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2021, Vol. 61, No. 10　Online: 15 October 2021

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Adjusting the SnZn defects in Cu2ZnSn(S,Se)4 absorber layer via Ge4+ implanting for efficient kesterite solar cells Yueqing Deng, Zhengji Zhou, Xin Zhang, Lei Cao, Wenhui Zhou, Dongxing Kou, Yafang Qi, Shengjie Yuan, Zhi Zheng, Sixin Wu 2021, 61(10): 1-7.  DOI: 10.1016/j.jechem.2021.02.011 Abstract ( 3 )   PDF (3203KB) ( 2 )   The development of kesterite photovoltaic solar cells has been hindered by large open-circuit voltage (Voc) deficit. Recently, SnZn deep point defect and associative defect cluster have been recognized as the main culprit for the Voc losses. Therefore, manipulating the deep-level donor of SnZn antisite defects is crucial for breaking through the bottleneck of present Cu2ZnSn(S,Se)4 (CZTSSe) photovoltaic technology. In this study, the SnZn deep traps in CZTSSe absorber layer are suppressed by incorporation of Ge. The energy levels and concentration of SnZn defects measured by deep-level transient spectroscopy (DLTS) decrease significantly. In addition, the grain growth of CZTSSe films is also promoted due to Ge implantation, yielding the high quality absorber layer. Consequently, the efficiency of CZTSSe solar cells increases from 9.15% to 11.48%, largely attributed to the 41 mV Voc increment.

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Residual solvent extraction via chemical displacement for efficient and stable perovskite solar cells Min Fang, Lei Tao, Wen Wu, Qi Wei, Yingdong Xia, Ping Li, Xueqin Ran, Qi Zhong, Guichuan Xing, Lin Song, Peter Müller-Buschbaum, Hui Zhang, Yonghua Chen 2021, 61(10): 8-14.  DOI: 10.1016/j.jechem.2021.02.017 Abstract ( 6 )   PDF (2939KB) ( 4 )   Solvent residue is inevitable to occur in solution processed thin films, but its influence on the thin film quality has not been identified and addressed to date. Methylammonium acetate (MAAc) ionic liquid has recently been realized as an environmentally friendly solvent for solution processed perovskites. The specific high viscosity, low vapor pressure and strong association with perovskite precursor of the MAAc solvent is a double-edged sword, which endowed an advantageously ambient air operational and anti-solvent free perovskite deposition, but the MAAc is likely to be retained within the film and bring in detrimental effects on device performance of the corresponding solar cells. Herein, we reported a novel route to eliminate the residual solvent via a facial hydrochloric acid (HCl) annealing post-treatment (HAAP). In particular, chemical displacement reaction between the incorporated HCl and residual MAAc can be initiated to form volatile MACl and HAc, efficiently extracting MAAc residue. In the meanwhile, the stimulated mass transport via downward penetration and upward escape can trigger secondary perovskite growth with enlarged grain size and smoothened surface, leading to reduced defect state and improved interfacial contact intimacy, and also partial chloride ions are able to enter the crystal lattice to stabilize perovskite phase structure. As a result, a champion efficiency up to 20.78% originating from enhanced Voc was achieved, and more than 96% of its initial efficiency can be maintained after 1000 h shelf-storage.

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Boosting alkaline hydrogen electrooxidation on an unconventional fcc-Ru polycrystal Tonghui Zhao, Dongdong Xiao, Yi Chen, Xi Tang, Mingxing Gong, Shaofeng Deng, Xupo Liu, Jianmin Ma, Xu Zhao, Deli Wang 2021, 61(10): 15-22.  DOI: 10.1016/j.jechem.2020.12.008 Abstract ( 2 )   PDF (6828KB) ( 2 )   Precisely controlling the crystalline phase structure and exposed facets at the atomic level opens up a new avenue for efficient catalyst design. Along this line, we report an unconventional face-centered cubic (fcc) Ru with twinned structure and stacking-fault defects as a competent electrocatalyst towards alkaline hydrogen oxidation reaction (HOR), which is now a major obstacle for the commercialization of anion exchange membrane fuel cells (AEMFC). With conventional hexagonal close packing (hcp) Ru as the counterpart, a novel scope from the phase-engineering is introduced to identify the activity origin and provide fundamental understanding of the sluggish HOR kinetics in alkaline medium. Systematic electrochemical analysis assisted by deconvoluting the hydrogen (H) desorption peaks indicates the superior performance of fcc Ru origins from the structure defects and higher proportion of the most active sites. DFT calculations, together with CO-stripping voltammograms further corroborate the stronger hydroxyl species (OH*) affinity lead to the higher activity on these sites. Meanwhile, it also demonstrates the H* adsorption/desorption on polycrystalline Ru among the conventional “hydrogen region” is accompanied by the surface bound OH* in alkaline medium, which is of great significance for subsequent alkaline HOR exploration and catalyst design.

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Room-temperature fast assembly of 3D macroscopically porous graphene frameworks for binder-free compact supercapacitors with high gravimetric and volumetric capacitances Sen Wang, Xiao Wang, Chenglin Sun, Zhong-Shuai Wu 2021, 61(10): 23-28.  DOI: 10.1016/j.jechem.2021.01.019 Abstract ( 4 )   PDF (7405KB) ( 2 )   Synthesis and applications of three-dimensional (3D) porous graphene frameworks (GFs) have attracted extensive interest owing to their intriguing advantages of high specific surface area, enriched porosity, excellent electrical conductivity, exceptional compressibility and processability. However, it is still challenging for economically viable, fast and scalable assembly of 3D GFs at room-temperature. Herein, we reported a one-step scalable strategy for fast self-assembly of graphene oxide into 3D macroscopically porous GFs, with assistance of polyoxometalates (POM) as functional cross-linker and hydrazine hydrate as reductant at room-temperature. The resulting 3D interconnected macroporous POM-GFs uniformly decorated with ultrasmall POM nanoclusters were directly processed into binder-/additive-free film compact electrodes (1.68 g cm-3) with highly aligned, layer-stacked structure and electrically conductivity (622 S m-1) for high-performance supercapacitors, showing an impressive gravimetric capacitance of 205 F g-1, volumetric capacitance of 334 F cm-3 at 1 mV s-1, and remarkable cycling stability with capacitance retention of 83% after 10,000 cycles, outperforming the most reported GFs. Further, the solid-state supercapacitors offered excellent gravimetric capacitance of 157 F g-1, exceptionally volumetric capacitance of 115 F cm-3 at 2 mV s-1 based on single electrode, and volumetric energy density of 2.6 mWh cm-3. Therefore, this work will open novel opportunities to room-temperature fast assembly of 3D porous graphene architectures for high-energy-density supercapacitors.

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Realization of high performance for PM6:Y6 based organic photovoltaic cells Runnan Yu, Guangzheng Wu, Zhan'ao Tan 2021, 61(10): 29-46.  DOI: 10.1016/j.jechem.2021.01.027 Abstract ( 10 )   PDF (14649KB) ( 5 )   With advances in material science and a more in-depth understanding of device engineering, the power conversion efficiency (PCE) of solution-processed organic photovoltaic (OPV) cells have significantly boosted in the past few years. In 2019, a high PCE of 15.7% was achieved in the OPV cells adopting a wide bandgap polymer PM6 and a new emerging non-fullerene acceptor Y6. Such outstanding performance has attracted lots of research attention, driving considerable efforts to improve or take advantage of the high-performance PM6:Y6-based system. In this review, we first concentrate on the structural characteristics of PM6 and Y6 with the focus on understanding why their combination for OPV application can obtain such high efficiency. We also update the recent progress in highly efficient PM6:Y6-based OPV cells via various optimizing strategies. Then we summarize the other applications of the PM6:Y6-based system in semi-transparent, flexible or laye-by-layer devices. The prospects for future OPV studies will be suggested in the end.

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Mixed structures as a new strategy to develop outstanding oxides-based cathode materials for sodium ion batteries: A review Charifa Hakim, Noha Sabi, Ismael Saadoune 2021, 61(10): 47-60.  DOI: 10.1016/j.jechem.2021.02.027 Abstract ( 7 )   PDF (15694KB) ( 6 )   Sodium ion batteries (SIBs) are an exciting alternative for post-lithium energy storage. They can be regarded as a promising and cost-efficient solution for grid applications as they exhibit similar ‘rocking chair’ mechanism as lithium ion batteries, in addition to the abundance and low cost of sodium resources. Indeed, electrode materials, electrolytes, separators and smart design strategies are under spot and researchers are competing to come up with the ideal battery. Layered oxides with mixed structures are regarded as new concept that can offer a set of desired structural and energetic properties and are an attractive choice for next generation sodium ion batteries. However, unlocking this system chemistry, kinetics and reliable understanding of the intercalation/deintercalation mechanism upon electrochemical cycling is quite challenging. This review, through the examination of literature, gives a brief summary of the research progress and recent advances in the investigation of electrode materials based on layered oxides with mixed structures for sodium ion batteries. This new strategy leads in fact to positive electrodes with enhanced energetic performance as they consist of a combination of the energetic or/and structural properties of the existing structures.

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Sodiophilic and conductive carbon cloth guides sodium dendrite-free Na metal electrodeposition Haijun Liu, Markus Osenberg, Ling Ni, André Hilger, Libao Chen, Dong Zhou, Kang Dong, Tobias Arlt, Xiayin Yao, Xiaogang Wang, Ingo Manke, Fu Sun 2021, 61(10): 61-70.  DOI: 10.1016/j.jechem.2021.03.004 Abstract ( 6 )   PDF (10393KB) ( 3 )   Sodium metal battery (SMB) technology is one of the most promising candidates for next-generation rechargeable energy storage systems due to its high theoretical capacity and economical cost-effectiveness. Unfortunately, its practical implementation is hindered by several challenges including short life-span and fast capacity decay, which is closely related to the uncontrollable generation of the sodium dendrites. Herein, a nitrogen and oxygen co-doped three-dimensional carbon cloth with hollow tubular fiber units was constructed as the host material for Na plating (Na@CC) to tackle these challenges. The obtained composite electrode can effectively reduce the nucleation overpotential of Na, guide the homogeneous Na+ flux, increase the kinetics of Na electrodeposition, lower the effective current density and eventually suppress the formation of electrochemically inactive Na dendrites. As a result, batteries built with the Na@CC composites exhibited stable long-term cycling stability. To gain an in-depth and comprehensive understanding of such phenomena, non-destructive and three-dimensional synchrotron X-ray tomography was employed to investigate the cycled batteries. Moreover, the COMSOL Multiphysics simulation was further employed to reveal the Na electrodeposition mechanisms. The current work not only showcases the feasibility of currently proposed sodiophilic 3D Na@CC composite electrode but also provides fundamental insights into the underlying working mechanisms that govern its outstanding electrochemical performance.

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Mo3(C6X6)2 (X = NH,S,O) monolayers: two-dimensional conductive metal-organic frameworks as effective electrocatalysts for the nitrogen reduction reaction Juan Zhang, Xinyue Zhu, Weixiang Geng, Tianchun Li, Manman Li, Chubo Fang, Xiaocao Shan, Yafei Li, Yu Jing 2021, 61(10): 71-76.  DOI: 10.1016/j.jechem.2021.02.029 Abstract ( 3 )   PDF (4949KB) ( 2 )

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Oxygen-vacancy-anchoring NixOy loading towards efficient hydrogen evolution via photo-thermal coupling reaction Qiliang Wu, Zheng Li, Xuhan Zhang, Chenyu Xu, Mingjiang Ni, Kefa Cen, Yanwei Zhang 2021, 61(10): 77-87.  DOI: 10.1016/j.jechem.2021.03.007 Abstract ( 4 )   PDF (7020KB) ( 3 )   Oxygen vacancy (VO) is a significant component in defect engineering. The present work reports the anchoring effects of initial VO for further loading modifications and the reducing capacity of photo-induced VO for pure water splitting. Herein, we propose Ni-loaded Cu-doped TiO2 (NCT) materials by successive doping and loading. The continuously added Ni ions should accumulate around the VOs and gradually grow into complete nickel oxide crystals, achieving a higher average valence state of the Ni species. NiO crystals can be detected on a 0.5% NCT sample, while the structure of Ni2O3 has been confirmed with a higher nickel mass ratio. Moreover, the introduction of nickel oxide effectively improves the photochemical and electrochemical performance by the interface charge separation, finally reaching an H2 yield of 30.6 μmol/g-cat on 0.5% NCT for VO-based photo-thermal coupling reaction, which consists of VO generation in photo and VO consumption in thermal environment. In situ infrared spectroscopy further indicated that the presence of high valence state nickel oxide hindered the H2 formation but effectively promoted the conventional oxidizing reaction, with an H2 yield of 20.6 mmol/g-cat in a methanol-water reaction on the 2.0% NCT material. In summary, VO controls the morphological structure of Ni loading and produces diverse effects for reactions with dissimilar mechanisms, which provides a novel way to design modifications for promoting various chemical reactions.

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Ionic thermoelectric materials and devices Dan Zhao, Alois Würger, Xavier Crispin 2021, 61(10): 88-103.  DOI: 10.1016/j.jechem.2021.02.022 Abstract ( 11 )   PDF (4610KB) ( 8 )   The tremendous amount of wasted heat from solar radiation and industry dissipation has motivated the development of thermoelectric concepts that directly convert heat into electricity. The main challenge in practical applications for thermoelectrics is the high cost from both materials and manufacturing. Recently, breakthrough progresses in ionic thermoelectrics open up new possibilities to charge energy storage devices when submitted to a temperature gradient. The charging voltage is internally from the ionic Seebeck effect of the electrolyte between two electrodes. Hence electrolytes with high thermoelectric figure of merit are classified as ionic thermoelectric materials. Most ionic thermoelectric materials are composed of abundant elements, and they can generate hundreds of times larger thermal voltage than that of electronic materials. This emerging thermoelectric category brings new hope to fabricate low cost and large area heat-to-energy conversion devices, and triggers a renewed interest for ionic thermodiffusion. In this review, we summarize the state of the art in the new field of ionic thermoelectrics, from the driving force of the ionic thermodiffusion to material and application developments. We present a general map of ionic thermoelectric materials, discuss the unique characters of each type of the reported electrolytes, and propose potential optimization and future topics of ionic thermoelectrics.

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Rechargeable metal (Li, Na, Mg, Al)-sulfur batteries: Materials and advances Xue Liu, Yan Li, Xu Xu, Liang Zhou, Liqiang Mai 2021, 61(10): 104-134.  DOI: 10.1016/j.jechem.2021.02.028 Abstract ( 8 )   PDF (24921KB) ( 4 )   Energy and environmental issues are becoming more and more severe and renewable energy storage technologies are vital to solve the problem. Rechargeable metal (Li, Na, Mg, Al)-sulfur batteries with low-cost and earth-abundant elemental sulfur as the cathode are attracting more and more interest for electrical energy storage in recent years. Lithium-sulfur (Li-S), room-temperature sodium-sulfur (RT Na-S), magnesium-sulfur (Mg-S) and aluminum-sulfur (Al-S) batteries are the most prominent candidates among them. Many obvious obstacles are hampering the developments of metal-sulfur batteries. Li-S and Na-S batteries are encumbered mainly by anode dendrite issues, polysulfides shuttle and low conductivity of cathodes. Mg-S and Al-S batteries are short of suitable electrolytes. In this review, relationships between various employed nanostructured materials and electrochemical performances of metal-sulfur batteries have been demonstrated. Moreover, the selections of suitable electrolytes, anode protection, separator modifications and prototype innovations are all crucial to the developments of metal-sulfur batteries and are discussed at the same time. Herein, we give a review on the advances of Li-S, RT Na-S, Mg-S and Al-S batteries from the point of view of materials, and then focus on perspectives of their future developments.

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Ordered lithium ion channels of covalent organic frameworks with lithiophilic groups enable uniform and efficient Li plating/stripping Xuyan Ni, Jie Liu, Haoqing Ji, Libao Chen, Tao Qian, Chenglin Yan 2021, 61(10): 135-140.  DOI: 10.1016/j.jechem.2021.03.006 Abstract ( 13 )   PDF (3159KB) ( 3 )

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Annealing-free alcohol-processable MoOX anode interlayer enables efficient light utilization in organic photovoltaics Ke Yang, Shanshan Chen, Yongli Zhou, George Omololu Odunmbaku, Zhenghong Xiong, Qianguang Yang, Ming Wang, Zhipeng Kan, Zeyun Xiao, Shirong Lu, Kuan Sun 2021, 61(10): 141-146.  DOI: 10.1016/j.jechem.2021.03.010 Abstract ( 3 )   PDF (5076KB) ( 2 )   Molybdenum oxide (MoOX) is a commonly used hole extraction material in organic photovoltaics. The MoOX interlayer is deposited typically via thermal evaporation in vacuum. To meet the need for roll-to-roll manufacturing, solution processing of MoOX without post-annealing treatment is essential. Herein, we demonstrate an effective approach to produce annealing-free, alcohol-processable MoOX anode interlayers, namely S-MoOX, by utilizing the bis(catecholato) diboron (B2Cat2) molecule to modify the surface oxygen sites in MoOX. The formation of surface diboron-oxygen complex enables the alcohol solubility of S-MoOX. An enhanced light utilization is realized in the S-MoOX-based organic photovoltaics. This affords a superior short-circuit current density (JSC) close to 26 mA cm-2 and ultimately a high power-conversion efficiency (PCE) of 15.2% in the representative PM6:Y6 based inverted OPVs, which is one of the highest values in the inverted OPVs using an as-cast S-MoOX anode interlayer.

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Designing electrolyte additives for lithium metal batteries through multi-factor principle Biyi Xu, Yutao Li 2021, 61(10): 147-148.  DOI: 10.1016/j.jechem.2021.02.030 Abstract ( 6 )   PDF (1786KB) ( 4 )

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The pitfalls in electrocatalytic nitrogen reduction for ammonia synthesis Huimin Liu, Néstor Guijarro, Jingshan Luo 2021, 61(10): 149-154.  DOI: 10.1016/j.jechem.2021.01.039 Abstract ( 7 )   PDF (905KB) ( 4 )   Ammonia synthesis by electrocatalytic nitrogen reduction reaction (EC-NRR) has gained momentum in recent years fueled by its potential to operate at ambient conditions, unlike the highly energy-intensive yet long-standing Haber-Bosch process. However, the large disparity of the yields and Faradic efficiencies reported for EC-NRR raises serious concerns about the reliability of the experimental results. In this perspective, we elaborate on the potential sources of error when assessing EC-NRR and update the testing protocols to circumvent them, and more importantly, we pose a general call for consensus on ammonia production analysis and reporting to lay the solid foundations that this burgeoning field requires to thrive.

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Effect of the protection layer formed by cross-linked gelatin on the stability and performance of glucose and oxygen fuel cells Kyuhwan Hyun, Joonyoung Lee, Suhyeon Kang, Yongchai Kwon 2021, 61(10): 155-162.  DOI: 10.1016/j.jechem.2021.01.033 Abstract ( 7 )   PDF (8307KB) ( 2 )   A glucose oxidation catalyst comprising carbon nanotube, tetrathiafulvalene (TTF), gelatin, glutaraldehyde (GA) and glucose oxidase (GOx) (CNT/[TTF-GOx]/Gelatin + GA) is suggested to enhance the reactivity of glucose oxidation reaction (GOR), and the performance and stability of enzymatic biofuel cells (EBCs) using this catalyst. In this catalyst, TTF is used as mediator to transfer electron effectively, while GA is crosslinked to gelatin to form non-soluble network. The structure prevents the dissolution of gelatin from aqueous electrolyte and reduces the leaching-out of GOx and TTF molecules. To confirm the crosslinking effect of GA and gelatin, Fourier-transform infrared spectroscopy (FT-IR) and electrochemical evaluations are utilized. According to FT-IR analysis, it was observed that the amide I peak shifted after crosslinking. This is evidence showing the appropriate network formation and the reactivity of CNT/[TTF-GOx]/Gelatin + GA is well preserved even after multiple potential cycling. In addition, its GOx activity is regularly monitored for one month and the measurements prove that the structure prevents the leaching out of GOx molecules. Based on that, EBC using the anodic catalyst shows excellent performances, such as open circuit voltage of 0.75 V and maximum power density of 184 μW/cm2.

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Reducing defect of inorganic perovskite film by sulphur-containing Lewis base for robust photodetectors Jian Du, Jialong Duan, Xiya Yang, Qingwei Zhou, Yanyan Duan, Tingting Zhang, Qunwei Tang 2021, 61(10): 163-169.  DOI: 10.1016/j.jechem.2021.02.004 Abstract ( 7 )   PDF (5108KB) ( 2 )   Sluggish charge transfer in perovskite film induced by inherent defects such as uncoordinated Pb2+ undoubtedly hinders the rapid response of self-powered photovoltaic-typed detector. Based on interaction between Lewis acids and bases, herein, we employ thiourea molecule as a multifunctional Lewis base to significantly improve the quality of all-inorganic CsPbIBr2 perovskite film. After careful characterizations, the quality of perovskite film has been well regulated. Arising from the reduced defect and the reinforced the interfacial charge extraction owing to the strong interaction between uncoordinated Pb2+ ions and the -C = S groups in thiourea and the formation of hydrogen bond at perovskite/TiO2 interface, an enhanced responsivity of 0.335 A W-1 and specific detectivity of 3.92 × 1012 Jones has been achieved for the self-powered, carbon-electrode based photodetector, which is comparable to the state-of-the-art device based on CsPbIBr2 film. More importantly, the device free of encapsulation remains 82.8% of initial performance after storage over 56 days in ambient atmosphere, promoting the practical deployment of perovskite products.

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Cobalt coordination with pyridines in sulfurized polyacrylonitrile cathodes to form conductive pathways and catalytic M-N4S sites for accelerated Li-S kinetics Amir Abdul Razzaq, Ganwen Chen, Xiaohui Zhao, Xietao Yuan, Jiapeng Hu, Ziwei Li, Yufeng Chen, Jiabin Xu, Rahim Shah, Jun Zhong, Yang Peng, Zhao Deng 2021, 61(10): 170-178.  DOI: 10.1016/j.jechem.2021.01.012 Abstract ( 3 )   PDF (6472KB) ( 2 )   Sulfurized polyacrylonitrile (SPAN) represents a unique class of cathode material for lithium sulfur (Li-S) batteries as it eradicates the polysulfides shuttling issue in carbonate-based electrolyte. However, due to the essential chemical S-linking and organic nature of SPAN, the active mass percentage and rate capability are two bottleneck issues preventing its ultimate deployment outside of laboratories. In the current work, aiming to endow both the charge conductivity and catalytic activity to SPAN for maximizing the redox kinetics of S conversion, a freestanding nanofibrous SPAN cathode embedding conductive CNTs and atomically dispersed Co centers is fabricated via multivariate electrospinning. While the CNTs enable dramatically enhancing the fiber conductivity and generating mesoscopic porosity for facilitating charge and mass transportation, the cross-linking of SPAN by Co-N4S motifs creates extra charge conduction pathways and further serves as the catalytic active sites for expediting redox S conversion. As a result, an extraordinary Li-SPAN performance is achieved with a high specific capacity up to 1856 mAh g-1@0.2 C, a superb rate capability up to 10 C, and an ultra-long battery life up to 1500 cycles@1 C. Consequently, our study here provides insights into the adoption of coordination chemistry to maximize the sulfur utilization by ensuring a more complete redox conversion from SPAN to Li2S, and vice versa.

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Activity origin and alkalinity effect of electrocatalytic biomass oxidation on nickel nitride Bo Zhou, Chung-Li Dong, Yu-Cheng Huang, Nana Zhang, Yandong Wu, Yuxuan Lu, Xu Yue, Zhaohui Xiao, Yuqin Zou, Shuangyin Wang 2021, 61(10): 179-185.  DOI: 10.1016/j.jechem.2021.02.026 Abstract ( 3 )   PDF (4027KB) ( 2 )   Electro-oxidation of 5-hydroxymethylfurfural (HMFOR) is a promising green approach to realize the conversion of biomass into value-added chemicals. However, considering the complexity of the molecular structure of HMF, an in-depth understanding of the electrocatalytic behavior of HMFOR has rarely been investigated. Herein, the electrocatalytic mechanism of HMFOR on nickel nitride (Ni3N) is elucidated by operando X-ray absorption spectroscopy (XAS), in situ Raman, quasi in situ X-ray photoelectron spectroscopy (XPS), and operando electrochemical impedance spectroscopy (EIS), respectively. The activity origin is proved to be Ni2+δN(OH)ads generated by the adsorbed hydroxyl group. Moreover, HMFOR on Ni3N relates to a two-step reaction: Initially, the applied potential drives Ni atoms to lose electrons and adsorb OH- after 1.35 VRHE, giving rise to Ni2+δN(OH)ads with the electrophilic oxygen; then Ni2+δN(OH)ads seizes protons and electrons from HMF and leaves as H2O spontaneously. Furthermore, the high electrolyte alkalinity favors the HMFOR process due to the increased active species (Ni2+δN(OH)ads) and the enhanced adsorption of HMF on the Ni3N surface. This work could provide an in-depth understanding of the electrocatalytic mechanism of HMFOR on Ni3N and demonstrate the alkalinity effect of the electrolyte on the electrocatalytic performance of HMFOR.

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High-efficiency ultra-thin Cu2ZnSnS4 solar cells by double-pressure sputtering with spark plasma sintered quaternary target Ping Fan, Zhigao Xie, Guangxing Liang, Muhammad Ishaq, Shuo Chen, Zhuanghao Zheng, Chang Yan, Jialiang Huang, Xiaojing Hao, Yi Zhang, Zhenghua Su 2021, 61(10): 186-194.  DOI: 10.1016/j.jechem.2021.01.026 Abstract ( 5 )   PDF (2527KB) ( 5 )   In recent years, Cu2ZnSnS4 (CZTS) semiconductor materials have received intensive attention in the field of thin-film solar cells owing to its non-toxic and low-cost elements. In this work, double-pressure sputtering technology is applied to obtain highly efficient and ultra-thin (~450 nm) pure Cu2ZnSnS4 (CZTS) solar cell. Using mixed materials with sulfides and copper powder as a quaternary target via spark plasma sintering (SPS) method and adopting double-layer sputtering (high + low pressure), a highly adhesive and large-grained CZTS thin film is achieved. As a result, the damage to the surface of Mo contact is decreased so that the reflectivity of incident light can be improved. Moreover, the composition of CZTS film was more uniform and the secondary phase separation at the Mo interface was reduced. Therefore, the interface defect state and deep level defect density in corresponding device with double-pressure is reduced and the ratio of depletion thickness to absorption layer thickness can reached to 0.58, which promoted the collection of photogenerated carriers. Finally, an efficiency of 9.3% for ultra-thin (~450 nm) CZTS film solar cell is obtained.

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Visible-light driven room-temperature coupling of methane to ethane by atomically dispersed Au on WO3 Xing Yang Wu, Zhiyuan Tang, Xiaoxu Zhao, Xin Luo, Stephen John Pennycook, Song Ling Wang 2021, 61(10): 195-202.  DOI: 10.1016/j.jechem.2021.03.029 Abstract ( 4 )   PDF (4170KB) ( 3 )   Gold (Au) as co-catalyst is remarkable for activating methane (CH4), especially atomically dispersed Au with maximized exposing active sites and specific electronic structure. Furthermore, singlet oxygen (1O2) typically manifests a mild redox capacity with a high selectivity to attack organic substrates. Peroxomonosulfate (PMS) favors to produce oxidative species 1O2 during the photocatalytic reactions. Thus, combining atomic Au as co-catalyst and 1O2 as oxidant is an effective strategy to selectively convert CH4. Herein, we synthesized atomically dispersed Au on WO3 (Au/WO3), where Au was in the forms of single atoms and clusters. At room temperature, such Au/WO3 exhibited enhanced photocatalytic conversion of CH4 to CH3CH3 with a selectivity, up to 94%, under visible light. The radicals-pathway mechanism of CH4 coupling has also been investigated through detection and trapping experiment of active species. Theoretical calculations further interpret the electronic structure of Au/WO3 and tip-enhanced local electric field at the Au sites for promoting CH4 conversion.

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Catalytic activity of Cu/ZnO catalysts mediated by MgO promoter in hydrogenation of methyl acetate to ethanol Fang Zhang, Zhiyang Chen, Xudong Fang, Hongchao Liu, Yong Liu, Wenliang Zhu 2021, 61(10): 203-209.  DOI: 10.1016/j.jechem.2021.03.028 Abstract ( 7 )   PDF (3398KB) ( 7 )   Hydrogenation of methyl acetate is a key step in ethanol synthesis from dimethyl ether carbonylation and Cu-based catalysts are widely studied. We report here that the hydrogenation activity of Cu/ZnO catalysts can be enhanced by the addition of MgO promoter. The evolution of crystal phases during coprecipitation and the physicochemical properties of calcined and reduced catalysts by X-ray diffraction (XRD), thermogravimetric (TG)-mass spectrometry (MS), Brunauer-Emmett-Teller (BET), transmission electron microscopy (TEM), N2O titration, in situ CO-Fourier transform infrared spectroscopy (FTIR) and H2-temperature programmed reduction (H2-TPR) reveal that the promoter effect likely lies in the presence of Mg2+. A proper amount of Mg2+ mediates the precipitation process of Cu and Zn, leading to preferable formation of aurichalcite (CuxZn1-x)5(CO3)2(OH)6 crystal phase and a small amount of basic carbonates such as hydrozincite Zn5(CO3)2(OH)6 and malachite Cu2CO3(OH)2. The presence of aurichalcite strengthens the interaction between Cu and Zn species, and thus enhances the dispersity of Cu0 species and helps generation of Cu+ species on reduced catalysts. Furthermore, the performance of Cu/ZnO catalysts exhibits an optimal dependence on the Mg loading, i.e., 17.5%. However, too much Mg2+ in the precipitation liquid prohibits formation of aurichalcite but enhances formation of basic nitrates, leading to a dramatically reduced hydrogenation activity. These findings may find applications for optimization of other Cu-based catalysts in a wider range of hydrogenation reactions.

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Svacancy modulated ZnxCd1-xS/CoP quantum dots for efficient H2 evolution from water splitting under visible light Qi Xie, Min Wang, Yong Xu, Xiaoke Li, Xin Zhou, Liang Hong, Luhua Jiang, Wen-Feng Lin 2021, 61(10): 210-218.  DOI: 10.1016/j.jechem.2021.03.019 Abstract ( 3 )   PDF (6099KB) ( 2 )   Energy band structure and interfacial compatibility of heterojunctions are crucial for photocatalysts in promoting photogenerated charge separation and transfer. Here, a combined strategy of vacancy engineering and quantum effect via a facile phosphating process is reported, for the first time, to modulate the energy band structure and the interface of ZnxCd1-xS/CoP quantum dots (ZCSv/CoP QDs) heterojunction. The combined experimental and theoretical investigation revealed that phosphating process transformed CoOx QDs to CoP QDs, and more importantly, generated considerable amount of sulfur vacancies in ZCSv. As a result, a Type II ZCSv/CoP QDs heterojunction with compatible interfaces was constructed via in-situ generated P-Zn, P-Cd and S-Co bonds, which facilitated the separation and transfer of the photogenerated charge and thus resulted in a high ability towards hydrogen evolution under visible light (17.53 mmol g-1 h-1). This work provides an effective and adaptable strategy to modulate band structure and interfacial compatibility of heterojunctions via vacancy engineering and quantum effect.

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Quo vadis carbocatalysis? Robert Schlögl 2021, 61(10): 219-227.  DOI: 10.1016/j.jechem.2021.02.024 Abstract ( 3 )   PDF (1500KB) ( 3 )

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Tuning the photocatalytic water-splitting performance with the adjustment of diameter in an armchair WSSe nanotube Lin Ju, Penglan Liu, Yifan Yang, Liran Shi, Gui Yang, Li Sun 2021, 61(10): 228-235.  DOI: 10.1016/j.jechem.2021.03.037 Abstract ( 4 )   PDF (5070KB) ( 5 )   Due to the enigmatical electrostatic potential difference between the inside and outside layers, the relationship between the diameter and the photocatalytic property of the Janus transition metal dichalcogenides nanotube is still unclear. In this job, for the first time we calculate the electrostatic potential difference of the Janus WSSe armchair nanotubes with corresponding building block models through the first principles calculations. The electrostatic potential difference increases as the diameter increases. Then, it is observed that the WSSe armchair nanotubes with smaller diameter have stronger oxidation capacity, weaker reduction capacity, and higher solar-to-hydrogen conversion efficiency. Furthermore, the diminution of diameter could make the band gap drop, and even cause a direct-indirect transformation of band structure. The adjustment of diameter could also regulate the ability of adsorbing water molecules at the insider and outside layers. Moreover, the suitable band edge positions, wide optical absorbance region (to the near-infrared), outstanding solar-to-hydrogen efficiency (up to 28.99%), high carrier separation, adequate photoexcited carrier driving forces, as well as the energetic and thermal stability, render these nanotubes befitting the photocatalytic water-splitting application. Our study not only predicts a kind of ideal water-splitting photocatalyst, but also shows an effective way to improve their photocatalytic performances.

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Interfacial electron rearrangement: Ni activated Ni(OH)2 for efficient hydrogen evolution Wenda Zhong, Wenlong Li, Chenfan Yang, Jing Wu, Rong Zhao, Memona Idrees, Hui Xiang, Qin Zhang, Xuanke Li 2021, 61(10): 236-242.  DOI: 10.1016/j.jechem.2021.02.013 Abstract ( 5 )   PDF (3898KB) ( 2 )   The rational modulation of electronic structure is highly desirable to develop an efficient alkaline hydrogen evolution reaction (HER) catalyst for renewable energy applications. Metal hydroxide such as Ni(OH)2 has been proven useful for promoting alkaline HER, but the performance remains unsatisfactory. Herein, the electronic structure of Ni(OH)2 is modulated by the interfacial electron rearrangement between Ni-Ni(OH)2 heterojunction. Combined experiments with DFT simulations, the electrons of Ni species accumulate to the interfacial Ni-Ni(OH)2 sites, which modifies the d band center for promoting conversion of hydrogen intermediates and narrows the energy gap for boosting charge transfer in the HER process. Thus, the integrated electrode exhibits an efficient HER performance to drive 10 mA cm-2 at the overpotential of 72 mV with a low Tafel slope of 43 mV dec-1. Our work renders a valuable insight for understanding and rationally designing efficient catalysts in alkaline HER.

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Stress release in high-capacity flexible lithium-ion batteries through nested wrinkle texturing of graphene Jing Chen, Lei Wen, Ruopian Fang, Da-Wei Wang, Hui-Ming Cheng, Feng Li 2021, 61(10): 243-249.  DOI: 10.1016/j.jechem.2021.03.021 Abstract ( 3 )   PDF (3168KB) ( 2 )   Flexible lithium-ion batteries (LIBs) are critical for the development of next-generation smart electronics. Conversion reaction-based electrodes have been considered promising to construct high energy-density flexible LIBs, which satisfy the ever-increasing demand for practical use. However, these electrodes suffer from inferior lithium-storage performance and structural instability during deformation and long-term lithiation/delithiation. These are caused by the sluggish reaction kinetics of active-materials and the superposition of responsive strains originating from the large lithiation-induced stress and applied stress. Here, we propose a stress-release strategy through elastic responses of nested wrinkle texturing of graphene, to achieve high deformability while maintaining structural integrity upon prolonged cycles within high-capacity electrodes. The wrinkles endow the electrode with a robust and flexible network for effective stress release. The resulting electrode shows large reversible stretchability, along with excellent electrochemical performance including high specific capacity, high-rate capability and long-term cycling stability. This strategy offers a new way to obtain high-performance flexible electrodes and can be extended to other energy-storage devices.

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ChemSuChem-a memorial to Dangsheng Su Robert Schlögl, Bingsen Zhang, Qiang Zhang, Xinhe Bao 2021, 61(10): 250-252.  DOI: 10.1016/j.jechem.2021.02.008 Abstract ( 2 )   PDF (402KB) ( 2 )

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Research progress in electrospinning engineering for all-solid-state electrolytes of lithium metal batteries Manxi Wang, Yaling Wu, Min Qiu, Xuan Li, Chuanping Li, Ruiling Li, Jiabo He, Ganggang Lin, Qingrong Qian, Zhenhai Wen, Xiaoyan Li, Ziqiang Wang, Qi Chen, Qinghua Chen, Jinhyuk Lee, Yiu-Wing Mai, Yuming Chen 2021, 61(10): 253-268.  DOI: 10.1016/j.jechem.2021.02.023 Abstract ( 13 )   PDF (15023KB) ( 7 )   Owing to safety issue and low energy density of liquid lithium-ion batteries (LIBs), all-solid-state lithium metal batteries (ASLMBs) with unique all-solid-state electrolytes (SEs) have attracted wide attentions. This arises mainly from the advantages of the SEs in the suppression of lithium dendrite growth, long cycle life, and broad working temperature range, showing huge potential applications in electronic devices, electric vehicles, smart grids, and biomedical devices. However, SEs suffer from low lithium-ion conductivity and low mechanical integrity, slowing down the development of practical ASLMBs. Nanostructure engineering is of great efficiency in tuning the structure and composition of the SEs with improved lithium-ion conductivity and mechanical integrity. Among various available technologies for nanostructure engineering, electrospinning is a promising technique because of its simple operation, cost-effectiveness, and efficient integration with different components. In this review, we will first give a simple description of the electrospinning process. Then, the use of electrospinning technique in the synthesis of various SEs is summarized, for example, organic nanofibrous matrix, organic/inorganic nanofibrous matrix, and inorganic nanofibrous matrix combined with other components. The current development of the advanced architectures of SEs through electrospinning technology is also presented to provide references and ideas for designing high-performance ASLMBs. Finally, an outlook and further challenges in the preparation of advanced SEs for ASLMBs through electrospinning engineering are given.

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Internal short circuit evaluation and corresponding failure mode analysis for lithium-ion batteries Lishuo Liu, Xuning Feng, Christiane Rahe, Weihan Li, Languang Lu, Xiangming He, Dirk Uwe Sauer, Minggao Ouyang 2021, 61(10): 269-280.  DOI: 10.1016/j.jechem.2021.03.025 Abstract ( 2 )   PDF (15051KB) ( 2 )   Internal short circuit (ISC) is the major failure problem for the safe application of lithium-ion batteries, especially for the batteries with high energy density. However, how to quantify the hazard aroused by the ISC, and what kinds of ISC will lead to thermal runaway are still unclear. This paper investigates the thermal-electrical coupled behaviors of ISC, using batteries with Li(Ni1/3Co1/3Mn1/3)O2 cathode and composite separator. The electrochemical impedance spectroscopy of customized battery that has no LiPF6 salt is utilized to standardize the resistance of ISC. Furthermore, this paper compares the thermal-electrical coupled behaviors of the above four types of ISC at different states-of-charge. There is an area expansion phenomenon for the aluminum-anode type of ISC. The expansion effect of the failure area directly links to the melting and collapse of separator, and plays an important role in further evolution of thermal runaway. This work provides guidance to the development of the ISC models, detection algorithms, and correlated countermeasures.

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Oxygen migration triggering molybdenum exposure in oxygen vacancy-rich ultra-thin Bi2MoO6 nanoflakes: Dual binding sites governing selective CO2 reduction into liquid hydrocarbons Weili Dai, Jianfei Long, Lixia Yang, Shuqu Zhang, Yong Xu, Xubiao Luo, Jianping Zou, Shenglian Luo 2021, 61(10): 281-289.  DOI: 10.1016/j.jechem.2021.01.009 Abstract ( 8 )   PDF (5942KB) ( 8 )   Oxygen vacancy plays vital roles in regulating the electronic and charge distribution of the oxygen deficient materials. Herein, abundant oxygen vacancies are created during assembling the two-dimensional (2D) ultra-thin Bi2MoO6 nanoflakes into three dimensional (3D) Bi2MoO6 nanospheres, resulting in significantly improved performance for photocatalytical conversion of CO2 into liquid hydrocarbons. The increased performance is contributed by two primary sites, namely the abundant oxygen vacancy and the exposed molybdenum (Mo) atom induced by oxygen-migration, as revealed by the theoretical calculation. The oxygen vacancy (Ov) and uncovered Mo atom serving as dual binding sites for trapping CO2 molecules render the synchronous fixation-reduction process, resulting in the decline of activation energy for CO2 reduction from 2.15 eV on bulk Bi2MoO6 to 1.42 eV on Ov-rich Bi2MoO6. Such a striking decrease in the activation energy induces the efficient selective generation of liquid hydrocarbons, especially the methanol (C2H5OH) and ethanol (CH3OH). The yields of CH3OH and C2H5OH over the optimal Ov-Bi2MoO6 is high up to 106.5 and 10.3 μmol g-1 respectively, greatly outperforming that on the Bulk-Bi2MoO6.

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Amorphous urchin-like copper@nanosilica hybrid for efficient CO2 electroreduction to C2+ products Rui Yang, Zipeng Zeng, Zhen Peng, Jiafang Xie, Yiyin Huang, Yaobing Wang 2021, 61(10): 290-296.  DOI: 10.1016/j.jechem.2020.12.032 Abstract ( 4 )   PDF (4010KB) ( 3 )   Currently most of research efforts for selective electrocatalysis CO2 reduction to C2+ products have relied on crystalline Cu-based catalysts; amorphous Cu with abundant low-coordinated atoms holds greater promise for this conversion yet remains relatively underexplored. Here we report an amorphous urchin-like Cu@nanosilica hybrid synthesized by electrostatic coupling Si polyanions with Cu salt in hydrothermal processes. The Cu@nanosilica electrocatalyst displays excellent CO2 electroreduction activity and selectivity with a Faradic efficiency of 70.5% for C2+ product production, and higher stability compared to the crystalline Cu counterpart. The solar-driven CO2 electrolysis yields an energy efficiency of 20% for C2+ product production. Mechanism study reveals that the urchin-like Cu@nanosilica catalyst with amorphous Cu/Cu+ dispersion enhances CO2 adsorption and activation to facilitate generation of CO2-* and possible CO* intermediates, and suppresses hydrogen evolution concurrently. The combined effects of both aspects promote efficient C2+ product production from CO2 electroreduction.

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A novel carbon cycle process assisted by Ni/La2O3 catalyst for enhanced thermochemical CO,2 splitting Yu Kang, Yujia Han, Cong Wei, Kuo Liu, Ming Tian, Chuande Huang, Chaojie Wang, Jian Lin, Baolin Hou, Xiaoli Pan, Yang Su, Lin Li, Riguang Zhang, Yong Hao, Xiaodong Wang 2021, 61(10): 297-303.  DOI: 10.1016/j.jechem.2021.03.026 Abstract ( 1 )   PDF (4668KB) ( 2 )   Thermochemical two-step CO2 splitting is a potential approach that fixes the sustainable resource into transportable liquid fuels. However, the harsh CO2 splitting conditions, the limited oxygen release kinetics and capacity of metal oxides block further promoted the CO yield and solar-to-fuel energy efficiency. Here, we propose a different carbon cycle assisted by Ni/La2O3 via coupling methane decomposition with thermochemical CO2 splitting, replacing conventional metal oxides cycle. Superior performance was demonstrated with methane conversion reached around 94% with almost pure H2 generation. Encouragingly, CO2 conversion of 98% and CO yield of 6.9 mmol g-1 derived from CO2 were achieved, with peak CO evolution rate (402 mL min-1 g-1) of orders of magnitude higher than that in metal oxide process and outstanding thermodynamic solar-to-fuel energy efficiency (55.5% vs. 18.5%). This was relevant to the synergistic activation of La2O3 and Ni for CO2 in carbon cycle, thus improving CO2 splitting reaction with carbon species.

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Effect on electrochemical reduction of nitrogen to ammonia under ambient conditions: Challenges and opportunities for chemical fuels Lijuan Niu, Li An, Xiayan Wang, Zaicheng Sun 2021, 61(10): 304-318.  DOI: 10.1016/j.jechem.2021.01.018 Abstract ( 3 )   PDF (7065KB) ( 3 )   The nitrogen cycle plays an important role in nature, but N-containing products cannot meet human needs. The electrochemical synthesis of ammonia under ambient conditions has attracted the interest of many researchers because it provides a clean and pollution-free synthesis method; however, it has certain difficulties, including a high activation energy, multiple electron transfer, and hydrogenation. Thermodynamic factors limit the selectivity and activity of ammonia synthesis techniques. This review summarizes progress in the electrochemical synthesis of ammonia from theory and experiment. Theoretically, the reduction of nitrogen molecules is analyzed using orbit theory and the thermodynamic reaction pathways. Experimentally, we first discuss the effect of the experimental setup on the nitrogen reduction reaction, and then the four critical of catalysts, including size, electronic, coordination, and orientation effects. These issues must be considered to produce highly-efficient catalysts for electrochemical nitrogen reduction (eNRR). This review provides an overview of the eNRR to enable future researchers to design rational catalysts.

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Amorphous Se species anchored into enclosed carbon skeleton bridged by chemical bonding toward advanced K-Se batteries Li Zhou, Yongpeng Cui, Dongqing Kong, Wenting Feng, Xiuli Gao, Youguo Yan, Hao Ren, Han Hu, Qingzhong Xue, Zifeng Yan, Wei Xing 2021, 61(10): 319-326.  DOI: 10.1016/j.jechem.2021.03.027 Abstract ( 4 )   PDF (13386KB) ( 1 )   Potassium-selenium (K-Se) batteries have attracted significant attention as one of the most promising alternatives of lithium-ion storage systems owing to high energy density and low cost. In the design of Se-based cathode materials, however, the low utilization rate of active Se and the rapid dissolution of polyselenides seriously weaken the capacity and cycle stability. Therefore, how to make full use of Se species without loss during the charge and discharge process is the key to design high-performance Se-based cathode. In this paper, a 3D “water cube”-like Se/C hybrid (denoted as Se-O-PCS) is constructed with the assistance of Na2CO3 templates. Thanks to the abundant carbonate groups (CO32-) originated from the Na2CO3 templates, the molten Se species are firmly anchored into the pore of carbon skeleton by strong C-O-Se bonding. Thus, this unique Se-O-PCS model not only improves the utilization of active Se species, but also can reduce the contact with the electrolyte to inhibit the shuttle effect of polyselenides. Moreover, flexible carbon skeleton gives Se-O-PCS hybrid a good electrical conductivity and excellent structural robustness. Consequently, the resultant Se-O-PCS hybrid is endowed with an obviously enhanced K-ions storage property.

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Porous carbon layers wrapped CoFe alloy for ultrastable Zn-Air batteries exceeding 20,000 charging-discharging cycles Fang Shi, Kaiyue Zhu, Xiaoke Li, Erdong Wang, Xuefeng Zhu, Weishen Yang 2021, 61(10): 327-335.  DOI: 10.1016/j.jechem.2021.01.032 Abstract ( 2 )   PDF (4746KB) ( 2 )   Developing high active and stable bifunctional electrocatalysts towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is essential for the development of rechargeable Zn-air batteries. Herein, a facile strategy to synthesize the porous carbon layers wrapped CoFe alloy (C/CoFe) through the pyrolysis of a homogeneous mixture containing Co, Fe ions and N-doped carbon quantum dots (N-doped CQDs) was reported. The prepared carbon layers with multi-level pore structures provides more active sites and optimizes the homogeneity of the electron and mass transport. In addition, the carbon layers, which is doped by Co/Fe/N atoms, is responsible for high ORR activity, while the CoFe alloy plays a vital role in OER performance. The as-synthesized catalyst exhibits an excellent bifunctionality for electrochemical oxygen reactions, which is comparable to the commercial Pt/C and IrO2 benchmarks. Owing to the carbon layers protects CoFe alloy nanoparticles from the harsh environment, the rechargeable Zn-air battery with the C/CoFe catalyst delivers excellent stability during 20,000 charging-discharging cycles.

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Boosting polysulfide redox conversion of Li-S batteries by one-step-synthesized Co-Mo bimetallic nitride Yingying Yan, Hongtai Li, Chen Cheng, Tianran Yan, Wenping Gao, Jing Mao, Kehua Dai, Liang Zhang 2021, 61(10): 336-346.  DOI: 10.1016/j.jechem.2021.03.041 Abstract ( 6 )   PDF (13263KB) ( 1 )   Lithium-sulfur (Li-S) batteries are considered as one of the most promising next generation energy storage systems due to the high theoretical specific capacity, low cost, and environmental benignity. However, the notorious shuttle effect of polysulfides hinders the practical application of Li-S batteries. Herein, we have rationally designed and synthesized sea urchin-like Co-Mo bimetallic nitride (Co3Mo3N) in the absence of additional nitrogen sources with only one step, which was applied as the sulfur host materials for Li-S batteries. The results indicate that Co3Mo3N can efficiently anchor and catalyze the conversion of polysulfides, thus accelerating the electrochemical reaction kinetics and enabling prominent electrochemical properties. As a consequence, the S@Co3Mo3N cathode exhibits a high rate performance of 705 mAh g-1 at 3 C rate and an excellent cycling stability with a low capacity fading rate of 0.08% per cycle at 1 C over 600 cycles. Even at a high sulfur loading of 5.4 cmg cm-2, it delivers a high initial areal capacity of 4.50 mAh cm-2, which is still retained at 3.64 mAh cm-2 after 120 cycles. Furthermore, the catalytic mechanism and structural stability of Co3Mo3N during cycling were elucidated by a combination of X-ray photoelectron spectroscopy and X-ray absorption fine structure. This work highlights the strategy of structure-catalysis engineering of bimetallic nitride, which is expected to have a wide application in Li-S batteries.

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Metal cyanamides: Open-framework structure and energy conversion/storage applications Bingquan Jia, Du Sun, Wei Zhao, Fuqiang Huang 2021, 61(10): 347-367.  DOI: 10.1016/j.jechem.2021.01.006 Abstract ( 2 )   PDF (23617KB) ( 2 )   Metal cyanamides are an emerging class of functional materials with potential applications in sustainable energy conversion and storage technologies such as catalysis, supercapacitors, photoluminescence and next-gen batteries. The [NCN]2- as the anion, which is isolobal with [O]2- endows metal cyanamides with similar physicochemical properties as oxides and chalcogenides. Whereas the unique quasi-linear structure and electronic resonance between [N=C=N]2- and [N-C≡N]2- of [NCN] entity bring out superior properties beyond oxides and chalcogenides. In this review, we present research status, challenges, and the recent striking progress on the metal cyanamides in the synthesis and applications. Specifically, the characteristic structures, physicochemical properties, synthetic methods with corresponding merits/demerits and latest applications in energy conversion and storage of cyanamides are summarized. The detailed outlooks for the new compounds design, morphology manipulation and potential applications are also exhibited.

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Recent progress in Li and Mn rich layered oxide cathodes for Li-ion batteries Yiwei Li, Zhibo Li, Cong Chen, Kai Yang, Bo Cao, Shenyang Xu, Ni Yang, Wenguang Zhao, Haibiao Chen, Mingjian Zhang, Feng Pan 2021, 61(10): 368-385.  DOI: 10.1016/j.jechem.2021.01.034 Abstract ( 4 )   PDF (15919KB) ( 4 )   Li and Mn rich (LMR) layered oxides, written as xLi2MnO3·(1 - x)LiMO2 (M = Mn, Ni, Co, Fe, etc.), have been widely reported in recent years due to their high capacity and high energy density. The stable structure and superior performance of LMR oxides make them one of the most promising candidates for the next-generation cathode materials. However, the commercialization of these materials is hindered by several drawbacks, such as low initial Coulombic efficiency, the degradation of voltage and capacity during cycling, and poor rate performance. This review summarizes research progress in solving these concerns of LMR cathodes over the past decade by following three classes of strategies: morphology design, bulk design, and surface modification. We elaborate on the processing procedures, electrochemical performance, mechanisms, and limitations of each approach, and finally put forward the concerns left and the possible solutions for the commercialization of LMR cathodes.

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Chromium trioxide modified spiro-OMeTAD for highly efficient and stable planar perovskite solar cells Xiaobing Wang, Jihuai Wu, Yuqian Yang, Guodong Li, Zeyu Song, Xuping Liu, Weihai Sun, Zhang Lan, Peng Gao 2021, 61(10): 386-394.  DOI: 10.1016/j.jechem.2021.03.047 Abstract ( 4 )   PDF (6159KB) ( 2 )   Hole transporting materials (HTMs) play an unparalleled role in heightening the stability and photovoltaic performance of perovskite solar cells (PSCs). The organic small molecule spiro-OMeTAD is frequently utilized for HTM in PSCs. However, the raw spiro-OMeTAD without dopant would be harmful to the development of highly efficient PSCs, due to its unsatisfied hole mobility and conductivity. Therefore, we introduce an inorganic dopant (chromium trioxide, CrO3) into the lithium-salt doped spiro-OMeTAD. Because of the exclamatory oxidizability of CrO3, it can accelerate the oxidation of spiro-OMeTAD and thereby enhancing the hole mobility of HTM. The introduction of CrO3 not only substantially decreases the density of defects, but also adjusts spiro-OMeTAD energy band, and thus effectively suppresses the hysteresis and improving stability of PSCs. In the end, we obtained a power conversion efficiency (PCE) as high as 22.6% after doping CrO3 in spiro-OMeTAD. The facile, low cost and outstanding photovoltaic performance render CrO3 an excellent dopant for HTMs in PSCs.

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Stability of mixed-halide wide bandgap perovskite solar cells: Strategies and progress Lei Tao, Jian Qiu, Bo Sun, Xiaojuan Wang, Xueqin Ran, Lin Song, Wei Shi, QiZhong, Ping Li, Hui Zhang, Yingdong Xia, Peter Müller-Buschbaum, Yonghua Chen 2021, 61(10): 395-415.  DOI: 10.1016/j.jechem.2021.03.038 Abstract ( 12 )   PDF (19952KB) ( 8 )   Benefiting from the superior optoelectronic properties and low-cost manufacturing techniques, mixed-halide wide bandgap (WBG) perovskite solar cells (PSCs) are currently considered as ideal top cells for fabricating multi-junction or tandem solar cells, which are designed to beyond the Shockley-Queisser (S-Q) limit of single-junction solar cells. However, the poor long-term operational stability of WBG PSCs limits their further employment and hinders the marketization of multi-junction or tandem solar cells. In this review, recent progresses on improving environmental stability of mixed-halide WBG PSCs through different strategies, including compositional engineering, additive engineering, interface engineering, and other strategies, are summarized. Then, the outlook and potential direction are discussed and explored to promote the further development of WBG PSCs and their applications in multi-junction or tandem solar cells.

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Strongly coupled Te-SnS2/MXene superstructure with self-autoadjustable function for fast and stable potassium ion storage Hongyang Sun, Yelong Zhang, Xiaodan Xu, Jianwen Zhou, Fan Yang, Hao Li, Hao Chen, Yucheng Chen, Zheng Liu, Zhenping Qiu, Da Wang, Lipo Ma, Jiawei Wang, Qingguang Zeng, Zhangquan Peng 2021, 61(10): 416-424.  DOI: 10.1016/j.jechem.2021.02.001 Abstract ( 5 )   PDF (13352KB) ( 1 )   Potassium‐ion batteries (PIBs) are a promising candidate for next‐generation electric energy storage applications because of the abundance and low cost of potassium. However, the development of PIBs is limited by sluggish kinetics and huge volume expansion of anodes, leading to poor rate capability and cycling stability. Herein, an advanced superstructure anode, including Te-doped SnS2 nanosheets uniformly anchored on MXene surface (Te-SnS2/MXene), is rationally designed for the first time to boost K+ storage performance. Featuring with strong interface interaction and self-autoadjustable interlayer spacings, the Te-SnS2/MXene can efficiently accelerate electron/ion transfer, accommodate volume expansion, inhibit crack formation, and improve pseudocapacitive contribution during cycling. Thus, the novel Te-SnS2/MXene anode delivers a high reversible capacity (343.2 mAh g-1 after 50 cycles at 0.2 A g-1), outstanding rate capability (186.4 mAh g-1 at 20 A g-1), long cycle stability (165.8 mAh g-1 after 5000 cycles at 10 A g-1 with a low electrode swelling rate of only 15.4%), and reliable operation in flexible full battery. The present Te-SnS2/MXene becomes among the best transition metal-based anode materials for PIBs reported to date.

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Efficient catalytic conversion of jatropha oil to high grade biofuel on Ni-Mo2C/MCM-41 catalysts with tuned surface properties Xiangze Du, Keyao Zhou, Linyuan Zhou, Xiaomei Lei, Huiru Yang, Dan Li, Changwei Hu 2021, 61(10): 425-435.  DOI: 10.1016/j.jechem.2021.02.006 Abstract ( 7 )   PDF (12896KB) ( 1 )   The activity of Mo2C-based catalyst on vegetable oil conversion into biofuel could be greatedly promoted by tuning the carbon content, while its modification mechanism on the surface properties remained elusive. Herein, the exposed active sites, the particle size and Lewis acid amount of Ni-Mo2C/MCM-41 catalysts were regulated by varying CH4 content in carbonization gas. The activity of Ni-Mo2C/MCM-41 catalysts in jatropha oil (JO) conversion showed a volcano-like trend over the catalysts with increasing CH4 content from 15% to 50% in the preparation process. The one prepared by 25% CH4 content (Ni-Mo2C(25)/MCM-41) exhibited the outstanding catalytic performance with 83.9 wt% biofuel yield and 95.2% C15-C18 selectivity. Such a variation of activity was ascribed to the most exposed active sites, the smallest particle size, and the lowest Lewis acid amount from Ni0 on the Ni-Mo2C(25)/MCM-41 catalyst surface. Moreover, the Ni-Mo2C(25)/MCM-41 catalyst could also effectively catalyze the conversion of crude waste cooking oil (WCO) into green diesel. This study offers an effective strategy to improve catalytic performance of molybdenum carbide catalyst on vegetable oil conversion.

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Stability of highly supersaturated vanadium electrolyte solution and characterization of precipitated phases for vanadium redox flow battery Waldemir M. Carvalho Jr, Laurent Cassayre, Delphine Quaranta, Fabien Chauvet, Ranine El-Hage, Theodore Tzedakis, Béatrice Biscans 2021, 61(10): 436-445.  DOI: 10.1016/j.jechem.2021.01.040 Abstract ( 5 )   PDF (3060KB) ( 2 )   The vanadium redox flow battery (VRFB) has been receiving great attention in recent years as one of the most viable energy storage technologies for large-scale applications. However, higher concentrations of vanadium species are required in the H2O-H2SO4 electrolyte in order to improve the VRFB energy density. This might lead to unwanted precipitation of vanadium compounds, whose nature has not been accurately characterized yet. For this purpose, this study reports the preparation of V(II), V(III), V(IV) and V(V) supersaturated solutions in a 5 M H2SO4-H2O electrolyte by an electrolytic method, from the only vanadium sulfate compound commercially available (VOSO4). The precipitates obtained by ageing of the stirred solutions are representative of the solids that may form in a VRFB operated with such supersaturated solutions. The solid phases are identified using thermogravimetric analysis, X-ray diffraction and SEM. We report that dissolved V(II), V(III) and V(IV) species precipitate as crystals of VSO4, V2(SO4)3 and VOSO4 hydrates and not in their anhydrous form; conversely V(V) precipitates as an amorphous V2O5 oxide partially hydrated. The measured hydration degrees (respectively 1.5, 9, 3 and 0.26 mol of H2O per mol of compound) might significantly affect the overall engineering of VRFB operating with high vanadium concentrations.

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Role of the Cu-ZrO2 interface in the hydrogenation of levulinic acid to γ-valerolactone Ziyi Li, Haigang Hao, Jingjing Lu, Chengming Wu, Rui Gao, Jifan Li, Chun-Ling Liu, Wen-Sheng Dong 2021, 61(10): 446-458.  DOI: 10.1016/j.jechem.2021.01.046 Abstract ( 4 )   PDF (4348KB) ( 2 )   Here we exquisitely fabricated Cu/ZrO2-dp catalysts with plentiful Cu-ZrO2 interfaces by depositing amorphous ZrO2 onto Cu nanoparticles for the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL). With the created plentiful Cu-ZrO2 interfaces, the optimal catalyst 3Cu/ZrO2-dp exhibited exceptional catalytic performance under mild reaction conditions, and achieved the highest GVL mass productivity of 266.0 mmol GVL·h-1·g-1 Cu, which was 12.5 and 2.3 times of Cu/ZrO2 catalysts with equivalent Cu loadings prepared by traditional impregnation (3Cu/ZrO2-im) or co-precipitation (3Cu/ZrO2-cp). As far as we know, this GVL mass productivity stood at the highest level compared with those obtained using non-noble metal catalysts under similar reaction conditions. By systematic investigation with multiple characterizations, density functional theory (DFT) calculations, and kinetic studies, it was found that interfacial active centers were created at Cu-ZrO2 interfaces, which contained oxygen vacancies (Ov), negatively charged Cuδ- and partially reduced Zr3+. The Ov favored the adsorption and activation of LA via its ketone group, while negatively charged Cuδ- was able to enhance heterolysis of H2, which resulted in the formation of H+-Cuδ- and Zr3+-H- active species via hydrogen spillover. Also, plentiful acid sites, which derived from coordinatively unsaturated and defective Zr species, generated at Cu-ZrO2 interfaces. With the cooperation of interfacial active centers (Cuδ--Ov-Zr3+) and acid sites, the fabricated 3Cu/ZrO2-dp with plentiful Cu-ZrO2 interfaces achieved excellent catalytic performance for the hydrogenation of LA to GVL. Hence, the synergistic catalysis of Cu-ZrO2 interfaces provided an effective strategy for designing catalysts with a satisfactory performance for the hydrogenation of LA, which also can be expanded to other hydrodeoxygenation reactions.

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A porous puckered V2O5 polymorph as new high performance cathode material for aqueous rechargeable zinc batteries Dauren Batyrbekuly, Barbara Laïk, Jean-Pierre Pereira-Ramos, Zhumabay Bakenov, Rita Baddour-Hadjean 2021, 61(10): 459-468.  DOI: 10.1016/j.jechem.2021.01.042 Abstract ( 5 )   PDF (6885KB) ( 4 )   Aqueous rechargeable zinc batteries are getting increasing attention for large-scale energy storage owing to their advantages in terms of cost, environmental friendliness and safety. Here, the layered puckered γ′-V2O5 polymorph with a porous morphology is firstly introduced as cathode for an aqueous zinc battery system in a binary Zn2+/Li+ electrolyte. The Zn|| γ′-V2O5 cell delivers high capacities of 240 and 190 mAh g-1 at current densities of 29 and 147 mA g-1, respectively, and remarkable cycling stability in the 1.6 V-0.7 V voltage window (97% retention after 100 cycles at 0.15 A g-1). The detailed structural evolution during first discharge-charge and subsequent cycling is investigated using X-ray diffraction and Raman spectroscopy. We demonstrate a reaction mechanism based on a selective Li insertion in the 1.6 V-1.0 V voltage range. It involves a reversible exchange of 0.8 Li+ in γ′-V2O5 and the same structural response as the one reported in lithiated organic electrolyte. However, in the extended 1.6 V-0.7 V voltage range, this work puts forward a concomitant and gradual phase transformation from γ′-V2O5 to zinc pyrovanadate Zn3V2O7(OH)2.2H2O (ZVO) during cycling. Such mechanism involving the in-situ formation of ZVO, known as an efficient Zn and Li intercalation material, explains the high electrochemical performance here reported for the Zn|| γ′-V2O5 cell. This work highlights the peculiar layered-puckered γ′-V2O5 polymorph outperforms the conventional α-V2O5 with a huge improvement of capacity of 240 mAh g-1 vs 80 mAh g-1 in the same electrolyte and voltage window.

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Toward practical photoelectrochemical water splitting and CO2 reduction using earth-abundant materials Yubin Chen, Ya Liu, Feng Wang, Xiangjiu Guan, Liejin Guo 2021, 61(10): 469-488.  DOI: 10.1016/j.jechem.2021.02.003 Abstract ( 4 )   PDF (9433KB) ( 2 )   Photoelectrochemical (PEC) fuel generation from water splitting and CO2 reduction (CO2R) utilizing solar energy holds immense potential to solve the current energy and environmental issues. In the past decades, numerous studies have been devoted to this fast-growing research field, and it is essential to develop efficient photoelectrodes with earth-abundant materials for the practical application of PEC systems. A thorough review of earth-abundant materials and associated devices for PEC fuel generation is beneficial to uncover the inherent obstacles and pave the way for future research. Herein, we summarize the recent progress of earth-abundant light-absorbers and cocatalysts in the PEC systems. The unbiased configurations and scaling-up strategies of PEC devices using earth-abundant materials are examined. A comparison between PEC water splitting and CO2R is carried out to promote better understanding of the design principles for practical materials and devices. Last, the prospects on advanced materials, underlying mechanisms, and reaction systems of PEC water splitting and CO2R are proposed.

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Rational design of three-dimensional branched NiCo-P@CoNiMo-P core/shell nanowire heterostructures for high-performance hybrid supercapacitor Yijing Huang, Chong Luo, Qiaobao Zhang, Hehe Zhang, Ming-Sheng Wang 2021, 61(10): 489-496.  DOI: 10.1016/j.jechem.2021.02.005 Abstract ( 5 )   PDF (4662KB) ( 3 )   Owing to the dramatically enhanced charge-mass transport and abundant electrochemically active sites, transition metal compound electrodes are increasingly attractive for achieving high-performance supercapacitors (SCs). Here, we report the fabrication of nickel foam supported three-dimensional (3D) branched nickel-cobalt phosphides@tri-metal cobalt-nickel-molybdenum phosphides core/shell nanowire heterostructures (denoted as NiCo-P@CoNiMo-P) as high-performance electrode materials for hybrid supercapacitors. The presence of multiple valences of the cations in such NiCo-P@CoNiMo-P enables rich redox reactions and promoted synergy effects. Benefiting from their collective effects, the resulting electrode demonstrates high specific capacity of 1366 C g-1 at 2 A g-1 (2.03 C cm-2 at 2 mA cm-2) and 922 C g-1 at 10 A g-1, as well as good cycling stability (retaining ~ 94% of the initial capacity after 6000 cycles at 15 A g-1). A hybrid SC using the NiCo-P@CoNiMo-P as the positive electrode and N-doped rGOs as the negative electrode exhibits a high energy density of 81.4 Wh kg-1 at a power density of 1213 W kg-1 and a capacity retention of 132% even after 6000 cycles at 10 A g-1. Our findings can facilitate the material design for boosting the performance of transition metal compounds based materials for fast energy storage.

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Unraveling the reaction mechanism of low dose Mn dopant in Ni(OH)2 supercapacitor electrode Zhiguo Zhang, Hua Huo, Zhenjiang Yu, Lizhi Xiang, Bingxing Xie, Chunyu Du, Jiajun Wang, Geping Yin 2021, 61(10): 497-506.  DOI: 10.1016/j.jechem.2021.02.002 Abstract ( 4 )   PDF (10465KB) ( 4 )   Mn doping is deemed as a promising strategy to improve the electrochemical performance of the α-Ni(OH)2 battery-type supercapacitor electrode. However, the internal structure evolution, the pathways and the dynamics of the proton/intercalated anion migration, as well as the functioning mechanism of Mn dopant to stabilize the layered structure during cycles remain unclear. Here, we unveil that irreversible oxidization of Mn3+ at the initial CV cycles, which will remain as Mn4+ in the NiO2 slabs after the first oxidization to effectively suppress the phase transformation from α-Ni(OH)2/γ-NiOOH to β-Ni(OH)2/β-NiOOH and further maintain the structural integrity of electrode. With a synergistic combination of theoretical calculations and various structural probes including XRD and 2H MAS solid state NMR, we decode the structure evolution and dynamics in the initial CV (cyclic voltammetry) cycles, including the absorption/desorption of hydrogen containing species, migration of intercalated anions/water molecules and the change of interlayer space. This present work elucidates a close relationship between doping chemistry and structural reliability, paving a novel way of reengineering supercapacitor electrode materials.

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Dual-atom active sites embedded in two-dimensional C2N for efficient CO2 electroreduction: A computational study Haimei Liu, Qingliang Huang, Wei An, Yuanqiang Wang, Yong Men, Shuang Liu 2021, 61(10): 507-516.  DOI: 10.1016/j.jechem.2021.02.007 Abstract ( 3 )   PDF (9290KB) ( 1 )   Double-atom catalysts (DACs) have emerged as an enhanced platform of single-atom catalyst for promoting electrocatalytic CO2 reduction reaction (CO2RR). Herein, we present a density-functional theory study on CO2RR performance of seven C2N-supported homo- and heteronuclear DACs, denoted as M2@C2N. Our results demonstrate that there exists substantial synergistic effect of dual-metal-atom N2M2N2 active site and C2N matrix on O=C=O bond activation. The dual-atom M2 sites are able to drive CO2RR beyond C1 products with low limiting potential (UL). Specifically, C2H4 formation is preferred on FeM@C2N (M = Fe, Co, Ni, Cu) versus CH4 formation on CuM@C2N (M = Co, Ni, Cu). Furthermore, *CO+*CO co-binding strength can serve as a descriptor for CO2RR activity for making C2 products such that the moderate binding results in the lowest UL. Remarkably, C-affinity matters most to C-C bond coupling and C2H4 formation while both C- and O-affinity control CH4 formation. Our results provide theoretical insight into rational design of DACs for efficient CO2RR.

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Bismuth based photoelectrodes for solar water splitting Sabiha Akter Monny, Zhiliang Wang, Muxina Konarova, Lianzhou Wang 2021, 61(10): 517-530.  DOI: 10.1016/j.jechem.2021.01.047 Abstract ( 7 )   PDF (6585KB) ( 4 )   Photoelectrochemical water splitting is a sustainable path to generate valuable hydrogen using sunlight and water as the only inputs. Despite significant efforts to date, it is still a challenge to achieve photoelectrode with superior performance and long-term stability. Many bismuth-based semiconductor materials have demonstrated excellent visible light harvesting capability and suitable band edge for water splitting. Herein, we summarized the latest studies conducted on bismuth-based photoelectrodes for photoelectrochemical water splitting. Specifically, photoelectrochemical properties of copper bismuth oxide (CuBi2O4), bismuth ferrites (BiFeO3, Bi2Fe4O9), bismuth vanadate (BiVO4), bismuth tungstate (Bi2WO6), bismuth molybdate (Bi2MoO6) and bismuth oxyhalids (BiOX, X = I, Cl, Br) are presented. Strategies to achieve high stability and photolectrochemical performance were discussed in the aspects of nanostructure formation, heterostructure assembly, practical defect engineering, preferential facet growth and oxygen evolution catalyst incorporation.

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A review on nanoconfinement engineering of red phosphorus for enhanced Li/Na/K-ion storage performances Yuanyuan Sun, Fanyou Zeng, Yukun Zhu, Ping Lu, Dongjiang Yang 2021, 61(10): 531-552.  DOI: 10.1016/j.jechem.2021.02.019 Abstract ( 12 )   PDF (16018KB) ( 3 )   Secondary batteries are widely used in energy storage equipment. To obtain high-performance batteries, the development and utilization of electrode materials with cheap price and ideal theoretical gravimetric and volumetric specific capacities have become particularly important. Naturally abundant and low-cost red phosphorus (RP) is recognized as an anode material with great promise because it has a theoretical capacity of 2596 mA h g-1 in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). However, owing to the inferior discharging, the capacity of pure RP has a fast decay. Nanoconfinement of RP nanoparticles within porous carbon framework is one of the efficient methods to overcome these problems. In this review, we introduce the recent progress of RP confinement into carbon matrix as an energy storage anode material in LIBs, SIBs and potassium-ion batteries (PIBs). The synthetic strategies, lithiation/sodiation/potassiation mechanism, and the electrochemical performances of RP/carbon composites (RP/C) with kinds of designed structures and P-C and P-O-C bond by kinds of methods are included. Finally, the challenges and perspectives of RP faced in the application development as anodes for LIBs/SIBs/PIBs are covered. This review will strengthen the understanding of composites of RP nanoparticles in porous carbon materials and aid researchers to carry out future work rationally.

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A facile solution processed ZnO@ZnS core-shell nanorods arrays for high-efficiency perovskite solar cells with boosted stability Kun Chen, Weijian Tang, Yu Chen, Ruihan Yuan, Yinhua Lv, Wenjuan Shan, Wen-Hua Zhang 2021, 61(10): 553-560.  DOI: 10.1016/j.jechem.2021.02.018 Abstract ( 8 )   PDF (3708KB) ( 5 )   Zinc Oxide (ZnO) has been extensively applied as electron transport material (ETM) in perovskite solar cells (PSCs) since the emergence of PSCs. However, some chemisorbed oxygen species on the surface of ZnO can cause the degradation of CH3NH3+ (MA+) based perovskite. To avoid the destructive effect of ZnO, a facile solution strategy was proposed to produce a ZnS shell around the ZnO nanorods arrays (ZnO-NRs), i. e. ZnO@ZnS core-shell nanorods (ZnO-NRs@ZnS). The ZnO-NRs@ZnS cascade structure can not only facilitate carrier transport, but also enhance the stability of ZnO based PSCs. A power conversion efficiency (PCE) of 20.6% was finally yielded, which is the-state-of-the-art efficiency for PSCs with one-dimensional (1D) ZnO electron transport materials (ETMs). Moreover, over 90% of the initial efficiency was retained for the unencapsulated device with ZnO-NRs@ZnS ETMs at 85 °C for 500 h, demonstrating excellent stability. This work provides a simple and efficient avenue to simultaneously enhance the photovoltaic (PV) performance and stability of 1D ZnO nanostructure-based PSCs.

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A systematic correlation between morphology of porous carbon cathode and electrolyte in lithium-sulfur battery Jihyeon Park, Seoyoung Yoon, Seoyeah Oh, Jiyoon Kim, Dongjun Kim, Geonho Kim, Jiyeon Lee, Myeong Jun Song, Ilto Kim, Kwonnam Sohn, Jiwon Kim 2021, 61(10): 561-573.  DOI: 10.1016/j.jechem.2021.03.036 Abstract ( 5 )   PDF (6956KB) ( 3 )   Porous carbon has been applied for lithium-sulfur battery cathodes, and carbonized metal-organic framework (MOF) is advantageous in tuning the morphology. Herein, we have systematically synthesized water-distorted MOF (WDM) derived porous carbon via controlling the proportion of both water in a mixed solvent (dimethylformamide and water) and ligand in MOF-5 precursors (metal and ligand), which is categorized by its morphology (i.e. Cracked stone (closed), Tassel (open) and Intermediate (semi-open)). For example, decrease in water and increase in ligand content induce Cracked stone WDMs which showed the highest specific surface area (2742-2990 m2/g) and pore volume (2.81-3.28 cm3/g) after carbonization. Morphological effect of carbonized WDMs (CWDMs) on battery performance was examined by introducing electrolytes with different sulfur reduction mechanisms (i.e. DOL/DME and ACN2LiTFSI-TTE): Closed framework effectively confines polysulfide, whereas open framework enhances electrolyte accessibility. The initial capacities of the batteries were in the following order: Cracked stone > Intermediate > Tassel for DOL/DME and Intermediate > Tassel > Cracked stone for ACN2LiTFSI-TTE. To note, Intermediate CWDM exhibited the highest initial capacity and retained capacity after 100 cycles (1398 and 747 mAh/g) in ACN2LiTFSI-TTE electrolyte having advantages from both open and closed frameworks. In sum, we could correlate cathode morphology (openness and pore structure) and electrolyte type (i.e. polysulfide solubility) with lithium-sulfur battery performance.

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Suppressing irreversible phase transition and enhancing electrochemical performance of Ni-rich layered cathode LiNi0.9Co0.05Mn0.05O2 by fluorine substitution Qi-Qi Qiu, Shan-Shan Yuan, Jian Bao, Qin-Chao Wang, Xin-Yang Yue, Xun-Lu Li, Xiao-Jing Wu, Yong-Ning Zhou 2021, 61(10): 574-581.  DOI: 10.1016/j.jechem.2021.02.012 Abstract ( 7 )   PDF (4645KB) ( 4 )   Ni-rich layered oxide LiNixCoyMn1-x-yO2 (x ≥ 0.8) is the most promising cathodes for future high energy automotive lithium-ion batteries. However, its application is hindered by the undesirable cycle stability, mainly due to the irreversible structure change at high voltage. Herein, we demonstrate that F substitution with the appropriate amount (1 at%) is capable for improve the electrochemical performance of LiNi0.9Co0.05Mn0.05O2 cathode significantly. It is revealed that F substitution can reduce cation mixing, stabilize the crystal structure and improve Li transport kinetics. The resulted LiNi0.9Co0.05Mn0.05O1.99F0.01 cathode can deliver a high capacity of 194.4 mAh g-1 with capacity retention of 95.5% after 100 cycles at 2C and 165.2 mAh g-1 at 5C. In-situ synchrotron X-ray technique proves that F ions in the cathode materials can suppress the irreversible phase transition from H2 phase to H3 phase in high voltage region by preventing oxygen gliding in a-b planes, ensuring a long-term cycle stability.

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Unraveling the catalytically active phase of carbon dioxide hydrogenation to methanol on Zn/Cu alloy: Single atom versus small cluster Xiao-Kuan Wu, Hui-Min Yan, Wei Zhang, Jie Zhang, Guang-Jie Xia, Yang-Gang Wang 2021, 61(10): 582-593.  DOI: 10.1016/j.jechem.2021.02.016 Abstract ( 8 )   PDF (11086KB) ( 4 )   Methanol synthesis from CO2 hydrogenation catalyzed by Zn/Cu alloy has been widely studied, but there is still debate on its catalytic active phase and whether the Zn can be oxidized during the reaction process. What is more, as Zn atoms could locate on Zn/Cu alloy surface in forms of both single atom and cluster, how Zn surface distribution affects catalytic activity is still not clear. In this work, we performed a systematic theoretical study to compare the mechanistic natures and catalytic pathways between Zn single atom and small cluster on catalyst surface, where the surface oxidation was shown to play the critical role. Before surface oxidation, the Zn single atom/Cu is more active than the Zn small cluster/Cu, but its surface oxidation is difficult to take place. Instead, after the easy surface oxidation by CO2 decomposition, the oxidized Zn small cluster/Cu becomes much more active, which even exceeds the hardly-oxidized Zn single atom/Cu to become the active phase. Further analyses show this dramatic promotion of surface oxidation can be ascribed to the following factors: i) The O from surface oxidation could preferably occupy the strongest binding sites on the center of Zn cluster. That makes the O intermediates bind at the Zn/Cu interface, preventing their too tight binding for further hydrogenation; ii) The higher positive charge and work function on the oxidized surface could also promote the hydrogenation of O intermediates. This work provided one more example that under certain condition, the metal cluster can be more active than the single atom in heterogeneous catalysis.

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Metallic vanadium trioxide intercalated with phase transformation for advanced aqueous zinc-ion batteries Kang Hu, Danqing Jin, Yao Zhang, Longwei Ke, Huan Shang, Yan Yan, Huijuan Lin, Kun Rui, Jixin Zhu 2021, 61(10): 594-601.  DOI: 10.1016/j.jechem.2021.02.014 Abstract ( 4 )   PDF (10681KB) ( 3 )   Aqueous zinc-ion batteries have broad application prospects due to the eco-friendliness, cost-economy and high safety. However, the scarcity of high-performance cathodes with outstanding rate capability and long lifespan has affected their development. Herein, we report a metallic vanadium trioxide material intercalated with phase transformation as cathode applied in aqueous zinc-ion batteries. It offers satisfactory electrochemical performances with a high specific capacity (435 mAh g-1 at 0.5 A g-1), decent power density (5.23 kW kg-1) and desired energy density (331 Wh kg-1), as well as good cyclability. The superior performance originates from the stable structure and fast Zn2+ diffusion, enabled by the pre-intercalation of Zn2+ and water molecules.

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Effect of Ni particle size on the production of renewable methane from CO2 over Ni/CeO2 catalyst Lili Lin, Clifford A. Gerlak, Chang Liu, Jordi Llorca, Siyu Yao, Ning Rui, Feng Zhang, Zongyuan Liu, Sen Zhang, Kaixi Deng, Christopher B.Murray, José A. Rodriguez, Sanjaya D. Senanayake 2021, 61(10): 602-611.  DOI: 10.1016/j.jechem.2021.02.021 Abstract ( 6 )   PDF (9492KB) ( 4 )   Production of ‘renewable Methane’ has attracted renewed research interest as a fundamental probe reaction and process for CO2 utilization through potential use in C1 fuel production and even for future space exploration technologies. CO2 methanation is a structure sensitive reaction on Ni/CeO2 catalysts. To precisely elucidate the size effect of the Ni metal center on the CO2 methanation performance, we prepared 2%Ni/CeO2 catalysts with pre-synthesized uniform Ni particles (2, 4 and 8 nm) on a high surface area CeO2 support. Transmission electron microscopy (TEM) and ambient pressure X-ray photo spectroscopy (AP-XPS) characterization have confirmed that the catalyst structure and chemical state was uniform and stable under reaction conditions. The 8 nm sized catalyst showed superior methanation selectivity over the 4 and 2 nm counterparts, and the methanation activity in term of TOF is 10 times and 70 times higher than for the 4 and 2 nm counterparts, respectively. The DRIFTS studies revealed that the larger Ni (8 nm particles) over CeO2 efficiently facilitated the hydrogenation of the surface formate intermediates, which is proposed as the rate determining step accounting for the excellent CO2 methanation performance.

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Molten salt assisted fabrication of Fe@FeSA-N-C oxygen electrocatalyst for high performance Zn-air battery Wenjun Zhang, Kaicai Fan, Cheng-Hao Chuang, Porun Liu, Jian Zhao, Dongchen Qi, Lingbo Zong, Lei Wang 2021, 61(10): 612-621.  DOI: 10.1016/j.jechem.2021.02.015 Abstract ( 6 )   PDF (8552KB) ( 1 )   Non-noble-metal-based electrocatalysts with superior oxygen reduction reaction (ORR) activity to platinum (Pt) are highly desirable but their fabrications are challenging and thus impeding their applications in metal-air batteries and fuel cells. Here, we report a facile molten salt assisted two-step pyrolysis strategy to construct carbon nanosheets matrix with uniformly dispersed Fe3N/Fe nanoparticles and abundant nitrogen-coordinated Fe single atom moieties (Fe@FeSA-N-C). Thermal exfoliation and etching effect of molten salt contribute to the formation of carbon nanosheets with high porosity, large surface area and abundant uniformly immobilized active sites. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image, X-ray absorption fine spectroscopy, and X-ray photoelectron spectroscopy indicate the generation of Fe (mainly Fe3N/Fe) and FeSA-N-C moieties, which account for the catalytic activity for ORR. Further study on modulating the crystal structure and composition of Fe3N/Fe nanoparticles reveals that proper chemical environment of Fe in Fe3N/Fe notably optimizes the ORR activity. Consequently, the presence of abundant FeSA-N-C moieties, and potential synergies of Fe3N/Fe nanoparticles and carbon shells, markedly promote the reaction kinetics. The as-developed Fe@FeSA-N-C-900 electrocatalyst displays superior ORR performance with a half-wave potential (E1/2) of 0.83 V versus reversible hydrogen electrode (RHE) and a diffusion limited current density of 5.6 mA cm-2. In addition, a rechargeable Zn-air battery device assembled by the Fe@FeSA-N-C-900 possesses remarkably stable performance with a small voltage gap without obvious voltage loss after 500 h of operation. The facile synthesis strategy for the high-performance composites represents another viable avenue to stable and low-cost electrocatalysts for ORR catalysis.

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Molten salt synthesis of porous carbon and its application in supercapacitors: A review Zhongya Pang, Guangshi Li, Xiaolu Xiong, Li Ji, Qian Xu, Xingli Zou, Xionggang Lu 2021, 61(10): 622-640.  DOI: 10.1016/j.jechem.2021.02.020 Abstract ( 13 )   PDF (10635KB) ( 6 )   Carbon materials have taken an important role in supercapacitor applications due to their outstanding features of large surface area, low price, and stable physicochemical properties. Considerable research efforts have been devoted to the development of novel synthesis strategy for the preparation of porous carbon materials in recent years. In particular, molten salt strategy represents an emerging and promising method, whereby it has shown great potential in achieving tailored production of porous carbon. It has been proved that the molten salt-assisted production of carbon via the direct carbonization of carbonaceous precursors is an effective approach. Furthermore, with the incorporation of electrochemical technology, molten salt synthesis of porous carbon has become flexible and diversiform. Here, this review focuses on the mainstream molten salt synthesis strategies for the production of porous carbon materials, which includes direct molten salt carbonization process, capture and electrochemical conversion of CO2 to value-added carbon, electrochemical exfoliation of graphite to graphene-based materials, and electrochemical etching of carbides to new-type carbide-derived carbon materials. The reaction mechanisms and recent advances for these strategies are reviewed and discussed systematically. The morphological and structural properties and capacitive performances of the obtained carbon materials are summarized to reveal their appealing points for supercapacitor applications. Moreover, the opportunities and challenges of the molten salt synthesis strategy for the preparation of carbon materials are also discussed in this review to provide inspiration to the future researches.