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2021, Vol. 56, No. 5　Online: 15 May 2021

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Magnetron sputtering deposition of silicon nitride on polyimide separator for high-temperature lithium-ion batteries Can Liao, Wei Wang, Junling Wang, Longfei Han, Shuilai Qiu, Lei Song, Zhou Gui, Yongchun Kan, Yuan Hu 2021, 56(5): 1-10.  DOI: 10.1016/j.jechem.2020.07.046 Abstract ( 4 )   PDF (10618KB) ( 1 )   To date, lithium-ion batteries are becoming increasingly significant in the application of portable devices and electrical vehicles, and revolutionary progress in theoretical research and industrial application has been achieved. However, the commercial polyolefin separators with unsatisfying electrolytes affinity and poor thermal stability have extremely restricted the further application of lithium-ion batteries, especially in the high-temperature fields. In this work, magnetron sputtering deposition technique is employed to modify the commercial polyimide separator by coating silicon nitride on both sides. Magnetron sputtering deposition modified polyimide (MSD-PI) composite separator shows high thermal stability and ionic conductivity. More importantly, compared with the cells using Celgard separator, the cells with MSD-PI separator exhibit superior electrochemical performance, especially long-term cycle performance under high temperature environment, owing to the high thermal conductivity of surface Si3N4 particles. Hence, lithium-ion batteries with MSD-PI separator are capable of improving thermal safety and capacity retention, which demonstrates that magnetron sputtering deposition technique could be regarded as a promising strategy to develop advanced organic/inorganic composite separators for high-temperature lithium-ion batteries.

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Corrigendum to “In situ decoration of nanosized metal oxide on highly conductive MXene nanosheets as efficient catalyst for Li-O2 battery” [J. Energy. Chem. 47 (2020) 272-280] Xingyu Li, Caiying Wen, Huifeng Li, Genban Sun 2021, 56(5): 11-13.  DOI: 10.1016/j.jechem.2020.07.053 Abstract ( 5 )   PDF (1819KB) ( 3 )

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New insights into the formation of silicon-oxygen layer on lithium metal anode via in situ reaction with tetraethoxysilane Yang Luo, Tianyu Li, Hongzhang Zhang, Ying Yu, Arshad Hussain, Jingwang Yan, Huamin Zhang, Xianfeng Li 2021, 56(5): 14-22.  DOI: 10.1016/j.jechem.2020.07.036 Abstract ( 10 )   PDF (5848KB) ( 5 )   Lithium metal-based secondary batteries are very promising for next generation power battery due to their high energy density. However, lithium anodes suffer from poor electrochemical reversibility in organic electrolytes due to Li dendrites and instability of the solid electrolyte interphase. Recent research demonstrated that the problem can be alleviated via tetraethoxysilane (TEOS) treated lithium metal to form a silicon oxide layer on the lithium surface, however, its reaction mechanism is controversial. Herein, we deeply explore the reaction mechanism between TEOS and Li and propose: Fresh Li can directly react with TEOS even though no lithium hydroxide exists on the lithium surface, and the participation of water will accelerate the reaction process. Moreover, it was found that the silicon oxide layer can promote the uniform deposition of lithium ions by providing lithiophilic nucleation sites, thereby achieving a long cycle life of Li metal batteries.

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Boosting electrocatalytic hydrogen generation by a renewable porous wood membrane decorated with Fe-doped NiP alloys Bin Hui, Jian Li, Yun Lu, Kewei Zhang, Hongjiao Chen, Dongjiang Yang, Liping Cai, Zhenhua Huang 2021, 56(5): 23-33.  DOI: 10.1016/j.jechem.2020.07.037 Abstract ( 15 )   PDF (6202KB) ( 3 )   Porous biomass electrodes have emerged as a critical material for electrocatalytic hydrogen evolution reaction (HER). However, most approaches for synthesizing porous electrodes from biomass require high energy consumption, which is resulted from the smash of biomass and the undergoing of serial assembly. Herein, a self-supported wood-derived “breathable” membrane is utilized directly as electrodes for high-efficient HER via an assembly of Fe-doped NiP alloys. The well-designed hierarchical porous structures in natural wood membrane (NWM) are unusually beneficial for electrolytes accessibility and hydrogen gas removal. The obtained wood-derived membrane exhibits a high electrocatalytic activity and good cycling durability in acidic and alkaline electrolytes. Remarkably, the Fe0.074NiP alloys/NWM electrode affords a large current density of 100 mA cm-2 at extremely low overpotentials of 168 mV in acidic electrolyte and 174 mV in alkaline electrolyte. Density functional theory calculations unveil that the Fe atom doped in NiP alloys can create much more charge accumulation around Fe and Ni active sites, which helps decrease the ΔGH* and ΔGH2O and significantly promote the HER process. This new insight will promote further explorations of economic, high-efficient, and biodegradable wood-derived electrocatalysts for HER.

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Cautious interpretation of coulombic efficiency (CE) in lithium metal batteries Fu Sun, Dong Zhou, Xiaogang Wang, Ingo Manke, Libao Chen 2021, 56(5): 34-36.  DOI: 10.1016/j.jechem.2020.07.039 Abstract ( 9 )   PDF (132KB) ( 3 )

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WO3 homojunction photoanode: Integrating the advantages of WO3 different facets for efficient water oxidation Minji Yang, Jie Li, Gaili Ke, Binyao Liu, Faqin Dong, Long Yang, Huichao He, Yong Zhou 2021, 56(5): 37-45.  DOI: 10.1016/j.jechem.2020.07.059 Abstract ( 8 )   PDF (5532KB) ( 2 )   The manipulation of the surface property of WO3 photoanode is the main breakthrough direction to improve its solar water oxidation performance both in thermodynamics and kinetics. Here, we report a WO3(002)/m-WO3 homojunction film that is composed of an upper WO3 layer with predominant (002) facet (WO3(002)) and a lower WO3 layer with multi-crystal facets (m-WO3) as a photoanode for solar water oxidation. Due to the synergistic effect of WO3(002) layer and m-WO3 layer, better water oxidation activity and stability are achieved on the WO3(002)/m-WO3 homojunction film relative to the m-WO3 and WO3(002) film. Specifically, the improved water oxidation performance on the WO3(002)/m-WO3homojunction film is attributed to the followings. In thermodynamics, the band position differences between WO3(002) layer and m-WO3 layer lead to the formation of WO3(002)/m-WO3 homojunction, which has positive function of improving their charge separation and transfer. In kinetics, the upper WO3(002) layer of the WO3(002)/m-WO3 film has superior activity in the adsorption and activation of water molecules, water oxidation on this homojunction film photoanode is inclined to follow the four-holes pathway, and the corrosion of photoanode from the H2O2intermediate is restrained. The present work provides a new strategy to modify the WO3 photoanodes for thermodynamically and kinetically efficient water oxidation.

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Plasma assisted synthesis of LiNi0.6Co0.2Mn0.2O2cathode materials with good cyclic stability at subzero temperatures Fanbo Meng, Renzong Hu, Zhiwei Chen, Liang Tan, Xuexia Lan, Bin Yuan 2021, 56(5): 46-55.  DOI: 10.1016/j.jechem.2020.07.044 Abstract ( 11 )   PDF (5905KB) ( 3 )   Layered Ni-rich cathode materials, LiNi0.6Co0.2Mn0.2O2 (NCM622), are synthesized via solid reaction assisted with a plasma milling pretreatment, which is resulted in lowering sintering temperatures for solid precursors. The plasma milling pretreated NCM622 cathode material sintered at 780 ℃ (named as PM-780) demonstrates good cycling stability at both room and subzero temperatures. Specifically, the PM-780 cathode delivers an initial discharge capacity of 171.2 mAh g-1 and a high capacity retention of 99.7% after 300 cycles with current rate of 90 mA g-1 at 30 ℃, while stable capacities of 120.3 and 94.0 mAh g-1 can be remained at -10 ℃ and -20 ℃ in propylene carbonate contained electrolyte,respectively. In-situ XRD together with XPS and SEM reveal that the NCM622 cycled at -10 ℃ presented better structural stability and more intact interface than that of cathodes cycled at 30 ℃. It is also found that subzero temperatures only limit the discharge potential of NCM622 without destroying its structure during cycling since it still exhibits high discharge capacity at 30 ℃ after cycled at subzero temperatures. This work may expand the knowledge about the low-temperature characteristics of layered cathode materials for Li-ion batteries and lay the foundation for its further applications.

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Valence modulated nickel oxynitride network as integrated bifunctional electrodes for enhanced energy storage Shouzhi Wang, Hengshuai Li, Weidong He, Hehe Jiang, Yongliang Shao, Yongzhong Wu, Xiaopeng Hao 2021, 56(5): 56-63.  DOI: 10.1016/j.jechem.2020.07.038 Abstract ( 6 )   PDF (5857KB) ( 3 )   As promising electrode materials, transition metal oxides have attracted considerable attention owing to their excellent performance in electrochemical energy storage. However, their poor conductivity and fragile structure limit their practical application. In this study, a binder-free nickel oxide/oxynitride network (NiON WS) bifunctional electrodes with cation multivalent states that exhibit high energy storage performance were synthesized for the first time. The massive active sites, high specific surface areas, and multiple cation valence states of NiON WS were advantageous for electrochemical redox reaction during its application in supercapacitors (1283.5 mF cm-2) and lithium-ion batteries (1345.0 mA h g-1). Particularly, the NiON WS based flexible asymmetric SCs exhibit excellent capacitance and energy densities. First-principle calculations were employed to study the mechanism of the electrochemical performance improvement of NiON WS. This study demonstrates the potential of transition metal oxides electrode with high capacity and activity for electrochemical energy storage and conversion.

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FeCo alloy/N, S dual-doped carbon composite as a high-performance bifunctional catalyst in an advanced rechargeable zinc-air battery Shengming Chang, Hui Zhang, Zhongyi Zhang 2021, 56(5): 64-71.  DOI: 10.1016/j.jechem.2020.07.047 Abstract ( 7 )   PDF (3082KB) ( 4 )   The rational design and development of cost-effective, high-performance, and stable bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts are essential for rechargeable zinc-air batteries. Herein, a novel FeCo composite composed of alloy nanoparticles embedded in an N, S dual-doped carbon matrix (FeCo/NSC) was prepared via one-step carbonization of amphiphilic dodecanethiol-metal salts wrapped in carbon nitride (C3N4). The compact combination of dual metal-alloys and dual-doped carbon endowed the composite with the active sites for the ORR and OER, achieving efficient electrical transmission and highly efficient bifunctional catalytic performance. The obtained FeCo-1/NSC catalyst exhibited excellent electrocatalytic activity with a half-wave potential of 0.82 V (vs. RHE) for the ORR and a low overpotential of 0.325 V at 10 mA cm-2 for the OER. The liquid Zn-air battery with FeCo-1/NSC as an air electrode displayed excellent charge-discharge performance, high power density, and robust charge-discharge stability for 150 h compared to the 20% Pt/C + RuO2 counterpart. Furthermore, the FeCo-1/NSC-based flexible solid-state Zn-air battery exhibited a higher power density and good charge-discharge stability over 10 h of operation. Thus, a promising strategy for bifunctional electrocatalyst development as part of rechargeable and wearable Zn-air batteries was provided.

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Ultrafine Fe/Fe3C decorated on Fe-Nx-C as bifunctional oxygen electrocatalysts for efficient Zn-air batteries Lingbo Zong, Xin Chen, Siliang Liu, Kaicai Fan, Shuming Dou, Jie Xu, Xiaoxian Zhao, Wenjun Zhang, Yaowen Zhang, Weicui Wu, Fenghong Lu, Lixiu Cui, Xiaofei Jia, Qi Zhang, Yu Yang, Jian Zhao, Xia Li, Yida Deng, Yanan Chen, Lei Wang 2021, 56(5): 72-79.  DOI: 10.1016/j.jechem.2020.07.048 Abstract ( 2 )   PDF (4003KB) ( 2 )   Efficient bifunctional oxygen electrocatalysts for ORR and OER are fundamental to the development of high performance metal-air batteries. Herein, a facile cost-efficient two-step pyrolysis strategy for the fabrication of a bifunctional oxygen electrocatalyst has been proposed. The efficient non-precious-metal-based electrocatalyst, Fe/Fe3C@Fe-Nx-C consists of highly curved onion-like carbon shells that encapsulate Fe/Fe3C nanoparticles, distributed on an extensively porous graphitic carbon aerogel. The obtained Fe/Fe3C@Fe-Nx-C aerogel exhibited superb electrochemical activity, excellent durability, and high methanol tolerance. The experimental results indicated that the assembly of onion-like carbon shells with encapsulated Fe/Fe3C yielded highly curved carbon surfaces with abundant Fe-Nx active sites, a porous structure, and enhanced electrocatalytic activity towards ORR and OER, hence displaying promising potential for application as an air cathode in rechargeable Zn-air batteries. The constructed Zn-air battery possessed an exceptional peak power density of ~147 mW cm-2, outstanding cycling stability (200 cycles, 1 h per cycle), and a small voltage gap of 0.87 V. This study offers valuable insights regarding the construction of low-cost and highly active bifunctional oxygen electrocatalysts for efficient air batteries.

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A highly stable membrane with hierarchical structure for wide pH range flow batteries Jing Hu, Donglei Yu, Tianyu Li, Huamin Zhang, Zhizhang Yuan, Xianfeng Li 2021, 56(5): 80-86.  DOI: 10.1016/j.jechem.2020.07.043 Abstract ( 9 )   PDF (3830KB) ( 6 )   A membrane with high stability and ion conductivity in wide pH range is essential for energy storage devices. Here, we report a novel membrane with hierarchical core-shell structure, which demonstrates high stability and ion conductivity, simultaneously under a wide pH range applications. Spectral characterizations and theoretical calculation indicate that the non-solvent induces the chain segment configuration and eventually leads to polymer-polymer phase separation, thus forming hierarchical porous core-shell structure. Benefiting from this structure, an acidic vanadium flow battery (VFB) with such a membrane shows excellent performance over 400 cycles with an energy efficiency (EE) of above 81% at current density of 120 mA cm-2 and an alkaline zinc-iron flow battery (AZIFB) delivers a cycling stability for more than 200 cycles at 160 mA cm-2, along with an EE of above 82%. This paper provides a cost-effective and simple way to fabricate membranes with high performance for variety of energy-related devices.

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Earth-abundant coal-derived carbon nanotube/carbon composites as efficient bifunctional oxygen electrocatalysts for rechargeable zinc-air batteries Zhenjie Lu, Songdong Yao, Yanzeng Dong, Dongling Wu, Haoran Pan, Xinning Huang, Tao Wang, Zhenyu Sun, Xingxing Chen 2021, 56(5): 87-97.  DOI: 10.1016/j.jechem.2020.07.040 Abstract ( 4 )   PDF (6343KB) ( 2 )   The exploration of active and robust electrocatalysts for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is the bottleneck to realize the commercialization of rechargeable metal-air batteries and regenerative fuel cells. Here we report facile synthesis of three-dimensional (3D) carbon nanotube (CNT)/carbon composites using earth-abundant coal as the carbon source, hydrogen reductant and heteroatom dopant to grow CNTs. The prepared composite featuring 3D structural merits and multiple active sites can efficiently catalyze both ORR and OER, affording high activity, fast kinetics, and long-term stability. With the additional incorporation of manganese, the developed catalyst afforded a potential difference of 0.80 V between ORR at the half wave potential and OER at a current density of 10 mA cm-2. The optimized sample has presented excellent OER performance within a constructed solar-powered water splitting system with continuously generating oxygen bubbles at anode. Notably, it can be further used as a durable air-electrode catalyst in constructed Zn-air battery, delivering an initial discharge/charge voltage gap of 0.73 V, a remained voltaic efficiency of 61.2% after 160 cycles and capability to power LED light for at least 80 h. This study provides an efficient approach for converting traditional energy resource i.e. coal to value-added alternative oxygen electrocatalysts in renewable energy conversion systems.

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Model-guided design of a high performance and durability Ni nanofiber/ceria matrix solid oxide fuel cell electrode Mengzheng Ouyang, Antonio Bertei, Samuel J. Cooper, Yufei Wu, Paul Boldrin, Xinhua Liu, Huizhi Wang, Max Naylor Marlow, Jingyi Chen, Xiaolong Chen, Yuhua Xia, Billy Wu, Nigel P. Brandon 2021, 56(5): 98-112.  DOI: 10.1016/j.jechem.2020.07.026 Abstract ( 11 )   PDF (10445KB) ( 2 )   Mixed ionic electronic conductors (MIECs) have attracted increasing attention as anode materials for solid oxide fuel cells (SOFCs) and they hold great promise for lowering the operation temperature of SOFCs. However, there has been a lack of understanding of the performance-limiting factors and guidelines for rational design of composite metal-MIEC electrodes. Using a newly-developed approach based on 3D-tomography and electrochemical impedance spectroscopy, here for the first time we quantify the contribution of the dual-phase boundary (DPB) relative to the three-phase boundary (TPB) reaction pathway on real MIEC electrodes. A new design strategy is developed for Ni/gadolinium doped ceria (CGO) electrodes (a typical MIEC electrode) based on the quantitative analyses and a novel Ni/CGO fiber-matrix structure is proposed and fabricated by combining electrospinning and tape-casting methods using commercial powders. With only 11.5 vol% nickel, the designer Ni/CGO fiber-matrix electrode shows 32% and 67% lower polarization resistance than a nano-Ni impregnated CGO scaffold electrode and conventional cermet electrode respectively. The results in this paper demonstrate quantitatively using real electrode structures that enhancing DPB and hydrogen kinetics are more efficient strategies to enhance electrode performance than simply increasing TPB.

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Efficient CO2 electroreduction over N-doped hieratically porous carbon derived from petroleum pitch Hui Ning, Dianliang Guo, Xiaoshan Wang, Zhonghao Tan, Wenhang Wang, Zhongxue Yang, Linqing Li, Qingshan Zhao, Jian Hao, Mingbo Wu 2021, 56(5): 113-120.  DOI: 10.1016/j.jechem.2020.07.049 Abstract ( 5 )   PDF (2444KB) ( 2 )   Developing of economic and efficient catalysts is critical for the application of electroreduction of carbon dioxide to highly valuable chemicals. Herein, we present a facile method to synthesize N-doped hieratically porous carbon through pyrolysis of petroleum pitch followed by ammonia etching. We found mesopores are favored formation by removing of asphaltene from petroleum pitch during the carbonation process. Simultaneously, ammonia etching can not only increase the pyridinic-N content, but also upgrade the ratio of meso- to micro- pores of carbon materials. Using the N-doped hieratically porous carbon as catalyst for carbon dioxide electroreduction, the Faradaic efficiency of carbon monoxide reaches 83% at -0.9 V vs. the reversible hydrogen electrode (RHE) in 0.1 M KHCO3. This superior performance is attributed to the synergistic effects of highly pyridinic-N content in conjunction with the hieratically porous architecture, rendering abundant exposed and accessible active sites for electroreduction of CO2. Our work provides a new strategy for the large-scale preparation of high-performance, low-cost catalysts for CO2 electroreduction.

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Effects of charging rates on LiNi0.6Mn0.2Co0.2O2 (NMC622)/graphite Li-ion cells Xianyang Wu, Yaocai Bai, Zhenglong Li, Jue Liu, Kejie Zhao, Zhijia Du 2021, 56(5): 121-126.  DOI: 10.1016/j.jechem.2020.08.008 Abstract ( 4 )   PDF (2639KB) ( 2 )   Enabling fast charging capability of lithium-ion battery is of great importance to widespread adoption of electric vehicles. Increasing the charging rates from state-of-the-art 2C (30 min) to 6C (10 min) requires deep understanding on the cell aging mechanism. In this study, 400 mAh pouch cells are cycled at 1C, 4C and 6C charging rates with 1C discharging rate. Capacity fading, cathode structural changes, Li inventory loss, electrolyte composition changes and Li plating on graphite electrodes are thoroughly studied by various characterization techniques. The rapid capacity fading in cells at 6C charging rate is mainly due to Li inventory loss from cathode structure and metallic Li plating on graphite electrode at higher charging rate. Post-mortem analysis also revealed changes in electrolyte such as increased salt molarity and transesterification during fast charging.

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Multiple methoxy-substituted hole transporter for inverted perovskite solar cells Wei Yu, Sajjad Ahmad, Hengkai Zhang, Zhiliang Chen, QingYang, XinGuo, CanLi, GangLi 2021, 56(5): 127-131.  DOI: 10.1016/j.jechem.2020.07.056 Abstract ( 8 )   PDF (2630KB) ( 2 )

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Rational design of Co nano-dots embedded three-dimensional graphene gel as multifunctional sulfur cathode for fast sulfur conversion kinetics Tongtao Wan, Shuming Liu, Changcheng Wu, Zhaoyang Tan, Shuanglong Lin, Xiaojie Zhang, Zisheng Zhang, GuihuaLiu 2021, 56(5): 132-140.  DOI: 10.1016/j.jechem.2020.07.057 Abstract ( 2 )   PDF (5601KB) ( 2 )   Lithium-sulfur (Li-S) batteries hold great promises to serve as next-generation energy storage devices because of their high theoretical energy density and environmental benignity. However, the shuttle effect of the soluble lithium polysulfides (LiPS) and intrinsic insulating nature of sulfur lead to low sulfur utilization and coulombic efficiency, leading to poor cycling performance. The impeded charge transportation and retard LiPS catalytic conversion also endows the Li-S batteries with sluggish redox reaction, leading to unsatisfied rate capability. In this study, Co-based MOF material ZIF-67 is used as the precursor to prepare Co nano-dots decorated three-dimensional graphene aerogel as sulfur immobilizer. This porous architecture establishes a highly conductive interconnected framework for fast charge/mass transportation. The exposed Co nano-dots serve as active sites to strongly trap LiPS, which endows Co-NDs@G with low decomposition energy barrier for fast LiPS conversion reaction and promote the completely Li2S catalytic transformation. Li-S cells based on the Co-NDs@G cathode exhibits excellent cyclability and a high capacity retention rate of 91.1% in 100 cycles. This strategy offers a new direction to design sulfur immobilizer for accelerated LiPS conversion kinetics of Li-S batteries.

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Synergistic effects of carbon doping and coating of TiO2 with exceptional photocurrent enhancement for high performance H2 production from water splitting Yingying Wang, Yan-Xin Chen, Tarek Barakat, Tian-Ming Wang, Alain Krief, Yu-Jia Zeng, Marvin Laboureur, Luca Fusaro, Hong-Gang Liao, Bao-Lian Su 2021, 56(5): 141-151.  DOI: 10.1016/j.jechem.2020.08.002 Abstract ( 4 )   PDF (14329KB) ( 2 )   The “one pot” simultaneous carbon coating and doping of TiO2 materials by the hydrolysis of TiCl4 in fructose is reported. The synergistic effect of carbon doping and coating of TiO2 to significantly boost textural, optical and electronic properties and photocurrent of TiO2 for high performance visible light H2 production from water splitting has been comprehensively investigated. Carbon doping can significantly increase the thermal stability, thus inhibiting the phase transformation of the Titania material from anatase to rutile while carbon coating can suppress the grain aggregation of TiO2. The synergy of carbon doping and coating can not only ensure an enhanced narrowing effect of the electronic band gap of TiO2 thus extending the absorption of photocatalysts to the visible regions, but also promote dramatically the separation of electron-hole pairs. Owing to these synergistic effects, the carbon coated and doped TiO2 shows much superior photocatalytic activity for both degradation of organics and photocatalytic/photoelectrochemical (PEC) water splitting under simulated sunlight illumination. The photocatalytic activity of obtained materials can reach 5, 4 and 2 times higher than that of pristine TiO2, carbon doped TiO2 and carbon coated TiO2, respectively in the degradation of organic pollutants. The carbon coated and doped TiO2 materials exhibited more than 37 times and hundreds of times photocurrent enhancement under simulated sunlight and visible light, respectively compared to that of pristine TiO2. The present work providing new comprehensive understanding on carbon coating and doping effect could be very helpful for the development of advanced TiO2 materials for a large series of applications.

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Chelation-mediated in-situ formation of ultrathin cobalt (oxy)hydroxides on hematite photoanode towards enhanced photoelectrochemical water oxidation Zhen zhenWang, Jiayue Rong, Jiaqi Lv, Ruifeng Chong, Ling Zhang, Li Wang, Zhixian Chang, Xiang Wang 2021, 56(5): 152-161.  DOI: 10.1016/j.jechem.2020.08.009 Abstract ( 12 )   PDF (4567KB) ( 2 )   In this work, a facile chelation-mediated route was developed to fabricate ultrathin cobalt (oxy)hydroxides (CoOOH) nanosheets on hematite photoanode (Fe2O3). The route contains two steps of the adsorption of [Co-EDTA]2- species on Fe2O3 nanorod array followed by the hydrolysis in alkaline solution. The resulting CoOOH/Fe2O3 exhibits a remarkably improved photocurrent density of 2.10 mA cm-2 at 1.23 V vs. RHE, which is ca. 2.8 times that of bare Fe2O3. In addition, a negative shift of onset potential ca. 200 mV is achieved. The structural characterizations reveal the chelate EDTA plays important roles that enhance the adsorption of Co species and the formation of contact between CoOOH and Fe2O3. (Photo)electrochemical analysis suggests, besides providing active sites for water oxidation, CoOOH at large extent promotes the charge separation and the charge transfer via passivating surface states and suppressing charge recombination. It also found CoOOH possesses some oxygen vacancies, which could act as trapping centers for photogenerated holes and facilitate the charge separation. Intensity modulated photocurrent spectroscopy (IMPS) shows that, under low applied potential the water oxidation mainly occurs on CoOOH, while under high applied potential the water oxidation could occur on both CoOOH and Fe2O3. The findings not only provide an efficient strategy for designing ultrathin (oxy)hydroxides on semiconductors for PEC applications but also put forward a new insight on the role of CoOOH during water oxidation.

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Diverse morphologies of zinc oxide nanoparticles and their electrocatalytic performance in hydrogen production Veronica M. Sofianos, Junqiao Lee, Debbie S. Silvester, Pralok K. Samanta, Mark Paskevicius, Niall J. English, Craig E. Buckley 2021, 56(5): 162-170.  DOI: 10.1016/j.jechem.2020.07.051 Abstract ( 5 )   PDF (4440KB) ( 7 )   Hydrogen is considered an attractive alternative to fossil fuels, but only a small amount of it is produced from renewable energy, making it not such a clean energy carrier after all. Producing hydrogen through water electrolysis is promising, but using a cost-effective and high-performing catalyst that has long-term stability is still a challenge. This study exploits, for the first time, the potential of zinc oxide nanoparticles with diverse morphologies as catalysts for the electrocatalytic production of hydrogen from water. The morphology of the nanoparticles (wires, cuboids, spheres) was easily regulated by changing the concentration of sodium hydroxide, used as the shape controlling agent, during the synthesis. The spherical morphology exhibited the highest electrocatalytic activity at the lowest potential voltage. These spherical nanoparticles had the highest number of oxygen vacancies and lowest particle size compared to the other two morphologies, features directly linked to high catalytic activity. However, the nanowires were much more stable with repeated scans. Density-functional theory showed that the presence of oxygen vacancies in all three morphologies led to diminished band gaps, which is of catalytic interest.

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A three-dimensional crosslinked chitosan sulfate network binder for high-performance Li-S batteries Jianwen Feng, Huan Yi, Zhiwen Lei, Jun Wang, Hongbo Zeng, Yonghong Deng, Chaoyang Wang 2021, 56(5): 171-178.  DOI: 10.1016/j.jechem.2020.07.060 Abstract ( 6 )   PDF (3043KB) ( 3 )   Poor cycling performance caused by the shuttle effect of polysulfides is the main obstacle in the development of advanced lithium-sulfur (Li-S) batteries. Functional polymer binders with polar groups can effectively adsorb polysulfides chemically, thereby suppressing the shuttle effect. Herein, a robust three-dimensional crosslinked polymer network, which demonstrates excellent mechanical property and strong affinity for polysulfides, is prepared by the aldimine condensation and coordination reactions. The crosslinked chitosan sulfate network (CCSN) significantly enhances the cycling performance and rate capability of the sulfur cathode. The CCSN-based sulfur cathode exhibits a high initial discharge capacity of 824 mAh g-1 with only 0.082% average capacity loss per cycle at 1 C. At a high rate of 4 C, the cathode exhibits a high capacity retention of 84.8% after 300 cycles. Moreover, the CCSN-based sulfur cathode exhibits an excellent cycling performance at a high sulfur loading of 2.5 mg cm-2, which indicates the excellent mechanical strength and binding performance of the CCSN binder for high-energy density Li-S batteries. This study demonstrates a viable approach for developing high-performance Li-S batteries for practical application.

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Modulating MAPbI3 perovskite solar cells by amide molecules: Crystallographic regulation and surface passivation Jin Xie, Ziren Zhou, Hongwei Qiao, Mengjiong Chen, Lijie Wang, Shuang Yang, Yu Hou, Huagui Yang 2021, 56(5): 179-185.  DOI: 10.1016/j.jechem.2020.07.050 Abstract ( 6 )   PDF (3205KB) ( 2 )   A controllable crystallization is of practical importance to produce high-quality perovskite thin films with reduced structural defects. Lewis bases as electron-pair donor chemicals can strongly coordinate to lead ions and have been extensively employed to manipulate the growth of perovskite crystals. In this work, we demonstrate a series of Lewis-base amides, for morphological regulation of methylammonium lead triiodide (MAPbI3) thin films. The screened acetamide was demonstrated to decently improve the grain size, along with a spatial distribution at grain boundaries (GBs). The mesostructured solar cells of acetamide-modified absorbers yielded an optimized power conversion efficiency (PCE) of 20.04% with a mitigated open-circuit voltage (VOC) deficit of 0.39 V. This work provides a facile and cost-effective strategy toward controllable fabrication of high-performance MAPbI3 solar cells.

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CeOx-supported monodispersed MoO3 clusters for high-efficiency electrochemical nitrogen reduction under ambient condition Jie Liu, Guanghua Wang, Shiyuan Zhou, Sangui Liu, Gen Li, Hong-Gang Liao, Shi-Gang Sun 2021, 56(5): 186-192.  DOI: 10.1016/j.jechem.2020.07.042 Abstract ( 3 )   PDF (3178KB) ( 2 )   Developing efficient and low-cost electrocatalysts is essential for the electroreduction of N2 to NH3. Here, highly monodispersed MoO3 clusters loaded on a coral-like CeOx compound with abundant oxygen vacancies are successfully prepared by an impregnation-reduction method. The MoO3 clusters with small sizes of 2.6 ± 0.5 nm are induced and anchored by the oxygen vacancies of CeOx, resulting in excellent nitrogen reduction reaction (NRR) performance. Additionally, the synergistic effects between MoO3 and CeOx lead to a further improvement of the electrochemical performance. The as-prepared MoO3-CeOx catalyst shows an NH3 yield rate of 32.2 μg h-1 mgcat-1 and a faradaic efficiency of 7.04% at -0.75 V (vs. reversible hydrogen electrode) in 0.01 M Dulbecco's Phosphate Buffered Saline. Moreover, it displays decent electrochemical stability over 30,000 s. Besides, the electrochemical NRR mechanism for MoO3-CeOx is investigated by in-situ Fourier transform infrared spectroscopy. N-H stretching, H-N-H bending, and N-N stretching are detected during the reaction, suggesting that an associative pathway is followed. This work provides an approach to designing and synthesizing potential electrocatalysts for NRR.

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An economic analysis of twenty light olefin production pathways Zhitong Zhao, Jingyang Jiang, Feng Wang 2021, 56(5): 193-202.  DOI: 10.1016/j.jechem.2020.04.021 Abstract ( 79 )   PDF (9537KB) ( 102 )   A comprehensive economic analysis of twenty light olefin production pathways has been performed, covering current and promising processes from fossil (petroleum, coal and natural gas) and renewable resources (biomass and CO2). Taking steam cracking of naphtha as the benchmark, this study gives an economic perspective and points out the bottleneck in different olefin production pathways. The assessment indicates that nearly all renewable pathways are economically unattractive currently and the raw material cost accounts for dominant contribution in most pathways, especially in the oil-, natural gas- and CO2-derived pathways. For the ways of methanol-to-olefins and methanol-to-propylene, fossil pathways are cost-competitive according to the date of current Chinese market prices. However, the price of feedstock hydrogen needs to be lowered by 55% to fill the cost gap between CO2-derived pathways and the benchmark. For the ways of oxidative coupling of methane and Fischer-Tropsch synthesis to olefins, fossil pathways enable cost-competitive processes by feedstock price fall, but further process improvement is required to approach benchmark in renewable pathways. Conditionally, a decrease in ethanol price by 45% can make ethanol dehydration pathway profitable. In addition, costs can reduce by 4%-23% in different pathways as the production scales expand from 100 to 1000 kt/a, resulting in a change from high cost to economic profit for some of the pathways. The results quantify the need for improvements on feedstock price, scale size and process improvement to achieve competitive production costs.

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Regulation of carbon distribution to construct high-sulfur-content cathode in lithium-sulfur batteries Meng Zhao, Yan-Qi Peng, Bo-Quan Li, Xue-Qiang Zhang, Jia-Qi Huang 2021, 56(5): 203-208.  DOI: 10.1016/j.jechem.2020.07.054 Abstract ( 16 )   PDF (2287KB) ( 2 )   Lithium-sulfur (Li-S) battery is regarded as one of the most promising next-generation energy storage systems due to the ultra-high theoretical energy density of 2600 Wh kg-1. To address the insulation nature of sulfur, nanocarbon composition is essential to afford acceptable cycling capacity but inevitably sacrifices the actual energy density under working conditions. Therefore, rational structural design of the carbon/sulfur composite cathode is of great significance to realize satisfactory electrochemical performances with limited carbon content. Herein, the cathode carbon distribution is rationally regulated to construct high-sulfur-content and high-performance Li-S batteries. Concretely, a double-layer carbon (DLC) cathode is prepared by fabricating a surface carbon layer on the carbon/sulfur composite. The surface carbon layer not only provides more electrochemically active surfaces, but also blocks the polysulfide shuttle. Consequently, the DLC configuration with an increased sulfur content by nearly 10 wt% renders an initial areal capacity of 3.40 mAh cm-2 and capacity retention of 83.8% during 50 cycles, which is about two times than that of the low-sulfur-content cathode. The strategy of carbon distribution regulation affords an effective pathway to construct advanced high-sulfur-content cathodes for practical high-energy-density Li-S batteries.

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Progress and challenges of carbon-fueled solid oxide fuel cells anode Minjian Ma, Xiaoxia Yang, Jinshuo Qiao, Wang Sun, Zhenhua Wang, Kening Sun 2021, 56(5): 209-222.  DOI: 10.1016/j.jechem.2020.08.013 Abstract ( 11 )   PDF (6200KB) ( 4 )   Carbon-fueled solid oxide fuel cells (CF-SOFCs) can electrochemically convert the chemical energy in carbon into electricity, which demonstrate both superior electrical efficiency and fuel utilisation compared to all other types of fuel cells. However, using solid carbon as the fuel of SOFCs also faces some challenges, the fluid mobility and reactive activity of carbon-based fuels are much lower than those of gaseous fuels. Therefore, the anode reaction kinetics plays a crucial role in determining the electrochemical performance of CF-SOFCs. Herein, the progress of various anodes in CF-SOFCs is reviewed from the perspective of material compositions, electrochemical performance and microstructures. Challenges faced in developing high performance anodes for CF-SOFCs are also discussed.

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Review of vanadium-based electrode materials for rechargeable aqueous zinc ion batteries Ying Liu, Xiang Wu 2021, 56(5): 223-237.  DOI: 10.1016/j.jechem.2020.08.016 Abstract ( 5 )   PDF (33780KB) ( 5 )   In recent years, rechargeable aqueous zinc ion batteries (ZIBs), as emerging energy storage devices, stand out from numerous metal ion batteries. Due to the advantages of low cost, environmentally friendly characteristic and safety, ZIBs can be considered as alternatives to lithium-ion batteries (LIBs). Vanadium-based compounds with various structures and large layer spacings are considered as suitable cathode candidates for ZIBs. In this review, the recent research advances of vanadium-based electrode materials are systematically summarized. The electrode design strategy, electrochemical performances and energy storage mechanisms are emphasized. Finally, we point out the limitation of vanadium-based materials at present and the future prospect.

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Insight into the reaction mechanism of sulfur chains adjustable polymer cathode for high-loading lithium-organosulfur batteries Jinqiu Zhou, Xi Zhou, Yawen Sun, Xiaowei Shen, Tao Qian, Chenglin Yan 2021, 56(5): 238-244.  DOI: 10.1016/j.jechem.2020.08.010 Abstract ( 18 )   PDF (3610KB) ( 1 )   Small molecules with adjustable sulfur atoms in the confined structure were acted as precursor for the synthesis of polymer cathodes for lithium-organosulfur batteries. Among them, poly(diallyl tetrasulfide) (PDATtS) delivered a high capacity of 700 mAh g-1, stable capacity retention of 85% after 300 cycles, high areal capacity ~ 4 mAh cm-2 for electrode with up to 10.3 mg cm-2 loading. New insight into the reaction mechanism of PDATtS electrode that radicals arisen from the homolytic cleavage of S - S bond in PDATtS reacted with Li+ to generate thiolates (RSLi) and insoluble lithium sulfides (Li2S) or lithium disulfide (Li2S2) was clearly verified by in-situ UV/Vis spectroscopy, nuclear magnetic resonance (NMR) studies and density-functional theory (DFT) calculations. Therefore, based on the unique reaction mechanism, problems of rapid capacity fading due to the formation of soluble polysulfide intermediates and their serious shuttle effect in conventional lithium-sulfur (Li-S) batteries was totally avoided, realizing the dendrite-free lithium sulfur batteries. This study sets new trends for avenues of further research to advance Li - S battery technologies.

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Tuning electronic structure of δ-MnO2 by the alkali-ion (K, Na, Li) associated manganese vacancies for high-rate supercapacitors Lengyuan Niu, Lijin Yan, Zhengwei Lu, Yinyan Gong, Taiqiang Chen, Can Li, Xinjuan Liu, Shiqing Xu 2021, 56(5): 245-258.  DOI: 10.1016/j.jechem.2020.08.004 Abstract ( 5 )   PDF (29186KB) ( 2 )   Cation vacancies can bring numerous surprising characters due to its multifarious electron and orbit distribution. In this work, δ-MnO2 with alkali-ion (K, Na, Li) associated manganese (Mn) vacancies is fabricated by a simple hydrothermal reaction, and the correlation between their electronic structure and pseudocapacitance are systematically investigated. FESEM/TEM images have shown that the morphology of MnO2 is obviously changed after the introducing of cation vacancies. The position of alkali-ion in MnO2 structure can be controlled by adjusting the ion concentration. XRD patterns and Raman spectra demonstrate that the alkali-ion is embedded in Mn vacancies at low concentration, while entered the interlayer of MnO2 at high concentration. The existence of Mn vacancies will resulting in the distortion of neighboring atoms, leading to the electronic delocalization, and thus enhancing the conductivity, pseudocapacitance and rate capability of MnO2. Accordingly, the specific capacitances of optimized 0.4KMO, 0.4NaMO and 0.4LiMO samples are enhanced about 1.9, 1.6 and 1.6 times compared to pure MnO2. Meanwhile, the rate performance has also been improved about 76%, 46% and 42%, respectively. Theoretical calculations further confirm that the Mn vacancies can generate additional occupancy states and cause an increase in carrier concentration, which will improve the conductivity and further boost the pseudocapacitance of MnO2. This result open up a promising approach to explore active and durable electrode materials.

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FeTe2 as an earth-abundant metal telluride catalyst for electrocatalytic nitrogen fixation Yali Guo, Yonghua Cheng, Qingqing Li, Ke Chu 2021, 56(5): 259-263.  DOI: 10.1016/j.jechem.2020.07.055 Abstract ( 19 )   PDF (3102KB) ( 5 )   Design of cost-effective, yet highly active electrocatalysts for nitrogen reduction reaction (NRR) is of vital significance for sustainable electrochemical NH3 synthesis. Herein, we have demonstrated, from both computational and experimental perspectives, that FeTe2 can be an efficient and durable NRR catalyst. Theoretical computations unveil that FeTe2 possesses abundant surface-terminated and low-coordinate Fe sites that can activate the NRR with a low limiting potential (-0.84 V) and currently impede the competing hydrogen evolution reaction. As a proof-of-concept prototype, we synthesized FeTe2 nanoparticles supported on reduced graphene oxide (FeTe2/RGO), which exhibited a high NRR activity with the exceptional combination of NH3 yield (39.2 μg h-1 mg-1) and Faradaic efficiency (18.1%), thus demonstrating the feasibility of using FeTe2 and other earth-abundant metal tellurides for electrocatalytic N2 fixation.

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Influence of Pt/Ru anodic ratio on the valorization of ethanol by PEM electrocatalytic reforming towards value-added products Alberto Rodríguez-Gómez, Fernando Dorado, Antonio de Lucas-Consuegra, Ana Raquel de la Osa 2021, 56(5): 264-275.  DOI: 10.1016/j.jechem.2020.07.061 Abstract ( 3 )   PDF (2315KB) ( 2 )   The ethanol electro-reforming process was studied over PtRu/C catalysts synthesized by the modified polyol method with different compositions. In particular, this work reports the influence of anodic Pt:Ru ratio (5:1, 2:1 and 1:2) on the organic product distribution (acetaldehyde, acetic acid and ethyl acetate) and pure hydrogen generation at different current densities operation levels. Physicochemical characterization of the catalysts was made by X-ray diffraction (XRD), temperature-programmed reduction (TPR) and N2 adsorption-desorption measurements. XRD patterns showed that Ru is introduced into the Pt structure, forming an alloy between both metals. Also, the degree of alloy was higher by increasing the Ru amounts. From TPR profiles Pt was found to be properly reduced while Ru was both in metallic state and forming RuO2. The electrochemical behaviour of each catalyst towards ethanol electro-reforming process was investigated through electrochemical techniques in a half cell and a single proton exchange membrane (PEM) cell systems. An intermediate Pt:Ru ratio was found to result in high current density and electrochemical surface area (ECSA) values along with lower amounts of adsorbed species. Also, Ru addition seems to diminish the degree of degradation of the catalyst. Based on characterization and in agreement with essays carried out in a PEM cell at mild conditions (80 °C and 1 atm), PtRu/C 2:1 anode provided the best electrocatalytic results in terms of current density (740 mA cm-2), hydrogen production and selectivity toward acetic acid (up to 15% apart from acetaldehyde and ethyl acetate) while requiring the lowest energy consumption.

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Enhanced hydrogen evolution from the face-sharing [RuO6] octahedral motif Fan Zhang, Shaoyun Hao, Guokui Zheng, Lecheng Lei, Xingwang Zhang 2021, 56(5): 276-282.  DOI: 10.1016/j.jechem.2020.08.015 Abstract ( 5 )   PDF (3834KB) ( 3 )   Hampered by the ambiguous mechanism of hydrogen evolution reaction (HER) in basic media, the exploration of highly efficient catalytically active sites for alkaline HER is of significance. Herein, a metal oxide Sr4Ru2O9 engineering a face-sharing [RuO6] octahedra motif was synthesized through the solid-state method, and served as HER electrocatalyst. Benefited from the Ru-Ru metallic bonding crossing the common plane, the H* adsorption and reaction energy barriers were optimized. Sr4Ru2O9 only required an ultra-small overpotential (ƞ10) of 28 mV at a current density of 10 mA cm-2 for HER in 1.0 M KOH with an exceptional stability (180 hours), outperforming the commercial Pt/C (ƞ10 = 38 mV). These findings suggest a fresh insight in designing novel active sites for electrocatalysis.

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Nitrogen doped FeS2 nanoparticles for efficient and stable hydrogen evolution reaction Jian Ye, Yipeng Zang, Qingyu Wang, Yida Zhang, Da Sun, Leijie Zhang, Gongming Wang, Xusheng Zheng, Junfa Zhu 2021, 56(5): 283-289.  DOI: 10.1016/j.jechem.2020.08.014 Abstract ( 6 )   PDF (3762KB) ( 2 )   Performance breakthrough of electrocatalysts highly relies on the regulation of internal structures and electronic states. In present work, for the first time, we successfully synthesized nitrogen doped FeS2 nanoparticles (N-FeS2) as the electrocatalysts for hydrogen evolution reaction (HER). The band structure and electronic state of FeS2 are modulated by a nitrogen doping strategy, as confirmed by X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations. Owing to the band structure and electronic state regulation as well as the weakening of H-S interaction, the designed N-FeS2 electrocatalyst exhibits superior catalytic performance with a low overpotential (~126 mV at 10 mA cm-2) and excellent activity stability under alkaline conditions, which is substantially improved as compared with that of the pure FeS2 counterpart. Our work demonstrates that the modulation of electron state and band structure of an electrocatalyst, which can provide a valuable guidance for designing excellent catalysts for hydrogen evolution reaction and beyond.

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MOF-derived Co-MOF,O-doped carbon as trifunctional electrocatalysts to enable highly efficient Zn-air batteries and water-splitting Xinde Duan, Na Pan, Can Sun, Kexin Zhang, Xukun Zhu, Mingdao Zhang, Li Song, Hegen Zheng 2021, 56(5): 290-298.  DOI: 10.1016/j.jechem.2020.08.007 Abstract ( 6 )   PDF (3566KB) ( 5 )   Development of high-efficiency non-noble electrocatalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is urgently needed for high-performance Zn-air batteries and overall water splitting. Here, a facile strategy to synthesize novel Co-MOF,O-doped carbon (Co-MOF-T) based on Zn, Co-doped glucosamine and ZIF-8 by pyrolysis at temperature T was demonstrated. The prepared Co-MOF-800 showed a superior oxygen reduction reaction (ORR) activity comparable to that of commercial Pt/C catalyst. In addition, this catalyst shows great potential in the overall water splitting due to the excellent oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activities. Based on the trifunctional activity, the primary Zn-air batteries using a Co-MOF-800 air electrode achieved a high open-circuit voltage of 1.38 V, a specific capacity of 671.6 mAh gZn-1, and a prominent peak power density of 144 mW cm-2. Also, the rechargeable Zn-air batteries based on Co-MOF-800 air electrode could be smoothly run for 510 cycles with a low voltage gap of 0.58 V. Finally, the trifunctional Co-MOF-800 catalyst was applied to boost the electrochemical water splitting, demonstrating its promising potential as a green energy material for practical applications.

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Tuning the electronic structure of the earth-abundant electrocatalysts for oxygen evolution reaction (OER) to achieve efficient alkaline water splitting - A review Mohammed-Ibrahim Jamesh, Moussab Harb 2021, 56(5): 299-342.  DOI: 10.1016/j.jechem.2020.08.001 Abstract ( 7 )   PDF (36686KB) ( 4 )   Tuning the electronic structure of the electrocatalysts for oxygen evolution reaction (OER) is a promising way to achieve efficient alkaline water splitting for clean energy production (H2). At first, this paper introduces the significance of the tuning of electronic structure, where modifying the electronic structure of the electrocatalysts could generate active sites having optimal adsorption energy with OER intermediates, and that could diminish the energy barrier for OER, and that could improve the activity for OER. Later, this paper reviews the tuning of electronic structure along with catalytic performances, synthetic methodologies, chemical properties, and DFT calculations on various nanostructured earth-abundant electrocatalysts for OER in alkaline environment. Further, this review discusses the tuning of the electronic structure of the several nanostructured earth-abundant electrocatalysts including oxide, (oxy)hydroxide, layered double hydroxide, alloy, metal phosphide/phosphate, nitride, sulfide, selenide, carbon containing materials, MOF, core-shell/hetero/hollow structured materials, and materials with vacancies/defects for OER in alkaline environment (including activity: overpotential (η) of ≤200 mV at 10 mA cm-2; stability: ≥100 h; durability: ≥5000 cycles). Then, this review discusses the robust stability of the electrocatalysts for OER towards practical application. Moreover, this review discusses the in situ formation of thin layer on the catalyst surface during OER. In addition, this review discusses the influence of the adsorption energy of the OER intermediates on OER performance of the catalysts. Finally, this review summarizes the various promising strategies for tuning the electronic structure of the electrocatalysts to achieve enhanced performance for OER in alkaline environment.

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Regulating the d band in WS2@NC hierarchical nanospheres for efficient lithium polysulfide conversion in lithium-sulfur batteries Jintao Liu, Shuhao Xiao, Le Chang, Long Lai, Rui Wu, Yong Xiang, Xingquan Liu, Jun Song Chen 2021, 56(5): 343-352.  DOI: 10.1016/j.jechem.2020.08.011 Abstract ( 7 )   PDF (6391KB) ( 3 )   The performance of lithium-sulfur batteries is deteriorated by the inferior conductivity of sulfur, the shuttle effect of lithium polysulfides (LiPSs), sluggish redox kinetics of polysulfide intermediates and serious volumetric expansion of sulfur. To overcome these challenges, we report a versatile route to prepare multi-functional nanocomposites with tuable hierarchical structure via ammonium hydroxide (NH3·H2O) induced self-assembly. The versatility of the system has been demonstrated that the organization of the hierarchical structure can be regulated by adding different amounts of NH3·H2O, and WS2 and Co9S8 with nitrogen-doped carbon coating (denoted as WS2@NC and Co9S8@NC) can be prepared by adding different precursor salts. When the as-prepared materials are applied for Li-S batteries, the WS2@NC composite exhibits a reversible capacity of 1107.4 mAh g-1 at 0.1C after 500 cycles and even 728.9 mAh g-1 at 2C for 1000 cycles, which is significantly better than the Co9S8 counterpart and other reported WS2 sulfur hosts. Experimentally, the advantageous performance of WS2 could be attributed to its higher surface area and total pore volume, giving rise to the easier access to electrolyte and better ability to buffer the volume change during the charge/discharge process. Theoretically, the density function theory (DFT) calculation reveals that the as-prepared WS2 has a higher binding energy towards LiPSs as well as a lower energy barrier for Li+ diffusion on the surface than Co9S8. More significantly, the density of states (DOS) analysis further confirms that the superior performance is mainly ascribed to the more prominent shifting and the more charge compensation from d band of W than Co, which increase electronic concentration and give more hybridization of d-p orbitals in the Fermi level of the adsorbed Li2S4 to accelerate the lithium polysulfide interfacial redox and conversion dynamics in WS2. By proposing this mechanism, this work sheds new light on the understanding of catalytic conversion of lithium polysulfides at the atomic level and the strategy to develop advanced cathode materials for high-performance lithium-sulfur batteries.

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Exploring the mechanism of Ta3N5/KTaO3photocatalyst for overall water splitting by first-principles calculations Yanxia Ma, Yumeng Fo, Miaomiao Wang, Xixi Liang, Hao Dong, Xin Zhou 2021, 56(5): 353-264.  DOI: 10.1016/j.jechem.2020.07.058 Abstract ( 6 )   PDF (7966KB) ( 3 )   The rational fabrication of heterostructures is one of efficient strategies for improving photocatalytic performance of semiconductor photocatalysts. Very recently, Domen and co-workers found that Ta3N5 single crystals grown on the surface of KTaO3 can accomplish photocatalytic overall water splitting for the first time. In order to comprehend the underlying mechanism of this photocatalytic system, we have performed a systematic study based on density functional theory first-principles calculations. Ta3N5(010)/KTaO3(110) slab models have been built according to experimental observations by considering two common terminations of KTaO3(110) surface, named as Ta3N5/O2 and Ta3N5/KTaO. The formations of interfacial bonds are thermodynamically stable, showing a covalent interaction between two components of a heterostructure. Ta3N5/O2 has a higher mobility of photogenerated charge carriers and lower recombination rate of charge carriers than Ta3N5/KTaO. The light absorption of heterostructures displays the feature of KTaO3 in the short wavelength region and the characteristic of Ta3N5 in the long wavelength region. The calculated band offsets show that Ta3N5/O2 and Ta3N5/KTaO have distinct Type-II band alignments, with Ta3N5 as the accumulator of photoinduced electrons in the former and the collector of photogenerated holes in the latter, respectively. The difference in charge density and electrostatic potentialbetween two components acts as a driving force to promote the transfer of electrons and holes to different domains of the interface, which is beneficial to extend the lifetime of photoinduced carriers. Our results demonstrate that the function of Ta3N5 in Ta3N5/KTaO3 photocatalytic system is determined by the termination property of KTaO3(110) surface, which provides a likely reason of the observed photocatalytic activity of overall water splitting achieved by Ta3N5 synthesized by using KTaO3 as a precursor for the nitridation reaction.

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β-MnO2 with proton conversion mechanism in rechargeable zinc ion battery Wenbao Liu, Xiaoyu Zhang, Yongfeng Huang, Baozheng Jiang, Ziwen Chang, Chengjun Xu, Feiyu Kang 2021, 56(5): 365-373.  DOI: 10.1016/j.jechem.2020.07.027 Abstract ( 4 )   PDF (10070KB) ( 1 )   Rechargeable aqueous zinc ion battery (RAZIB) is a promising energy storage system due to its high safety, and high capacity. Among them, manganese oxides with low cost and low toxicity have drawn much attention. However, the under-debate proton reaction mechanism and unsatisfactory electrochemical performance limit their applications. Nanorod β-MnO2 synthesized by hydrothermal method is used to investigate the reaction mechanism. As cathode materials for RAZIB, the Zn//β-MnO2 delivers 355 mAh g-1 (based on cathode mass) at 0.1 A g-1, and retain 110 mAh g-1 after 1000 cycles at 0.2 A g-1. Different from conventional zinc ion insertion/extraction mechanism, the proton conversion and Mn ion dissolution/deposition mechanism of β-MnO2 is proposed by analyzing the evolution of phase, structure, morphology, and element of β-MnO2 electrode, the pH change of electrolyte and the determination of intermediate phase MnOOH. Zinc ion, as a kind of Lewis acid, also provides protons through the formation of ZHS in the proton reaction process. This study of reaction mechanism provides a new perspective for the development of Zn//MnO2 battery chemistry.

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Spatial configuration engineering of perylenediimide-based non-fullerene electron transport materials for efficient inverted perovskite solar cells Mengmeng Zheng, Yawei Miao, Ali Asgher Syed, Cheng Chen, Xichuan Yang, Liming Ding, Huaming Li, Ming Cheng 2021, 56(5): 374-382.  DOI: 10.1016/j.jechem.2020.08.012 Abstract ( 11 )   PDF (3480KB) ( 6 )   Due to their excellent photoelectron chemical properties and suitable energy level alignment with perovskite, perylene diimide (PDI) derivatives are competitive non-fullerene electron transport material (ETM) candidates for perovskite solar cells (PSCs). However, the conjugated rigid plane structure of PDI units result in PDI-based ETMs tending to form large aggregates, limiting their application and photovoltaic performance. In this study, to restrict aggregation and further enhance the photovoltaic performance of PDI-type ETMs, two PDI-based ETMs, termed PDO-PDI2 (dimer) and PDO-PDI3 (trimer), were constructed by introducing a phenothiazine 5,5-dioxide (PDO) core building block. The research manifests that the optoelectronic properties and film formation property of PDO-PDI2 and PDO-PDI3 were deeply affected by the molecular spatial configuration. Applied in PSCs, PDO-PDI3 with three-dimensional spiral molecular structure, exhibits superior electron extraction and transport properties, further achieving the best PCE of 18.72% and maintaining 93% of its initial efficiency after a 720-h aging test under ambient conditions.

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Understanding the low temperature electrochemistry of magnesium-lithium hybrid ion battery in all-phenyl-complex solutions Muhammad Rashad, Muhammad Asif 2021, 56(5): 383-390.  DOI: 10.1016/j.jechem.2020.08.018 Abstract ( 10 )   PDF (5371KB) ( 2 )   Magnesium-lithium hybrid ion batteries have emerged as a new class of energy storage systems owing to dendrite free cycling of magnesium anode and possibility of practice of numerous conventional lithium cathodes. In present work, we used hybrid ion strategy to analyze the performance of lithium titanate based lithium cathode, magnesium metal anode, and all-phenyl complex (APC) electrolytes at different temperatures (25 °C, 10 °C, 0 °C, -10 °C, and -20 °C). The hybrid ion battery exhibited excellent rate performance (228 mAh g-1/20 mA g-1 and 163 mAh g-1/1000 mA g-1) with stable voltage plateaus at 0.90 and 0.75 V, which corresponds to specific energy of 178 Wh kg-1 at room temperature (25 °C). Experimental results revealed that APC-THF solutions have strong potential to suppress the freezing of electrolyte solutions owing to low boiling point of THF. The low temperature electrochemical testing revealed the reversible capacities of 213.4, 165.5, 143.8, 133.2 and 78.56 mAh g-1 at 25, 10, 0, -10, and -20 °C, respectively. Furthermore, ex-situ XRD, SEM, and EIS tests were carried out to understand the reaction kinetics of both Mg2+ and Li+ ions inside the lithium titanate cathode. We hope this work will shed light on low temperature prospective of electrochemical devices for use in cold environments.

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A two-dimension laminar composite protective layer for dendrite-free lithium metal anode Xiang-Qun Xu, Rui Xu, Xin-Bing Cheng, Ye Xiao, Hong-Jie Peng, Hong Yuan, Fangyang Liu 2021, 56(5): 391-394.  DOI: 10.1016/j.jechem.2020.08.029 Abstract ( 10 )   PDF (2969KB) ( 4 )

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In-situ construction of conducting alloy interphase towards modulating Li-ion storage kinetics Lingjie Li, Dandan Wang, Xiaoxia Xu, Xiaosong Guo, Jing Liu, Changming Mao, Zhonghua Zhang, Guicun Li 2021, 56(5): 395-403.  DOI: 10.1016/j.jechem.2020.08.031 Abstract ( 5 )   PDF (10877KB) ( 1 )   Interface engineering strategy shows great promise in promoting the reaction kinetic and cycling performance in the field of electrochemical energy storage application. In this work, an in-situ interface growth strategy is proposed to introduce a robust and conducting MoGe2 alloy interphase between the electrochemical active Ge nanoparticle and flexible MoS2 nanosheets to modulate their Li-ion storage kinetics. The structural evolution processes of the Ge@MoGe2@MoS2 composite are unraveled, during which the initially-generated Ge metals serve as a crucial reduction mediator in the formation of MoGe2 species bridging the Ge and MoS2. The as-generated MoGe2 interface, chemically bonding with both Ge and MoS2, possesses multi-fold merits, including the maintaining stable framework of electrochemically inactive Mo matrix to buffer the strain-stress effect and the “welding spot” effects to facilitate the efficient Li+/e- conduction. As well, the introduction of MoGe2 interface leads to a unique sequential lithiation/de-lithiation process, namely in the order of the electrochemically active MoS2-MoGe2-Ge during lithiation and vice versa, during which the electrode strain could be more effectively released. Benefited from the robust and rigid MoGe2 interface, the delicately designed Ge@MoGe2@MoS2 composite exhibits an improved charge/discharge performances (866.7 mAh g-1 at 5.0 A g-1 and 838.5 mAh g-1 after 400 cycles) while showing a high tap density of 1.23 g cm-3. The as-proposed in-situ interface growth strategy paves a new avenue for designing novel high-performance electrochemical energy storage materials.

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Pyridinic nitrogen enriched porous carbon derived from bimetal organic frameworks for high capacity zinc ion hybrid capacitors with remarkable rate capability Yao Li, Pengfei Lu, Ping Shang, Lisha Wu, Xiao Wang, Yanfeng Dong, Ronghuan He, Zhong-Shuai Wu 2021, 56(5): 404-411.  DOI: 10.1016/j.jechem.2020.08.005 Abstract ( 5 )   PDF (5571KB) ( 2 )   Aqueous zinc ion hybrid capacitors (ZIHCs) hold great potential for large-scale energy storage applications owing to their high safety and low cost, but suffer from low capacity and energy density. Herein, pyridinic nitrogen enriched porous carbon (nPC) was successfully synthesized via the growth, subsequent annealing and acid etching of bimetal organic frameworks for high capacity and safe ZIHCs with exceptional rate capability. Benefiting from the mesopores for easy ion diffusion, high electrical conductivity enabled by in-situ grown carbon nanotubes matrix and residual metal Co nanoparticles for fast electron transfer, sufficient micropores and high N content (8.9 at%) with dominated pyridinic N (54%) for enhanced zinc ion storage, the resulting nPC cathodes for ZIHCs achieved high capacities of 302 and 137 mAh g-1 at 1 and 18 A g-1, outperforming most reported carbon based cathodes. Theoretical results further disclosed that pyridinic N possessed larger binding energy of -4.99 eV to chemically coordinate with Zn2+ than other N species. Moreover, quasi-solid-state ZIHCs with gelatin based gel electrolytes exhibited high energy density of 157.6 Wh kg-1 at 0.69 kW kg-1, high safety and mechanical flexibility to withstand mechanical deformation and drilling. This strategy of developing pyridinic nitrogen enriched porous carbon will pave a new avenue to construct safe ZIHCs with high energy densities.

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Effect of mass transfer and solution composition on the quantification of reaction kinetics by differential electrochemical mass spectrometry Wei Chen, Nestor Uwitonze, Fan He, Matthew M. Sartin, Jun Cai, Yan-Xia Chen 2021, 56(5): 412-419.  DOI: 10.1016/j.jechem.2020.08.006 Abstract ( 3 )   PDF (932KB) ( 3 )   Differential electrochemical mass spectrometry (DEMS) is one of the most powerful techniques for both the mechanistic and kinetic study of complicated electrocatalytic reactions. It can provide information on the nature and yields of the products generated, their production rate, and the structure-activity relationship between the electrocatalysts and the target reactions. The precise calibration of the mass signal is a prerequisite for the accurate evaluation of reaction kinetics. In this work, we use the oxidation reactions of CO and HCOOH to demonstrate how certain conditions, such as the flow rate and solution composition, affect the collection efficiency and ionization probability of the species to be detected. These parameters can affect the determination of the mass calibration constant and the accuracy of the subsequent quantitative DEMS analysis. We show the relationship between the mass calibration constant and the flow rate, and provide strategies for eliminating this and the related problems.

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Research progress on gel polymer electrolytes for lithium-sulfur batteries Jie Qian, Biyu Jin, Yuanyuan Li, Xiaoli Zhan, Yang Hou, Qinghua Zhang 2021, 56(5): 420-437.  DOI: 10.1016/j.jechem.2020.08.026 Abstract ( 18 )   PDF (11550KB) ( 10 )   Lithium-sulfur (Li-S) batteries have become a promising candidate for advanced energy storage system owing to low cost and high theoretical specific energy. In the last decade, in pursuit of Li-S batteries with enhanced safety and energy density, the investigation on the electrolytes has leaped form liquid organic electrolytes to solid polymer ones. However, such solid-state Li-S battery system is greatly limited by unfavorable ionic conductivity, poor interfacial contact and narrow electrochemical windows on account of the absence of any liquid components. To address these issues, gel polymer electrolytes (GPEs), the incorporation of liquid electrolytes into solid polymer matrixes, have been newly developed. Although the excellent ionic transport and low interfacial resistance provided by GPEs have prompted numerous researchers to make certain progress on high-performance Li-S coins, a comprehensive review on GPEs for Li-S batteries remains vacant. Herein, this review focuses on recent development and progress on GPEs in view of their physical and chemical properties for the applications in Li-S batteries. Studies on the components including solid hosts, liquid solutions and fillers of GPEs are systematically summarized with particular emphasis on the relationship between components and performance. Finally, current challenges and directional outlook for fabricating GPEs-based Li-S batteries with outstanding performance are outlined.

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Atomic/nano-scale in-situ probing the shuttling effect of redox mediator in Na-O2 batteries Kai Yang, Yiwei Li, Langlang Jia, Yan Wang, Zijian Wang, YuChen Ji, Magda Titirici, Xinhua Liu, Luyi Yang, Feng Pan 2021, 56(5): 438-443.  DOI: 10.1016/j.jechem.2020.08.025 Abstract ( 6 )   PDF (7866KB) ( 3 )   Sodium-oxygen batteries (Na-O2) have attracted extensive attention as promising energy storage systems due to their high energy density and low cost. Redox mediators are often employed to improve Na-O2 battery performance, however, their effect on the formation mechanism of the oxygen reduction product (NaO2) is still unclear. Here, we have investigated the formation mechanism of NaO2 during the discharge process in the presence of a redox mediator with the help of atomic/nano-scale in-situ characterization tools used in concert (e.g. atomic force microscope, electrochemical quartz crystal microbalance (EQCM) and laser nano-particle analyzer). As a result, real-time observations on different time scales show that by shuttling electrons to the electrolyte, the redox mediator enables formation of NaO2 in the solution-phase instead of within a finite region near the electrode surface. These findings provide new fundamental insights on the understanding of Na-O2 batteries and new consequently perspectives on designing high performance metal-O2 batteries and other related functions.

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Valence state of transition metal center as an activity descriptor for CO2 reduction on single atom catalysts Shisheng Zheng, Changjian Zuo, Xianhui Liang, Shunning Li, Feng Pan 2021, 56(5): 444-448.  DOI: 10.1016/j.jechem.2020.08.023 Abstract ( 8 )   PDF (3533KB) ( 10 )

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The synergy of modulated surface polarity and oxygen vacancy for CO2 to methanol over Zn(δ-)-Ti(δ+)Ovacancy Junfu Zhou, Lin Ye, Daofeng Huang, Meiyin Wang, Yuanhang Ren, Bin Yue, Heyong He 2021, 56(5): 449-454.  DOI: 10.1016/j.jechem.2020.08.021 Abstract ( 11 )   PDF (2742KB) ( 3 )

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Simultaneously enhanced moisture tolerance and defect passivation of perovskite solar cells with cross-linked grain encapsulation Ke Xiao, Qiaolei Han, Yuan Gao, Shuai Gu, Xin Luo, Renxing Lin, Jia Zhu, Jun Xu, Hairen Tan 2021, 56(5): 455-462.  DOI: 10.1016/j.jechem.2020.08.020 Abstract ( 3 )   PDF (3572KB) ( 2 )   The grain surfaces (film surface and grain boundary) of polycrystalline perovskite films are vulnerable sites in solar cells since they pose a high defect density and initiate the degradation of perovskite absorber. Achieving simultaneously defect passivation and grain protection from moisture is crucial for the viability of perovskite solar cells. Here, an in situ cross-linked grain encapsulation (CLGE) strategy that improves both device stability and defect passivation is reported. Cross-linkable semiconducting small molecules are mixed into the antisolvent to uniformly form a compact and conducting cross-linked layer over the grain surfaces. This cross-linked coating layer not only passivates trap states and facilitates hole extraction, but also enhances the device stability by preventing moisture diffusion. Using the CLGE strategy, a high power conversion efficiency (PCE) of 22.7% is obtained in 1.55-eV bandgap planar perovskite solar cells. The unencapsulated devices with CLGE exhibit significantly enhanced device stability again moisture and maintain >90% of their initial PCE after shelf storage under ambient condition for over 10,000 h.

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Boron-doping induced lithophilic transition of graphene for dendrite-free lithium growth Wei Liu, Pengbo Zhai, Shengjian Qin, Jing Xiao, Yi Wei, Weiwei Yang, Shiqiang Cui, Qian Chen, Chunqiao Jin, Shubin Yang, Yongji Gong 2021, 56(5): 463-469.  DOI: 10.1016/j.jechem.2020.08.019 Abstract ( 7 )   PDF (10688KB) ( 4 )   Li metal, possessing advantages of high theoretical specific capacity and low electrochemical potential, is regarded as the most promising anode material for next-generation batteries. However, despite decades of intensive research, its practical application is still hindered by safety hazard and low Coulombic efficiency, which is primarily caused by dendritic Li deposition. To address this issue, restraining dendrite growth at the nucleation stage is deemed as the most effective method. By utilizing the difference of electronegativity between boron atoms and carbon atoms, carbon atoms around boron atoms in boron-doped graphene (BG) turn into lithiophilic sites, which can enhance the adsorption capacity to Li+ at the nucleation stage. Consequently, an ultralow overpotential of 10 mV at a current density of 0.5 mA/cm2 and a high average Coulombic efficiency of 98.54% over more than 140 cycles with an areal capacity of 2 mAh/cm2 at a current density of 1 mA/cm2 were achieved. BG-Li|LiFePO4 full cells delivered a long lifespan of 480 cycles at 0.5 C and excellent rate capability. This work provides a novel method for rational design of dendrite-free Li metal batteries by regulating nucleation process.

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Insights into efficient transition metal-nitrogen/carbon oxygen reduction electrocatalysts Hao-Yu Wang, Chen-Chen Weng, Zhong-Yong Yuan 2021, 56(5): 470-485.  DOI: 10.1016/j.jechem.2020.08.030 Abstract ( 1 )   PDF (15181KB) ( 1 )   It is of vital importance to accelerate the sluggish oxygen reduction reaction (ORR) process at the cathode with earth-abundant metal-based catalysts for the commercialization of low-temperature polymer electrolyte membrane fuel cells. In consideration of high catalytic activity, long-term stability and low cost of potential ORR electrocatalysts, transition metal species have attracted much interest and transition metal-nitrogen-carbon (M-N/C, M = Fe, Co, Ni, Mn, etc.) catalysts have been widely considered as the most promising non-precious metal catalysts for ORR. Herein, the fundamental understanding of ORR catalytic mechanism and the identification of active centers are briefly introduced, and then different M-N/C catalysts classified by precursors with the strategies for design and optimization are highlighted. The challenges and possible opportunity for future development of high-performance ORR catalysts are finally proposed.

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A highly selective catalyst of Co/La4Ga2O9 for CO2hydrogenation to ethanol Kang An, Siran Zhang, Jiaming Wang, Qiang Liu, Ziyang Zhang, Yuan Liu 2021, 56(5): 486-495.  DOI: 10.1016/j.jechem.2020.08.045 Abstract ( 17 )   PDF (7799KB) ( 6 )   A new catalyst of Co/La4Ga2O9 for CO2 hydrogenation to produce ethanol was prepared by reducing LaCo0.5Ga0.5O3, which showed excellent selectivity to ethanol (≈35C-mol%) at mild reaction conditions (270 °C, 3.5 MPa, 3000 mL g-1 h-1). The catalysts were characterized by N2 adsorption/desorption, XRD, XAFS, CO and CO2-TPD, H2 chemisorption, XPS and TEM techniques. The interaction between Co nanoparticles (NPs) and La4Ga2O9 oxide resulted in Co0-Co2+ on the surface of Co NPs. It was proposed that La4Ga2O9 could catalyze reverse water gas shift reaction (r-WGS), which converted CO2 to CO. Then, the CO migrated to Co0-Co2+ on Co NPs, where it was hydrogenated to form ethanol like higher alcohols synthesis from syngas. The results suggest that by controlling the oxidation state of cobalt, and combined with a kind of active site for activating CO2 to form CO, a catalyst with excellent selectivity to ethanol could be obtained for CO2 hydrogenation, which means that the complex reaction may be proceed with high selectivity using only one active metal component.

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A low temperature processable tin oxide interlayer via amine-modification for efficient and stable organic solar cells Shun Guang, Jiangsheng Yu, Hongtao Wang, Xin Liu, Shenya Qu, Rihong Zhu, Weihua Tang 2021, 56(5): 496-503.  DOI: 10.1016/j.jechem.2020.08.036 Abstract ( 7 )   PDF (3947KB) ( 4 )   The exploitation of proper electron transport layers (ETLs) and interface optimization can play a pivotal role to promote the performance of organic solar cells (OSCs). In this work, low temperature processable tin oxide (SnO2) colloidal nanoparticles with ethanolamine (EA) treatment are successfully employed for efficient and stable OSCs with light soaking free. The EA is chemically bonded with SnO2, and the ethanolamine treated tin oxide (E-SnO2) layer delivers a suitable work function of 4.10 eV and a unique surface texture with suspended polar moieties. The enhanced performance of E-SnO2 based OSCs can be attributed to the improved charge transport and electron extraction, which is correlated with the regulated energy level alignment and contact quality of E-SnO2/active layer. As a result, considerable power conversion efficiencies (PCEs) of 10.30%, 13.93% and 15.38% for PTB7-Th/PC71BM, PM7/ITC6-4F and PM6/Y6 based OSCs have been realized with E-SnO2 as ETL, respectively. Compared with ZnO based devices, the E-SnO2 based OSCs exhibit an improved light aging stability, which can retain 94.3% of their initial PCE of 15.38% after 100 h light aging for E-SnO2/PM6/Y6 based OSCs. This work demonstrates that the enormous potential of E-SnO2 to serve as ETL for high-efficiency and stable OSCs.

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Structural limiting factors of mixed-valent tin oxides in photoelectrochemical application: A comparative exploration Yalong Zou, Deyu Liu, Xiangrui Meng, Qitao Liu, Yang Zhou, Jianming Li, Zhiying Zhao, Ding Chen, Yongbo Kuang 2021, 56(5): 504-511.  DOI: 10.1016/j.jechem.2020.08.027 Abstract ( 8 )   PDF (4732KB) ( 3 )   Photoelectrocatalytic (PEC) materials for harvesting solar energy can be discovered from existing photocatalytic semiconductors. Nonetheless, mixed valence tin oxides, a group of widely reported visible light active photocatalysts, can hardly be developed into efficient PEC photoelectrodes. To overcome this difficulty by clarifying its origin, two typical mixed valence tin oxides, Sn2+:SnO2 microrods and porous Sn3O4 particles were deliberately prepared as the models. Sn2+:SnO2 microrods of less porosity exhibited a photocurrent over ten times higher than Sn3O4 particles. Photo-electrochemical impedance spectroscopy revealed this was due to their charge kinetics difference, specifically the internal transport/transfer responding to the morphology. Moreover, hydroxyl residuals from synthesis were found to be very inhibitive for the PEC efficiency as well, which was in coherence with our TGA and Raman spectroscopic study. These finding experimentally proved the necessity of reconsidering the surface area, crystallinity, and defects when developing photocatalysts into efficient PEC structures.

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An integrated strategy towards the facile synthesis of core-shell SiC-derived carbon@N-doped carbon for high-performance supercapacitors Zhongya Pang, Guangshi Li, Xingli Zou, Chenteng Sun, Conghui Hu, Wei Tang, Li Ji, Hsien-Yi Hsu, Qian Xu, Xionggang Lu 2021, 56(5): 512-521.  DOI: 10.1016/j.jechem.2020.08.042 Abstract ( 9 )   PDF (12526KB) ( 3 )   Porous active core-shell carbon material with excellent synergistic effect has been regarded as a prospective material for supercapacitors. Herein, we report an integrated method for the facile synthesis of carbide-derived carbon (CDC) encapsulated with porous N-doped carbon (CDC@NC) towards high-performance supercapacitors. Polydopamine (PDA) as nitrogen and carbon sources was simply coated on SiC nanospheres to form SiC@PDA, which was then directly transformed into CDC@NC via a one-step molten salt electro-etching/in-situ doping process. The synthesized CDC@NC with hierarchically porous structure has a high specific surface area of 1191 m2 g-1. The CDC core and NC shell are typical amorphous carbon and more ordered N-doped carbon, respectively. Benefitting from its unique dual porous structures, the CDC@NC demonstrates high specific capacitances of 255 and 193 F g-1 at 0.5 and 20 A g-1, respectively. The reaction mechanism of the electro-etching/in-situ doping process has also been investigated through experimental characterizations and theoretical density functional theory calculations. It is suggested that the molten salt electro-etching/in-situ doping strategy is promising for the synthesis of active core-shell porous carbon materials with synergistic properties for supercapacitors without the need for additional doping/activation processes.