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2020, Vol. 51, No. 12　Online: 15 December 2020

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Sodiophilicity/potassiophilicity chemistry in sodium/potassium metal anodes Xiang Chen, Yun-Ke Bai, Xin Shen, Hong-Jie Peng, Qiang Zhang 2020, 51(12): 1-6.  DOI: 10.1016/j.jechem.2020.03.051 Abstract ( 5 )   PDF (1696KB) ( 3 )   Heteroatom-doped carbon materials have been widely used as sodium (Na) and potassium (K) metal anode frameworks to achieve uniform Na and K depositions. If the origin of the Sodiophilicity and potas- siophilicity of doping sites in heteroatom-doped carbon host are clearly understood, the nucleation and growth behavior of Na and K can be precisely regulated in working batteries. Herein the Sodiophilicity and potassiophilicity chemistries of carbon materials are probed through first-principles calculations. The local dipole of doping functional groups and charge transfer during Na/K deposition are regarded as key principles to reveal the sodiophilic and potassiophilic nature of doping sites. Especially, O-B, O-S, and O-P co-doping strategy are predicted to be effective methods to improve the Sodiophilicity and potassio- philicity of carbon hosts and thus render safe and dendrite-free Na and K metal anodes. This work affords a deep and insightful understanding of Sodiophilicity and potassiophilicity chemistry of Na and K anodes and establishes general principles of designing highly sodiophilic and potassiophilic carbon frameworks.

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Diflurobenzothiadiazole core-based noncovalently fused small molecule acceptor exhibiting over 12% efficiency and high fill factor Qin Chang, Honggang Chen, Jun Yuan, Yunbin Hu, Jiefeng Hai, Wei Liu, Fangfang Cai, Juan Hong, Xuxian Xiao, Yingping Zou 2020, 51(12): 7-13.  DOI: 10.1016/j.jechem.2020.03.036 Abstract ( 7 )   PDF (1958KB) ( 2 )   The versatility and flexibility of organic photoelectric materials endow organic photovoltaic cells fine function modulation and huge commercial potential. In this work, a new noncovalent fused-ring small molecule acceptor (SMA) BID-4F has been synthesized for high-efficient organic solar cells (OSCs). BID-4F consists of a diflurobenzothiadiazole (DFBT) core, ladder-like indacenodithiophene (IDT) spacers, and di- cyanoindanone electron-withdrawing end groups, which are supposed to be conformationally interlocked by noncovalent interactions, leading to good molecular planarity. In addition, compact solid state stack- ing was revealed by UV-vis-NIR absorption spectrum. The optimized PM6:BID-4F based device delivers an eminent power conversion efficiency (PCE) of 12.30% with a high open-circuit voltage (Voc) of 0.92 V and a high fill factor (FF) of 74.3%. Most importantly, the PCE and FF are among one of the highest values reported for the OSCs based on the unfused-ring SMAs. Overall, our work demonstrates that the unfused ring central framework with high molecular planarity through noncovalent interactions provides a good strategy to construct highly efficient SMAs.

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Enhanced stability of Pt/Al2O3 modified by Zn promoter for catalytic dehydrogenation of ethane✩ Xiaoyu Li, Yanliang Zhou, Botao Qiao, Xiaoli Pan, Chaojie Wang, Liru Cao, Lin Li, Jian Lin, Xiaodong Wang 2020, 51(12): 14-20.  DOI: 10.1016/j.jechem.2020.03.045 Abstract ( 5 )   PDF (2359KB) ( 1 )   Catalytic ethane dehydrogenation (EDH) to ethylene over Pt-based catalysts has received increasing in- terests in recent years as it is a potential alternative route to conventional steam cracking. However, the catalysts used in this reaction often suffer from rapid deactivation due to serious coke deposition and metal sintering. Herein, we reported the effects of Zn modification on the stability of Pt/Al2O3 for EDH. The Zn-modified sample (PtZn2/Al2O3) exhibits stable ethane conversion (20%) with over 95% ethylene se- lectivity. More importantly, it exhibits a significantly low deactivation rate of only 0.003 h-1 at 600 °C for 70 h, which surpasses most of previously reported catalysts. Detailed characterizations including in situ FT-IR, ethylene adsorption microcalorimetry, and HAADF-STEM etc. reveal that Zn modifier reduces the number of Lewis acid sites on the catalyst surface. Moreover, it could modify Pt sites and preferentially cover the step sites, which decrease surface energy and retard the sintering of Pt particle, then prohibit- ing the further dehydrogenation of ethylene to ethylidyne. Consequently, the good stability is realized due to anti-sintering and the decrease of coke formation on the PtZn2/Al2O3 catalyst.

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Flower-like ZnO modified with BiOI nanoparticles as adsorption/catalytic bifunctional hosts for lithium-sulfur batteries Peng Zeng, Hao Yu, Manfang Chen, Wensheng Xiao, Yongfang Li, Hong Liu, Jing Luo, Jiao Peng, Dingsheng Shao, Ziyi Zhou, Zhigao Luo, Ying Wang, Baobao Chang, Xianyou Wang 2020, 51(12): 21-29.  DOI: 10.1016/j.jechem.2020.03.040 Abstract ( 7 )   PDF (3508KB) ( 2 )   Due to the high specific capacity and energy density, lithium-sulfur battery is regarded as a potential energy storage conversion system. However, the serious shuttle effect and the sluggish electrochemical reaction kinetics impede the practical use of lithium-sulfur battery. In the interests of breaking through the above knotty problems, herein we propose to use the polar flower-like ZnO modified by BiOI nanopar- ticles as bifunctional host with catalytic and adsorption ability for polysulfides in lithium-sulfur battery. It can be found that this adsorption/catalytic host integrates the functions of adsorption and mutual cat- alytic conversion of polysulfides, in which the polar flower-like ZnO can effectively capture the poly- sulfides through strong polar-polar interaction, simultaneously the BiOI nanoparticles can accelerate the mutual conversion of polysulfides to Li2S through reducing the activation energy and conversion energy barrier required for the electrochemical reaction. As a result, under a sulfur loading of 2.5 mg cm-2, the lithium-sulfur battery with ZnO/BiOI/CNT/S as cathode reveals a considerable initial specific capacity of 1267 mAh g-1 at a current density of 0.1C. Even the current density increased to 1C, the capacity can reach as 873.4 mAh g-1, together with a good capacity retention of 67.1% after 400 cycles. Therefore, after systematically study the positive effects of the flower-like ZnO modified by catalytic BiOI nanopar- ticles on the adsorption and catalytic conversion of polysulfides, this work provides a new idea for the development and application of high-performance lithium-sulfur batteries.

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Fluorination over Cr doped layered perovskite Sr2TiO4 for efficient photocatalytic hydrogen production under visible light illumination Jinxing Yu, Xiaoxiang Xu 2020, 51(12): 30-38.  DOI: 10.1016/j.jechem.2020.03.025 Abstract ( 3 )   PDF (2508KB) ( 1 )   Cr doped Ruddlesden-Popper compound Sr2TiO4 has been successfully modified by fluorine to form a new compound Sr2Ti0.95Cr0.05O3F2. Structure analysis suggests two types of fluorine in the structure of this new compound, i.e. intralayer and interlayer F, which induce strong built-in electric field within this layered compound. The electric field stems from uneven distribution of F atoms on the two sides of perovskite layers therefore leads to charge disproportionation. DFT calculations suggest that this unique structural feature is highly beneficial for charge dissociations as it breaks the coplanar settlement of con- duction band minimum and valence band maximum whilst maintains the 2D charge transportation prop- erties. This is clearly demonstrated by the superior photocatalytic activities of Sr2Ti0.95Cr0.05O3F2 for hy- drogen production from water. Apparent quantum efficiency (AQE) as high as 1.16% at 420 ± 20 nm has been achieved which stands as the highest AQE reported on Sr2TiO4 to date. Photoelectrochemical (PEC) analysis confirms improved charge separation conditions and prolonged charge lifetime.

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Enhanced high-temperature performance of Li-rich layered oxide via surface heterophase coating Yuefeng Su, Feiyu Yuan, Lai Chen, Yun Lu, Jinyang Dong, Youyou Fang, Shi Chen, Feng Wu 2020, 51(12): 39-47.  DOI: 10.1016/j.jechem.2020.03.033 Abstract ( 6 )   PDF (3732KB) ( 2 )   Li-rich layered oxides have become one of the most concerned cathode materials for high-energy lithium- ion batteries, but they still suffer from poor cycling stability and detrimental voltage decay, especially at elevated temperature. Herein, we proposed a surface heterophase coating engineering based on amor- phous/crystalline Li3PO4 to address these issues for Li-rich layered oxides via a facile wet chemical method. The heterophase coating layer combines the advantages of physical barrier effect achieved by amorphous Li3PO4 with facilitated Li+ diffusion stemmed from crystalline Li3PO4. Consequently, the mod- ified Li1.2Ni0.2Mn0.6O2 delivers higher initial coulombic efficiency of 92% with enhanced cycling stability at 55 °C (192.9 mAh/g after 100 cycles at 1 C). More importantly, the intrinsic voltage decay has been in- hibited as well, i.e. the average potential drop per cycle decreases from 5.96 mV to 2.99 mV. This surface heterophase coating engineering provides an effective strategy to enhance the high-temperature electro- chemical performances of Li-rich layered oxides and guides the direction of surface modification strate- gies for cathode materials in the future.

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Reduction and carburization of iron oxides for Fischer-Tropsch Synthesis Monia Runge Nielsen, Asger Barkholt Moss, Anton Simon Bjørnlund, Xi Liu, Axel Knop-Gericke, Alexander Yu. Klyushin, Jan-Dierk Grunwaldt, Thomas L. Sheppard, Dmitry E. Doronkin, Anna Zimina, Thomas Eric Lyck Smitshuysen, Christian Danvad Damsgaard, Jakob Birkedal Wagner, Thomas Willum Hansen 2020, 51(12): 48-61.  DOI: 10.1016/j.jechem.2020.03.026 Abstract ( 4 )   PDF (5572KB) ( 1 )   The activation of iron oxide Fischer-Tropsch Synthesis (FTS) catalysts was investigated during pretreat- ment: reduction in hydrogen followed by carburization in either CO or syngas mixture, or simultaneously reduction and carburization in syngas. A combination of different complementary in situ techniques was used to gain insight into the behavior of Fe-based FTS catalysts during activation. In situ XRD was used to identify the crystalline structures present during both reduction in hydrogen and carburization. An increase in reduction rate was established when increasing the temperature. A complete reduction was demonstrated in the ETEM and a grain size dependency was proven, i.e. bigger grains need higher tem- perature in order to reduce. XPS and XAS both indicate the formation of a small amount of carbonaceous species at the surface of the bulk metallic iron during carburization.

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Sandwiched N-carbon@Co9S8@Graphene nanosheets as high capacity anode for both half and full lithium-ion batteries Ningning Li, Li Sun, Kai Wang, Sheng Xu, Jun Zhang, Xiangxin Guo, Xianghong Liu 2020, 51(12): 62-71.  DOI: 10.1016/j.jechem.2020.03.028 Abstract ( 6 )   PDF (4150KB) ( 2 )   Transition metal sulfides (TMSs) are promising candidates for replacing graphite anode in LIBs. However, the low conductivity and structural collapse caused by the large volume change during lithium inser- tion and extraction greatly limit its application. Herein, we report a unique design of a two-dimensional (2D) sandwich structure of N-doped carbon@Co9S8@graphene (N-C@Co9S8@G) with multilayer struc- ture. Electrochemical tests reveal that the N-C@Co9S8@G nanosheets possess a high reversible capacity (1009 mA h g-1 at 0.1 A g-1), and excellent rate capability (422 mA h g-1 at 10 A g-1) and long cycle life (853 mA h g-1 at 1 A g-1 for 500 cycles). Experimental studies reveal that capacitive storage contributes to the high reversible capacity. The lithium storage kinetics are studied by Galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS). Meanwhile, the potential of N-C@Co9S8@G anode in a full cell using LiCoO2 as the cathode is also demonstrated, exhibiting a high reversible capacity of 300 mA h g-1 cycles at 0.1 A g-1. The strategy proposed in this work paves the way to engineering high performance anodes in LIBs.

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Reversible Al3+ storage mechanism in anatase TiO2 cathode material for ionic liquid electrolyte-based aluminum-ion batteries Na Zhu, Feng Wu, Zhaohua Wang, Liming Ling, Haoyi Yang, Yaning Gao, Shuainan Guo, liumin Suo, Hong Li, Huajie Xu, Ying Bai, Chuan Wu 2020, 51(12): 72-80.  DOI: 10.1016/j.jechem.2020.03.032 Abstract ( 7 )   PDF (2754KB) ( 1 )   Rechargeable aluminum ion battery (AIB) with high theoretical specific capacity, abundant elements and low cost engages considerable attention as a promising next generation energy storage and conversion system. Nevertheless, to date, one of the major barriers to pursuit better AIB is the limited applicable cathode materials with the ability to store aluminum highly reversibly. Herein, a highly reversible AIB is proposed using mesoporous TiO2 microparticles (M-TiO2) as the cathode material. The improved perfor- mance of TiO2/Al battery is ascribed to the high ionic conductivity and material stability, which is caused by the stable architecture with a mesoporous microstructure and no random aggregation of secondary particles. In addition, we conducted detailed characterization to gain deeper understanding of the Al3+ storage mechanism in anatase TiO2 for AIB. Our findings demonstrate clearly that Al3+ can be reversibly stored in anatase TiO2 by intercalation reactions based on ionic liquid electrolyte. Especially, DFT calcu- lations were used to investigate the accurate insertion sites of aluminum ions in M-TiO2 and the volume changes of M-TiO2 cells during discharging. As for the controversial side reactions in AIBs, in this work, by normalized calculation, we confirm that M-TiO2 alone participate in the redox reaction. Moreover, cyclic voltammetry (CV) test was performed to investigate the pseudocapacitive behavior.

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γ -MnO2 nanorod-assembled hierarchical micro-spheres with oxygen vacancies to enhance electrocatalytic performance toward the oxygen reduction reaction for aluminum-air batteries Ge Huo, Xue-Wan Wang, Zhi-Bin Zhang, Zhongxin Song, Xiao-Min Kang, Ming-Xing Chen, Qi Wang, Xian-Zhu Fu, Jing-Li Luo 2020, 51(12): 81-89.  DOI: 10.1016/j.jechem.2020.03.030 Abstract ( 9 )   PDF (3557KB) ( 2 )   γ -MnO2 nanorod-assembled hierarchical micro-spheres with abundant oxygen defects are synthesized by a simple thermal treatment approach as oxygen reduction electrocatalysts for Al (aluminum) - air batteries. The rich oxygen vacancies on the surface of γ -MnO2 are verified by morphology, structure, electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS) results. The oxygen reduction reaction (ORR) electrocatalytic activity of γ -MnO2 is significantly improved by the incoming oxygen vacancies. The γ -MnO2 nanorod-assembled hierarchical micro-spheres calcined under 300 °C in Ar atmosphere show the best ORR performance. The primary Al-air batteries using γ -MnO2 catalysts as the cathode, which demonstrates excellent peal power density of 318 mW cm-2 when applying the γ -MnO2 catalysts with optimal amount of oxygen vacancies.

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Boosting the polysulfide confinement in B/N-codoped hierarchically porous carbon nanosheets via Lewis acid-base interaction for stable Li-S batteries Dong-Gen Xiong, Ze Zhang, Xiao-Yun Huang, Yan Huang, Ji Yu, Jian-Xin Cai, Zhen-Yu Yang 2020, 51(12): 90-100.  DOI: 10.1016/j.jechem.2020.03.071 Abstract ( 6 )   PDF (5056KB) ( 2 )   Carbon materials have shown remarkable usefulness in facilitating the performance of insulating sulfur cathode for lithium-sulfur batteries owing to their excellent conductivity and porous structure. However, the anxiety is the poor affinity toward polar polysulfides due to the intrinsic nonpolar surface of carbon. Herein, we report a direct pyrolysis of the mixture urea and boric acid to synthesize B/N-codoped hi- erarchically porous carbon nanosheets (B-N-CSs) as efficient sulfur host for lithium-sulfur battery. The graphene-like B-N-CSs provides high specific surface area and porous structure with abundant microp- ores (1.1 nm) and low-range mesopores (2.3 nm), thereby constraining the sulfur active materials within the pores. More importantly, the codoped B/N elements can further enhance the polysulfide confinement through strong Li-N and B-S interaction based on the Lewis acid-base theory. These structural superior- ities significantly suppress the shuttle effect by both physical confinement and chemical interaction, and promote the redox kinetics of polysulfide conversion. When evaluated as the cathode host, the S/B-N- CSs composite displays the excellent performance with a high reversible capacity up to 772 mA h g-1 at 0.5 C and a low fading rate of ~0.09% per cycle averaged upon 500 cycles. In particular, remarkable stability with a high capacity retention of 87.1% can be realized when augmenting the sulfur loading in the cathode up to 4.6 mg cm-2.

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Into the “secret” double layer: Alkali cation mediates the hydrogen evolution reaction in basic medium Fanan Wang, Gang Xu, Yanghua He, Zhipeng Liu, Zhigang Zhang, Qing Mao, Yanqiang Huang 2020, 51(12): 101-104.  DOI: 10.1016/j.jechem.2020.03.037 Abstract ( 4 )   PDF (879KB) ( 3 )   The hydrogen evolution reaction (HER) - as an essential half reaction in water electrolysis and chlor-alkali process has been well studied in acidic electrolyte, but much less has been known in basic medium. In this study, by combining kinetic modeling and electrochemical measurements, we show that hydrated alkali cation clusters can adsorb on the surface of HER catalyst in basic electrolyte. The bound H2O molecules in the “clusters” can thus be in-situ activated through the hydration effect, which dissociate on the catalyst surface as the reactant of HER. The effective concentration and hydration energy of alkali cation can influence the H2O dissociation rate, and hence the kinetics of HER. Our work demonstrates a new understanding of the HER mechanism in basic reaction electrolyte.

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Metal-organic interface engineering for boosting the electroactivity of Pt nanodendrites for hydrogen production Juan Bai, Nan Jia, Pujun Jin, Pei Chen, Jia-Xing Jiang, Jing-Hui Zeng, Yu Chen 2020, 51(12): 105-112.  DOI: 10.1016/j.jechem.2020.03.054 Abstract ( 3 )   PDF (2308KB) ( 1 )   Recently, the surface chemical functionalization and morphology control of precious metal nanostruc- tures have been recognized as two efficient strategies for improving their electroactivity and/or selectiv- ity. In this work, 1, 10-phenanthroline monohydrate (PM) functionalized Pt nanodendrites (Pt-NDs) on carbon cloth (CC) (denoted as PM@Pt-NDs/CC) and polyethylenimine (PEI) functionalized Pt-NDs on CC (denoted as PEI@Pt-NDs/CC) are successfully achieved by immersing Pt-NDs/CC into PM and PEI aque- ous solutions, respectively. PEI functionalization of Pt-NDs/CC improves its electroactivity for hydrogen evolution reaction (HER) due to local proton enrichment whereas PM functionalization of Pt-NDs/CC im- proves its electroactivity for formic acid oxidation reaction (FAOR) by facilitating dehydrogenation path- way. With such high activity, a two-electrode electrolyzer is assembled using PM@Pt-NDs/CC as the an- odic electrocatalyst and PEI@Pt-NDs/CC as the cathodic electrocatalyst for electrochemical reforming of formic acid, which only requires 0.45 V voltage to achieve the current density of 10 mA cm-1 for high- purity hydrogen production, much lower than conventional water electrolysis (1.59 V). The work presents an example of interfacial engineering enhancing electrocatalytic activity and indicates that electrochem- ical reforming of formic acid is an energy-saving electrochemical method for high-purity hydrogen production.

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Recent progress of precious-metal-free electrocatalysts for efficient water oxidation in acidic media Samarjeet Singh Siwal, Wenqiang Yang, Qibo Zhang 2020, 51(12): 113-133.  DOI: 10.1016/j.jechem.2020.03.079 Abstract ( 11 )   PDF (5553KB) ( 1 )   The realization of efficient oxygen evolution reaction (OER) is critical to the development of multiple sus- tainable energy conversion and storage technologies, especially hydrogen production via water electroly- sis. To achieve the massive application of hydrogen energy and mass-scale hydrogen production from wa- ter splitting drives the pursuit of competent precious-metal-free electrocatalysts in acidic media, where the hydrogen evolution reaction (HER) is more facilitated. However, the development of high-efficient and acid-stable OER electrocatalysts, which are robust to function stably at high oxidation potentials in the acidic electrolyte, remains a great challenge. This article contributes a focused, perceptive review of the up-to-date approaches toward this emerging research field. The OER reaction mechanism and fundamen- tal requirements for oxygen evolution electrocatalysts in acid are introduced. Then the progress and new discoveries of precious-metal-free active materials and design concepts with regard to the improvement of the intrinsic OER activity are discussed. Finally, the existing scientific challenges and the outlooks for future research directions to the fabrication of emerging, earth-abundant OER electrocatalysts in acid are pointed out.

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Hexagonally ordered microbowl arrays decorated with ultrathin CuInS2 nanosheets for enhanced photoelectrochemical performance Ming Li, Le Chen, Yanjie Su, Huan Yin, Kexiang Hu 2020, 51(12): 134-142.  DOI: 10.1016/j.jechem.2020.03.070 Abstract ( 4 )   PDF (4120KB) ( 1 )   This paper demonstrates the design and fabrication of three-dimensional (3D) hexagonally ordered mi- crobowl arrays (MBAs) decorated with CuInS2 nanosheets for enhanced photoelectrochemical (PEC) per- formance. The 3D MBAs are fabricated by a micro-fabrication technique. The ultrathin CuInS2 nanosheets are grown on the 3D electrodes by solvothermal transformation of Cu film. The photocurrent density of 3D photocathode (CuInS2@MBAs) is about two times higher than that of the planar counterpart (CuInS2@Planar). The improved PEC performance can be ascribed to the elevated light trapping ability and the increased surface area for loading photocatalysts. In addition, CdS quantum dots as cocatalysts are modified onto the CuInS2 nanosheets to further enhance the PEC activity because the formed p-n heterojunction can accelerate the separation of photogenerated carriers. As a result, the 3D photocathode of CuInS2/CdS@MBAs shows an optimal incident photon to current efficiency of 10% at the wavelength of 400 nm. It is believed that this work can be generalized to design other hierarchical 3D photoelectrodes for improved solar water splitting.

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Controlled WS2 crystallinity effectively dominating sodium storage performance Xiaomin Luo, Jianfeng Huang, Jiayin Li, Liyun Cao, Yong Wang, Zhanwei Xu, Ling Guo, Yayi Cheng, Koji Kajiyoshi, Shaoyi Chen 2020, 51(12): 143-153.  DOI: 10.1016/j.jechem.2020.03.086 Abstract ( 5 )   PDF (3938KB) ( 2 )   WS2 exhibits tremendous potentials for Na-ions storage owing to high capacity (433 mAh g-1). Neverthe- less, WS2 layered structure is often exfoliated with rapid capacity decay and sluggish reaction kinetics. In this work, WS2 nanosheets with different crystallinities are controlled by different synthesis methods. The high crystallinity WS2 exhibits high degree of interlayer order and strong interlayer force. It exhibits superior electrochemical properties, at the current density of 200 mA g-1 after 300 cycles with reversible capacity of 471 mAh g-1. Even at 5.0 A g-1, the capacities can still arrive at 240 mAh g-1 after 250 cy- cles, exhibiting stable cycling performance. Further electrochemical research finds that the high degree of interlayer order of layered WS2 structure can perform highly conducive Na+ insertion/extraction with greatly improved contribution of intercalation capacity. Moreover, the strong interlayer force can effec- tively restrain the exfoliating of the WS2 nanosheets, guaranteeing the stability of the structure. Combin- ing the above result reveals that controlling the order and force of the interlayer is an effective way to enhance the electrochemical properties of WS2 as SIBs anode materials. This work can provide new in- sight for inhibiting the exfoliation of layered compounds to pursue excellent electrochemical performance in Na-ion storage systems.

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Flame-retardant concentrated electrolyte enabling a LiF-rich solid electrolyte interface to improve cycle performance of wide-temperature lithium-sulfur batteries Zhe Yu, Jianjun Zhang, Chao Wang, Rongxiang Hu, Xiaofan Du, Ben Tang, Hongtao Qu, Han Wu, Xin Liu, Xinhong Zhou, Xiaoyan Yang, Guanglei Cui 2020, 51(12): 154-160.  DOI: 10.1016/j.jechem.2020.03.034 Abstract ( 8 )   PDF (2231KB) ( 2 )   Lithium-sulfur batteries have been regarded as the most promising high-energy electrochemical en- ergy storage device owing to the high energy density, low cost and environmental friendliness. How- ever, traditional lithium-sulfur batteries using ether-based electrolytes often suffer from severe safety risks (i.e. combustion). Herein, we demonstrated a novel kind of flame-retardant concentrated electrolyte (6.5 M lithium bis(trifluoromethylsulphonyl)imide/fluoroethylene carbonate) for highly-safe and wide- temperature lithium-sulfur batteries. It was found that such concentrated electrolyte showed superior flame retardancy, high lithium-ion transference number (0.69) and steady lithium plating/stripping be- havior (2.5 mAh cm-2 over 3000 h). Moreover, lithium-sulfur batteries using this flame-retardant concen- trated electrolyte delivered outstanding cycle performance in a wide range of temperatures (-10 °C, 25 °C and 90 °C). This superior battery performance is mainly attributed to the LiF-rich solid electrolyte inter- phase formed on lithium metal anode, which can effectively suppress the continuous growth of lithium dendrites. Above-mentioned fascinating characteristics would endow this flame-retardant concentrated electrolyte a very promising candidate for highly-safe and wide-temperature lithium-sulfur batteries.

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Improved ethane conversion to ethylene and aromatics over a Zn/ZSM-5 and CaMnO3-δ composite catalyst Yan Zhang, Xia Xu, Heqing Jiang 2020, 51(12): 161-166.  DOI: 10.1016/j.jechem.2020.03.084 Abstract ( 6 )   PDF (1488KB) ( 1 )   Ethane conversion to ethylene and aromatics over Zn/zeolite catalysts is a promising technology for effi- cient exploitation of light alkanes. However, the reaction faces two major hurdles including the limited ethane conversion due to thermodynamics and the drastic catalyst deactivation by kinetical coke accu- mulation. Here we present a route to improve ethane conversion using a composite catalyst, involving Zn/HZSM-5 for ethane dehydroaromatization and CaMnO3-δ perovskite for in situ selective hydrogen ox- idation. The in situ H2 consumption shifts ethane dehydrogenation equilibrium to the desired side and can obviously increase the yield of target product. Furthermore, it is found that the in situ generated H2O through H2 combustion can significantly suppress the coke formation and consequently enhance the stability of the composite catalyst. After 400 min reaction, a product yield of 23% was retained over the composite catalyst, almost a threefold increase with respect to the Zn/HZSM-5 reference (8%). It is antic- ipated that this novel composite catalyst combined with an efficient reactor technology may improve the viability of ethane aromatization in utilization.

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In-situ transformation of Co(OH)2 into NH4CoPO4•H2O on Co foil: 3D self-supported electrocatalyst with asymmetric local atomic and electronic structure for enhanced oxygen evolution reaction Quande Che, Xiaobin Xie, Qian Ma, Junpeng Wang, Yuanna Zhu, Ruixia Shi, Ping Yang 2020, 51(12): 167-174.  DOI: 10.1016/j.jechem.2020.03.072 Abstract ( 4 )   PDF (2311KB) ( 1 )   Development of high efficient and stable water oxidation catalysts is essential for the realization of in- dustrial water-splitting systems. Herein, a novel approach involving an in-situ transformation of Co(OH)2 nanosheets into NH4CoPO4•H2O nanoplates on Co foil is reported. As a 3D self-supported oxygen rev- olution reaction (OER) electrocatalyst, the as-prepared NH4CoPO4•H2O/Co exhibits remarkable catalytic activity and exceptional stability. Specifically, it can deliver a current density of 10 mA cm-2 at a quite low overpotential of 254 mV with a small Tafel slope of 64.4 mV dec-1 in alkaline electrolyte. Through experimental study and theoretical analysis, the excellent OER performance can be attributed to enriched exposed active sites, favorable electron/proton transfer and mass transport, and its unique asymmetric local atomic and electronic structure. Thus, this present research not only provides a practicable in-situ transformation strategy to design 3D self-supported electrocatalysts, but also enlightens a new way of developing transition-metal phosphates for efficient and stable water oxidation at atomic level.

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Optimistic performance of carbon-free hydrazine fuel cells based on controlled electrode structure and water management Hongsun Hwang, Sujik Hong, Do-Hyeong Kim, Moon-Sung Kang, Jin-Soo Park, Sunghyun Uhm, Jaeyoung Lee 2020, 51(12): 175-181.  DOI: 10.1016/j.jechem.2020.03.081 Abstract ( 7 )   PDF (2974KB) ( 1 )   In this study, we first attempted to discover the optimal configuration of membrane-electrode assemblies (MEAs) used to achieve a high performance of direct hydrazine fuel cells (DHFCs). We have investigated the effect of water management and the electrode thickness on the performance of DHFCs, depending on the hydrophobicity of the gas diffusion layers in the cathode and the catalyst loading in the anode with the carbon-supported Ni, synthesized by a polyol process. With the optimal water management and electrode thickness, the MEA constructed using the as-prepared Ni/C anode catalyst containing the metallic and low oxidative state and ultra-low Pt loading cathode reduced the ohmic resistance and mass transfer limitation in the current-voltage curves observed for the alkaline DHFC, achieving an impressive power performance over 500 mW cm-2.

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Highly efficient H-bonding charge-transfer complex for microsupercapacitors under extreme conditions of low temperatures Libin Wang, Ting Shu, Songtao Guo, Shi Chen, Yingjun Jiang, Xianluo Hu 2020, 51(12): 182-189.  DOI: 10.1016/j.jechem.2020.03.056 Abstract ( 8 )   PDF (2535KB) ( 2 )   Owing to sluggish ionic mobility at low temperatures, supercapacitors, as well as other energy-storage devices, always suffer from severe capacity decay and even failure under extreme low-temperature cir- cumstances. Solar-thermal-enabled self-heating promises an attractive approach to overcome this issue. Here, we report a unique H-bonding charge-transfer complex with a high photothermal conversion effi- ciency of 79.5% at 405 nm based on chloranilic acid and albendazole. Integrated with a microsuperca- pacitor, the chloranilic acid-albendazole complex (CAC) film prompts an apparent temperature increase of 22.7 °C under 1 sun illumination at -32.6 °C, effectively elevating the working temperature of devices. As a result, the rate capability of the microsupercapacitor has been significantly improved with a 17- fold increase in capacitance at a current density of 60 μA cm-2, leading to outstanding low-temperature performances. Importantly, the integrated device is capable of working at a low temperature of -30 °C in the open air, which demonstrates the potential of CAC in practical applications for low-temperature ultracapacitive energy-storage devices.

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Molecular design towards two-dimensional electron acceptors for efficient non-fullerene solar cells Yan Liu, Zixian Liu, Zhicheng Hu, Yuanying Liang, Zhenfeng Wang, Zhongxin Chen, Fei Huang, Yong Cao 2020, 51(12): 190-198.  DOI: 10.1016/j.jechem.2020.04.007 Abstract ( 8 )   PDF (2819KB) ( 1 )   Non-fullerene polymer solar cells (NF-PSCs) have gained wide attention recently. Molecular design of non-fullerene electron acceptors effectively promotes the photovoltaic performance of NF-PSCs. However, molecular electron acceptors with 2-dimensional (2D) configuration and conjugation are seldom reported. Herein, we designed and synthesized a series of novel 2D electron acceptors for efficient NF-PSCs. With rational optimization on the conjugated moieties in both vertical and horizontal direction, these 2D elec- tron acceptors showed appealing properties, such as good planarity, full-spectrum absorption, high ab- sorption extinction coefficient, and proper blend morphology with donor polymer. A high PCE of 9.76% was achieved for photovoltaic devices with PBDB-T as the donor and these 2D electron acceptors. It was also found the charge transfer between the conjugated moieties in two directions of these 2D molecules contributes to the utilization of absorbed photos, resulting in an exceptional EQE of 87% at 730 nm. This work presents rational design guidelines of 2D electron acceptors, which showed great promise to achieve high-performance non-fullerene polymer solar cells.

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Controllable synthesis of core-shell Co@C@SiO2 catalysts for enhancing product selectivity in Fischer-Tropsch synthesis by tuning the mass transfer resistance Yao Chen, Xin Li, Liya Dai, Mehar U Nisa, Chengchao Liu, Shuai Lv, Jing Lv, Zhenhua Li 2020, 51(12): 199-206.  DOI: 10.1016/j.jechem.2020.03.074 Abstract ( 4 )   PDF (2646KB) ( 1 )   Fischer-Tropsch synthesis (FTS) is the key step in converting syngas into clean fuels. Traditional supported catalysts for FTS are problematic because the active metal crystalline size is positively related to metal loading. Therefore, increasing active metal loading may reduce the cobalt time yield (CTY) since a high CTY is usually obtained when the Co size is 8 nm. Here, a ZIF-67 (Zeolitic imidazolate framework-67) with a MOF (Metal organic framework) structure is used as a precursor to prepare the Co@C catalyst with not only high cobalt loading (55.6 wt%) but also with a small cobalt crystal size (as small as 8.6 nm). Core- shell Co@C@SiO2-X catalysts with different SiO2 shell thicknesses were successfully prepared by coating different amounts of TEOS on the outer surface of Co@C to modify product selectivity. Compared with 40 wt% Co/SiO2 catalyst, core-shell Co@C@SiO2-X catalysts exhibited improved FTS performance. Further- more, different gaseous hourly space velocities (GHSVs) were used to obtain CO conversion at similar levels to compare CTY and the turnover frequency (TOF). Among the catalysts, the Co@C@SiO2-1 cata- lyst, with its better mass transfer ability and suitable hydrophilic property, presented the highest TOF (9.75 × 10-3 s-1) and lowest CH4 selectivity (9.75%). In addition, heavy hydrocarbons were effectively suppressed with the increase in shell thickness due to the increased mass transfer resistance.

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Decorating ketjen black with ultra-small Mo2C nanoparticles to enhance polysulfides chemisorption and redox kinetics for lithium-sulfur batteries Nan Jiang, Guangyu Jiang, Dechao Niu, Jiayi Mao, Meiwan Chen, Kaiyuan Li, Yongsheng Li 2020, 51(12): 207-215.  DOI: 10.1016/j.jechem.2020.04.008 Abstract ( 4 )   PDF (3497KB) ( 1 )   The low sulfur utilization and fast capacity fading resulting from the sluggish redox reaction and abom- inable polysulfides shuttle greatly hinder the practical applications of lithium-sulfur (Li-S) batteries. Herein, we develop a facile “in-situ growth” method to decorate ultra-small Mo2C nanoparticles (US- Mo2C) on the surface of Ketjen Black (KB) to functionalize the commercial polypropylene (PP) separators, which can accelerate the redox kinetics of lithium polysulfides conversion and effectively increase the utilization of sulfur for Li-S batteries. Importantly, the US-Mo2C nanoparticles have abundant sites for chemical adsorption towards polysulfides and the conductive carbon networks of KB have cross-linked pore channels, which can promote electron transport and provide physical barrier and volume expansion space for polysulfides. Due to the combined effects of the US-Mo2C and KB, Li-S cells employing the mul- tifunctional PP separators modified with KB/US-Mo2C composite (KB/US-Mo2C@PP) exhibit a high specific capacity (1212.8 mAh g-1 at 0.2 C), and maintain a reversible capacity of 1053.3 mAh g-1 after 100 cycles. More importantly, the KB/US-Mo2C@PP cells with higher sulfur mass loading of 4.9 mg cm-2 have superb areal capacity of 2.3 mAh cm-2. This work offers a novel and promising perspective for high-performance Li-S batteries from both the shuttle effect and the complex polysulfides conversion.

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A novel bifunctional oxygen electrode architecture enabled by heterostructures self-scaffolding for lithium-oxygen batteries Liang Xiao, Zhong Qin, Jingyu Yi, Haoyang Dong, Jinping Liu 2020, 51(12): 216-221.  DOI: 10.1016/j.jechem.2020.04.006 Abstract ( 9 )   PDF (1768KB) ( 2 )

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Robust interface layers with redox shuttle reactions suppress the dendrite growth for stable solid-state Li metal batteries Shuaibo Zeng, Gowri Manohari Arumugam, Wentao Li, Xiahu Liu, Xin Li, Hai Zhong, Fei Guo, Yaohua Mai 2020, 51(12): 222-229.  DOI: 10.1016/j.jechem.2020.03.060 Abstract ( 4 )   PDF (2277KB) ( 2 )   Designing a durable lithium metal anode for solid state batteries requires a controllable and uniform de- position of lithium, and the metal lithium layer should maintain a good interface contact with solid state electrolyte during cycles. In this work, we construct a robust functional interface layer on the modified Li-B electrode which considerably improves the electrochemical stability of lithium metal electrode in solid state batteries. It is found that the functional interface layer consisting of polydioxolane, polyiodide ion and LiTFSI effectively restrains the growth of lithium dendrites through the redox shuttle reaction of I-/I3- and maintains a good contact between lithium anode and solid electrolyte during cycles. Benefit from these two advantages, the modified Li-B anode exhibits a remarkable cyclic performance in compar- ison with those of the bare Li-B anode.

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Metal-organic framework (MOF)-derived catalysts for Fischer-Tropsch synthesis: Recent progress and future perspectives Kabir Opeyemi Otun, Xinying Liu, Diane Hildebrandt 2020, 51(12): 230-245.  DOI: 10.1016/j.jechem.2020.03.062 Abstract ( 9 )   PDF (3221KB) ( 3 )   Fischer-Tropsch Synthesis (FTS) is an important catalytic chemical reaction that converts a mixture of CO and H2 (syngas) derived from biomass, coal or natural gas into ultra-clean fuels or value-added chemi- cals. However, most traditional catalysts used in the Fischer-Tropsch process are faced with the problems of high deactivation rate triggered by sintering, phase changes and oxidation which hamper their cat- alytic performance. Metal-organic frameworks (MOFs)-derived materials have been a promising alterna- tive in addressing the catalyst deactivation problems in FTS because of the encapsulation of their metal nanoparticles in carbon matrix and absence of large particle size, among other reasons. Therefore, this re- view emphasizes the most recent research headway in the investigation of MOFs as precursors to achieve high-performance FTS catalysts. Precisely, the design of iron and cobalt-based FTS catalysts from parent MOFs via MOF-mediated synthesis, the catalytic activity of the MOF-derived materials and the promoter effects under FTS operation were outlined and discussed. We have also evaluated the influence of MOF structures on the FTS performance and compared them with traditional/commercially available catalysts to show the importance of this approach. Finally, the challenges and opportunities to further expedite the extensive research efforts and promote their applications in material design and FT technology were mentioned.

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Enhancement of oxygen reduction activity and stability via introducing acid-resistant refractory Mo and regulating the near-surface Pt content Shouquan Feng, Jiajia Lu, Lin Luo, Guangfu Qian, Jinli Chen, Hanna S. Abbo, Salam J. J. Titinchi, Shibin Yin 2020, 51(12): 246-252.  DOI: 10.1016/j.jechem.2020.03.063 Abstract ( 7 )   PDF (2310KB) ( 1 )   Although PtNi catalyst possesses good oxygen reduction activity, its poor stability is the main obstacle for the commercialization of proton exchange membrane fuel cells (PEMFCs). In this work, we introduce the acid-resistant refractory Mo to enhance the structure stability and modify the electronic structure of Pt in the prepared PtNi catalyst, improving the catalytic activity for oxygen reduction reaction (ORR). In addition, near-surface Pt content in the nanoparticle is also optimized to balance the ORR activity and stability. The electrochemical results show that the alloy formed by Mo and PtNi is obviously more stable than the PtNi alloy alone, because the acid-resistant Mo and its oxides effectively prevent the dissolution of Pt. Especially, the Pt3Ni3MoN/C exhibits the optimal ORR catalytic performance in O2-saturated 0.1 mol L-1 HClO4 aqueous solutions, with mass activity (MA) of 900 mA mg-1Pt at 0.90 V vs. RHE, which is 3.75 times enhancement compared with the commercial Pt/C (240 mA mg-1Pt). After 30k accelerated durability tests, its MA (690 mA mg-1Pt) is still 2.88 times higher than the pristine Pt/C. This study thus provides a valuable method to design stable ORR catalysts with high efficiency and has great significance for the commercialization of PEMFCs.

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Carbon-coated cubic-phase molybdenum carbide nanoparticle for enhanced photocatalytic H2-evolution performance of TiO2 Jinfeng Liu, Ping Wang, Jiajie Fan, Huogen Yu 2020, 51(12): 253-261.  DOI: 10.1016/j.jechem.2020.03.085 Abstract ( 6 )   PDF (3111KB) ( 3 )   Conventional hexagonal dimolybdenum carbide (Mo2C) as a good cocatalyst has been widely applied for the enhanced photocatalytic hydrogen production of various photocatalysts. Compared with the hexag- onal Mo2C, however, the investigation about cubic molybdenum carbide (MoC) is still very limited in photocatalytic field. In this study, carbon-coated cubic molybdenum carbide (MoC@C) nanoparticle was synthesized and used as an effective cocatalyst to improve the H2-evolution efficiency of TiO2. The cubic MoC@C can be obtained by adjusting the mass ratio of C3N3(NH2)3 to (NH4)6Mo7O24 (2:1) and controlling the calcination temperature to 800 °C. When the above cubic MoC@C nanoparticles were evenly loaded on the TiO2 via a sonication-assisted deposition, a homogeneous composite of TiO2/MoC@C was formed due to the strong coupling interface between TiO2 and cubic MoC nanoparticles. More importantly, the highest H2-production rate of TiO2/MoC@C reached 504 μmol h-1 g-1 (AQE=1.43%), which was 50 times as high as that of the pure TiO . The enhanced performance of TiO /MoC@C can be attributed to the synergistic effect of carbon layer as an electron mediator and the cubic MoC as interfacial H2-evolution active sites. This work provides a feasible guideline to develop high-efficiency Mo-based cocatalysts for potential applications in the H2-evolution field.

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Rational design of MoS2 nanosheets decorated on mesoporous hollow carbon spheres as a dual-functional accelerator in sulfur cathode for advanced pouch-type Li-S batteries Qinjun Shao, Pengfei Lu, Lei Xu, Decai Guo, Jing Gao, Zhong-Shuai Wu, Jian Chen 2020, 51(12): 262-271.  DOI: 10.1016/j.jechem.2020.03.035 Abstract ( 8 )   PDF (2901KB) ( 4 )   Developing sulfur cathodes with high catalytic activity on accelerating the sluggish redox kinetics of lithium polysulfides (LiPSs) and unveiling their mechanisms are pivotal for advanced lithium-sulfur (Li-S) batteries. Herein, MoS2 is verified to reduce the Gibbs free energy for rate-limiting step of sulfur reduc- tion and the dissociation energy of lithium sulfide (Li2S) for the first time employing theoretical calcu- lations. The MoS2 nanosheets coated on mesoporous hollow carbon spheres (MHCS) are then reasonably designed as a sulfur host for high-capacity and long-life Li-S battery, in which MHCS can guarantee the high sulfur loading and fast electron/ion transfer. It is revealed that the shuttle effect is efficiently inhib- ited because of the boosted conversion of LiPSs. As a result, the coin cell based on the MHCS@MoS2-S cathode exhibits stable cycling performance maintaining 735.7 mAh g-1 after 500 cycles at 1.0 C. More importantly, the pouch cell employing the MHCS@MoS2-S cathodes achieves high specific capacity of 1353.2 mAh g-1 and prominent cycle stability that remaining 960.0 mAh g-1 with extraordinary capac- ity retention of 79.8% at 0.1 C after 170 cycles. Therefore, this work paves a new avenue for developing practical high specific energy and long-life pouch-type Li-S batteries.

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Highly performed platinum nanosheets synthesized under in situ reaction conditions for hydrogen generation Xiaobing Bao, Yutong Gong, Xiaozhong Zheng, Jiayi Chen, Shanjun Mao, Yong Wang 2020, 51(12): 272-279.  DOI: 10.1016/j.jechem.2020.03.064 Abstract ( 7 )   PDF (2112KB) ( 1 )   Surface properties of a catalyst, especially exposed crystal facets and coordination states, directly affect the catalyst’s performance. Herein, we illustrate how reaction conditions direct the fabrication of a well- behaved catalyst with desired structures in the case of hydrogen evolution reaction (HER). Stable ad- sorbed PtClx ions on CNTs are in situ electrochemically reduced into a unique Pt nanosheet structure enclosed by high-index (311) and low-index (200) and (111) facets during HER process. Experimental results and density functional theory (DFT) calculation disclose the function mechanism between these unique structures and reactants. The adsorbed H2O and reactive species act as capping agents protecting the (311) facet where the dissociation of water molecule is promoted, and the produced H∗ intermediates favorably combine and release on the nearby low-index Pt sites. The joint collaborations of these active sites afford Pt nanosheets comparable activity to 20 wt% Pt/C and a 12.7-fold over mass activity. These findings provide novel insight into the synthesis of heterogeneous catalysts with high specificity.

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Ultralow-temperature assisted synthesis of single platinum atoms anchored on carbon nanotubes for efficiently electrocatalytic acidic hydrogen evolution Wenwu Zhong, Wenguang Tu, Zongpeng Wang, Zhiping Lin, Aijiao Xu, Xiufang Ye, Dongchu Chen, Beibei Xiao 2020, 51(12): 280-284.  DOI: 10.1016/j.jechem.2020.04.035 Abstract ( 8 )   PDF (1354KB) ( 6 )   Although platinum (Pt) is highly active for hydrogen evolution reaction (HER)[1], it is crucial to explore the effective approach for minimizing the Pt loading amount in the practical application. Herein, one ultralow-temperature solution reduction approach is developed to anchor atomically dispersed Pt atoms on carbon nanotubes (Pt-CNTs), which decelerates the diffusion rate of PtCl 6 2- ion reached onto the carbon nanotubes and lowers the free energy of Pt atoms in the solution to reduce the probability of the Pt aggregation. The obtained Pt-CNTs exhibits a low overpotential of 41 mV@10 mA cm -2 for HER in acidic media. The calculation results revealed that the improvement of the electrocatalytic activity is contributed by the interaction between CNTs and Pt atoms, which descreases the the Pt d band cneter referred to the Fermi level and lowers the Gibbs free energy of H∗ adsorption. This work may provide one easy and convenient strategy for the large-scale use of Pt catalysts in practical applications.

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Fast ion/electron conducting scaffold of Li-Zn dual-phase alloy enable uniform deposition of Li metal at high current densities Zeyu Yao, Weishang Jia, Zihao Wang, Jin Ruan, Xianggang Kong, Xin Guan, Zhihong Wang, Jingze Li, Ying Wang, Wei Zou, Fu Zhou 2020, 51(12): 285-292.  DOI: 10.1016/j.jechem.2020.04.038 Abstract ( 6 )   PDF (2645KB) ( 1 )   The commercial application of Li metal anodes is hindered by the dendrite growth and short cycling lifespan under high current density that are caused in part by the imbalance in the charge transport capability in the anode. Here, we present a design principle of a three-dimensional (3D) skeleton to in- troduce highly efficient ion- and electron- conducting channels in the Li anode. A process of thermal infusion followed by cooling is used to synthesize a dual-phase Li-rich Li-Zn alloy that consists of an LiZn intermetallic compound phase as the 3D framework and the uniformly distributed Li metal phase as the active material. The phase-segregated Li-Zn phase endows the Li10Zn alloy with built-in fast ion transport channels, in addition to the ionic conducting pathway of the liquid electrolyte, leading to bet- ter charge balance and conformal deposition of Li on the scaffold. Consequently, the Li10Zn alloy anode can be operated for more than 10000 cycles at a high current density of 5 mA cm-2 and areal capac- ity of 1 mAh cm-2. Remarkably, even for the high current density of 10 mA cm-2 and areal capacity as large as 10 mAh cm-2, the cycling lifetime is still greater than 500 cycles. Thus, the scaffold with high ion/electron mixed conductivity is highly effective for inhibiting Li dendrite growth and prolonging the cycling lifespan, highlighting the great promise of the fast ion conducting alloy framework for use in Li secondary batteries at high current densities.

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Hollow carbon microbox from acetylacetone as anode material for sodium-ion batteries ✩ Tianyun Qiu, Wanwan Hong, Lin Li, Yu Zhang, Peng Cai, Cheng Liu, Jiayang Li, Guoqiang Zou, Hongshuai Hou, Xiaobo Ji 2020, 51(12): 293-302.  DOI: 10.1016/j.jechem.2020.03.073 Abstract ( 6 )   PDF (3629KB) ( 3 )   Carbon-based materials have attracted much interest as one of the promising anodes for sodium-ion bat- teries. However, low utilization of electrolyte and slow ion-transfer rate during electrochemical process hinder the further application of traditional bulk carbon. In order to enhance the diffusion kinetics and maintain the reversibility, hierarchical hollow carbon microbox was successfully prepared through a tun- able bottom-up self-template routine for sodium-ion batteries. During annealing process, the morphol- ogy construction and activation happened synchronously. Based on that, a range of cross-linked porous nanosheet and hollow microbox were attained by manipulating reactant condition. The generation of tex- ture and physical property are analyzed and are established linkages related to the electrochemical be- havior. As results depicted in kinetic exploration and simulation based on cyclic voltammetry, the surface- controlled electrochemical behavior gradually turns to be the diffusion-controlled behavior as the hollow microbox evolves to porous nanosheet. The probable reason is that the rational microstructure/texture design leads to the accelerated diffusion kinetic procedure and the reduced concentration difference po- larization. Sodium storage mechanism was deduced as reversible binding of Na-ions with local defects, including vacancies on sp2 graphitic layers, at the edges of flakes and other structural defects instead of intercalation. Bestowed by the morphology design, the broad pore width distribution, abundant de- fects/active sites and surface functionality, hollow microbox electrode delivers great electrochemical per- formances. This work is expected to propose a novel and effective strategy to prepare tunable hierarchical hollow carbon microbox and induce the fast kinetic of carbon anode material.

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Extended π-conjugated N-containing heteroaromatic hexacarboxylate organic anode for high performance rechargeable batteries Shu-Biao Xia, Teng Liu, Wen-Jin Huang, Hong-Bo Suo, Fei-Xiang Cheng, Hong Guo, Jian-Jun Liu 2020, 51(12): 303-311.  DOI: 10.1016/j.jechem.2020.04.039 Abstract ( 4 )   PDF (3009KB) ( 1 )   Organic electrode materials are desirable for green and sustainable Li-ion batteries (LIBs) due to their light-weight, low cost, abundance and multi-electron transfer reactions during battery operation. How- ever, the successful utilization of organic electrodes is hindered by their poor electrical conductivity and low cyclic stability. Herein, a facile synthesis of π-conjugated N-containing heteroaromatic hexacarboxy- late (Li6-HAT) compound and its electrochemical performance as an anode material in LIBs is reported. The as-synthesized Li6-HAT electrode renders an ultrahigh initial capacity of 1126.3 mAh g-1 at the cur- rent density of 100 mA g-1. Moreover, π-conjugated N-containing heteroaromatic center provide excel- lent reversibility of (de)lithiation process, resulting in excellent capacity retention. Furthermore, a combi- nation of density functional theory (DFT) calculations, in-situ Fourier transform infrared (FTIR) and ex-situ X-ray photoelectron spectroscopy (XPS) characterization reveal that the π-conjugated nitrogen and car- boxyl oxygen act as electrochemically active sites during the charge/discharge process. The current work provides novel insights into the charge storage mechanism of organic electrodes and opens up avenues for further development and utilization of organic electrodes in Li-ion batteries.

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Synergistic effect of size-dependent PtZn nanoparticles and zinc single-atom sites for electrochemical ozone production in neutral media Bowen Yuan, Zihao Yao, Chenlong Qiu, Haiyang Zheng, Yilong Yan, Qiaoqiao Zhang, Xiang Sun, Yu Gu, Xing Zhong, Jianguo Wang 2020, 51(12): 312-322.  DOI: 10.1016/j.jechem.2020.03.066 Abstract ( 6 )   PDF (3350KB) ( 1 )   Electrochemical ozone production (EOP) via water electrolysis represents an attractive method for the generation of high-purity O3. Herein, the X-PtZn/Zn-N-C electrocatalysts show a strong structural sensitive behavior depends on the size of the PtZn nanoparticles and their EOP activity exhibits a volcano-type dependence for the O3 performance in neutral media. The 7.7-PtZn/Zn-N-C exhibits EOP current efficiency of 4.2%, and shows the prominent performance in the production of gaseous O3 with a value of 1647 ppb at 30 min, which is almost 4-fold compared to 2.2-PtZn/Zn-N-C. Based on the experiments and theoretical calculations, the performance of the EOP process was determined by the nanoparticle size-effect and the synergistic effect between the PtZn nanoparticles and atomically dispersed Zn-N-C. Furthermore, the five- membered cyclic structure of O3 can be stabilized between the PtZn nanoparticle and the Zn-N-C support, indicating that O3 is produced at the interface.

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CoNxC active sites-rich three-dimensional porous carbon nanofibers network derived from bacterial cellulose and bimetal-ZIFs as efficient multifunctional electrocatalyst for rechargeable Zn-air batteries Wenming Zhang, Jingjing Chu, Shifeng Li, Yanan Li, Ling Li ⇑ 2020, 51(12): 323-332.  DOI: 10.1016/j.jechem.2020.04.067 Abstract ( 4 )   PDF (4264KB) ( 1 )   In this work, a CoNxC active sites-rich three-dimensional porous carbon nanofibers network derived from bacterial cellulose and bimetal-ZIFs is prepared via a nucleation growth strategy and a pyrolysis process. The material displays excellent electrocatalytic activity for the oxygen reduction reaction, reaching a high limiting diffusion current density of -7.8 mA cm-2, outperforming metal-organic frameworks derived multifunctional electrocatalysts, and oxygen evolution reaction and hydrogen evolution reaction with low overpotentials of 380 and 107 mV, respectively. When the electrochemical properties are further evaluated, the electrocatalyst as an air cathode for Zn-air batteries exhibits a high cycling stability for 63 h as well as a maximum power density of 308 mW cm-2, which is better than those for most Zn-air batteries reported to date. In addition, a power density of 152 mW cm-2 is provided by the solid-state Zn-air batteries, and the cycling stability is outstanding for 24 h. The remarkable electrocat- alytic properties are attributed to the synergistic effect of the 3D porous carbon nanofibers network and abundant inserted CoNxC active sites, which enable the fast transmission of ions and mass and simultaneously provide a large contact area for the electrode/electrolyte.

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Investigating the effect of cosolvents on P3HT/O-IDTBR film-forming kinetics and film morphology Jiangang Liu, Shuyi Zeng, Peng Jing, Kui Zhao, Qiuju Liang 2020, 51(12): 333-341.  DOI: 10.1016/j.jechem.2020.04.048 Abstract ( 4 )   PDF (2483KB) ( 2 )   The morphology of active layer in bulk heterojunction (BHJ) organic solar cells is decisive to the device performance. Previous works have shown that the solvent engineering is an effective method to optimize the morphology of active layer. However, screening the proper solvent is a tedious task, and we know very little about how to select a proper solvent for a particular system, especially for polymer/non- fullerene blend systems. Here, we combined the spectroscopic analysis in various solvent mixtures dur- ing film-forming process to reveal the relationship among the cosolvent characteristics, film-forming kinetics and film morphology. In this article, P3HT/O-IDTBR blend was selected as model system due to being facile synthesized under a large-scale. Chlorobenzene (CB) was selected as main solvent, and the cosolvents were grouped into three categories according to its boiling point (bp) compared to CB. The cosolvents with lower bp, like chloroform (CF), can facilitate a faster film-forming process, reducing the domain size but sacrificing the crystallinity of both components. For the cosolvents with higher bp, like o-dichlorobenzene (DCB) and 1,2,4-trichlorobenzene (TCB), the self-organization process of P3HT and O-IDTBR is separated and its duration was extended, constructing highly crystalline nano- interpenetrating network. However, the cosolvents with very high bp, such as chlornaphthalene (CN), would residue in film and keep P3HT and O-IDTBR self-organizing for longer time, leading to larger phase separation. This work systematically investigated the effect of cosolvent on the film-forming kinetics, and proposed a guideline of how to select a proper cosolvent according to the crystallinity and domain size of active layer.

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Research progress of nanocellulose for electrochemical energy storage: A review Ruiqi Guo, Lixue Zhang, Yun Lu, Xiaoli Zhang, Dongjiang Yang 2020, 51(12): 342-361.  DOI: 10.1016/j.jechem.2020.04.029 Abstract ( 17 )   PDF (5177KB) ( 8 )   Recently, in response to the major challenges in energy development and environmental issues, tremen- dous efforts are being devoted to developing electrochemical energy storage devices based on green sus- tainable resources. As a class of green materials, nanocellulose (NC) has received extensive attention. In this review, we summarize the research progress of NC derived materials in electrochemical energy stor- age. Specifically, we first introduce various synthesis methods based on NC and the pretreatment process to increase the conductivity. Then we focus on the specific application of NC in electrochemical energy storage devices. Finally, we summarize the previously reported work and put forward views on the fur- ther development of NC in the field of electrochemical energy storage.

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A multifunctional electrolyte with highly-coordinated solvation structure-in-nonsolvent for rechargeable lithium batteries Hui Zhao, Jinlei Gu, Yuliang Gao, Qian Hou, Zengying Ren, Yaqin Qi, Kun Zhang, Chao Shen, Jun Zhang ⇑, Keyu Xie ⇑ 2020, 51(12): 362-371.  DOI: 10.1016/j.jechem.2020.04.044 Abstract ( 9 )   PDF (3778KB) ( 2 )   Rechargeable lithium-based battery is hailed as next-generation high-energy-density battery systems. However, growth of lithium dendrites, shuttle effect of lithium polysulfides intermediates and unstable interphase of high-voltage intercalation-type cathodes largely prevent their practical deployment. Herein, to fully conquer the three challenges via one strategy, a novel electrolyte with highly- coordinated solvation structure-in-nonsolvent is designed. On account of the particular electrolyte struc- ture, the shuttle effect is completely suppressed by quasi-solid conversion of S species in Li-S batteries, with a stable cycle performance even at lean electrolyte (5 lL mg-1). Simultaneously, in-situ-formed highly-fluorinated interphases can not only lower Li+ diffusion barrier to ensure uniform nucleation of Li but also improve stability of NCM cathodes, which enable excellent capacity retention of Li LiNi0.5Co0.2Mn0.3O2 batteries under conditions toward practical applications (high loading of 2.7 mAh cm-2 and lean electrolyte of 5 mL Ah-1). Besides, the electrolyte is also nonflammable. This elec- trolyte structure offers useful guidelines for the design of novel organic electrolytes for practical lithium-based batteries.

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Boosting fast lithium ion storage of Li4Ti5O12 by synergistic effect of vertical graphene and nitrogen doping Yan Lin, Jianbo Wu, Xiaohua Huang, Guoxiang Pan, Xinhui Xia 2020, 51(12): 372-377.  DOI: 10.1016/j.jechem.2020.04.037 Abstract ( 8 )   PDF (2649KB) ( 1 )   The advancement of power-type lithium ion batteries (LIBs) mainly depends on the construction of elec- trodes with superior electronic & ionic conductivity. In this work, a synergistic combination of nitro- gen doped Li4Ti5O12 (N-LTO) nanoparticles and highly conductive vertical graphene (VG) skeleton is pro- posed to obtain ultrafast Li ion storage performance via a facile hydrothermal-nitridation method. The as-synthesized composite nanosheets are composed of interconnected N-LTO shell and VG core to form the final N-LTO/VG core-shell arrays, which are systematically studied as the anodes of LIBs. In virtue of the positive synergistic effect of high conductive VG backbone and nitrogen doping, overwhelming ad- vantages including high specific surface area, superb structural stability and enhanced conductivity are achieved in the well-designed N-LTO/VG electrodes. Accordingly, the as-synthesized N-LTO/VG electrode shows outstanding high rate capacity (142.5 mAh g-1 at 20 C) and superior long-term cycling stability (capacity retention of 98.9% after 10000 cycles at 5 C), better than LTO/VG electrode without N doping. Our research provides a new strategy for the synthesis of high-performance hybrid electrodes for appli- cation in power-type LIBs.

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Confining sulfur in intact freestanding scaffold of yolk-shell nanofibers with high sulfur content for lithium-sulfur batteries Xilai Zhang, Peng Zhang, Shijie Zhang, Yongshang Zhang, Ruohan Hou, Kangli Liu, Fujun Miao, Guosheng Shao 2020, 51(12): 378-387.  DOI: 10.1016/j.jechem.2020.03.065 Abstract ( 7 )   PDF (2769KB) ( 1 )   Nanostructure design holds great potential in fabricating sulfur electrodes that host a high sulfur loading and still attain high electrochemical utilization for the developing of high-energy-density lithium-sulfur (Li-S) batteries. In this contribution, we introduce the yolk-shell structure into a freestanding carbon nanofibers film and construct a complete hollow yolk-shell TiO2/carbon nanofibers@void@TiN@carbon (TiO2-CNFs@void@TiN@C) composite. With inherent double conductive network and strong adsorption capability for polysulfides, the TiO2-CNFs@void@TiN@C composite can not only provide sufficient electri- cal contact for the insulating sulfur, but also effectively entrap polysulfides for prolonged cycle life. As a result, an excellent capacity retention ratio of 60.9% after 1000 cycles at 1 C as well as a high capacity of 688.5 mAh g-1 at 5 C rate is accomplished with the cells employing TiO2-CNFs@void@TiN@C as a cath-ode substrate for sulfur. Moreover, the TiO2-CNFs@void@TiN@C composite, with a high S mass loading of 9.5 mg cm-2, delivers a superb areal capacity of 8.2 mAh cm-2.

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Large-scale carambola-like V2O5 nanoflowers arrays on microporous reed carbon as improved electrochemical performances lithium-ion batteries cathode Hua Tan, Xin Zhi Yu, Kai Huang, Jianxin Zhong, Bingan Lu 2020, 51(12): 388-395.  DOI: 10.1016/j.jechem.2020.03.053 Abstract ( 8 )   PDF (2382KB) ( 1 )   To search for new cathode materials with high energy density of Lithium-ion batteries (LIBs) is one of the most challenging issues. Vanadium pentoxide (V2O5) with high theoretical specific capacity is believed to be a promising candidate for the next generation cathode materials, yet still suffers from low lithium ion diffusion coefficient and poor electronic conductivity resulting in low cycling life and poor rate performances. Here, we report new large-scale carambola-like V2O5 nanoflowers arrays an- chored on microporous reed carbon as high performances LIBs cathode. Each individual pore space of the microporous reed carbon is like a hexagonal cylinder, and the area of each carbon wall is more than 103 um2, which is favorable for the growth of V2O5 nanostructure arrays. After hydrothermal, the large- scale carambola-like V2O5 nanoflowers arrays can directly grow on the surface of microporous carbon. Due to the novel composite structures, the V2O5 nanoflowers arrays@microporous carbon stabilizes at 273 mA h g-1 after 100 cycles at 0.2 C. When cycling at 1.0 C over 500 cycles, the capacity still maintains at 180 mAh g-1. The demonstrated approach in this work paves the way for the development of high rate capability and excellent cycling stability V2O5-based cathode materials.

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Structure evolution of oxygen removal from porous carbon for optimizing supercapacitor performance Siting Yuan, Xianhong Huang, Hao Wang, Lijing Xie, Jiayao Cheng, Qingqiang Kong, Guohua Sun, Cheng-Meng Chen 2020, 51(12): 396-404.  DOI: 10.1016/j.jechem.2020.04.004 Abstract ( 18 )   PDF (2896KB) ( 1 )   The presence of oxygen functional groups is detrimental to the capacitive performance of porous carbon electrode in organic electrolyte. In this regards, hydrogen thermal reduction has been demonstrated ef- fective approach in removing the unstable surface oxygen while maintaining the high porosity of carbon matrix. However, the exact evolution mechanism of various oxygen species during this process, as well as the correlation with electrochemical properties, is still under development. Herein, biomass-based porous carbon is adopted as the model material to trace its structure evolution of oxygen removal under hydro- gen thermal reduction process with the temperature range of 400-800 °C. The optimum microstructure with low oxygen content of 0.90% and proper pore size distribution was achieved at 700°C. XPS, TPR- MS and Boehm titration results indicate that the oxygen elimination undergoes three distinctive stages (intermolecular dehydration, hydrogenation and decomposition reactions). The optimum microstructure with low oxygen content of 0.90% and proper pore size distribution was achieved at 700 °C. Benefiting from the stable electrochemical interface and the optimized porous structure, the as-obtained HAC-700 exhibit significantly suppressed self-discharge and leak current, with improved cycling stability, which is attributable to the stabilization of electrochemical interface between carbon surface and electrolyte. The result provides insights for rational design of surface chemistry for high-performance carbon electrode towards advanced energy storage.

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Decarbonising energy: The developing international activity in hydrogen technologies and fuel cells John Meurig Thomas, Peter P. Edwards, Peter J. Dobson, Gari P. Owen 2020, 51(12): 405-415.  DOI: 10.1016/j.jechem.2020.03.087 Abstract ( 17 )   PDF (2334KB) ( 6 )   Hydrogen technologies and fuel cells offer an alternative and improved solution for a decarbonised en- ergy future. Fuel cells are electrochemical converters; transforming hydrogen (or energy sources contain- ing hydrogen) and oxygen directly into electricity. The hydrogen fuel cell, invented in 1839, permits the generation of electrical energy with high efficiency through a non-combustion, electrochemical process and, importantly, without the emission of CO2 at its point of use. Hitherto, despite numerous efforts to exploit the obvious attractions of hydrogen technologies and hydrogen fuel cells, various challenges have been encountered, some of which are reviewed here. Now, however, given the exigent need to urgently seek low-carbon paths for humankind’s energy future, numerous countries are advancing the deployment of hydrogen technologies and hydrogen fuel cells not only for transport, but also as a means of the stor- age of excess renewable energy from, for example, wind and solar farms. Furthermore, hydrogen is also being blended into the natural gas supplies used in domestic heating and targeted in the decarbonisation of critical, large-scale industrial processes such as steel making. We briefly review specific examples in countries such as Japan, South Korea and the People’s Republic of China, as well as selected examples from Europe and North America in the utilization of hydrogen technologies and hydrogen fuel cells.

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Multi-electron reaction concept for the universal battery design Feng Wu, Haoyi Yang, Ying Bai, Chuan Wu 2020, 51(12): 416-417.  DOI: 10.1016/j.jechem.2019.11.026 Abstract ( 8 )   PDF (295KB) ( 6 )   Ceaseless pursuit of energy storage and conversion animates the research and development of electro- chemical batteries. Energy density is a prior parameter concerned for practical use which represents the specific energy a battery carries. The concept of “multi-electron reactions” opens up an avenue toward the batteries with high energy densities in theory, and triumphantly advances the course of battery de- velopment to cover the increasing demands. Representative electrode materials of the “multi-electron re- actions” mechanism will be sketched, with the aim to provide a rationale for high energy density battery design. Challenge still faces the future work in the thorough understanding of mechanism and evocation of multi-electron reactions.

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The capacitive performances of carbon obtained from the electrolysis of CO2 in molten carbonates: Effects of electrolysis voltage and temperature Diyong Tang, Yanpeng Dou, Huayi Yin, Xuhui Mao, Wei Xiao, Dihua Wang 2020, 51(12): 418-424.  DOI: 10.1016/j.jechem.2019.11.006 Abstract ( 5 )   PDF (2178KB) ( 1 )   The electrochemical reduction of CO2 to capacitive carbon in molten Li2CO3-Na2CO3-K2CO3 is an effective strategy for capturing and utilizing CO2. This paper reports the effects of the cell voltages and operating temperatures (450-650 °C) of the molten salt electrolysis on the capacitive performance of electrolytic carbon. The electrolytic carbon delivers excellent specific capacitance when the cell voltage is 4.5 V and the temperature of molten salt is 450 °C. The carbon obtained at 450 °C and under 4.5 V delivers a specific capacitance of 550 F g-1 at 0.2 A g-1 in 1 M aqueous H2SO4, and the capacity retention rate is 73% after 10000 cycles. The specific capacitance of the electrolytic carbon increases as the electrolysis temperature decreases, and the optimal cell voltage is 4.5 V.

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Critical role of corrosion inhibitors modified by silyl ether functional groups on electrochemical performances of lithium manganese oxides Min Ji Seong, Taeeun Yim 2020, 51(12): 425-433.  DOI: 10.1016/j.jechem.2020.02.029 Abstract ( 11 )   PDF (2468KB) ( 4 )   Lithium manganese oxides (LiMn2O4, LMO) have attracted significant attention as important cathode materials for lithium-ion batteries (LIBs), which require fast charging based on their intrinsic electro- chemical properties. However, these properties are limited by the rapid fading of cycling retention, par- ticularly at high temperatures, because of the severe Mn corrosion triggered by the chemical reaction with fluoride (F-) species existing in the cell. To alleviate this issue, three types of silyl ether (Si-O)- functionalized task-specific additives are proposed, namely methoxytrimethylsilane, dimethoxydimethyl- silane, and trimethoxymethylsilane. Ex-situ NMR analyses demonstrated that the Si-additives selectively scavenged the F- species as Si forms new chemical bonds with F via a nucleophilic substitution reaction due to the high binding affinity of Si with F-, thereby leading to a decrease in the F concentration in the cell. Furthermore, the addition of Si-additives in the electrolyte did not significantly affect the ionic conductivity or electrochemical stability of the electrolyte, indicating that these additives are compatible with conventional electrolytes. In addition, the cells cycled with Si-additives exhibited improved cycling retention at room temperature and 45 °C. Among these candidates, a combination of MTSi and the LMO cathode was found to be the most suitable choice in terms of cycling retention (71.0%), whereas the cell cycled with the standard electrolyte suffered from the fading of cycling retention triggered by Mn disso- lution (64.4%). Additional ex-situ analyses of the cycled electrodes using SEM, TEM, EIS, XPS, and ICP-MS demonstrated that the use of Si-additives not only improved the surface stability of the LMO cathode but also that of the graphite anode, as the Si-additives prevent Mn corrosion. This inhibits the formation of cracks on the surface of the LMO cathode, facilitating the formation of a stable solid electrolyte in- terphase layer on the surface of the graphite anode. Therefore, Si-additives modified by Si-O functional groups can be effectively used to increase the overall electrochemical performance of the LMO cathode material.

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One-step wet-spinning assembly of twisting-structured graphene/carbon nanotube fiber supercapacitor Zhengpeng Yang, Yuanheng Jia, Yutao Niu, Yongyi Zhang, Chunjing Zhang, Ping Li, Meng Zhu, Qingwen Li 2020, 51(12): 434-441.  DOI: 10.1016/j.jechem.2020.02.023 Abstract ( 3 )   PDF (3086KB) ( 1 )   Graphene fiber-based supercapacitors hold great promise as flexible energy-storage devices. However, si- multaneously achieving high ion-transport ability in electrode and electrolyte layer, which is crucial for realizing the high electrochemical performance, still remains challenging. Here, a facile and effective strat- egy to solve the problem was proposed by developing a twisting-structured graphene/carbon nanotube (CNT) fiber supercapacitor via one-step wet-spinning process with customized multi-channel spinneret. The remarkable structure features of the resulting fiber supercapacitor with wrinkled and thin electrolyte layer, and well-developed porosity of fiber electrode favored the rapid infiltration and transport of elec- trolyte ions inside the electrode, as well as between electrode and electrolyte, thus boosting high specific capacitance of 187.6 mF cm-2 and energy density of 30.2 μWh cm-2, and featuring long cycling life (93% capacitance retention after 10,000 cycles) and excellent flexibility. Moreover, the specific capacitance and energy density could be further improved to 267.2 mF cm-2 and 66.8 μWh cm-2, respectively, when MnO2 was incorporated into the fiber.