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2021, Vol. 60, No. 9　Online: 15 September 2021

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Interface engineering of p-n heterojunction for kesterite photovoltaics: A progress review Mingrui He, Kaiwen Sun, Mahesh P. Suryawanshi, Jianjun Li, Xiaojing Hao* 2021, 60(9): 1-8.  DOI: 10.1016/j.jechem.2020.12.019 Abstract ( 9 )   PDF (196KB) ( 5 )   Kesterite Cu2ZnSn(S,Se)4 (CZTSSe) is considered one of the most promising thin-film photovoltaic (PV) technologies due to its bandgap tunability (1.0 ~ 1.5 eV) and high absorption coefficient (>104 cm -1). However, the highest power conversion efficiency (PCE) of CZTSSe has so far only reached up to 12.6%, much lower than the theoretical limit defined by the Shockley-Queisser (SQ) theory. The large open- circuit voltage (Voc) deficit and inferior fill factor (FF) are prevalent in kesterite PV and hamper the improvement in efficiency. In this review, unfavourable energy band alignment at the CZTSSe/buffer junction, as well as defective interface are identified as two obstacles at the p-n heterojunction. These issues contribute to the interface induced recombination, thus significantly reducing efficiency. Subsequently, we review recent advances in strategies to improve the efficiency by altering the charac- teristics of the interface, covering alternative buffer layers, heterojunction treatments and passivation layers. Finally, future research directions of heterojunction engineering are proposed as schemes towards the ideal interface in kesterite solar cells.

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Real-time monitoring of the lithiation process in organic electrode 7,7,8,8-tetracyanoquinodimethane by in situ EPR Mingxue Tang, Nhat N. Bui, Jin Zheng, Likai Song, Yan-Yan Hu 2021, 60(9): 9-15.  DOI: 10.1016/j.jechem.2020.12.009 Abstract ( 10 )   PDF (777KB) ( 2 )   Organic electrodes are advantageous for rechargeable lithium-ion batteries owing to their high theoretical capacities, diverse functionalities, and environmental compatibility. Understanding the working mechanism of organic electrodes is vital to strategic materials design. However, due to lack of suitable characterization tools, it has been challenging to probe the reaction processes of organic electrodes in real-time. Here, non-destructive in situ electron paramagnetic resonance (EPR) was performed on a model organic electrode, 7,7,8,8-tetracyanoquinodimethane (TCNQ) used in rechargeable lithium-ion batteries, to directly follow the redox reactions in real-time. In order to minimize interfering signals from other parts of the batteries than the TCNQ electrode of interest, two sets of batteries are fabricated and studied with in situ EPR: (1) a LiCoO2//Li4Ti5O12 full-cell battery to determine the EPR signal evolution of additives and electrolytes; (2) a LiCoO2//TCNQ battery, and the difference in the observed EPR signals reflects purely the redox reactions of TCNQ upon lithiation and delithiation. A two-electron reversible redox reaction is delineated for TCNQ. TCNQ dimers form during the first electron injection upon lithiation and followed by the break-down of the dimers and associated electron coupling to produce massive delocalized electrons, resulting in increased EPR signal during the 2nd electron injection. Reversible trends are observed during electron ejection upon delithiation. In situ EPR is very sensitive to electron activities, thus is a powerful tool to follow redox reactions of organic electrodes, allowing for improved fundamental understanding of how organic electrodes work and for informed design of high-performance organic materials for energy storage.

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Understanding the geometric and electronic factors of PtNi bimetallic surfaces for efficient and selective catalytic hydrogenation of biomass-derived oxygenates Jingcheng Wu, Chuangwei Liu, Yuting Zhu, Xiangbo Song, Chengyan Wen, Xinghua Zhang, Chenguang Wang, Longlong Ma 2021, 60(9): 16-24.  DOI: 10.1016/j.jechem.2020.12.011 Abstract ( 11 )   PDF (1473KB) ( 1 )   Ni-base catalysts are promising candidate for the hydrogenation of furfural (FAL) to high-value chemicals. However, slow intermediate desorption and low selectivity limit its implementation. Identifying the catalytic performance of each active sites is vital to design hydrogenation catalyst, and tuning the geometrical sites at molecule level in PtNi could lead to the modification of electronic structure, and thus the selectity for the hydrogenation of FAL was modulated. Herein, PtNi hollow nanoframes (PtNi HNFs) with three dimensional (3D) molecular accessibility were synthesized, EDX results suggested that Ni was evenly distributed inside of the hollow nanoframes, whereas Pt was relatively concentrated at the edges. DFT calculation demonstrated that PtNi significant decrease the desorption energy of the intermediates. This strategy could not only enhance the desorption of intermediates to improve the catalytic performance, but also transfer the adsorption mode of FAL on catalyst surface to selective hydrogenation of FAL to FOL or THFA. The PtNi HNFs catalyst afforded excellent catalytic performance for selective hydrogenation of a broad range of biomass-derived platform chemicals under mild conditions, especially of FAL to furfuryl alcohol (FOL), in quantitative FOL yields (99%) with a high TOF of 2.56 h-1. It is found that the superior performance of PtNi HNFs is attributed to its 3D hierarchical structure and synergistic electronic effects between Pt and Ni. Besides, the kinetic study demonstrated that the activation energy for hydrogenation of FAL was as low as 54.95 kJ mol-1.

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Pressure-dependent band-bending in ZnO: A near-ambient-pressure X-ray photoelectron spectroscopy study Zhirui Ma, Xu Lian, Kaidi Yuan, Shuo Sun, Chengding Gu, Jia Lin Zhang, Jing Lyu, Jian-Qiang Zhong, Lei Liu, Hexing Li, Wei Chen 2021, 60(9): 25-31.  DOI: 10.1016/j.jechem.2020.12.018 Abstract ( 16 )   PDF (656KB) ( 5 )   ZnO-based catalysts have been intensively studied because of their extraordinary performance in lower olefin synthesis, methanol synthesis and water-gas shift reactions. However, how ZnO catalyzes these reactions are still not well understood. Herein, we investigate the activations of CO2, O2 and CO on single crystalline ZnO polar surfaces at room temperature, through in-situ near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS). It is revealed that O2 and CO2 can undergo chemisorption on ZnO polar surfaces at elevated pressures. On the ZnO (0001) surface, molecular CO2 (O2) can chemically interact with the top layer Zn atoms, leading to the formation of $ \mathrm{CO}_{2}^{\delta-}\left(\mathrm{O}_{2}^{\delta-}\right)$ or partially dissociative atomic oxygen ($\mathrm{O}^{-}$) and hence the electron depletion layer in ZnO. Therefore, an apparent upward band-bending in ZnO (0001) is observed under the CO2 and O2 exposure. On the ZnO (0001) surface, the molecular chemisorbed CO2 (O2) mainly bond to the surface oxygen vacancies, which also results in an upward band-bending in ZnO (0001). In contrast, no band-bending is observed for both ZnO polar surfaces upon CO exposure. The electron-acceptor nature of the surface bounded molecules/atoms is responsible for the reversible binding energy shift of Zn 2p3/2 and O 1s in ZnO. Our findings can shed light on the fundamental understandings of CO2 and O2 activation on ZnO surfaces, especially the role of ZnO in heterogeneous catalytic reactions.

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Interface engineering for composite cathodes in sulfide-based all-solid-state lithium batteries Yu Li, Dechao Zhang, Xijun Xu, Zhuosen Wang, Zhengbo Liu, Jiadong Shen, Jun Liu, Min Zhu 2021, 60(9): 32-60.  DOI: 10.1016/j.jechem.2020.12.017 Abstract ( 10 )   PDF (2583KB) ( 4 )   All-solid-state lithium battery (ASLB) based on sulfide-based electrolyte is considered to be a candidate for the next-generation high-energy storage system. Despite the high ionic conductivity of sulfide solid electrolyte, the poor interfacial stability (mechanically and chemically) between active materials and sulfide solid electrolytes in composite cathodes leads to inferior electrochemical performances, which impedes the practical application of sulfide electrolytes. In the past years, various of strategies have been carried out to achieve an interface with low impedance in the composite cathodes. Herein, a review of recent progress of composite cathodes for all-solid-state sulfide-based lithium batteries is summarized, including the interfacial issues, design strategies, fabrication methods, and characterization techniques. Finally, the main challenges and perspectives of composite cathodes for high-performance all-solid-state batteries are highlighted for future development.

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Synthesis of noble metal-based intermetallic electrocatalysts by space-confined pyrolysis: Recent progress and future perspective Lei Zhao, Rui Wu, Junjie Wang, Zhao Li, Xinxin Wei, Jun Song Chen, Yuan Chen 2021, 60(9): 61-74.  DOI: 10.1016/j.jechem.2020.12.021 Abstract ( 4 )   PDF (1762KB) ( 2 )   Noble metal-based intermetallics are promising electrocatalysts for sustainable energy conversion and consumption processes. High-temperature pyrolysis (>500°C) methods are used to control their crystalline orderings, critical to their electrocatalytic activity and durability. However, the high temperature would cause severe aggregation, resulting in a low catalytic active surface area. Significant research efforts have been devoted to addressing this issue. This short review summarizes recent research progress on synthesizing noble metal-based intermetallic electrocatalysts by space-confined pyrolysis. We focus on three strategies: isolation in pores, coverture by shells, and immobilization by salts. The advantages and existing problems of different methods are highlighted. Last, important issues to be addressed in future research are also discussed. We hope that this article will stimulate future research to develop high-performance intermetallic catalysts for practical applications.

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Lithium-ion mobility in layered oxides Li2Ca1.5Nb3O10, Li2Ca1.5TaNb2O10and Li2Ca1.5Ta2NbO10, enhanced by supercell formation Selorm Joy Fanah, Farshid Ramezanipour* 2021, 60(9): 75-84.  DOI: 10.1016/j.jechem.2020.12.014 Abstract ( 5 )   PDF (1303KB) ( 2 )   The formation of a supercell and its impact on lithium-ion conductivity have been studied through synthesis of three layered oxides, Li2Ca1.5Nb3O10, Li2Ca1.5TaNb2O10 and Li2Ca1.5Ta2NbO10, related to Ruddlesden-Popper structure-type. Neutron diffraction experiments show that these materials feature a supercell, which is significantly larger (~√2a ~√2b ~ 1c) than that of a typical Ruddlesden-Popper oxide. Electrochemical impedance spectroscopy shows that the formation of the new supercell is associated with enhanced lithium-ion conductivity of these materials as compared with the Sr-analogue, Li2Sr1.5Nb3O10, which lacks the supercell. In addition, a systematic trend is observed in the ionic conductivity: Li2Ca1.5Ta2NbO10 < Li2Ca1.5TaNb2O10 < Li2Ca1.5Nb3O10. The Arrhenius analysis in the temperature range 25-400 °C shows that activation energy for the temperature-dependent rise in conductivity follows a similar trend. Detailed analyses of real and imaginary components of impedance, dielectric properties, tangent loss, and complex modulus show the systematic increase in lithium-ion mobility. The dielectric values mirror the same trend as ionic conductivity, where the most conductive material shows the highest dielectric properties. In addition, the same trend is observed in the peak and dispersion of dielectric loss and complex modulus as a function of angular frequency, indicating a systematic rise in lithium-ion mobility. This fundamental study is aimed at exploring the impact of structural modifications on ionic conductivity in solids.

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Insights into the sandwich-like ultrathin Ni-doped MoS2/rGO hybrid as effective sulfur hosts with excellent adsorption and electrocatalysis effects for lithium-sulfur batteries Ran Zhang, Yutao Dong, Mohammed A. Al-Tahan, Yingying Zhang, Ruipeng Wei, Yuhang Ma, Changchun Yang, Jianmin Zhang 2021, 60(9): 85-94.  DOI: 10.1016/j.jechem.2021.01.004 Abstract ( 4 )   PDF (1106KB) ( 2 )   The design of sulfur hosts with high conductivity, large specific surface area, strong adsorption and electrocatalytic ability is crucial to advance high performance lithium-sulfur batteries. Herein, a novel ultrathin sandwich-type Ni-doped MoS2/reduced graphene oxide (denote as Ni-doped MoS2/rGO) hybrid is developed as a sulfur host through a simple one-step hydrothermal route. The two-dimensional layered structure Ni-doped MoS2/rGO hybrid with heterostructure and heteroatom architecture defects not only plays a key role in adsorption of lithium polysulfide but also catalyzes on redox kinetics of sulfur and polysulfide species. Meanwhile, it can contribute to the large specific surface area for Li2S/S8 deposition, fast Li-ion and electron transportation, thus enhancing the electrocatalytic properties, as confirmed firstly by cyclic voltammetry (CV) results. Due to the adsorption-catalytic synergistic effect, the Ni-doped MoS2/rGO cathode exhibits high specific capacity (1343.6 mA h g-1 at 0.2 C, 921.6 mA h g-1 at 1 C), high coulombic efficiency and an outstanding cycle stability (with the low attenuation rate of 0.077% per cycle over 140 cycles at 0.5 C and 0.11% per cycle over 400 cycles at 1 C, respectively). This work proposes some inspiration for exploring the construction of advanced lithium-sulfur batteries through the rational design defects of atomic structure and electronic states of MoS2 as sulfur host.

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Microzone-explosion synthesis of porous carbon electrodes for advanced aqueous solid-state supercapacitors with a high-voltage gel electrolyte Yongxu Du, Wei Liu*, Yongpeng Cui, Hongguang Fan, Yuan Zhang, Tianqi Wang, Huanlei Wang, Yongcheng Jin*, Shuang Liu, Wenting Feng, Ming Chen 2021, 60(9): 95-103.  DOI: 10.1016/j.jechem.2020.12.015 Abstract ( 8 )   PDF (1224KB) ( 2 )   A new microzone-combustion synthesis is proposed for preparing S, N-doped hierarchically porous carbons (CAC-CN) with a novel mixed microstructure of sp2 short-range order area and sp3 defective area, achieving a coexistence of high conductivity and high capacitance as well as good access for electrolyte. By engineering “water in salts” into a polymer matrix, a high-voltage (2.5 V) aqueous gel electrolyte (HG-WIS) is prepared and used to construct an aqueous solid-state SCs by in situ polymerization between the electrodes. The good match of CAC-CN electrode and HG-WIS electrolyte endows the assembled devices with superior high energy density and excellent capacitance retention, also a good temperature robustness, as well a high flexibility in 0-180° bending cycles. This study indicates that the collaborative design strategy of electrode materials and electrolyte would be great potential in exploring advanced aqueous solid-state SCs.

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Unrevealing the effects of low temperature on cycling life of 21700-type cylindrical Li-ion batteries Daozhong Hu, Gang Chen, Jun Tian, Ning Li, Lai Chen, Yuefeng Su, Tinglu Song, Yun Lu, Duanyun Cao, Shi Chen, Feng Wu 2021, 60(9): 104-110.  DOI: 10.1016/j.jechem.2020.12.024 Abstract ( 5 )   PDF (1042KB) ( 1 )   The low-temperature performance of Li-ion batteries (LIBs) has important impacts on their commercial applications. Besides the metallic lithium deposition, which is regarded as one of the main failure mechanisms of the LIBs at low temperatures, the synergistic effects originating from the cathode, anode, electrolyte, and separators to the batteries are still not clear. Here, the 21700-type cylindrical batteries were evaluated at a wide range of temperatures to investigate the failure mechanism of batteries. Voltage relaxation, and the post-mortem analysis combined with the electrochemical tests, unravel that the capacity degradation of batteries at low temperature is related to the lithium plating at graphite anodes, the formation of unsatisfied solid deposited/decomposed electrolyte mixture phase on the anode, the precipitation of solvent in the electrolytes and the block of separator pores, and the uneven dissolved transition metal-ions from the cathode. We hope this finding may open up a new avenue to alleviate the capacity degradation of advanced LIBs at low temperatures and shed light on the development of outstanding low-temperature LIBs via simultaneous optimization of all the components including electrodes, electrolytes and separators.

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In-situ growth of CNTs encapsulating P-doped NiSe2nanoparticles on carbon framework as efficient bifunctional electrocatalyst for overall water splitting Jing Yu, Wei-Jian Li, Guibo Kao, Cheng-Yan Xu, Rongrong Chen, Qi Liu, Jingyuan Liu, Hongsen Zhang, Jun Wang 2021, 60(9): 111-120.  DOI: 10.1016/j.jechem.2020.12.030 Abstract ( 6 )   PDF (1004KB) ( 3 )   Nickel diselenide (NiSe2) is a promising low-cost catalyst for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), due to its suitable d-electron configuration and high electrical conductivity. Several representative elements, e.g., Co, Fe and P, have been utilized as cation or anion to promote the electrocatalytic activity of NiSe2 by modulating the interaction with Se element, whilst the catalyst stability is less concerned. In this work, the catalytic Ni nanoparticles were in-situ encapsulated in carbon nanotubes grown on three-dimensional conducting carbon framework. Subsequent phosphorization and selenization yield dispersed P-doped NiSe2 nanoparticles protected by carbon shell with highly exposed yet stable active sides, resulting in significantly promoted HER and OER activities as well as accelerated kinetics. In detail, the P-NiSe2@N-CNTs/NC hybrid catalyst deliver low overpotentials of 95 and 306 mV at 10 mA cm-2 for HER and OER in alkaline media, respectively. DFT calculations reveal that P doping reduces the electron density surrounding Ni atoms while accumulates the charges to Se, respectively, which in turn reduces the energy barriers for both water dissociation and intermediates adsorption for both HER and OER. As a concept of proof, a cell assembled by P-NiSe2@N-CNTs/NC hybrid catalyst-based anode and cathode performs a low applied voltage of 1.609 V to reach 10 mA cm-2, and outstanding long-term stability.

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Ultrathin defective high-entropy layered double hydroxides for electrochemical water oxidation Kaizhi Gu, Xiaoyan Zhu, Dongdong Wang, Nana Zhang, Gen Huang, Wei Li, Peng Long, Jing Tian, Yuqin Zou, Yanyong Wang, Ru Chen *, Shuangyin Wang * 2021, 60(9): 121-126.  DOI: 10.1016/j.jechem.2020.12.029 Abstract ( 7 )   PDF (862KB) ( 3 )

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Active facet determination of layered double hydroxide for oxygen evolution reaction Yunqi Zhang, Wenfu Xie, Jialing Ma, Lifang Chen, Chunyuan Chen, Xin Zhang*, Mingfei Shao* 2021, 60(9): 127-134.  DOI: 10.1016/j.jechem.2020.12.038 Abstract ( 6 )   PDF (927KB) ( 3 )   Oxygen evolution reaction (OER) plays an indispensable role in developing renewable clean energy resources. One of the critical bottlenecks for the reaction is the development of highly efficient electrocatalyst to decrease the high overpotentials of four-electron transfer process of OER. Recently, layered double hydroxides (LDHs) have been widely investigated among the most promising electrocatalysts for OER due to their high intrinsic activity, excellent stability as well as low-cost. However, it remains unclear how the exposed facet of the LDHs affects their electrocatalytic activity. Here we elucidate the active edge facet of LDHs towards OER by combining the finely control of edge facet ratio coupled with molecular probe method and computational calculation. The LDHs with higher edge facet area ratio show superior activity with low onset potential as well as decreased Tafel slope. The active edge site is further proved by blocking the unsaturated edge sites with cyanate probe anion, of which the adsorption largely inhibits OER activity. Furthermore, based on density functional theory (DFT) calculation, two-dimensional map of theoretical overpotentials as a function of Gibbs free energy reveals that the edge (100) facet exhibits a much higher OER activity than basal plane (001) facet.

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Strategies to suppress the shuttle effect of redox mediators in lithium-oxygen batteries Xinbin Wu, Wei Yu, Kaihua Wen, Huanchun Wang, Xuanjun Wang, Ce-Wen Nan, Liangliang Li 2021, 60(9): 135-149.  DOI: 10.1016/j.jechem.2020.12.034 Abstract ( 6 )   PDF (1084KB) ( 2 )   Rechargeable lithium-oxygen (Li-O2) batteries are the next generation energy storage devices due to their ultrahigh theoretical capacity. Redox mediators (RMs) are widely used as a homogenous electrocatalyst in non-aqueous Li-O2 batteries to enhance their discharge capacity and reduce charge overpotential. However, the shuttle effect of RMs in the electrolyte solution usually leads to corrosion of the Li metal anode and uneven Li deposition on the anode surface, resulting in unwanted consumption of electrocatalysts and deterioration of the cells. It is therefore necessary to take some measures to prevent the shuttle effect of RMs and fully utilize the soluble electrocatalysts. Herein, we summarize the strategies to suppress the RM shuttle effect reported in recent years, including electrolyte additives, protective separators and electrode modification. The mechanisms of these strategies are analyzed and their corresponding requirements are discussed. The electrochemical properties of Li-O2 batteries with different strategies are summarized and compared. The challenges and perspectives on preventing the shuttle effect of RMs are described for future study. This review provides guidance for achieving shuttle-free redox mediation and for designing Li-O2 cells with a long cycle life, high energy efficiency and highly reversible electrochemical reactions.

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Exploring the phase transformation in ZnO/Cu(111) model catalysts in CO2hydrogenation Rui Wang, Hengwei Wang, Xuefei Weng, Jiuxiang Dai, Zhongmiao Gong, Changbao Zhao, Junling Lu, Yi Cui, Xinhe Bao 2021, 60(9): 150-155.  DOI: 10.1016/j.jechem.2020.12.023 Abstract ( 11 )   PDF (607KB) ( 3 )   Sustainable methanol production via CO2 hydrogenation leads to increased interest in the understanding of active phase of Cu/ZnO/Al2O3 (CZA) catalyst. Model catalysts of ZnO/Cu(111) with structures varied from two-dimensional planar to three-dimensional nanoparticles were prepared by atomic layer deposition (ALD) method. By combing scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) at near-ambient pressure of CO2 hydrogenation, we reveal that the submonolayer ZnO/Cu(111) transformed into Cu-Zn alloy under 10 mbar CO2/H2 at 493 K, and underwent a partial re-oxidation during evacuation. The dynamic phase transformation of ZnO/Cu(111) may partly explain the existence of differences and apparently contradictory theories to account for the origin of active phase in CZA catalysts.

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Functional copolymer binder for nickel-rich cathode with exceptional cycling stability at high temperature through coordination interaction Mihan Jin, Bing Li, Linlin Hu, Peiyu Zhao, Qilu Zhang*, Jiangxuan Song* 2021, 60(9): 156-161.  DOI: 10.1016/j.jechem.2020.12.028 Abstract ( 6 )   PDF (599KB) ( 2 )   Nickel-rich layered oxide LiNi1-x-yCoxAlyO2 (NCA) with high theoretical capacity is a promising cathode material for the next-generation high-energy batteries. However, it undergoes a rapid capacity fading when operating at high temperature due to the accelerated cathode/electrolyte interfacial reactions and adhesive efficacy loss of conventional polyvinylidenefluoride (PVdF) binder. Herein, poly(acrylonitrile-co-methyl acrylate) copolymer is designed with electron-rich $-\mathrm{C} \equiv \mathrm{N}$ groups as a novel binder for LiNi0.8Co0.1Al0.1O2 cathode at high temperature. The electron-rich $-\mathrm{C} \equiv \mathrm{N}$ groups are able to coordinate with the active Ni3+ on the surface of NCA, alleviating electrolyte decomposition and cathode structure degradation. Moreover, the strong adhesive ability is conducive to maintain integrity of electrodes upon cycling at 55 °C. In consequence, the NCA electrodes with this functional binder display improved cycling stability (81.5% capacity retention after 100 cycles) and rate performance at 55 °C.

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Heterogeneous electrolyte membranes enabling double-side stable interfaces for solid lithium batteries Shuang Mu, Weilin Huang, Wuhui Sun, Ning Zhao, Mengyang Jia, Zhijie Bi*, Xiangxin Guo* 2021, 60(9): 162-168.  DOI: 10.1016/j.jechem.2020.12.026 Abstract ( 11 )   PDF (676KB) ( 7 )   The solid polymer electrolyte (SPE) is one of the most promising candidates for building solid lithium batteries with high energy density and safety due to its advantages of flexibility and light-weight. However, the conventional monolayered electrolytes usually exhibit unstable contacts with either high-voltage cathodes or Li-metal anodes during cell operation. Herein, heterogeneous dual-layered electrolyte membranes (HDEMs) consisting of the specific functional polymer matrixes united with the designed solid ceramic fillers are constructed to address the crucial issues of interfacial instability. The electrolyte layers composed of the high-conductivity and oxidation-resistance polyacrylonitrile (PAN) combined with Li0.33La0.557TiO3 nanofibers are in contact with the high-voltage cathodes, achieving the compatible interface between the cathodes and the electrolytes. Meanwhile, the electrolyte layers composed of the high-stability and dendrite-resistance polyethylene oxide (PEO) with Li6.4La3Zr1.4Ta0.6O12 nanoparticles are in contact with the Li-metal anodes, aiming to suppress the dendrite growth, as well as avoid the passivation between the PAN and the Li-metal. Consequently, the solid LiNi0.6Co0.2Mn0.2O2||Li full cells based on the designed HDEMs show the good rate and cycling performance, i.e. the discharge capacity of 170.1 mAh g-1 with a capacity retention of 78.2% after 100 cycles at 0.1C and 30 °C. The results provide an effective strategy to construct the heterogeneous electrolyte membranes with double-side stable electrode/electrolyte interfaces for the high-voltage and dendrite-free solid lithium batteries.

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Tailoring the mercaptan ligands for high performance inverted perovskite solar cells with efficiency exceeding 21% Shuangjie Wang, Ziwei He, Jiabao Yang, Tongtong Li, Xingyu Pu, Jian Han, Qi Cao, Bingyu Gao, Xuanhua Li 2021, 60(9): 169-177.  DOI: 10.1016/j.jechem.2020.12.035 Abstract ( 3 )   PDF (1013KB) ( 1 )   Interface passivation engineering has been recognized as an effective way to simultaneously contribute to the optoelectronic characteristic and stability of perovskite solar cells (PSCs). Herein, a π-conjugated dual-ligand 1,4-phenylmercaptan (PHMT) is explored to rationally tailor the surface of perovskite film. The experimental and theoretical results show that the PHMT presents planar structure and obvious electron delocalization characteristics, which allow it to anchor on the surface of perovskite with a certain orientation, thereby promoting the transport of interface charge. Moreover, the two sulfhydryl groups in PHMT reduce the trap density of the perovskite film by passivating under-coordinated lead ions. Consequently, the PHMT-modified inverted device based on MAPbI3 (MA: methylammonium) achieves enhanced efficiency from 18.11% (control) to 21.11%, along with the ambient stability up to 3500 h. After being placed at 85 °C for 500 h or illuminated for 600 h, the modified device remains over 89% or 86% of initial efficiency. This discovery opens a new window for the choice of passivators to improve the performance of PSCs.

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Tuning the solution structure of electrolyte for optimal solid-electrolyte-interphase formation in high-voltage lithium metal batteries Juner Chen, Tingyu Liu, Lina Gao, Yumin Qian, Yaqin Liu, Xueqian Kong 2021, 60(9): 178-185.  DOI: 10.1016/j.jechem.2021.01.007 Abstract ( 10 )   PDF (754KB) ( 2 )   The continuous reduction of electrolytes by Li metal leads to a poor lifespan of lithium metal batteries (LMBs). Low Coulombic efficiency (CE) and safety concern due to dendrite growth are the challenging issues for LMB electrolyte design. Novel electrolytes such as highly concentrated electrolytes (HCEs) have been proposed for improving interphase stability. However, this strategy is currently limited for high cost due to the use of a large amount of lithium salts as well as their high viscosity, reduced ion mobility, and poor wettability. In this work, we propose a new type of electrolyte having a moderate concentration. The electrolyte has the advantage of HCEs as the anion is preferentially reduced to form inorganic solid-electrolyte-interphase (SEI). Such optimization has been confirmed through combined spectroscopic and electrochemical characterizations and supported with the first-principle molecular dynamics simulation. We have shown the intrinsic connections between solution structure and their electrochemical stability. The 2.0 M LiDFOB/PC electrolyte, as predicted by our characterizations and simulations, allows stable charge-discharge of LNMO|Li cells at 5C for more than 1500 cycles. The 2.0 M electrolyte generates a dense layer of SEI containing fluoro-oxoborates, Li3BO3, LiF, Li2CO3, and some organic species effectively passivating the lithium metal, as confirmed by electron microscopy, X-ray photoelectron spectroscopy, and solid-state nuclear magnetic resonance.

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Increasing sulfur utilization in lithium-sulfur batteries by a Co-MOF-74@MWCNT interlayer SiHyeon Sung, Byung Hyuk Kim, SeungTaek Lee, Sanghyeon Choi, Woo Young Yoon* 2021, 60(9): 186-193.  DOI: 10.1016/j.jechem.2020.12.033. Abstract ( 10 )   PDF (731KB) ( 2 )   To improve lithium-sulfur battery performance, Co-MOF-74 has been applied for the first time as an interlayer with multiwalled carbon nanotubes (MWCNTs). Co-MOF-74@MWCNT was synthesized using a solvothermal method. The fabrication of Co-MOF-74@MWCNT was confirmed by scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, and Brunauer-Emmett-Teller testing. The interlayer was fabricated using a filtration method. Assembled batteries were prepared using a Co-MOF-74@MWCNT interlayer and an MWCNT interlayer and subsequently investigated via cyclic voltammetry tests. Co-MOF-74 promotes a redox reaction and shows a small peak at 1.85 V. A symmetric and full cell test revealed that the Co-MOF-74@MWCNT cell enables a faster redox reaction and higher capacity than that of the MWCNT cell. After 15 cycles, the Co-MOF-74@MWCNT cell achieved a value of 1112 mAh g-1, which is 26% greater than that of the MWCNT cell (880 mAh g-1) at 0.2C. Voltage profile testing showed that the reason for the higher capacity of the Co-MOF-74@MWCNT cell is that it promotes the conversion of Li2S2 to Li2S. Various electrochemical analyses confirmed that the Co-MOF-74@MWCNT interlayer acts not only as a physical and chemical barrier but also promotes the transformation of Li2S2 to Li2S.

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Efficient electrocatalytic overall water splitting and structural evolution of cobalt iron selenide by one-step electrodeposition Haonan Ren, Lingxiao Yu, Leping Yang, Zheng-Hong Huang, Feiyu Kang, Ruitao Lv 2021, 60(9): 194-201.  DOI: 10.1016/j.jechem.2021.01.002 Abstract ( 4 )   PDF (971KB) ( 1 )   Developing bifunctional electrocatalysts with both high catalytic activity and high stability is crucial for efficient water splitting in alkaline media. Herein, a Fe-incorporated dual-metal selenide on nickel foam (Co0.9Fe0.1-Se/NF) is synthesized via a facile one-step electrodeposition method. As-synthesized materials could serve as self-supported bifunctional electrocatalysts with excellent catalytic activity towards oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline media. Experimental results show that delivering a 10 mA cm-2 water splitting current density only requires a cell voltage of 1.55 V. In addition, a very stable performance could be kept for about 36 hours, indicating their excellent working stability. Moreover, by means of phase analysis, we have identified that the evolution of the synthesized Co0.9Fe0.1-Se/NF experiences two entirely different processes in HER and OER, which hydroxide and oxyhydroxide are regarded as the real active sites, respectively. This work may pave the way to further understanding the relationships between the reactivity and stability of chalcogenide-based electrocatalysts and facilitating the rational design of efficient electrocatalysts for future renewable energy system applications.

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Polypyrrole reinforced ZIF-67 with modulated facet exposure and billion-fold electrical conductivity enhancement towards robust photocatalytic CO2reduction Xuzhou Yuan, Qiaoqiao Mu, Songlin Xue, Yanhui Su, Yanlei Zhu, Hao Sun, Zhao Deng, Yang Peng 2021, 60(9): 202-208.  DOI: 10.1016/j.jechem.2020.12.025 Abstract ( 4 )   PDF (744KB) ( 2 )   The implementation of metal organic frameworks (MOFs) as the co-catalysts in hybrid photocatalytic systems puts requirements on both their charge-carrying capability and solvent stability. In the current study, in order to simultaneously promote the electrical conductivity and water stability of ZIF-67, an in-situ monomer trapping strategy is deployed to synthesize polypyrrole (PPy)-reinforced ZIF-67 ensembles. Through coordination modulation, the incremental addition of pyrrole monomers enables to alter the crystal morphology of ZIF-67 from rhombic dodecahedra to truncated rhombic dodecahedra, and further to cubes. Upon polymerization, the resulted composite, in comparison to ZIF-67, demonstrates a billion-fold conductivity enhancement, much improved chemical stability in pronated solvents, as well as largely retained specific surface area and porosity, enabling it functioning as an outstanding co-catalyst for catalyzing robust photocatalytic CO2 reduction. Furthermore, a PPy-mediated electron harvest and relay mechanism is proposed for rationalizing the enhanced photocatalytic performance.

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Revealing dual capacitive mechanism of carbon cathode toward ultrafast quasi-solid-state lithium ion capacitors Kangyu Zou, Peng Cai, Xinglan Deng, Baowei Wang, Cheng Liu, Jiayang Li, Hongshuai Hou, Guoqiang Zou, Xiaobo Ji 2021, 60(9): 209-221.  DOI: 10.1016/j.jechem.2020.12.039 Abstract ( 3 )   PDF (1844KB) ( 2 )   High-performance lithium ion capacitors (LICs) have been seriously hindered by the very low capacity and unclear capacitive mechanism of carbon cathode. Herein, after the combination of experimental results and theoretical calculations, it is found that the critical pore size of 0.8 nm for PF6- ion adsorption decreases strong interactive repulsion of electrons and largely reduces adsorption energy barrier, which greatly improves the charge accommodation capacity in electrical double-layer behavior. Most importantly, the chemical-bond evolution process of C=O group has been firstly revealed by X-ray photoelectron spectroscopy (XPS), indicating that the introduction of C=O group can provide abundant redox active sites for PF6- ion adsorption accompanied with enhanced pseudocapacitive capacity. Attributed to the synergistic effect of dual capacitive mechanism, porous carbon sheet (PCS) cathode shows a reversible specific capacity of 53.6 mAh g-1 even at a high current density of 50 A g-1. Significantly, the quasi-solid-state LIC manifests state-of-the-art electrochemical performances with an integrated maximum energy density of 163 Wh kg-1 and an outstanding power density of 15,000 W kg-1. This elaborate work promotes better fundamental understanding about capacitive mechanism of PF6- ion and offers a rational dual-capacitive strategy for the design of advanced carbon cathodes.

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The effect of electrochemically inactive Ti substituted for Ru in Li2Ru1-xTixO3on structure and electrochemical performance Ye Yao, Lu Zhang, Florian Sigel, Björn Schwarz, Helmut Ehrenberg, Gang Chen, Fei Du, Chunzhong Wang 2021, 60(9): 222-228.  DOI: 10.1016/j.jechem.2020.12.037 Abstract ( 8 )   PDF (534KB) ( 2 )   The approach of substituting electrochemically active with inactive elements has widely been used to improve the electrochemical performance of Li-rich intercalation cathode materials. This especially is true for Li-rich compounds where almost all of the Li+ ions are reversibly (de)intercalated during electrochemical cycling. The beneficial mechanism behind this substitution with electrochemically inactive elements is still not clear yet. Li2RuO3 is chosen as basis for a model solid solution system to investigate the effect of electrochemically inactive elements owing to its high specific capacity of more than 300 mAh g-1 and the significant contribution of anion redox mechanism. Herein, Li2Ru1-xTixO3 solid solution series are synthesized and the effect of substituting with electrochemical inactive Ti for Ru on structure and electrochemical performance have been comprehensively investigated. The electrochemical performance is significantly improved, especially for Li2Ru0.8Ti0.2O3, and the capacity retention after 50 cycles increases from 81% to 90%, as compared to the end member Li2RuO3. Results of electrochemical impedance spectroscopy show that Ti substitution reduces the charge transfer impedance, which favors the Li+ diffusion across the electrolyte-electrode interface and improves the electronic conductivity. For the first time, nuclear magnetic resonance was utilized to confirm that a small part of Ti ions exchange their position with Li ions in the Li layer. This research provides a better understanding of electrochemical inactive element substitution and strong insights for the functional design of the next generation of Li-rich cathode materials.

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Designing electrode materials for aluminum-ion batteries towards fast diffusion and multi-electron reaction Lumin Zheng, Haoyi Yang, Ying Bai, Chuan Wu* 2021, 60(9): 229-232.  DOI: 10.1016/j.jechem.2020.12.027 Abstract ( 4 )   PDF (494KB) ( 2 )

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High-performance zinc-ion batteries enabled by electrochemically induced transformation of vanadium oxide cathodes Yang Li, Wang Yang, Wu Yang, Yongfeng Huang, Guoxiu Wang, Chengjun Xu, Feiyu Kang, Liubing Dong 2021, 60(9): 233-240.  DOI: 10.1016/j.jechem.2021.01.025 Abstract ( 6 )   PDF (909KB) ( 9 )   Rechargeable aqueous zinc-ion batteries (ZIBs) have become a research hotspot in recent years, due to their huge potential for high-energy, fast-rate, safe and low-cost energy storage. To realize good electrochemical properties of ZIBs, cathode materials with prominent Zn2+ storage capability are highly needed. Herein, we report a promising ZIB cathode material based on electrochemically induced transformation of vanadium oxides. Specifically, K2V6O16·1.5H2O nanofibers were synthesized through a simple stirring method at near room temperature and then used as cathode materials for ZIBs in different electrolytes. The cathode presented superior Zn2+ storage capability in Zn(OTf)2 aqueous electrolyte, including high capacity of 321 mAh/g, fast charge/discharge ability (96 mAh/g delivered in 35 s), high energy density of 235 Wh/kg and good cycling performance. Mechanism analysis evidenced that in Zn(OTf)2 electrolyte, Zn2+ intercalation in the first discharge process promoted K2V6O16·1.5H2O nanofibers to transform into Zn3+xV2O7(OH)2·2H2O nanoflakes, and the latter served as the Zn2+-storage host in subsequent charge/discharge processes. Benefiting from open-framework crystal structure and sufficiently exposed surface, the Zn3+xV2O7(OH)2·2H2O nanoflakes exhibited high Zn2+ diffusion coefficient, smaller charge-transfer resistance and good reversibility of Zn2+ intercalation/de-intercalation, thus leading to superior electrochemical performance. While in ZnSO4 aqueous electrolyte, the cathode material cannot sufficiently transform into Zn3+xV2O7(OH)2·2H2O, thereby corresponding to inferior electrochemical behaviors. Underlying mechanism and influencing factors of such a transformation phenomenon was also explored. This work not only reports a high-performance ZIB cathode material based on electrochemically induced transformation of vanadium oxides, but also provides new insights into Zn2+-storage electrochemistry.

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Ultrafine SnSSe/multilayer graphene nanosheet nanocomposite as a high-performance anode material for potassium-ion half/full batteries Zuyue Yi, Jingyi Xu, Zhenhua Xu, Min Zhang, Yanan He, Jianchun Bao, Xiaosi Zhou* 2021, 60(9): 241-248.  DOI: 10.1016/j.jechem.2021.01.022 Abstract ( 7 )   PDF (1009KB) ( 2 )   Layer-structured SnSSe attracts much attention as an anode material for potassium storage due to its large theoretical capacity. Unfortunately, their practical application is severely restrained by the dramatic volumetric variation of SnSSe. Herein, we synthesize ultrafine SnSSe/multilayer graphene nanosheet (SnSSe/MGS) by a vacuum solid-phase reaction and subsequent ball milling. Owing to the strong synergistic effect between the two components, the obtained SnSSe/MGS nanocomposite exhibits a high reversible capacity (423 mAh g-1 at 100 mA g-1), excellent rate property (218 mAh g-1 at 5 A g-1), and stable cycling performance (271 mAh g-1 after 500 cycles at 100 mA g-1) in potassium-ion half batteries. Moreover, the full cell assembled by the SnSSe/MGS anode and the potassiated 3,4,9,10-perylene-tetracarboxylic aciddianhydride cathode shows excellent electrochemical performance between 0.2 and 3.3 V (209 mAh g-1 at 50 mA g-1 after 100 cycles). The presented two-step synthesis strategy of SnSSe/MGS may also provide ideas to craft other alloy-type anode materials.

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Catalytic role of assembled Ce Lewis acid sites over ceria for electrocatalytic conversion of dinitrogen to ammonia Jiamin Qi, Shulan Zhou, Ke Xie, Sen Lin 2021, 60(9): 249-258.  DOI: 10.1016/j.jechem.2021.01.016 Abstract ( 4 )   PDF (1133KB) ( 2 )   CeO2-based catalysts are emerging as novel candidates for catalyzing nitrogen reduction reaction (NRR). However, despite the increasing amount of experimental and theoretical research, the design of more efficient ceria catalysts for NRR remains a challenge due to the poor knowledge of the catalytic mechanism, particularly the nature of the active sites and how they catalyze NRR. Here, using first-principle calculations, we investigated the NRR catalysis process involving adjacent Ce Lewis acid clusters formed on (111), (110), and (100) facets of CeO2 as active sites. Our results revealed that the assembled structures of the Ce Lewis acid as active centers after the oxygen vacancies (Ovs) were opened. The exposed Ce sites on CeO2(111), CeO2(110), and CeO2(100) can cause N2 to be adsorbed in a “lying-down” manner, which facilitates the N2 activation and thus leads to much higher NRR activity. Furthermore, from the perspective of electronic structure, we establish two useful descriptors for assessing the NRR activity on ceria with Ovs: The N-N bond strength of the adsorbed N2 and the adsorption energy of the *N2H intermediate. This work thus provides direct guidance for the design of more-effective oxide catalysts without the use of scarce metals.

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MOF-derived multifunctional filler reinforced polymer electrolyte for solid-state lithium batteries Zheng Zhang, Ying Huang*, Heng Gao, Chao Li, Jiaxin Hang, Panbo Liu 2021, 60(9): 259-271.  DOI: 10.1016/j.jechem.2021.01.013 Abstract ( 14 )   PDF (2090KB) ( 3 )   Solid-state lithium batteries (SSLBs) have attracted great interest from researchers due to their inherent high energy density and high safety performance. In order to develop SSLBs, the following two key problems should be solved: (1) Improving the lithium ion conductivity of solid electrolyte at room temperature; and (2) improving the interface between the electrode and the electrolyte. Herein, we propose a new multifunctional filler for reinforcing polymer electrolytes. The composite solid electrolytes (CSEs) mainly contain a MOF-derived Co-doped hollow porous carbon nanocage, which absorbs Li+ containing ionic liquid (Li-ILs@HPCN), polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imide. By optimizing the composition of the CSEs, the CSEs membrane with high ionic conductivity (1.91 × 10-4 S cm-1 at 30 °C), wide electrochemical stability (5.2 V) and high mobility of lithium ion (0.5) was obtained. Even at a current density of 0.2 mA cm-2, the PILH electrolyte possesses excellent interfacial stability against Li metal in Li symmetrical batteries exceeds 1600 h. Finally, the SSLBs (LFP/PILH/Li) showed excellent cycle stability, and the capacity was maintained at 152.9 and 140.0 mA h g-1 after 150 cycles at a current density of 0.2C and 0.5C. This work proposes a completely new strategy for building high-performance SSLBs.

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CoS2nanowires supported graphdiyne for highly efficient hydrogen evolution reaction Wangjing Xie, Kang Liu, Guodong Shi, Xinliang Fu, Xiaojie Chen, Zixiong Fan, Min Liu, Mingjian Yuan, Mei Wang 2021, 60(9): 272-278.  DOI: 10.1016/j.jechem.2021.01.005 Abstract ( 9 )   PDF (913KB) ( 4 )   Transition metal sulfides are an important category for hydrogen evolution reaction (HER). However, only few edge unsaturated sulfurs functionalize as catalytic sites, which has dramatically limited the catalytic activity and stability. In this work, planar unsaturated sulfurs in (211) plane of the CoS2 nanowires have been successfully activated through constructing Graphdiyne-CoS2 heterojunction nanocomposites. The corresponding electrons transfer energy barriers for these planar unsaturated sulfurs have been significantly diminished, which are induced by the synergetic effects of the sp1 hybridized carbons and unsaturated planar sulfurs. In addition, DFT simulations reveal the synergetic effects of the sp1 hybridized carbons and unsaturated planar sulfurs can promote electron transfer kinetics of the key step, Volmer-Heyrovsky step, of the reaction. As expected, the Graphdiyne-CoS2 heterojunction nanocomposites exhibit superior HER catalytic performance with low overpotential of 97 mV at 10 mA cm-2, and the Tafel slope of 56 mV dec-1. Furthermore, the heterojunction shows outstanding stability as well due to the protection of the Graphdiyne (GDY). The approach thus paves the way for the further efficient transition metal disulfides catalyst manufactures.

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Raman probing carbon & aqueous electrolytes interfaces and molecular dynamics simulations towards understanding electrochemical properties under polarization conditions in supercapacitors Rafael Vicentini, Leonardo M. Da Silva, Débora V. Franco, Willian G. Nunes, Juliane Fiates, Gustavo Doubek, Luís F.M. Franco, Renato G. Freitas, Cristiano Fantini, Hudson Zanin 2021, 60(9): 279-292.  DOI: 10.1016/j.jechem.2021.01.003 Abstract ( 4 )   PDF (1170KB) ( 2 )   Raman probing of carbon electrode and electrolyte under dynamic conditions is performed here using different aqueous electrolytes to elucidate the fundamental events occurring in electrochemical supercapacitor during charge-discharge processes. The areal capacitance ranges from 1.54 to 2.31 mF cm-2 and it is determined using different techniques. These findings indicate that the Helmholtz capacitance governs the overall charge-storage process instead of the space charge (quantum) capacitance commonly verified for HOPG electrodes in the range of ~ 3 to 7 µF cm-2. Molecular dynamics simulations are employed to elucidate the origin of the reversible Raman spectral changes during the charge-discharge processes. A correlation is verified between the reversible Raman shift and the surface excesses of the different ionic species. A theoretical framework is presented to relate the effect of the applied potential on the Raman shift and its correlation with the surface ionic charge. It is proposed that the Raman shift is governed by the interaction of solvated cations with graphite promoted by polarization conditions. It is the first time that a comparative study on different aqueous electrolyte pH and cation ion size has been performed tracking the Raman spectra change under dynamic polarization conditions and contrasting with comprehensive electrochemistry and dynamic molecular simulations studies. This study shines lights onto the charge-storage mechanism with evidence of Kohn anomaly reduction in the carbon electrode during the reversible adsorption/desorption and insertion/extraction of ionic species.

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Subsurface intercalation activating basal plane of black phosphorus for nitrogen reduction Xue Zhang, Haitao Zhao, Paul K. Chu, Jiahong Wang, Xue-Feng Yu 2021, 60(9): 293-299.  DOI: 10.1016/j.jechem.2021.01.010 Abstract ( 6 )   PDF (630KB) ( 2 )

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Strategies and methods for fabricating high quality metal halide perovskite thin films for solar cells Helian Sun, Pengfei Dai, Xiaotong Li, Jinyan Ning, Shenghao Wang, Yabing Qi 2021, 60(9): 300-333.  DOI: 10.1016/j.jechem.2021.01.001 Abstract ( 12 )   PDF (2985KB) ( 5 )   With the development of human society, the problems of environmental deterioration and energy shortage have become increasingly prominent. In order to solve these problems, metal halide perovskite solar cells (PSCs) stand out because of their excellent properties (i.e., high optical absorption coefficient, long carrier lifetime and carrier diffusion length, adjustable band gap) and have been widely studied. PSCs with low cost, high power conversion efficiency and high stability are the future development trend. The quality of perovskite film is essential for fabricating PSCs with high performance. To provide a full picture of realizing high performance PSCs, this review focuses on the strategies for preparing high quality perovskite films (including antisolvent, Lewis acid-base, additive engineering, scaleable fabrication, strain engineering and band gap adjustment), and therefore to fabricate high performance PSCs and to accelerate the commercialization.

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Ion shielding functional separator using halloysite containing a negative functional moiety for stability improvement of Li-S batteries Yong Min Kwon, Jihoon Kim, Kuk Young Cho, Sukeun Yoon 2021, 60(9): 334-340.  DOI: 10.1016/j.jechem.2021.01.029 Abstract ( 6 )   PDF (780KB) ( 2 )   Lithium-sulfur batteries are one of the attractive next-generation energy storage systems owing to their environmental friendliness, low cost, and high specific energy densities. However, the low electrical conductivity of sulfur, shuttling of soluble intermediate polysulfides between electrodes, and low capacity retention have hampered their commercial use. To address these issues, we use a halloysite-modulated (H-M) separator in a lithium-sulfur battery to mitigate the shuttling problem. The H-M separator acts as a mutual Coulombic repulsion in lithium-sulfur batteries, thereby selectively permitting Li ions and efficiently suppressing the transfer of undesired lithium polysulfides to the Li anode side. Moreover, the use of halloysite switches the surface of the separator from hydrophobic to hydrophilic, consequently improving the electrolyte wettability and adhesion between the separator and cathode. When sulfur-multi-walled carbon nanotube (S-MWCNT) composites are used as cathode active materials, a lithium-sulfur battery with an H-M separator exhibits first discharge and charge capacities of 1587 and 1527 mAh g-1, respectively. Moreover, there is a consistent capacity retention up to 100 cycles. Accordingly, our approach demonstrates an economical and easily accessible strategy for commercialization of lithium-sulfur batteries.

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Fluorine-substituted O3-type NaNi0.4Mn0.25Ti0.3Co0.05O2?xFxcathode with improved rate capability and cyclic stability for sodium-ion storage at high voltage Chaojin Zhou, Lichun Yang, Chaogang Zhou, Jiangwen Liu, Renzong Hu, Jun Liu, Min Zhu 2021, 60(9): 341-350.  DOI: 10.1016/j.jechem.2021.01.038 Abstract ( 7 )   PDF (1542KB) ( 2 )   O3-type NaNiO2-based cathode materials undergo irreversible phase transition and serious capacity decay at high voltage above 4.0 V in sodium-ion batteries. To address these challenges, effects of F-substitution on the structure and electrochemical performance of NaNi0.4Mn0.25Ti0.3Co0.05O2 are investigated in this article. The F-substitution leads to expanding of interlayer, which can enhance the mobility of Na+. NaNi0.4Mn0.25Ti0.3Co0.05O1.92F0.08 (NMTC-F0.08) with the optimal F-substitution degree exhibits much improved rate capability and cyclic stability. It delivers reversible capacities of 177 and 97 mAh g-1 at 0.05 and 5 C within 2.0-4.4 V, respectively. Galvanostatic intermittent titration technique verifies faster kinetics of Na+ diffusion in NMTC-F0.08. And in-situ XRD investigation reveals the phase evolution of NMTC-F0.08, indicating enhanced structural stability results from F-substitution. This study may shed light on the development of high performance cathode materials for sodium-ion storage at high voltage.

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Machine learning aided design of perovskite oxide materials for photocatalytic water splitting Qiuling Tao, Tian Lu, Ye Sheng, Long Li, Wencong Lu, Minjie Li 2021, 60(9): 351-359.  DOI: 10.1016/j.jechem.2021.01.035 Abstract ( 25 )   PDF (747KB) ( 8 )   Suffering from the inefficient traditional trial-and-error methods and the huge searching space filled by millions of candidates, discovering new perovskite visible photocatalysts with higher hydrogen produc- tion rate (RH2 ) still remains a challenge in the field of photocatalytic water splitting (PWS). Herein, we established structural-property models targeted to RH2 and the proper bandgap (Eg ) via machine learning (ML) technology to accelerate the discovery of efficient perovskite photocatalysts for PWS. The Pearson correlation coefficients (R) of leave-one-out cross validation (LOOCV) were adopted to compare the per-formances of different algorithms including gradient boosting regression (GBR), support vector regression (SVR), backpropagation artificial neural network (BPANN), and random forest (RF). It was found that the BPANN model showed the highest R values from LOOCV and testing data of 0.9897 and 0.9740 for RH2 , while the GBR model had the best values of 0.9290 and 0.9207 for Eg . Furtherly, 14 potential PWS per- ovskite candidates were screened out from 30,000 ABO3-type perovskite structures under the criteria of structural stability, Eg , conduction band energy, valence band energy and RH2 . The average RH2 of these 14 perovskites is 6.4% higher than the highest value in the training data set. Moreover, the online web servers were developed to share our prediction models, which could be accessible in http://materials-data-mining.com/ocpmdm/material_api/ahfga3d9puqlknig (Eg prediction) and http://materials-data-mining.com/ocpmdm/material_api/i0ucuyn3wsd14940 (RH2 prediction).

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A crosslinking hydrogel binder for high-sulfur content S@pPAN cathode in rechargeable lithium batteries Huanhuan Yuan, Cheng Guo, Jiahang Chen, Huichao Lu, Jun Yang, Yanna Nuli, Jiulin Wang 2021, 60(9): 360-367.  DOI: 10.1016/j.jechem.2021.01.045 Abstract ( 11 )   PDF (952KB) ( 2 )   High-energy density lithium-sulfur (Li-S) batteries have received intensive attention as promising energy storage system. Among diverse sulfur-based cathodes, sulfurized pyrolyzed poly(acrylonitrile) (S@pPAN) cathode delivered superior electrochemical performance. However, the sulfur content of S@pPAN is relatively low (<50 wt%), which significantly limits the energy density. Herein, a hydrogel SA-Cu binder was proposed with a crosslinking network constructed by Cu2+ ions. The introduction of Cu2+ ions enabled excellent electrochemical behaviors of S@pPAN cathode even with high sulfur content of 52.6 wt% via chemical interaction with sulfur and polysulfide. Moreover, a favorable cathode interphase was formed containing electrochemically active and conductive CuSx. S@pPAN/SA-Cu exhibited a high sulfur utilization of 85.3%, long cycling stability over 1000 cycles and remarkable capacity of 1200 mAh gs-1 even at 10 C. Furthermore, ascribed to the improved electrode structure, high-loading electrode (sulfur loading: 4 mg cm-2) displayed stable cycling with areal capacity of 5.26 mAh cm-2 (1315 mAh gs-1) after 40 cycles. This study provides new directions to prepare high-sulfur content and high-loading S@pPAN cathode for higher energy density.

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Eu-based anolytes for high-voltage and long-lifetime aqueous flow batteries Pan Sun, Yahua Liu, Peipei Zuo, Yuanyuan Li, Qianru Chen, Zhengjin Yang, Tongwen Xu 2021, 60(9): 368-375.  DOI: 10.1016/j.jechem.2021.01.041 Abstract ( 4 )   PDF (1743KB) ( 2 )   Aqueous flow batteries (AFBs) are among the most promising electrochemical energy storage solutions for the massive-scale adoption of renewable electricity because of decoupled energy and power, design flexibility, improved safety and low cost. The development of high-voltage AFB is, however, limited by the lack of stable anolytes that have low redox potential. Here we report Eu-based anolytes for high-voltage pH-neutral AFB applications. Eu3+ has a reduction potential of -0.39 V vs. SHE, which can be dramatically lowered when forming stable complex with inexpensive organic chelates. A typical complex, EuDTPA, features a low redox potential of -1.09 V vs. SHE, fast redox kinetics, and a high water solubility of 1.5 M. When paired with ferrocyanide, the battery had an open-circuit voltage of 1.56 V and demonstrated stable cell cycling performance, including a capacity retention rate of 99.997% per cycle over 500 cycles at 40 mA cm-2, a current efficiency of >99.9%, and an energy efficiency of >83.3%. A high concentration anolyte at 1.5 M exhibited a volumetric capacity of 40.2 Ah L-1, which is one of the highest known for pH-neutral AFBs, promising a potent solution for the grid-scale storage of renewable electricity.

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Achieving 20% photovoltaic efficiency by manganese doped methylammonium lead halide perovskites Liangliang Deng, Hanjun Yang, Ruiheng Pan, Haomiao Yu, Jinpeng Li, Ling Xu, Kai Wang 2021, 60(9): 376-383.  DOI: 10.1016/j.jechem.2021.01.028 Abstract ( 6 )   PDF (831KB) ( 3 )   We report a transition metal such as manganese doped methylammonium lead halide perovskite (MA(Pb:Mn)I3) solar cell with an power conversion efficiency (PCE) over 20%. The rational design and fabrication of MA(Pb:Mn)I3 lead to the enhancements of all the photovoltaic parameters. To incorporate Mn can effectively eliminate the trap-assist and bi-molecular recombination. The photo-absorption ability at shorter wavelengths (i.e., less than 500 nm) and charge carrier lifetime can be elaborated. More importantly, the existence of the Mn2+-I--Mn3+ motif contributes for the double exchange effect, giving rise to the charge/spin transport. By a combination of linearly and circularly polarized photo-excitations, we have explicitly determined the role of intrinsic spin-orbit coupling (SOC) in MA(Pb:Mn)I3. More dark states are expected to be available for the photocurrent generation. This study may pave the way for deep understandings of transition metals doped hybrid perovskites for highly efficient solar cell applications.

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An option for green and sustainable future: Electrochemical conversion of ammonia into nitrogen Bo Zhou, Nana Zhang, Yujie Wu, Weijun Yang*, Yanbing Lu*, Yanyong Wang*, Shuangyin Wang 2021, 60(9): 384-402.  DOI: 10.1016/j.jechem.2021.01.011 Abstract ( 3 )   PDF (1149KB) ( 2 )   Green and sustainable options are needed to ease the current energy and environmental crisis, and alleviate the greenhouse effect and energy shortage. As an alternative carbon-neutral synthetic fuel, ammonia shows great potential due to its high energy density, non-toxic by-products, and mature related infrastructures. However, related practical applications have been severely hampered on ammonia-oxidation due to the high cost of catalysts and immature energy utilization systems. Here, we comprehensively summarized the efforts which have been made in recent years with the aim of providing a deep sight into the development and deficiencies in this territory and trying to establish a simple framework of basic knowledge for researchers. The exploration of mechanism is discussed first and then the relevant catalysts studied in recent years are summarized. Besides, the progress of direct ammonia fuel cells (DAFCs) is also presented and the challenges as well as perspectives on future developments of electrocatalysts for ammonia electro-oxidation and its practical application are provided at the end.

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Improving the ammonia synthesis activity of Ru/CeO2through enhancement of the metal-support interaction Chunyan Li, Yuying Shi, Zecheng Zhang, Jun Ni, Xiuyun Wang, Jianxin Lin, Bingyu Lin*, Lilong Jiang* 2021, 60(9): 403-409.  DOI: 10.1016/j.jechem.2021.01.031 Abstract ( 9 )   PDF (1124KB) ( 2 )   The metal-support interactions induced by high-temperature hydrogen reduction have a strong influence on the catalytic performance of ceria-supported Ru catalysts. However, the appearance of the strong metal-support interaction leads to covering of the Ru species by Ce suboxides, which is detrimental to the ammonia synthesis reaction that requires metallic species as active sites. In the present work, the interaction between Ru and ceria in the Ru/CeO2 catalyst was induced by NaBH4 treatment. NaBH4 treatment enhanced the fraction of metallic Ru, proportion of Ce3+, content of exposed Ru species, and amount of surface oxygen species. As a result, a larger amount of hydrogen species would desorb by the H2-formation pathway and the strength of hydrogen adsorption would be weaker, weakening the inhibition effect of the hydrogen species on ammonia synthesis. In addition, the strong electronic metal-support interaction aids in nitrogen dissociation. Consequently, Ru/CeO2 with NaBH4 treatment showed higher ammonia synthesis rates than that with only hydrogen reduction.

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Innovative strategies toward challenges in PV-powered electrochemical CO2reduction Siraj Sultan, Jin Hyun Kim, SeungHyeon Kim, Youngkook Kwon*, Jae Sung Lee* 2021, 60(9): 410-416.  DOI: 10.1016/j.jechem.2021.01.043 Abstract ( 3 )   PDF (442KB) ( 2 )   The solar energy-driven electrochemical CO2 reduction to value-added fuels or chemicals is considered as an attractive path to store renewable energy in the form of chemical energy to close the carbon cycle. However, CO2 reduction suffers from a number of challenges including slow reaction rates, low selectivity, and low energy conversion efficiency. Recently, innovative strategies have been developed to mitigate this challenges. Especially the development of flow cell reactors with a gas diffusion electrode, ionic liquid electrolytes, and new electrocatalysts have dramatically improved the reaction rates and selectivity to desired products. In this perspective, we highlight the key recent developments and challenges in PV-powered electrochemical CO2 reduction and propose effective strategies to improve the reaction kinetics, to minimize the electrical energy losses, and to tune the selectivity of the catalysts for desired products, and then suggest future direction of research and development.

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Interfacial assembly of two-dimensional MXenes Chuanfang (John) Zhang 2021, 60(9): 417-434.  DOI: 10.1016/j.jechem.2020.12.036 Abstract ( 10 )   PDF (1420KB) ( 4 )   Two-dimensional (2D) transition metal carbides, carbonitrides and nitrides, known as MXenes, are emerging quickly at the frontiers of 2D materials world. Their exotic properties such as the highest electrical conductivity among all solution-processed 2D materials, the best electromagnetic interference shielding performance outperforming that of copper or aluminum at a nanoscale thickness, as well as the highest volumetric capacitance for pseudocapacitors, have been attracting extensive fundamental research and applications. Their unique surface chemistries, that is, hydrophilic groups terminated on the surface of MXenes after etching and delamination, enable plenty of opportunities for assembling into MXene building blocks. Particularly, assembling at liquid-liquid, liquid-solid, liquid-air, and solid-solid interfaces allows the efficient fabrication of various structures, including MXene surfactants, MXene heterostructures, MXene transparent films. Interfacial assembly of MXenes is of significance in unveiling more versatilities of MXenes as well as impacts on novel MXene-based architectures, based on which enhanced performance of devices is achieved. As such, this review focuses on the interfacial assembly of MXenes, explaining mechanisms behind various assembling and providing classical examples for corresponding interfacial assembling techniques. Applications of these as-assembled architectures are also discussed in brief. We believe this review may shed light on the interfacial chemistry of MXenes, thus guiding more efficient fabrication of MXene-based functional films/coatings/electrodes/devices.

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A review: Modification strategies of nickel-rich layer structure cathode (Ni ≥ 0.8) materials for lithium ion power batteries Haijian Lv, Chunli Li, Zhikun Zhao, Borong Wu, Daobin Mu 2021, 60(9): 435-450.  DOI: 10.1016/j.jechem.2021.01.044 Abstract ( 5 )   PDF (9276KB) ( 3 )   Lithium ion power batteries have undoubtedly become one of the most promising rechargeable batteries at present; nonetheless, they still suffer from the challenges such as requirement of even higher energy density and capacity retention. Nickel-rich layer oxides (Ni ≥ 0.8) become ideal cathode materials to achieve the high specific capacity. Integration of optimization of synthesis process and modification of crystal structure to suppress the capacity fading can obviously improve the performance of the lithium ion batteries. This review presents the recent modification strategies of the nickel-rich layered oxide materials. Unlike in previous reviews and related papers, the specific mechanism about each type of the modification strategies is specially discussed in detail, which is mainly about inhibiting the anisotropic lattice strain and adjusting the cation mixing degree to maintain crystal structure. Based on the recent progress, the prospects and challenges of the modified nickel-rich layer cathodes to upgrade the property of lithium ion batteries are also comprehensively analyzed, and the potential applications in the field of plug-in hybrid vehicles and electric vehicles are further discussed.

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Recent advances in the electrochemistry of layered post-transition metal chalcogenide nanomaterials for hydrogen evolution reaction Yong Wang*, Yang Zhao, Xiang Ding, Liang Qiao* 2021, 60(9): 451-479.  DOI: 10.1016/j.jechem.2021.01.021 Abstract ( 8 )   PDF (2782KB) ( 5 )   Layered two-dimensional (2D) materials have received tremendous attention due to their unique physical and chemical properties when downsized to single or few layers. Several types of layered materials, especially transition metal dichalcogenides (TMDs) have been demonstrated to be good electrode materials due to their interesting physical and chemical properties. Apart from TMDs, post-transition metal chalcogenides (PTMCs) recently have emerged as a family of important semiconducting materials for electrochemical studies. PTMCs are layered materials which are composed of post-transition metals raging from main group IIIA to group VA (Ga, In, Ge, Sn, Sb and Bi) and group VI chalcogen atoms (S, selenium (Se) and tellurium (Te)). Although a large number of literatures have reviewed the electrochemical and electrocatalytic applications of TMDs, less attention has been focused on PTMCs. In this review, we focus our attention on PTMCs with the aim to provide a summary to describe their fundamental electrochemical properties and electrocatalytic activity towards hydrogen evolution reaction (HER). The characteristic chemical compositions and crystal structures of PTMCs are firstly discussed, which are different from TMDs. Then, inherent electrochemistry of PTMCs is discussed to unveil the well-defined redox behaviors of PTMCs, which could potentially affect their efficiency when applied as electrode materials. Following, we focus our attention on electrocatalytic activity of PTMCs towards HER including novel synthetic strategies developed for the optimization of their HER activity. This review ends with the perspectives for the future research direction in the field of PTMC based electrocatalysts.

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Guest ions pre-intercalation strategy of manganese-oxides for supercapacitor and battery applications Lina Chen, Chongyang Hao, Yamin Zhang, Youri Wei, Linna Dai, Jun Cheng, Hongqiang Zhang, Lijie Ci 2021, 60(9): 480-493.  DOI: 10.1016/j.jechem.2021.01.023 Abstract ( 7 )   PDF (1665KB) ( 2 )   Optimization of intrinsic structure of electrode materials plays decisive roles in promoting the development of energy storage systems to meet the fast-growing requirements in the market. Interlayer engineering has been proved to be an effective way to obtain adequate active sites, preferable ion diffusion channels and stable structure, thus enhance the performance of batteries. An in-depth understanding of the correlation among synthesis, structure and performance will significantly promote the development of excellent materials and energy storage devices. Therefore, in this review, recent advances in regards to cation preintercalation engineering in Mn-based electrode materials for rechargeable metal ion batteries are systematically summarized. Preintercalated guest cations can expand interlayer space to promote ion diffusion kinetics, serve as pillars to stabilize structure, control composition and valence to switch electrochemical behavior, thus improve the overall performance of secondary batteries. Moreover, the existing challenges and perspectives are provided for the interlayer engineering and its promotion to battery industry.

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The role of defects association in structural and transport properties of the Ce1-x(Nd0.74Tm0.26)xO2-x/2 system Cristina Artini, Sabrina Presto, Massimo Viviani, Sara Massardo, Maria Maddalena Carnasciali, Lara Gigli, Marcella Pani 2021, 60(9): 494-502.  DOI: 10.1016/j.jechem.2020.11.030 Abstract ( 9 )   PDF (644KB) ( 3 )   An experimental investigation of the crystallographic, Raman and transport properties of the Ce1-x(Nd0.74Tm0.26)xO2-x/2 (0.1 ≤ x ≤ 0.6) doped ceria system was performed with the aim of setting out correlations between structural features and ionic conductivity of the material. The chosen composition ensures that the average size of the Nd3+ and Tm3+ doping ions coincides with the one of Sm3+; even so, the studied system presents larger cell parameters and a wider compositional extent of the CeO2-based solid solution than Sm-doped ceria. Moreover, the occurrence of two different activation energies to ionic conduction below and above ~750 K determines the existence of two distinct conduction regimes. The described experimental results agree with the formation below the threshold temperature of 1Vö2Tm'Ce trimers, which promote the incorporation of Nd'Ce isolated defects into the CeO2-based solid solution. In the high temperature range the dissociation of trimers induces the appearance of a lower activation energy; the extrapolation of its value at infinite dilution provides a result in good accordance with the expected binding energy of 1Vö2Tm'Ce dimers, pointing at their stability even in the high temperature conduction regime.

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Engineering heterointerfaces coupled with oxygen vacancies in lanthanum-based hollow microspheres for synergistically enhanced oxygen electrocatalysis Jie Zhang, Jinwei Chen, Yan Luo, Yihan Chen, Chenyang Zhang, Yingjian Luo, Yali Xue, Honggang Liu, Gang Wang, Ruilin Wang 2021, 60(9): 503-511.  DOI: 10.1016/j.jechem.2020.11.037 Abstract ( 14 )   PDF (1099KB) ( 3 )   The development of high-efficiency and low-cost bifunctional oxygen electrocatalysts is critical to enlarge application of zinc-air batteries (ZABs). However, it still remains challenges due to their uncontrollable factor at atomic level during the catalysts preparation, which requires the precise regulation of active sites and structure engineering to accelerate the reaction kinetics for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, a novel Co-doped mixed lanthanum oxide and hydroxide heterostructure (termed as Co-LaMOH|OV@NC) was synthesized by pyrolysis of La-MOF-NH2 with spontaneous cobalt doping. Synergistic coupling of its hollow structure, doping effect and abundant oxygen vacancies creates more active sites and leads to higher electroconductivity, which contribute to the better performance. As employed as a bifunctional oxygen electrocatalyst, the resulting 3Co-LaMOH|OV@NC exhibits superior electrocatalytic activity for both ORR and OER. In assembled ZAB, it also demonstrates an excellent power density of 110.5 mW cm-2, high specific capacity of 810 mAh gZn-1, and good stability over 100 h than those of Pt/C + RuO2. Density functional theory (DFT) calculation reveals that the heterointerfaces coupled with oxygen vacancies lead to an enhanced charge state and electronic structure, which may optimize the conductivity, charge transfer, and the reaction process of catalysts. This study provides a new strategy for designing highly efficient bifunctional oxygen electrocatalysts based on rare earth oxide and hydroxides heterointerface.

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Self-assembled CoOOH on TiO2for enhanced photoelectrochemical water oxidation Xiangrong Ren, Yujin Ji, Yiyue Zhai, Ningyi Yuan, Jianning Ding, Youyong Li, Junqing Yan, Shengzhong Frank Liu 2021, 60(9): 512-521.  DOI: 10.1016/j.jechem.2020.11.038 Abstract ( 13 )   PDF (945KB) ( 4 )   The development of high-efficiency and low-cost bifunctional oxygen electrocatalysts is critical to enlarge application of zinc-air batteries (ZABs). However, it still remains challenges due to their uncontrollable factor at atomic level during the catalysts preparation, which requires the precise regulation of active sites and structure engineering to accelerate the reaction kinetics for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, a novel Co-doped mixed lanthanum oxide and hydroxide heterostructure (termed as Co-LaMOH|OV@NC) was synthesized by pyrolysis of La-MOF-NH2 with spontaneous cobalt doping. Synergistic coupling of its hollow structure, doping effect and abundant oxygen vacancies creates more active sites and leads to higher electroconductivity, which contribute to the better performance. As employed as a bifunctional oxygen electrocatalyst, the resulting 3Co-LaMOH|OV@NC exhibits superior electrocatalytic activity for both ORR and OER. In assembled ZAB, it also demonstrates an excellent power density of 110.5 mW cm-2, high specific capacity of 810 mAh gZn-1, and good stability over 100 h than those of Pt/C + RuO2. Density functional theory (DFT) calculation reveals that the heterointerfaces coupled with oxygen vacancies lead to an enhanced charge state and electronic structure, which may optimize the conductivity, charge transfer, and the reaction process of catalysts. This study provides a new strategy for designing highly efficient bifunctional oxygen electrocatalysts based on rare earth oxide and hydroxides heterointerface.

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Corrigendum to ‘‘Directional construction of Cu2S branch arrays for advanced oxygen evolution reaction” 39 (2019) 61-67 Shengjue Deng, Yanbin Shen, Dong Xie, Yangfan Lu, Xiaolong Yu, Liang Yang, Xiuli Wang, Xinhui Xia, Jiangping Tu 2021, 60(9): 522-522.  DOI: 10.1016/j.jechem.2020.11.003 Abstract ( 6 )   PDF (142KB) ( 3 )

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A comparative study on the reactivity of charged Ni-rich and Ni-poor positive electrodes with electrolyte at elevated temperatures using accelerating rate calorimetry Dongxu Ouyang, Yulong Liu, Ines Hamam, Jian Wang, Jeff Dahn 2021, 60(9): 523-530.  DOI: 10.1016/j.jechem.2021.01.036 Abstract ( 17 )   PDF (956KB) ( 10 )   The reactivity between charged Li(Li0.115Mn0.529Ni0.339Al0.017)O2 (Li-rich), single crystal Li(Ni0.8Mn0.1Co0.1)O2 (SC-NMC811), LiFePO4 (LFP) and LiMn0.8Fe0.2PO4 (LMFP) positive electrodes at different states of charge (SOCs) and traditional carbonate-based electrolyte at elevated temperatures is systematically studied using accelerating rate calorimetry (ARC). The results show that the SOC greatly affects the thermal stability of the Li-rich and SC-NMC811 when traditional carbonate-based electrolyte is used. Although an increase in the SOC increases the energy density of lithium-ion cells, it also increases the reactivity between charged Li-rich and SC-NMC811 samples with electrolyte at elevated temperatures. In comparison with SC-NMC811, the Li-rich samples are much more stable at elevated temperatures, and the latter have higher specific capacity. SC-NMC811 samples are less reactive than traditional polycrystalline NMC811. Both LFP and LMFP samples show excellent thermal stability at elevated temperatures. The substitution of Fe by Mn in the olivine series positive materials does not impact the reactivity with

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Engineering the morphology/porosity of oxygen-doped carbon for sulfur host as lithium-sulfur batteries Limin Zhang, Wenqing Zhao, Shaohui Yuan, Feng Jiang, Xingqi Chen, Yue Yang, Peng Ge, Wei Sun, Xiaobo Ji 2021, 60(9): 531-545.  DOI: 10.1016/j.jechem.2020.12.031 Abstract ( 5 )   PDF (2227KB) ( 2 )   Despite the intriguing merits of lithium-sulfur (Li-S) systems, they still suffer from the notorious “shuttling-effect” of polysulfides. Herein, carbon materials with rational tailoring of morphology and pores were designed for strong loading/adsorption with the controlling of energy-storage ability. Through rational tailoring, it is strongly verified that such engineering of evolutions result in variational of sulfur immobilization in the obtained carbon. As expected, the targeted sample delivers a stable capacity of 925 mAh g-1 after 100 loops. Supporting by the “cutting-off” manners, it is disclosed that mesopores in carbon possess more fascinated traits than micro/macropores in improving the utilization of sulfur and restraining Li2Sx (4 ≤ x ≤ 8). Moreover, the long-chain polysulfide could be further consolidated by auto-doping oxygen groups. Supported by in-depth kinetic analysis, it is confirmed that the kinetics of ion/e- transfer during charging and discharging could be accelerated by mesopores, especially in stages of the formation of solid S8 and Li2S, further improving the capacity of ion-storage in Li-S battery. Given this, the elaborate study provide significant insights into the effect of pore structure on kinetic performance about Li-storage behaviors in Li-S battery, and give guidance for improving sulfur immobilization.

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Metal-Free C3N4with plentiful nitrogen vacancy and increased specific surface area for electrocatalytic nitrogen reduction Ziming Zhao, Yu Long, Sha Luo, Yutong Luo, Ming Chen, Jiantai Ma* 2021, 60(9): 546-555.  DOI: 10.1016/j.jechem.2021.01.015 Abstract ( 6 )   PDF (1038KB) ( 2 )   As a substitute for synthetic ammonia under mild condition, electrocatalytic nitrogen reduction reaction (NRR) provides a hopeful approach for the development of ammonia. Nevertheless, the current development of NRR electrocatalysts is far from enough and a systematic research is needed to gain a better improvement. This article presents that 2D C3N4-NV with a large specific surface area and abundant nitrogen vacancies is prepared by a simple and feasible method, and used as a metal-free catalyst for electrocatalytic NRR. Experiment result and density functional theory (DFT) calculation reveal that nitrogen vacancies in 2D C3N4-NV can act as an efficient active site for catalytic NRR, which is conducive to capturing and activating N2, lowering Gibbs free energy (ΔG) in reaction and inhibiting hydrogen evolution reaction (HER) at the same time. In addition, the larger specific surface area also makes more active site exposed, which is good for the contact between the electrolyte and the active site, thus enhancing its NRR activity. The electrocatalyst shows an excellent catalytic activity for NRR in 0.1 M HCl, including Faradaic efficiency of 10.96%, NH3 yields of 17.85 μg h-1mgcat.-1, and good stability (over 20 h).

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A long-life and safe lithiated graphite-selenium cell with competitive gravimetric and volumetric energy densities Xiaoqun Qi, Qiang Jin, Fengyi Yang, Ruining Jiang, Quan Sun, Long Qie*, Yunhui Huang 2021, 60(9): 556-563.  DOI: 10.1016/j.jechem.2021.02.010 Abstract ( 8 )   PDF (1607KB) ( 5 )   Lithium-selenium (Li-Se) battery is a promising system with high theoretical gravimetric and volumetric energy densities, while its long-term cyclability is hard to realize, especially when a practical Se cathode with high Se content, high Se loading, and high density is employed. The main obstacles are the sluggish conversion kinetics of the dense Se cathodes and the continuous deterioration of the Li-metal anodes. Here, by introducing an acetonitrile (AN)-based electrolyte and replacing the Li electrode with a lithiated graphite, we successfully build a hybrid conversion-intercalation system using a high-content (80 wt%), decent-loading (3.0 mg cm-2), and low-porosity (44%) Se cathode. The as-designed lithiated graphite||Se (LG||Se) cell demonstrated a high Se utilization (97.4%), a long cycle life (3000 cycles), and an ultrahigh average Coulombic efficiency (99.98%). The cell also works well under lean-electrolyte (2 μL mg-1) condition and shows outstanding safety performance in the nail-penetrating test. The combination affords the competitive comprehensive performances, including high volumetric and gravimetric energy densities, long cycling life, and superb safety of the LG||Se cell. In addition, with a newly-designed three-electrode pouch cell, the lithiation of the graphite anodes could be done with an in-situ lithiation process, indicating the high potential of the as-proposed LG||Se cell for the practical applications.

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LiPO2F2electrolyte additive for high-performance Li-rich cathode material Bing Jiang, Jingru Li, Bi Luo, Qizhang Yan, Hao Li, Lehao Liu, Lihua Chu, Yingfeng Li, Qiaobao Zhang, Meicheng Li 2021, 60(9): 564-571.  DOI: 10.1016/j.jechem.2021.01.024 Abstract ( 7 )   PDF (1160KB) ( 2 )   Li-rich layered oxide cathodes have received considerable attention because of the high operating potential and specific capacity. However, the structural instability and parasitic reactions at high potential cause severe degradation of the electrochemical performance. In our studies, the cycling stability of Li1.14Ni0.133Co0.133Mn0.544O2 cathode is improved with LiPO2F2 electrolyte additive. After 500 cycles, the capacity retention is increased from 53.6% to 85% at 3C by LiPO2F2 modification. This performance is mainly attributed to the enhanced interfacial stability of the Li-rich cathode. Based on systematic characterization, LiPO2F2 additive was found to promote a stable interface film on the cathode surface during the cycling and mitigates the interfacial side reactions. This study provides new insights for improving high-potential Li-rich layered oxide batteries.

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A review on novel activation strategy on carbonaceous materials with special morphology/texture for electrochemical storage Yueming Li, Ziyan Pu, Qimeng Sun, Ning Pan 2021, 60(9): 572-590.  DOI: 10.1016/j.jechem.2021.01.017 Abstract ( 8 )   PDF (1669KB) ( 4 )   Various novel carbonaceous materials including carbon nanotubes, nano-onions, carbon microspheres, graphene nanosheets, and carbon microfibers with unique properties, such as tunable surface area and pore size, high chemical stability, cost-effective and facile preparation, have attracted enormous interest for many applications. Also essential, the activation processes play a critical role to achieve these valuable properties. In this review, we provide a thorough analysis of the emerging nano- and microscopic carbon species with special morphology/textures and currently available types of chemical activation agents, and novel activation strategy to enhance electrochemical performance of activated carbon material in electrical energy storage devices including supercapacitor and alkaline ions batteries. A particular emphasis is set on recent advance in activated carbon materials with special morphology/textures for supercapacitors and sodium ion batteries.

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Suppress voltage decay of lithium-rich materials by coating layers with different crystalline states Zhiwei Zhou, Ziyan Luo, Zhenjiang He, Junchao Zheng, Yunjiao Li, Cheng Yan 2021, 60(9): 591-598.  DOI: 10.1016/j.jechem.2021.01.020 Abstract ( 6 )   PDF (999KB) ( 3 )   Li-rich oxides are considered as the most commercial potential cathode materials due to the high theoretical specific discharge capacity. Here, ZrO2 in different crystalline states are applied as the coating layers to enhance the electrochemical performance of hollow Li[Li0.2Mn0.54Ni0.13Co0.13]O2 materials. Meanwhile, a series of characterizations (XRD, SEM, TEM, EDX etc.) are conducted to compare the effects of ZrO2 coating layer with different crystalline states on the host material. The results elucidate that the Li-rich Mn-based material with the polycrystal ZrO2 coating layer has a slight advantage in rate performance, while the host material with the single crystal ZrO2-coating layer has a better cycling performance and effectively suppresses voltage decay with the effect of excellently inhibiting layered to spinel-like phase transition and metal dissolution during charging and discharging process.

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Additive engineering for stable halide perovskite solar cells Carlos Pereyra, Haibing Xie*, Mónica Lira-Cantu* 2021, 60(9): 599-634.  DOI: 10.1016/j.jechem.2021.01.037 Abstract ( 15 )   PDF (3009KB) ( 6 )   Halide perovskite solar cells (PSCs) have already demonstrated power conversion efficiencies above 25%, which makes them one of the most attractive photovoltaic technologies. However, one of the main bottlenecks towards their commercialization is their long-term stability, which should exceed the 20-year mark. Additive engineering is an effective pathway for the enhancement of device lifetime. Additives applied as organic or inorganic compounds, improve crystal grain growth enhancing power conversion efficiency. The interaction of their functional groups with the halide perovskite (HP) absorber, as well as with the transport layers, results in defect passivation and ion immobilization improving device performance and stability. In this review, we briefly summarize the different types of additives recently applied in PSC to enhance not only efficiency but also long-term stability. We discuss the different mechanism behind additive engineering and the role of the functional groups of these additives for defect passivation. Special emphasis is given to their effect on the stability of PSCs under environmental conditions such as humidity, atmosphere, light irradiation (UV, visible) or heat, taking into account the recently reported ISOS protocols. We also discuss the relation between deep-defect passivation, non-radiative recombination and device efficiency, as well as the possible relation between shallow-defect passivation, ion immobilization and device operational stability. Finally, insights into the challenge and criteria for additive selection are provided for the further stability enhancement of PSCs.

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Mixed polyanion cathode materials: Toward stable and high-energy sodium-ion batteries Along Zhao, Yongjin Fang*, Xinping Ai, Hanxi Yang, Yuliang Cao* 2021, 60(9): 635-648.  DOI: 10.1016/j.jechem.2021.01.014 Abstract ( 17 )   PDF (1685KB) ( 6 )   Sodium-ion batteries (SIBs) are considered as one of the most fascinating alternatives to lithium-ion batteries for grid-scale energy storage applications because of the low cost and wide abundance of sodium resources. Among various cathode materials, mixed polyanion compounds come into the spotlight as promising electrode materials due to their superior electrochemical properties, such as high working voltage, long cycling stability, and facile reaction kinetics. In this review, we summarize the recent development in the exploration of different mixed polyanion cathode materials for SIBs. We provide a comprehensive understanding of the structure-composition-performance relationship of mixed polyanion cathode materials together with the discussion of their sodium storage mechanisms. It is anticipated that further innovative works on the material design of advanced cathode materials for batteries can be inspired.

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Active oxygen center in oxidative coupling of methane on La2O3catalyst Xiaohong Zhou, Yaoqi Pang, Zebang Liu, Evgeny I. Vovk, Alexander P. van Bavel, Shenggang Li, Yong Yang 2021, 60(9): 649-659.  DOI: 10.1016/j.jechem.2021.01.008 Abstract ( 9 )   PDF (758KB) ( 3 )   La2O3 catalyzed oxidative coupling of methane (OCM) is a promising process that converts methane directly to valuable C2 (ethylene and ethane) products. Our online MS transient study results indicate that pristine surface without carbonate species demonstrates a higher selectivity to C2 products, and a lower light-off temperature as well. Further study is focused on carbonate-free La2O3 catalyst surface for identification of active oxygen species associated with such products behavior. XPS reveals unique oxygen species with O 1 s binding energy of 531.5 eV correlated with OCM catalytic activity and carbonates removal. However, indicated thermal stability of this species is much higher than the surface peroxide or superoxide structures proposed by earlier computation models. Motivated by experimental results, DFT calculations reveal a new more stable peroxide structure, formed at the subsurface hexa-coordinate lattice oxygen sites, with energy 2.18 eV lower than the previous models. The new model of subsurface peroxide provides a perspective for understanding of methyl radicals formation and C2 products selectivity in OCM over La2O3 catalyst.