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2019, Vol. 29, No. 2　Online: 2019-02-15


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Carbon dioxide methanation: Ni catalysts supported on nano γ-Al₂O₃ (Pages 3–7)

Prof. Wang and coworkers reported Ni catalysts supported on nanosheet (S) and nanoplate (P) γ-Al₂O₃ for CO₂ methanation. Superior catalytic performance was obtained on Ni/Al₂O₃-S due to tiny Ni size and suitable basic sites. This work highlights the importance of support and sheds light on the design of nanostructured catalysts.

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Preface

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A metal nitride interlayer for long life lithium sulfur batteries Jin-Lei Qin, Huiyou Zhao, Jia-Qi Huang 2019, 28(2): 1-2.  DOI: 10.1016/j.jechem.2018.07.001 摘要 ( 576 )

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Ni catalysts supported on nanosheet and nanoplate γ -Al2O3 for carbon dioxide methanation Jinwei Sun, Yujiang Wang, Haikui Zou, Xiaoguang Guo, Zhou-jun Wang 2019, 28(2): 3-7.  DOI: 10.1016/j.jechem.2017.09.029 摘要 ( 562 )   Nanosheet (S) and nanoplate (P) γ -Al2O3 were synthesized by simple hydrothermal methods and employed as supports for Ni catalysts in CO2 methanation. Both of the nanostructured Ni/Al2O3 catalysts displayed good activity. In comparison, the Ni/Al2O3-S catalyst showed higher CO2 conversion than the Ni/Al2O3-P counterpart at the reaction temperature ranging from 250 to 400℃. The physical and chemical properties of the catalysts were systematically characterized by N2 sorption, X-ray diffraction (XRD), high resolution-transmission electron microscopy (HR-TEM), hydrogen temperature-programmed reduction (H2-TPR) and CO2 temperature-programmed desorption (CO2-TPD) techniques. Higher specific surface area and stronger metal-support interactions were confirmed on the Ni/Al2O3-S catalyst, which may lead to smaller particle size of Ni nanoparticles. Moreover, the Ni/Al2O3-S catalyst possessed more abundant weak and medium basic sites, which would benefit the activation of CO2. The smaller Ni size and more suitable basic sites may rationalize the superior activity of the Ni/Al2O3-S catalyst. Besides, the Ni/Al2O3-S catalyst exhibited excellent stability at 325℃ for 40 h.

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Ultra-deep desulfurization by reactive adsorption desulfurization on copper-based catalysts Yaqing Liu, Hongying Wang, Jinchong Zhao, Yunqi Liu, Chenguang Liu 2019, 28(2): 8-16.  DOI: 10.1016/j.jechem.2018.01.016 摘要 ( 630 )   In this paper, a novel copper-based catalyst for FCC gasoline improving the ability of removal the sulfur and avoiding the loss of the octane number from olefin saturation by reactive adsorption desulfurization (RADS) was investigated. The series of Cu/ZnO-Al2O3 catalysts were characterized by X-ray powder diffraction (XRD), N2 adsorption analysis and temperature-programmed reduction (TPR) studies, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The experiment results showed that the catalysts had an optimum desulfurization ability with copper loading 6 wt%, which the sulfur contents of product decreased less than 10 μg/g and olefin contents decreased from 16.19% to 14.14% for the long period operation. The appropriate Cu loading content could lead to the high active and low apparent activation energy (Ea). Therefore, the Cu-based catalyst may become a novel catalyst for second-generation for reactive adsorption desulfurization, which achieves the high desulfurization active and low olefins saturation to satisfy the upgrading the product.

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Hard carbon derived from rice husk as low cost negative electrodes in Na-ion batteries Maria K. Rybarczyk, Yunming Li, Mo Qiao, Yong-Sheng Hu, Maria-Magdalena Titirici, Marek Lieder 2019, 28(2): 17-22.  DOI: 10.1016/j.jechem.2018.01.025 摘要 ( 525 )   Here, we report the synthesis of hard carbon materials (RH) made from natural rice husk through a single pyrolysis process and their application as an anode in sodium-ion batteries. The studies show that the electrochemical properties of RHs are affected by the treatment temperatures, which determine the materials morphology, in particular, their degree of graphitization and extent of continuous channels (nanovoids). The latter are accessible to sodium ions and significantly contribute to charge storage capacity of the produced anodes. The RHs obtained at 1600℃ deliver the highest reversible capacity of 276 mAh g-1 mainly due to insertion of sodium ions into the nanovoids. This work deepens the basic understanding of the influence of the carbonization temperature on the sodium storage mechanism.

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Synthesis of jet fuel additive with cyclopentanone Hao Tang, Fang Chen, Guangyi Li, Xiaofeng Yang, Yancheng Hu, Aiqin Wang, Yu Cong, Xiaodong Wang, Tao Zhang, Ning Li 2019, 28(2): 23-30.  DOI: 10.1016/j.jechem.2018.01.017 摘要 ( 623 )   A new route was developed for the synthesis of renewable decalin with cyclopentanone which can be derived from lignocellulose. It was found that 1,2,3,4,5,6,7,8-octahydronaphthalene could be selectively produced by the hydrogenation/dehydration/rearrangement of[1,1 -bi(cyclopentylidene)]-2-one (i.e. the selfaldol condensation product of cyclopentanone) over a dual-bed catalyst system. Among the investigated catalysts, the Ru/C and Amberlyst-15 resin exhibited the highest activities for the hydrogenation of[1,1-bi(cyclopentylidene)]-2-one to[1,1 -bi(cyclopentan)]-2-ol and the dehydration/rearrangement of[1,1-bi(cyclopentan)]-2-ol to 1,2,3,4,5,6,7,8-octahydronaphthalene, respectively. Using Ru/C and Amberlyst-15 resin as the first bed and the second bed catalysts, 1,2,3,4,5,6,7,8-octahydronaphthalene was directly produced in high carbon yield (83.7%) under mild conditions (393 K, 1 MPa). After being hydrogenated, the 1,2,3,4,5,6,7,8-octahydronaphthalene was converted to decalin which can be used as additive to improve the thermal stability and volumetric heat value of jet fuel.

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AgBF4/[emim] [BF4] supported ionic liquid membrane for carbon monoxide/nitrogen separation Shichao Feng, Yuanyuan Wu, Jianquan Luo, Yinhua Wan 2019, 28(2): 31-39.  DOI: 10.1016/j.jechem.2018.02.004 摘要 ( 615 )   In this paper, AgBF4/[emim] [BF4] supported ionic liquid membranes (SILMs) were prepared successfully for CO/N2 separation using nitrogen pressure immobilization procedures. The incorporation of AgBF4 could decrease membrane weight loss, improve the pressure-resistant ability, and keep the critical pressure (0.45 MPa) of the SILMs. The high viscosity and undissolved AgBF4 solids in membrane liquid would disturb gas molecular transport through membrane and give rise to the gas transport resistance. Therefore, the gas permeability decreased remarkably with increasing AgBF4 carrier content in the membrane. When the molar ratio of AgBF4 to[emim] [BF4] increased from 0:1 to 0.3:1, the CO/N2 selectivity of the SILMs showed a great increase from ～1 to ～9 at 20℃ and 0.4 MPa, suggesting that AgBF4 was an effective carrier for CO facilitated transport. The permeabilities of N2 and CO increased at higher transmembrane pressure, indicating that molecular transport would dominate the transport process at high pressure. The temperature-dependent gas permeability followed the Arrhenius equation. Moreover, the differences between the activation energies of CO and N2 became larger after introducing AgBF4, resulting in more obvious decrease in the CO/N2 selectivity at higher operating temperature.

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Selective hydrogenation of acetylene on SiO2-supported Ni-Ga alloy and intermetallic compound Lei Wang, Fengxu Li, Yanjun Chen, Jixiang Chen 2019, 28(2): 40-49.  DOI: 10.1016/j.jechem.2018.02.001 摘要 ( 566 )   Ni/SiO2 and bimetallic NixGa/SiO2 catalysts with different Ni/Ga atomic ratios (x=10~2) were investigated for the selective hydrogenation of acetylene. It was found that NixGa/SiO2 showed higher selectivity to ethylene than Ni/SiO2. This is attributed to the formation Ni-Ga alloy and Ni3Ga intermetallic compound (IMC) where there was a charge transfer from Ga to Ni, which is favorable for reducing the adsorption strength and amount of ethylene on Ni atoms. As a result, the over-hydrogenation, the C-C bond hydrogenolysis and the polymerization were suppressed, and subsequently the selectivity to ethylene was enhanced. With the decrease of Ni/Ga atomic ratio, the activity and stability of the NixGa/SiO2 catalysts increased first and then decreased, while the ethylene selectivity tended to increase. Ni5Ga/SiO2 exhibited the best performance. Under the conditions of 180℃, 0.1 MPa, and a reactant (1.0 vol% acetylene, 5.0 vol% H2 and 94 vol% N2) with the space velocity of 36,000 mL h-1 g-1, the acetylene conversion maintained at 100% on Ni5Ga/SiO2 during 120 h time on stream and the selectivity to ethylene was 75%～81% after reaction for 68 h. It was also found that the formation of Ni-Ga alloy and Ni3Ga IMC suppressed the incorporation of carbon to form NiCx, subsequently enhancing the catalyst stability. Additionally, with increasing the Ga content, the catalyst acid amount and strength tended to increase, which promoted the polymerization and carbon deposition and so the catalyst deactivation.

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Fe-substituted Ba-hexaaluminate with enhanced oxygen mobility for CO2 capture by chemical looping combustion of methane Fei Huang, Ming Tian, Yanyan Zhu, Xiaodong Wang, Aiqin Wang, Lin Li, Jian Lin, Junhu Wang 2019, 28(2): 50-57.  DOI: 10.1016/j.jechem.2018.02.003 摘要 ( 503 )   While Fe-based oxygen carriers (OC) are regarded to be promising for chemical looping combustion (CLC), the decrease of CO2 selectivity during deep reduction process and the severe agglomeration of Fe2O3 often occur after multiple redox cycles due to the low oxygen mobility. Herein, Fe-substituted Bahexaaluminates (BaFexAl12-xO19, denoted as BFxA-H, x=1 and 2) prepared by a modified two-step method exhibited not only higher amount of converted oxygen (Ot) and CH4 conversion (77% and 81% vs. 17% and 75%) than those prepared by the traditional co-precipitation method (BFxA-C, x=1 and 2) but also high CO2 selectivity above 92% during the nearly whole reduction from Fe3+ to Fe2+. Furthermore, the BFxA-H exhibited the excellent recyclability during 50 cycles. The better performance was ascribed to the markedly enhanced oxygen mobility which resulted from dominant occupancy of Fe cations in Al(5) sites (Fe5:71% and 70% vs. 49% and 41%) in mirror planes of hexaaluminate leading to larger amount of lattice oxygen coordinated with Fe5 (O-Fe5) (0.45 and 0.85 mmol/g vs. 0.31 and 0.50 mmol/g). The improvement of oxygen mobility also favored the preservation of chemical state of Fe cations in hexaaluminate structure in the re-oxidation step, resulting in the excellent recyclability of BFxA-H.

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In-situ growth of nanowire WO2.72 on carbon cloth as a binder-free electrode for flexible asymmetric supercapacitors with high performance Xiao Huang, Zhiguo Zhang, Huan Li, Hongxia Wang, Tingli Ma 2019, 28(2): 58-64.  DOI: 10.1016/j.jechem.2018.01.024 摘要 ( 627 )   For the first time, WO2.72 nanowires were in-situ grown on carbon cloth by a simple solvothermal reaction. The nanowire WO2.72/carbon cloth (NW WO2.72/CC) electrode showed good electrochemical performance with specific capacitance (Cs) reaching up to 398 F g-1 at a current density of 2 A g-1. The capacitance of 240 F g-1 was retained at a high current density of 16 A g-1. To further evaluate the energy storage performance, flexible asymmetric supercapacitors (FASCs) were fabricated using the activated carbon/carbon cloth (AC/CC) as negative electrode and NW WO2.72/CC as positive electrode, respectively. The FASCs delivered a high energy density of 28 Wh kg-1 at a power density of 745 W kg-1 and 13 Wh kg-1 even at a high power density of 22.5 kW kg-1. More impressively, 81% of the specific capacitance of the FASCs was retained after 10,000 cycles, indicating excellent cycle stability. This work indicates the NW WO2.72/CC holds a great potential for application in energy storage devices.

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Construction of a few-layer g-C3N4/α-MoO3 nanoneedles all-solid-state Z-scheme photocatalytic system for photocatalytic degradation Xiaoni Zhang, Jianjian Yi, Hanxiang Chen, Mao Mao, Liang Liu, Xiaojie She, Haiyan Ji, Xiangyang Wu, Shouqi Yuan, Hui Xu, Huaming Li 2019, 28(2): 65-71.  DOI: 10.1016/j.jechem.2018.01.014 摘要 ( 580 )   The suppression of the recombination of electrons and holes (e-h) and the enhancement of the light absorption of semiconductors are two key points toward efficient photocatalytic degradation. Here, we report a few-layer g-C3N4/α-MoO3 nanoneedles (flg-C3N4/α-MoO3 NNs) all-solid-state Z-scheme mechanism photocatalyst synthesized via a typical hydrothermal method in a controlled manner. The recombination of the photo-induced e-h pairs could be effectively restrained by the Z-scheme passageway between the flg-C3N4 and α-MoO3 NNs in the composite, which could also promise a high redox ability to degrade pollutants. And it became possible for the prepared photocatalyst to absorb light in a wide range of wavelengths. The detailed mechanism was studied by electron spin-resonance spectroscopy (ESR). The low-dimensional nanostructure of the two constituents (α-MoO3 NNs with one-dimensional structure and flg-C3N4 with two-dimensional structure) endowed the composite with varieties of excellent physicochemical properties, which facilitated the transfer and diffusion of the photoelectrons and increased the specific surface area and the active sites. The 10 wt% flg-C3N4/α-MoO3 NNs showed the best photocatalytic performance toward RhB degradation, the rate of which was 71.86%, ～2.6 times higher than that of α-MoO3 NNs.

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Reduced graphene oxide supported Pd-Cu-Co trimetallic catalyst: synthesis, characterization and methanol electrooxidation properties Fan Yang, Bing Zhang, Sen Dong, Chunxia Wang, Andong Feng, Xiaoxu Fan, Yongfeng Li 2019, 28(2): 72-78.  DOI: 10.1016/j.jechem.2018.02.007 摘要 ( 592 )   Trimetallic palladium-copper-cobalt nanoparticles supported on reduced graphene oxide (PdCuCo/RGO) with different molar ratios of Pd, Cu and Co can be synthesized by facile chemical reduction with NaBH4 as reductant and cetrimonium bromide as stabilizer. The morphology, structure and composition of the as-synthesized catalysts are characterized by transmission electron microscopy, X-ray diffraction and Xray photoelectron spectroscopy. The cyclic voltammetry and chronoamperometry are utilized to investigate the electrochemical activities and stabilities of the as-obtained catalysts. The results demonstrate that the PdCuCo/RGO catalyst shows superior catalytic activity and stability for methanol electrooxidation in alkaline media compared with PdCu/RGO, PdCo/RGO, and Pd/RGO catalysts. These findings suggest that the PdCuCo/RGO catalyst possesses a great potential as a promising anode catalyst for direct methanol fuel cells.

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One step synthesis of high efficiency nickel/mesoporous TiO2 hybrid catalyst for hydrogen evolution reaction Esteban A. Franceschini, Melisa J. Gomez, Gabriela I. Lacconi 2019, 28(2): 79-87.  DOI: 10.1016/j.jechem.2018.02.005 摘要 ( 514 )   Nickel-TiO2 hybrid catalysts are synthesized by electrodeposition and their catalytic activity with respect to the hydrogen evolution reaction is analyzed. Two types of titanium oxide particles, which are commercial particles of dense TiO2 and mesoporous TiO2 particles synthesized by an aerosol method, are incorporated into the matrix of the nickel catalyst. Both nickel catalysts containing TiO2 particles presented higher catalytic activity than the conventional nickel Watts catalyst. Mesoporous TiO2-modified nickel catalyst showed the highest catalytic activity towards HER in alkaline medium. In addition, this type of nickel catalyst increases its catalytic activity after ageing treatment, which is an indication of an increase in the electro-active area of the electrode.

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Ultrafast laser dynamics of metal organic frameworks/TiO2 nano-arrays hybrid composites for energy conversion applications Fatma M. Ismail, Daniel O'Neil, Tareq Youssef, Souad A. Elfeky 2019, 28(2): 88-94.  DOI: 10.1016/j.jechem.2018.02.017 摘要 ( 535 )   Herein, we report the victorious synthesis of metal-organic frameworks (MOFs) on TiO2 nanotubes (NTs) using a layer-by-layer (LbL) approach. Highly crystalline and homogenous thin films of MOFs were grown and characterized using XRD, SEM, FT-IR and UV/Vis spectroscopy. Moreover, the utilization of the MOF films as sensitizers was probed in bespoke Graetzel type liquid junction solar cells. The constructed cell performance revealed an Isc of 1.16 mA cm-2, Voc of 0.63 V, FF of 0.33, and Eff of 0.42%. Further, pumpprobe transient laser spectroscopy was performed to investigate the energy and charge transfer dynamics of the MOFs/TiO2 NTs interface. The results indicated 86% injection efficiency. The ultrafast pump-probe spectroscopy allows the investigation of this process and the differences between MOFs. It also showed that the relaxation of the MOF chromophores is in competition with electron injection in the TiO2 motif. Thus this study provides a new insight into electron transfer from photoexcited metal-organic frameworks (MOFs) into titanium dioxide.

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Reversible and irreversible heat generation of NCA/Si-C pouch cell during electrochemical energy-storage process Ying Bai, Limin Li, Yu Li, Guanghai Chen, Huichun Zhao, Zhaohua Wang, Chuan Wu, Hongyun Ma, Xinquan Wang, Hongyue Cui, Jiang Zhou 2019, 28(2): 95-102.  DOI: 10.1016/j.jechem.2018.02.016 摘要 ( 520 )   To meet the requirements of electronic vehicles (EVs) and hybrid electric vehicles (HEVs), the high energy density LiNi0.8Co0.15Al0.05O2 (NCA) cathode and Si-C anode have attracted more attention. Here we report the thermal behaviors of NCA/Si-C pouch cell during the charge/discharge processes at different current densities. The total heat generations are derived from the surface temperature change during electrochemical Li+ insertion/extraction in adiabatic surrounding. The reversible heat is determined by the entropic coefficients, which are related with open-circuit voltage at different temperatures; while the irreversible heat is determined by the internal resistance, which can be obtained via V-I characteristic, electrochemical impedance spectroscopy and hybrid pulse power characterization (HPPC). During the electrochemical process, the reversible heat contributes less than 10% to total heat generation; and the heat generated in charge process is less than that in discharge process. The results of thermal behaviors analyses are conducive to understanding the safety management and paving the way for building a reliable thermal model of high energy density lithium ion battery.

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KHCO3 activated carbon microsphere as excellent electrocatalyst for VO2+/VO2+ redox couple for vanadium redox flow battery Chen Zhao, Yuehua Li, Zhangxing He, Yingqiao Jiang, Lu Li, Fengyun Jiang, Huizhu Zhou, Jing Zhu, Wei Meng, Ling Wang, Lei Dai 2019, 28(2): 103-110.  DOI: 10.1016/j.jechem.2018.02.006 摘要 ( 591 )   In this paper, carbon microsphere prepared by hydrothermal treatment was activated by KHCO3 at high temperature, and employed as the catalyst for VO2+/VO2+ redox reaction for vanadium redox flow battery (VRFB). Carbon microsphere can be etched by KHCO3 due to the reaction between the pyrolysis products of KHCO3 and carbon atoms. Moreover, KHCO3 activation can bring many oxygen functional groups on carbon microsphere, further improving the wettability of catalyst and increasing the active sites. The electrocatalytic properties of carbon microsphere from hydrothermal treatment are improved by high temperature carbonization, and can further be enhanced by KHCO3 activation. Among carbon microsphere samples, the VO2+/VO2+ redox reaction exhibits the highest electrochemical kinetics on KHCO3 activated sample. The cell using KHCO3 activated carbon microsphere as the positive catalyst demonstrates higher energy efficiency and larger discharge capacity, especially at high current density. The results reveal that KHCO3 activated carbon microsphere is an efficient, low-cost carbon-based catalyst for VO2+/VO2+ redox reaction for VRFB system.

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Ni(OH)2-Ni/C for hydrogen oxidation reaction in alkaline media Yangxin Pan, Gaohe Hu, Juntao Lu, Li Xiao, Lin Zhuang 2019, 28(2): 111-115.  DOI: 10.1016/j.jechem.2018.02.011 摘要 ( 666 )   The development of the hydrogen electrode is vital for the application of alkaline polymer electrolyte fuel cells (APEFCs). In this study, a series of Ni(OH)2 decorated Ni/C catalysts (Ni(OH)2-Ni/C) were prepared by a three-step electrochemical treatment of Ni/C. The existence of Ni(OH)2 was demonstrated by X-ray photoelectron spectroscopy (XPS), and the surface molar ratio of Ni(OH)2/Ni of the samples was estimated via an electrochemical method. The HOR catalytic activity of the catalysts was evaluated by a rotation disk electrode (RDE) method, and a "volcano plot" was established between the HOR exchange current (j0) and the surface molar ratio of Ni(OH)2/Ni. On top of the "volcano", the surface molar ratio of Ni(OH)2/Ni is 1.1:1, the j0 of which was 6.8 times of that of Ni/C. The stability of the samples toward HOR was evaluated to be good. Our study added a systematic experimental evidence to the HOR research, showing that the HOR catalytic activity of Ni can be deliberately controlled via decoration of Ni(OH)2, which may help understanding the HOR mechanism on Ni.

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Preparation of Fe2P/Al2O3 and FeP/Al2O3 catalysts for the hydrotreating reactions Yamei Yuan, Jiayou Zhang, Hui Chen, Qiumei Hou, Jianyi Shen 2019, 28(2): 116-121.  DOI: 10.1016/j.jechem.2018.02.013 摘要 ( 498 )   A 60%Fe/Al2O3 catalyst was prepared by the co-precipitation method. It was reduced by H2 to produce metallic Fe, which was then sulfided by CS2 to Fe0.96S and Fe3S4 or phosphided by triphenylphosphine (PPh3) in liquid phases to Fe2P and FeP. It was found that the iron sulfides (Fe0.96S and Fe3S4) exhibited the low activity for the hydrodesulfurization (HDS) reactions. The HDS activity was also low on the Fe(metal)/Al2O3 and Fe2P/Al2O3 catalysts since they were converted into Fe0.96S and Fe3S4 during the HDS reactions. In contrast, the FeP/Al2O3 was found to be stable and active for the HDS reactions. In particular, FeP/Al2O3 possessed significantly smaller FeP particles than FeP/C, leading to the significant higher HDS activity of FeP/Al2O3 than FeP/C.

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Thickness evolution of graphite-based cathodes in the dual ion batteries via in operando optical observation Na Li, Yaoda Xin, Haosen Chen, Shuqiang Jiao, Hanqing Jiang, Wei-Li Song, Daining Fang 2019, 28(2): 122-128.  DOI: 10.1016/j.jechem.2018.03.003 摘要 ( 588 )   Graphite has been currently considered as a promising cathode material in dual ion batteries (DIBs) due to its unique features of sp2 hybridized carbon and stacked two-dimensional layered structures. However, unexpected volume/thickness changes in the graphite cathodes, induced by the intercalation/deintercalation of anions with large molecular size have been known to be a critical problem in designing DIB cells. To understand the volume/thickness changes in the DIB electrodes, in operando optical observing apparatus has been employed to observe the cross-section view of a graphite-based cathode upon cycles in the present work. The observation suggests that the cathode initially presented a huge irreversible thickness change (60%), and such thickness variation was prone to reduce and remain <20% in the following cycles. The results from both in operando observation and electrochemical characterizations collectively indicate that the greater thickness variation at initial cycle should be attributed to both anion intercalation into graphite-based cathodes and irreversible decomposition of chemical components in the DIB system. The method here highlights a universal route for fundamentally understanding the electrodes of huge volume variation.

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In situ growth of N-doped carbon coated CoNi alloy with graphene decoration for enhanced HER performance Linlin Chen, Saisai Yang, Kun Qian, Wei Wei, Cheng Sun, Jimin Xie 2019, 28(2): 129-135.  DOI: 10.1016/j.jechem.2018.03.005 摘要 ( 574 )   Non-noble metal-based catalysts, especially stable ones, have gained increasing attentions in the field of electronically catalytic hydrogen evolution reaction (HER). In this work, an N-doped carbon confined Co-Ni alloy with reduced graphene oxide (rGO) decoration (CoNi@N-C/rGO) was fabricated for HER. The prepared catalyst exhibited excellent HER activity in an acidic electrolyte (Tafel slope of ～133.7 mV). The results showed that the enhanced HER performance of the nanostructures is attributed to the chemical and electronic synergic effect between the confined Co-Ni alloy and rGO. Stability tests, realized via longterm potential cycles and extended electrolysis, provided the confirmation of the exceptional durability of the catalyst, which originated from the confining effect of the N-doped carbon shell. This versatile method provides a strategy for designing stable non-precious metal electrocatalysts confined by carboncoating.

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Utilization of the superior properties of highly mesoporous PVP modified NiCo2O4 with accessible 3D nanostructure and flower-like morphology towards electrochemical methanol oxidation reaction Gracita M. Tomboc, Medhen W. Abebe, Anteneh F. Baye, Hern Kim 2019, 28(2): 136-146.  DOI: 10.1016/j.jechem.2018.08.009 摘要 ( 558 )   Up to this date, researchers are still facing difficulties to expand the technology of direct methanol fuel cells (DMFCs) because of the high overpotential required to oxidize the methanol and its relatively poor performance due to CO poisoning of the leading-high cost anode catalyst. In line with this, we have successfully modified the morphological structure and composition of low cost cobalt based-metal oxides, MCo2O4 (M=Zn and Ni), with the simple and noble use of polyvinyl pyrrolidone (PVP) as growth modifier and surface stabilizer during the synthesis of nanoparticles in our previous reports, which shown high electrocatalytic activity and strong stability. Due to the good performance of our PVP modified MCo2O4 towards pseudocapacitor and oxygen evolution reaction applications, we decided to extend our research study to methanol oxidation reaction. Remarkably, PVP modified NiCo2O4 electrode directly grown on nickel foam substrate via a simple hydrothermal process exhibited better performance compared with PVP modified ZnCo2O4 and NiCo2O4 without PVP. It had obtained a remarkably low onset potential of 0.285 V and high current density of 280 mA cm-2, and shown great stability and high poison tolerance during a continuous CV cycling and Chronoamperometry test, which attained high efficiency of 86.86% and 98.52%, respectively. These positive results of PVP modified NiCo2O4 electrode towards MOR might be attributed to its hierarchical 3D nanostructures with highly mesoporous surface and large surface area which may have provided numerous electroactive sites, and the exceptional corrosion stability of NiCo2O4 electrode in alkaline solution.