能源化学(英文版)

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Oxidative coupling of methane over LaAlO₃ perovskite catalysts prepared by a co-precipitation method: Effect of co-precipitation pH value

Yujin Sim, Jihoon Yoo, Jeong-Myeong Ha, Ji Chul Jung

2019, 28(8): 1-8. DOI: 10.1016/j.jechem.2018.10.002

摘要 ( 45 )

Oxidative coupling of methane (OCM) was conducted over LaAlO₃_X catalysts that were prepared by a coprecipitation method using different co-precipitation pH values (X=6-10). The aim is to investigate the effect of pH values on the catalytic activity of LaAlO₃ catalysts in this reaction. The results showed that the co-precipitation pH value affected greatly on the formation of chemical species of precipitate precursors in the co-precipitation step, leading to different phases of the finally obtained LaAlO₃ catalysts. When the co-precipitation pH value increased up to 8, the lanthanum-related phases such as La₂O₃ and La(OH)₃ were gradually formed as by-products, preventing the formation of LaAlO₃ perovskite crystalline structure and facilitating the formation of oxygen vacancies on catalyst surface. However, at pH value of 9 or higher, the lanthanum content in the precipitate precursor was increased greatly. Not LaAlO₃ perovskite but lanthanum-related phases were developed as main phases, reducing their catalytic activities in this reaction. Among LaAlO₃ catalysts, the one prepared at pH=8 showed the highest C₂ yield due to its well-developed oxygen vacancies and electrophilic lattice oxygen. Therefore, the co-precipitation pH value strongly affected the LaAlO₃ catalyst activity in OCM reaction. A precious pH control should be required to prepare various perovskite catalysts for the OCM.

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Facile synthesis and enhanced catalytic activity of electrochemically dealloyed platinum-nickel nanoparticles towards formic acid electro-oxidation

Maryam Kiani, Jie Zhang, Yan Luo, Yihan Chen, Jinwei Chen, Jinlong Fan, Gang Wang, Ruilin Wang

2019, 28(8): 9-16. DOI: 10.1016/j.jechem.2018.10.011

摘要 ( 22 )

To obtain the electrocatalyst with an improved electrocatalytic performance towards formic acid electrooxidation (FAEO), a simple impregnation method is used to prepare Pt₃Ni nanoparticles loaded on carbon black, assisted with electrochemically dealloying process. The X-ray powder diffraction (XRD) results as well as transmission electron microscopy (TEM) analysis of as-synthesized electrocatalyst demonstrates that the reduction temperature has a great influence on the FAEO activity of the dealloyed Pt₃Ni nanoparticles. X-ray photoelectron spectroscopy (XPS) analyses confirm the variation in the electronic structure of platinum by incorporation of nickel atoms which reduces chemisorption of toxic carbon monoxide and promotes the dehydrogenation pathway of FAEO. The size of the dealloyed Pt₃Ni nanoparticles remains within the range of about 2.7 nm. All electrochemical results illustrate that the performance of the asobtained electrocatalyst towards the FAEO is significantly enhanced. Moreover, the carbon black content, incorporation of Ni atoms, and reduction temperature conditions have been proven to be the key factors for modification of the crystal structure and morphology which leads to enhanced catalytic performance.

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Hydrogen etching induced hierarchical meso/micro-pore structure with increased active density to boost ORR performance of Fe-N-C catalyst

Liqin Gao, Meiling Xiao, Zhao Jin, Changpeng Liu, Junjie Ge, Wei Xing

2019, 28(8): 17-23. DOI: 10.1016/j.jechem.2018.09.019

摘要 ( 23 )

Rational regulation on pore structure and active site density plays critical roles in enhancing the performance of Fe-N-C catalysts. As the microporous structure of the carbon substrate is generally regarded as the active site hosts, its hostility to electron/mass transfer could lead to the incomplete fulfillment of the catalytic activity. Besides, the formation of inactive metallic Fe particles during the conventional catalyst synthesis could also decrease the active site density and complicate the identification of real active site. Herein, we developed a facial hydrogen etching methodology to yield single site Fe-N-C catalysts featured with micro/mesoporous hierarchical structure. The hydrogen concentration in pyrolysis process was designated to effectively regulate the pore structure and active site density of the resulted catalysts. The optimized sample achieves excellent ORR catalytic performance with an ultralow H₂O₂ yield (1%) and superb stability over 10,000 cycles. Our finding provides new thoughts for the rational design of hierarchically porous carbon-based materials and highly promising non-precious metal ORR catalysts.

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Transforming Co₃O₄ nanosheets into porous N-doped Co_xO_y nanosheets with oxygen vacancies for the oxygen evolution reaction

Lei Xu, Yuqin Zou, Zhaohui Xiao, Shuangyin Wang

2019, 28(8): 24-29. DOI: 10.1016/j.jechem.2018.09.013

摘要 ( 19 )

Cobalt oxides have been widely investigated as promising replacements for noble metal-based catalysts for oxygen evolution reaction (OER). Herein, we, for the first time, have obtained porous Co_xO_y nanosheets with N-doping and oxygen vacancies by etching Co₃O₄ nanosheets with NH₃ plasma. Comparing with the pristine Co₃O₄ nanosheets (1.79 V), the porous Co_xO_y nanosheets with N-doping and oxygen vacancies have a much lower potential of 1.51 V versus RHE to reach the current density of 10 mA cm^-2. The obtained sample has a lower Tafel slope of 68 mV dec^-1 than the pristine Co₃O₄ nanosheets (234 mV dec^-1). The disclosed Co²⁺, which is responsible for the formation of active sites (CoOOH), N-doping and oxygen vacancies, gives rise to better performance of OER.

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Ti, Zn co-doped hematite photoanode for solar driven photoelectrochemical water oxidation

Quansong Zhu, Chunlin Yu, Xingwang Zhang

2019, 28(8): 30-36. DOI: 10.1016/j.jechem.2018.10.012

摘要 ( 39 )

Although there have been many reports of metal doping to ameliorate the drawbacks of hematite as the photoanode for water oxidation, most of them focused on monometallic doping, and only a few of them payed attention to bimetallic doping. What is worse, the synergetic mechanism between two metal dopants was not sufficiently studied, especially the density functional theory (DFT) calculation. In this work, the n-type hematite was synthesized by introducing Ti dopant into hematite through the hydrothermal method, and dipping-sintering treatment was employed to further introduce homogeneously dispersed Zn dopant into that, forming the Ti, Zn co-doped hematite. Under the optimal condition, Tidoped hematite photoanode reached approximately 2-times enhancement of the photocurrent density compared with the pristine one at 1.23 V vs. RHE, while Ti, Zn co-doped hematite anode obtained another 25% elevation. UV-Vis spectroscopy, Mott-Schottky plots, EIS analysis, photo-oxidation of hole scavenger (H₂O₂), and DFT calculation were employed to understand the role of Ti, Zn dopant. Based on the obtained results, the synergetic mechanism of two dopants was discussed, i.e., the improvement of PEC performance of Ti, Zn co-doped hematite photoanode was possibly attributed to greater carrier density and improved charge separation efficiency at the surface of hematite. This work provides new strategy and understanding of the improvement of PEC performance of hematite by doping engineering.

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Synthesis of a ternary amide Li_xK_y(NH₂)_x+y and a novel Li₃K(NH₂)₄-xMgH₂ combination system for hydrogen storage

Chao Li, Changlong Li, Meiqiang Fan, Haichao Chen, Kangying Shu, Yu Zhang, Mingxia Gao, Yongfeng Liu, Hongge Pan

2019, 28(8): 37-43. DOI: 10.1016/j.jechem.2018.09.014

摘要 ( 18 )

The ternary amides LiK₂(NH₂)₃, LiK(NH₂)₂, and Li₃K(NH₂)₄ are successfully synthesized by ball milling mixtures of LiNH₂ and KNH₂, and the hydrogen storage properties of Li₃K(NH₂)₄-xMgH₂ (x=1, 2, 3, 4) are systematically investigated. The Li₃K(NH₂)₄-2MgH₂ sample displays optimized hydrogen storage properties, releasing 6.37 wt% of hydrogen in a two-stage reaction with an onset temperature of 60℃. The first dehydrogenation stage exhibits good reaction kinetics and thermodynamic properties because of a lower activation energy and appropriate enthalpy change. After full dehydrogenation at 130℃, the Li₃K(NH₂)₄-2MgH₂ sample absorbs 3.80 wt% of H₂ below 160℃ in a variable temperature hydrogenation mode. Mechanistic investigations indicate that Li₃K(NH₂)₄ reacts with MgH₂ to produce Mg(NH₂)₂, LiH, and KH during ball milling. In the heating process, Mg(NH₂)₂ first reacts with LiH to form Li₂Mg₂N₃H₃ and LiNH₂, while KH works as a catalyst, and then, KH reacts with Li₂Mg₂N₃H₃ and LiNH₂ to generate a new K-containing compound.

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Enhanced aromatic selectivity by the sheet-like ZSM-5 in syngas conversion

Junhao Yang, Ke Gong, Dengyun Miao, Feng Jiao, Xiulian Pan, Xiangju Meng, Fengshou Xiao, Xinhe Bao

2019, 28(8): 44-48. DOI: 10.1016/j.jechem.2018.10.008

摘要 ( 39 )

Aromatics are important basic chemicals. However, direct conversion of syngas via the conventional Fischer-Tropsch synthesis produces little aromatics. We presented herein that a bifunctional composite of ZSM-5 in combination with ZnCrO_x catalyzes syngas conversion to aromatics. Particularly, ZSM-5 crystals with a sheet-like morphology can enhance significantly the aromatization activity. The lower length ratio of the b/a axes of the crystals, the more aromatics form but without influencing the selectivity of small molecules such as CH₄ and C₂-C₄. Since the acid properties and the Al chemical environment were not altered while the morphology changed, the enhanced aromatic selectivity is likely attributed to the favored diffusion of aromatics in these sheet-like crystals.

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A steady composite molecular anode Ru1/MWCNTsCOOH/GC for robust catalytic water oxidation

Yan Gao, Yu Wei, Zhongkai Lu, Xuyang Chen, Dongping Wang

2019, 28(8): 49-54. DOI: 10.1016/j.jechem.2018.10.013

摘要 ( 15 )

Development of efficient molecular devices for overall water splitting has always been a hotspot of research to realize clean and sustainable energy conversion. In the case, long-term durability of molecular devices is a crucial factor to determine their practical application. Here, an efficient composite molecular anode was assembled by immobilization of charge-neutral mononuclear Ru1 complex on COOHfunctionalized multiwalled carbon nanotubes (MWCNTsCOOH) sticking on a glassy carbon (GC) electrode (Ru1/MWCNTsCOOH/GC). The prepared hybrid anode showed a low onset overpotential of only 380 mV for electrocatalytic water oxidation. Moreover, the anode displayed a steady catalytic current density of 1.25 mA/cm² for more than 5 h at the overpotential of 580 mV, a high TON of 186000 (5 h), a TOF of 10.3 s^-1 and a faradic efficiency of 96%, indicating the significant efficiency and extremely durability. The excellent durability of the molecular anode should be attributed to the key charge-neutral catalytic intermediates (Ru1a~d) of the catalytic step and the two long flexible carbon chains of the catalyst.

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P-doped electrode for vanadium flow battery with high-rate capability and all-climate adaptability

Lihong Yu, Feng Lin, Lin Xu, Jingyu Xi

2019, 28(8): 55-59. DOI: 10.1016/j.jechem.2018.11.004

摘要 ( 32 )

A phosphorous-doped graphite felt (PGF) is fabricated and examined as electrode for vanadium flow battery (VFB). P doping improves the electrolyte wettability of GF and induces more defect sites on its surface, resulting in significantly enhanced activity and reversibility towards VO²⁺/VO₂⁺ and V²⁺/V³⁺ couples. VFB with PGF electrode demonstrates outstanding performance such as high-rate capability under 50-400 mA cm^-2, wide-temperature tolerance at -20℃-60℃, and excellent durability over 1000 charge-discharge cycles. These merits enable PGF a promising electrode for the next-generation VFB, which can operate at high-power and all-climate conditions.

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The influence of intimacy on the ‘iterative reactions’ during OX-ZEO process for aromatic production

Xiaoli Yang, Ting Sun, Junguo Ma, Xiong Su, Ruifeng Wang, Yaru Zhang, Hongmin Duan, Yanqiang Huang, Tao Zhang

2019, 28(8): 60-65. DOI: 10.1016/j.jechem.2018.11.003

摘要 ( 16 )

The oxide-zeolite process provides a promising way for one-step production of aromatics from syngas, whereas the reasons for the dramatic effect of intimacy between oxide and zeolite in the composite catalyst on the product selectivity are still unclear. In order to explore the optimal intimacy and the essential influence factors, ZnCrO_x combined with ZSM-5 are employed to prepare the composite catalysts with different distances between the two components by changing the mixing methods. An aromatic selectivity of 74% (with CO conversion to be 16%) is achieved by the composite catalyst when the intimacy is in the range of nanometer. A so-called ‘iterative reactions’ mechanism of intermediates over oxides is then proposed and studied:the intermediate chemical can undergo a hydrogenation reaction on oxide. So the shorter the intermediates stay on oxide, the more of chance for C-C coupling takes place on zeolite to form aromatics. Moreover, the aero-environments of reaction is found to impact on the extent of iterative reaction as well. Therefore, when the intimacy between the two components changes, the extent of iterative reactions vary, resulting in alteration of product distribution. This work provides new insight in understanding the mechanisms during the complex process of OX-ZEO composite catalysis and sheds light to the design of a high-yield catalyst for synthetization of aromatics from syngas.

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Understanding the synergetic interaction within α-MoC/β-Mo₂C heterostructured electrocatalyst

Hao Zhang, Haiyan Jin, Yuqi Yang, Fanfei Sun, Yang Liu, Xianlong Du, Shuo Zhang, Fei Song, Jianqiang Wang, Yong Wang, Zheng Jiang

2019, 28(8): 66-70. DOI: 10.1016/j.jechem.2018.10.010

摘要 ( 24 )

Constructing heterostructure is an important strategy to design efficient electrocatalysts. The synergetic interaction between dissimilar materials has been considered as the origin of the activity enhancement, however, the interfacial interaction is challenging to probe, thus, the underlying mechanism remains obscure. Here, we reported a heterostructured α-MoC/β-Mo₂C electrocatalyst for hydrogen evolution in alkaline media, which shows a significant electrocatalytic activity improvement as compared to the single component. Based on extensive characterizations including high-resolution transmission electron microscopy and X-ray absorption fine structure (XAFS) spectroscopy, together with density functional theory, we unraveled the synergetic interaction between α-MoC and β-Mo₂C, implying that α-MoC sites are beneficial for water dissociation and hydrogen prefers to release on β-Mo₂C sites.

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Infiltration of Ce_0.8Gd_0.2O_1.9 nanoparticles on Sr₂Fe_1.5Mo_0.5O_6-δ cathode for CO₂ electroreduction in solid oxide electrolysis cell

Houfu Lv, Yingjie Zhou, Xiaomin Zhang, Yuefeng Song, Qingxue Liu, Guoxiong Wang, Xinhe Bao

2019, 28(8): 71-78. DOI: 10.1016/j.jechem.2018.11.002

摘要 ( 54 )

Solid oxide electrolysis cell (SOEC) can electrochemically convert CO₂ to CO at the gas-solid interface with a high current density and Faradaic efficiency, which has attracted increasing attentions in recent years. Exploring efficient catalyst for electrochemical CO₂ reduction reaction (CO₂RR) at the cathode is a grand challenge for the research and development of SOEC. Sr₂Fe_1.5Mo_0.5O_6-δ (SFM) is one kind of promising cathode materials for SOEC, but suffers from insufficient activity for CO₂RR. Herein, Gd_0.2Ce_0.8O_1.9 (GDC) nanoparticles were infiltrated onto the SFM surface to construct a composite GDC-SFM cathode and improve the CO₂RR performance in SOEC. The current density over the GDC infiltrated SFM cathode with a GDC loading of 12.8 wt% reaches 0.446 A cm^-2 at 1.6 V and 800℃, which is much higher than that over the SFM cathode (0.283 A cm^-2). Temperature-programmed desorption of CO₂ measurements suggest that the infiltration of GDC nanoparticles significantly increases the density of surface active sites and three phase boundaries (TPBs), which are beneficial for CO₂ adsorption and subsequent conversion. Electrochemical impedance spectroscopy results indicate that the polarization resistance of 12.8 wt% GDCSFM cathode was obviously decreased from 0.46 to 0.30 Ω cm² after the infiltration of GDC nanoparticles.

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Theoretical study of CO₂ hydrogenation to methanol on isolated small Pd_x clusters

Adhitya G. Saputro, Refaldi I. D. Putra, Arifin L. Maulana, Muhammad U. Karami, Mochamad R. Pradana, Mohammad K. Agusta, Hermawan K. Dipojono, Hideaki Kasai

2019, 28(8): 79-87. DOI: 10.1016/j.jechem.2018.11.005

摘要 ( 15 )

CO₂ hydrogenation to methanol on small size Pd_x clusters (x=7, 9 and 13) has been studied using density functional theory calculations. It has been found that in contrast to metallic Pd system, these small Pd_x clusters can interact well with CO₂ molecule. CO₂ molecule can be adsorbed with a bidendate configuration on the Pd_x clusters. The formation of CO₂ bidendate adsorption configuration facilitates the first step of CO₂ hydrogenation reaction on the clusters. The energy profiles for formate pathway and reverse water gas shift + CO hydrogenation pathways on Pd_x clusters are quite similar with Cu(111) surface, except for the first and last hydrogenation steps where the Pd_x clusters have lower activation energies. This improvement causing the Pd_x clusters to have a tolerable turn over frequencies values. In general, the usage of Pd in the form of small size cluster can improve the catalytic performance of metallic Pd for the CO₂ hydrogenation to methanol because small size Pd cluster can act not only as an H₂ dissociation center but also as a CO₂ hydrogenation center.

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Layered double hydroxide nanosheets via solvothermal delamination

Katarina Cermelj, Kanittika Ruengkajorn, Jean-Charles Buffet, Dermot O'Hare

2019, 28(8): 88-94. DOI: 10.1016/j.jechem.2018.11.008

摘要 ( 39 )

A new solvothermal post-synthesis treatment for preparing high aspect ratio magnesium aluminium layered double hydroxides (MgAl-LDHs) has been developed. Treating laurate-intercalated MgAl-LDHs in pure ethanol in an autoclave for 48 h at 150℃ was found to produce delaminated MgAl-LDH nanosheets with a thickness of~2.6 nm and an aspect ratio of~105. It is proposed that the high pressure solvothermal process promotes the insertion of ethanol molecules into the LDH interlayer space, thereby facilitating delamination. This new post-synthesis treatment provides the opportunity for a facile, large scale route to highly delaminated high aspect ratio LDHs, which might be of interest towards novel nanomaterials for energy conversion and storage.

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Effect of electrode Pt-loading and cathode flow-field plate type on the degradation of PEMFC

Lijuan Qu, Zhiqiang Wang, Xiaoqian Guo, Wei Song, Feng Xie, Liang He, Zhigang Shao, Baolian Yi

2019, 28(8): 95-103. DOI: 10.1016/j.jechem.2018.09.004

摘要 ( 18 )

The electrode Pt-loading has an effect on the number of active sites and the thickness of catalyst layer, which has huge influence on the mass transfer and water management during dynamic process in PEMFCs. In this study, membrane electrode assemblies with different Pt-loadings were prepared, and PEMFCs were assembled using those membrane electrode assemblies with traditional solid plate and water transport plate as cathode flow-field plates, respectively. The performance and electrochemical surface area of cells were characterized to evaluate the membrane electrode assemblies degradation after rapid currentvariation cycles. Scanning electron microscope and transmission electron microscope were used to investigate the decay of catalyst layers and Pt/C catalyst. With the increase of Pt-loading, the performance degradation of membrane electrode assemblies will be mitigated. But higher Pt-loading means thicker catalyst layer, which leads to a longer pathway of mass transfer, and it may result in carbon material corrosion in membrane electrode assemblies. The decay of Pt/C catalyst in cathode is mainly caused by the corrosion of carbon support, and the degradation of anode Pt/C catalyst is a consequence of migration and aggregation of Pt particles. And using water transport plate is beneficial to alleviating the age of cathode Pt/C catalyst.

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Nanomorphology in A-D-A type small molecular acceptors-based bulk heterojunction polymer solar cells

Delong Liu, Ying Zhang, Gang Li

2019, 28(8): 104-123. DOI: 10.1016/j.jechem.2018.11.001

摘要 ( 21 )

Recent developments in acceptor-donor-acceptor (A-D-A) type non-fullerene acceptors have led to substantial improvements in bulk-heterojunction polymer solar cells efficiency. The device performance strongly depends on photoactive layer morphology, as the molecular packing, donor-acceptor interface and phase separation significantly affect the charge-transfer states and charge carrier dynamics. In this review, we start with a brief introduction of the techniques most effectively utilized to characterize multiphase morphology. Then, we summarize recent progress in A-D-A type acceptors, with the emphasis on understanding the molecular structure-morphology-performance relationships. Finally, an outlook on correlating morphological characteristics with photovoltage losses is presented for further improving device performance.

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ZnO@MOF@PANI core-shell nanoarrays on carbon cloth for high-performance supercapacitor electrodes

Chunmei Zhu, Ying He, Yijun Liu, Natalia Kazantseva, Petr Saha, Qilin Cheng

2019, 28(8): 124-131. DOI: 10.1016/j.jechem.2018.11.006

摘要 ( 43 )

Hierarchical ZnO@metal-organic framework@polyaniline (ZnO@MOF@PANI) core-shell nanorod arrays on carbon cloth has been fabricated by combining electrodeposition and hydrothermal method. Well-ordered ZnO nanorods not only act as a scaffold for growth of MOF/PANI shell but also as Zn source for the formation of MOF. The morphology of ZnO@MOF@PANI composite is greatly influenced by the number of PANI electrodeposition cycles. Their structural and electrochemical properties were characterized with different techniques. The results indicate that the ZnO@MOF@PANI with 13 CV cycles of PANI deposition demonstrates the maximum specific capacitance of 340.7 F g^-1 at 1.0 A g^-1, good rate capability with 84.3% capacitance retention from 1.0 to 10 A g^-1 and excellent cycling life of 82.5% capacitance retention after 5000 cycles at high current density of 2.0 A g^-1. This optimized core-shell nanoarchitecture endows the composite electrode with short ion diffusion pathway, rapid ion/electron transfer and high utilization of active materials, which thus result in excellent electrochemical performance of the ternary composite.

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Exploring NiCo₂S₄ nanosheets arrays by hydrothermal conversion for enhanced high-rate batteries

Jianbo Wu, Xiaohua Huang, Xinhui Xia

2019, 28(8): 132-137. DOI: 10.1016/j.jechem.2018.11.007

摘要 ( 18 )

Highly cross-linked porous NiCo₂S₄ nanosheets arrays are synthesized by a high-efficiency hydrothermal conversion from the preformed electrodeposited NiCo₂O₄ arrays. By using thioacetamide as the sulfur source, the electrodeposited NiCo₂O₄ is directly converted into NiCo₂S₄ nanosheets arrays without hightemperature sulfurization. Higher porosity and better electrical conductivity are obtained for the NiCo₂S₄ nanosheets arrays. In addition, reduced diffusion paths of electrons/ions and alleviated volume expansion during cycling are achieved due to the unique porous structure of NiCo₂S₄. Consequently, as the cathode of alkaline batteries, the obtained NiCo₂S₄ nanosheets arrays show better electrochemical performance with a high specific capacity (83.5 mAh g^-1 at 0.5 A g^-1) and better cycling stability (capacity retention of 93% after 5000 cycles) than the NiCo₂O₄ counterpart arrays (40.3 mAh g^-1 at 0.5 A g^-1). Our work demonstrates that sulfurization on binary metal oxides can greatly enhance electrochemical performance and shows a new way for construction of advanced electrodes for high-rate batteries.

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Impact of alkyl chain branching positions on molecular packing and electron transport of dimeric perylenediimide derivatives

Yuan Guo, Guangchao Han, Yuanping Yi

2019, 28(8): 138-143. DOI: 10.1016/j.jechem.2018.11.012

摘要 ( 14 )

Side chains play a critical role in tuning intermolecular interaction and charge transport in organic semiconductors. Here, we have systematically investigated the impact of branching positions of the alkyl side chains on the molecular packing and electron transport properties of a series of bay-linked dimeric perylenediimide (PDI) derivatives by atomistic molecular dynamics simulations in combination with charge transfer rate theory and kinetic Monte Carlo simulations. The results show that despite of different branching positions of the alkyl chains, π-π stacking is effectively inhibited for all the dimeric PDI derivatives. As the branching position moves away from the PDI backbone, the appearance of the alkyl atoms around the PDI backbone will first decrease and then increase. Correspondingly, the short contacts between the PDI moieties are first enhanced and then reduced. In particular, when the branching position is at the third carbon atom, the intermolecular connectivity becomes the most effective and the electron mobility is significantly increased by 2 times.

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SnO₂-based electron transporting layer materials for perovskite solar cells: A review of recent progress

Yichuan Chen, Qi Meng, Linrui Zhang, Changbao Han, Hongli Gao, Yongzhe Zhang, Hui Yan

2019, 28(8): 144-167. DOI: 10.1016/j.jechem.2018.11.011

摘要 ( 17 )

In recent years, due to their high photo-to-electric power conversion efficiency (PCE) (up to 23% (certified)) and low cost, perovskite solar cells (PSCs) have attracted a great deal of attention in photovoltaics field. The high PCE can be attributed to the excellent physical properties of organic-inorganic hybrid perovskite materials, such as a long charge diffusion length and a high absorption coefficient in the visible range. There are different diffusion lengths of holes in electrons in a PSC device, and thus the electron transporting layer (ETL) plays a critical role in the performance of PSCs. An alternative for TiO₂, to the most common ETL material is SnO₂, which has similar physical properties to TiO₂ but with much higher electron mobility, which is beneficial for electron extraction. In addition, there are many facile methods to fabricate SnO₂ nanomaterials with low cost and low energy consumption. In this review paper, we focus on recent developments in SnO₂ as the ETL of PSCs. The fabrication methods of SnO₂ materials are briefly introduced. The influence of multiple SnO₂ types in the ETL on the performance of PSCs is then reviewed. Different methods for improving the PCE and long-term stability of PSCs based on SnO₂ ETL are also summarized. The review provides a systematic and comprehensive understanding of the influence of different SnO₂ ETL types on PSC performance and potentially motivates further development of PSCs with an extension to SnO₂-based PSCs.

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Evaluation of hot pressing parameters on the electrochemical performance of MEAs based on Aquivion^® PFSA membranes

Irene Gatto, Ada Saccà, Vincenzo Baglio, Antonino Salvatore Aricò, Claudio Oldani, Luca Merlo, Alessandra Carbone

2019, 28(8): 168-173. DOI: 10.1016/j.jechem.2019.03.020

摘要 ( 18 )

The membrane-electrodes assembly (MEA) is the core of the Polymer Electrolyte Fuel Cell (PEFC). It consists of a membrane, catalytic (CL) and gas diffusion layers (GDL). In order to manufacture MEAs with suitable performance, a hot-pressing procedure is generally used. The relevant parameters are the temperature, pressure and time of hot-pressing. Such variables need to be adjusted as a function of the type of ionomer used in the catalytic layer and membrane. In this study, an evaluation of the temperature of hot-pressing was carried out and its influence on MEA electrochemical performance was assessed. In particular, preparation trials of MEAs were carried out with reinforced experimental membranes based on Aquivion^® short-side-chain PFSA (by Solvay Specialty Polymers). The membranes were coupled to gas diffusion electrodes, and MEAs were manufactured using different temperatures for the hot-pressing procedure in order to evaluate their influence on the electrochemical performance of PEFCs, in the temperature range of 80-95℃, with low relative humidity of the reactant gases. The electrochemical performance of the prepared MEAs was tested in a H₂/Air 25 cm² single cell in terms of polarization curves and accelerated stress test (AST).

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The preconditions of reversible hydrogenation-dehydrogenation of B/N and B/P frustrated Lewis Pairs

Kun Wang, Zuxiong Pan, Wei Xu, Zijiang Chen, Xuebin Yu

2019, 28(8): 174-180. DOI: 10.1016/j.jechem.2019.03.016

摘要 ( 14 )

Boron-nitrogen-hydrogen compounds have been investigated and developed very fast in last decades caused by its excellent hydrogen-storage performances. The bottleneck problem hindering its application is the irreversibility after its dehydrogenation. However, the traditional B-N (or B-P) bond can be hindered by connecting with large steric hindrances, which results in the possible reversible hydrogenationdehydrogenation properties. In this research, we analyse the structural characters based on the experiments to obtain the required electronic structure properties for realizing the reversibility of FLPs in the hydrogenation (or dehydrogenation).

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Improving the performance of solid oxide electrolysis cell with gold nanoparticles-modified LSM-YSZ anode

Yuefeng Song, Xiaomin Zhang, Yingjie Zhou, Houfu Lv, Qingxue Liu, Weicheng Feng, Guoxiong Wang, Xinhe Bao

2019, 28(8): 181-187. DOI: 10.1016/j.jechem.2019.03.013

摘要 ( 15 )

Gold, as the common current collector in solid oxide electrolysis cell (SOEC), is traditionally considered to be inert for oxygen evolution reaction at the anode of SOEC. Herein, gold nanoparticles were loaded onto conventional strontium doped lanthanum manganite-yttria stabilized zirconia (LSM-YSZ) anode, which evidently improved the performance of oxygen evolution reaction at 800℃. The current densities at 1.2 V and 1.4 V increased by 60.0% and 46.9%, respectively, after loading gold nanoparticles onto the LSM-YSZ anode. Physicochemical characterizations and electrochemical measurements suggested that the improved SOEC performance was attributed to the accelerated electron transfer of elementary process in anodic polarization reaction and the newly generated triple phase boundaries in gold nanoparticles-loaded LSMYSZ anode.

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Formation of the front-gradient bandgap in the Ag doped CZTSe thin films and solar cells

Dongxiao Wang, Jianyu Wu, Xiyu Liu, Li Wu, Jianping Ao, Wei Liu, Yun Sun, Yi Zhang

2019, 28(8): 188-196. DOI: 10.1016/j.jechem.2019.03.026

摘要 ( 17 )

The graded bandgap of kesterite based absorber layer is an important way to achieve high efficiency solar cells. Incorporation of Ag into CZTSSe thin films can adjust the bandgap and thus reduce the V_OC-deficit and improve the quality of crystallization. However, the distribution of Ag is difficult to control due to the quick diffusion of Ag under the high temperature. In this study, we achieve the front Ag-gradient in kesterite structured compound films by prealloying followed by selenization process at 550℃. AgZn₃, Ag₃Sn, and Sn-Ag-Cu alloy phases were formed during prealloying stage at 250℃. After prealloying process, Ag tends to distribute at the front surface of the ACZTSe thin films. Combining the results of experiment and SCAPS simulation, the significantly V_OC improvement of devices is ascribed to the formation of the front Ag-gradient bandgap structure in the absorber layer. This facile prealloying selenization process affords a feasible method to design the graded bandgap structure absorber layers, which will promote the fabrication of high efficient graded bandgap structure solar cells.

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Substrate participation ultrafast synthesis of amorphous NiFe nanosheets on iron foam at room temperature toward highly efficient oxygen evolution reaction

Xiao Yang, Qian-Qian Chen, Chuan-Jun Wang, Chun-Chao Hou, Yong Chen

2019, 28(8): 197-203. DOI: 10.1016/j.jechem.2019.03.018

摘要 ( 18 )

The earth-abundant transition metal based nanomaterials are regarded as state-of-the-art oxygen evolution reaction (OER) electrocatalyst. Recent studies have shown that amorphous materials are more active than their crystalline forms. Herein, we demonstrate a facile and rapid substrate participation method to fabricate amorphous NiFe nanosheets on iron foam (a-NiFe NS/IF) at ambient temperature as a highly efficient electrocatalyst for OER. This method only takes 200 s to fabricate the a-NiFe NS/IF and the electrocatalyst possesses excellent catalytic activities which only needs overpotentials of about 211 and 240 mV to reach 10 and 100 mA cm^-2 current densities in 1.0 M KOH.

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Graphene/RuO₂ nanocrystal composites as sulfur host for lithium-sulfur batteries

Jian-Qiu Huang, Jiaqiang Huang, Woon Gie Chong, Jiang Cui, Shanshan Yao, Baoling Huang, Jang-Kyo Kim

2019, 28(8): 204-211. DOI: 10.1016/j.jechem.2019.03.017

摘要 ( 20 )

An optimized graphene/RuO₂/S composite is prepared by hydrothermal growth of RuO₂ particles on graphene oxide sheets as the positive electrode for rechargeable lithium-sulfur batteries. The electrode with 6.1 wt% RuO₂ nanocrystals and a high sulfur content of 79.0 wt% delivers an optimal electrochemical performance with high residual capacities of 508 mAh g^-1 after 200 cycles and 389 mAh g^-1 after 800 cycles at 1 C with a low capacity decay of 0.054%. The RuO₂ nanocrystals promote the redox reaction kinetics and facilitate the transformation of sulfur chemistry, leading to large improvements in reversibility and rate capability of the composite electrode. The density functional theory calculations signify the formation of Li-O and Ru-S bonds through chemical interactions between RuO₂ and Li polysulfides while the adsorption energies between graphene and polysulfide species are much higher in the presence of RuO₂ than that of the neat graphene acting alone. These discoveries support the efficient entrapment of polysulfides by the composite electrode to the benefit of enhanced cyclic stability of the battery.

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Micro-meso-macroporous FeCo-N-C derived from hierarchical bimetallic FeCo-ZIFs as cathode catalysts for enhanced Li-O₂ batteries performance

Fufang Chao, Baoxing Wang, Jiaojiao Ren, Yingwei Lu, Wenrui Zhang, Xizhang Wang, Lin Cheng, Yongbing Lou, Jinxi Chen

2019, 28(8): 212-219. DOI: 10.1016/j.jechem.2019.03.025

摘要 ( 14 )

Developing bifunctional catalysts that increase both the OER and ORR kinetics and transport reactants with high efficiency is desirable. Herein, micro-meso-macroporous FeCo-N-C-X (denoted as "MFeCo-N-C-X", X represents Fe/Co molar ratio in bimetallic zeolite imidazole frameworks FeCo-ZIFs) catalysts derived from hierarchical M-FeCo-ZIFs-X was prepared. The micropores in M-FeCo-N-C-X have strong capability in O₂ capture as well as dictate the nucleation and early-stage deposition of Li₂O₂, the mesopores provided a channel for the electrolyte wetting, and the macroporous structure promoted more available active sites when used as cathode for Li-O₂ batteries. More importantly, M-FeCoN-C-0.2 based cathode showed a high initial capacity (18,750 mAh g^-1@0.1 A g^-1), good rate capability (7900 mAh g^-1@0.5 A g^-1), and cycle stability up to 192 cycles. Interestingly, the FeCo-N-C-0.2 without macropores suffered relatively poorer stability with only 75 cycles, although its discharge capacity was still as high as 17,200 mAh g^-1(@0.1 A g^-1). The excellent performance attributed to the synergistic contribution of homogeneous Fe, Co nanoparticles and N co-doping carbon frameworks with special micro-meso-macroporous structure. The results showed that hierarchical FeCo-N-C architectures are promising cathode catalysts for Li-O₂ batteries.

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Closed-loop hydrometallurgical treatment of end-of-life lithium ion batteries: Towards zero-waste process and metal recycling in advanced batteries

Thomas Abo Atia, Giuseppe Elia, Robert Hahn, Pietro Altimari, Francesca Pagnanelli

2019, 28(8): 220-227. DOI: 10.1016/j.jechem.2019.03.022

摘要 ( 49 )

This work presents an enhanced hydrometallurgical process for recycling lithium ion batteries. First, endof-life batteries were processed in a physical pre-treatment plant to obtain a representative electrode material. The resulting leachate was purified forth by iron-precipitation, liquid-liquid extractions, and an innovative Li-Na separation, in order to obtain valuable products. These products include high-grade graphite, cobalt oxide (Co₃O₄, purity 83%), cobalt oxalate (CoC₂O₄, purity 96%), nickel oxide (NiO, purity 89%), and lithium carbonate (Li₂CO₃, purity 99.8%). The recovery rate was quantitative for graphite, between 80% and 85% for cobalt depending on the nature of the recovery method, 90% for nickel, and 72% for lithium. Secondary streams were also valorized to obtain sodium sulfate (Na₂SO₄, purity 96%), and MnCoFe₂O₄ magnetic nano-sorbents according to the zero-waste concept. In order to close the loop, recycled Co₃O₄ and NiO were used as conversion-type anode materials for advanced lithium ion batteries showing promising performances.

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