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2021, Vol. 59, No. 8　Online: 15 August 2021

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Revealing the working mechanism of a multi-functional block copolymer binder for lithium-sulfur batteries Xin He, Zhimeng Liu, Guoping Gao, Xiaotao Liu, Michal Swietoslawski, Jun Feng, Gao Liu, Lin-Wang Wang, Robert Kostecki 2021, 59(8): 1-8.  DOI: 10.1016/j.jechem.2020.10.002 Abstract ( 4 )   PDF (7405KB) ( 3 )   The lithium-sulfur (Li-S) battery is one of the most promising substitutes for current energy storage sys-tems because of its low cost, high theoretical capacity, and high energy density. However, the high sol-ubility of intermediate products (i.e., lithium polysulfides) and the resultant shuttle effect lead to rapidly fading capacity and a low coulombic efficiency, which hinder the practical application of Li-S batteries. In this study, block copolymers are constructed with both an ethylene oxide unit and a styrene unit and then used as binders for Li-S batteries. Electrochemical performance improvements are attributed to the synergistic effects contributed by the different units of the block copolymer. The ethylene oxide unit traps polysulfide, which bonds strongly with the intermediate lithium polysulfide, and enhances the transport of lithium ions to reach high capacity. Meanwhile, the styrene unit maintains cathode integrity by improving the mechanical properties and elasticity of the constructed block copolymer to accommo-date the large volume changes. By enabling multiple functions via different units in the polymer chain, high sulfur utilization is achieved, polysulfide diffusion is confined, and the shuttle effect is suppressed during the cycle life of Li-S batteries, as revealed by operando ultraviolet-visible spectroscopy and S K-edge X-ray absorption spectroscopy.

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3D hierarchical architecture collaborating with 2D/2D interface interaction in NiAl-LDH/Ti3C2 nanocomposite for efficient and selective photoconversion of CO2 Qunrong Shi, Xiaoyue Zhang, Yong Yang, Junjie Huang, Xiaolong Fu, Tianyu Wang, Xiaodong Liu, Aiwu Sun, Jianhua Ge, Jinyou Shen, Yong Zhou, Zuliang Liu 2021, 59(8): 9-18.  DOI: 10.1016/j.jechem.2020.10.038 Abstract ( 8 )   PDF (4991KB) ( 6 )   Photocatalytic conversion of CO2 into a special chemical fuel with high yield and selectivity is still a major challenge. Herein, a 3D hierarchical NiAl-LDH/Ti3C2 MXene (LDH/TC) nanocomposite is constructed through in situ loading of Ti3C2 nanosheets on the NiAl-LDH scaffold during the hydrothermal process. The formation of a uniform and well-defined 2D/2D heterogeneous interface can be realized by optimiz-ing the ratio of Ti3C2 and the precursors for NiAl-LDH. The 3D hierarchical scaffold with high specific sur-face area contributes to the favourable photon adsorption and utilization. The intimate contact between Ti3C2 and NiAl-LDH with numerous interfaces effectively promotes the separation of the photoinduced electron-hole pairs in NiAl-LDH. Together with the highly exposed oxidation-reduction active sites and the enhanced CO2 capture and activation. The maximum photocatalytic CO production rate on NiAl-LDH/Ti3C2 reaches 11.82 lmol g-1h-1 with 92% selectivity and superior stability. This work provides an effective approach for the development of an ideal photocatalyst by collaborative utilization of mate-rials with different dimensionalities.

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High-yield production of non-layered 2D carbon complexes: Thickness manipulation and carbon nanotube branches for enhanced lithium storage properties Dong Wang, Shuai Qi, Yao Qiu, Rui Zhang, Qiang Zhang, Shulong Liu, Chunjie Zhang, Ziyao Chen, Hong Pan, Jun Cao, Guangwu Wen 2021, 59(8): 19-29.  DOI: 10.1016/j.jechem.2020.10.048 Abstract ( 5 )   PDF (6196KB) ( 4 )   Non-layered two-dimensional (2D) carbon complexes manifest great potential in energy-related applica-tions owing to their exotic electronic structures, large electrochemically active surface, and intriguing synergistic effects. However, reliable method for mass production and thickness manipulation of 2D car-bon complexes remains great challenges. Here, inspired by blowing chewing gum into bubbles, a ‘‘tai-lored gel expanding” strategy is proposed for high-yield synthesis of non-layered 2D carbon complexes with tailored thickness from ~12 nm to ~1 lm, by controllable pyrolysis of metal-polymeric gel with ade-quate crosslinking degree. The key feature for thickness manipulation is introducing NH4NO3 in sol-gel process, which tailors the expansion behavior of gel precursor during subsequent pyrolysis. Various of 2D sheets with intimately coupled N,O-doped carbon (NOC) and NiCo-based (NiCo, (NiCo)S2, (NiCo)Se2, NiCo2O4, (NiCo)(PO3)2) nanocrystals are obtained on a large scale and without any impurities. Moreover, these 2D products are branched with in-situ grown CNTs on the surface, accelerating electrons transfer and preventing the nanosheets from stacking. As a demonstration, the 2D (NiCo)S2/NOC with optimized thickness manifests excellent lithium storage properties in both half and full cells. This method paves a new path for massive and controlled production of non-layered 2D materials with tailored thick-ness and robust structure stability for energy-related applications.

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Optimizing polymer aggregation and blend morphology for boosting the photovoltaic performance of polymer solar cells via a random terpolymerization strategy Tao Zhang, Cunbin An, Qianglong Lv, Jinzhao Qin, Yong Cui, Zhong Zheng, Bowei Xu, Shaoqing Zhang, Jianqi Zhang, Chang He, Jianhui Hou 2021, 59(8): 30-37.  DOI: 10.1016/j.jechem.2020.11.021 Abstract ( 3 )   PDF (4536KB) ( 3 )   Compared to regular conjugated polymers, the random conjugated terpolymers are usually not beneficial to achieve highly efficient non-fullerene (NF)-based polymer solar cells (PSCs) due to their disordered chemical structures. In this work, we report two random terpolymer donors (PBNB80 and PBNB50) by tuning the molar ratio of electron-accepting units of 1,3-di(thiophen-2-yl)naphtho[2,3-c]thiophene-4,9 -dione (NTD) and 1,3-bis(4-chlorothiophen-2-yl)-4H,8H-benzo[1,2-c:4,5-c’]dithiophene-4,8-dione (Cl-BDD), at the same time, the parent polymers (PBNB100 and PBNB00) are also compared to study. These four polymer donors exhibit similar optical bandgaps and gradually deepen highest occupied molecular orbital levels. Importantly, aggregation and self-organization properties of the random terpoly-mer donors are optimized, which result in the better morphology and crystal coherence length after blending with NF acceptor of BO-4Cl. Particularly, a PBNB80:BO-4Cl blend forms an optimal nanoscale phase-separation morphology, thereby producing an outstanding power conversion efficiency of 16.0%, which is much higher than those (12.8% and 10.7%) of their parent binary polymer donor-based devices. This work demonstrates that rational using terpolymerization strategy to prepare random terpolymer is a very important method to achieve highly efficient NF-PSCs.

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Interwoven scaffolded porous titanium oxide nanocubes/carbon nanotubes framework for high-performance sodium-ion battery Wen-Bei Yu, Wen-Da Dong, Chao-Fan Li, Nasiruddin Macadam, Jiu-Xiang Yang, Guo-Bin Zhang, Zhi-Yi Hu, Tien-Chun Wu, Yu Li, Tawfique Hasan, Li-Hua Chen, Li-Qiang Mai, Bao-Lian Su 2021, 59(8): 38-46.  DOI: 10.1016/j.jechem.2020.11.010 Abstract ( 8 )   PDF (4900KB) ( 3 )   Supercapacitor-like Na-ion batteries have attracted much attention due to the high energy density of bat-teries and power density of capacitors. Titanium dioxide (TiO2), is a promising anode material. Its perfor-mance is however seriously hindered by its low electrical conductivity and the sluggish diffusion of sodium ions (Na+) in the TiO2 matrix. Herein, this work combines porous TiO2 nanocubes with carbon nanotubes (CNTs) to enhance the electrical conductivity and accelerate Na+ diffusivity for Na-ion batter-ies (NIBs). In this composite, an interwoven scaffolded TiO2/CNTs framework is formed to provide abun-dant channels and shorter diffusion pathways for electrons and ions. The in-situ X-ray diffraction and cyclic voltammetry confirm the low strain and superior transport kinetics in Na+ intercalation/extraction processes. In addition, the chemically bonded TiO2/CNTs hybrid provides a more feasible channel for Na+ insertion/extraction with a much lower energy barrier. Consequently, the TiO2/CNTs composite exhibits excellent electrochemical performance with a capacity of 223.4 mAh g-1 at 1 C and a capacity of 142.8 mAh g-1 at 10 C (3.35 A g-1). The work here reveals that the combination of active materials with CNTs can largely improve the utilization efficiency and enhance their sodium storage.

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Filling the in situ-generated vacancies with metal cations captured by C-N bonds of defect-rich 3D carbon nanosheet for bifunctional oxygen electrocatalysis Dawei Chen, Wei Cao, Jing Liu, Jie Wang, Xiaoke Li, Luhua Jiang 2021, 59(8): 47-54.  DOI: 10.1016/j.jechem.2020.11.009 Abstract ( 6 )   PDF (4546KB) ( 3 )   Nitrogen-doped carbon materials with vacancies/defects have been developed as highly efficient ORR electrocatalysts but with poor activity for OER, which limits their application in rechargeable metal-air batteries. Filling the vacancies/defects with heteroatoms is expected to be an effective strategy to obtain surprising catalytic activities and improve their stability especially under the strongly oxidizing condi-tions during the OER process. Herein, we successfully transformed the defect-rich 3D carbon nanosheets (DCN) into a bifunctional ORR/OER electrocatalyst (DCN-M) by utilizing the in-situ generated vacancies to capture metal cations via a modified salt-sealed strategy. By varying the metal (Fe, Ni) content, the captured metal cations in DCN-M existed in different chemical states, i.e., metal atoms were stabilized by C—N bonds at low metal contents, while at high metal contents, bimetal particles were covered by gra-phene layers, taking responsibility for catalyzing the ORR and OER, respectively. In addition, the in-situ formed graphene layers with an interconnected structure facilitate the electron transport during the reactions. The Janus-feature of DCN-M in structures ensures superior bifunctional activity and good sta-bility towards ORR/OER for the rechargeable Zn-air battery. This work provides an effective strategy to design multifunctional electrocatalysts by heteroatom filling into vacancies of carbon materials.

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Superior surface electron energy level endows WP2 nanowire arrays with N2 fixation functions Dongdong Han, Xiaojing Liu, Jinyan Cai, Yufang Xie, Shuwen Niu, Yishang Wu, Yipeng Zang, Yanyan Fang, Fengqi Zhao, Wengang Qu, Minghua Chen, Gongming Wang, Yitai Qian 2021, 59(8): 55-62.  DOI: 10.1016/j.jechem.2020.11.006 Abstract ( 3 )   PDF (8866KB) ( 1 )   Nitrogen reduction reaction (NRR) under ambient conditions is always a long-standing challenge in science, due to the extreme difficulty in breaking the strong N„N triple bond. The key to resolving this issue undoubtedly lies in searching superior catalysts to efficiently activate and hydrogenate the stable nitrogen molecules. We herein evaluate the feasibility of WP2 for N2 activation and reduction, and first demonstrate WP2 with an impressive ammonia yield rate of 7.13 lg h-1 cm-2, representing a promising W-based catalyst for NRR. DFT analysis further reveals that the NRR catalysis on WP2 proceeds in a distal reaction pathway, and the exceptional NRR activity is originated from superior surface electron energy level matching between WP2 and NRR potential which facilitates the interfacial proton-coupled electron transfer dynamics. The successfully unraveling the intrinsic catalytic mechanism of WP2 for NRR could offer a powerful platform to manipulate the NRR activity by tuning the electron energy levels.

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Altering polythiophene derivative substrates to explore the mechanism of heterogeneous lithium nucleation for dendrite-free lithium metal anodes Yanchen Fan, Yi Zhao, Shuang Li, Yue Liu, You Lv, Yuan Zhu, Rong Xiang, Shigeo Maruyama, Hao Zhang, Qianfan Zhang 2021, 59(8): 63-68.  DOI: 10.1016/j.jechem.2020.10.035 Abstract ( 4 )   PDF (1838KB) ( 3 )   Lithium metal batteries (LMBs) possess outstanding theoretical energy density and have attracted wide-spread attention as the next generation of energy storage devices for various crucial applications. However, the commercialization of LMBs has to simultaneously overcome numerous challenges, such as inferior Coulombic efficiency and cycling performance, high self-discharge, and complicated interfacial reactions. It has traditionally been an enormous challenge about the uniform deposition of lithium on the surface of current collector to relieve the formation of lithium dendrites. In this study, a novel efficient strategy of plating uniform lithiophilic polythiophene derivatives substrates on Cu foils was developed and the nucleation mechanism of Li ions on polythiophene derivatives substrates was further explored. We first explored the interaction between polythiophene derivatives substrates and Li ions by first-principles calculations, and found shorter side chains of polythiophene derivatives can enhance the adsorption energy and promote the diffusion rate of Li ions. Polythiophene derivatives substrates have a large number of dispersive lipophilic sites and Li ions diffusion channels in the main chain, which can effectively regulate the nucleation and growth stages of Li ions deposition. We further found poly-thiophene derivatives with different side chains can induce the electrodeposition of Li ions with different morphology, while the polythiophene derivatives with the shortest side chains can contribute to the most excellent cycle efficiency, resulting in a uniform lithium deposition with less lithium dendritic growth experimentally.

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A review of pulse electrolysis for efficient energy conversion and chemical production Tao Liu, Jinling Wang, Xuejing Yang, Ming Gong 2021, 59(8): 69-82.  DOI: 10.1016/j.jechem.2020.10.027 Abstract ( 7 )   PDF (7818KB) ( 3 )   Electrochemical transformation emerges as an important solution to sustainable energy conversion and chemical production. Conventional electrolytic systems usually operate under galvanostatic or potentio-static conditions that sometimes result in unsatisfactory efficiencies or selectivities. Pulse electrolysis by pulsating and programming the potentials/currents can feature unique tunability to the electrode-electrolyte interface properties that can give rise to drastically different electrochemical behaviors com-pared to the steady-state counterparts. Although invented almost 100 years ago, pulse electrolysis has received little attention over the period, but has recently attracted a revived focus toward the energy-efficient electrolysis. This review will summarize the history and recent efforts of pulse electrolysis in three categories: water electrolysis, CO2 electrolysis and other electrolysis. In each section, the advantage of pulse electrolysis over steady-state electrolysis will be discussed in detail, giving a comprehensive overview of the pulse effect on the electrolytic systems. Finally, we will provide our vision of future direc-tions in pulse electrolysis based on previous works.

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A review of lithium-ion battery safety concerns: The issues, strategies, and testing standards Yuqing Chen, Yuqiong Kang, Yun Zhao, Li Wang, Jilei Liu, Yanxi Li, Zheng Liang, Xiangming He, Xing Li, Naser Tavajohi, Baohua Li 2021, 59(8): 83-99.  DOI: 10.1016/j.jechem.2020.10.017 Abstract ( 83 )   PDF (6407KB) ( 37 )   Efficient and reliable energy storage systems are crucial for our modern society. Lithium-ion batteries (LIBs) with excellent performance are widely used in portable electronics and electric vehicles (EVs), but frequent fires and explosions limit their further and more widespread applications. This review sum-marizes aspects of LIB safety and discusses the related issues, strategies, and testing standards. Specifically, it begins with a brief introduction to LIB working principles and cell structures, and then pro-vides an overview of the notorious thermal runaway, with an emphasis on the effects of mechanical, elec-trical, and thermal abuse. The following sections examine strategies for improving cell safety, including approaches through cell chemistry, cooling, and balancing, afterwards describing current safety stan-dards and corresponding tests. The review concludes with insights into potential future developments and the prospects for safer LIBs.

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Combined DFT and experiment: Stabilizing the electrochemical interfaces via boron Lewis acids Zhe-Fan Wang, Zonglin Yi, Aziz Ahmad, Lijing Xie, Jing-Peng Chen, Qingqiang Kong, Fangyuan Su, Da-Wei Wang, Cheng-Meng Chen 2021, 59(8): 100-107.  DOI: 10.1016/j.jechem.2020.10.041 Abstract ( 6 )   PDF (5661KB) ( 2 )   The incorporation of boron into carbon material can significantly enhance its capacity performances. However, the origin of the promotion effect of boron doping on electrochemical performances is still unclear, in part due to the inadequate exposure of boron configurations resulting from the complexity of traditional carbon materials. To overcome this issue, herein, a series of boron-doped graphene with highly-exposed boron configurations are prepared by tuning annealing temperature. Then the correlation between boron configurations and the electrochemical performances is investigated. The combination of density-functional theory (DFT) computation and NH3-TPD/Py-FTIR indicates that the BCO2 configuration formed on the surface of graphene is easier to accept lone-pair electrons than BC2O and BC3 configura-tions due to the stronger Lewis acidity. Such an electronic structure can effectively reduce the number of unstable electron donors and stabilize the electrochemical interface, which is proved by NMR, and crit-ical for improving the electrochemical performances. Further experiments confirm that the optimized BG800 with the largest amount of BCO2 configuration presents ultralow leak current, improved cyclic sta-bility, and better rate performance in SBPBF4/PC. This work would provide an insight into the design of high-performance boron-doped carbon materials towards energy storage.

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Emerging material engineering strategies for amplifying photothermal heterogeneous CO2 catalysis Bingqiao Xie, Emma Lovell, Tze Hao Tan, Salina Jantarang, Mengying Yu, Jason Scott, Rose Amal 2021, 59(8): 108-125.  DOI: 10.1016/j.jechem.2020.11.005 Abstract ( 5 )   PDF (7352KB) ( 3 )   Closing the carbon loop, through CO2 capture and utilization, is a promising route to mitigate climate change. Solar energy is a sustainable energy source which can be exploited to drive catalytic reactions for utilizing CO2, including converting the CO2 into useful products. Solar energy can be harnessed through a range of different pathways to valorize CO2. Whilst using solar energy to drive CO2 reduction has vast potential to promote catalytic CO2 conversions, the progress is limited due to the lack of under-standing of property-performance relations as well as feasible material engineering approaches. Herein, we outline the various driving forces involved in photothermal CO2 catalysis. The heat from solar energy can be utilized to induce CO2 catalytic reduction reactions via the photothermal effect. Further, solar energy can act to modify reaction pathways through light-matter interactions. Light-induced chemical functions have demonstrated the ability to regulate intermediary reaction steps, and thus control the reaction selectivity. Photothermal catalyst structures and specific catalyst design strategies are discussed in this context. This review provides a comprehensive understanding of the heat-light synergy and guid-ance for rational photothermal catalyst design for CO2 utilization.

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A flexible carbon nanotube@V2O5 film as a high-capacity and durable cathode for zinc ion batteries Xiaowei Wang, Liqun Wang, Bao Zhang, Jianmin Feng, Jiafeng Zhang, Xing Ou, Feng Hou, Ji Liang 2021, 59(8): 126-133.  DOI: 10.1016/j.jechem.2020.10.007 Abstract ( 5 )   PDF (9235KB) ( 1 )   Aqueous zinc-ion batteries (ZIBs) are receiving a continuously increasing attention for mobile devices, especially for the flexible and wearable electronics, due to their non-toxicity, non-flammability, and low-cost features. Despite the significant progress in achieving higher capacities for electrode materials of ZIBs, to endow them with high flexibility and economic feasibility is, however, still a significant chal-lenge remaining unsolved. Herein, we present a highly flexible composite film composed of carbon nan-otube film and V2O5 (CNTF@V2O5) with high strength and high conductivity, which is prepared by simply impregnating a porous CNT film with an aqueous V2O5 sol under vacuum. For this material, intimate incorporation between V2O5 and CNTs has been achieved, successfully integrating the high zinc ion stor-age capability with high mechanical flexibility. As a result, this CNTF@V2O5 film delivers a high capacity of 356.6 mAh g-1 at 0.4 A g-1 and excellent cycling stability with 80.1% capacity retention after 500 cycles at 2.0 A g-1. The novel strategy and the outstanding battery performance presented in this work should shed light on the development of high-performance and flexible ZIBs.

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Recent advances and perspectives on vanadium-and manganese-based cathode materials for aqueous zinc ion batteries Na Liu, Bin Li, Zhangxing He, Lei Dai, Haiyan Wang, Ling Wang 2021, 59(8): 134-159.  DOI: 10.1016/j.jechem.2020.10.044 Abstract ( 10 )   PDF (15889KB) ( 9 )   The growing demand for energy storage has inspired researchers’ exploration of advanced batteries. Aqueous zinc ion batteries (ZIBs) are promising secondary chemical battery system that can be selected and pursued. Rechargeable ZIBs possess merits of high security, low cost, environmental friendliness, and competitive performance, and they are received a lot of attention. However, the development of suitable zinc ion intercalation-type cathode materials is still a big challenge, resulting in failing to meet the com-mercial needs of ZIBs. Both vanadium-based and manganese-based compounds are representative of the most advanced and most widely used rechargeable ZIBs electrodes. The valence state of vanadium is +2 ~+5, which can realize multi-electron transfer in the redox reaction and has a high specific capacity. Most of the manganese-based compounds have tunnel structure or three-dimensional space frame, with enough space to accommodate zinc ions. In order to understand the energy storage mechanism and elec-trochemical performance of these two materials, a specialized review focusing on state-of-the-art devel-opments is needed. This review offers access for researchers to keep abreast of the research progress of cathode materials for ZIBs. The latest advanced researches in vanadium-based and manganese-based cathode materials applied in aqueous ZIBs are highlighted. This article will provide useful guidance for future studies on cathode materials and aqueous ZIBs.

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An account of the strategies to enhance the water splitting efficiency of noble-metal-free electrocatalysts Subhasis Shit, Saikat Bolar, Naresh Chandra Murmu, Tapas Kuila 2021, 59(8): 160-190.  DOI: 10.1016/j.jechem.2020.10.022 Abstract ( 2 )   PDF (11890KB) ( 2 )   The electrolysis of water for hydrogen generation has shown immense promise as an energy conversion technology for the green energy economy. Two concurrently occurring electrochemical reactions in water electrolysis (hydrogen and oxygen evolution reactions) are sluggish in nature and therefore the employ-ment of electrocatalysts is highly essential. Noble-metal-based electrocatalysts (Pt, RuO2, IrO2, etc.) have shown superior activity towards these reactions. However, their lower natural abundance and inferior stability make the cost to performance ratio of water electrolysis too high. Thus, huge amount of research efforts are being carried out to develop electrocatalysts consisting of earth abundant elements (transition metals, carbon etc.) as the replacement of these noble-metal-based materials. Transition metal com-pounds, carbonaceous and hybrid materials have shown promise as efficient electrocatalysts but there is still huge gap between the activities of these materials and the noble-metal-based electrocatalysts. Several strategies like morphology modulation, elemental doping, defect engineering etc. are being deployed to enhance the activity of these noble-metal-free electrocatalysts. This review summarizes these strategies and thoroughly discusses the reason behind the changes in activity of the electrocatalysts owing to these modifications. Finally, the remaining research gaps and future prospects in this field are also discussed in detail.

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In-situ/operando characterization techniques in lithium-ion batteries and beyond Haoyu Li, Shaohua Guo, Haoshen Zhou 2021, 59(8): 191-211.  DOI: 10.1016/j.jechem.2020.11.020 Abstract ( 5 )   PDF (17438KB) ( 3 )   Nowadays, in-situ/operando characterization becomes one of the most powerful as well as available means to monitor intricate reactions and investigate energy-storage mechanisms within advanced bat-teries. The new applications and novel devices constructed in recent years are necessary to be reviewed for inspiring subsequent studies. Hence, we summarize the progress of in-situ/operando techniques employed in rechargeable batteries. The members of this large family are divided into three sections for introduction, including bulk material, electrolyte/electrode interface and gas evolution. In each part, various energy-storage systems are mentioned and the related experimental details as well as data anal-ysis are discussed. The simultaneous strategies of various in-situ methods are highlighted as well. Finally, current challenges and potential solutions are concluded towards the rising influence and enlarged appli-ance of in-situ/operando techniques in the battery research.

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High-temperature treatment to engineer the single-atom Pt coordination environment towards highly efficient hydrogen evolution Shanyong Chen, Changchang Lv, Ling Liu, Muhong Li, Jian Liu, Jinyang Ma, Panpan Hao, Xuan Wang, Weiping Ding, Mingjiang Xie, Xuefeng Guo 2021, 59(8): 212-219.  DOI: 10.1016/j.jechem.2020.11.004 Abstract ( 6 )   PDF (5906KB) ( 2 )   Development of high-performance and cost-effective catalysts for electrocatalytic hydrogen evolution reaction (HER) play crucial role in the growing hydrogen economy. Recently, the atomically dispersed metal catalysts have attracted increasing attention due to their ultimate atom utilization and great potential for highly cost-effective and high-efficiency HER electrocatalyst. Herein, we propose a high-temperature treatment strategy to furtherly improve the HER performance of atomically dispersed Pt-based catalyst. Interestingly, after appropriate high-temperature treatment on the atomically dispersed Pt0.8@CN, the Pt species on the designed N-doped porous carbon substrate with rich defect sites can be re-dispersed to single atom state with new coordination environment. The obtained Pt0.8@CN-1000 shows superior HER performance with overpotential of 13 mV at 10 mA cm-2 and mass activity of 11,284 mA/mgPt at —0.1 V, much higher than that of the pristine Pt0.8@CN and commercial Pt/C cata-lyst. The experimental and theoretical investigations indicate that the high-temperature treatment induces the restructuring of coordination environment and then the optimized Pt electronic state leads to the enhanced HER performances. This work affords new strategy and insights to develop the atomi-cally dispersed high-efficiency catalysts.

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CoB and BN composites enabling integrated adsorption/catalysis to polysulfides for inhibiting shuttle-effect in Li-S batteries Tianli Wu, Ting Yang, Jizong Zhang, Xuewen Zheng, Kunlin Liu, Chengyang Wang, Mingming Chen 2021, 59(8): 220-228.  DOI: 10.1016/j.jechem.2020.11.015 Abstract ( 6 )   PDF (3097KB) ( 4 )   Lithium-sulfur (Li-S) batteries are hampered by the infamous shuttle effect and slow redox kinetics, resulting in rapid capacity decay. Herein, a bifunctional catalysis CoB/BN@rGO with integrated structure and synergy effect between adsorption and catalysis is proposed to solve the above problems. The inte-grated CoB and BN are simultaneously and uniformly introduced on the rGO substrate through a one-step calcination strategy, applied to modify the cathode side of PP separator. The transition metal borides can catalyze the conversion of lithium polysulfides (Li2Sn, n ≥ 4), whereas the bond of B-S is too weak to absorb LPS. Thus BN introduced can effectively restrict the diffusion of polysulfides via strong chemisorp-tion with LiSnLi+ ·· ·N, while the rGO substrate ensures smooth electron transfer for redox reaction. Therefore, through the integrated adsorption/catalysis, the shuttle effect is suppressed, the kinetics of redox reaction is enhanced, and the capacity decay is reduced. Using CoB/BN@rGO modified PP separator, the Li-S batteries with high initial capacity (1450 mAh g-1 at 0.35 mA cm-2) and long-cycle stability (700 cycles at 1.74 mA cm-2 with a decay rate of 0.032% per cycle) are achieved. This work provides a novel insight for the preparation of bifunctional catalysis with integrated structure for long-life Li-S batteries.

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Self-consistent assessment of Li+ ion cathodes: Theory vs. experiments Hongjie Xu, Weidong Xiao, Zhuo Wang, Junhua Hu, Guosheng Shao 2021, 59(8): 229-241.  DOI: 10.1016/j.jechem.2020.11.008 Abstract ( 7 )   PDF (9638KB) ( 2 )   Transition metal oxide cathodes such as layered LiCoO2, spinel LiMn2O4 and olivine LiFePO4 have been commercialized for several decades and widely used in the rechargeable Li-ion batteries (LIBs). While great theoretical efforts have been made using the density functional theory (DFT) method, leading to insightful understanding covering materials stability and functional properties, the lack of consistency in choices of functionals and/or convergence criteria makes it somewhat difficult to compare results. It is therefore highly useful to assess these established systems towards self-consistency, thus offering a reliable working basis for theoretical formulation of novel cathodes. Here in this work, we have carried out systematic DFT calculations on the basis of recently established framework covering both thermody-namic stability, functional properties and associated mechanisms. Efforts have been made in self-consistent selection of exchange-correlation (XC) functionals in terms of dependable accuracy with affordable computational cost, which is essential for high-throughput first-principles calculations. The outcome of the current work on three established cathode systems is in very good agreement with exper-imental data, and the methodology is to provide a solid basis for designing novel cathode materials with-out using costing non-local exchange-correlation functionals for structure-energy calculations.

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Perspective on ultramicroporous carbon as sulphur host for Li-S batteries Helen Maria Joseph, Maximilian Fichtner, Anji Reddy Munnangi 2021, 59(8): 242-256.  DOI: 10.1016/j.jechem.2020.11.001 Abstract ( 6 )   PDF (17116KB) ( 4 )   Lithium-sulphur (Li-S) batteries are currently considered as next-generation battery technology. Sulphur is an attractive positive electrode for lithium metal batteries, mainly due to its high capacity (1675 mAh g-1) and high specific energy (2600 Wh kg-1). The electrochemical reaction of lithium with sulphur in non-aqueous electrolytes results in the formation of electrolyte soluble intermediate lithium-polysul-phides. The dissolved polysulphides shuttle to the anode and get reduced at the anode resulting in Li metal corrosion. The solubility of polysulphide gradually reduces the amount of sulphur in the cathode, thereby limiting the cycle life of Li-S batteries. Several strategies have been proposed to improve the cycling stability of Li-S batteries. A unique approach to eliminate the polysulphide shuttle is to use ultra-microporous carbon (UMC) as a host for sulphur. The pore size of UMC which is below 7 Å, is the bottle-neck for carbonate solvents to access sulphur/polysulphides confined in the pores, thereby preventing the polysulphide dissolution. This perspective article will emphasise the role of UMC host in directing the lithiation mechanism of sulphur and in inhibiting polysulphide dissolution, including the resulting par-asitic reaction on the lithium anode. Further, the challenges that need to be addressed by UMC-S based Li-S batteries, and the strategies to realise high power density, high Coulombic efficiency, and resilient Li-S batteries will be discussed.

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Discrete composition control of two-dimensional morphologic all-inorganic metal halide perovskite nanocrystals Andrew Hunter Davis, Weiwei Zheng 2021, 59(8): 257-275.  DOI: 10.1016/j.jechem.2020.10.023 Abstract ( 6 )   PDF (12556KB) ( 5 )   Metal halide perovskite nanocrystals (NCs) exhibit impressive optical and electronic properties, making them an important class of functional materials with promising applications in solar cells, light emitting diodes (LEDs), photodetectors, and photocatalysts. In addition to the widely studied 0-dimensional (0D) metal halide perovskite NCs, such as nanocubes, low dimensional perovskites, such as 2D all-inorganic perovskite (AIP) NCs, subsist with directionally relevant quantum confinement. These anisotropic NCs have the propensity to exhibit interesting optoelectronic properties that are exceedingly difficult to intro-duce into 0D systems, yet as of late are largely unexplored. In this review, we discuss the recent synthetic progress of 2D all-inorganic metal halide perovskite NCs with ABX3 structure. Specifically, we highlight the discrete composition control of the cations (A and B sites) and anions (X site) by dopant incorporation and alloying in 2D metal halide perovskite NCs. We will also discuss more complex perovskite crystal structures, such as Ruddlesden-Popper double perovskites, and compare these materials to 0D perovskite systems. Ultimately, our work culminates in the future interests and perspectives of this field with a focus on the wide applicability of 2D systems and the large variance in structure capable with discrete compo-sitional tuning.

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Review on supercapacitors: Technologies and performance evaluation Jingyuan Zhao, Andrew F. Burke 2021, 59(8): 276-291.  DOI: 10.1016/j.jechem.2020.11.013 Abstract ( 6 )   PDF (2483KB) ( 3 )   The development of electrochemical capacitors (i.e. supercapacitors) have attracted a lot of attention in recent years because of the increasing demand for efficient, high-power energy storage. Electrochemical capacitors (ECs) are particularly attractive for transportation and renewable energy generation applica-tions, taking advantage of their superior power capability and outstanding cycle life. Over the past dec-ade, various advanced electrode materials and cell design are being studied to improve the energy density of ECs. Hybrid Li-ion capacitors and pseudo-capacitors that utilize fast surface redox reactions of metal oxide and doped polymers are the prime candidates being considered. This paper is concerned with the metrics being used to describe the performance of ECs and how the metrics are evaluated by testing devices and how the data from the testing are best interpreted. Emphasize is on relating testing of advanced ECs using materials more complex than activated carbons to testing electric double-layer capacitors (EDLCs) using carbon in both electrodes. A second focus of the paper is projecting the potential of the advanced materials and ionic liquid electrolytes for the development of complete EC cells having an energy density more than a factor of ten greater the energy density of the EDLC devices currently on the market. This potential was evaluated by calculating the performance (energy and power) of a series of ECs that utilize the advanced materials that have been studied by electrochemists over the past 10-15 years. The capacitance and resistance of the advanced ECs were calculated utilizing specific capaci-tance (F/g or F/cm3) and porosity data for the electrode materials and ionic conductivity of the elec-trolytes. It was concluded that hybrid ECs can be developed with energy densities of at least 50 Wh/ kg, 70 Wh/L with efficient power greater than 3 kW/kg. Continued research on micro-porous carbons with specific capacitance of 200F/g and greater is needed.to achieve these EC performance goals.

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A novel approach for synthesis of expanded graphite and its enhanced lithium storage properties Xianghong Chen, Feng Xiao, Yu Lei, Haiyin Lu, Jiakui Zhang, Min Yan, Jiantie Xu 2021, 59(8): 292-298.  DOI: 10.1016/j.jechem.2020.10.006 Abstract ( 11 )   PDF (12949KB) ( 3 )

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Tailoring electron transfer with Ce integration in ultrathin Co(OH)2 nanosheets by fast microwave for oxygen evolution reaction Ya-Nan Zhou, Ruo-Yao Fan, Shu-Yue Dou, Bin Dong, Yu Ma, Wen-Li Yu, Meng-Xuan Li, Yu-Lu Zhou, Chen-Guang Liu, Yong-Ming Chai 2021, 59(8): 299-305.  DOI: 10.1016/j.jechem.2020.10.037 Abstract ( 2 )   PDF (4221KB) ( 2 )   The intrinsic activity of Co(OH)2 for oxygen evolution reaction (OER) may be elaborately improved through the suitable valence adjustment. Ce modification at electronic level is proved to be an efficient strategy owing to the flexible transformation of Ce3+/Ce4+. Herein, Ce0.21@Co(OH)2 with the optimized Ce doping have been fabricated to tailor the fast electron transfer for the enhanced activity and stability for OER. Firstly, the obtained core-shell structure composed of vertical loose Co(OH)2 sheets not only exposes a large number of active sites, but also provides channels for Ce doping. Secondly, the high pres-sure microwave with instantaneous heating can fast introduce Ce into Co(OH)2, obtaining Cex@Co(OH)2 with well dispersion and close integration. The intimated interaction between Ce and Co species may pro-vide the ‘‘d-f electronic ladders” for accelerating electron transfer of the catalytic surface. Meanwhile, Ce promotes the formation of Co-superoxide intermediate and/or the release of oxygen, which is considered to be the rate-determining step for OER. The electrochemical measurements confirmed the low overpo-tential of 300 mV at 10 mA cm-2 and great stability of Ce0.21@Co(OH)2 for OER. This work demonstrates a meaningful approach to realize the tuned electronic structure through metal doping.

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A review on the failure and regulation of solid electrolyte interphase in lithium batteries Jun-Fan Ding, Rui Xu, Chong Yan, Bo-Quan Li, Hong Yuan, Jia-Qi Huang 2021, 59(8): 306-319.  DOI: 10.1016/j.jechem.2020.11.016 Abstract ( 17 )   PDF (4724KB) ( 12 )   Solid electrolyte interphase (SEI) has been widely recognized as the most important and the least under-stood component in lithium batteries. Considering the intrinsic instability in both chemical and mechan-ical, the failure of SEI is inevitable and strongly associated with the performance decay of practical working batteries. In this Review, the failure mechanisms and the corresponding regulation strategies of SEI are focused. Firstly, the fundamental properties of SEI, including the formation principles, and the typical composition and structures are briefly introduced. Moreover, the common SEI failure modes involving thermal failure, chemical failure, and mechanical failure are classified and discussed, respec-tively. Beyond that, the regulation strategies of SEI with respect to different failure modes are further con-cluded. Finally, the future endeavor in further disclosing the mysteries of SEI is prospected.

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Ionic liquids for high performance lithium metal batteries Kexin Liu, Zhuyi Wang, Liyi Shi, Siriporn Jungsuttiwong, Shuai Yuan 2021, 59(8): 320-333.  DOI: 10.1016/j.jechem.2020.11.017 Abstract ( 11 )   PDF (7940KB) ( 8 )   The pursuit of high energy density has promoted the development of high-performance lithium metal batteries. However, it faces a serious security problem. Ionic liquids have attracted great attention due to their high ionic conductivity, non-flammability, and the properties of promoting the formation of stable SEI films. Deeply understanding the problems existing in lithium metal batteries and the role of ionic liquids in them is of great significance for improving the performance of lithium metal batteries. This article reviews the effects of the molecular structure of ionic liquids on ionic conductivity, Li+ ion transference number, electrochemical stability window, and lithium metal anode/electrolyte interface, as well as the application of ionic liquids in Li-high voltage cathode batteries, Li-O2 batteries and Li-S bat-teries. The molecular design, composition and polymerization will be the main strategies for the future development of ionic liquid-based electrolytes for high performance lithium metal battery.

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Enhancing the CO2 methanation activity of Ni/CeO2 via activation treatment-determined metal-support interaction Shuangxi Lin, Ziwen Hao, Jindong Shen, Xiao Chang, Shouying Huang, Maoshuai Li, Xinbin Ma 2021, 59(8): 334-342.  DOI: 10.1016/j.jechem.2020.11.011 Abstract ( 3 )   PDF (5852KB) ( 2 )   The metal-support interaction is of critical importance to enhance the catalytic activity and selectivity. However, it is still challenging to construct an appropriate interaction starting from the catalyst fabrica-tion and/or activation. We herein established low-temperature treatment of Ni2+ ions impregnated on ceria in reductive atmosphere and reduction-oxidation cycles as effective approachs to regulate the metal-support interaction and raise the catalytic performance in the CO2 methanation. The proposed con-struction approach yielded Ni/CeO2 that displayed highly dispersed Ni nanoparticles in contact with CeO2 (111) and (100) facet, higher density of surface oxygen vacancies and larger amounts of weak basic sites relative to the reference samples, which increased the capacity for H2 and CO2 adsorption/activation. The interaction resulted in appreciably (2-3 fold) higher activity in the CO2 methanation with maintaining almost full selectivity to CH4 and high stability. Coverage of Ni surface by CeO2—x thin layer as a typical structure of strong metal-support interaction resulting from high-temperature reduction, can be allevi-ated via reduction-oxidation cycles. We also demonstrate the activation treatment-determined metal-support interaction effect can generally extend to (TiO2 and ZrO2) supported Ni catalysts.

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Recent progress in rate and cycling performance modifications of vanadium oxides cathode for lithium-ion batteries Xi Zhang, Xiaohong Sun, Xin Li, Xudong Hu, Shu Cai, Chunming Zheng 2021, 59(8): 343-363.  DOI: 10.1016/j.jechem.2020.11.022 Abstract ( 8 )   PDF (11837KB) ( 2 )   The emergency of high-power electrical appliances has put forward higher requirements for the power density of lithium-ion batteries. Vanadium oxides with large theoretical capacities and high operating voltages are considered as prospective alternatives for the cathode of a new generation of lithium-ion batteries. However, the poor rate and cycling performance caused by the sluggish electrons/lithium transportation, irreversible phase changes, vanadium dissolution and large volume changes during the repeated lithium intercalation/deintercalation hinder their commercial development. Several optimizing routes have been carried out and extensively explored to address these problems. Taking V2O5, VO2(B), V6O13, and V2O3 as examples, this article reviewed their crystal structures and lithium storage reactions. Besides, recent progress in modification methods for the electrochemical insufficiencies of vanadium oxi-des, including nanostructure, heterogeneous atom doping, composite and self-supported electrodes has been systematically summarized and finally, the challenges for the industrialization of vanadium oxide cathodes and their development opportunities are proposed.

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Acceptor-acceptor-type conjugated polymer semiconductors Dunshuai Qu, Ting Qi, Hui Huang 2021, 59(8): 364-387.  DOI: 10.1016/j.jechem.2020.11.019 Abstract ( 6 )   PDF (3422KB) ( 5 )   The rapid development of electronic devices such as organic field-effect transistors (OFETs) and solar cells makes the research and development of electronic transport materials imminent. The acceptor-acceptor-type (A—A-type) conjugated n-type polymer semiconductors have caught much attention due to the out-standing advantages on excellent electron-accepting capabilities, the precise adjustment of energy levels and the mass production at low fabrication cost. This article systematically reviews the polymerization methods of A—A-type polymers and the recent advancements applied in OFETs and polymer solar cells (PSCs). The analyses of the synthesis and the relationship between device performances and polymer molecular structures may provide a constructive guidance for the further development of high-performance n-type polymer materials.

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Nitrogen and atomic Fe dual-doped porous carbon nanocubes as superior electrocatalysts for acidic H2-O2 PEMFC and alkaline Zn-air battery Xiudong Shi, Zonghua Pu, Bin Chi, Mingrui Liu, Siyan Yu, Long Zheng, Lijun Yang, Ting Shu, Shijun Liao 2021, 59(8): 388-395.  DOI: 10.1016/j.jechem.2020.11.026 Abstract ( 6 )   PDF (5307KB) ( 2 )   Air cathodes with high electrocatalytic activity are vital for developing H2/O2 proton exchange membrane fuel cells (PEMFC) and Zn-air batteries. However, the state-of-the-art air cathodes suffer from either lim-ited catalytic activity or high cost, which thus hinder their applications. Herein, we designed ZIF-8 derived nitrogen and atomic iron dual-doped porous carbon nanocubes as high-quality catalysts for ORR, through a novel gas-doping approach. The porous carbon nanocubic architecture and abundant Fe-Nx active species endow ZIF-8 derived single atomic iron catalyst (PCN-A@Fe SA) with superior cat-alytic activity, and surpass Pt/C and a majority of the reported catalysts. Both XAS and DFT calculations suggest that Fe2+N4 moieties are the main active centers that are favorable for oxygen affinity and OH* intermediate desorption, which can result in promising catalytic performance. Most importantly, PCN-A@Fe SA can achieve power density of 514 mW cm-2 as cathodic catalyst in a PEMFC and discharge peak power density of 185 mW cm-2 in an alkaline Zn-air battery. The outstanding performance is derived from both the high specific surface area and high-density of iron single atom in nitrogen doped nanocubic carbon matrix.

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Weaving 3D highly conductive hierarchically interconnected nanoporous web by threading MOF crystals onto multi walled carbon nanotubes for high performance Li-Se battery Chao Li, Yingying Wang, Hongyan Li, Jing Liu, Jianping Song, Luca Fusaro, Zhi-Yi Hu, Yanxin Chen, Yu Li, Bao-Lian Su 2021, 59(8): 396-404.  DOI: 10.1016/j.jechem.2020.11.023 Abstract ( 9 )   PDF (10931KB) ( 1 )   Lithium-selenium (Li-Se) battery has attracted growing attention. Nevertheless, its practical application is still impeded by the shuttle effect of the formed polyselenides. Herein, we report in-situ hydrothermal weaving the three-dimensional (3D) highly conductive hierarchically interconnected nanoporous web by threading microporous metal organic framework MIL-68(Al) crystals onto multi-walled carbon nan-otubes (MWCNTs). Such 3D hierarchically nanoporous web (3D MIL-68 (Al)@MWCNTs web) with a very high surface area, a large amount of micropores, electrical conductivity and elasticity strongly traps the soluble polyselenides during the electrochemical reaction and significantly facilitates lithium ion diffu-sion and electron transportation. Molecular dynamic calculation confirmed the strong affinity of MIL-68 (Al) for the adsorption of polyselenides, quite suitable for Li-Se battery. Their hexahedral channels (1.56 nm) are more efficient for the confinement of polyselenides and for the diffusion of electrolytes compared to their smaller triangular channels (0.63 nm). All these excellent characteristics of 3D MIL-68 (Al)@MWCNTs web with suitable confinement of a large amount of selenium and the conductive link-age between MIL-68(Al) host by MWCNTs result in a high capacity of 453 mAh/g at 0.2C with 99.5% coulombic efficiency after 200 cycles with significantly improved cycle stability and rate performance. The 3D MIL-68 (Al)@MWCNTs web presents a good performance in Li-Se battery in term of the specific capacity and cycling stability and also in terms of rate performance compared with all the metal-organic framework (MOF) based or MOF derived porous carbons used in Li-Se battery.

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Revealing the structure design of alloyed based electrodes for alkali metal ion batteries with in situ TEM Huawen Huang, Ran Bi, Jie Cui, Ming-Ming Hu, Li Tian, Xianfeng Yang, Lei Zhang 2021, 59(8): 405-418.  DOI: 10.1016/j.jechem.2020.11.027 Abstract ( 5 )   PDF (18890KB) ( 1 )   Alloyed based anode materials with high theoretical specific capacity and low reaction potential are con-sidered to be highly potential high-energy density anode materials for alkali metal ion batteries (AMIBs). Thus, the design of alloyed based materials with high electrochemical performance has attracted great attention. Among the numerous characterization methods for guiding electrode materials design, in situ transmission electron microscopy (TEM) gradually plays an irreplaceable role due to its high tem-poral and spatial resolution in directly observing the change of morphology, crystal structure and ele-ment evolutions. Herein, we reviewed the two current research hotspots and mainly focused on the structure design of alloyed based electrode material under the guidance of in situ TEM. Specifically, var-ious nanostructure designs of alloyed based electrode materials with guidance of in situ TEM were employed to solve the key scientific issues of the violent volume change during alloying/dealloying pro-cesses for enhanced electrochemical performances. Mainly through introducing buffer space in the elec-trode material to reduce volume change to improve structural stability, including porous structure (0D), nanotube structure (1D), simple hollow structure, yolk-shell structure and some hybrid hollow structures (3D). Furthermore, the direct guidance of in situ TEM is expected for creating new opportunities to next-generation electrode material design for AMIBs.

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Single-layer graphene as a highly selective barrier for vanadium crossover with high proton selectivity Saheed Bukola, Zhaodong Li, Jason Zack, Christopher Antunes, Carol Korzeniewski, Glenn Teeter, Jeffrey Blackburn, Bryan Pivovar 2021, 59(8): 419-430.  DOI: 10.1016/j.jechem.2020.11.025 Abstract ( 5 )   PDF (4978KB) ( 3 )   We report near-zero crossover for vanadium cross-permeation through single-layer graphene immobi-lized at the interface of two Nafion® polymer electrolyte membranes. Vanadium ion diffusion and migra-tion, including proton mobility through membrane composites, were studied with and without graphene under diffusion and migration conditions. Single-layer graphene was found to effectively inhibit vana-dium ion diffusion and migration under specific conditions. The single-layer graphene composites also enabled remarkable ion transmission selectivity improvements over pure Nafion® membranes, with pro-ton transport being four orders of magnitude faster than vanadium ion transport. Resistivity values of 0. 02 ± 0.005 O cm2 for proton and 223 ± 4 O cm2 for vanadium ion through single atomic layer graphene are reported. This high selectivity may have significant impact on flow battery applications or for other elec-trochemical devices where proton conductivity is required, and transport of other species is detrimental. Our results emphasize that crossover may be essentially completely eliminated in some cases, enabling for greatly improved operational viability.

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Progress in electrochemical lithium ion pumping for lithium recovery Guolang Zhou, Linlin Chen, Yanhong Chao, Xiaowei Li, Guiling Luo, Wenshuai Zhu 2021, 59(8): 431-445.  DOI: 10.1016/j.jechem.2020.11.012 Abstract ( 8 )   PDF (7287KB) ( 2 )   Accelerating the development of lithium resources has attracted a great deal of attention with the explo-sive growth of new energy vehicles. As a new technology, electrochemical lithium ion pumping (ELIP) is featured by environment-friendly, low energy consumption and high efficiency. This review summarizes the research progress in ELIP, and focuses on the evaluation methods, electrode materials and electro-chemical systems of ELIP. It can be concluded that ELIP is expected to achieve an industrial application and has a promising prospect. In addition, challenges and perspective of electrochemical lithium extrac-tion are also highlighted.

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Transition-metal redox evolution and its effect on thermal stability of LiNixCoyMnzO2 based on synchrotron soft X-ray absorption spectroscopy Chen Liang, Wenhua Zhang, Zesen Wei, Zhaoyu Wang, Qingsong Wang, Jinhua Sun 2021, 59(8): 446-454.  DOI: 10.1016/j.jechem.2020.11.024 Abstract ( 8 )   PDF (8988KB) ( 3 )   Based on the synchrotron soft X-ray absorption spectroscopy experiments, the fundamental electronic structures of layered LiNixCoyMnzO2 (NCM) are investigated systematically and the data of transition-metal (TM) L-and O K-edges spectra are collected. Distribution of Ni ions under different oxidation states is evaluated according to linear combination fit. It is found that the ratio of Ni4+ expands with the increase of Ni since it dominates in charge compensation during charging, and that the existence of Ni3+ is nearly negligible in delithiated NCM. The valence state of Co also strongly depends on Ni content, the perceptible position shift of Co L3-edge absorption peak towards higher energy in Ni-rich material agrees well with the small voltage plateau at around 4.2 V. The stability of Mn is verified as no obvious spectral change with the Mn L-edge is observed. Moreover, as Ni content rises, the O 2p holes near the Femi level increases with higher oxidation state of Ni, indicating the enhanced hybridization of O 2p-TM 3d. Delithiated NCMs with higher Ni content are prior to lose electron existing in highly hybridized Ni 3d-O 2p bands upon heating, which accounts for the pronounced O2 release in phase transitions and the deterioration in thermal stability. These detailed observation of the electronic structure evolution is one of the key ingredients to improving the electrochemical and thermal performance of NCM.

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Ultrafine PdAg alloy nanoparticles anchored on NH2-functionalized 2D/ 2D TiO2 nanosheet/rGO composite as efficient and reusable catalyst for hydrogen release from additive-free formic acid at room temperature Xi Zhao, Ping Dai, Dongyan Xu, Xumei Tao, Xien Liu, Qingjie Ge 2021, 59(8): 455-464.  DOI: 10.1016/j.jechem.2020.11.018 Abstract ( 13 )   PDF (8316KB) ( 4 )   A 2D-2D titanium dioxide nanosheet-reduced graphene oxide (TNS-rGO) composite with better elec-tronic conductivity and hydrophilicity was prepared by the hydrothermal method. The as-obtained TNS-rGO composite was further functionalized with 3-aminopropyltriethoxysilane (APTES) to provide a large amount of -NH2 groups on the surface for anchoring ultrafine PdAg alloy nanoparticles with an average particle size of 1.69 nm by a facile wet reduction approach. Benefiting from the combined effects of well-dispersed PdAg alloy nanoparticles, facilitated electron transfer from TNS-rGO to Pd, and increased electron density of active sites, the Pd8Ag1/NH2-TNS-rGO catalyst exhibited excellent activity towards dehydrogenation of formic acid without adding any additives at 298 K, corresponding to an ini-tial turn over frequency as high as 1090 h-1, which is much higher than that of most other state-of-the-art catalysts.

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Effects of Cr doping on structural and electrochemical properties of Li4Ti5O12 nanostructure for sodium-ion battery anode Sang Hyuk Gong, Ji Hyeon Lee, Dong Won Chun, Jee-Hwan Bae, Sung-Chul Kim, Seungho Yu, Sahn Nahm, Hyung-Seok Kim 2021, 59(8): 465-472.  DOI: 10.1016/j.jechem.2020.11.029 Abstract ( 7 )   PDF (8014KB) ( 2 )   Sodium-ion batteries are considered as promising alternatives to lithium-ion batteries, owing to their low cost and abundant raw materials. Among the several candidate materials for the anode, spinel-type Li4Ti5O12 (LTO) has potential owing to its superior safety originating from an appropriate operating volt-age and the reversible Na+ intercalation properties. However, a low diffusion coefficient for Na+ and the insulating nature of LTO remains challenging for practical sodium-ion battery systems. Herein, we pre-sent a strategy for integrating physical and chemical approaches to achieve superior electrochemical properties in LTO. We demonstrate that carefully controlling the amount of Cr doping is crucial to enhance the electrochemical properties of nanostructured LTO. Optimized Cr doped LTO shows a superior reversible capacity of 110 mAh g-1 after 400 cycles at 1C, with a three-fold higher capacity (75 mAh g-1) at 10C compared with undoped LTO material. This suggests that appropriately Cr doped nanostructured LTO is a promising anode material for sodium-ion batteries.

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Bi2S3 spheres coated with MOF-derived Co9S8 and N-doped carbon composite layer for half/full sodium-ion batteries with superior performance Youzhang Huang, Xueshuang Zhu, Daoping Cai, Zhixiang Cui, Qianting Wang, Hongbing Zhan 2021, 59(8): 473-481.  DOI: 10.1016/j.jechem.2020.11.007 Abstract ( 6 )   PDF (13933KB) ( 3 )   Bismuth sulfide (Bi2S3) has attracted particular interest as a potential anode material for sodium-ion bat-teries (SIBs). However, the low electrical conductivity and dramatic volumetric change greatly restrict its practical applications. In view of the apparent structural and compositional advantages of metal-organic frameworks (MOFs) derived carbon-based composite, herein, as a proof of concept, Bi2S3 spheres coated with the MOF-derived Co9S8 and N-doped carbon composite layer (Bi2S3@Co9S8/NC composite spheres) have been rational designed and synthesized. As expected, the core-shell Bi2S3@Co9S8/NC composite spheres exhibit remarkable electrochemical performance in terms of high reversible capacity (597 mAh g-1 after 100 cycles at 0.1 A g-1), good rate capability (341 mAh g-1 at 8 A g-1) and long-term cycling stability (458 mAh g-1 after 1000 cycles at 1 A g-1) when investigated as anode materials for SIBs. Electrochemical analyses further reveal the favorable reaction kinetics in the Bi2S3@Co9S8/NC com-posite spheres. In addition, the possible sodium storage mechanism has been studied by ex-situ X-ray diffraction technique. More importantly, a sodium-ion full cell based on Na3V2(PO4)3/rGO as cathode and Bi2S3@Co9S8/NC as anode is also fabricated, suggesting their potential for practical applications. It is anticipated that the present work could be extended to construct other advanced electrode materials using MOFs-derived carbon-based composites as surface coating materials for various energy storage-related applications.

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In situ surface-confined fabrication of single atomic Fe-N4 on N-doped carbon nanoleaves for oxygen reduction reaction Xiaojing Jiang, Jianian Chen, Fenglei Lyu, Chen Cheng, Qixuan Zhong, Xuchun Wang, Ayaz Mahsud, Liang Zhang, Qiao Zhang 2021, 59(8): 482-491.  DOI: 10.1016/j.jechem.2020.11.036 Abstract ( 9 )   PDF (9993KB) ( 2 )   Controllable fabrication of Fe-N-C based single-atom catalysts (SACs) for enhanced electrocatalytic per-formance is highly desirable but still challenging. Here, an in situ surface-confined strategy was demon-strated for the synthesis of single atomic Fe-N4 on N-doped carbon nanoleaves (L-FeNC). The in situ generated Zn3[Fe(CN)6]2 could not only serve as a protection layer against collapse of nanoleaves but also provide abundant Fe source for the formation of Fe-N moieties during pyrolysis, leading to high surface area and high graphitization degree of L-FeNC simultaneously. Benefiting from abundant Fe-N4 active sites, enhanced mass and charge transfer, the as-prepared L-FeNC manifested a half-wave potential of 0.89 V for oxygen reduction reaction (ORR) in 0.1 M KOH. A maximum power density of 140 mW cm-2 and stable discharge voltage even after operation for 50,000 s have been demonstrated when the L-FeNC was used as air cathode for Zn-air battery. This work not only provided a unique surface-confined strategy for the synthesis of two-dimensional nanocarbons, but also demonstrated the signifi-cant benefit from rational design and engineering of Fe-N-C SACs, thus offering great opportunities for fabrication of efficient energy conversion and storage devices.

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Electrospinning as a route to advanced carbon fibre materials for selected low-temperature electrochemical devices: A review Yue Wen, Matt D.R. Kok, Jorge Pavel Victoria Tafoya, Ana B. Jorge Sobrido, Ellsworth Bell, Jeff T. Gostick, Servann Herou, Philipp Schlee, Maria-Magdalena Titirici, Dan J.L. Brett, Paul R. Shearing, Rhodri Jervis 2021, 59(8): 492-529.  DOI: 10.1016/j.jechem.2020.11.014 Abstract ( 9 )   PDF (14128KB) ( 3 )   Electrospinning has been proven as a highly versatile fabrication method for producing nano-structured fibres with controllable morphology, of both the fibres themselves and the void structure of the mats. Additionally, it is possible to use heteroatom doped polymers or to include catalytic precursors in the electrospinning solution to control the surface properties of the fibres. These factors make it an ideal method for the production of electrodes and flow media for a variety of electrochemical devices, enabling reduction in mass transport and activation overpotentials and therefore increasing efficiency. Moreover, the use of biomass as a polymer source has recently gained attention for the ability to embed sustainable principles in the materials of electrochemical devices, complementing their ability to allow an increase in the use of renewable electricity via their application. In this review, the historical and recent develop-ments of electrospun materials for application in redox flow batteries, fuel cells, metal air batteries and supercapacitors are thoroughly reviewed, including an overview of the electrospinning process and a guide to best practice. Finally, we provide an outlook for the emerging use of this process in the field of electrochemical energy devices with the hope that the combination of tailored microstructure, surface functionality and computer modelling will herald a new era of bespoke functional materials that can significantly improve the performance of the devices in which they are used.

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Sn-O dual-doped Li-argyrodite electrolytes with enhanced electrochemical performance Ting Chen, Dewu Zeng, Long Zhang, Meng Yang, Dawei Song, Xinlin Yan, Chuang Yu 2021, 59(8): 530-537.  DOI: 10.1016/j.jechem.2020.11.031 Abstract ( 8 )   PDF (9746KB) ( 2 )   As a type of candidate for all-solid-state Li batteries, argyrodite solid electrolytes possess high ionic con-ductivity, but poor compatibility against Li metal. Here, we report novel Li6PS5I-based argyrodite sulfides with Sn-O dual doping, which is a powerful solution to comprehensively improve the performance of a material. The combination of O and Sn-aliovalent doping not only enables an improved ionic conductivity but more importantly realizes an intensively enhanced interfacial compatibility between argyrodite and Li metal and Li dendrite suppression capability. The assembled battery with Sn-O dual-doped electrolyte and Li anode demonstrates high capacity and decent cycling stability. Dual doping is thus believed to be an effective way to develop high performance sulfide solid electrolytes.

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Constructing bifunctional Co/MoC@N-C catalyst via an in-situ encapsulation strategy for efficient oxygen electrocatalysis Hui Huang, Lingjun Kong, Ming Liu, Jie He, Wei Shuang, Yunhua Xu, Xian-He Bu 2021, 59(8): 538-546.  DOI: 10.1016/j.jechem.2020.11.028 Abstract ( 9 )   PDF (7538KB) ( 3 )   The large-scale application of Zn-air battery requires the development of efficient, low-cost, and stable bifunctional electrocatalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Herein, an electrocatalyst of a Co/MoC-nanoparticles embedded N-doped carbon (Co/MoC@N-C) was prepared via the in-situ encapsulation of Co2(CO)8 and Mo(CO)6 in ZIF-8 using ball-milling, followed by pyrolysis under an Ar atmosphere. When used as a bifunctional electrocatalyst, the as-prepared Co/ MoC@N-C showed an ORR half-wave potential of 0.824 V in an alkaline medium and an overpotential of only 290 mV for the OER at 10 mA cm-2, which was 70 mV lower than RuO2. The Co/MoC@N-C was also evaluated as a cathode in a solid-state Zn-air battery and delivered a higher peak discharge power density and better cycling stability (over 1600 min) than Pt/C-RuO2. Most importantly, our work provides a new strategy to prepare bifunctional catalysts and promotes their applications in the energy conversion field.

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Nanostructured Mn-based oxides as high-performance cathodes for next generation Li-ion batteries Guodong Hao, Qinzhi Lai, Hongzhang Zhang 2021, 59(8): 547-571.  DOI: 10.1016/j.jechem.2020.11.035 Abstract ( 16 )   PDF (30967KB) ( 20 )   Mn-based oxides have been regarded as a promising family of cathode materials for high-performance lithium-ion batteries, but the practical applications have been limited because of severe capacity deteri-oration (such as LiMnO2 and LiMn2O4) as well as further complications from successive structure changes during cycling, low initial coulombic efficiency (such as Li-rich cathode) and oxidization of organic car-bonate solvents at high charge potential (such as LiNi0.5Mn1.5O4). Large amounts of efforts have been con-centrated on resolving these issues towards practical applications, and many vital progresses have been carried out. Hence, the primary target of this review is focused on different proposed strategies and breakthroughs to enhance the rate performance and cycling stability of nanostructured Mn-based oxide cathode materials for Li-ion batteries, including morphology control, ion doping, surface coatings, com-posite construction. The combination of delicate architectures with conductive species represents the perspective ways to enhance the conductivity of the cathode materials and further buffer the structure transformation and strain during cycling. At last, based on the elaborated progress, several perspectives of Mn-based oxide cathodes are summarized, and some possible attractive strategies and future develop-ment directions of Mn-based oxide cathodes with enhanced electrochemical properties are proposed. The review will offer a detailed introduction of various strategies enhancing electrochemical performance and give a novel viewpoint to shed light on the future innovation in Mn-based oxide cathode materials, which benefits the design and construction of high-performance Mn-based oxide cathode materials in the future.

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Recent advances in catalytic conversion of carbon dioxide to propiolic acids over coinage-metal-based catalysts Tianyu Zhang, Jiawei Zhong, Zhilian Wu 2021, 59(8): 572-580.  DOI: 10.1016/j.jechem.2020.12.006 Abstract ( 6 )   PDF (3091KB) ( 3 )   The conversion of inexpensive, available C1 feedstock of carbon dioxide (CO2) into value-added fine chemicals via homogeneous or heterogeneous catalysis has attracted great recent interest. Coinage-metal-based (Cu, Ag, and Au) catalysis has emerged as a synthetic strategy for a wide range of organic chemical reactions in past decades. In coinage-metal-catalyzed carboxylation, CO2 is adopted as a car-boxylation reagent, while coinage-metal salts, complexes, and nanoparticles (NPs) serve as a Lewis acid catalyst to activate unsaturated chemicals, particularly alkynes. This mini-review focuses on the recent advances of coinage-metal-catalyzed carboxylation of terminal alkynes with CO2. Other respects, such as the role of bases, the influence of trace water, and solvent effects are also highlighted.

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Novel photoelectric material of perovskite-like (CH3)3SPbI3 nanorod arrays with high stability Ruiyuan Hu, Chuangye Ge, Liang Chu, Yifei Feng, Shanshan Xiao, Yuhui Ma, Wei Liu, Xing'ao Li, Mohammad Khaja Nazeeruddin 2021, 59(8): 581-588.  DOI: 10.1016/j.jechem.2020.12.003 Abstract ( 6 )   PDF (10214KB) ( 1 )   Organometallic halide perovskite materials make great achievements in optoelectronic fields, especially in solar cells, in which the organic cations contain amine components. However, the amine with N—H bonds is easily hydrolyzed with moisture in the air, weakening the perovskite materials stability. It is desirable to develop other non-amine stable perovskite materials. In this work, sulfur-based perovskite-like (CH3)3SPbI3 nanorod arrays were fabricated by a solution-processed method, which can be indexed hexagonal crystal structure in the space group P63mc. The binding force is exceptionally strong between the non-amine (CH3)3S+ and [PbI6]4— octahedral, leading to high stability of (CH3)3SPbI3. The (CH3)3SPbI3 nanorod arrays can keep the morphology and crystal structure in an ambi-ent atmosphere over 60 days. In addition, the (CH3)3SPbI3 nanorod arrays can offer direct charge transfer channels, which show excellent optoelectronic properties. The (CH3)3SPbI3 nanorod arrays-based solar cells with VOx hole transfer layers achieved a power conversion efficiency of 2.07% with negligible hys-teresis. And the (CH3)3SPbI3 nanorod arrays were also effectively applied in photodetectors with interdig-itated gold electrodes. This work demonstrates that sulfur-based perovskite-like (CH3)3SPbI3 is a novel promising stable compound with great potential for practical optoelectronic applications.

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Tempura-like carbon/carbon composite as advanced anode materials for K-ion batteries Hao-Jie Liang, Zhen-Yi Gu, Xue-Ying Zheng, Wen-Hao Li, Ling-Yun Zhu, Zhong-Hui Sun, Yun-Feng Meng, Hai-Yue Yu, Xian-Kun Hou, Xing-Long Wu 2021, 59(8): 589-598.  DOI: 10.1016/j.jechem.2020.11.039 Abstract ( 3 )   PDF (9707KB) ( 1 )   Graphite as a promising anode candidate of K-ion batteries (KIBs) has been increasingly studied currently, but corresponding rate performance and cycling stability are usually inferior to amorphous carbon mate-rials. To protect the layer structure and further boost performance, tempura-like carbon/carbon nanocomposite of graphite@pitch-derived S-doped carbon (G@PSC) is designed and prepared by a facile and low-temperature modified molten salt method. This robust encapsulation structure makes their respective advantages complementary to each other, showing mutual promotion of electrochemical per-formances caused by synergy effect. As a result, the G@PSC electrode is applied in KIBs, delivering impres-sive rate capabilities (465, 408, 370, 332, 290, and 227 mA h g-1 at 0.05, 0.2, 0.5, 1, 2, and 5 A g-1) and ultralong cyclic stability (163 mA g-1 remaining even after 8000 cycles at 2 A g-1). On basis of ex-situ studies, the sectionalized K-storage mechanism with adsorption (pseudocapacitance caused by S doping)-intercalation (pitch-derived carbon and graphite) pattern is revealed. Moreover, the exact insights into remarkable rate performances are taken by electrochemical kinetics tests and density func-tional theory calculation. In a word, this study adopts a facile method to synthesize high-performance carbon/carbon nanocomposite and is of practical significance for development of carbonaceous anode in KIBs.

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Triple-phase interfaces of graphene-like carbon clusters on antimony trisulfide nanowires enable high-loading and long-lasting liquid Li2S6-based lithium-sulfur batteries Chenyang Zha, Donghai Wu, Xiuquan Gu, Houyang Chen 2021, 59(8): 599-607.  DOI: 10.1016/j.jechem.2020.11.032 Abstract ( 4 )   PDF (9447KB) ( 1 )   High performance of lithium-sulfur batteries have been dragged down by their shuttling behavior which is complicated multiphase transition-based 16-electron redox reactions of the S8/Li2S. In this article, the triple-phase interfaces of graphene-like carbon clusters on antimony trisulfide (C-Sb2S3) nanowires are tailored to design a multifunctional polysulfide host which can inhibit migration of polysulfides and accelerate conversion kinetics of redox electrochemical reactions. Benefiting from the triple-interface design of polysulfides/Sb2S3/carbon clusters, the C-Sb2S3 electrode not only anchors polysulfide migration by the synergistic effect of Sb, S, and C atoms as interfacial active sites, but also the graphene-like carbon clusters shorten the diffusion paths to further favor redox electron/ion transport through the liquid (elec-trolyte/polysulfide) and solid (Li2S/S8, carbon clusters, and Sb2S3)-based triple-phases. Therefore, these Li2S6-based C-Sb2S3 cells possess high sulfur loading, excellent cycling stability, impressive specific capacity, and great rate capability. This work of interfacial engineering reveals insight for powering reac-tion kinetics in the complicated multistep catalysis reaction with multiphase evolution-based charge-transfer/non-transfer processes.

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Porous polymer electrolytes for long-cycle stable quasi-solid-state magnesium batteries Tiantian Wang, Xudong Zhao, Fanfan Liu, Li-Zhen Fan 2021, 59(8): 608-614.  DOI: 10.1016/j.jechem.2020.12.004 Abstract ( 3 )   PDF (5243KB) ( 2 )   The development of applicable electrolytes is the key point for high-performance rechargeable magne-sium batteries (RMBs). The use of liquid electrolyte is prone to safety problems caused by liquid elec-trolyte leakage. Polymer-based gel electrolytes with high ionic conductivity, great flexibility, easy processing, and high safety have been studied by many scholars in recent years. In this work, a novel por-ous poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) membrane is prepared by a phase inversion method. By immersing porous PVDF-HFP membranes in MgCl2-AlCl3/TEGDME (Tetraethylene glycol dimethyl ether) electrolytes, porous PVDF-HFP based electrolytes (PPEs) are formed. The PPE exhi-bits a high ionic conductivity (4.72 × 10-4 S cm-1, 25 °C), a high liquid electrolyte uptake of 162%, as well as a wide voltage window (3.1 V). The galvanostatic cycling test of Mg//Mg symmetric cell with PPE reveals that the reversible magnesium ion (Mg2+) plating/stripping occurs at low overpotentials (~0.13 V). Excellent long cycle stability (65.5 mAh g-1 over 1700 cycles) is achieved for the quasi-solid-state RMB assembled with MoS2/C cathode and Mg anode. Compared with the liquid electrolyte, the PPE could effectively reduce the side reactions and make Mg2+ plating/stripping more uniformly on the Mg electrode side. This strategy herein provides a new route to fabricate high-performance RMB through suitable cathode material and polymer electrolyte with excellent performance.

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Oxygen vacancies engineering by coordinating oxygen-buffering CeO2 with CoOx nanorods as efficient bifunctional oxygen electrode electrocatalyst Haihong Zhong, Luis Alberto Estudillo-Wong, Yuan Gao, Yongjun Feng, Nicolas Alonso-Vante 2021, 59(8): 615-625.  DOI: 10.1016/j.jechem.2020.11.033 Abstract ( 5 )   PDF (13349KB) ( 1 )   CeO2 decorated CoOx rod-like hybrid, supported onto holey reduced graphene (CoOx/CeO2/RGO) compos-ite, was fabricated via a surfactant-assisted route. Its corresponding electrocatalytic performance towards oxygen reduction/evolution reactions (ORR and OER) was systematically investigated in alkaline elec-trolyte. Structural, morphological and compositional studies revealed changes in electronic and surface properties when CeO2 was introduced as an oxygen buffer material. The oxygen vacancies effectively enhanced the electrocatalytic activity, while the synergistic effect of co-catalyst CeO2, CoOx active-centers, and defective graphene with many voids facilitate the charge/mass transfer, making CoOx/CeO /RGO an efficient and stable bifunctional electrocatalyst for OER/ORR with △E = 0.76 V (△E = E10 mA cm-2 , OER -E1/2, ORR). This parameter is 70 mV and 270 mV lower than CoOx/RGO and the benchmark Pt/ C, respectively. In addition, the OER/ORR bifunctionality of CoOx/CeO2/RGO composite outperforms that of Pt/C catalyst in a H2-O2 micro fuel cell platform.

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Large-area perovskite films for PV applications: A perspective from nucleation and crystallization Yuanhang Yang, Zexu Xue, Long Chen, Cho Fai Jonathan Lau, Zhiping Wang 2021, 59(8): 626-641.  DOI: 10.1016/j.jechem.2020.12.001 Abstract ( 5 )   PDF (10800KB) ( 0 )   Perovskite solar cells (PSCs) have attracted significant research interest due to the rapid rise in efficiency. However, a large efficiency gap still exists between laboratory-based small devices and industrial-oriented large-scale modules. One of the main reasons for the efficiency losses is the degraded quality and morphology of the deposited large-area films, which is closely associated with crystallization pro-cesses. In this review, we discuss the nucleation and crystallization processes in solution and vapor-based up-scaling deposition methods for large-area perovskite films. We review recent scientific achieve-ments and technical developments that have been made in the field of large-area cells. We present the existing problems that limit the performance of large devices and extensively discuss the key influencing parameters from the perspective of nucleation and crystallization over large areas. This review highlights the importance of crystallization control in up-scaling fabrications and presents promising strategies towards large-area perovskite-based optoelectronic devices.

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Laser fabrication of functional micro-supercapacitors Ying Wang, Yang Zhao, Liangti Qu 2021, 59(8): 642-665.  DOI: 10.1016/j.jechem.2020.12.002 Abstract ( 3 )   PDF (28542KB) ( 2 )   Due to the rapid development of portable, wearable and implantable electronics in the fields of mobile communications, biomonitoring, and aerospace or defense, there is an increasing demand for miniatur-ized and lightweight energy storage devices. Micro-supercapacitors (MSCs) possessing long lifetime, high power density, environment friendliness and safety, have attracted great attention recently. Since the performance of the MSCs is mainly related to the structure of the active electrode, there is a great need to explore the efficient fabricating strategies to deterministically coordinate the structure and function-ality of microdevices. Considering that laser technology possesses many superior features of facility, high-precision, low-cost, high-efficiency, shape-adaptability and maneuverability, herein we summarize the development of laser technologies in MSCs manufacturing, along with their strengths and weak-nesses. The current achievements and challenges are also highlighted and discussed, aiming to provide a valuable reference for the rational design and manufacture of MSCs in the future.

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Lithium metal batteries for high energy density: Fundamental electrochemistry and challenges Mingda Gao, Hui Li, Li Xu, Qing Xue, Xinran Wang, Ying Bai, Chuan Wu 2021, 59(8): 666-687.  DOI: 10.1016/j.jechem.2020.11.034 Abstract ( 23 )   PDF (12608KB) ( 6 )   The dependence on portable devices and electrical vehicles has triggered the awareness on the energy storage systems with ever-growing energy density. Lithium metal batteries (LMBs) has revived and attracted considerable attention due to its high volumetric (2046 mAh cm-3), gravimetric specific capac-ity (3862 mAh g-1) and the lowest reduction potential (—3.04 V vs. SHE.). However, during the electro-chemical process of lithium anode, the growth of lithium dendrite constitutes the biggest stumbling block on the road to LMBs application. The undesirable dendrite not only limit the Coulombic efficiency (CE) of LMBs, but also cause thermal runaway and other safety issues due to short-circuits. Understanding the mechanisms of lithium nucleation and dendrite growth provides insights to solve these problems. Herein, we summarize the electrochemical models that inherently describe the lithium nucleation and dendrite growth, such as the thermodynamic, electrodeposition kinetics, internal stress, and interface transmission models. Essential parameters of temperature, current density, internal stress and interfacial Li+ flux are focused. To improve the LMBs performance, state-of-the-art optimization pro-cedures have been developed and systematically illustrated with the intrinsic regulation principles for better lithium anode stability, including electrolyte optimization, artificial interface layers, three-dimensional hosts, external field, etc. Towards practical applications of LMBs, the current development of pouch cell LMBs have been further introduced with different assembly systems and fading mechanism. However, challenges and obstacles still exist for the development of LMBs, such as in-depth understand-ing and in-situ observation of dendrite growth, the surface protection under extreme condition and the self-healing of solid electrolyte interface.

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Advancing green energy solution with the impetus of COVID-19 pandemic Mohamedazeem M. Mohideen, Seeram Ramakrishna, Sivaprasath Prabu, Yong Liu 2021, 59(8): 688-705.  DOI: 10.1016/j.jechem.2020.12.005 Abstract ( 8 )   PDF (8144KB) ( 1 )   The global energy system needs a revolutionary transition from today’s fossil fuel to a low carbon energy system by having deep carbonization in all energy demand sectors. Especially in the transport sector, fos-sil fuel-based vehicles contribute to a more massive amount of greenhouse gas emissions (GHG), mainly carbon dioxide (CO2) and particulate matter (PM2.5), affecting human health, society, and the climate system. Hydrogen and fuel cell technology is a promising low carbon transition pathway that supports GHG mitigation and achieves sustainable development. Although hydrogen and fuel cells are assuring, fuel cell vehicle expensiveness and the high cost of hydrogen production with the low carbon footprint are significant hindrances for its widespread deployment. Besides the situation above, the present corona virus (COVID-19) has devastated our global economy and ramps down the future of fossil fuel. It provides opportunities to rethink and reshape our energy system to a low carbon footprint. By utilizing the situ-ation, governments and policymakers need to eliminate fossil fuel and invest in the hydrogen and fuel cell technologies deployment as future energy systems. This review article provides a technical overview of a low carbon energy system, production, and end-use service in a hydrogen economy perspective for developing a sustainable energy future. The techno-economic analysis of the different hydrogen produc-tion routines and fuel cell vehicles and their infrastructures are primarily focused. Finally, a long-term policy alignment was outlined to advance the hydrogen energy system for post-COVID-19 in the United Nation’s (UN) sustainable development goals framework.

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Nanostructured N-doped carbon materials derived from expandable biomass with superior electrocatalytic performance towards V2+/V3+ redox reaction for vanadium redox flow battery Yingqiao Jiang, Mengchen Du, Gang Cheng, Peng Gao, Tingting Dong, Jing Zhou, Xiaojian Feng, Zhangxing He, Yuehua Li, Lei Dai, Wei Meng, Ling Wang 2021, 59(8): 706-714.  DOI: 10.1016/j.jechem.2020.12.013 Abstract ( 5 )   PDF (5249KB) ( 4 )   Vanadium redox flow battery (VRFB) is one of the most promising large-scale energy storage systems, which ranges from kilowatt to megawatt. Nevertheless, poor electrochemical activity of electrode for two redox couples still restricts the extensive applications of VRFB. Compared with VO2+/VO+ redox reac-tion, V2+/V3+ reaction plays a more significant role in voltage loss of VRFB owing to slow heterogeneous electron transfer rate. Herein, N-doped carbon materials derived from scaphium scaphigerum have been developed as negative electrocatalyst by hydrothermal carbonization and high-temperature nitridation treatments. The undoped carbon material hardly has electrocatalytic ability for V2+/V3+ reaction. Based on this, N-doped carbon materials with urea as nitrogen source exhibit excellent electrocatalytic proper-ties. And the material nitrided at 850 °C (SSC/N-850) exhibits the best performance among those from 700 to 1000 °C. SSC/N-850 can accelerate the electrode process including V2+/V3+ reaction and mass transfer of active ions due to the large reaction place, more active sites, and good hydrophilicity. The effect of catalyst on comprehensive performance of cell was evaluated. SSC/N-850 can improve the charge-discharge performance greatly. Utilization of SSC/N-850 can lessen the electrochemical polariza-tion of cell, further resulting in increased discharge capacity and energy efficiency. Discharge capacity and energy efficiency increase by 81.5% and 9.8% by using SSC/N-850 as negative catalyst at 150 mA cm-2, respectively. Our study reveals that the developed biomass-derived carbon materials are the low-cost and efficient negative electrocatalyst for VRFB system.

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Facile synthesis of bimetallic N-doped carbon hybrid material for electrochemical nitrogen reduction Linchuan Cong, Kaida Yao, Siqi Zhang, Ziqi Zhang, Zhuochen Yu, Miaomiao Qian, Lina Qu, Weimin Huang 2021, 59(8): 715-720.  DOI: 10.1016/j.jechem.2020.12.012 Abstract ( 1 )   PDF (3909KB) ( 2 )

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Direct Z-scheme WO3-x nanowire-bridged TiO2 nanorod arrays for highly efficient photoelectrochemical overall water splitting Sheng Lin, He Ren, Zhi Wu, Lan Sun, Xia-Guang Zhang, Yu-Mei Lin, Kelvin H. L. Zhang, Chang-Jian Lin, Zhong-Qun Tian, Jian-Feng Li 2021, 59(8): 721-729.  DOI: 10.1016/j.jechem.2020.12.010 Abstract ( 3 )   PDF (4096KB) ( 3 )   All-solid-state Z-scheme photocatalysts for overall water splitting to evolve H2 is a promising strategy for efficient conversion of solar energy. However, most of these strategies require redox mediators. Herein, a direct Z-scheme photoelectrocatalytic electrode based on a WO3-x nanowire-bridged TiO2 nanorod array heterojunction is constructed for overall water splitting, producing H2. The as-prepared WO3-x/TiO2 nanorod array heterojunction shows photoelectrochemical (PEC) overall water splitting activity evolving both H2 and O2 under UV-vis light irradiation. An optimum PEC activity was achieved over a 1.67-WO3-x/ TiO2 photoelectrode yielding maximum H2 and O2 evolution rates roughly 11 times higher than that of pure TiO2 nanorods without any sacrificial agent or redox mediator. The role of oxygen vacancy in WO3-x in affecting the H2 production rate was also comprehensively studied. The superior PEC activity of the WO3-x/TiO2 electrode for overall water splitting can be ascribed to an efficient Z-scheme charge transfer pathway between the WO3-x nanowires and TiO2 nanorods, the presence of oxygen vacancies in WO3-x, and a bias potential applied on the photoelectrode, resulting in effective spatial charge separa-tion. This study provides a novel strategy for developing highly efficient PECs for overall water splitting.

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A highly-efficient concentrated perovskite solar cell-thermoelectric generator tandem system Yangying Zhou, Yanan Chen, Qi Zhang, Yu Zhou, Meiqian Tai, Kunihito Koumoto, Hong Lin 2021, 59(8): 730-735.  DOI: 10.1016/j.jechem.2020.12.020 Abstract ( 8 )   PDF (3663KB) ( 4 )   Concentrated photovoltaic (CPV) has been identified as an effective method to further enhance the effi-ciency of photovoltaic cells. Previous studies on CPV mainly focused on III-V multi-junction cells. Nevertheless, III-V CPV technology is mainly used in niche applications due to its high cost. Here, we use metal-halide perovskite solar cell (PSC) to demonstrate a concentrated photovoltaic-thermoelectric tandem device. The thermoelectric generator (TEG) is utilized to reduce the effect of heat generation under concentrated solar irradiance. Our tandem system achieved a peak power conversion efficiency (PCE) of 25.0% at a solar concentration of 3 suns. This efficiency exceeded that of the single PSC by ~4.7%. Our work proves that by controlling the heat flow in concentrated PSC-TEG tandem system, the redundant heat produced by upper PSC can be effectively reused. This tandem structure provides a promising approach to improve the efficiency and stability of PSC under low-concentrated solar irradiation.

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Tunable oxygen defect density and location for enhancement of energy storage Jun Chen, Jiangao Li, Ling Sun, Zhong Lin, Zhengguang Hu, Hongtao Zhang, Xiaoling Wu, Dongbo Zhang, Guoan Cheng, Ruiting Zheng 2021, 59(8): 736-747.  DOI: 10.1016/j.jechem.2020.12.016 Abstract ( 6 )   PDF (20422KB) ( 1 )   Defect engineering is in the limelight for the fabrication of electrochemical energy storage devices. However, determining the influence of the defect density and location on the electrochemical behavior remains challenging. Herein, self-organized TiO2 nanotube arrays (TNTAs) are synthesized by anodiza-tion, and their oxygen defect location and density are tuned by a controllable post-annealing process. TNTAs annealed at 600 °C in N2 exhibit the highest capacity (289.2 mAh g-1 at 0.8C) for lithium-ion stor-age, while those annealed at 900 °C in N2 show a specific capacitance of 35.6 mF cm-2 and stability above 96% after 10,000 cycles for supercapacitor. Ex situ electron paramagnetic resonance spectra show that the surface-exposed oxygen defects increase, but the bulk embedded oxygen defects decrease with increas-ing annealing temperature. Density functional theory simulations reveal that a higher density of bulk oxygen defects corresponds to higher localized electrons states, which upshift the Fermi level and facil-itate the lithium intercalation kinetic process. Meanwhile, differential charge density calculation indi-cates that the increase of surface oxygen defects in the anatase (1 0 1) plane leads to higher density excess electrons, which act as negative charge centers to enhance the surface potential for ion adsorption. This oxygen-deficient location and density tunable strategy introduce new opportunities for high-energy and high-power-density energy storage systems.

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PdNi/N-doped graphene aerogel with over wide potential activity for formic acid electrooxidation Yufei Bao, Meng Zha, Pengliang Sun, Guangzhi Hu, Ligang Feng 2021, 59(8): 748-754.  DOI: 10.1016/j.jechem.2020.12.007 Abstract ( 7 )   PDF (4637KB) ( 2 )   Anti-CO poisoning ability is significant in formic acid oxidation in the fuel cell technique. Herein, PdNi alloy supported on N-doped graphene aerogel (PdNi/GA-N) was found to have catalytic ability toward formic acid electrooxidation over a wide potential range because of the improved anti-CO poisoning abil-ity. This catalyst was fabricated by simple freeze-drying of mixture solution of graphene aerogel, polyvinylpyrrolidone, Pd2+ and Ni2+ and the subsequent thermal annealing reduction approach in the N2/H2 atmosphere. Pd-Ni alloy particles anchored over the folding N-doped graphene surface with a por-ous hierarchical architecture structure in the 3D directions. It showed the catalytic performance of its maximum mass activity of 836 mA mg-1 in a broad potential range (0.2-0.6 V) for formic acid oxidation. The CO stripping experiment demonstrated its largely improved anti-CO poisoning ability with the peak potential of 0.67 V, approximately 60 and 40 mV less compared to those of Pd/GA-N and Pd/C samples. The high anti-CO poisoning ability and strong electronic effect resulting from the interaction between the 3D GA-N support and the Pd-Ni alloy makes it a promising catalyst for application in direct formic acid fuel cells.

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Synergistic passivation of MAPbI3 perovskite solar cells by compositional engineering using acetamidinium bromide additives Kyungeun Jung, Weon-Sik Chae, Jae Won Choi, Ki Chul Kim, Man-Jong Lee 2021, 59(8): 755-762.  DOI: 10.1016/j.jechem.2020.12.022 Abstract ( 4 )   PDF (9513KB) ( 2 )   For the global commercialization of highly efficient and stable perovskite solar cells (PSCs), it is necessary to effectively suppress the formation of various defects acting as nonradiative recombination sources in perovskite light-harvesting materials. Interfacial defects between the charge-selective layer and the per-ovskite are easily formed in the solution process used to fabricate perovskite films. In addition, owing to the difference in thermal expansion coefficients between the substrate and the perovskite film, internal residual tensile stress inevitably occurs, resulting in increased nonradiative recombination. Herein, a sim-ple compositional engineering scheme for realizing efficient and stable PSCs, which incorporates acetami-dinium bromide (AABr) as an additive into the MAPbI3 lattice, is proposed. As an additive, AABr has been found to provide synergistic multiple passivation for both internal and interfacial defects. AABr was found to effectively release the tensile strain of the MAPbI3 film by forming a structure stabilized by NH-I hydrogen bonds, as evidenced by calculations based on density functional theory (DFT). Furthermore, the incorporated AABr additives created a charge carrier recombination barrier to enhance charge collection capability by reducing interfacial defects. Accordingly, a power conversion efficiency (PCE) of 20.18% was achieved using a planar device employing AABr-incorporated MAPbI3. This was sub-stantially higher than the 18.32% PCE of a pristine MAPbI3-based device. Notably, unencapsulated PSCs using AABr-incorporated MAPbI3 absorbers exhibited excellent long-term stability, maintaining >95% of initial PCE up to 1200 hours in ambient air.