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2021, Vol. 57, No. 6　Online: 15 June 2021

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Oxygen-doping of ZnIn2S4 nanosheets towards boosted photocatalytic CO2 reduction Bao Pan, Yu Wu, Baker Rhimi, Jiani Qin, Ying Huang, Mingzhe Yuan, Chuanyi Wang 2021, 57(6): 1-9.  DOI: 10.1016/j.jechem.2020.08.024 Abstract ( 7 )   PDF (7977KB) ( 3 )   Engineering the electronic properties of semiconductor-based photocatalysts using elemental doping is an effective approach to improve their catalytic activity. Nevertheless, there still remain contradictions regarding the role of the dopants played in photocatalysis. Herein, ultrathin ZnIn2S4 (ZIS) nanosheets with oxygen doping were synthesized by a one-pot solvothermal method. XRD, XPS and Raman spectral measurements support the presence of lattice oxygen in the oxygen-doped ZIS (O-ZIS) sample. With optimum doping of oxygen, the ultrathin O-ZIS nanosheets show enhanced CO2-to-CO conversion activity with a CO-evolving rate of 1680 μmol h-1 g-1 under visible light irradiation, which is about 7 times higher than that of the pristine ZIS. First-principle calculations support that doping of oxygen in the lattice of ZnI2S4 nanosheets plays a key role in tuning its electronic properties. The remarkable photocatalytic performance of O-ZIS can be assigned to a synergistic consequence of a unique ultrathin-layered structure and an upward shift of the conduction band minimum (CBM) caused by the oxygen doping into ZIS and the quantum confinement effect (QCE) induced by the decreased particle size after doping as well as to the improved charge separation efficiency. The present work offers a simple elemental doping method to promote charge separation at atomic level and illustrates the roles played by oxygen doping in photocatalysis, giving new insights into highly efficient artificial photosynthesis.

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N-doped carbon-embedded TiN nanowires as a multifunctional separator for Li-S batteries with enhanced rate capability and cycle stability Yoongon Kim, Yuseong Noh, Jaejin Bae, Hyunwoo Ahn, Minho Kim, Won Bae Kim 2021, 57(6): 10-18.  DOI: 10.1016/j.jechem.2020.08.050 Abstract ( 13 )   PDF (6776KB) ( 3 )   Lithium-sulfur (Li-S) batteries have attracted considerable attention as next-generation energy storage devices owing to their high theoretical specific capacity and safety. However, the commercialization of Li-S batteries is hindered by critical issues, including the migration of the dissolved lithium polysulfides (LiPSs) from the sulfur electrode to the lithium metal anode, resulting in poor cycling stability. Here, we report a multifunctional interlayer configured with an N-doped carbon framework and titanium nitride nanowires on a polypropylene separator (NC/TiN NWs@PP) to suppress the polysulfide shuttling problem. NC/TiN NWs@PP can be obtained by electrospinning and the subsequent scalable solution-based vacuum filtration. The one-dimensional structure of the TiN NWs can shorten the Li-ion diffusion distance with large electrode/electrolyte interfaces. Furthermore, the N-doped carbon framework in the NWs enables facile electron transportation and allows the suppression of the shuttle effect to improve the electrochemical reaction kinetics. The Li-S battery with a NC/TiN NWs@PP separator exhibited enhanced cycling stability and rate capability, indicating that this could be a new research direction for Li-S batteries.

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ZIF-7@carbon composites as multifunctional interlayer for rapid and durable Li-S performance Xingbo Wang, Yan Zhao, Feichao Wu, Shuming Liu, Zisheng Zhang, Zhaoyang Tan, Xiaohang Du, Jingde Li 2021, 57(6): 19-27.  DOI: 10.1016/j.jechem.2020.09.019 Abstract ( 12 )   PDF (9842KB) ( 1 )   The notorious “shuttle effect” of polysulfide during charge-discharge process induces grievous capacity fading, while the sluggish polysulfide conversion kinetics significantly hinders the development of practically viable lithium-sulfur (Li-S) batteries. In this study, a novel ZIF-7@carbon composite with ZIF-7 sheets vertically rooted on carbon cloth was developed as multifunctional interlayer to address these issues. The composite shows directional layered structure with outstanding compactness, and thus can provide massive active sites for accelerated redox reactions. The pore channels are perpendicular to the square surface, resulting in extremely high utilization of one-dimensional channels. Therefore, this structure can not only maintain the structural stability during the charge-discharge process by providing enough space for volume expansion, but also contribute to efficient exposure and utilization of active sites for the physical/chemical adsorption and catalytic conversion of polysulfide. As a result, Li-S batteries with the as-developed interlayer deliver a considerable areal capacity of 4.75 mAh cm-2 at an elevated sulfur loading of 5.5 mg cm-2, and an impressive cyclability with an extremely low capacity-fading rate of merely 0.04% per cycle over 500 cycles at 1 C.

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An all-organic aqueous potassium dual-ion battery Junmin Ge, Xianhui Yi, Ling Fan, Bingan Lu 2021, 57(6): 28-33.  DOI: 10.1016/j.jechem.2020.08.049 Abstract ( 10 )   PDF (5957KB) ( 4 )   Benefiting from the environmental friendliness of organic electrodes and the high security of aqueous electrolyte, an all-organic aqueous potassium dual-ion full battery (APDIB) was assembled with 21 M potassium bis(fluoroslufonyl)imide (KFSI) water-in-salt as the electrolyte. The APDIB could deliver a reversible capacity of around 50 mAh g-1 at 200 mA g-1 (based on the weight of total active materials), a long cycle stability over 900 cycles at 500 mA g-1 and a high coulombic efficiency of 98.5%. The reaction mechanism of APDIB during the charge/discharge processes is verified: the FSI- could associate/disassociate with the nitrogen atom in the polytriphenylamine (PTPAn) cathode, while the K+ could react with C＝O bonds in the 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) anode reversibly. Our work contributes toward the understanding the nature of water-into-salt electrolyte and successfully constructed all-organic APDIB.

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Open and close-ended CoMoS3 nanotubes for hydrogen evolution in acidic and basic conditions Yuan Li, Xuewei Hou, Jing Gu, Veronika Mikhaylova, Kangli Chen, Hongming Zhang, Shumin Han 2021, 57(6): 34-40.  DOI: 10.1016/j.jechem.2020.08.068 Abstract ( 6 )   PDF (3294KB) ( 2 )   Electrochemical hydrogen evolution reaction (HER) is a promising route to harvest high-purity hydrogen (H2). Efficient and selective energy transformations rely on the development of novel catalytic materials in terms of compositions and structures that survive under harsh conditions. This study focuses on a unique nanostructured CoMoS3 catalyst for HER under strong acidic and basic electrolyte. The morphologies of the catalysts are fine-tuned by altering reaction times in a hydrothermal reaction. Limited reaction time generates twisted thin-sheet CoMoS3 (12 h), which spins into a nanotube with an extended synthetic time (16 h). As the reaction time increases to 20 h, the CoMoS3 composite creates open-ended nanotubes, facilitating reactants to penetrate and react actively in the inner space of the nanotubes. Further, prolonged reaction time (24 h) results in the formation of the close-ended CoMoS3 nanotubes. We find out that the open-ended structure plays an important role in achieving fast kinetics as well as creating more active sites in HER reaction. The catalyst delivers a profound performance under both acidic and basic conditions, with overpotentials of 93 mV and 115 mV (at a current density of 10 mA/cm2) in the acidic and basic electrolytes, respectively. Moreover, it shows superior long-term durability in both solutions. This work will provide a great foundation for understanding the morphology effect with the same composited catalyst towards energy conversion reactions, not limited to HER.

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Recent advances in interlayer and separator engineering for lithium-sulfur batteries Deming Zhu, Tao Long, Bin Xu, Yixin Zhao, Haitao Hong, Ruijie Liu, Fancheng Meng, Jiehua Liu 2021, 57(6): 41-60.  DOI: 10.1016/j.jechem.2020.08.039 Abstract ( 13 )   PDF (10840KB) ( 7 )   Lithium-sulfur (Li-S) batteries have great potential in next-generation energy storage due to its high theoretical specific capacity and energy density. However, there are several challenges to the practical application of Li-S batteries including the growth of lithium dendrites and the shuttle effect of polysulfide. Introducing interlayeres (freestanding or coated on the separator) is an effective approach to reduce these obstacles and improve the electrochemical performance of Li-S batteries. In this review, we briefly summarize the interlayer materials and structures modified on both cathodic and anodic sides including (i) carbon-based materials, (ii) polymers, (iii) inorganic metal compounds, (iv) metal-organic frameworks, as well as (v) the novel separators in recent years. We also systematically address the fabrication processes, assembling methods, and functions of interlayers for enhancing the performance of Li-S batteries. Furthermore, the prospects and outlooks of the future development of advanced interlayers and separators are also presented.

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Thin buffer layer assist carbon-modifying separator for long-life lithium metal anodes Jiaqi Li, Hongsheng Jia, Haibo Li, Xing Zhao, Guiru Sun, Zhiyong Chang, Lei Li, Ming Jin, Zhao Wang, Ming Feng 2021, 57(6): 61-68.  DOI: 10.1016/j.jechem.2020.08.044 Abstract ( 4 )   PDF (7658KB) ( 2 )   The guided Li dendrite growth by carbon-modifying separator is believed to be an effective strategy for enhancing life of lithium metal batteries (LMBs). However, the weak adhesions, as well as the large interface impedance between the smooth separator and the carbon functional layer (CFL) lead to an easily peeling of the CFL after repetitive cycles. Herein, we propose a promising solution by an inserting thin buffer layer (TBL) to strengthen the adhesion between CFL and separator as a double modifying layer (C-TBL) of the LMBs separator, which greatly improves the stability of the CFL and provides an effective Li metal anode protection. Owing to the sufficient ionic conductivity, chemical stability and strong adhesion to the separator of the TBL, it can avoid the failure of the CFL functionality with small interface impedance. Moreover, the CFL effectively reduces localized flux of Li+ through its abundant pores. The Li/Li cell with C-TBL separator displays the Li dendrite-free and stable cycling performance for at least 1500 h. When LiFePO4 (LFP) is employed as the cathode electrode, the assembled full cell with C-TBL separator shows the excellent rate performance and outstanding cycling capability. Our study builds a stable Li+ conducting “bridge” between the functional layer and the separator in stabilizing Li metal anode, and provides a fresh idea of the artificial separator of LMBs.

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Superior photovoltaics/optoelectronics of two-dimensional halide perovskites Lili Gao, Jiaxue You, ShengzhongLiu 2021, 57(6): 69-82.  DOI: 10.1016/j.jechem.2020.08.022 Abstract ( 7 )   PDF (15903KB) ( 2 )   Taking advantage of the excellent stability and photoelectric properties, two-dimensional (2D) organic-inorganic halide perovskites have been widely researched and applied in optoelectronic and photovoltaic devices. The remarkable properties are attributed to the unique quantum well structures by intercalating large organic ammonium space layers. In this review, we first summarize the crystal structures and growth methods of 2D halide perovskite crystals. Then, the distinctive optical characteristics and enhanced stability under high humidity, phase stability, suppressed ion migration, and high formation energy, are discussed in detail. Furthermore, we discuss orientation control in 2D perovskite films. The applications of 2D perovskites in solar cells, photo detectors and X-ray detectors are discussed in detail. Finally, we propose an outlook and perspectives to overcome the present challenges and broaden this new class of perovskite materials with other 2D nanomaterials.

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Efficient Co@Co3O4 core-shell catalysts for photocatalytic water oxidation and its behaviors in two different photocatalytic systems Di Wang, Shanshan Qiao, Jia Guo, Yuan Guo, Qian Xu, Naeem Akram, Jide Wang 2021, 57(6): 83-91.  DOI: 10.1016/j.jechem.2020.09.005 Abstract ( 6 )   PDF (3985KB) ( 2 )   The photocatalytic performances of water oxidation were usually carried out in two different systems, photosensitizer and non-photosensitizer systems. There is few report about the same catalyst used in two systems and therefore it is of great significant to compare its role of the same catalyst in two systems and explore its different reaction mechanisms. In this work, first 4 kinds of metallic Co microparticles were obtained by different reduction methods through hydrothermal processes, and Co@Co3O4 core-shell microparticles (1-4) were obtained from these metallic Co microparticles oxidized in air or in the reacting solution in situ. The core-shell structure of 1 was characterized by a series of analytical techniques. 1-4 exhibited excellent activities and stabilities in the [Ru(bpy)3]2+/S2O82-/light system when they were used as catalysts for the photocatalytic water oxidation. The maximum O2 evolution of 1 after 20 min's illumination was 98.2 μmol, the O2 yield was 65.5%, the initial turnover frequency was 6.6 × 10-3, the initial quantum efficiency (ΦQY initial) was 15.0% higher than Co (8.3%), CoO (11.7%), Co2O3 (1.2%), Co3O4 (2.8%) and 5 (2.2%). Even after the sixth run, the catalytic activity of recovered 1 still remained 85.1% of initial activity. In addition, the photocatalytic performances of 1 in the [Ru(bpy)3]2+/S2O82-/light system and S2O82-/light system were compared for the first time. In the non-photosensitizer system, 1 shows bifunctional roles and acts as optical absorption center and active catalytic site, and oxygen evolution rate is lower and it takes longer time. In the photosensitizer system, 1 only acts as a catalyst, the photosensitizer enhances the light absorption and promotes water oxidation reaction with higher O2 yield and QE, meanwhile the photosensitizer brings the defect of high cost and instability into the system. Based on the results the two different reaction mechanisms were deeply discussed.

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Optimizing zeolite stabilized Pt-Zn catalysts for propane dehydrogenation Linjun Xie, Yuchao Chai, Lanlan Sun, Weili Dai, Guangjun Wu, Naijia Guan, Landong Li 2021, 57(6): 92-98.  DOI: 10.1016/j.jechem.2020.08.058 Abstract ( 5 )   PDF (9266KB) ( 1 )   Propane dehydrogenation (PDH) provides an alternative route to non-petroleum based propylene and eligible catalysts with good overall performance are still being explored. Herein, we report the construction of zeolite stabilized Pt-Zn catalysts Pt-Zn/Si-Beta for PDH. Characterization results from transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) and Fourier transform infrared (FTIR) spectroscopy reveal that highly-dispersed Zn species are stabilized by the silanols from zeolite framework dealumination, which then act as the anchoring sites for Pt species. The close contact between Pt-Zn species and the electronic interaction thereof make Pt-Zn/Si-Beta robust PDH catalysts. Under optimized conditions, a high propylene production rate of 4.11 , high propylene selectivity of 98% and a sustainable deactivation rate of ~ 0.02 h-1 can be simultaneously achieved at 823 K. Coke deposition is not the key reason for the catalytic deactivation, while the loss of Zn species and the resulting aggregation of Pt species under high temperatures are responsible for the irreversible deactivation of Pt-Zn/Si-Beta catalyst in PDH reaction.

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Abundant heterointerfaces in MOF-derived hollow CoS2-MoS2 nanosheet array electrocatalysts for overall water splitting Yuanjian Li, Wenyu Wang, Baojun Huang, Zhifei Mao, Rui Wang, Beibei He, Yansheng Gong, Huanwen Wang 2021, 57(6): 99-108.  DOI: 10.1016/j.jechem.2020.08.064 Abstract ( 5 )   PDF (9721KB) ( 1 )   Rational coupling of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysts is extremely important for practical overall water splitting, but it is still challenging to construct such bifunctional heterostructures. Herein, we present a metal-organic framework (MOF)-etching strategy to design free-standing and hierarchical hollow CoS2-MoS2 heteronanosheet arrays for both HER and OER. Resulting from the controllable etching of MOF by MoO42- and in-situ sulfuration, the obtained CoS2-MoS2 possesses abundant heterointerfaces with modulated local charge distribution, which promote water dissociation and rapid electrocatalytic kinetics. Moreover, the two-dimensional hollow array architecture can not only afford rich surface-active sites, but also facilitate the penetration of electrolytes and the release of evolved H2/O2 bubbles. Consequently, the engineered CoS2-MoS2 heterostructure exhibits small overpotentials of 82 mV for HER and 266 mV for OER at 10 mA cm-2. The corresponding alkaline electrolyzer affords a cell voltage of 1.56 V at 10 mA cm-2 to boost overall water splitting, along with robust durability over 24 h, even surpassing the benchmark electrode couple composed of IrO2 and Pt/C. The present work may provide valuable insights for developing MOF-derived heterogeneous electrocatalysts with tailored interface/surface structure for widespread application in catalysis and other energy-related areas.

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In situ XRD and electrochemical investigation on a new intercalation-type anode for high-rate lithium ion capacitor Bobo Zou, Ting Wang, Shengyuan Li, Rong Kang, Guochun Li, Sherif A. El-Khodary, Dickon H.L. Ng, Xianhu Liu, Jingxia Qiu, Yan Zhao, Jiabiao Lian, Huaming Li 2021, 57(6): 109-117.  DOI: 10.1016/j.jechem.2020.08.037 Abstract ( 5 )   PDF (3623KB) ( 3 )   A new intercalation-type anode material is reported herein to improve the lithium storage kinetics for high-rate lithium ion capacitors. The crystal structure of orthorhombic NaNbO3 indicates two possible tunnels for lithium ions insertion into NaNbO3 host along the <101> and <141> directions. Moreover, in situ XRD is conducted to investigate the lithium storage mechanism and structural evolution of the NaNbO3 anode, demonstrating its intercalation behavior through (101) and (141) planes. Furthermore, the rGO nanosheets are introduced to facilitate the charge transfer, which also effectively prevent the aggregation of NaNbO3 nanocubes. As expected, the NaNbO3/rGO nanocomposites possess remarkable reversible capacity (465 mA h g-1 at 0.1 A g-1), superior rate capability (325 mA h g-1 at 1.0 A g-1) and cycling stability, attributed to their synergistic effect and high Li+ diffusion coefficient DLi [D(NaNbO3/rGO)/D(NaNbO3) ≈ 31.54]. Remarkably, the NaNbO3/rGO-based LIC delivers a high energy density of 166.7 W h kg-1 at 112.4 W kg-1 and remains 24.1 W h kg-1 at an ultrahigh power density of 26621.2 W kg-1, with an outstanding cycling durability (90% retention over 3000 cycles at 1.0 A g-1). This study provides new insights on novel intercalation-type anode material to enrich the materials system of LICs.

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Enhancing water splitting via weakening H2 and O2 adsorption on NiCo-LDH@CdS due to interstitial nitrogen doping: A close look at the mechanism of electron transfer Azam Pirkarami, Sousan Rasouli, Ebrahim Ghasemi 2021, 57(6): 118-130.  DOI: 10.1016/j.jechem.2020.08.043 Abstract ( 4 )   PDF (18718KB) ( 1 )   This paper is a report on the development of a convenient approach to fabricating a very efficient hybrid photoelectrocatalyst for water splitting. This photoelectrocatalyst consists of nickel-cobalt layered double hydroxide as the core, cadmium sulfide as the shell, and nitrogen, hence NiCo-LDH@CdS-N. For the electrocatalytic activity to be improved, the H2 and O2 binding energy needs to be weakened. The interstitial nitrogen doping on NiCo-LDH@CdS can increase electrocatalytic activity to a great extent. NiCo-LDH@CdS nanoparticles are obtained by subjecting to nitriding the NiCo-LDH@CdS electrode coated with polyvinylpyrrolidone nanosheets. This electrode has a large specific surface area, allows fast transfer of electrons, and exhibits long-term stability. The experimental results presented in this paper reveal that interstitial nitrogen doping largely reduces H2 and O2 binding energy and lowers the activation barrier for the formation and splitting of water.

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Alternating nanolayers as lithiophilic scaffolds for Li-metal anode Pinxian Jiang, Yifei Liao, Wei Liu, Yungui Chen 2021, 57(6): 131-139.  DOI: 10.1016/j.jechem.2020.08.034 Abstract ( 6 )   PDF (11565KB) ( 1 )   Nanostructured scaffolds offer promising opportunities in enabling dendrite-free long-cycle life Li metal anode. The rational design and controllable synthesis of scaffolding architectures are imperative for development of rechargeable Li metal batteries. In this study, we explore the fabrication and application of a tin monoxide/graphene hybrid architecture as a lithiophilic host for high-performance Li metal anode. Using a polymer-assisted sonochemical synthesis route, we tuned the thickness of SnO nanolayers and the nanostructure of alternatively stacking thin SnO nanosheet/graphene (SnO-NS/G) heterostructure. Offering abundant nucleation sites, fast ion transport tunnels, and 3D-conductivity, the unique 2D-2D architecture enables stable lithium plating-stripping cycling with low nucleation overpotential and high coulombic efficiency (CE). Hosted by SnO-NS/G scaffold, the resulting Li metal anode exhibits stable cycling over 200 cycles at 0.5 mA cm-2 (2 mAh). Full cell pairing high-mass-loading cathode LiCoO2 (LCO) (12 mg cm-2) with SnO-NS/G hosted Li metal anode delivers high energy density of 402 Wh kg-1 and stable cyclability of over 100 cycles. We elucidate the structure-property relationship between nanolayer thickness and Li-metal plating behaviors, giving new insight on structuring 2D-nanomaterials with ideal architectures for stable lithium metal batteries.

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Target-oriented confinement of Ru-Co nanoparticles inside N-doped carbon spheres via a benzoic acid guided process for high-efficient low-temperature ammonia synthesis Jun Ni, Zhenni Tan, Qianjin Sai, Jie Zhu, Xiuyun Wang, Bingyu Lin, Jianxin Lin, Chak-tong Au, Lilong Jiang 2021, 57(6): 140-146.  DOI: 10.1016/j.jechem.2020.08.067 Abstract ( 4 )   PDF (4553KB) ( 2 )   Ru-based heterogeneous catalysts have been used in a wide range of important reactions. However, due to the sintering of Ru nanoparticles their practical applications are somewhat restricted. Herein, for the first time we report a new and facile strategy to confine Ru and/or Co nanoparticles (NPs) in the channels of N-doped carbon using benzoic acid to guide the deposition location of Ru. The developed catalyst with confined RuCo alloy particles exhibits high resistance against Ru sintering and displays excellent activity and long term stability for NH3 synthesis, achieving an NH3 synthesis rate of up to 18.9 mmolNH3 gcat-1h-1 at 400 °C, which is ca. 2.25 times that of the catalyst prepared without confinement (with metal deposited on the support surface). In the latter case, there is an increase of nanoparticle size from 2.52 to 4.25 nm together with ca. 48% decrease of NH3 synthesis rate after 68 h at 400 °C. This study provides a new avenue for simple fabrication of precious-metal-based catalysts that are highly resistant against sintering, specifically suitable for low-temperature synthesis of ammonia with outstanding efficiency.

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Interfacial engineering in lead-free tin-based perovskite solar cells Zhenxi Wan, Huagui Lai, Shengqiang Ren, Rui He, Yiting Jiang, Jincheng Luo, Qiyu Chen, Xia Hao, Ye Wang, Jingquan Zhang, Lili Wu, Dewei Zhao 2021, 57(6): 147-168.  DOI: 10.1016/j.jechem.2020.08.053 Abstract ( 8 )   PDF (24252KB) ( 3 )   Lead (Pb)-free Tin (Sn)-based perovskite solar cells (PSCs) have been favored by the community due to their low toxicity, preferable bandgaps, and great potential to achieve high power conversion efficiencies (PCEs). Interfaces engineering plays important roles in developing highly efficient Sn-based PSCs via passivation of trap defects, alignment of energy levels, and incorporation of low-dimensional Sn-based perovskites. In this review, we summarize the development of Pb-free Sn-based perovskites and their applications in devices, especially the strategies of improving the interfaces. We also provide perspectives for future research. Our aim is to help the development of new and advanced approaches to achieving high-performance environment-friendly Pb-free Sn-based PSCs.

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Advancement of technology towards high-performance non-aqueous aluminum-ion batteries Ting-Ting Wei, Panpan Peng, Si-Yu Qi, Yan-Rong Zhu, Ting-Feng Yi 2021, 57(6): 169-188.  DOI: 10.1016/j.jechem.2020.08.035 Abstract ( 4 )   PDF (22487KB) ( 4 )   Al-ion batteries (AIBs) have been identified as one of the most hopeful energy storage systems after Li-ion batteries on account for the ultrahigh volumetric capacity, high safety and low cost from the rich abundance of Al. Nonetheless, some inevitable shortcomings, such as the formation of passive oxide film, hydrogen side reactions and anode corrosion, finally limit the large-scale application of aqueous AIBs. The nonaqueous AIBs have been considered as one of most hopeful alternatives for high-powered electrochemical energy storage devices. Nonetheless, various technical and scientific obstacles should be resolved because nonaqueous AIBs are still nascent. Some significant efforts have aimed to resolve these issues towards large-scale applications, and some important advancement has been made. In the present review, we mainly intended to offer an overview of non-aqueous AIBs systems, and we comprehensively reviewed the recent research advancement of the cathode materials, anode materials electrolyte and collectors as well as the fundamental understanding of the functional mechanisms. In addition, we have also analyzed several technical challenges and summarized the strategies used for overcoming the challenges in improving the electrochemical properties, including morphology control, surface engineering, doping and construction of composite electrodes as well as the charge storage mechanisms of the materials with different crystal structures. At last, future research orientation and development prospect of the AIBs are proposed.

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sp3-like defect structure of hetero graphene-carbon nanotubes for promoting carrier transfer and stability Shan-Shan Fan, Ling Shen, Yuan Dong, Ge Tian, Si-Ming Wu, Gang-Gang Chang, Christoph Janiak, Ping Wei, Jin-Song Wu, Xiao-Yu Yang 2021, 57(6): 189-197.  DOI: 10.1016/j.jechem.2020.09.020 Abstract ( 3 )   PDF (8068KB) ( 1 )   Three-dimensional (3D) hybrid of nanocarbons is a very promising way to the high-performance design of electrocatalysis materials. However, sp3-like defect structure, a combination of high strength and conduction of graphene and carbon nanotubes (CNTs) is rarely reported. Herein, 3D neural-like hybrids of graphene (from reduced graphene oxide) and carbon nanotubes (CNTs) have been integrated via sp3-like defect structure by a hydrothermal approach. The sp3-like defect structure endows 3D nanocarbon hybrids with an enhanced carrier transfer, high structural stability, and electrocatalytic durability. The neural-like structure is shown to demonstrate a cascade effect of charges and significant performances regarding bio-electrocatalysis and lithium-sulfur energy storage. The concept and mechanism of “sp3-like defect structure” are proposed at an atomic/nanoscale to clarify the generation of rational structure as well as the cascade electron transfer.

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Carbon dots-confined CoP-CoO nanoheterostructure with strong interfacial synergy triggered the robust hydrogen evolution from ammonia borane Han Wu, Yaojia Cheng, Boyang Wang, Yao Wang, Min Wu, Weidong Li, Baozhong Liu, Siyu Lu 2021, 57(6): 198-205.  DOI: 10.1016/j.jechem.2020.08.051 Abstract ( 12 )   PDF (11042KB) ( 2 )   Ammonia borane (NH3BH3, AB) is promising for chemical hydrogen storage; however, current systems for rapid hydrogen production are limited by the expensive noble metal catalysts required for AB hydrolysis. Here we report the design and synthesis of a highly efficient and robust non-noble-metal catalyst for the hydrolysis of AB at 298 K (TOF = 89.56 molH2 min-1 molCo-1). Experiments and density functional theory calculations were performed to explore the catalyst's hybrid nanoparticle heterostructure and its catalytic mechanism. The catalyst comprised nitrogen-doped carbon dots confining CoO and CoP, and exhibited strong interface-induced synergistic catalysis for AB hydrolysis that effectively decreased the energy barriers for the dissociation of both AB and water molecules. The co-doping of N and P introduced numerous defects, and further regulated the reactivity of the carbon layers. The heterogeneous interface design technique presented here provides a new strategy for developing efficient and inexpensive non-noble-metal catalysts that may be applicable in other fields related to energy catalysis.

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Immobilizing polysulfide jointly via chemical absorbing and physical blocking in polytungstates-embedded carbon nanofibers Yanmei Nie, Lei Tan, Guangchao Li, Sanghao Li, Jun Yan, Jiexi Wang 2021, 57(6): 206-211.  DOI: 10.1016/j.jechem.2020.08.032 Abstract ( 4 )   PDF (8607KB) ( 1 )   Lithium-sulfur (Li-S) battery is regarded as one of the most fascinating candidates for energy storage due to its dominant advantage of high energy density. However, the shuttling effect of soluble polysulfides and low electrical conductivity of sulfur and Li2S still hinder its commercialization. In this work, high electrical-conductive carbon nanofibers (CNFs) with uniformly embedded polytungstates (HPW@CNFs) are proposed for advanced Li-S batteries. H3PW12O40 (HPW) is a kind of molecular nano-sized metal cluster which contains rich Lewis acid/base sites that can stabilize polysulfide effectively through chemical bonding, while CNFs play the role of physical barriers for polysulfides and transmission channel for electrons. The HPW@CNFs/S cathode shows an ultra-stable cycling performance with extremely small decay rate of 0.015% per cycle over 400 cycles at 0.5 C.

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Topotactically constructed nickel-iron (oxy)hydroxide with abundant in-situ produced high-valent iron species for efficient water oxidation Zhichong Kuang, Song Liu, Xuning Li, Meng Wang, Xinyi Ren, Jie Ding, Rile Ge, Wenhui Zhou, Alexandre I. Rykov, Moulay T. Sougrati, Pierre-Emmanuel Lippens, Yanqiang Huang, Junhu Wang 2021, 57(6): 212-218.  DOI: 10.1016/j.jechem.2020.09.014 Abstract ( 5 )   PDF (3681KB) ( 1 )   The low efficiency of oxygen evolution reaction (OER) is regarded as one of the major roadblocks for metal-air batteries and water electrolysis. Herein, a high-performance OER catalyst of NiFe0.2 (oxy)hydroxide (NiFe0.2-OxHy) was developed through topotactic transformation of a Prussian blue analogue in an alkaline solution, which exhibits a low overpotential of only 263 mV to reach a current density of 10 mA cm-2 and a small Tafel slope of 35 mV dec-1. Ex-situ/operando Raman spectroscopy results indicated that the phase structure of NiFe0.2-OxHy was irreversibly transformed from the type of α-Ni(OH)2 to γ-NiOOH with applying an anodic potential, while ex-situ/operando 57Fe Mössbauer spectroscopic studies evidenced the in-situ production of abundant high-valent iron species under OER conditions, which effectively promoted the OER catalysis. Our work elucidates that the amount of high-valent iron species in-situ produced in the NiFe (oxy)hydroxide has a positive correlation with its water oxidation reaction performance, which further deepens the understanding of the mechanism of NiFe-based electrocatalysts.

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New types of hybrid electrolytes for supercapacitors Wuquan Ye, Haiyan Wang, Jiqiang Ning, Yijun Zhong, Yong Hu 2021, 57(6): 219-232.  DOI: 10.1016/j.jechem.2020.09.016 Abstract ( 9 )   PDF (5654KB) ( 3 )   Supercapacitors (SCs) are emerging as efficient energy storage devices but still suffering from limited energy density compared with batteries. Electrolytes have been regarded as the key to determine the energy storage performance of SCs. However, none of the conventional electrolytes can fully meet the increasing requirements of SCs in terms of high ion conductivity, excellent stability, wide voltage window and operating temperature range, as well as environmentally friend concerns. To this end, hybrid electrolytes have sprung up in recent years, which are believed to be the candidate to solve these shortcomings. Herein, the state-of-the-art types of hybrid electrolytes for SCs, including the combination of aqueous and organic, aqueous and gel polymer, ionic liquids (ILs) and organic, and ILs and gel polymer hybrid electrolytes, are reviewed. The effects of different hybrid systems on the performance of SCs and the underlying mechanisms are among the focal points of the review, and prospects and possible directions are discussed as well to provide further insight into the future development of this field.

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Quasi-Grotthuss mechanism in a nonporous sulphate Bo Li, Yinuo Wang, Jiasheng Wang, Xue Yong, Jingping Zhang 2021, 57(6): 233-237.  DOI: 10.1016/j.jechem.2020.09.012 Abstract ( 5 )   PDF (8460KB) ( 1 )

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A highly concentrated vanadium protic ionic liquid electrolyte for the vanadium redox flow battery Georgios Nikiforidis, Amal Belhcen, Mérièm Anouti 2021, 57(6): 238-246.  DOI: 10.1016/j.jechem.2020.09.001 Abstract ( 9 )   PDF (6364KB) ( 1 )   A protic ionic liquid is designed and implemented for the first time as a solvent for a high energy density vanadium redox flow battery. Despite being less conductive than standard aqueous electrolytes, it is thermally stable on a 100 °C temperature window, chemically stable for at least 60 days, equally viscous and dense with typical aqueous solvents and most importantly able to solubilize to 6 mol L-1 vanadium sulfate, thus increasing the VRFB energy density by a factor of 2.5. Electrochemical measurements revealed quasi-reversible redox transitions for both catholyte and anolyte at 25 °C while a proof-of-concept redox flow cell with the proposed electrolyte was tested for a total of 150 cycles at 25 °C, showing an open circuit potential of 1.39 V and energy and coulombic efficiencies of 65% and 93%, respectively. What's more, the battery can be equally cycled at 45 °C showing good thermal stability. This study underlines a new route to improve the energy-to-volume ratio of energy storage system.

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Lignocellulosic biomass as sustainable feedstock and materials for power generation and energy storage Fangqian Wang, Denghao Ouyang, Ziyuan Zhou, Samuel J. Page, Dehua Liu, Xuebing Zhao 2021, 57(6): 247-280.  DOI: 10.1016/j.jechem.2020.08.060 Abstract ( 139 )   PDF (7267KB) ( 68 )   Lignocellulosic biomass has attracted great interest in recent years for energy production due to its renewability and carbon-neutral nature. There are various ways to convert lignocellulose to gaseous, liquid and solid fuels via thermochemical, chemical or biological approaches. Typical biomass derived fuels include syngas, bio-gas, bio-oil, bioethanol and biochar, all of which could be used as fuels for furnace, engine, turbine or fuel cells. Direct biomass fuel cells mediated by various electron carriers provide a new direction of lignocellulose conversion. Various metal and non-metal based carriers have been screened for mediating the electron transfer from biomass to oxygen thus generating electricity. The power density of direct biomass fuel cells can be over 100 mW cm-2, which shows promise for practical applications. Lignocellulose and its isolated components, primarily cellulose and lignin, have also been paid considerable attention as sustainable carbonaceous materials for preparation of electrodes for supercapacitors, lithium-ion batteries and lithium-sulfur batteries. In this paper, we have provided a state-of-the-art review on the research progress of lignocellulosic biomass as feedstock and materials for power generation and energy storage focusing on the chemistry aspects of the processes. It was recommended that process integration should be performed to reduce the cost for thermochemical and biological conversion of lignocellulose to biofuels, while efforts should be made to increase efficiency and improve the properties for biomass fuelled fuel cells and biomass derived electrodes for energy storage.

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Visualization of atomic scale reaction dynamics of supported nanocatalysts during oxidation and ammonia synthesis using in-situ environmental (scanning) transmission electron microscopy Michael R. Ward, Robert W. Mitchell, Edward D. Boyes, Pratibha L. Gai 2021, 57(6): 281-290.  DOI: 10.1016/j.jechem.2020.08.069 Abstract ( 8 )   PDF (7231KB) ( 1 )   Reaction dynamics in gases at operating temperatures at the atomic level are the basis of heterogeneous gas-solid catalyst reactions and are crucial to the catalyst function. Supported noble metal nanocatalysts such as platinum are of interest in fuel cells and as diesel oxidation catalysts for pollution control, and practical ruthenium nanocatalysts are explored for ammonia synthesis. Graphite and graphitic carbons are of interest as supports for the nanocatalysts. Despite considerable literature on the catalytic processes on graphite and graphitic supports, reaction dynamics of the nanocatalysts on the supports in different reactive gas environments and operating temperatures at the single atom level are not well understood. Here we present real time in-situ observations and analyses of reaction dynamics of Pt in oxidation, and practical Ru nanocatalysts in ammonia synthesis, on graphite and related supports under controlled reaction environments using a novel in-situ environmental (scanning) transmission electron microscope with single atom resolution. By recording snapshots of the reaction dynamics, the behaviour of the catalysts is imaged. The images reveal single metal atoms, clusters of a few atoms on the graphitic supports and the support function. These all play key roles in the mobility, sintering and growth of the catalysts. The experimental findings provide new structural insights into atomic scale reaction dynamics, morphology and stability of the nanocatalysts.

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Characterization methods of organic electrode materials Meng Zhang, Wenjun Zhou, Weiwei Huang 2021, 57(6): 291-303.  DOI: 10.1016/j.jechem.2020.08.054 Abstract ( 7 )   PDF (16390KB) ( 5 )   The development of novel organic electrode materials is of great significance for improving the reversible capacity and cycle stability of rechargeable batteries. Before practical application, it is essential to characterize the electrode materials to study their structures, redox mechanisms and electrochemical performances. In this review, the common characterization methods that have been adopted so far are summarized from two aspects: experimental characterization and theoretical calculation. The experimental characterization is introduced in detail from structural characterization, electrochemical characterization and electrode reaction characterization. The experimental purposes and working principles of various experimental characterization methods are briefly illustrated. As the auxiliary means, theoretical calculation provides the theoretical basis for characterizing the electrochemical reaction mechanism of organic electrode materials. Through these characterizations, we will have a deep understanding about the material structures, electrochemical redox mechanisms, electrochemical properties and the relationships of structure-property. It is hoped that this review would help researchers to select the suitable characterization methods to analyze the structures and performances of organic electrode materials quickly and effectively.

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Engineering heterogenous catalysts for chemical CO2 utilization: Lessons from thermal catalysis and advantages of yolk@shell structured nanoreactors Cameron Alexander Hurd Price, Tomas Ramirez Reina, Jian Liu 2021, 57(6): 304-324.  DOI: 10.1016/j.jechem.2020.08.061 Abstract ( 12 )   PDF (5616KB) ( 2 )   The development of catalytic materials for the recycling CO2 through a myriad of available processes is an attractive field, especially given the current climate change. While there is increasing publication in this field, the reported catalysts rarely deviate from the traditionally supported metal nanoparticle morphology, with the most simplistic method of enhancement being the addition of more metals to an already complex composition. Encapsulated catalysts, especially yolk@shell catalysts with hollow voids, offer answers to the most prominent issues faced by this field, coking and sintering, and further potential for more advanced phenomena, for example, the confinement effect, to promote selectivity or offer greater protection against coking and sintering. This work serves to demonstrate the current position of catalyst development in the fields of thermal CO2 reforming and hydrogenation, summarizing the most recent work available and most common metals used for these reactions, and how yolk@shell catalysts can offer superior performance and survivability in thermal CO2 reforming and hydrogenation to the more traditional structure. Furthermore, this work will briefly demonstrate the bespoke nature and highly variable yolk@shell structure. Moreover, this review aims to illuminate the spatial confinement effect and how it enhances yolk@shell structured nanoreactors is presented.

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Perovskite - A wonder catalyst for solar hydrogen production Hui Bian, Deng Li, Junqing Yan, ShengzhongLiu 2021, 57(6): 325-340.  DOI: 10.1016/j.jechem.2020.08.057 Abstract ( 26 )   PDF (9005KB) ( 6 )   Hydrogen generation via artificial photosynthesis paves a promising way to remit the ever-increasing energy crisis and deteriorative environmental issues. Among all the materials utilized for solar hydrogen production, perovskite has emerged as a rising star due to its superior optoelectronic properties. This manuscript aims to provide a comprehensive review summarizing the recent inspiring advancements on perovskite-based solar hydrogen production systems, including the particulate photocatalysis, photoelectrochemical cells, and photovoltaic-electrocatalytic cells. We start with a brief introduction of the advantages of perovskites for solar hydrogen production and the basic principles of the three most prominent solar hydrogen production systems. The representative progresses in this field are then detailed with a special emphasis on the strategies to improve the efficiency and the stability of the systems. Finally, challenges and opportunities for the further development of the PVK-based solar hydrogen production systems are presented with perspective given on outlook, performance, cost and stability.

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Fluorine substitution position effects on spiro(fluorene-9,9'-xanthene) cored hole transporting materials for high-performance planar perovskite solar cells Zhaoning Li, Yikai Yun, Hongyan Huang, Zhucheng Ding, Xuewei Li, Baomin Zhao, Wei Huang 2021, 57(6): 341-350.  DOI: 10.1016/j.jechem.2020.08.041 Abstract ( 7 )   PDF (3922KB) ( 1 )   Fluorine substitution in molecular design has become an effective strategy for improving the overall performance of organic photovoltaics. In this study, three low-cost small molecules of spiro-linked hole transporting materials (SFX-o-2F, SFX-m-2F, and SFX-p-2F) endowed with two-armed triphenylamine moieties were synthesized via tuning of the fluorine substitution position, and they were employed for use in highly efficient perovskite solar cells (PSCs). Despite the fluorine substitution position playing a negligible role in the optical and electrochemical properties of the resulting small molecules, the photovoltaic performance thereof was observed to vary significantly. The planar n-i-p PSCs based on SFX-m-2F demonstrated superior performance (18.86%) when compared to that of the corresponding SFX-o-2F (9.7%) and SFX-p-2F (16.33%) under 100 mW cm-2 AM1.5G solar illumination, which is competitive with the performance of the benchmark spiro-OMeTAD-based device (18.98%). Moreover, the SFX-m-2F-based PSCs were observed to be more stable than the spiro-OMeTAD-based devices under ambient conditions. The improved performance of SFX-m-2F is primarily associated with improved morphology, more efficient hole transport, and extraction characteristics at the perovskite/HTM interface. This work demonstrated the application of fluorination engineering to the tuning of material film morphology and charge transfer properties, showing the promising potential of fluorinated SM-HTMs for the construction of low-cost, high-efficiency PSCs.

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High-throughput computational screening of oxide double perovskites for optoelectronic and photocatalysis applications Xiaowei Jiang, Wan-Jian Yin 2021, 57(6): 351-358.  DOI: 10.1016/j.jechem.2020.08.046 Abstract ( 7 )   PDF (4076KB) ( 2 )   Oxide double perovskites A2B'B''O6 are a class of emerging materials in the fields of optoelectronics and catalysis. Due to the chemical flexibilities of perovskite structures, there are multiple elemental combinations of cations A, B', and B'', which leading to tremendous candidates. In this study, we comprehensively screened stable oxide double perovskite A2B'B''O6 from a pool of 2,018 perovskite candidates using a high-throughput computational approach. By considering a tolerance factor (t)-octahedral factor (μ) phase diagram, 138 candidates withFm$\bar{3}$m, P21/c, and R3c phases were selected and systematically studied via first-principles calculations based on density functional theory. The screening procedure finally predicted the existence of 21 stable perovskites, and 14 among them have never been reported. Verification with existing experimental results demonstrates that the prediction accuracy for perovskite formability is approximately 90%. The predicted oxide double perovskites exhibit quasi-direct bandgaps ranging from 0 to 4.4 eV with a significantly small direct-indirect bandgap difference, balanced electron and hole effective masses, and strong optical absorptions. The newly predicted oxide double perovskites may enlarge the pool of material candidates for applications in optoelectronics and photocatalysis. This study provides a route for computational screening of novel perovskites for functional applications.

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Atomically precise metal nanoclusters for (photo)electroreduction of CO2: Recent advances, challenges and opportunities Lubing Qin, Guanyu Ma, Likai Wang, Zhenghua Tang 2021, 57(6): 359-370.  DOI: 10.1016/j.jechem.2020.09.003 Abstract ( 4 )   PDF (5216KB) ( 2 )   To alleviate the global warming by removing excess CO2 and converting them into value-added chemicals, (photo)electrochemical reduction has been recognized as a promising strategy. As the CO2 reduction reaction (CO2RR) is involved with multiple electrons and multiple products, plus the complexity of the surface chemical environment of the catalyst, it is extremely challenging to establish the structure/function relationship. Atomically precise metal nanoclusters (NCs), with crystallographically resolved structure, molecule-like characters and strong quantum confinement effects, have been emerging as a new type of catalyst for CO2RR, and more importantly, they can provide an ideal platform to unravel the comprehensive mechanistic insights and establish the structure/function relationship eventually. In this review, the recent advances regarding employing molecular metal NCs with well-defined structure including Au NCs, Au-based alloy NCs, Ag NCs, Cu NCs for CO2RR and relevant mechanistic studies are discussed, and the opportunities and challenges are proposed at the end for paving the development of CO2RR by using atomically precise metal NCs.

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Single-atom Pt promoted Mo2C for electrochemical hydrogen evolution reaction Shanshan Niu, Ji Yang, Haifeng Qi, Yang Su, Zhiyu Wang, Jieshan Qiu, Aiqin Wang, Tao Zhang 2021, 57(6): 371-377.  DOI: 10.1016/j.jechem.2020.08.028 Abstract ( 9 )   PDF (6544KB) ( 2 )   Hydrogen generation from electrochemical water splitting powered by renewable energy is important to the sustainable society, but the prohibitive cost of current Pt electrocatalyst has impeded the large-scale production of hydrogen by water electrolysis. In this contribution, a new low-Pt electrocatalyst for hydrogen evolution reaction (HER) has been fabricated by a facile one-pot synthesis approach, in which Pt2+ cations and phosphomolybdic acid confined in the metal-organic frameworks (MOFs) were submitted to pyrolysis to yield Pt single atoms dispersed into Mo2C nanocrystals in 3D porous carbon matrix. The as-synthesized Pt1-Mo2C-C catalyst with Pt content of only 0.7 wt% exhibited remarkably enhanced activity for HER in 1 M KOH, with overpotential at 10 mA/cm2 lowered from 211 mV to 155 mV and 7-fold higher mass activity (7.14 A/mgPt) than the benchmark 20 wt% Pt/C. The promoted activity can be attributed to the electronic interaction between Pt single atoms and Mo2C surface, which not only improved water activation but also strengthened hydrogen adsorption, as indicated by FTIR and microcalorimetric characterizations.

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Hierarchical N-doped porous carbon hosts for stabilizing tellurium in promoting Al-Te batteries Xuefeng Zhang, Mingyong Wang, Jiguo Tu, Shuqiang Jiao 2021, 57(6): 378-385.  DOI: 10.1016/j.jechem.2020.09.015 Abstract ( 4 )   PDF (7789KB) ( 1 )   Aluminum batteries are attractive in electrochemical energy storage due to high energy density and low-cost aluminum, while the energy density is limited for the lack of favorable positive electrode materials to match aluminum negative electrodes. Tellurium positive electrode is intrinsically electrically conductive among chalcogen and holds high theoretical specific capacity (1260.27 mAh g-1) and discharge voltage plateau (~1.5 V). However, the chemical and electrochemical dissolution of Te active materials results in the low material utilization and poor cycling stability. To enhance the electrochemical performance, herein a nitrogen doped porous carbon (N-PC) is derived from zeolite imidazolate framework (ZIF-67) as an effective tellurium host to suppress the undesired shuttle effect. In order to inhibit the volume expansion of N-PC during the charge/discharge process, the reduced graphene oxide (rGO) nanosheets are introduced to form a stable host materials (N-PC-rGO) for stabilizing Te. The physical encapsulation and chemical confinement to soluble tellurium species are achieved. N-PC-rGO-Te positive electrode exhibits an improved initial specific capacity and long-term cycling performance at a current density of 500 mA g-1 (initial specific capacity: 935.5 mAh g-1; after 150 cycles: 467.5 mAh g-1), highlighting a promising design strategy for inhibiting chemical and electrochemical dissolution of Te.

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Understanding the precursor chemistry for one-step deposition of mixed cation perovskite solar cells by methylamine route Manuel Vásquez-Montoya, Juan F. Montoya, Daniel Ramirez, Franklin Jaramillo 2021, 57(6): 386-391.  DOI: 10.1016/j.jechem.2020.08.059 Abstract ( 4 )   PDF (2043KB) ( 1 )   Upscaling perovskite solar cell fabrication is one of the key challenges in the pathway for commercialization. The slow evaporation of frequently used solvents (DMF or DMSO) limits the fast perovskite layer crystallization, hindering their implementation in large scale deposition methods. Alternatively, methylamine-based precursors have demonstrated rapid crystallization, leading to uniform and specular films. Nonetheless, their application has been limited to MAPbI3 perovskites with limited efficiency and stability. In this work, we report the requirements for stabilizing α-phase of mixed cation perovskites with high amount of formamidinium by using a methylamine-based precursor. We found that even though, there are many methods for incorporating the methylamine (MA) in precursors or films; the MA content determines stabilization of the α-phase and therefore the viscous-solution route is the only method to incorporate high amounts of MA. At low amounts of MA, perovskite tend to crystallize in 1D dimensional FA3(MA)PbI5 phases due to the incomplete solvation of the PbI6- clusters. In contrast, high MA ratio induces a full solvation of the clusters, leading to a rapid crystallization and a full stabilization of the active 3D α-phase. These results open a window in the development and understanding of new precursors for the fabrication of high efficient, stable and scalable perovskite devices.

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Homogeneous bottom-growth of lithium metal anode enabled by double-gradient lithiophilic skeleton Li Zhang, Hongfei Zheng, Ben Liu, Qingshui Xie, Qiulin Chen, Liang Lin, Jie Lin, Baihua Qu, Laisen Wang, Dong-Liang Peng 2021, 57(6): 392-400.  DOI: 10.1016/j.jechem.2020.09.004 Abstract ( 13 )   PDF (6698KB) ( 3 )   Lithium (Li) metal is considered as the most promising anode material for the next-generation high performance Li batteries. However, the uncontrollable dendritic growth impedes its commercial application. Herein, we design a 3D Si@carbon nanofibers (CNFs) @ZnO-ZnO-Cu skeleton (SCZ) for guiding the homogeneous bottom-growth of Li metal. The top LixSi@CNFs and bottom LiyZn@CNFs layers could form conductivity and overpotential gradient to avoid the “top-growth” of Li metal. Moreover, the top lithiophilic LixSi@CNFs layer could regulate the nucleation and deposition of Li-ions even if the lithium dendrites grow out of the skeleton under high capacity Li deposition (30 mAh cm-2). As a result, the SCZ-Li||LiFePO4 full cell delivers a high capacity of ~104 mAh g-1 (~94.82% capacity retention) after 2000 cycles at 5C, elucidating the potential application of the 3D double-gradient Li metal composite anode.

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LiOH: A “double-edged” effect toward electrochemical oxidation of Li2O2 Qinghua Cui, Lipo Ma, Peng Zhang b, Yuliang Cao, Jiawei Wang 2021, 57(6): 401-405.  DOI: 10.1016/j.jechem.2020.09.018 Abstract ( 10 )   PDF (1350KB) ( 2 )

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Recent advances and perspectives of fluorite and perovskite-based dual-ion conducting solid oxide fuel cells Jiafeng Cao, Chao Su, Yuexia Ji, Guangming Yang, Zongping Shao 2021, 57(6): 406-427.  DOI: 10.1016/j.jechem.2020.09.010 Abstract ( 18 )   PDF (10557KB) ( 6 )   High-temperature solid-state electrolyte is a key component of several important electrochemical devices, such as oxygen sensors for automobile exhaust control, solid oxide fuel cells (SOFCs) for power generation, and solid oxide electrolysis cells for H2 production from water electrolysis or CO2 electrochemical reduction to value-added chemicals. In particular, internal diffusion of protons or oxygen ions is a fundamental and crucial issue in the research of SOFCs, hypothetically based on either oxygen-ion-conducting electrolytes or proton-conducting electrolytes. Up to now, some electrolyte materials based on fluorite or perovskite structure were found to show certain degree of dual-ion transportation capability, while in available electrolyte database, particularly in the field of SOFCs, such dual-ion conductivity was seriously overlooked. Actually, few concerns arising to the simultaneous proton and oxygen-ion conductivities in electrolyte of SOFCs inevitably induce various inadequate and confusing results in literature. Understanding dual-ion transportation behavior in electrolyte is indisputably of great importance to explain some unusual fuel cell performance as reported in literature and enrich the knowledge of solid state ionics. On the other hand, exploration of novel dual-ion conducting electrolytes will benefit the development of SOFCs. In this review, we provide a comprehensive summary of the understanding of dual-ion transportation in solid electrolyte and recent advances of dual-ion conducting SOFCs. The oxygen ion and proton conduction mechanisms at elevated temperature inside oxide-based electrolyte materials are first introduced, and then (mixed) oxygen ion and proton conduction behaviors of fluorite and perovskite-type oxides are discussed. Following on, recent advances in the development of dual-ion conducting SOFCs based on fluorite and perovskite-type single-phase or composite electrolytes, are reviewed. Finally, the challenges in the development of dual-ion conducting SOFCs are discussed and future prospects are proposed.

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Strong coupled spinel oxide with N-rGO for high-efficiency ORR/OER bifunctional electrocatalyst of Zn-air batteries Wenjun Liu, Dewei Rao, Jian Bao, Li Xu, Yucheng Lei, Huaming Li 2021, 57(6): 428-435.  DOI: 10.1016/j.jechem.2020.08.066 Abstract ( 8 )   PDF (4991KB) ( 1 )   The high cost, scarcity, and poor stability of precious-metal-based catalysts have hindered their extensive application in energy conversion and storage. This stimulates the search for earth-abundant alternatives to replace noble metal electrocatalysts. Hence, in this study, we investigate a novel and low-cost bifunctional electrocatalyst consisting of ZnCoMnO4 anchored on nitrogen-doped graphene oxide (ZnCoMnO4/N-rGO). Benefiting from the strong Co-N interaction in ZnCoMnO4 and the coupled conductive N-rGO, the catalysts exhibit high electrocatalytic activity. Moreover, density functional theory calculations support the dominant role of the strong Co-N electronic interaction, which leads to ZnCoMnO4/N-rGO having more favorable binding energies with O2 and H2O, resulting in fast reaction kinetics. The obtained ZnCoMnO4/N-rGO electrocatalyst exhibits superb bifunctional activity, with a half-wave potential of 0.83 V for the oxygen reduction reaction and a low onset potential of 1.57 V for the oxygen evolution reaction in 0.1 M KOH solution. Furthermore, a Zn-air battery driven by the ZnCoMnO4/N-rGO catalyst shows remarkable discharge/charge performance, with a power density of 138.52 mW cm-2 and long-term cycling stability for 48 h. This work provides a promising multifunctional electrocatalyst based on non-noble metals for the storage and conversion of renewable energy.

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Necessity of structural rearrangements for O-O bond formation between O5 and W2 in photosystem II Yu Guo, Biaobiao Zhang, Lars Kloo, Licheng Sun 2021, 57(6): 436-442.  DOI: 10.1016/j.jechem.2020.09.008 Abstract ( 6 )   PDF (4414KB) ( 1 )   Numerous aspects of the water oxidation mechanism in photosystem II have not been fully elucidated, especially the O—O bond formation pathway. However, a body of experimental evidences have identified the O5 and W2 ligands of the oxygen-evolving complex as the highly probable substrate candidates. In this work, we studied O—O bond formation between O5 and W2 based on the native Mn4Ca cluster by density functional calculations. Structural rearrangements before the formation of the S4 state were found as a prerequisite for O—O bond formation between O5 and W2, regardless if the suggested pathways involving the typical Mn1(IV)-O species or the recently proposed Mn4(VII)(O)2 species. Possible alternatives for the S2 → S3 and S3 → S4 transitions accounting for such required rearrangements are discussed. These findings reflect that the structural flexibility of the Mn4Ca cluster is essential to allow structural rearrangements during the catalytic cycle.

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Anchoring Mo on C9N4 monolayers as an efficient single atom catalyst for nitrogen fixation Zhe Xue, Xinyu Zhang, Jiaqian Qin, Riping Liu 2021, 57(6): 443-450.  DOI: 10.1016/j.jechem.2020.09.002 Abstract ( 6 )   PDF (7656KB) ( 2 )   Electrochemical nitrogen fixation via a convenient and sustainable manner, exhibits an intriguing prospect for ammonia generation under ambient conditions. Currently, the design and development of high-efficiency and low-cost electrocatalysts remains the major challenge confronting nitrogen reduction reaction (NRR). Herein, anchoring the single Mo atom on the C9N4 substrate (Mo@C9N4) to form an efficient single-atom catalyst (SAC) is proposed for the conversion of N2 to NH3. By employing density functional theory (DFT) calculations, we demonstrated that gas phase N2 can be sufficiently activated and efficiently reduced to NH3 on the surface of Mo@C9N4. Meanwhile, we found that the NRR dominantly occurred on the Mo center via a preferred distal pathway with favorable limiting potential of 0.40 V. Importantly, the as-established Mo@C9N4 catalyst exhibits an outstanding structural stability and good selectivity toward NRR. These findings provide a promising platform for designing Mo-based SACs for electrochemical N2 fixation.

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Recent progress of advanced anode materials of lithium-ion batteries Hui Cheng, Joseph G. Shapter, Yongying Li, Guo Gao 2021, 57(6): 451-468.  DOI: 10.1016/j.jechem.2020.08.056 Abstract ( 13 )   PDF (8442KB) ( 5 )   The rapid development of electric vehicles and mobile electronic devices is the main driving force to improve advanced high-performance lithium ion batteries (LIBs). The capacity, rate performance and cycle stability of LIBs rely directly on the electrode materials. As far as the development of the advanced LIBs electrode is concerned, the improvement of anode materials is more urgent than the cathode materials. Industrial production of anode materials superior to commercial graphite still faces some challenges. This review sets out the most basic LIBs anode material design. The reaction principles and structural design of carbon materials, various transition metal oxides, silicon and germanium are summarized, and then the progress of other anode materials are analyzed. Due to the rapid development of metal organic frameworks (MOFs) in energy storage and conversion in recent years, the synthesis process and energy storage mechanism of nanostructures derived from MOF precursors are also discussed. From the perspective of novel structural design, the progress of various MOFs-derived materials for alleviating the volume expansion of anode materials is discussed. Finally, challenges for the future development of advanced anode materials for LIBs will be considered.

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Hybrid co-based MOF nanoboxes/CNFs interlayer as microreactors for polysulfides-trapping in lithium-sulfur batteries Jing Li, Caiming Jiao, Jinghui Zhu, Liubiao Zhong, Tuo Kang, Sehrish Aslam, Jianyong Wang, Sanfei Zhao, Yejun Qiu 2021, 57(6): 469-476.  DOI: 10.1016/j.jechem.2020.03.024 Abstract ( 7 )   PDF (7838KB) ( 4 )   Lithium-sulfur battery is desirable for the future potential electrochemical energy storage device with advantages of high theoretical energy density, low cost and environmental friendliness. However, some natural hindrances, particularly fast capacity degradation resulting from the migration of dissolved polysulfide intermediates, remain to be significant challenges prior to the practical applications. In this work, a composite interlayer of carbon nanofibers (CNFs) which are enriched by Co-based metal organic frameworks (ZIF-67) growth in-situ is exploited. Notably, physical blocking and chemical trapping abilities are obtained synergistically from the ZIF/CNFs interlayer, which enables to restrain the dissolution of polysulfides and alleviate shuttle effect. Moreover, the three-dimensional fiber networks provide an interconnected conductive framework between each ZIF microreactor to promote fast electron transfer during cycling, thus contributing to excellent rate and cycling performance. As a result, Li-S cells with ZIF/CNFs interlayer show a high specific capacity of 1334 mAh g-1 at 1 C with an excellent cycling stability over 300 cycles. Besides, this scalable and affordable electrospinning fabrication method provides a promising approach for the design of MOFs-derived carbon materials for high performance Li-S batteries.

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Boron nitride for enhanced oxidative dehydrogenation of ethylbenzene Rui Han, Jiangyong Diao, Sonu Kumar, Andrey Lyalin, Tetsuya Taketsugu, Gilberto Casillas, Christopher Richardson, Feng Liu, Chang Won Yoon, Hongyang Liu, Xudong Sun, Zhenguo Huang 2021, 57(6): 477-484.  DOI: 10.1016/j.jechem.2020.03.027 Abstract ( 8 )   PDF (2237KB) ( 3 )   It is demonstrated experimentally and confirmed theoretically that highly defective boron nitride showed outstanding performance for oxidative dehydrogenation of ethylbenzene. The catalyst is derived from carbon-doped hexagonal boron nitride nanosheets synthesized via a two-step reaction when participating the oxidative dehydrogenation reaction. The first step yields a polymeric precursor with the atomic positions of B, C, N relatively constrained, which is conducive for the formation of carbon atomic clusters uniformly dispersed throughout the BN framework. During the oxidative dehydrogenation of ethylbenzene to styrene, the nanoscale carbon clusters are removed and highly defective boron nitride (D-BN) is obtained, exposing boron-rich zigzag edges of BN that act as the catalytic sites. The catalytic performance of D-BN is therefore remarkably better than un-doped h-BN. Our results indicate that dispersed C-doping in h-BN is highly effective in terms of defect formation and resultant enhanced activity in oxidative dehydrogenation reactions.

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Surface functionalized N-C-TiO2/C nanocomposites derived from metal-organic framework in water vapour for enhanced photocatalytic H2 generation Mian Zahid Hussain, Zhuxian Yang, Bart van der Linden, Zheng Huang, Quanli Jia, Erik Cerrato, Roland A. Fischer, Freek Kapteijn, Yanqiu Zhu, Yongde Xia 2021, 57(6): 485-495.  DOI: 10.1016/j.jechem.2020.08.048 Abstract ( 6 )   PDF (2129KB) ( 3 )   Surface-functionalized nitrogen/carbon co-doped polymorphic TiO2 phase junction nanoparticles uniformly distributed in porous carbon matrix were synthesized by a simple one-step pyrolysis of titanium based metal-organic framework (MOF), NH2-MIL-125(Ti) at 700 °C under water vapour atmosphere. Introducing water vapour during the pyrolysis of NH2-MIL-125(Ti) not only functionalizes the derived porous carbon matrix with carboxyl groups but also forms additional oxygen-rich N like interstitial/intraband states lying above the valence band of TiO2 along with the self-doped carbon, which further narrows the energy band gaps of polymorphic TiO2 nanoparticles that enhance photocatalytic charge transfer efficiency. Without co-catalyst, sample N-C-TiO2/CArW demonstrates H2 evolution activity of 426 µmol gcat-1 h-1, which remarkably outperforms commercial TiO2 (P-25) and N-C-TiO2/CAr with a 5-fold and 3-fold H2 generation, respectively. This study clearly shows that water vapour atmosphere during the pyrolysis increases the hydrophilicity of the Ti-MOF derived composites by functionalizing porous carbon matrix with carboxylic groups, as well as enhancing the electrical conductivity and charge transfer efficiency due to the formation of additional localized oxygen-rich N like interstitial/intraband states. This work also demonstrates that by optimizing the anatase-rutile phase composition of the TiO2 polymorphs, tuning the energy band gaps by N/C co-doping and functionalizing the porous carbon matrix in the N-C-TiO2/C nanocomposites, the photocatalytic H2 generation activity can be further enhanced.

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Recent progress in water splitting and hybrid supercapacitors based on nickel-vanadium layered double hydroxides Josué M. Gonçalves, Paulo R. Martins, Koiti Araki, Lucio Angnes 2021, 57(6): 496-515.  DOI: 10.1016/j.jechem.2020.08.047 Abstract ( 11 )   PDF (11076KB) ( 2 )   Environmentally friendly energy sources alternatives to fossil fuels such as solar and wind are strategic for meeting the needs of an increasingly energy demanding society, despite their periodic/intermittent nature. Thus, urge the development of clean and renewable energy sources such as based on solar energy and water in a cyclic way, by photoinduced water-splitting and regeneration in fuel cells. In this context, energy storage devices such as hybrid supercapacitors become fundamental for realization of a sustainable society. In this review, the early discovery and recent advances concerning synthetic strategies, hierarchical structures, and oxygen evolution reaction (OER)/hydrogen evolution reactions (HER) catalytic performances of nickel-vanadium double hydroxides (NiV-LDHs) based nanomaterials are summarized. A discussion about the role of vanadium ions in HER/OER was also included, highlighting the recent progress in theoretical calculations in this field. Finally, some hybrid supercapacitor electrode materials based on NiV-LDHs are described, including the strategies to circumvent the parasitic oxygen evolution reaction during charge-discharge of those energy storage devices. In short, catalysts for HER/OER and hybrid supercapacitor electrode materials based on NiV-LDHs were reviewed considering their key multifunctional role in the way to a more sustainable society.

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Oxide-based cathode materials for rechargeable zinc ion batteries: Progresses and challenges Yingze Zhou, Fandi Chen, Hamidreza Arandiyan, Peiyuan Guan, Yunjian Liu, Yuan Wang, Chuan Zhao, Danyang Wang, Dewei Chu 2021, 57(6): 516-542.  DOI: 10.1016/j.jechem.2020.08.038 Abstract ( 24 )   PDF (35176KB) ( 13 )   With the increasing demands for electrical energy storage technologies, rechargeable zinc ion batteries (ZIBs) have been rapidly developed in recent years owing to their high safety, low cost and high energy storage capability. The cathode is an essential part of ZIBs, which hosts zinc ions and determines the capacity, rate and cycling performance of the battery. The mainstream cathodes for ZIBs are oxide-based materials with tunnel, layer or 3D crystal structures. In this review, we mainly focus on the latest advanced oxide-based cathode materials in ZIBs, including manganese oxides, vanadium oxides, spinel compounds, and other metal oxide based cathodes. In addition, the mechanisms of zinc storage and recent development in cathode design have been discussed in detail. Finally, current challenges and perspectives for the future research directions of oxide-based cathodes in ZIBs are presented.

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Corrigendum to “N-doped CoO nanowire arrays as efficient electrocatalysts for oxygen evolution reaction” 37 (2019) 13-17 Kaili Zhang, Xinhui Xia, Shengjue Deng, Dong Xie, Yangfan Lu, Yadong Wang, Jianbo Wu, Xiuli Wang, Jiangping Tu 2021, 57(6): 543-543.  DOI: 10.1016/j.jechem.2020.08.017 Abstract ( 8 )   PDF (211KB) ( 2 )

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Corrigendum to “Assembling Co9S8 nanoflakes on Co3O4 nanowires as advanced core/shell electrocatalysts for oxygen evolution reaction” 26 (2017) 1203-1209 Shengjue Deng, Shenghui Shen, Yu Zhong, Kaili Zhang, Jianbo Wu, Xiuli Wang, Xinhui Xia, Jiangping Tu 2021, 57(6): 544-546.  DOI: 10.1016/j.jechem.2020.08.003 Abstract ( 4 )   PDF (3095KB) ( 2 )

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Electrodeposition: Synthesis of advanced transition metal-based catalyst for hydrogen production via electrolysis of water Ruopeng Li, Yun Li, Peixia Yang, Dan Wang, Hao Xu, Bo Wang, Fan Meng, Jinqiu Zhang, Maozhong An 2021, 57(6): 547-566.  DOI: 10.1016/j.jechem.2020.08.040 Abstract ( 15 )   PDF (16872KB) ( 4 )   Developing lower-cost and higher-effective catalyst to support hydrogen (H2) production by electrochemical water-splitting has been recognized as a preferred strategy to drive the clean energy utilization. As a credible technology for the synthesis of functional materials, electrodeposition has attracted widespread attention, especially suitable for non-noble transition metal-based catalysts (TMCs). Recently, lots of researchers have been devoted to this hot research direction with plentiful achievements, however, a comprehensive review towards this area is still missing. Hence, we summarize the past research progress, presents the technical characteristics of electrodeposition from the viewpoint of fundamental theory and influence factors for the electrochemical deposition behavior, and introduce its application in various of TMCs with versatile nanostructures and compositions. Except a deeper and more comprehensive cognition of electrodeposition, we further discuss the catalyst's optimized hydrogen evolution reaction (HER), oxygen evolution reaction (OER) performance as well as overall water splitting that combined with the synthetic process. Finally, we conclude the technical advantages towards electrodeposition, propose challenge and future research directions in this promising field. This timely review aims to promote a deeper understanding of effective catalysts obtained via electrodeposition strategy, and provide new guidance for the design and synthesis of future catalysts for hydrogen production.

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Strategies from small-area to scalable fabrication for perovskite solar cells Huanhuan Yao, Shenghuan Shi, Zhizai Li, Zhipeng Ci, Ge Zhu, Liming Ding, Zhiwen Jin 2021, 57(6): 567-586.  DOI: 10.1016/j.jechem.2020.08.033 Abstract ( 7 )   PDF (7512KB) ( 2 )   Recently, perovskite solar cells (PSCs) have flourished, and their power conversion efficiency (PCE) has increased from the initial 3.8% to 25.2% in 2019, which is an unprecedented advance. However, usually high-efficiency and stable PSCs are small-area devices prepared by spin coating. This method is not suitable for the preparation of large-area devices in commercialization. Therefore, there is an urgent need to develop new materials and methods for the scalable fabrication of PSCs. In this review, we first describe the common small-area PSCs preparation methods, understand the nucleation and crystal growth kinetics of perovskite, and analyze the reasons that hinder the development of small-area devices to large-area devices. Next, in order to meet the challenges of PSC's scalable fabrication, we summarize and analyze four strategies: scaling up precursor solutions, scalable deposition methods for large-area films, scaling up charge-transport layers and back electrodes, developing solar modules. Finally, challenges and prospects are proposed to help researchers prepare high-efficiency large-area PSCs.

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Hierarchical molybdenum disulfide nanosheet arrays stemmed from nickel-cobalt layered double hydroxide/carbon cloth for highly-efficient hydrogen evolution reaction Yuxuan Wei, Yanlong Lv, Beidou Guo, Jianru Gong 2021, 57(6): 587-592.  DOI: 10.1016/j.jechem.2020.09.024 Abstract ( 5 )   PDF (4485KB) ( 2 )   The hierarchical structure of molybdenum disulfide (MoS2) nanosheet arrays stemmed from nickel-cobalt layered double hydroxide (NiCo-LDH)/carbon cloth was prepared by growing the MoS2 nanosheet arrays onto the NiCo-LDH template which was pre-deposited onto the carbon cloth substrate. In this electrode configuration, carbon cloth is the three dimensional and conductive skeleton; NiCo-LDH nanosheets, as the template, ensure the oriented growth of MoS2 nanosheet arrays. Therefore, more MoS2 active sites are exposed and the catalyst exhibits good hydrogen evolution reaction activity.

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Highly efficient and stable perovskite solar cells with strong hydrophobic barrier via introducing poly(vinylidene fluoride) additive Haiying Zheng, Guozhen Liu, Weiwei Wu, Huifen Xu, Xu Pan 2021, 57(6): 593-600.  DOI: 10.1016/j.jechem.2020.09.026 Abstract ( 13 )   PDF (2837KB) ( 7 )   Perovskite solar cells (PSCs) have become the promising next-generation photovoltaic devices due to their excellent photoelectric performances, and the power conversion efficiencies (PCEs) have experienced unprecedented rapid increase in recent years. However, to realize the practical application of PSCs, high performance and long-term stability are required and the preparation of high-quality perovskite film is the key. Herein, we adopt a simple and effective method to prepare high-quality perovskite films by introducing the poly(vinylidene fluoride) (PVDF) polymer additive with abundant hydrophobic F. As the growth template, the PVDF promotes the growth of perovskite crystal, improves the crystallinity and film morphology, thus reducing defect density and inhibiting carrier recombination. The results show that the photovoltaic performances of the perovskite device with PVDF are meaningfully improved, and a high PCE of 21.42% is achieved with an improvement of 10.87%. More importantly, the PVDF-based perovskites display greatly enhanced humidity and heat stability due to the protection of strong hydrophobic barrier from F and PVDF long chain. Aging at 45% ± 5% relative humidity (RH) for 2400 h and 85 °C for 300 h, respectively, the unsealed PVDF devices can maintain over 90% of the initial PCE. It indicates that suitable polymer additives can improve the film quality to acquire high-performance and stable PSCs and lay a foundation to design new perovskite light absorption layer with different polymers for the further development of PSCs.

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Controllable synthesis of grain boundary-enriched Pt nanoworms decorated on graphitic carbon nanosheets for ultrahigh methanol oxidation catalytic activity Huajie Huang, Yujie Wei, Ying Yang, Minmin Yan, Haiyan He, Quanguo Jiang, Xiaofei Yang, Jixin Zhu 2021, 57(6): 601-609.  DOI: 10.1016/j.jechem.2020.08.063 Abstract ( 15 )   PDF (11938KB) ( 2 )   Although one-dimensional Pt nanocrystals have long been regarded as ideal electrode catalysts for fuel cells, the synthetic techniques commonly involve the use of various complicated templates or surfactants, which have largely hampered their large-scale industrial application. Herein, we present a convenient and cost-effective approach to the stereoassembly of quasi-one-dimensional grain boundary-enriched Pt nanoworms on nitrogen-doped low-defect graphitic carbon nanosheets (Pt NWs/NL-CNS). Benefiting from its numerous catalytically active grain boundaries as well as optimized electronic structure, the as-derived Pt NWs/NL-CNS catalyst possesses exceptionally good electrocatalytic properties for methanol oxidation, including an ultrahigh mass activity of 1949.5 mA mg-1, reliable long-term durability, and strong poison tolerance, affording one of the most active Pt-based electrocatalysts for methanol oxidation reaction. Density functional theory calculation further reveals that the formation of worm-shape Pt morphology is attributed to the modified electronic structure as well as controllable defect density of the carbon matrix, which could also weaken the adsorption ability of Pt towards CO molecule and meanwhile synergistically promotes the catalytic reaction kinetics.

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14.46% Efficiency small molecule organic photovoltaics enabled by the well trade-off between phase separation and photon harvesting Chunyu Xu, Haiyan Chen, Zijin Zhao, Jinhua Gao, Xiaoling Ma, Shirong Lu, Xiaoli Zhang, Zeyun Xiao, Fujun Zhang 2021, 57(6): 610-617.  DOI: 10.1016/j.jechem.2020.09.025 Abstract ( 3 )   PDF (4401KB) ( 4 )   Small molecule organic photovoltaics (SMPVs) were prepared by utilizing liquid crystalline donor material BTR-Cl and two similar optical bandgap non-fullerene acceptor materials BTP-BO-4F and Y6. The BTP-BO-4F and Y6 have the similar optical bandgap and different absorption coefficients. The corresponding binary SMPVs exhibit different short circuit current density (JSC) (20.38 vs. 23.24 mA cm-2), and fill factor (FF) (70.77% vs. 67.21%). A 14.46% power conversion efficiency (PCE) is acquired in ternary SMPVs with 30 wt% Y6, companied with a JSC of 24.17 mA cm-2, a FF of 68.78% and an open circuit voltage (VOC) of 0.87 V. The improvement on PCE of ternary SMPVs should originate from the well trade-off between phase separation and photon harvesting of ternary active layers by incorporating 30 wt% Y6 in acceptors. This work may deliver insight onto the improved performance of SMPVs by superposing the superiorities of binary SMPVs with similar optical bandgap acceptors into one ternary cell.

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Na-doping-induced modification of the Cu2ZnSn(S,Se)4/CdS heterojunction towards efficient solar cells Yali Sun, Hongling Guo, Pengfei Qiu, Shengli Zhang, Siyu Wang, Li Wu, Jianping Ao, Yi Zhang 2021, 57(6): 618-626.  DOI: 10.1016/j.jechem.2020.09.007 Abstract ( 9 )   PDF (14627KB) ( 5 )   It is very important to understand why a small amount of alkali metal doping in Cu2ZnSn(S,Se)4 (CZTSSe) solar cells can improve the conversion efficiency. In this work, Na-doped CZTSSe is prepared by a simple solution method, and then the effects on the surface properties of the absorber layer, the buffer layer growth, and the modifications of the solar cell performance induced by the Na doping are studied. The surface of the absorber layer is more Cu-depletion and less roughness due to the Na doping. In addition, the contact angle of the surface increases because of Na doping. As a consequence, the thickness of the CdS buffer layer is significantly reduced and the optical losses in the CdS buffer layer are decreased. The difference of quasi-Fermi levels (EFn-EFp) increases with a small amount of Na doping in the CZTSSe solar cell, so that open circuit voltage (VOC) increased significantly. This work offers new insights into the effects of Na doping on CZTSSe via a solution-based approach and provides a deeper understanding of the origin of the efficiency improvement of Na-doped CZTSSe thin film solar cells.

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Ultrathin two-dimensional metal-organic framework nanosheets for efficient electrochemical CO2 reduction Lu Ye, Xuyang Chen, Yan Gao, Xin Ding, Jungang Hou, Shuyan Cao 2021, 57(6): 627-631.  DOI: 10.1016/j.jechem.2020.09.021 Abstract ( 5 )   PDF (2530KB) ( 2 )

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Formamidinium-incorporated Dion-Jacobson phase 2D perovskites for highly efficient and stable photovoltaics Sajjad Ahmad, Wei Yu, Ruixue Lu, Yang Liu, Tonggang Jiu, Shuping Pang, Xin Guo, Can Li 2021, 57(6): 632-638.  DOI: 10.1016/j.jechem.2020.08.055 Abstract ( 13 )   PDF (7439KB) ( 2 )   Dion-Jacobson phase two-dimensional (DJ 2D) perovskites, recently attracting considerable interests, exhibit excellent environmental stability and structural tunability, but their solar cells still offer unsatisfactory power conversion efficiencies (PCEs). Herein, we develop DJ 2D perovskites employing formamidinium (FA+) as a ternary cation in the perovskite cages ((PDA)(FA)x(MA)3-xPb4I13, x = 0, 0.15, 0.3 and 0.6, PDA = 1,3-propanediammonium) for highly efficient and stable perovskite solar cells (PSCs). We found that the DJ 2D perovskite with a 10% FA+ fraction presents improved crystallinity, preferred vertical orientation, and longer charge carrier lifetime compared to that without FA+ doping. As a result, the FA-doped DJ 2D PSCs exhibit a champion PCE of 14.74% with superior device stability. The unencapsulated devices sustain over 92% of its initial PCE after storage at a constant relative humidity (RH) of 65% for 6000 h, 90% by heat at 85 °C in air for 800 h, and 94% under 1-sun illumination for 5000 h. These findings demonstrate that the incorporation of FA cation into the DJ 2D perovskite is a promising strategy to develop highly efficient and stable DJ 2D PSCs.

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Inorganic matter in rice husk derived carbon and its effect on the capacitive performance Wanlu Li, Meruyert Nazhipkyzy, Teresa J. Bandosz 2021, 57(6): 639-649.  DOI: 10.1016/j.jechem.2020.10.046 Abstract ( 3 )   PDF (3682KB) ( 3 )   Porous carbons were obtained from rice husk using two different chemical activation methods and they were investigated as supercapacitors. Their properties were studied using X-ray photoelectron spectroscopy, thermal analysis, potentiometric titration, and nitrogen adsorption isotherm. The specific capacitance measured in both H2SO4 and KOH electrolytes in two-electrode cell was up to ~150 F/g. The activation method used affected the resulting carbons' features. As expected, the dependence of the capacitance on porosity was found. The ash content reached 36 wt.% and that inorganic mater blocked some pores and limited their accessibility to electrolyte ions and increased the charge transfer resistance. Nevertheless, the main ash constituents such as CaCO3, MgCO3, Ca3(PO4)2 (or P2O5), and Fe- and Zn- containing species did not affect the specific capacitance to a large extent. Especially SiO2, even in a relatively large amount (~20 wt.%), did not play a detrimental role in the capacitance behavior. The results showed that in spite of a high ash content, carbon can exhibit a good capacitive performance provided that it has a favorable porosity and is rich in sp2 configurations.

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Achieving long-cycling sodium-ion full cells in ether-based electrolyte with vinylene carbonate additive Juan Shi, Lina Ding, Yanhua Wan, Liwei Mi, Linjie Chen, Dan Yang, Yuxiong Hu, Weihua Chen 2021, 57(6): 650-655.  DOI: 10.1016/j.jechem.2020.10.047 Abstract ( 3 )   PDF (4518KB) ( 3 )   Application of sodium-ion batteries is suppressed due to the lack of appropriate electrolytes matching cathode and anode simultaneously. Ether-based electrolytes, preference of anode materials, cannot match with high-potential cathodes failing to apply in full cells. Herein, vinylene carbonate (VC) as an additive into NaCF3SO3-Diglyme (DGM) could make sodium-ion full cells applicable without pre-activation of cathode and anode. The assembled FeS@C || Na3V2(PO4)3@C full cell with this electrolyte exhibits long term cycling stability and high capacity retention. The deduced reason is additive VC, whose HOMO level value is close to that of DGM, not only change the solvent sheath structure of Na+, but also is synergistically oxidized with DGM to form integrity and consecutive cathode electrolyte interphase on Na3V2(PO4)3@C cathode, which could effectively improve the oxidative stability of electrolyte and prevent the electrolyte decomposition. This work displays a new way to optimize the sodium-ion full cells easily with bright practical application potential.