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2018, Vol. 27, No. 5　Online: 2018-09-15


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Vanadium flow battery: Bi promotes all-climate energy storage

Vanadium flow battery (VFB) is a fast going and promising system for large-scale stationary energy storage. However, drawbacks such as low power density and narrow temperature window caused by poor catalytic activity of graphite felt (GF) electrodes limit its worldwide application. In this paper, Bi, as a low-cost, no-toxic and high-activity electrocatalyst, is used to modify the thermal activated GF (TGF) via a facile hydrothermal method. Bi can effectively inhibit the side reaction of hydrogen evolution in wide temperature range, while promoting the V²⁺/V³⁺ redox reaction. As a result, the VFB assembled with Bi/TGF as negative electrode demonstrates outstanding rate performance and excellent durability in all-climate conditions.

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Preface

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Preface to Special Column: Flow Battery Xianfeng Li, Wei Wang 2018, 27(5): 0-0.  摘要 ( 1049 )   The transition of the current energy infrastructure from fossil fuels to renewable energy sources is critical to the continuous prosperity of our society and economy. In order to accelerate the extensive adoption of the sustainable energy sources, challenges of intermittence and instability from the renewables must be resolved. Therefore, large-scale energy storage technologies, especially flow batteries, have attracted more and more attention, mainly because flow batteries own very intriguing characteristics of independently tuned power and capacity, high safety, high efficiency, long cycle life, flexible modular design, and low cost. In recent years, research and development (R&D) on various kinds of flow batteries have reported, including traditional zinc-bromine flow batteries (ZBFBs) and vanadium flow batteries (VFBs). Many of these possess variable attractive features and can consequently satisfy diverse users' demands. Up to now, VFBs and other types of flow batteries have been demonstrated, such as 5 MW/10 MWh VFB system combined with a 50 MW wind farm in Faku, Shenyang. However, there are still challenges for traditional flow batteries to further expand their industrialization. Thus, many novel aqueous and organic flow battery systems have been proposed recently, such as organic-based flow batteries. In fact, for both conventional and novel flow battery systems, the improvement in their energy density and power density, along with the decrease in their cost is the ultimate aim of the R&D. In general, this aim will be accomplished mainly by designing and optimizing the key materials of flow batteries, including electrolytes, electrodes, separators, and so forth. In recent years, many significant breakthroughs and achievements in the field of flow batteries have been reported. Herein, in order to better understand and promote the R&D in the field of flow batteries, a special column titled "Flow battery" on Journal of Energy Chemistry is ensued for the interested readers. This special column consists of three reviews, seven articles and one communication, authors of which all experts in the field of flow batteries. And these papers cover the main researches and advancements for the key materials of flow batteries. The three reviews cover the investigation and process for the key materials of aqueous and organic flow battery systems. The seven articles and one communication focus on the newest results about the key components of flow batteries, largely including modifications on electrolytes and electrodes. A common theme of this special column is that the energy density of flow batteries can be enhanced by improving the solubility and thermal stability of electrolytes, while their increased power density can be derived from the reduction in the battery polarization. Besides, the improvement in the performances of the separators, bipolar plates and other battery components also contributes to the elevated power and energy density of flow batteries. With the development of the key materials in redox flow batteries, their performances are bound to improve, propelling their successful industrialization. This special column is a comprehensive reference on the recent science and technology advancement of various redox flow battery technologies for the researchers in this field, as well as the readers who are interested in the flow battery related materials, chemistry and system development.

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A review of electrolyte additives and impurities in vanadium redox flow batteries Liuyue Cao, Maria Skyllas-Kazacos, Chris Menictas, Jens Noack 2018, 27(5): 1269-1291.  DOI: 10.1016/j.jechem.2018.04.007 摘要 ( 1151 )   As one of the most important components of the vanadium redox flow battery (VRFB), the electrolyte can impose a significant impact on cell properties, performance and capital cost. In particular, the electrolyte composition will influence energy density, operating temperature range and the practical applications of the VRFB. Various approaches to increase the energy density and operating temperature range have been proposed. The presence of electrolyte impurities, or the addition of a small amount of other chemical species into the vanadium solution can alter the stability of the electrolyte and influence cell performance, operating temperature range, energy density, electrochemical kinetics and cost effectiveness. This review provides a detailed overview of research on electrolyte additives including stabilizing agents, immobilizing agents, kinetic enhancers, as well as electrolyte impurities and chemical reductants that can be used for different purposes in the VRFBs.

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Progress on the electrode materials towards vanadium flow batteries (VFBs) with improved power density Tao Liu, Xianfeng Li, Huamin Zhang, Jizhong Chen 2018, 27(5): 1292-1303.  DOI: 10.1016/j.jechem.2018.07.003 摘要 ( 1028 )   The vanadium flow battery (VFB) has been considered as one of the most promising large-scale energy storage technologies in terms of its design flexibility, long cycle life, high efficiency and high safety. However, the high cost prevents the VFB technology from broader market penetration. Improving the power density of the VFB is an effective solution to reduce its cost due to the reduced material consumption and stack size. Electrode, as one of the main components in the VFB, providing the reactions sites for redox couples, has an important effect on the voltage loss of the VFB associated with electrochemical polarization, ohmic polarization and concentration polarization. Extensive research has been carried out on the electrode modification to reduce polarizations and hence improve the power density of the VFB. In this review, state-of-the-art of various modification methods on the VFB electrode materials is overviewed and summarized, and the future research directions helpful to reduce polarization loss are presented.

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Recent progress in organic redox flow batteries: Active materials, electrolytes and membranes Hongning Chen, Guangtao Cong, Yi-Chun Lu 2018, 27(5): 1304-1325.  DOI: 10.1016/j.jechem.2018.02.009 摘要 ( 1149 )   Redox flow batteries (RFBs) have great potentials in the future applications of both large scale energy storage and powering the electrical vehicle. Critical challenges including low volumetric energy density, high cost and maintenance greatly impede the wide application of conventional RFBs based on inorganic materials. Redox-active organic molecules have shown promising prospect in the application of RFBs, benefited from their low cost, vast abundance, and high tunability of both potential and solubility. In this review, we discuss the advantages of redox active organic materials over their inorganic compart and the recent progress of organic based aqueous and non-aqueous RFBs. Design considerations in active materials, choice of electrolytes and membrane selection in both aqueous and non-aqueous RFBs are discussed. Finally, we discuss remaining critical challenges and suggest future directions for improving organic based RFBs.

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Two electron utilization of methyl viologen anolyte in nonaqueous organic redox flow battery Bo Hu, T. Leo Liu 2018, 27(5): 1326-1332.  DOI: 10.1016/j.jechem.2018.02.014 摘要 ( 1156 )   Methyl viologen (MV) as a bench-mark anolyte material has been frequently applied in aqueous organic redox flow batteries (AORFBs) towards large-scale renewable energy storage. However, only the first reduction of MV was utilized in aqueous electrolytes because of the insoluble MV0 generated from the second reduction of MV. Herein, we report that methyl viologen with bis(trifluoromethane)sulfonamide counter anion, MVTFSI, can achieve two reversible reductions in a nonaqueous supporting electrolyte. Paired with (Ferrocenylmethyl)trimethylammonium bis(trifluoromethanesulfonyl)imide, FcNTFSI, as catholyte, the MVTFS/FcNTFSI nonaqueous organic redox flow battery (NOARFB) can take advantage of either one electron or two electron storage of the methyl viologen moiety and provide theoretical energy density of 24.9 Wh/L and a cell voltage of up to 1.5 V. Using a highly conductive LiTFSI/CH3CN supporting electrolyte and a porous Daramic separator, the NOARFB displayed excellent cycling performance, including up to a 68.3% energy efficiency at 40 mA/cm2, and more than 88% total capacity retention after 100 cycles.

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Broad temperature adaptability of vanadium redox flow battery-part 4: Unraveling wide temperature promotion mechanism of bismuth for V2+/V3+ couple Yuchen Liu, Feng Liang, Yang Zhao, Lihong Yu, Le Liu, Jingyu Xi 2018, 27(5): 1333-1340.  DOI: 10.1016/j.jechem.2018.01.028 摘要 ( 1099 )   Vanadium flow battery (VFB) is a fast going and promising system for large-scale stationary energy storage. However, drawbacks such as low power density and narrow temperature window caused by poor catalytic activity of graphite felt (GF) electrodes limit its worldwide application. In this paper, bismuth, as a low-cost, no-toxic and high-activity electrocatalyst, is used to modify the thermal activated GF (TGF) via a facile hydrothermal method. Bismuth can effectively inhibit the side reaction of hydrogen evolution in wide temperature range, while promoting the V2+/V3+ redox reaction. As a result, the VFB assembled with Bi/TGF as negative electrode demonstrates outstanding rate performance under the current density up to 400 mA cm-2, as well as a long-term stability over 600 charging/discharging cycles at a high current density of 150 mA cm-2. Moreover, it also shows excellent temperature adaptability from -10℃ to 50℃ and high durability for life test at the temperature of 50℃.

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The influence of electrochemical treatment on electrode reactions for vanadium redox-flow batteries Jens Noack, Nataliya Roznyatovskaya, Jessica Kunzendorf, Maria Skyllas-Kazacos, Chris Menictas, Jens Tübke 2018, 27(5): 1341-1352.  DOI: 10.1016/j.jechem.2018.03.021 摘要 ( 1165 )   Through targeted and reproducible electrochemical treatment of glassy carbon electrodes, investigations have been carried out on the electrochemical behaviour of the oxidation of V2+, VO2+ and the reductions of VO2+, VO2+ and V3+ in order to pretreat electrodes specifically for use in vanadium redox flow batteries and, if possible, to treat them in situ. For this purpose, a glassy carbon electrode was treated potentiostatically for a period of 30 s at different potentials in the range of 500 mV-2000 mV vs. Hg/Hg2SO4 in 2 M H2SO4 and then linear sweep voltammograms were performed in the different vanadium-containing solutions. With this method, it could be shown that all reactions are extremely surface sensitive and the reaction speeds changed by several decades. The reaction rates increased significantly in all reactions compared to polished electrodes and had an optimum treatment potential of approx. 1600 mV vs. Hg/Hg2SO4, although the oxidation reaction of V2+ and the reduction reactions of V3+ and VO2+ had opposite tendencies to oxidation of VO2+ and the reduction of VO2+ in the area of low treatment potentials. In the former, the kinetics increased and in the latter, they decreased. In addition, causes were investigated using confocal microscopy and XPS. No correlation was found to the roughness or size of the stretched surfaces, although these changed significantly as a result of the treatment. XPS measurements gave indications of a dependence on hydroxyl groups for the oxidation of VO2+ and the reduction of VO2+, while for the reactions of oxygen-free cations and the reduction of VO2+ weak indications of a dependence on carboxyl groups were obtained.

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In situ compression and X-ray computed tomography of flow battery electrodes Rhodri Jervis, Matt D. R. Kok, Tobias P. Neville, Quentin Meyer, Leon D. Brown, Francesco Iacoviello, Jeff T. Gostick, Dan J. L. Brett, Paul R. Shearing 2018, 27(5): 1353-1361.  DOI: 10.1016/j.jechem.2018.03.022 摘要 ( 1083 )   Redox flow batteries offer a potential solution to an increase in renewable energy generation on the grid by offering long-term, large-scale storage and regulation of power. However, they are currently underutilised due to cost and performance issues, many of which are linked to the microstructure of the porous carbon electrodes used. Here, for the first time, we offer a detailed study of the in situ effects of compression on a commercially available carbon felt electrode. Visualisation of electrode structure using X-ray computed tomography shows the non-linear way that these materials compress and various metrics are used to elucidate the changes in porosity, pore size distribution and tortuosity factor under compressions from 0%-90%.

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Biphenyl-lithium-TEGDME solution as anolyte for high energy density non-aqueous redox flow lithium battery Feng Pan, Jing Yang, Chuankun Jia, Hong Li, Qing Wang 2018, 27(5): 1362-1368.  DOI: 10.1016/j.jechem.2018.04.008 摘要 ( 1032 )   Non-aqueous redox flow batteries, because of larger operating voltage, have attracted considerable attention for high-density energy storage applications. However, the study of the anolyte is rather limited compared with the catholyte due to the labile properties of redox mediators at low potentials. Here, we report a new strategy that exploits high concentration organic lithium metal solution as a robust and energetic anolyte. The solution formed by dissolving metallic lithium with biphenyl (BP) in tetraethylene glycol dimethyl ether (TEGDME) presents a redox potential of 0.39 V versus Li/Li+, and a concentration up to 2 M. When coupled with a redox-targeted LiFePO4 catholyte system, the constructed redox flow lithium battery full cell delivers a cell voltage of 3.0 V and presents reasonably good cycling performance.

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Preparation and surface modification of PVDF-carbon felt composite bipolar plates for vanadium flow battery Zhenhao Liu, Baoguo Wang, Lixin Yu 2018, 27(5): 1369-1375.  DOI: 10.1016/j.jechem.2018.04.010 摘要 ( 1143 )   The performance of vanadium flow batteries (VFBs) is closely related to the materials used in the bipolar plates. Carbon-based composite bipolar plates are particularly suitable for VFB applications. However, most original preparation methods cannot simultaneously achieve good electrical conductivity and mechanical performance. In this paper, we propose a novel approach to fabricating bipolar plates with carbon plastic materials, including four steps, namely coating a poly (vinylidene fluoride) (PVDF) solution onto carbon felt, solvent evaporation, hot-pressing, and surface modification. The resulting bipolar plates showed high conductivity, good mechanical strength, and corrosion resistance. Surface modification by coating with carbon nanotubes (CNTs) removed the PVDF-rich layer from the surface of the carbon fibers. The high surface area of the CNT withdrew PVDF resin from the carbon fiber surface, and promoted the formation of a conductive network. The flexibility and battery charge-discharge cycle measurements showed that the composite bipolar plates can meet requirements for VFB applications.

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The effect of phosphate additive on the positive electrolyte stability of vanadium redox flow battery Fengyu Tian, Lei Wang, Chang-Sheng Wang 2018, 27(5): 1376-1380.  DOI: 10.1016/j.jechem.2018.05.018 摘要 ( 1215 )   The electrolyte is one of the most important components of vanadium redox flow battery (VRFB), and its stability and solubility determines the energy density of a VRFB. The performance of current positive electrolyte is limited by the low stability of VO2+ at a higher temperature. Phosphate is proved to be a very effective additive to improve the stability of VO2+. Even though, the stabilizing mechanism is still not clear, which hinders the further development of VRFBs. In this paper, to clarify the effect of phosphate additive on the positive electrolyte stability, the hydration structures of VO2+ cations and the reaction mechanisms of precipitation with or without phosphate in the supporting electrolyte of H2SO4 solutions were investigated in detail based on calculations of electronic structure. The stable configurations of complexes were optimized at the B3LYP/6-311+G(d,p) level of theory. The zero-point energies and Gibbs free energies for these complexes were further evaluated at the B3LYP/aug-cc-pVTZ level of theory. It shows that a structure of[VO2(H2O)2]+ surrounded by water molecules in H2SO4 solution can be formed at the room temperature. With the temperature rises,[VO2(H2O)2]+ will lose a proton and form the intermediate of VO(OH)3, and the further dehydration among VO(OH)3 molecules will create the precipitate of V2O5. When H3PO4 was added into electrolytes, the V-O-P bond-containing neutral compound could be formed through interaction between VO(OH)3 and H3PO4, and the activation energy of forming the V-O-P bond-containing neutral compound is about 7 kcal mol-1 lower than that of the VO(OH)3 dehydration, which could avoid the precipitation of V2O5 and improve the electrolyte stability.

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Towards an all-vanadium redox flow battery with higher theoretical volumetric capacities by utilizing the VO2+/V3+ couple Wentao Duan, Bin Li, Dongping Lu, Xiaoliang Wei, Zimin Nie, Vijayakumar Murugesan, James P. Kizewski, Aaron Hollas, David Reed, Vincent Sprenkle, Wei Wang 2018, 27(5): 1381-1385.  DOI: 10.1016/j.jechem.2018.05.020 摘要 ( 1062 )   An all-vanadium redox flow battery with V(IV) as the sole parent active species is developed by accessing the VO2+/V3+ redox couple. These batteries, referred to as V4RBs, possess a higher theoretical volumetric capacity than traditional VRBs. Copper ions were identified as an effective additive to boost the battery performance.

REGULAR ARTICLES

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Preparation of CH3NH3PbI3 thin films for solar cells via Vapor Transfer Method Kejie Feng, Yitong Liu, Yuancheng Zhang, Yujie Liu, Xiaoliang Mo 2018, 27(5): 1386-1389.  DOI: 10.1016/j.jechem.2018.01.007 摘要 ( 1167 )   Organometal halide perovskite based solar cells have emerged as one of the most promising candidates for low-cost and high-efficiency solar cell technologies. Here a Vapor Transfer Method (VTM) is used to fabricate high quality perovskite thin films in a balanced vacuum capsule. By adjusting the reaction temperature, CH3NH3I saturated vapor which then reacts with PbI2 films can be controlled and the formation process of CH3NH3PbI3 perovskite films can be further influenced. Prepared perovskite films which exhibit pure phase, smooth surface and high crystallinity are assembled into planar heterojunction inverted solar cells. The whole fabrication process of solar cell devices is organic solution free. Finally, the champion cell achieved power conversion efficiency (PCE) of 13.08% with negligible current-voltage hysteresis under fully open-air conditions. The photovoltaic performance could be further enhanced by optimizing perovskite composition and the device structure.

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Cooperation of nitrogen-doping and catalysis to improve the Li-ion storage performance of lignin-based hard carbon Zhewei Yang, Huajun Guo, Feifei Li, Xinhai Li, Zhixing Wang, Lizhi Cui, Jiexi Wang 2018, 27(5): 1390-1396.  DOI: 10.1016/j.jechem.2018.01.013 摘要 ( 1063 )   Hard carbon draws great interests as anode material in lithium ion batteries (LIBs) due to its high theoretical capacity, high rate capability and abundance of its precursors. Herein we firstly synthesize the lignin-melamine resins by grafting melamine onto lignin. Afterwards, nitrogen doped hard carbon is prepared by the pyrolysis of lignin-melamine resins with the aid of catalyst (Ni(NO3)2·6H2O) at 1000℃. Compared with the samples without nitrogen-doping and catalysis, as-prepared nitrogen doped hard carbon exhibits higher reversible capacity (345 mAh g-1 at 0.1 A g-1), higher rate capability (145 mAh g-1 at 5 A g-1) and excellent cycling stability. The superior electrochemical performance is ascribed to the synergistic effect of nitrogen doping, graphitic structure and amorphous structure. Among them, nitrogen doping could create the vacancies around the nitrogen sites, which enhance the reactivity and the electronic conductivity of materials. Additionally, graphitic structure also enhances the electronic conductivity of materials, thus improving the electrochemical performance of hard carbon. It is worthwhile that lignin, renewable and abundant biopolymer, is converted to hard carbon with good electrochemical performance, which realizes the high value utilization of lignin.

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Interface charges boosted ultrafast lithiation in Li4Ti5O12 revealed by in-situ electron holography Yuren Wen, Xiao Chen, Xia Lu, Lin Gu 2018, 27(5): 1397-1401.  DOI: 10.1016/j.jechem.2018.02.019 摘要 ( 938 )   PDF(9KB) ( 2 )   It is still a great challenge at present to combine the high rate capability of the electrochemical capacitor with the high electrochemical capacity feature of rechargeable battery in energy storage and transport devices. By studying the lithiation mechanism of Li4Ti5O12 (LTO) using in-situ electron holography, we find that double charge layers are formed at the interface of the insulating Li4Ti5O12 (Li4) phase and the semiconducting Li7Ti5O12 (Li7) phase, and can greatly boost the lithiation kinetics. The electron wave phase of the LTO particle is found to gradually shrink with the interface movement, leaving a positive electric field from Li7 to Li4 phase. Once the capacitive interface charges are formed, the lithiation of the core/shell particle could be established within 10 s. The ultrafast kinetics is attributed to the built-in interface potential and the mixed Ti3+/Ti4+ sites at the interface that could be maximally lowering the thermodynamic barrier for Li ion migration.

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Protonation effect on catalytic water oxidation activity of a mononuclear Ru catalyst containing a free pyridine unit Zhao Liu, Yan Gao, Jing Wang, Ya'nan Yao, Yu Wei, Xuyang Chen 2018, 27(5): 1402-1408.  DOI: 10.1016/j.jechem.2017.09.033 摘要 ( 946 )   Two efficient single-site Ru water oxidation catalysts[Ru(bda)(pic)(Ln)] (bda=2,2'-bipyridine-6,6'-dicarboxylic acid, pic=picoline, L1=4,5-bipyridine-2,7-di-tert-butyl-9,9-dimethylxanthene, L2=4-pyridine-5-phenyl-2,7-di-tert-butyl-9,9-dimethylxanthene) were only synthesized containing different xanthene ligands at the axial site. These complexes have been thoroughly characterized by spectroscopic (UV-vis, NMR) and electrochemical (CV and DPV) techniques. Kinetic analysis proved that the mechanism of water oxidation comprises the water nucleophilic attack process on high-valence ruthenium species. It is found that the catalyst 1 displayed higher activity than catalyst 2 on water oxidation, caused by the protonation of the axial ligand L1 with a free pyridine.

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Improving the performance of arylamine-based hole transporting materials in perovskite solar cells: Extending π-conjugation length or increasing the number of side groups? Xuepeng Liu, Fantai Kong, Wangchao Chen, Ting Yu, Yin Huang, Tasawar Hayat, Ahmed Alsaedi, Hongxia Wang, Jian Chen, Songyuan Dai 2018, 27(5): 1409-1414.  DOI: 10.1016/j.jechem.2017.09.019 摘要 ( 1157 )   In this work, we prepared three simple arylamine-based hole transporting materials from commercially available starting materials. The effect of extending π-conjugation length or increasing the number of side groups compared with reference compound on the photophysical, electrochemical, hole mobility properties and performance in perovskite solar cells were further studied. It is noted that these two kinds of molecular modifications can significantly lower the HOMO level and improve the hole mobility, thus improving the hole injection from valence band of perovskite. On the other hand, the compound with more side groups showed higher hole injection efficiency due to lower HOMO level and higher hole mobility compared with the compound with extending π-conjugation length. The perovskite solar cells with the modified molecules as hole transporting materials showed a higher efficiency of 15.40% and 16.95%, respectively, which is better than that of the reference compound (13.18%). Moreover, the compound with increasing number of side groups based devices showed comparable photovoltaic performance with that of conventional spiro-OMeTAD (16.87%).

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Synthesis and visible-light-induced sacrificial photocatalytic water oxidation of quinary oxynitride BaNb0.5Ta0.5O2N crystals Kenta Kawashima, Mirabbos Hojamberdiev, Kunio Yubuta, Kazunari Domen, Katsuya Teshima 2018, 27(5): 1415-1421.  DOI: 10.1016/j.jechem.2017.09.006 摘要 ( 1290 )   PDF(17KB) ( 2 )   Quinary oxynitride BaNb0.5Ta0.5O2N crystals were fabricated through the partial nitridation and acidification of the KCl flux grown Ba5Nb2Ta2O15 crystals. The parameters of both the solute concentrations and cooling rates are optimized for the KCl flux growth of the larger Ba5Nb2Ta2O15 crystals with clearer crystal habits. Here, the optimal Ba5Nb2Ta2O15 crystals mainly have a hexagonal plate-like shape. After the partial nitridation and acidification, the porous BaNb0.5Ta0.5O2N crystals maintained the crystal shape of the oxide precursor and had a single-crystalline nature. For the Ba5Nb2Ta2O15 crystals, the wavelength of the absorption edge was about 707 nm. Especially, the CoOx-loaded BaNb0.5Ta0.5O2N photocatalyst demonstrated the comparatively high amount of O2 gas (150.7 μmol) during the 5 h visible-light-induced sacrificial water oxidation half-reaction, which might be achieved due to the high crystallinity and visible-light absorption property.

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Lignin in storage and renewable energy applications: A review José Luis Espinoza-Acosta, Patricia I. Torres-Chávez, Jorge L. Olmedo-Martínez, Alejandro Vega-Rios, Sergio Flores-Gallardo, E. Armando Zaragoza-Contreras 2018, 27(5): 1422-1438.  DOI: 10.1016/j.jechem.2018.02.015 摘要 ( 1191 )   Lignin is a cheap, abundant and non-toxic group of complex phenolic polymers obtained in large amounts from the papermaking and cellulosic biofuel industries. Although the application of lignin has been explored in these and several more industries, there are limited applications of lignin in the energy industry. However, numerous research revealed a great interest in the exploration of this renewable biopolymer in storage energy devices. Some of these applications include the use of lignin as an expander for lead-acid batteries, electrodes for primary and rechargeable batteries, electrodes for electronic double layer capacitors and electrochemical pseudocapacitors, and to feed different types of fuel cells. The use of lignin in energy storage devices improves not only the performance of these devices but also decreases the price and toxicity, contributing to obtaining greener energy devices. Based on the above, this review provides an overview of the main research work related to the use of lignin as a renewable component, suitable to replace some synthetic and toxic compounds used in the fabrication of energy storage devices with particular emphasis on batteries, advanced supercapacitors, and solar and fuel cells.

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Ultrahigh rate binder-free Na3V2(PO4)3/carbon cathode for sodium-ion battery Le Yang, Wei Wang, Mingxiang Hu, Jiaojing Shao, Ruitao Lv 2018, 27(5): 1439-1445.  DOI: 10.1016/j.jechem.2017.08.021 摘要 ( 1017 )   Sodium ion batteries (SIBs) are very promising for large-scale energy storage in virtue of its high energy density, abundant sodium resources and low environmental impact, etc. However, it is still a big challenge to develop high-performance and durable cathode materials for SIBs. Among different candidate materials, Na3V2(PO4)3 has attracted great attentions due to its high theoretical capacity (117 mAh/g), stable framework structure and excellent ionic conductivity. However, Na3V2(PO4)3 delivers inferior rate capability and cycling stability due to its poor electronic conductivity. In this work, free-standing Na3V2(PO4)3/carbon nanofiber membranes are synthesized by an electrospinning-sintering route. The sample could deliver excellent cycling capability with specific capacity of 112 mAh/g at 1 C after 250 cycles and ultrahigh rate capability with 76.9 mAh/g even at 100 C, which is superior to many state-ofthe-art SIB cathode materials. This can be attributed to the hierarchically distributed Na3V2(PO4)3 crystals in carbon nanofiber network, which possesses outstanding electronic/ionic conductivity and thus leads to an ultrahigh rate capability.

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Activation of commercial Pt/C catalyst toward glucose electro-oxidation by irreversible Bi adsorption Petri Kanninen, Tanja Kallio 2018, 27(5): 1446-1452.  DOI: 10.1016/j.jechem.2017.09.030 摘要 ( 1788 )   The effect of irreversibly adsorbed Bi on commercial Pt/C catalyst toward glucose electro-oxidation reaction (GOR) in different electrolytes (acidic, neutral, alkaline) is studied. Bi is successfully deposited on Pt/C from Bi3+ containing acidic solution from 0 to 90% coverage degree. The stability of the Bi layer in acid and alkaline corresponded to previous studies and started to dissolve at 0.7 V and 0.8 V versus reversible hydrogen electrode (RHE), respectively. However, in neutral phosphate buffer the layer showed remarkable stability to at least 1.2 V versus RHE. Bi modification at low (20%) and high (80%) coverage showed the highest increase in the activity of Pt/C toward GOR by a factor up to 7 due to the increased poisoning resistance of the modified catalyst. The effect of poisoning was especially reduced at high Bi coverage (80%), which shows that adsorbate blocked by Bi through the third-body effect is effective. Finally, with or without Bi modification GOR on Pt/C was most active in alkaline conditions.

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N-doped coaxial CNTs@α-Fe2O3@C nanofibers as anode material for high performance lithium ion battery Peng Huang, Wei Tao, Haixia Wu, Xiaogang Li, Ting Yin, Qian Zhang, Wen Qi, Guo Gao, Daxiang Cui 2018, 27(5): 1453-1460.  DOI: 10.1016/j.jechem.2017.09.011 摘要 ( 1346 )   N-doped coaxial CNTs@α-Fe2O3@C nanofibers have been successfully synthesized according to a facile solvothermal/hydrothermal method. The obtained CNTs@α-Fe2O3@C nanofibers composites exhibited special three-dimensional (3-D) network structure, which endows they promising candidate for anode materials of lithium ion battery. The coaxial property of CNTs@α-Fe2O3@C nanofibers could significantly improve the cycling and rate performance owing to the acceleration of charge/electron transfer, improvement of conductivity, maintaining of structural integrity and inhibiting the aggregation. The α-Fe2O3 nanoparticles with small size and high percentage of N-doped amount could further improve the electrochemical performance. As for the CNT@α-Fe2O3@C nanofibers, the capacity presented a high value of 1255.4 mAh/g at 0.1 C, and retained at 1213.4 mAh/g after 60 cycles. Even at high rate of 5 C, the capacity still exhibited as high as 319 mAh/g. The results indicated that the synthesized N-doped coaxial CNTs@α-Fe2O3@C nanofibers exhibited high cycling and rate performance.

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ZnO/ZnS core-shell composites for low-temperature-processed perovskite solar cells Enqiang Zheng, Yaqin Wang, Jiaxing Song, Xiao-Feng Wang, Wenjing Tian, Gang Chen, Tsutomu Miyasaka 2018, 27(5): 1461-1467.  DOI: 10.1016/j.jechem.2017.09.026 摘要 ( 1193 )   Electron transport layers (ETLs) in perovskite solar cells (PSCs) are a key factor to determine the photovoltaic performance. Herein, we demonstrate preparation of ZnO/ZnS core-shell composites through directly synthesizing ZnS on the ZnO nanoparticles in solution. We confirmed the formation of ZnO/ZnS core-shell composites by the uses of X-ray diffraction patterns and the Fourier transform infrared spectroscopy. ZnO/ZnS composites exhibit much homogeneous surface morphology as compared with the bare ZnO as revealed in the scanning electronic microscopy. Moreover, the upper shift of conduction band level upon composition of the ZnO/ZnS film results in a better alignment of energy level, which facilitates cascade charge extraction and thus improves the current density of perovskite solar cell. The shift of conduction band also improves the voltage of the PSCs. The photoluminescence (PL) spectroscopies measured in both steady and transient states were carried out to characterize the charge extraction at the interface between CH3NH3PbI3 and the electron transport layers of either ZnO or ZnO/ZnS composite. The ZnO/ZnS composite can more efficiently quench the PL signal of perovskite absorber than bare ZnO resulting in enhanced photocurrent generation in PSCs.

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The critical role of bulk density of graphene oxide in tuning its defect concentration through microwave-driven annealing Isao Ogino, Go Fukazawa, Shunsuke Kamatari, Shinichiroh Iwamura, Shin R. Mukai 2018, 27(5): 1468-1474.  DOI: 10.1016/j.jechem.2017.09.010 摘要 ( 1031 )   Controlling the concentration of defects in reduced graphene oxide (rGO) to tailor its electrical and physicochemical properties has remained a significant challenge. We report that extent of microwave (MW)-driven annealing of rGO is influenced significantly by its bulk density, which allows us to vary its defect density and crystallite size over wide ranges by controlling this parameter. Extent of annealing was investigated by multiple techniques including Raman and X-ray photoelectron spectroscopies, and electrical conductivity measurements. Improved corrosion resistance of rGOs upon annealing was examined by cyclic voltammetry in H2SO4 electrolyte and temperature-programmed oxidation of rGO. Our results indicate that a low bulk density of rGO facilitates defect annealing, yielding high-quality carbon with 99.3 wt% purity, oxidative resistance as high as graphite powder, and an electrical conductivity of 36,000 S m-1 in the compressed powder form. These results demonstrate a prospective synthesis route for tailor-made nanocarbons from rGO through MW-driven annealing.

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Modeling and optimization of methane dry reforming over Ni-Cu/Al2O3 catalyst using Box-Behnken design Seyedeh Molood Masoom Nataj, Seyed Mehdi Alavi, Golshan Mazloom 2018, 27(5): 1475-1488.  DOI: 10.1016/j.jechem.2017.10.002 摘要 ( 1164 )   In this work the effects of the contents of nickel (5, 7.5, 10 wt%) and copper (0, 1, 2 wt%) and reaction temperature (650, 700, 750℃) on the catalytic performance of Ni-Cu/Al2O3 catalyst in methane dry reforming were evaluated using Box-Behnken design in order to optimize methane conversion, H2/CO ratio and the catalyst deactivation. Different catalysts were prepared by co-impregnation method and characterized by XRD, BET, H2-TPR, FESEM and TG/DTA analyses. The results revealed that copper addition improved the catalyst reducibility. Promoted catalyst with low amounts of Cu gave higher activity and stability with high resistance to coke deposition and agglomeration of active phase especially during the reaction. However catalysts with high amounts of Cu were less active and rather deactivated due to the active sites sintering as well as Ni covering by Cu-enriched phase. The optimal conditions were determined by desirability function approach as 10 wt% of Ni, 0.83 wt% of Cu at 750℃. CH4 conversion of 95.1%, H2/CO ratio of 1 and deactivation of 1.4% were obtained experimentally under optimum conditions, which were in close agreement with the values predicted by the developed model.

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Effects of reduction on the catalytic performance of limonite ore Keisuke Abe, Ade Kurniawan, Takahiro Nomura, Tomohiro Akiyama 2018, 27(5): 1489-1495.  DOI: 10.1016/j.jechem.2017.09.032 摘要 ( 989 )   The catalytic performance of Ni-containing limonite ore in the dry reforming reaction of methane (CH4+CO2→2H2+2CO) was determined before and after hydrogen reduction, and under a flow of hydrogen. After hydrogen reduction, the limonite ore exhibited higher catalytic performance, because of the formation of Fe-Ni. However, the Fe in Fe-Ni was readily oxidized by the input CO2 gas, resulting in a rapid decrease in the catalytic performance of limonite ore. The performance decrease was due to a decrease in the Ni surface area; Ni could not dissolve in iron oxides and this caused segregation in the iron oxides. When the reaction was conducted under a hydrogen flow, the Fe-Ni was formed and maintained. Ni was highly dispersed in the Fe-Ni phase, resulting in greater surface area of Ni and higher conversion rate of CH4 and CO2. The catalytic performance of the limonite ore was inferior to the Ni/Al2O3 catalyst because the effect of catalyst support was small, however, the limonite ore was more stable during catalytic use and much cheaper than the Ni/Al2O3.

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New insight into the ultra-long lifetime of excitons in organic-inorganic perovskite: Reverse intersystem crossing Guanghao Meng, Yantao Shi, Xiangyuan Wang, Wei Wang, Shufeng Wang, Min Ji, Ce Hao 2018, 27(5): 1496-1500.  DOI: 10.1016/j.jechem.2017.10.018 摘要 ( 1086 )   Recently, an effective exciton diffusion length L exceeding 100 μm has been reported for organic-inorganic halide perovskites owing to both the high mobility and ultra-long lifetime of the excitons; however, the origin of ultra-long L is still unclear in nature. In some photoelectric materials, reverse intersystem crossing (RISC) from the triplet to the singlet state can enhance the quantum yield of photoluminescence greatly. In this study, our theoretical investigation indicated that the energy difference △Est between the singlet state and the triplet state of CH3NH3PbI3 was less than 0.1 eV, which represents one crucial prerequisite for the occurrence of RISC. Meanwhile, the experimental results showed that the photoluminescence lifetime increased with the increasing temperature, a typical feature of RISC. Based on this study, we put forward the hypothesis that the ultra-long lifetime of excitons in organic-inorganic halide perovskite might be caused by the RISC process. This may provide a new insight into the important photophysical properties of such novel photovoltaic materials.

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Al-incorporation into Li7La3Zr2O12 solid electrolyte keeping stabilized cubic phase for all-solid-state Li batteries Changbin Im, Dongwon Park, Hosung Kim, Jaeyoung Lee 2018, 27(5): 1501-1508.  DOI: 10.1016/j.jechem.2017.10.006 摘要 ( 1062 )   We observe the influence of Al occupancies in Li sites on the formation process of the garnet solid electrolyte of Li7La3Zr2O12 (LLZO). A direct incorporation of Al is first promoted in a Li-insufficient garnet solid electrolyte during the calcination process of 850℃ and then the cubic phase of LLZO is obtained after successive annealing step of 1000℃. Comparing to pristine LLZO, Al incorporated LLZO shows less formation of Li2CO3, keeping crystallographic and physicochemical properties. This Al incorporation improves both the ionic conductivity and interfacial resistance to poisoning procedure.

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Few-layered graphene via gas-driven exfoliation for enhanced supercapacitive performance Peiwen Wu, Jing He, Linlin Chen, Yingcheng Wu, Hongping Li, Huiyuan Zhu, Huaming Li, Wenshuai Zhu 2018, 27(5): 1509-1515.  DOI: 10.1016/j.jechem.2017.09.018 摘要 ( 1144 )   High-quality graphene flakes have long been desirable for numerous applications including energy storage, printable electronics, and catalysis. In this contribution, we report a green, efficient, facile gas-driven exfoliation process for the preparation of high-quality graphene in large scale. The gas exfoliation process was realized by the interplay between the expansion of interlayer at high temperature and the gasification of liquid nitrogen within the interlayer. Detailed experiments demonstrated that the higher temperature was critical to the formation of fewer layers. The exfoliated graphene was proved to be of high quality. We further investigated the electrochemical behavior of this exfoliated graphene. As a result, this few-layered graphene demonstrated an enhanced capability as a supercapacitor, much higher than its counterpart parent material.