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2021, Vol. 52, No. 1　Online: 15 January 2021

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Loading Fe3O4 nanoparticles on paper-derived carbon scaffold toward advanced lithium-sulfur batteries Jianmei Han, Qiang Fu, Baojuan Xi, Xuyan Ni, Chenglin Yan, Jinkui Feng, Shenglin Xiong 2021, 52(1): 1-11.  DOI: 10.1016/j.jechem.2020.04.002 Abstract ( 7 )   PDF (8561KB) ( 6 )   Lithium-sulfur batteries (LSBs) are regarded as a competitive next-generation energy storage device. However, their practical performance is seriously restricted due to the undesired polysulfides shuttling. Herein, a multifunctional interlayer composed of paper-derived carbon (PC) scaffold, Fe3O4 nanoparticles, graphene, and graphite sheets is designed for applications in LSBs. The porous PC skeleton formed by the interweaving long-fibers not only facilitates fast transfer of Li ions and electrons but also provides a physical barrier for the polysulfide shuttling. The secondary Fe3O4@graphene component can reduce the polarization, boost the attachment of polysulfides, and promote the charging-discharging kinetics. The outer graphitic sheets layers benefit the interfacial electrochemistry and the utilization of S-containing species. The efficient obstruction of polysulfides diffusion is further witnessed via in situ ultraviolet-visible characterization and first-principles simulations. When 73% sulfur/commercial acetylene black is used as the cathode, the cell exhibits excellent capacity retention with high capacities at 0.5 C for 1000 cycles and even up to 10 C for 500 cycles, an ultrahigh rate capability up to 10 C (478 mAh g-1), and a high areal-sulfur loading of 8.05 mg cm-2. The strategy paves the way for developing multifunctional composites for LSBs with superior performance.

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Co encapsulated N-doped carbon nanotubes as robust catalyst for valorization of levulinic acid in aqueous media Xiangjin Kong, Weijie Geng, Wenxiu Li, Lin Liu, Xiaoqi Yan, Longchen Gong, Junhai Liu 2021, 52(1): 12-19.  DOI: 10.1016/j.jechem.2020.04.050 Abstract ( 9 )   PDF (2713KB) ( 3 )   The construction of an acid resistant catalyst for synthesis of γ-valerolactone from levulinic acid in aqueous media is an important but highly challenging goal. Herein, an efficient Co@NCNT-800 (after 800 °C pyrolysis) catalyst was constructed by confining Co in N-doped carbon nano-tubes (NCNT) from low cost materials by a facile strategy. Combined with the characterization results and control experiments, the in situ formed Co and Co-Ox, but not Co-Nx, proved to be the main synergistic active sites of the catalyst. It was also found that Co species are completely isolated within the bamboo-like NCNT, which could protect the metal nanoparticles from agglomeration and leaching in the strong acid reaction system. The γ-valerolactone yield of no less than 99.9% can be obtained under a relatively mild condition, and the catalytic performance has not been significantly reduced within five cycles. Therefore, this work may pave a way for the design of robust non-noble catalyst, and has potential for the production of γ-valerolactone from biomass in large-scale industries.

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Study about thermal runaway behavior of high specific energy density Li-ion batteries in a low state of charge Shiqiang Liu, Tianyi Ma, Zhen Wei, Guangli Bai, Huitian Liu, Dapeng Xu, Zhongqiang Shan, Fang Wang 2021, 52(1): 20-27.  DOI: 10.1016/j.jechem.2020.03.029 Abstract ( 6 )   PDF (9576KB) ( 2 )   Lithium-ion batteries are widely used in electric vehicles and electronics, and their thermal safety receives widespread attention from consumers. In our study, thermal runaway testing was conducted on the thermal stability of commercial lithium-ion batteries, and the internal structure of the battery was analyzed with an in-depth focus on the key factors of the thermal runaway. Through the study of the structure and thermal stability of the cathode, anode, and separator, the results showed that the phase transition reaction of the separator was the key factor affecting the thermal runaway of the battery for the condition of a low state of charge.

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Superior performance for lithium-ion battery with organic cathode and ionic liquid electrolyte Xueqian Zhang, Wenjun Zhou, Meng Zhang, Zhinan Yang, Weiwei Huang 2021, 52(1): 28-32.  DOI: 10.1016/j.jechem.2020.04.053 Abstract ( 6 )   PDF (2343KB) ( 2 )   Organic small structure quinones go with ionic liquids electrolytes would exhibit ultrastable electrochemical properties. In this study, calix[6]quinone (C6Q) cathode was matched with ionic liquid electrolyte Li[TFSI]/[PY13][TFSI] (bis(trifluoromethane)sulfonimide lithium salt/N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)amide) to assemble lithium-ion batteries (LIBs). The electrochemical performance of LIBs was systematically studied. The capacity retention rates of C6Q through 1000 cycles at current densities of 0.2 C and 0.5 C were 70% and 72%, respectively. At 5 C, the capacity was maintained at 190 mAh g-1 after 1000 cycles, and 155 mAh g-1 even after 10,000 cycles, comparable to inorganic materials. This work would give a big push to the practical process of organic electrode materials in energy storage.

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Platelet carbon nanofibers as support of Pt-CoO electrocatalyst for superior hydrogen evolution Jie Gan, Zikun Huang, Wei Luo, Wenyao Chen, Yueqiang Cao, Gang Qian, Xinggui Zhou, Xuezhi Duan 2021, 52(1): 33-40.  DOI: 10.1016/j.jechem.2020.04.036 Abstract ( 4 )   PDF (7698KB) ( 1 )   Exploration of cost-effective Pt/C catalysts has been a significant issue for electrochemical hydrogen evolution reaction (HER) toward sustainable energy conversion and storage. Herein, we report a fabrication strategy by employing platelet carbon nanofibers (p-CNF) as the support to immobilize Pt-CoO HER electrocatalyst using atomic layer deposition method. The edge-rich p-CNF support is found to act as the anchoring sites of Pt nanoparticles and favorably capture electrons from Pt to yield electron-deficient Pt surfaces for the boosted HER. Additionally, the sequential growth of CoO onto the Pt/p-CNF catalyst elaborately constructs the Pt-CoO interface and facilitates the electron transfer from Pt to CoO, which further enhances the HER activity. These advantages endow the fabricated Pt-CoO/p-CNF catalyst with the superior HER activity, e.g., a very low overpotential of 26 mV at the current density of 10 mA·cm-2 and a mass activity of 4.42 A·mgPt-1 at the overpotential of 30 mV, 18.8 times higher than that of the commercial 20 wt% Pt/C catalyst. The insights reported here could shed light on for the fabrication of cost-effective Pt-based composite HER catalysts.

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Selective hydrocracking of light cycle oil into high-octane gasoline over bi-functional catalysts Zhengkai Cao, Xia Zhang, Chunming Xu, Xinlu Huang, Ziming Wu, Chong Peng, Aijun Duan 2021, 52(1): 41-50.  DOI: 10.1016/j.jechem.2020.04.055 Abstract ( 10 )   PDF (4383KB) ( 3 )   Light cycle oil (LCO) with high content of poly-aromatics was difficult to upgrade and convert, which had hindered upgrading fuel quality to meet with the standard of automotive diesel for the purpose of sustainable development. The hydrocracking behaviors of typical aromatics in LCO of naphthalene and tetralin were investigated over NiMo and CoMo catalysts. Several characterization methods including N2-adsoprtion and desorption, ammonia temperature-programmed desorption (NH3-TPD), Pyridine infrared spectroscopy (Py-IR), CO infrared spectroscopy (CO-IR), Raman and X-ray photoelectron spectroscopy (XPS) were applied to determine the properties of different catalysts. The results showed that CoMo catalyst with high concentration of S-edges could hydrosaturate more naphthalene to tetralin but exhibit lower yield of high-value light aromatics (carbon numbers less than 10) than NiMo catalyst. NiMo catalyst with high concentration of Mo-edges also presented a higher selectivity of converting naphthalene into cyclanes than CoMo catalyst. Subsequently, the naphthalene and LCO hydrocracking performances were also investigated over different catalysts systems. The activity evaluation and kinetic analysis results showed that the naphthalene hydrocracking conversion and the yield of light aromatics for CoMo-AY/NiMo-AY grading catalysts were higher than NiMo-AY/CoMo-AY grading catalysts at same condition. A stepwise reaction principle was proposed to explain the high efficiency of CoMo-AY/NiMo-AY grading catalysts. Finally, the LCO hydrocracking evaluation results confirmed that CoMo-AY/NiMo-AY catalysts grading system with low carbon deposition and high stability could remain high percentage of active phases, which was more efficient to convert LCO to high-octane gasoline.

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Surface defect-rich ceria quantum dots anchored on sulfur-doped carbon nitride nanotubes with enhanced charge separation for solar hydrogen production Mengru Li, Changfeng Chen, Liping Xu, Yushuai Jia, Yan Liu, Xin Liu 2021, 52(1): 51-59.  DOI: 10.1016/j.jechem.2020.04.003 Abstract ( 5 )   PDF (6127KB) ( 2 )   Designing defect-engineered semiconductor heterojunctions can effectively promote the charge carrier separation. Herein, novel ceria (CeO2) quantum dots (QDs) decorated sulfur-doped carbon nitride nanotubes (SCN NTs) were synthesized via a thermal polycondensation coupled in situ deposition-precipitation method without use of template or surfactant. The structure and morphology studies indicate that ultrafine CeO2 QDs are well distributed inside and outside of SCN NTs offering highly dispersed active sites and a large contact interface between two components. This leads to the promoted formation of rich Ce3+ ion and oxygen vacancies as confirmed by XPS. The photocatalytic performance can be facilely modulated by the content of CeO2 QDs introduced in SCN matrix while bare CeO2 does not show activity of hydrogen production. The optimal catalyst with 10% of CeO2 loading yields a hydrogen evolution rate of 2923.8 μmol h-1 g-1 under visible light, remarkably higher than that of bare SCN and their physical mixtures. Further studies reveal that the abundant surface defects and the created 0D/1D junctions play a critical role in improving the separation and transfer of charge carriers, leading to superior solar hydrogen production and good stability.

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Small bandgap non-fullerene acceptor enables efficient PTB7-Th solar cell with near 0 eV HOMO offset Chao Li, Qihui Yue, Hao Wu, Baolin Li, Haijun Fan, Xiaozhang Zhu 2021, 52(1): 60-66.  DOI: 10.1016/j.jechem.2020.03.058 Abstract ( 4 )   PDF (3730KB) ( 2 )   Three small bandgap non-fullerene (SBG NFAs) acceptors, BDTI, BDTI-2F and BDTI-4F, based on a carbon-oxygen bridged central core and thieno[3,4-b]thiophene linker, end-capped with varied electron-withdrawing terminal groups, were designed and synthesized. The acceptors exhibit strong absorption from 600 nm to 1000 nm. The optimal device incorporating designed NFA and PTB7-Th polymer donor achieves a power conversion efficiency of 9.11% with near 0 eV HOMO offset. The work presents a case study of efficient non-fullerene solar cells with small HOMO offsets, which is achieved by blending PTB7-Th with fine-tuned SBG acceptor.

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Block copolymer electrolyte with adjustable functional units for solid polymer lithium metal battery Zhiyuan Lin, Xianwei Guo, Yubo Yang, Mingxue Tang, Qi Wei, Haijun Yu 2021, 52(1): 67-74.  DOI: 10.1016/j.jechem.2020.04.052 Abstract ( 6 )   PDF (4052KB) ( 4 )   Solid polymer electrolytes have been considered as the promising candidates to improve the safety and stability of high-energy lithium metal batteries. However, the practical applications of solid polymer electrolytes are still limited by the low ionic conductivity, poor interfacial contact with electrodes, narrow electrochemical window and weak mechanical strength. Here, a series of novel block copolymer electrolytes with three-dimensional networks are designed by cross-linked copolymerization of the polyethylene glycol soft segments and hexamethylene diisocyanate trimer hard segments. Their ionic migration performances and interface compatibilities with Li metal anode have been optimized delicately by tailoring the ratio of these functional units. The optimized block copolymer electrolyte has shown an amorphous crystalline structure, a high ionic conductivity of ~5.7 × 10-4 S cm-1, high lithium ion transference number (~0.49), wide electrochemical window up to ~4.65 V (vs. Li+/Li) and favorable mechanical strength at 55 °C. Furthermore, the enhanced interface compatibility can well support the normal operations of lithium metal batteries using both LiFePO4 and LiNi0.8Co0.15Al0.05O2 cathodes. This study not only paves a new way to develop solid polymer electrolyte with optimizing functional units, but also provides a polymer electrolyte design strategy for the application demand of lithium metal battery.

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A multifunctional separator with Mg(OH)2 nanoflake coatings for safe lithium-metal batteries Dian-Hui Han, Meng Zhang, Peng-Xian Lu, Yun-Lu Wan, Qiu-Ling Chen, Hong-Yu Niu, Zhi-Wei Yu 2021, 52(1): 75-83.  DOI: 10.1016/j.jechem.2020.04.043 Abstract ( 3 )   PDF (4911KB) ( 3 )   Dendrite growth and thermal runaway induce serious safety hazards, impeding the practical applications of lithium metal batteries (LMBs). Although extensive advances have been attained in terms of LMB safety, most work only focus on a single aspect at a time. This paper reports a multifunctional separator coated by Mg(OH)2 nanoflakes with various excellent properties including electrolyte wettability, ionic conductivity, Li+ transference number, puncture strength, thermal stability and flame retardance. When used in LMBs, the Mg(OH)2 nanoflake coatings enable uniform Li+ distributing, which makes it homogeneous to deposit lithium, realizing effective dendrite suppression and less volume expansion. Meanwhile, Mg(OH)2 coatings can ensure LMBs are in normal conditions without thermal runaway until 140 °C. A part of lithium can be converted into Li+ ions by Mg(OH)2 during repeated charge/discharge cycles, not only reducing the risk of separator damage and consequent short circuit, but also replenishing the capacity loss of LMBs. The Mg(OH)2 nanoflakes can coat on all kinds of commercial separators to improve their performances, which offers a facile but effective strategy for fabricating multifunctional separators and a comprehensive insight into enhancing LMB safety.

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Surface passivation using pyridinium iodide for highly efficient planar perovskite solar cells Yitian Du, Jihuai Wu, Xinpeng Zhang, Qianjin Zhu, Mingjing Zhang, Xuping Liu, Yu Zou, Shibo Wang, Weihai Sun 2021, 52(1): 84-91.  DOI: 10.1016/j.jechem.2020.04.049 Abstract ( 10 )   PDF (3158KB) ( 4 )   Perovskite solar cells have developed rapidly in the past decades. However, there are large amounts of ionic defects at the surface and grain boundaries of perovskite films which are detrimental to both the efficiency and stability of perovskite solar cells. Here, an organic halide salt pyridinium iodide (PyI) is used in cation-anion-mixed perovskite for surface defect passivation. Different from the treatment with Lewis base pyridine (Py) which can only bind to the under-coordinated Pb ions, zwitterion molecule PyI can not only fill negative charged iodine vacancies, but also interact with positive charged defects. Compared with Py treatment, PyI treatment results in smoother surface, less defect densities and non-radiative recombination in perovskite, leading to an improved VOC, negligible J-V hysteresis and stable performance of devices. As a result, the champion PyI-treated planar perovskite solar cell with a high VOC of 1.187 V achieves an efficiency of 21.42%, which is higher than 20.37% of Py-treated device, while the pristine device without any treatment gets an efficiency of 18.83% at the same experiment conditions.

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FeCo alloy@N-doped graphitized carbon as an efficient cocatalyst for enhanced photocatalytic H2 evolution by inducing accelerated charge transfer Sibo Chen, Yun Hau Ng, Jihai Liao, Qiongzhi Gao, Siyuan Yang, Feng Peng, Xinhua Zhong, Yueping Fang, Shengsen Zhang 2021, 52(1): 92-101.  DOI: 10.1016/j.jechem.2020.04.040 Abstract ( 6 )   PDF (7111KB) ( 2 )   Cocatalysts play important roles in improving the activity and stability of most photocatalysts. It is of great significance to develop economical, efficient and stable cocatalysts. Herein, using Na2CoFe(CN)6 complex as precursor, a novel noble-metal-free FeCo@NGC cocatalyst (nano-FeCo alloy@N-doped graphitized carbon) is fabricated by a simple pyrolysis method. Coupling with g-C3N4, the optimal FeCo@NGC/g-C3N4 receives a boosted visible light driven photocatalytic H2 evolution rate of 42.2 μmol h-1, which is even higher than that of 1.0 wt% Pt modified g-C3N4 photocatalyst. Based on the results of density functional theory (DFT) calculations and practical experiment measurements, such outstanding photocatalytic performance of FeCo@NGC/g-C3N4 is mainly attributed to two aspects. One is the accelerated charge transfer behavior, induced by a photogenerated electrons secondary transfer performance on the surface of FeCo alloy nanoparticles. The other is related to the adjustment of H adsorption energy (approaching the standard hydrogen electrode potential) by the presence of external NGC thin layer. Both factors play key roles in the H2 evolution reaction. Such outstanding performance highlights an enormous potential of developing noble-metal-free bimetallic nano-alloy as inexpensive and efficient cocatalysts for solar applications.

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Intermediates transformation for efficient perovskite solar cells Zhizai Li, Yi Sun, Huanhuan Yao, Jing Zhao, Qian Wang, Liming Ding, Zhiwen Jin 2021, 52(1): 102-114.  DOI: 10.1016/j.jechem.2020.04.047 Abstract ( 6 )   PDF (8025KB) ( 1 )   Perovskite materials have made a great progress in terms of the power conversion efficiency (PCE), rising from 3.8% to 25.2%. To obtain pinhole-free, superior crystal, and high-quality perovskite films with less defect, intermediates transformation is important, which has been clearly studied and widely applied. In this review, we systematically summarize the commonly formed intermediates and detailedly analyze their mechanisms from five aspects: (1) Solvent-induced intermediate; (2) HI-induced intermediate; (3) CH3NH2-induced intermediate; (4) MAAc-induced intermediate; (5) other intermediates. Finally, we also provide some prospects on high-quality perovskite fabrication based on using intermediates prudently.

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Chlorine-anion doping induced multi-factor optimization in perovskties for boosting intrinsic oxygen evolution Yinlong Zhu, Qian Lin, Zhenbin Wang, Dongchen Qi, Yichun Yin, Yu Liu, Xiwang Zhang, Zongping Shao, Huanting Wang 2021, 52(1): 115-120.  DOI: 10.1016/j.jechem.2020.03.055 Abstract ( 5 )   PDF (3536KB) ( 4 )   The oxygen evolution reaction (OER) plays a crucial role in many electrochemical energy technologies, and creating multiple beneficial factors for OER catalysis is desirable for achieving high catalytic efficiency. Here, we highlight a new halogen-chlorine (Cl)-anion doping strategy to boost the OER activity of perovskite oxides. As a proof-of-concept, proper Cl doping at the oxygen site of LaFeO3 (LFO) perovskite can induce multiple favorable characteristics for catalyzing the OER, including rich oxygen vacancies, increased electrical conductivity and enhanced Fe-O covalency. Benefiting from these factors, the LaFeO2.9-δCl0.1 (LFOCl) perovskite displays significant intrinsic activity enhancement by a factor of around three relative to its parent LFO. This work uncovers the effect of Cl-anion doping in perovskites on promoting OER performance and paves a new way to design highly efficient electrocatalysts.

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Rational design of porous carbon allotropes as anchoring materials Tongtong Li, Cheng He, Wenxue Zhang 2021, 52(1): 121-129.  DOI: 10.1016/j.jechem.2020.04.042 Abstract ( 7 )   PDF (5020KB) ( 1 )   The shuttle effect seriously impedes the development and practical application of lithium sulfur (Li-S) batteries. It is still a long-term challenge to find effective anchoring materials to hinder the shuttle effect of Li-S batteries. Using carbon allotrope as anchoring materials is an effective strategy to alleviate the shuttling effect. However, the influence factors of carbon allotrope on the adsorption performance of LIPSS at the atomic level are not clear, which limits the application of carbon allotrope in Li-S batteries. Herein, using first - principles simulations, a systematical calculation of carbon allotropes with various ring size (6 ≤ S ≤ 16) and shape is conducted to understand the adsorption mechanism. The results show that the T-G monolayers with suitable ring structure and high charge transfer can significantly enhance the interaction between the monolayer and LiPSs, allowing them to have high capacity and high coulombic efficiency. Further diffusion studies show that LiPSs on the T-G monolayer have the low diffusion barriers, which ensures the charging and discharging rate of batteries. Our studies could provide material design principles of carbon allotrope monolayers used as anchoring materials of the high performance Li-S batteries.

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Cobalt phosphide nanoparticles supported within network of N-doped carbon nanotubes as a multifunctional and scalable electrocatalyst for water splitting Dongxu Yang, Wenqiang Hou, Yingjiong Lu, Wanli Zhang, Yuanfu Chen 2021, 52(1): 130-138.  DOI: 10.1016/j.jechem.2020.04.005 Abstract ( 5 )   PDF (9927KB) ( 1 )   In order to realize industrial production of hydrogen through water splitting, it is essential to develop a cost-efficient and scalable approach to synthesize nonprecious electrocatalysts with sufficiently high activity and stability to replace commercial noble-metal-based electrocatalysts. Herein we synthesize cobalt phosphide nanoparticles dispersed within nitrogen-doped carbon nanotube network (CP@NCNT) via scalable spray drying and thermal treatments. As a multifunctional electrocatalyst, the CP@NCNT hybrid delivers outstanding activity for HER (in both acidic and alkaline electrolytes), OER and overall water splitting. Remarkably, it shows an ultra-low overpotental of 94 mV to obtain 10 mA cm-2 in HER. It also demonstrates outstanding activity in overall water splitting, requiring only 1.619 V to deliver 10 mA cm-2 with more than 72 h’ long-term stability. The combination of notable performance, multi-functionality and highly scalable spray-drying synthesis method enables this material as a novel and cost-efficient transition metal-based electrocatalysts for overall water splitting.

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Engineering morphologies of cobalt oxide/phosphate-carbon nanohybrids for high-efficiency electrochemical water oxidation and reduction Shan-Shan Xu, Xian-Wei Lv, Yan-Mei Zhao, Tie-Zhen Ren, Zhong-Yong Yuan 2021, 52(1): 139-146.  DOI: 10.1016/j.jechem.2020.04.054 Abstract ( 4 )   PDF (4165KB) ( 2 )   Active non-noble metal catalysts plays a decisive role for water electrolysis, however, the rational design and development of cost-efficient electrocatalysts with Pt/IrO2-like activity is still a challenging task. Herein, a facile one-step electrodeposition route in deep eutectic solvents (DESs) is developed for morphology-controllable synthesis of cobalt oxide/phosphate-carbon nanohybrids on nickel foam (CoPO@C/NF). A series of CoPO@C/NF nanostructures including cubes, octahedrons, microspheres and nanoflowers are synthesized, which show promising electrocatalytic properties toward oxygen and hydrogen evolution reactions (OER/HER). Such surface self-organized microstructure with accessible active sites make a significant contribution to the enhanced electrochemical activity, and hybridizing cobalt oxide with cobalt pyrophosphates and carbon can result in enhanced OER performance through synergistic catalysis. Among all nanostructures, the obtained microspherical CoPO@C/NF-3 catalyst exhibits excellent catalytic activities for OER and HER in 1.0 M KOH, affording an anodic current density of 10 mA cm-2 at overpotentials of 293 mV for OER and 93 mV for HER, with good long-time stability. This work offers a practical route for engineering the high-performance electrocatalysts towards efficient energy conversion and storage devices.

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Unraveling the role of Ti3C2 MXene underlayer for enhanced photoelectrochemical water oxidation of hematite photoanodes Haiyan Ji, Shan Shao, Guotao Yuan, Cheng Lu, Kun Feng, Yujian Xia, Xiaoxin Lv, Jun Zhong, Hui Xu, Jiujun Deng 2021, 52(1): 147-154.  DOI: 10.1016/j.jechem.2020.04.024 Abstract ( 5 )   PDF (5521KB) ( 3 )   Hematite is regarded as a promising photoanode for photoelectrochemical (PEC) water splitting. However, the charge recombination occurred at the interface of FTO/hematite strictly limits the PEC performance of hematite. Herein, we reported a Ti3C2 MXene underlayer modified hematite (Ti-Fe2O3) photoanode via a simple drop-casting followed by hydrothermal and annealing processes. Owing to the bifunctional role of Ti3C2 MXene underlayer in improving the interfacial properties of FTO/hematite and providing Ti source for the construction of Fe2TiO5/Fe2O3 heterostructure in hematite nanostructure, the bulk and interfacial charge transfer dynamics of hematite are significantly enhanced, and consequently enhancing the PEC performance. Compared with the pristine hematite, the as-prepared Ti-Fe2O3 photoanode shows an increased photocurrent density from 0.80 mA/cm2 to 1.30 mA/cm2 at 1.23 V vs. RHE. Moreover, a further promoted PEC performance including a dramatically increased photocurrent density of 2.49 mA/cm2 at 1.23 V vs. RHE and an obviously lowered onset potential is achieved for the Ti-Fe2O3 sample after the subsequent surface F-treatment and the loading of FeNiOOH cocatalyst. Such results suggest that the introduction of Ti3C2 MXene underlayer is a facile but effective approach to improve the PEC water splitting activity of hematite.

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Exploring single atom catalysts of transition-metal doped phosphorus carbide monolayer for HER: A first-principles study Dachang Chen, Zhiwen Chen, Xiaoxing Zhang, Zhuole Lu, Song Xiao, Beibei Xiao, Chandra Veer Singh 2021, 52(1): 155-162.  DOI: 10.1016/j.jechem.2020.03.061 Abstract ( 7 )   PDF (4495KB) ( 2 )   Hydrogen has been identified as one of the most promising sustainable and clean energy. Developing hydrogen evolution reaction (HER) catalyst with high activity is essential for satisfying the future requirements. Considering novel advantages of two-dimensional materials and high catalytic activity of atomic transition metal, in this study, using density functional theory calculation, the HER on single transition-metal (23 different TM atoms) doped phosphorus carbide monolayer (α-PC) has been investigated. The Volmer-Tafel and Volmer-Heyrovsky reaction mechanisms, and the stability of the most promising HER catalyst are also included. The results show that Ir-αPC with high physical and thermal stability has the most optimal value of Gibbs free adsorption energy for H atom. The relationship of d band center and the HER activity shows a volcano-like curve. The calculation of reaction energy barrier indicates that the Volmer-Heyrovsky step is more favorable than the Volmer-Tafel step.

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Two-dimensional multimetallic sulfide nanosheets with multi-active sites to enhance polysulfide redox reactions in liquid Li2S6-based lithium-polysulfide batteries Chenyang Zha, Donghai Wu, Yuwei Zhao, Jun Deng, Jinghua Wu, Rong Wu, Meng Yang, Lin Wang, Houyang Chen 2021, 52(1): 163-169.  DOI: 10.1016/j.jechem.2020.04.059 Abstract ( 3 )   PDF (2941KB) ( 2 )   The lithium-sulfur battery has attracted enormous attention as being one of the most significant energy storage technologies due to its high energy density and cost-effectiveness. However, the “shuttle effect” of polysulfide intermediates represents a formidable challenge towards its wide applications. Herein, we have designed and synthesized two-dimensional Cu, Zn and Sn-based multimetallic sulfide nanosheets to construct multi-active sites for the immobilization and entrapment of polysulfides with offering better performance in liquid Li2S6-based lithium-polysulfide batteries. Both experimental measurements and theoretical computations demonstrate that the interfacial multi-active sites of multimetallic sulfides not only accelerate the multi-chained redox reactions of highly diffusible polysulfides, but also strengthen affinities toward polysulfides. By adopting multimetallic sulfide nanosheets as the sulfur host, the liquid Li2S6-based cell exhibits an impressive rate capability with 1200 mAh/g and retains 580 mAh/g at 0.5 mA/cm2 after 1000 cycles. With high sulfur mass loading conditions, the cell with 2.0 mg/cm2 sulfur loading delivers a cell capacity of 1068 mAh/g and maintains 480 mAh/g with 0.8 mA/cm2 and 500 cycles. This study provides new insights into the multifunctional material design with multi-active sites for elevated lithium-polysulfide batteries.

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ZIF-67@Cellulose nanofiber hybrid membrane with controlled porosity for use as Li-ion battery separator Xiuxuan Sun, Wangwang Xu, Xiuqiang Zhang, Tingzhou Lei, Sun-Young Lee, Qinglin Wu 2021, 52(1): 170-180.  DOI: 10.1016/j.jechem.2020.04.057 Abstract ( 10 )   PDF (8740KB) ( 15 )   Zeolitic imidazolate framework-67 (ZIF-67) was synthesized on the surface of cellulose nanofibers (CNFs) in methonal to address the problems of unhomogeneous pore size and pore distribution of pure CNF membrane. A combination of Energy Dispersive X-Ray Spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and X-ray powder diffraction (XRD) patterns were used to determine the successful synthesis of ZIF-67@CNFs. The size of the ZIF-67 particles and pore size of the ZIF-67@CNF membrane were 50-200 nm and 150-350 nm, respectively. The prepared ZIF-67@CNF membrane exhibited excellent thermal stability, lower thermal shrinkage and high surface wettability. The discharge capacity retention of the Li-ion batteries (LIBs) made with ZIF-67@CNF, glass fiber (GF), CNF and commercial polymer membranes after 100th cycle at 0.5C rate were 88.41%, 86.22%, 83.27%, and 81.03%, respectively. LIBs with ZIF-67@CNF membrane exhibited a better rate capability than these with other membranes. No damage of porous structure or peel-off of ZIF-67 was observed in the SEM images of ZIF-67@CNF membrane after 100th cycle. The improved cycling performance, rate capability, and good electrochemical stability implied that ZIF-67@CNFs membrane can be considered as a good alternative LIB separator.

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Recent process of plasma effect in organic solar cells Mei Wang, Shuo Han, Wei Wu, Zhuowei Li, Guanhua Ren, Chunyu Liu, Wenbin Han, Liang Shen, Wenbin Guo 2021, 52(1): 181-190.  DOI: 10.1016/j.jechem.2020.04.060 Abstract ( 5 )   PDF (4388KB) ( 2 )   Due to the compromise between exciton diffusion length and light absorption, the active layer thickness of organic solar cells (OSCs) is limited. As we all know, embedding metal nanostructures into OSCs can improve the performance of OSCs by triggering surface plasma resonance, scattering, and other effect without increasing the physical thickness of light trapping layer. Besides, the plasma response and other roles will distinguish when metal nanostructures are embedded into different position of OSCs, which are equally important to the performance of OSCs. In this paper, the enhancement mechanisms of various metal nanostructures in different layers of OSCs are summarized from the electricity and optics aspects. This review also further highlights the progress of plasma effect and their working mechanism in OSCs, and it is expected to provide more perspective of plasma effect for performance enhancement of OSCs.

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Highly active Pd containing EMT zeolite catalyst for indirect oxidative carbonylation of methanol to dimethyl carbonate Chunzheng Wang, Weisong Xu, Zhengxing Qin, Hailing Guo, Xinmei Liu, Svetlana Mintova 2021, 52(1): 191-201.  DOI: 10.1016/j.jechem.2020.04.045 Abstract ( 5 )   PDF (3803KB) ( 2 )   Palladium containing EMT zeolite catalyst (Pd/EMT) was prepared and used for the indirect oxidative carbonylation of methanol to dimethyl carbonate (DMC). The EMT zeolite was employed as a new catalyst support and compared with the conventional Pd containing FAU zeolite catalyst (Pd/FAU). The Pd/EMT in contrast to the Pd/FAU catalyst exhibited high intrinsic activity with the turnover frequency of 0.25 s-1 vs. 0.11 s-1. The Pd/EMT catalyst showed high CO conversion of 82% and DMC selectivity of 79%, that maintained for at least 130 h, while the activity of the Pd/FAU catalyst rapidly deteriorated within 12 h. The enhanced interactions between Pd and EMT zeolite inhibited the sintering of palladium clusters and maintained the Pd2+ active sites in the Pd/EMT catalyst. The stabilization of the mono-dispersed Pd clusters within the EMT zeolite is paramount to the excellent performance of the catalyst for the indirect oxidative carbonylation of methanol to DMC.

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Manipulating interfacial stability of LiNi0.5Co0.3Mn0.2O2 cathode with sulfide electrolyte by nanosized LLTO coating to achieve high-performance all-solid-state lithium batterie Jingguang Yi, Pingge He, Hong Liu, Haifang Ni, Zhiming Bai, Li-Zhen Fan 2021, 52(1): 202-209.  DOI: 10.1016/j.jechem.2020.03.057 Abstract ( 6 )   PDF (6024KB) ( 3 )   All-solid-state lithium batteries (ASSLBs) based on sulfide solid-state electrolytes and high voltage layered oxide cathode are regarded as one of the most promising candidates for energy storage systems with high energy density and high safety. However, they usually suffer poor cathode/electrolyte interfacial stability, severely limiting their practical applications. In this work, a core-shell cathode with uniformly nanosized Li0.5La0.5TiO3 (LLTO) electrolyte coating on LiNi0.5Co0.3Mn0.2O2 (NCM532) is designed to improve the cathode/electrolyte interface stability. Nanosized LLTO coating layer not only significantly boosts interfacial migration of lithium ions, but also efficiently alleviates space-charge layer and inhibits the electrochemical decomposition of electrolyte. As a result, the assembled ASSLBs with high mass loading (9 mg cm-2) LLTO coated NCM532 (LLTO@NCM532) cathode exhibit high initial capacity (135 mAh g-1) and excellent cycling performance with high capacity retention (80% after 200 cycles) at 0.1 C and 25 °C. This nanosized LLTO coating layer design provides a facile and effective strategy for constructing high performance ASSLBs with superior interfacial stability.

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Enhancing interfacial stability in solid-state lithium batteries with polymer/garnet solid electrolyte and composite cathode framework Long Chen, Xiaoming Qiu, Zhiming Bai, Li-Zhen Fan 2021, 52(1): 210-217.  DOI: 10.1016/j.jechem.2020.03.052 Abstract ( 5 )   PDF (6232KB) ( 4 )   The solid-state lithium battery is considered as an ideal next-generation energy storage device owing to its high safety, high energy density and low cost. However, the poor ionic conductivity of solid electrolyte and low interfacial stability has hindered the application of solid-state lithium battery. Here, a flexible polymer/garnet solid electrolyte is prepared with poly(ethylene oxide), poly(vinylidene fluoride), Li6.75La3Zr1.75Ta0.25O12, lithium bis(trifluoromethanesulfonyl)imide and oxalate, which exhibits an ionic conductivity of 2.0 × 10-4 S cm-1 at 55 °C, improved mechanical property, wide electrochemical window (4.8 V vs. Li/Li+), enhanced thermal stabilities. Tiny acidic OX was introduced to inhibit the alkalinity reactions between Li6.75La3Zr1.75Ta0.25O12 and poly(vinylidene fluoride). In order to improve the interfacial stability between cathode and electrolyte, an Al2O3@LiNi0.5Co0.2Mn0.3O2 based composite cathode framework is also fabricated with poly(ethylene oxide) polymer and lithium salt as additives. The solid-state lithium battery assembled with polymer/garnet solid electrolyte and composite cathode framework demonstrates a high initial discharge capacity of 150.6 mAh g-1 and good capacity retention of 86.7% after 80 cycles at 0.2 C and 55 °C, which provides a promising choice for achieving the stable electrode/electrolyte interfacial contact in solid-state lithium batteries.

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The pseudocapacitance mechanism of graphene/CoAl LDH and its derivatives: Are all the modifications beneficial? Chuan Jing, Xu Dong Liu, Kailin Li, Xiaoying Liu, Biqin Dong, Fan, Dong, Yuxin Zhang 2021, 52(1): 218-227.  DOI: 10.1016/j.jechem.2020.04.019 Abstract ( 4 )   PDF (8509KB) ( 1 )   Cobalt-Aluminum layered double hydroxide (CoAl LDH) is a hopeful electrode material due to the advantage of easy modifiability for preparing LDH-based derivatives. However, there is short of modification methods to prepare the Co-based derivatives from CoAl LDH and also short of an intuitive perspective to analyze the pseudocapacitance mechanism of CoAl LDH and its derivatives. Herein, Graphene/CoAl LDH and its derivatives including Graphene/CoS, Graphene/CoS-1, Graphene/CoOOH, Graphene/CoP were prepared by reasonably using alkali etching treatment, sulfofication and phosphorization. The specific capacitance of Graphene/CoAl LDH, Graphene/CoS, Graphene/CoS-1, Graphene/CoOOH, Graphene/CoP at 1 A g-1 are 260.7, 371.3, 440.8, 61.4 and 122.2 F g-1, especially. The pseudocapacitance mechanism of Graphene/CoAl LDH and its derivatives was analyzed. Due to the positive effect of sulfofication on the electrical conductivity of GO and cobalt sulfide, the Graphene/CoS and Graphene/CoS-1 exhibit the optimal electrochemical performance and superior rate capability. In addition, due to the repulsion effect between Graphene and OH-, the Graphene/CoAl LDH exhibits optimal cycling stability of 224.1% capacitance retention after 20000 cycles. Besides, the reason of terrible specific capacitance of Graphene/CoOOH is that the presence of H bond in interlayer of CoOOH inhibits the interaction between Co3+ and OH- species. Hence, not all modifications will increase the specific capacitance of the electrode materials. Overall, this work provides us with a detailed analysis of the electrochemical mechanism and correlation of CoAl LDH and its derivatives from the perspective of crystal structure and composition.

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Combining chlorination and sulfuration strategies for high-performance all-small-molecule organic solar cells Ruimin Zhou, Chen Yang, Wenjun Zou, Muhammad Abdullah Adil, Huan Li, Min Lv, Ziyun Huang, Menglan Lv, Jianqi Zhang, Kun Lu, Zhixiang Wei 2021, 52(1): 228-233.  DOI: 10.1016/j.jechem.2020.04.041 Abstract ( 5 )   PDF (2628KB) ( 2 )   Three small-molecule donors based on dithieno[2,3-d:2ʹ,3ʹ-dʹ]-benzo[1,2-b:4,5-bʹ] dithiophene (DTBDT) unit were designed and synthesized by side chain regulation with chlorinated or/and sulfurated substitutions (namely ZR1, ZR1-Cl, and ZR1-S-Cl respectively), along with a crystalline non-fullerene acceptor IDIC-4Cl with a chlorinated 1,1-dicyanomethylene-3-indanone (IC) end group. Energy levels, molar extinction coefficients and crystallinities of three donor molecules can be effectively altered by combining chlorination and sulfuration strategies. Especially, the ZR1-S-Cl exhibited the best absorption ability, lowest higher occupied molecular orbital (HOMO) energy level and highest crystallinity among three donors, resulting in the corresponding all-small-molecule organic solar cells to produce a high power conversion efficiency (PCE) of 12.05% with IDIC-4Cl as an acceptor.

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Wavelength-sensitive photocatalytic H2 evolution from H2S splitting over g-C3N4 with S,N-codoped carbon dots as the photosensitizer Zhanghui Xie, Shan Yu, Xiang-Bing Fan, Shiqian Wei, Limei Yu, Yunqian Zhong, Xue-Wang Gao, Fan Wu, Ying Zhou 2021, 52(1): 234-242.  DOI: 10.1016/j.jechem.2020.04.051 Abstract ( 6 )   PDF (3948KB) ( 3 )   Photocatalytic splitting of hydrogen sulfide (H2S) for hydrogen evolution is a promising method to solve the energy and environmental issues. In this work, S,N-codoped carbon dots (S,N-CDs)/graphitic carbon nitride (g-C3N4) nanosheet is synthesized by hydrothermal method as an efficient photocatalyst for the decomposition of H2S. In addition to the characterization of the morphology and structure, chemical state, optical and electrochemical performances of S,N-CDs/g-C3N4, hydrogen evolution tests show that the activity of g-C3N4 is improved by introducing S,N-CDs, and the enhancement depends strongly on the wavelength of incident light. The photocatalytic hydrogen production rate of S,N-CDs/g-C3N4 composite reaches 832 μmol g-1h-1, which is 38 times to that of g-C3N4 under irradiation at 460 nm. Density functional theory calculations and electron paramagnetic resonance as well as photoluminescence technologies have altogether authenticated that the unique wavelength-dependent photosensitization of S,N-CDs on g-C3N4; meanwhile, a good match between the energy level of S,N-CDs and g-C3N4 is pivotal for the effective photocatalytic activity. Our work has unveiled the detailed mechanism of the photocatalytic activity enhancement in S,N-CDs/g-C3N4 composite and showed its potential in photocatalytic splitting of H2S for hydrogen evolution.

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Self-propagating fabrication of 3D porous MXene-rGO film electrode for high-performance supercapacitors Jiawei Miao, Qizhen Zhu, Kangle Li, Peng Zhang, Qian Zhao, Bin Xu 2021, 52(1): 243-250.  DOI: 10.1016/j.jechem.2020.04.015 Abstract ( 8 )   PDF (6904KB) ( 6 )   2D MXene nanosheets with metallic conductivity and high pseudo-capacitance are promising electrode materials for supercapacitors. Especially, MXene films can be directly used as electrodes for flexible supercapacitors. However, they suffer from sluggish ion transport due to self-restacking, causing limited electrochemical performance. Herein, a flexible 3D porous MXene film is fabricated by incorporating graphene oxide (GO) into MXene film followed by self-propagating reduction. The self-propagating process is facile and effective, which can be accomplished in 1.25 s and result in 3D porous framework by releasing substantial gas instantaneously. As the 3D porous structure provides massive ion-accessible active sites and promotes fast ion transport, the MXene-rGO films exhibit superior capacitance and rate performance. With the rGO content of 20%, the MXene-rGO-20 film delivers a high capacitance of 329.9 F g-1 at 5 mV s-1 in 3 M H2SO4 electrolyte and remains 260.1 F g-1 at 1,000 mV s-1 as well as good flexibility. Furthermore, the initial capacitance is retained above 90% after 40,000 cycles at 100 A g-1, revealing good cycle stability. This work not only provides a high-performance flexible electrode for supercapacitors, but also proposes an efficient and time-saving strategy for constructing 3D structure from 2D materials.

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Surface-tailored PtPdCu ultrathin nanowires as advanced electrocatalysts for ethanol oxidation and oxygen reduction reaction in direct ethanol fuel cell Kaili Wang, Fei Wang, Yunfeng Zhao, Weiqing Zhang 2021, 52(1): 251-261.  DOI: 10.1016/j.jechem.2020.04.056 Abstract ( 3 )   PDF (8073KB) ( 2 )   The development of advanced electrocatalysts for efficient catalyzing ethanol oxidation reaction (EOR) and oxygen reduction reaction (ORR) is significant for direct ethanol fuel cells (DEFCs). However, in many previous studies, the major difficulties including lower utilization efficiency and weaker anti-CO-poison ability of Pt hamper the practical testing of such DEFCs. Herein, ternary Pt22Pd27Cu51 ultrathin (~5 nm) NWs are fabricated via a facile surfactant-free strategy. The surface and electronic structures of Pt22Pd27Cu51 NWs are further tailored via acid-etching treatment. The resulted PtPdCu NWs with an optimal atomic Pt/Pd/Cu ratio of 36:41:23 display excellent specific activities towards EOR (4.38 mA/cm2) and ORR (1.16 mA/cm2), which are 19.8- and 5.7-folds larger than that of Pt/C, respectively. A single-cell was fabricated using Pt36Pd41Cu23 NWs as electrocatalyst in both anode and cathode with Pt loading of 1.2 mgPt/cm2. The power density measured at 80 °C is 21.7 mW/cm2, which is ~3.9 folds enhancement relative to that fabricated by using Pt/C (2 mgPt/cm2). The enhanced catalytic performance of Pt36Pd41Cu23 NWs could be attributed to that synergistic effect between Pt, Pd and Cu enhances CO anti-poisoning ability and promotes the C-C bond cleavage. This work provides a promising strategy for developing efficient electrocatalysts for DEFCs.

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Functional lithiophilic polymer modified separator for dendrite-free and pulverization-free lithium metal batteries Lingdi Shen, Xin Liu, Jing Dong, Yuting Zhang, Chunxian Xu, Chao Lai, Shanqing Zhang 2021, 52(1): 262-268.  DOI: 10.1016/j.jechem.2020.04.058 Abstract ( 9 )   PDF (3687KB) ( 4 )   Severe performance drop and fire risk due to the uneven lithium (Li) dendrite formation and growth during charge/discharge process has been considered as the major obstacle to the practical application of Li metal batteries. So inhibiting dendrite growth and producing a stable and robust solid electrolyte interface (SEI) layer are essential to enable the use of Li metal anodes. In this work, a functional lithiophilic polymer composed of chitosan (CTS), polyethylene oxide (PEO), and poly(triethylene glycol dimethacrylate) (PTEGDMA), was homogeneously deposited on a commercial Celgard separator by combining electrospraying and polymer photopolymerization techniques. The lithiophilic environment offered by the CTS-PEO-PTEGDMA layer enables uniform Li deposition and facilitates the formation of a robust homogeneous SEI layer, thus prevent the formation and growth of Li dendrites. As a result, both Li/Li symmetric cells and LiFePO4/Li full cells deliver significantly enhanced electrochemical performance and cycle life. Even after 1000 cycles, the specific capacity of the modified full cell could be maintained at 65.8 mAh g-1, twice which of the unmodified cell (32.8 mAh g-1). The long-term cycling stability in Li/Li symmetric cells, dendrite-free anodes in SEM images and XPS analysis suggest that the pulverization of the Li anode was effectively suppressed by the lithiophilic polymer layer.

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Insight into the CO2 photoreduction mechanism over 9-hydroxyphenal-1-one (HPHN) carbon quantum dots Zhengyan Zhao, Heming Zhang, Xuedan Song, Yantao Shi, Duanhui Si, Hongjiang Li, Ce Hao 2021, 52(1): 269-276.  DOI: 10.1016/j.jechem.2020.04.065 Abstract ( 5 )   PDF (2666KB) ( 2 )   Converting CO2 to carbon-containing fuels is an effective approach to relieving energy shortages. Carbon quantum dots (CQDs) have shown distinct properties and attracted tremendous interest in CO2 reduction. Herein, we report a joint experimental-computational mechanistic study of photoreduction CO2 to CO on the model catalyst 9-hydroxyphenal-1-one (HPHN) CQDs with known structure. Our theoretical calculations reveal that the rate-determining step is COOH∙ formation, which is closely related to the proton and electron transfer induced by hydrogen bonding in the excited state. According to the calculated volcano plot, the solution we proposed is addition Zn2+ ions. The active center changed from the hydroxyl oxygen atom to the Zn atom and the barrier of the COOH∙ formation step is noticeably decreased when Zn2+ ions are added. It is further confirmed by the experimental data that the activity of CO2 reduction increases 2.9 times when Zn2+ ions are added.

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Charge storage mechanism of MOF-derived Mn2O3 as high performance cathode of aqueous zinc-ion batteries Min Mao, Xingxing Wu, Yi Hu, Qunhui Yuan, Yan-Bing He, Feiyu Kang 2021, 52(1): 277-283.  DOI: 10.1016/j.jechem.2020.04.061 Abstract ( 2 )   PDF (4257KB) ( 2 )   Aqueous Zinc-ion batteries (ZIB) are attracting immense attention because of their merits of excellent safety and quite cheap properties compared with lithium-ion batteries (LIB). Manganese oxide is one of the most important cathode materials of ZIB. In this paper, α-Mn2O3 used as cathode of ZIB is synthesized via Metal-Organic Framework (MOF)-derived method, which delivers a high specific capacity of 225 mAh g-1 at 0.05 A g-1 and 92.7 mAh g-1 after 1700 cycles at 2 A g-1. The charge storage mechanism of α-Mn2O3 cathode is found to greatly depend on the discharge current density. At lower current density discharging, the H+ and Zn2+ are successively intercalated into the α-Mn2O3 before and after the “turning point” of discharge voltage and their discharging products present obviously different morphologies changing from flower-like to large plate-like products. At a higher current density, the low-voltage plateau after the turning point disappears due to the decrease of amount of Zn2+ intercalation and the H+ intercalation is dominated in α-Mn2O3. This study provides significant understanding for future design and research of high-performance Mn-based cathodes of ZIB.

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Scalable and fast fabrication of graphene integrated micro-supercapacitors with remarkable volumetric capacitance and flexibility through continuous centrifugal coating Xiaoyu Shi, Lijun Tian, Sen Wang, Pengchao Wen, Ming Su, Han Xiao, Pratteek Das, Feng Zhou, Zhaoping Liu, Chenglin Sun, Zhong-Shuai Wu, Xinhe Bao 2021, 52(1): 284-290.  DOI: 10.1016/j.jechem.2020.04.064 Abstract ( 3 )   PDF (5067KB) ( 2 )   Microscale electrochemical energy storage devices, e.g., micro-supercapacitors (MSCs), possessing tailored performance and diversified form factors of lightweight, miniaturization, flexibility and exceptional integration are highly necessary for the smart power sources-unitized electronics. Despite the great progress, the fabrication of MSCs combining high integration with high volumetric performance remains largely unsolved. Herein, we develop a simple, fast and scalable strategy to fabricate graphene based highly integrated MSCs by a new effective continuous centrifugal coating technique. Notably, the resulting highly conductive graphene films can act as not only patterned microelectrodes but also metal-free current collectors and interconnects, endowing modular MSCs with high integrity, remarkable flexibility, tailored voltage and capacitance output, and outstanding performance uniformity. More importantly, the strong centrifugal force and shear force generated in continuous centrifugal coating process lead to graphene films with high alignment, compactness and packing density, contributing to excellent volumetric capacitance of ~31.8 F cm-3 and volumetric energy density of ~2.8 mWh cm-3, exceeding most reported integrated MSCs. Therefore, our work paves a novel way for simple and scalable fabrication of integrated MSCs and offers promising opportunities as standalone microscale power sources for new-generation electronics.

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An Fe-N/S-C hybrid electrocatalyst derived from bimetal-organic framework for efficiently electrocatalyzing oxygen reduction reaction in acidic media Shuqin Song, Mingmei Wu, Junwei Chen, Zhuohua Mo, Rui Chen, Kun Wang, Tongwen Yu 2021, 52(1): 291-300.  DOI: 10.1016/j.jechem.2020.04.066 Abstract ( 5 )   PDF (6844KB) ( 2 )   Heteroatoms doped Fe-N-C electrocatalysts have been widely acknowledged as one of the most promising candidates to replace Pt-based materials for electrocatalyzing oxygen reduction reaction (ORR). However, the complicated synthesis method and controversial catalytic mechanism represent a substantial impediment as of today. Herein, a very facile strategy to prepare Fe-N/S-C hybrid through pyrolyzing Zn and Fe bimetallic MOFs is rationally designed. The electrocatalytic ORR performance shows a volcano-type curve with the increment of added Fe content. The half-wave potential (E1/2) for ORR at optimized Fe-N/S-C-10% (10% = n (Fe)/(n (Fe) + n (Zn)), n (Fe) and n (Zn) represent the moles of Fe2+ and Zn2+ in the precursors, respectively) shifts significantly to the positive direction of 19.6 mV with respect to that of Pt/C in acidic media, as well as a high 4e selectivity and methanol tolerance. After 10,000 potential cycles, E1/2 exhibits a small negative shift of ~27.5 mV at Fe-N/S-C-10% compared favorably with Pt/C (~141.0 mV). This can be attributed to: (i) large specific surface area (849 m2/g) and hierarchically porous structure are favorable for the rapid mass transfer and active sites exposure; (ii) the embedded Fe-containing nanoparticles in porous carbon are difficult to be moved and further agglomerated during the electrochemical accelerated aging test, further improving its stability; (iii) there exist small Fe-containing nanoparticles, uniformly doped N and S, abundant Fe-N as efficiently active sites. This work represents a breakthrough in the development of high-efficient non-precious-metal catalysts (NPMCs) to address the current Pt-based electrocatalysts challenges.

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Synthesis of palladium-rhodium bimetallic nanoparticles for formic acid dehydrogenation Ilaria Barlocco, Sofia Capelli, Elisa Zanella, Xiaowei Chen, Juan J. Delgado, Alberto Roldan, Nikolaos Dimitratos, Alberto Villa 2021, 52(1): 301-309.  DOI: 10.1016/j.jechem.2020.04.031 Abstract ( 6 )   PDF (8776KB) ( 3 )   Herein, we report for the first time the synthesis of preformed bimetallic Pd-Rh nanoparticles with different Pd:Rh ratios (nominal molar ratio: 80-20, 60-40, 40-60, 20-80) and the corresponding Pd and Rh monometallic ones by sol immobilization using polyvinyl alcohol (PVA) as protecting agent and NaBH4 as reducing agent, using carbon nanofibers with high graphitization degree (HHT) as the desired support. The synthesized catalysts were characterized by means of Transmission Electron Microscopy (TEM) and inductively coupled plasma optical emission spectroscopy (ICP-OES). TEM shows that the average particle size of the Pd-Rh nanoparticles is the range of 3-4 nm, with the presence of few large agglomerated nanoparticles. For bimetallic catalysts, EDX-STEM analysis of individual nanoparticles demonstrated the presence of random-alloyed nanoparticles even in all cases Rh content is lower than the nominal one (calculated Pd:Rh molar ratio: 90-10, 69-31, 49-51, 40-60). The catalytic performance of the Pd-Rh catalysts was evaluated in the liquid phase dehydrogenation of formic acid to H2. It was found that Pd-Rh molar ratio strongly influences the catalytic performance. Pd-rich catalysts were more active than Rh-rich ones, with the highest activity observed for Pd90:Rh10 (1792 h-1), whereas Pd69:Rh31 (921 h-1) resulted the most stable during recycling tests. Finally, Pd90:Rh10 was chosen as a representative sample for the liquid-phase hydrogenation of muconic acid using formic acid as hydrogen donor, showing good yield to adipic acid.

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A gelatin-based artificial SEI for lithium deposition regulation and polysulfide shuttle suppression in lithium-sulfur batteries Naseem Akhtar, Xiaogang Sun, Muhammad Yasir Akram, Fakhar Zaman, Weikun Wang, Anbang Wang, Long Chen, Hao Zhang, Yuepeng Guan, Yaqin Huang 2021, 52(1): 310-317.  DOI: 10.1016/j.jechem.2020.04.046 Abstract ( 7 )   PDF (4600KB) ( 3 )   Lithium-sulfur (Li-S) battery is one of the best candidates for the next-generation energy storage system due to its high theoretical capacity (1675 mA h-1), low cost and environment friendliness. However, lithium (Li) dendrites formation and polysulfide shuttle effect are two major challenges that limit the commercialization of Li-S batteries. Here we design a facile bifunctional interlayer of gelatin-based fibers (GFs), aiming to protect the Li anode surface from the dendrites growth and also hinder the polysulfide shuttle effect. We reveal that the 3D structural network of GFs layer with abundant polar sites helps to homogenize Li-ion flux, leading to uniform Li-ion deposition. Meanwhile, the polar moieties also immobilize the lithium polysulfides and protect the Li metal from the side-reaction. As a result, the anode-protected batteries have shown significantly enhanced performance. A high coulombic efficiency of 96% after 160 cycles has been achieved in the Li-Cu half cells. The Li-Li symmetric cells exhibit a prolonged lifespan for 800 h with voltage hysteresis (10 mV). With the as-prepared GFs layer, the Li-S battery shows approximately 14% higher capacity retention than the pristine battery at 0.5 C after 100 cycles. Our work presents that this gelatin-based bi-functional interlayer provides a viable strategy for the manufacturing of advanced Li-S batteries.

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“Polymer-in-ceramic” based poly(Ɛ-caprolactone)/ceramic composite electrolyte for all-solid-state batteries Bohao Zhang, Yulong Liu, Jia Liu, Liqun Sun, Lina Cong, Fang Fu, Alain Mauger, Christian M. Julien, Haiming Xie, Xiumei Pan 2021, 52(1): 318-325.  DOI: 10.1016/j.jechem.2020.04.025 Abstract ( 5 )   PDF (4843KB) ( 3 )   Inspired by the concept of “polymer-in-ceramic”, a composite poly(Ɛ-caprolactone) (PCL)/ceramic containing LiTFSI is prepared and investigated as a solid electrolyte for all-solid-state batteries. The composite with the optimum concentration of 45 wt% LiTFSI and 75 wt% Li1.5Al0.5Ge1.5(PO4)3 (LAGP, NASICON-type structure) exhibits a high ionic conductivity (σi= 0.17 mS cm-1) at 30 °C, a transference number of 0.30, and is stable up to 5.0 V. The composite electrolyte is a flexible and self-standing membrane. Solid-state LiFePO4//Li batteries with this composite electrolyte demonstrate excellent cycling stability with high discharge capacity of 157 mA h g-1, high capacity retention of 96% and coulombic efficiency of 98.5% after 130 cycles at 30 °C and 0.1 C rate. These electrochemical properties are better than other PCL-based all-solid-lithium batteries, and validate the concept of “polymer-in-ceramic” by avoiding the drawback of lower conductivity in prior “polymer-in-ceramic” electrolyte at high concentration of the ceramic.

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Electrolyte accessibility of non-precious-metal catalysts with different spherical particle sizes under alkaline conditions for oxygen reduction reaction Jiyeon Lee, Jong Gyeong Kim, Chanho Pak 2021, 52(1): 326-331.  DOI: 10.1016/j.jechem.2020.04.032 Abstract ( 8 )   PDF (6051KB) ( 4 )

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Effect of fluorinated additives or co-solvent on performances of graphite//LiMn2O4 cells cycled at high potential Benjamin Flamme, Darius J. Yeadon, Satyajit Phadke, Mérièm Anouti 2021, 52(1): 332-342.  DOI: 10.1016/j.jechem.2020.04.030 Abstract ( 4 )   PDF (14199KB) ( 2 )   Herein, a comprehensive study of electrochemical performances of the combined effect of fluorinated additives; fluoroethylene carbonate (FEC); and tris(2,2,2-trifluoroethyl) phosphite (TTFP) or the 2,2,2-trifluoroethyl methyl carbonate (TFEMC) as co-solvent, on Graphite//LiMn2O4 cells cycled at high potential is reported. On one side, each additive has a specific function, the FEC is dedicated to the negative electrode and the TTFP to the opposite one. The electrolyte mixture with (4% FEC + 1% TTFP) additive has shown the best ability to reduce fading of the LiMn2O4 electrode, especially at high rates. On the other side, by studying the comparative thermal and transport properties of the formulated electrolytes with different proportions of TFEMC, we demonstrate that the difference in charge distribution of EMC and TFEMC molecules induced by the presence of fluorine atoms, modifies the solvation model of the Li+ cation, and changes its behavior at the CEI interface and impact strongly the electrochemical performances. Finally, the EIS investigation of the LMO/electrolyte interfaces in the presence of TFEMC demonstrates that despite a spontaneous chemical reactivity of the TFEMC at the cathode interface over time, the conductive and good quality CEI is formed, which positively impact the cyclability. This study shows that against LMO surface phenomena, the combination in adequate proportions of fluorinated additives or solvent can be a solution not only to avoid the oxidative reactivity of LMO-cathode, but also to prevent its harmful consequences on the Li-metal or graphite-anode by controlling the solvation of lithium-ion.

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Synergy of porous structure and cation doping in Ta3N5 photoanode towards improved photoelectrochemical water oxidation Yubin Chen, Hongyu Xia, Xiaoyang Feng, Ya Liu, Wenyu Zheng, Lijing Ma, Rui, Li 2021, 52(1): 343-350.  DOI: 10.1016/j.jechem.2020.04.034 Abstract ( 5 )   PDF (5164KB) ( 3 )   Herein, a cross-linked porous Ta3N5 film was prepared via a simple solution combustion route followed by a high-temperature nitridation process for photoelectrochemical (PEC) water oxidation. Meanwhile, the metal cations (Mg2+ and Zr4+) were incorporated into the porous Ta3N5 to enhance the PEC performance. The porous Mg/Zr co-doped Ta3N5 photoanode yielded a photocurrent density of 1.40 mA cm-2 at 1.23 V vs RHE, which is 5.6 times higher than that of the dense Ta3N5 photoanode. The enhanced performance should be ascribed to the synergistic effect of porous structure and cation doping, which can enlarge the electrochemical active surface area and accelerate the charge transfer by introducing ON substitution defects. Subsequently, Co(OH)2 cocatalyst was loaded on the Mg/Zr-Ta3N5 photoanode to negatively shift the onset potential to 0.45 V vs RHE and further improve the photocurrent density to 3.5 mA cm-2 at 1.23 V vs. RHE, with a maximum half-cell solar to hydrogen efficiency of 0.45%. The present study provides a new strategy to design efficient Ta3N5 photoelectrodes via the simultaneous control of the morphology and composition.

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Advances in perovskite quantum-dot solar cells Aili Wang, Zhiwen Jin, Ming Cheng, Feng Hao, Liming Ding 2021, 52(1): 351-353.  DOI: 10.1016/j.jechem.2020.04.010 Abstract ( 2 )   PDF (1650KB) ( 3 )

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Quasi-solid electrolyte membranes with percolated metal-organic frameworks for practical lithium-metal batteries Zijian Li, Qianqian Liu, Lina Gao, Yifei Xu, Xueqian Kong, Yang Luo, Huaxin Peng, Yurong Ren, Hao Bin Wu 2021, 52(1): 354-360.  DOI: 10.1016/j.jechem.2020.04.013 Abstract ( 18 )   PDF (14374KB) ( 13 )

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Protective electrode/electrolyte interphases for high energy lithium-ion batteries with p-toluenesulfonyl fluoride electrolyte additive Yanxia Che, Xiuyi Lin, Lidan Xing, Xiongcong Guan, Rude Guo, Guangyuan Lan, Qinfeng Zheng, Wenguang Zhang, Weishan Li 2021, 52(1): 361-371.  DOI: 10.1016/j.jechem.2020.04.023 Abstract ( 6 )   PDF (14996KB) ( 2 )   High energy density lithium-ion batteries using Ni-rich cathode (such as LiNi0.6Co0.2Mn0.2O2) suffer from severe capacity decay. P-toluenesulfonyl fluoride (pTSF) has been investigated as a novel film-forming electrolyte additive to enhance the cycling performances of graphite/LiNi0.6Co0.2Mn0.2O2 pouch cell. In comparison with the baseline electrolyte, a small dose of pTSF can significantly improve the cyclic stability of the cell. Theoretical calculations together with experimental results indicate that pTSF would be oxidized and reduced to construct protective interphase film on the surfaces of LiNi0.6Co0.2Mn0.2O2 cathode and graphite anode, respectively. These S-containing surface films derived from pTSF effectively mitigate the decomposition of electrolyte, reduce the interphasial impedance, as well as prevent the dissolution of transition metal ions from Ni-rich cathode upon cycling at high voltage. This finding is beneficial for the practical application of high energy density graphite/ LiNi0.6Co0.2Mn0.2O2 cells.

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Direct experimental detection of hydrogen radicals in non-oxidative methane catalytic reaction Jianqi Hao, Pierre Schwach, Lulu Li, Xiaoguang Guo, Junben Weng, Hailei Zhang, Hao Shen, Guangzong Fang, Xin Huang, Xiulian Pan, Chunlei Xiao, Xueming Yang, Xinhe Bao 2021, 52(1): 372-376.  DOI: 10.1016/j.jechem.2020.04.001 Abstract ( 5 )   PDF (2703KB) ( 3 )   Non-oxidative conversion of methane to olefins, aromatics and hydrogen (MTOAH) has been reported recently over metal single sites such as iron and platinum. The reaction was proposed to involve catalytic activation of methane followed by gas phase C-C coupling of methyl radicals. This study using H atom Rydberg Tagging time-of-flight technique provides direct experimental evidence for the formation of hydrogen radicals during MTOAH reaction over a catalytic quartz wall reactor containing embedded iron species (denoted as Fe-reactor). Fe-reactor gives 7.3% methane conversion at 1273 K with 41.2% selectivity toward C2 (ethane, ethylene and acetylene) and 31.8% toward BTX (benzene, toluene and xylene), respectively. The enhancing effects of hydrogen radicals on overall MTOAH performance are validated by cofeeding hydrogen donor benzene, which provides an additional route of methane activation apart from catalytic activation.

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Optimizing the electrolyte salt of aqueous zinc-ion batteries based on a high-performance calcium vanadate hydrate cathode material Weijun Zhou, Minfeng Chen, Anran Wang, Aixiang Huang, Jizhang Chen, Xinwu Xu, Ching-Ping Wong 2021, 52(1): 377-384.  DOI: 10.1016/j.jechem.2020.05.005 Abstract ( 7 )   PDF (8640KB) ( 2 )   It is urgent to develop high-performance cathode materials for the emerging aqueous zinc-ion batteries with a facile strategy and optimize the related components. Herein, a Ca0.23V2O5·0.95H2O nanobelt cathode material with a rather large interlayer spacing of 13.0 Å is prepared via a one-step hydrothermal approach. The battery with this cathode material and 3 M Zn(CF3SO3)2 electrolyte displays high specific capacity (355.2 mAh g-1 at 0.2 A g-1), great rate capability (240.8 mAh g-1 at 5 A g-1), and excellent cyclability (97.7% capacity retention over 2000 cycles). Such superior performances are ascribed to fast electrochemical kinetics, outstanding electrode/electrolyte interface stability, and nearly dendrite-free characteristic. Instead, when ZnSO4 or Zn(ClO4)2 is used to replace Zn(CF3SO3)2, the electrochemical performances become much inferior, due to the slow electrochemical kinetics, inhomogeneous Zn stripping/plating process, and the formation of large dendrites and byproducts. This work not only discloses a high-performance cathode material for aqueous zinc-ion batteries but also offers a reference for the choice of electrolyte salt.

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Designer uniform Li plating/stripping through lithium-cobalt alloying hierarchical scaffolds for scalable high-performance lithium-metal anodes Xinhua Liu, Xiaojuan Qian, Weiqiang Tang, Hui Luo, Yan Zhao, Rui Tan, Mo Qiao, Xinlei Gao, Yang Hua, Huizhi Wang, Shuangliang Zhao, Chao Lai, Magda Titirici, Nigel P. Brandon, Shichun Yang, Billy Wu 2021, 52(1): 385-392.  DOI: 10.1016/j.jechem.2020.03.059 Abstract ( 3 )   PDF (7635KB) ( 1 )   Lithium metal anodes are of great interest for advanced high-energy density batteries such as lithium-air, lithium-sulfur and solid-state batteries, due to their low electrode potential and ultra-high theoretical capacity. There are, however, several challenges limiting their practical applications, which include low coulombic efficiency, the uncontrollable growth of dendrites and poor rate capability. Here, a rational design of 3D structured lithium metal anodes comprising of in-situ growth of cobalt-decorated nitrogen-doped carbon nanotubes on continuous carbon nanofibers is demonstrated via electrospinning. The porous and free-standing scaffold can enhance the tolerance to stresses resulting from the intrinsic volume change during Li plating/stripping, delivering a significant boost in both charge/discharge rates and stable cycling performance. A binary Co-Li alloying phase was generated at the initial discharge process, creating more active sites for the Li nucleation and uniform deposition. Characterization and density functional theory calculations show that the conductive and uniformly distributed cobalt-decorated carbon nanotubes with hierarchical structure can effectively reduce the local current density and more easily absorb Li atoms, leading to more uniform Li nucleation during plating. The current work presents an advance on scalable and cost-effective strategies for novel electrode materials with 3D hierarchical microstructures and mechanical flexibility for lithium metal anodes.

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Nickel oxide for inverted structure perovskite solar cells Fei Ma, Yang Zhao, Jinhua Li, Xingwang Zhang, Haoshuang Gu, Jingbi You 2021, 52(1): 393-411.  DOI: 10.1016/j.jechem.2020.04.027 Abstract ( 11 )   PDF (30015KB) ( 2 )   The emergence of inverted perovskite solar cells (PSCs) has attached great attention derived from the potential in improving stability. Charge transporting layer, especially hole transporting layer is crucial for efficient inverted PSCs. Organic materials were used as hole transporting layer previously. Recently, more and more inorganic hole transporting materials have been deployed for further improving the device stability. Nickel oxide (NiOx) as p-type metal oxide, owning high charge mobility and intrinsic stability, has been widely adopted in inverted PSCs. High performance over 20% efficiency has been achieved on NiOx base inverted PSCs. Herein, we have summarized recent progresses and strategies on the NiOx based PSCs, including the synthesis or deposition methods of NiOx, doping and surface modification of NiOx for efficient and stable PSCs. Finally, we will discuss current challenges of utilizing NiOx HTLs in PSCs and attempt to give probable solutions to make further development in efficient as well as stable NiOx based PSCs.

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Synergistic cerium doping and MXene coupling in layered double hydroxides as efficient electrocatalysts for oxygen evolution Yangyang Wen, Zhiting Wei, Jiahao Liu, Rui Li, Ping Wang, Bin Zhou, Xiang Zhang, Jiang Li, Zhenxing Li 2021, 52(1): 412-420.  DOI: 10.1016/j.jechem.2020.04.009 Abstract ( 8 )   PDF (9237KB) ( 1 )   Oxygen evolution reaction (OER) is a bottle-neck process in many sustainable energy conversion systems due to its sluggish kinetics. The development of cost-effective yet efficient electrocatalysts towards OER is highly desirable but still a great challenge at current stage. Herein, a new type of hybrid nanostructure, consisting of two-dimensional (2D) Cerium-doped NiFe-layered double hydroxide nanoflakes directly grown on the 2D Ti3C2Tx MXene surface (denoted as NiFeCe-LDH/MXene), is designed using a facile in-situ coprecipitation method. The resultant NiFeCe-LDH/MXene hybrid presents a hierarchical nanoporous structure, high electrical conductivity and strong interfacial junction because of the synergistic effect of Ce doping and MXene coupling. As a result, the hybrid catalyst exhibits an excellent catalytic activity for OER, delivering a low onset overpotential of 197 mV and an overpotential of 260 mV at a current density of 10 mA·cm-2 in the alkaline medium, much lower than its pure LDH counterparts and IrO2 catalyst. Besides, the hybrid catalyst also displays a fast reaction kinetics and a remarkable stable durability. Further theoretic studies using density function theory (DFT) methods reveal that Ce doping could effectively narrow the bandgap of NiFe-LDH and reduce the overpotential in OER process. This work may shed light on the exploration of advanced electrocatalysts for renewable energy conversion and storage systems.

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Design and optimization of electrochemical cell potential for hydrogen gas production Nawar K. Al-Shara, Farooq Sher, Sania Z. Iqbal, Oliver Curnick, George Z. Chen 2021, 52(1): 421-427.  DOI: 10.1016/j.jechem.2020.04.026 Abstract ( 6 )   PDF (3020KB) ( 7 )   This study deals with the optimization of best working conditions in molten melt for the production of hydrogen (H2) gas. Limited research has been carried out on how electrochemical process occurs through steam splitting via molten hydroxide. 54 combinations of cathode, anode, temperature and voltage have been investigated for the optimization of best working conditions with molten hydroxide for hydrogen gas production. All these electrochemical investigations were carried out at 225 to 300°C temperature and 1.5 to 2.5 V applied voltage values. The current efficiency of 90.5, 80.0 and 68.6% has been achieved using stainless steel anodic cell with nickel, stainless steel and platinum working cathode respectively. For nickel cathode, an increase in the current directly affected the hydrogen gas flow rate at cathode. It can be hypothesized from the noted results that increase in current is directly proportional to operating temperature and applied voltage. Higher values were noted when the applied voltages increased from 1.5 to 2.5 V at 300°C, the flow rate of hydrogen gas increased from 1.5 to 11.3 cm3 min-1, 1.0 to 13 cm3 min-1 in case of electrolysis @stainless steel and @graphite anode respectively. It is observed that the current efficiency of stainless steel anodic cell was higher than the graphite anodic cell. Therefore, steam splitting with the help of molten salts has shown an encouraging alternate to current methodology for H2 fuel production.

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Aluminum hydride for solid-state hydrogen storage: Structure, synthesis, thermodynamics, kinetics, and regeneration Haizhen Liu, Longfei Zhang, Hongyu Ma, Chenglin Lu, Hui Luo, Xinhua Wang, Xiantun Huang, Zhiqiang Lan, Jin Guo 2021, 52(1): 428-440.  DOI: 10.1016/j.jechem.2020.02.008 Abstract ( 6 )   PDF (8537KB) ( 10 )   Aluminum hydride (AlH3) is a binary metal hydride that contains more than 10.1 wt% of hydrogen and possesses a high volumetric hydrogen density of 148 kg H2 m-3. Pristine AlH3 can readily release hydrogen at a moderate temperature below 200 °C. Such high hydrogen density and low desorption temperature make AlH3 one of most promising hydrogen storage media for mobile application. This review covers the research activity on the structures, synthesis, decomposition thermodynamics and kinetics, regeneration and application validation of AlH3 over the past decades. Finally, the future research directions of AlH3 as a hydrogen storage material will be revealed.