while the introduction of catalytic materials is a more effective strategy to accelerate the conversion of LiPSs. MXene with rich surface chemistry has shown its potential for facilitating the catalytic conversion, however, the aggregation of MXene sheets usually leads to the loss of the catalytic active sites. Herein, we report a diatomite/MXene (DE/MX) hybrid material as the bifunctional interlayer for improving the adsorption/conversion of LiPSs in Li-S batteries. The diatomite with porous structure and rich silica-hydroxyl functional groups could trap LiPSs effectively, while prevent the aggregation of MXene. The DE/MX based interlayer showed bifunctions of enhancing the chemical adsorption and promoting the conversion of LiPSs. The Li-S batteries with the DE/MX interlayer delivered an improved cycling stability with a low capacity decay of 0.059% per cycle over 1000 cycles at 1.0 C. Moreover, stable 200 cycles can be realized with a high sulfur loading electrode up to 6.0 mg cm-2. This work provides an effective strategy to construct bifunctional interlayers for hindering the shuttling of LiPSs and boosting the practical application of Li-S batteries.

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Rational construction of metal-base synergetic sites on Au/Mg-beta catalyst for selective aerobic oxidation of 5-hydroxymethylfurfural Zhiguo Zhu, Xiongjie Gao, Xiuming Wang, Mengdie Yin, Qingyao Wang, Wanzhong Ren, Bo Wang, Hongying Lü, Weiping Liao 2021, 62(11): 599-609.  DOI: 10.1016/j.jechem.2021.04.022 Abstract ( 5 )   PDF (4550KB) ( 2 )   The selective aerobic oxidation of biomass-derived 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid (FDCA, a potential renewable substitution of fossil-based terephthalic acid to produce polyethylene 2,5-furandicarboxylate plastic) is an appealing transformation for constructing eco-friendly and sustainable chemical processes. Au supported catalysts have showed encouraging performances for this well-received conversion, whose catalytic behavior was greatly affected by the adopted support derived from the existence of metal-support interactions. Herein, a series of Mg-Beta zeolites were hydrothermally synthesized via developed structural reconstruction, which were employed as basic supports for Au catalysts to construct bifunctional catalysts. The relationship between structure (Au particle size, basicity within zeolites and Auδ+ contents) and FDCA yield was concretely established. The conclusion was made that the utilization of Mg-Beta zeolites with strong basicity as the support could not only improve the FDCA yield but also decrease the amount of additional base. Furthermore, the possible reaction mechanism was also proposed via tracking time-dependent variations of corresponding organics and controlled experiment. This work provides some guidance for rationally designing multifunctional catalysts in the view of integrating metal catalysts with metallosilicate zeolites, which was beneficial to the catalytic upgrading of organic compounds with multiple functional groups.

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Modulating proton binding energy on the tungsten carbide nanowires surfaces for boosting hydrogen evolution in acid Qingshui Hong, Tangyi Li, Shisheng Zheng, Haibiao Chen, Wenju Ren, Honghao Chu, Kuangda Xu, Zongwei Mei, Feng Pan 2021, 62(11): 610-616.  DOI: 10.1016/j.jechem.2021.04.004 Abstract ( 6 )   PDF (4197KB) ( 3 )   Tungsten carbides have attracted wide attentions as Pt substitute electrocatalysts for hydrogen evolution reaction (HER), due to their good stability in an acid environment and Pt-like behaviour in hydrolysis. However, quantum chemistry calculations predict that the strong tungsten-hydrogen bonding hinders hydrogen desorption and restricts the overall catalytic activity. Synergistic modulation of host and guest electronic interaction can change the local work function of a compound, and therefore, improve its electrocatalytic activity over either of the elements individually. Herein, we develop a creative and facile solid-state approach to synthesize self-supported carbon-encapsulated single-phase WC hybrid nanowires arrays (nanoarrays) as HER catalyst. The theoretical calculations reveal that carbon encapsulation modifies the Gibbs free energy of H* values for the WC adsorption sites, endowing a more favorable C@WC active site for HER. The experimental results exhibit that the hybrid WC nanoarrays possess remarkable Pt-like catalytic behavior, with superior activity and stability in an acidic media, which can be compared to the best non-noble metal catalysts reported to date for hydrogen evolution reaction. The present results and the facile synthesis method open up an exciting avenue for developing cost-effective catalysts with controllable morphology and functionality for scalable hydrogen generation and other carbide nanomaterials applicable to a range of electrocatalytic reactions.

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Controlling a lithium surface with an alkyl halide nucleophile exchange Jung-Hun Lee, Thuy Hoai Linh Vuong, Soo Min Hwang, Jae-Hun Kim, Young-Jun Kim 2021, 62(11): 617-626.  DOI: 10.1016/j.jechem.2021.04.005 Abstract ( 3 )   PDF (4566KB) ( 3 )   Despite its high theoretical energy density, lithium metal faces huge challenges in its implementation as an anode for Li secondary batteries because of its uncontrollable dendritic growth and large volume change during plating/stripping processes. These geometric changes cause degradation in a cell's cycle life and performance and can lead to short-circuits and explosions. Here, we report a new approach to producing a LiF-rich phase on the lithium anode surface by employing a “bi-phase” separator. We fabricated it by coating polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) onto a cellulose separator. The coverage of coating was adjusted by varying its concentration in the coating solution. The combination of cellulose and PVDF-HFP produced a LiF-rich solid-electrolyte interphase layer on the Li metal surface via an alkyl halide nucleophile exchange in contact with the bi-phase separator during plating. Symmetric cell tests show that the bi-phase separator extends the cycle life by more than 300 h, with overpotentials of less than 100 mV under plating/stripping at 2 mA cm-2 for a capacity of 2 mAh cm-2. The formation mechanism of the LiF-rich phase is suggested from spectroscopic analyses.

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In operando study of orthorhombic V2O5 as positive electrode materials for K-ion batteries Qiang Fu, Angelina Sarapulova, Lihua Zhu, Georgian Melinte, Alexander Missyul, Edmund Welter, Xianlin Luo, Michael Knapp, Helmut Ehrenberg, Sonia Dsoke 2021, 62(11): 627-636.  DOI: 10.1016/j.jechem.2021.04.027 Abstract ( 5 )   PDF (7186KB) ( 2 )   Herein, the electrochemical performance and the mechanism of potassium insertion/deinsertion in orthorhombic V2O5 nanoparticles are studied. The V2O5 electrode displays an initial potassiation/depotassiation capacity of 200 mAh g-1/217 mAh g-1 in the voltage range 1.5-4.0 V vs. K+/K at C/12 rate, suggesting fast kinetics for potassium insertion/deinsertion. However, the capacity quickly fades during cycling, reaching 54 mAh g-1 at the 31st cycle. Afterwards, the capacity slowly increases up to 80 mAh g-1 at the 200th cycle. The storage mechanism upon K ions insertion into V2O5 is elucidated. In operando synchrotron diffraction reveals that V2O5 first undergoes a solid solution to form K0.6V2O5 phase and then, upon further K ions insertion, it reveals coexistence of a solid solution and a two-phase reaction. During K ions deinsertion, the coexistence of solid solution and the two-phase reaction is identified together with an irreversible process. In operando XAS confirms the reduction/oxidation of vanadium during the K insertion/extraction with some irreversible contributions. This is consistent with the results obtained from synchrotron diffraction, ex situ Raman, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Moreover, ex situ XPS confirms the “cathode electrolyte interphase” (CEI) formation on the electrode and the decomposition of CEI film during cycling.

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Li2S doping into CZTSe drives the large improvement of VOC of solar cell Zhan Shen, Siyu Wang, Yue Liu, Yali Sun, Jianyu Wu, Hongling Guo, Kaizhi Zhang, Shengli Zhang, Fangfang Liu, Yi Zhang 2021, 62(11): 637-644.  DOI: 10.1016/j.jechem.2021.04.018 Abstract ( 2 )   PDF (7662KB) ( 1 )   Alkali metal doping or sulfurization are commonly applied in Cu2ZnSnSe4 (CZTSe) solar cell to improve the open-circuit voltage (VOC). However, alkali metal sulfide affording both alkali metal and sulfur is seldom to be studied, which restrains the development of kesterite solar cells. In this study, we evaporate Li2S during selenization process and hope to provide both alkali metal and sulfur to CZTSe film. The result indicates that Li shows a gradient distribution near the surface of CZTSe film and the content of S is slight. The film quality is improved and the recombination at grain boundaries is decreased after Li2S treatment. Besides, the bandgap of the absorber gets wider. Under the synergy of sulfur and lithium (mainly from lithium), the work function of the treated absorber gets higher and the conduction band offset (CBO) is in the ideal range. Combined with these contributions, the VOC of the champion device treated by Li2S dramatically increase by 120 mV. This study discloses that alkali metal brings the main effect on the performance of the kesterite solar cell even an alkali metal sulfide is evaporated, which deepens the understanding of sulfurization of CZTSe and also promote the progress of kesterite solar cells.

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Covalent sulfur as stable anode for potassium ion battery Na Cheng, Patrick Xu, Bingan Lu, Zhigang Liu 2021, 62(11): 645-652.  DOI: 10.1016/j.jechem.2021.04.051 Abstract ( 5 )   PDF (4655KB) ( 2 )   The potassium bis(fluoro-sulfonyl)imide(KFSI)-based electrolyte has great application prospects in potassium ion batteries (PIBs). However, their development has been limited by the decomposition of electrolytes and the corrosion of Al foils (current collector) at high potential. Here, a N-doping, sulfur-rich chemically bonded porphyrin organic framework (SPOF) with a high potential plateau were synthesized as an anode to lower the redox potential of full cells and further inhibit the corrosion of Al foils. SPOF as anode delivers high reversible capacity (557 mAh g-1 at 50 mA g-1), excellent cycling performance (94% capacity retention over 1000 cycles at 500 mA g-1), and superior rate performance. Meanwhile, the ex-situ FTIR, Raman, and HRTEM revealed the stability of N-doping and the reversible covalent sulfur and S-S bonds changes during potassiation/depotassiation. In addition, full cells using SPOF anode and PTCDA cathode showed outstanding performance (high capacity of 300 mAh g-1 at 200 mA g-1). And the Al current collector of the full cell was not corroded after 150 cycles. Yet, the Al foils with PTCDA as cathode were seriously corroded. This work provides a new strategy for realizing ultra-high reversible capacity and cyclic stability of PIBs, and also accelerates the process of early commercial application of PIBs.

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Achieving exceptional activity and durability toward oxygen reduction based on a cobalt-free perovskite for solid oxide fuel cells Feifei Dong, Zhenghui Gao, Bingkai Zhang, Lu Li, Ziqi Kong, Zilin Ma, Meng Ni, Zhan Lin 2021, 62(11): 653-659.  DOI: 10.1016/j.jechem.2021.04.020 Abstract ( 5 )   PDF (3452KB) ( 2 )   In response to the shortcomings of cobalt-rich cathodes, iron-based perovskite oxides appear as promising alternatives for solid oxide fuel cells (SOFCs). However, their inferior electrochemical performance at reduced temperatures (<700 °C) becomes a major bottleneck for future progress. Here, a novel cobalt-free perovskite Ba0.75Sr0.25Fe0.875Ga0.125O3-δ (BSFG) is developed as an efficient oxygen reduction electrode for SOFCs, featuring cubic-symmetry structure, large oxygen vacancy concentration and fast oxygen transport. Benefiting from these merits, cells incorporated with BSFG achieve exceptionally high electrochemical performance, as evidenced by a low polarization area-specific resistance of 0.074 Ω cm2 and a high peak power density of 1145 mW cm-2 at 600 °C. Meanwhile, a robust short-term performance stability of BSFG cathode can be ascribed to the stable crystalline structure and favorable thermal expansion behavior. First-principles computations are also conducted to understanding the superior activity and durability toward oxygen reduction reaction. These pave the way for rationally developing highly active and robust cobalt-free perovskite-type cathode materials for reduced-temperature SOFCs.

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New insights into carbon-based and MXene anodes for Na and K-ion storage: A review Zhensheng Hong, Hajar Maleki, Tim Ludwig, Yichao Zhen, Michael Wilhelm, Damin Lee, Kwang-Ho Kim, Sanjay Mathur 2021, 62(11): 660-691.  DOI: 10.1016/j.jechem.2021.04.031 Abstract ( 6 )   PDF (24494KB) ( 3 )   Na-ion batteries and K-ion batteries are promising alternatives to vastly used lithium-ion batteries mainly due to the larger natural abundance of sodium and potassium resources. Carbon-based and MXene materials have received increasing attention due to their unique layered structure to accommodate the larger sodium and potassium ions. It's proposed that ionic size disparity (K+: 1.38 Å; Na+: 0.97 Å; Li+: 0.76 Å) leads to sluggish intercalation and extraction kinetics in larger alkali metal ions (AMIs). Nevertheless, the electrochemical inactivity of sodium intercalation in graphite suggests that different chemical properties of AMs and their interactions with carbon host and electrolytes is crucial for interfacial instability and irreversible capacity loss. Structural modifications by expanding interlayer spacing and defect engineering enable reduced diffusion barriers and enhanced insertion of sodium or potassium, but it blurs the electrochemical performance between battery and capacitor. This review provides insight into 2D carbon materials and their architectures for Na and K-ion batteries through an in-depth analysis of structure-property interdependence and different electrochemical mechanisms supported by both experimental and theoretical data to discuss the promises and challenges of post-lithium batteries. Finally, the perspectives and potential directions regarding material design concepts for 2D carbon-based nanomaterials and MXene phases for metal-ion storage are proposed.