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2021, Vol. 63, No. 12　Online: 15 December 2021

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Bimetallic water oxidation: One-site catalysis with two-sites oxidation Fei Xie, Ming-Tian Zhang 2021, 63(12): 1-7.  DOI: 10.1016/j.jechem.2021.08.047 Abstract ( 8 )   PDF (4191KB) ( 2 )   Water oxidation is the key half reaction to achieve full splitting of water to hydrogen and oxygen. Herein, a binuclear complex, [(L4-)CoIII2(OH)]ClO4, was reported as a stable and efficient homogenous catalyst for electrocatalytic water oxidation in 0.1 M phosphate buffer (pH 7.0). Cyclic voltammetry experiments indi- cated that the catalytic process proceed via "one-site catalysis with two-sites oxidation" mechanism in which both two metal sites store the required oxidation equivalents for water oxidation and O-O bond for- mation occurs by single-site water nucleophilic attack (WNA).

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Stabilization of mixed-halide lead perovskites under light by photothermal effects Juvinch R. Vicente, Martin E. Kordesch, Jixin Chen 2021, 63(12): 8-11.  DOI: 10.1016/j.jechem.2021.08.046 Abstract ( 5 )   PDF (1782KB) ( 3 )   Mixed-halide lead perovskites (MHLPs) are semiconductor materials with bandgaps that are tunable across the visible spectrum and have seen promising applications in photovoltaics and optoelectronics. However, their segregation into phases with enriched halide components, under resonant light illumination and/or electric field, have hindered their practical applications. Herein, we demonstrate the stabilization of the MHLP photoluminescence (PL) peak as a function of their excitation intensities. This effect is associated with the phase segregation of MHLPs and their subsequent remixing by pho- tothermal heating. We conclude that the balance between these opposing processes dictates the equilib- rium PL peak of the MHLPs. The findings in this work could serve as a potential approach to obtain MHLP with stable emission peaks under operating conditions.

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Methylammonium- and bromide-free perovskites enable efficient and stable photovoltaics Saisai Li, Tingwei He, Yuanzhi Jiang, Mingjian Yuan 2021, 63(12): 12-24.  DOI: 10.1016/j.jechem.2021.08.030 Abstract ( 5 )   PDF (6830KB) ( 4 )   Hybrid perovskite solar cell (PSC) has attracted extensive research interest due to its rapid increase in efficiency, regarding as one of the most promising candidates for the next-generation photovoltaic tech- nology. The certified power conversion efficiency of the devices based on formamidinium lead iodide (FAPbI3) perovskite has reached 25.5%, approaching the record of monocrystalline silicon solar cells. Unfortunately, the black a-phase FAPbI3 materials can spontaneously transform to non-optically active d-phase at room temperature, which greatly hinder their photovoltaic application. In order to overcome this problem, various strategies, especially introducing methylammonium (MA+), caesium (Cs+) and bro- mide (Br-) ions into the materials, have been widely adopted. However, MA+ can largely reduce the ther- mal stability of the materials. Furthermore, the introduction of Br- can enlarge the materials’ bandgap, resulting in a reduced theoretical efficiency. Keeping these in mind, developing the strategies which without using MA+ and Br- is the inevitable trend. Here, we focus on the recent progresses of stabilizing a FAPbI3 without employing MA+ and Br-, and discuss the advantages of inorganic ions doping and dimensionality engineering to stabilized a FAPbI3. Meanwhile, in order to deeply understand the rela- tionship between the semiconducting properties and device performance of the corresponding materials, we then summarize several significant strategies to suppress the non-radiation recombination, such as interface modification and trap passivation. Finally, we propose to develop more effective ‘A-site’ alter- natives to stabilize α FAPbI3, which is expected to achieve high-efficient PSCs with long-term stability, facilitating its commercialization process.

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In-plane micro-sized energy storage devices: From device fabrication to integration and intelligent designs Songshan Bi, Hongmei Cao, Rui Wang, Fang Wan, Zhiqiang Niu 2021, 63(12): 25-39.  DOI: 10.1016/j.jechem.2021.08.049 Abstract ( 5 )   PDF (9095KB) ( 3 )   The rapid development of micro-electronics raises the demand of their power sources to be simplified, miniaturized and highly integratable with other electronics on a chip. In-plane Micro-sized energy stor- age devices (MESDs), which are composed of interdigitated electrodes on a single chip, have aroused par- ticular attentions since they could be easily integrated with other miniaturized electronics, reducing the complexity of overall chip design via removing complex interconnections with bulky power sources. This review highlights the achievements in the device fabrication of in-plane MESDs, as well as their integra- tion and intelligent designs. We also discussed the current challenges and future perspectives for the development of in-plane MESDs.

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Plasmonic metal/semiconductor hybrid nanomaterials for solar to chemical energy conversion Cancan Zhang, Yuying Zhang, Wei Xie 2021, 63(12): 40-53.  DOI: 10.1016/j.jechem.2021.08.036 Abstract ( 9 )   PDF (14433KB) ( 5 )   Plasmonic nanomaterials are sources of light, heat and electrons at nanometer scale. Given the outstand- ing performance in harvesting and converting solar energy under visible light irradiation, hybrid nano- materials with plasmonic activity have recently emerged as a new class of advanced photocatalysts. Because of the enhanced charge-separation at hybrid interfaces, the hybrids usually exhibit higher cat- alytic activity compared with their monometallic counterparts. Here, we review the recent progress on synthesis of plasmonic hybrid nanomaterials and their applications in photocatalysis, including H2 pro- duction, CO2 reduction and N2 fixation. We hope this review will give systematic and valuable reference on plasmonic solar to chemical energy conversion.

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Heteroatom-doped porous carbon-supported single-atom catalysts for electrocatalytic energy conversion Yue Shao, Zhengtai Zha, Hong Wang 2021, 63(12): 54-73.  DOI: 10.1016/j.jechem.2021.04.041 Abstract ( 3 )   PDF (23517KB) ( 1 )   Electrocatalysts play a crucial role in the development of renewable energy conversion and storage nan- otechnologies. The unique advantages of heteroatom-doped porous carbon-supported single-atom electro- catalysts (SAC-HDPCs) are clear. These SAC-HDPCs exhibit outstanding activity, selectivity and stability due to their distinct electronic structure, satisfactory conductivity, controllable porosity and heteroatom- doping effect. Rapid and significant developments involving the synthesis, characterization, and structure-property-function relationship of SAC-HDPCs have been made in recent years. In this review, we describe recent research efforts involving advanced (in situ) characterization techniques, innovative synthetic strategies, and electrochemical energy conversion examples of SAC-HDPCs. The electrocatalytic performance of SAC-HDPCs is further considered at an atomic level, and the mechanisms underlying this performance are also discussed in detail. We expect that these analyses and deductions will be useful for the design of new materials and may help to establish a foundation for the design of future SAC-HDPCs.

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Porous catalytic membranes for CO2 conversion Yi Guo, Cheng Qian, Yinglong Wu, Jiawei Liu, Xiaodong Zhang, Dongdong Wang, Yanli Zhao 2021, 63(12): 74-86.  DOI: 10.1016/j.jechem.2021.06.008 Abstract ( 6 )   PDF (9907KB) ( 1 )   Catalytic CO2 conversion has witnessed a dynamic growth in recent decades. Various materials have been applied to reduce CO2 into fuels and value-added chemicals. Normally, the powder-based catalysts can- not be directly utilized for CO2 conversion. Much attention was paid to the study of catalytic membranes in order to overcome this issue, since it is convenient for catalytic membranes to be employed in devices for practical applications. In this review, the recent research development of porous catalytic membranes for CO2 conversion is summarized. The preparations of representative porous catalytic membranes and their CO2 conversion methods, including electrocatalysis, photocatalysis, photoelectrocatalysis, thermal- catalysis and biocatalysis, are discussed in detail. This review is expected to provide deep understanding on the utilization of porous catalytic membranes for CO2 conversion.

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Recent progress and strategies toward high performance zinc-organic batteries Shibing Zheng, Qiaoran Wang, Yunpeng Hou, Lin Li, Zhanliang Tao 2021, 63(12): 87-112.  DOI: 10.1016/j.jechem.2021.07.027 Abstract ( 10 )   PDF (22677KB) ( 1 )   Energy sustainable development has stimulated the pursuit of an eco-friendly energy storage system. Carbon peak and neutrality targets oriented energy storage development will guide the way of further studies on batteries system. However, conventional batteries system (lead-acid batteries, lithium-ion batteries) based on ungreen transition metal oxide, flammable electrolytes or hazardous metals cannot keep pace with the development of society sooner or later. Thus, vast explorations on the advanced rechargeable battery systems were conducted. Compared with other battery systems, zinc ion battery systems with inherent safety, low cost were widely investigated. Especially, the zinc organic batteries based on the eco-efficiency organic cathodes were promising alternative advanced batteries for future energy storage systems. Therefore, various organics and different electrochemistry mechanisms were explored in the zinc batteries system. Herein, a timely review on elaborate analysis about functional groups, fundamentals, progress accompanied by the discussion on the four core issues: voltage, capacity, rate performance, cycle life was presented. Specifically, aiming at these issues, three levels of solution strategies: materials design concepts, morphology structure optimization and electrolyte environment were summarized and proposed for the development and innovation of zinc organic batteries.

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Recent advances and perspectives of metal/covalent-organic frameworks in metal-air batteries Ming Zhong, Ming Liu, Na Li, Xian-He Bu 2021, 63(12): 113-129.  DOI: 10.1016/j.jechem.2021.09.029 Abstract ( 8 )   PDF (10335KB) ( 3 )   Metal-air batteries (MABs) have attracted considerable attention as a novel energy technology that can alleviate the severe energy crisis and environmental pollution. Two primary processes, including oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) occur on the air cathode and dominate the battery performance during battery charging and discharging. Recently, metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) emerge as promising cathode catalysts due to their structure and composition superiority. The unique characteristics of MOFs and COFs contribute to improved performance. This review mainly summarizes the recent applications of MOFs and COFs in a series of MABs, mainly including lithium- and zinc-air batteries. Additionally, some critical issues are emphasized regarding MOFs and COFs used in other MABs limited progress, their fabrication and alter- natives to potential problems.

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Gas-phase CO2 activation with single electrons, metal atoms, clusters, and molecules Ruijing Wang, Gaoxiang Liu, Seong Keun Kim, Kit H. Bowen, Xinxing Zhang 2021, 63(12): 130-137.  DOI: 10.1016/j.jechem.2021.09.030 Abstract ( 4 )   PDF (1984KB) ( 4 )   In this review, the history and outlook of gas-phase CO2 activation using single electrons, metal atoms, clusters (mainly metal hydride clusters), and molecules are discussed on both of the experimental and theoretical fronts. Although the development of bulk solid-state materials for the activation and conver- sion of CO2 into value-added products have enjoyed great success in the past several decades, this review focuses only on gas-phase studies, because isolated, well-defined gas-phase systems are ideally suited for high-resolution experiments using state-of-the-art spectrometric and spectroscopic techniques, and for simulations employing modern quantum theoretical methods. The unmatched high complementarity and comparability of experiment and theory in the case of gas-phase investigations bear an enormous potential in providing insights in the reactions of CO2 activation at the atomic level. In all of these exam- ples, the reduction and bending of the inert neutral CO2 molecule is the critical step determined by the frontier orbitals of reaction participants. Based on the results and outlook summarized in this review, we anticipate that studies of gas-phase CO2 activations will be an avenue rich with opportunities for the rational design of novel catalysts based on the knowledge obtained on the atomic level.

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Lithium sulfide nanocrystals as cathode materials for advanced batteries Fengming Wan, Liran Fang, Xin Zhang, Colin A. Wolden, Yongan Yang 2021, 63(12): 138-169.  DOI: 10.1016/j.jechem.2021.09.028 Abstract ( 7 )   PDF (43394KB) ( 5 )   The ever-increasing need for sustainable development requires advanced battery techniques beyond the current generation of lithium ion batteries. Among all candidates being explored, lithium-sulfur batteries are a very promising system to be commercialized in the near future. Towards this end, the development of lithium sulfide (Li2S) nanocrystal-based cathodes has received tremendous effort and witnessed mul- tiple reviews. Differentiated from the focus on performance improvement in previous reviews, this review summarizes the research progress in line with the approaches of materials synthesis and elec- trode fabrication. The key chemistry, operation procedure, materials characterizations and performance assessments are all given a balanced description. Moreover, all approaches are collectively analyzed along the lines of six criteria towards practical applications, i.e., electrode performance, materials quality, resources sustainability, production cost, operation procedure, and consumed energy. Finally, some per- spective viewpoints on the future research directions are offered.

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Single-atom catalysts for electrochemical energy storage and conversion Wei Ma, Hao Wan, Lili Zhang, Jin You Zheng, Zhen Zhou 2021, 63(12): 170-194.  DOI: 10.1016/j.jechem.2021.08.041 Abstract ( 6 )   PDF (15191KB) ( 1 )   The expedited consumption of fossil fuels has triggered broad interest in the fabrication of novel catalysts for electrochemical energy storage and conversion. Especially, single-atom catalysts (SACs) have attracted more attention owing to their high specific surface areas and abundant active centers. This review summarizes recent synthetic strategies to fabricate SACs with different metal loadings on various supports, and the structural influence of supports on metal loading. Then, the functions of SACs are illus- trated on electronic structure and electrocatalysis; the isolated SACs with an unsaturated coordination environment generally accelerate the electrocatalytic process and promote the selectivity. The applica- tions of SACs to some typical electrocatalytic reactions are also introduced in detail, as well as to electro- chemical energy storage and conversion systems. Finally, the challenges and the perspectives of SACs are discussed for future exploration.

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First-row transition metal compounds for aqueous metal ion batteries Mengmeng Zhou, Xinjun Huang, Xiaomeng Tian, Baohua Jia, Hongge Pan, Wenping Sun, Qin Zhao, Tianyi Ma 2021, 63(12): 195-216.  DOI: 10.1016/j.jechem.2021.09.002 Abstract ( 4 )   PDF (18970KB) ( 1 )   In recent years, a series of aqueous metal ion batteries (AMIBs) has been developed to improve the safety and cost-efficiency of portable electronics and electric vehicles. However, the significant gaps in energy density, power density, and cycle stability of AMIBs directly hinder them from replacing the currently widely used non-aqueous metal ion batteries, which stems from the lack of reasonable configuration and performance optimization of electrode materials. First-row transition metal compounds (FRTMCs), with the advantages of optional voltage ranges (from low to high), adjustable crystal structures (layered and tunnel types with large spacing), and designable morphology (multi-dimensional nanostructures), are widely used to construct high-performance AMIBs. However, no comprehensive review papers were generated to highlight their specific and significant roles in AMIBs. In this review, we first summarize the superiority and characteristics of FRTMCs in AMIBs. Then, we put forward control strategies of FRTMCs from subsurface engineering to inner construction to promote capacitance control and diffusion control energy storage. After that, the electrochemical performance of the FRTMCs regulation strategies in AMIBs is reviewed. Finally, we present potential directions and challenges for further enhancements of FRTMCs in AMIBs. The review aims to provide an in-depth understanding of regulation strategies for enhancing energy storage to build high-performance AMIBs that meet practical applications.

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Syntheses, challenges and modifications of single-crystal cathodes for lithium-ion battery Xinyue Zhang, Yudong Zhang, Jiuding Liu, Zhenhua Yan, Jun Chen 2021, 63(12): 217-229.  DOI: 10.1016/j.jechem.2021.10.022 Abstract ( 9 )   PDF (6687KB) ( 5 )   Single-crystal cathodes (SCCs) are promising substitute materials for polycrystal cathodes (PCCs) in lithium-ion batteries (LIBs), because of their unique ordered structure, excellent cycling stability and high safety performance. Cathode materials with layered (LiCoO2, LiNixCoyMnzO2, LiNixCoyAlzO2) and spinel structure (LiMn2O4, LiNi0.5Mn1.5O4) show a relatively stable electrochemical performance, but still lack of sufficient attention in research field. In this review, we begin with the definition, structural features and electrochemical advantages of SCCs. Common SCCs synthesis methods and the thermodynamic growth mechanism of SCCs with oriented facet exposure are summarized in the following part. Then we introduce the problems and challenges of SCCs faced and the corresponding modification strategies. Finally, the industrialization progress of SCCs is brifly outlined. We intend to tease out the difficulties and advances of SCCs to provide insights for future development of high-performance SCCs for practical LIBs.

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Two-dimensional bimetallic coordination polymers as bifunctional evolved electrocatalysts for enhanced oxygen evolution reaction and urea oxidation reaction Qiang Li, Lele Lu, Jingwei Liu, Wei Shi, Peng Cheng 2021, 63(12): 230-238.  DOI: 10.1016/j.jechem.2021.04.015 Abstract ( 4 )   PDF (5398KB) ( 3 )   Two-dimensional coordination polymers (CPs) have aroused tremendous interest as electrocatalysts because the catalytic performance could be fine-tuned by their well-designed coordination layers with highly accessible and active metal sites. However, it remains great challenge for CP-based catalysts to be utilized for electrocatalytic oxidation reactions due to their inefficient activities and low catalytic sta-bilities. Herein, we applied a mixed-metal strategy to fabricate two-dimensional Co Ni -CPs with dual active sites for electrocatalytic water and urea oxidation. By metal ratio regulation in the two- dimensional layer, an optimized Co2/3Ni1/3-CP exhibits a water oxidation performance with an overpoten- tial of 325 mV at a current density of 10 mA cm-2 and a Tafel slope of 86 mV dec-1 in alkaline solution for oxygen evolution reaction. Importantly, a lower potential than that of commercial RuO2 is observed over 20 mA cm-2. Co2/3Ni1/3-CP also displays a potential of 1.381 V at 10 mA cm-2 for urea oxidation reaction and a Tafel slope of 124 mV dec-1. This mixed-metal strategy to maximize synergistic effect of different metal centers may ultimately lead to promising electrocatalysts for small molecule oxidation reaction.

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Intercalation engineering of layered vanadyl phosphates for high performance zinc-ion batteries Kunjie Zhu, Zhiqin Sun, Pei Liu, Haixia Li, Yijing Wang, Kangzhe Cao, Lifang Jiao 2021, 63(12): 239-245.  DOI: 10.1016/j.jechem.2021.03.051 Abstract ( 8 )   PDF (3993KB) ( 3 )   Aqueous zinc-ion batteries (ZIBs) have attracted great attention as the candidates for large-scale energy storage system, recently, because of their low cost, environment-friendly, high safety, and high theoret- ical energy densities. Among the numerous cathode materials, layered structure vanadium based polyan- ionic compounds, such as VOPO4, exhibit high specific capacity for Zn ion storage. However, the low Zn ion diffusion coefficient and limited interlayer spacing make the cathodes low reversible capacity and inferior cycling stability. Herein, K ions were pre-intercalated into the VOPO4 layers via ions exchange adopting VOPO4 2H2O as the precursor. When evaluated as the cathode for ZIBs, an excellent cycle sta- bility of 400 cycles under a current density of 500 mA g-1 was achieved by the obtained KVOPO4 elec- trode, verifying the positive effect of intercalation engineering. Furtherly, a solid-solution reaction Zn ion storage mechanism was confirmed. This study provides a new insight to explore high performance cathode materials for ZIBs.

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CuP2 as high-capacity and long-cycle-life anode for potassium-ion batteries Lin Li, Zhe Hu, Yong Lu, Shuo Zhao, Qiu Zhang, Qiannan Liu, Zhenhua Yan, Shu-Lei Chou 2021, 63(12): 246-252.  DOI: 10.1016/j.jechem.2021.02.009 Abstract ( 4 )   PDF (7766KB) ( 2 )   Metal phosphides have shown great potential for potassium-ion batteries because of their high theoret- ical specific capacity. Nevertheless, most of the metal phosphide anodes are plagued by rapid capacity decay (caused by the large volume changes during the discharge/charge process), which would restrict their further practical application. Herein, a chemically bonded CuP2/C composite was prepared by a facile high-energy ball milling method. A potassium bis(trifluoromethanesulfonyl)imide (KFSI)-based electrolyte was adopted instead of a conventional KPF6-based electrolyte for the CuP2/C composite anode. Benefiting from the synergistic effects of the formation of strong P-O-C chemical bonds and the KFSI- based electrolyte, the CuP2/C composite anode exhibited high reversible capacity (451.4 mAh g-1 at 50 mA g-1), excellent rate performance (123.5 mAh g-1 at 1000 mA g-1), and superior cycling stability (300 mAh g-1 after 100 cycles). This work paves the way for the development of high-performance CuP2 anode for potassium-ion batteries.

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Encapsulation of bimetallic phosphides into graphitized carbon for pH-universal hydrogen evolution reaction Jian Zhou, Yibo Dou, Tao He, Xiang-Jing Kong, Lin-Hua Xie, Jian-Rong Li 2021, 63(12): 253-261.  DOI: 10.1016/j.jechem.2021.03.039 Abstract ( 5 )   PDF (4986KB) ( 3 )   Exploring nonprecious electrocatalysts for water splitting with high efficiency and durability is critically important. Herein, bimetallic phosphides are encapsulated into graphitized carbon to construct a C@NiCoP composite nanoarray using bimetallic metal-organic framework (MOF) as a self-sacrificial tem- plate. The resulting C@NiCoP exhibits superior performance for pH-universal electrocatalytic hydrogen evolution reaction (HER), particularly representing a low overpotential of 46.3 mV at 10 mA cm-2 and Tafel slope of 44.1 mV dec-1 in alkaline media. The structural characterizations combined with theoret- ical calculation demonstrate that tailored electronic structure from bimetal atoms and the synergistic effect with graphitized carbon layer could jointly optimize the adsorption ability of hydrogen on active sites in HER process, and enhance the electrical conductivity as well. In addition, the carbon layer served as a protecting shell also prevents highly dispersed NiCoP components from agglomeration and/or loss in harsh media, finally improving the durability. This work thus provides a new insight into optimizing activity and stability of pH-universal electrocatalysts by the nanostructural design and electronic struc- ture modulation.

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Propane dehydrogenation catalyzed by in-situ partially reduced zinc cations confined in zeolites Linjun Xie, Rui Wang, Yuchao Chai, Xuefei Weng, Naijia Guan, Landong Li 2021, 63(12): 262-269.  DOI: 10.1016/j.jechem.2021.04.034 Abstract ( 6 )   PDF (6494KB) ( 2 )   Propane dehydrogenation (PDH), employing Pt- or Cr-based catalysts, represents an emerging industrial route for propylene production. Due to the scarcity of platinum and the toxicity of chromium, alternative PDH catalysts are being pursued. Herein, we report the construction of Zn-containing zeolite catalysts, namely Zn@S-1, for PDH reaction. Well-isolated zinc cations are successfully trapped and stabilized by the Si-OH groups in S-1 zeolites via in-situ hydrothermal synthesis. The as-prepared Zn@S-1 catalysts exhibit good dehydrogenation activity, high propylene selectivity, and regeneration capability in PDH reaction under employed conditions. The in-situ partial reduction of zinc species is observed and the par- tially reduced zinc cations are definitely identified as the active sites for PDH reaction.

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Structurally tunable characteristics of ionic liquids for optimizing lithium plating/stripping via electrolyte engineering Shihan Qi, Jiandong Liu, Jian He, Huaping Wang, Mingguang Wu, Daxiong Wu, Junda Huang, Fang Li, Xin Li, Yurong Ren, Jianmin Ma 2021, 63(12): 270-277.  DOI: 10.1016/j.jechem.2021.05.040 Abstract ( 6 )   PDF (4111KB) ( 3 )   Electrolyte chemistry offers the opportunity to regulate the solid electrolyte interphase (SEI) and Li+ sol- vation, which is considered to be crucial to the growth of lithium crystals for safe lithium metal batteries (LMBs). Structurally tunable characteristics of ionic liquids (ILs) from anion type, cationic substituent chain length and cationic substituents, will contribute this field. Here, we explore the influence mecha- nism of imidazole-based ILs as electrolyte additives on Li+ solvation and the formation of SEI. ILs can par- ticipate into the formation of efficient SEI, together with cathode electrolyte interphase (CEI). Moreover, ILs can also regulate the sheath structure of Li+ solvation, to fasten the kinetics of Li. Furthermore, the imidazole-based cations with long alkyl chain can form an electrostatic shield around newly formed Li nucleus, and suppress further Li plating at this site. Under the optimized condition, the 1-octyl-3- methylimidazolium bis(trifluoromethylsulfonyl)imide ([OMIm]TFSI) additive shows the best ability to enhance the electrochemical performance, endowing the Li||Li symmetric cell with a stable life (over 800 h) at 0.5 mA cm-2 and the Li||LiNi0.6Mn0.2Co0.2O2 (NMC622) full cell with a high capacity of 141.7 mAh g-1 after 200 cycles at 0.5 C.

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Copper-indium hydroxides derived electrocatalysts with tunable compositions for electrochemical CO2 reduction Qixian Xie, Gastón O. Larrazábal, Ming Ma, Ib Chorkendorff, Brian Seger, Jingshan Luo 2021, 63(12): 278-284.  DOI: 10.1016/j.jechem.2021.09.008 Abstract ( 5 )   PDF (10937KB) ( 2 )   Bimetallic Cu-In hybrid electrocatalysts are promising noble metal-free catalysts for selective electrochem- ical CO2 reduction reaction (ECO2RR). Most reports show Cu-In catalysts are selective towards CO evolution. However, few show similarly high selectivity towards formate. Herein we fabricated composition tunable Cu-In hydroxides (CuxIny-OH) by the hydrothermal method and studied their composition effect on electro- chemical CO2 reduction in detail. We found that the selectivity of CO2 reduction products shifted from CO to formate when the content of In increased in the CuxIny-OH electrocatalysts. The Cu rich electrocatalyst mostly produced CO, which could achieve a Faradaic efficiency (FE) to 75.8% at -0.59 V vs. RHE (Cu76In24 based electrocatalysts). In comparison, the In rich electrocatalysts selectively produced formate, which pos- sessed the FE of formate up to 85% at -1.01 V vs. RHE. Our work systematically illustrates the composition effect on hybrid catalysts, and provides insights into the design of highly selective catalysts for ECO2RR.

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Single-atom catalysts with anionic metal centers: Promising electrocatalysts for the oxygen reduction reaction and beyond Jinxing Gu, Yinghe Zhao, Shiru Lin, Jingsong Huang, Carlos R. Cabrera, Bobby G. Sumpter, Zhongfang Chen 2021, 63(12): 285-293.  DOI: 10.1016/j.jechem.2021.08.004 Abstract ( 5 )   PDF (4147KB) ( 2 )   Ongoing efforts to develop single-atom catalysts (SACs) for the oxygen reduction reaction (ORR) typically focus on SACs with cationic metal centers, while SACs with anionic metal centers (anionic SACs) have been generally neglected. However, anionic SACs may offer excellent active sites for ORR, since anionic metal centers could facilitate the activation of O2 by back donating electrons to the antibonding orbitals of O2. In this work, we propose a simple guideline for designing anionic SACs: the metal centers should have larger electronegativity than the surrounding atoms in the substrate on which the metal atoms are supported. By means of density functional theory (DFT) simulations, we identified 13 anionic metal cen- ters (Co, Ni, Cu, Ru, Rh, Pd, Ag, Re, Os, Ir, Pt, Au, and Hg) dispersed on pristine or defective antimonene substrates as new anionic SACs, among which anionic Au and Co metal centers exhibit limiting potentials comparable to, or even better than, conventional Pt-based catalysts towards ORR. We also found that anionic Os and Re metal centers on the defective antimonene can electrochemically catalyze the nitrogen reduction reaction (NRR) with a limiting potential close to that of stepped Ru(0001). Overall, our work shows promise towards the rational design of anionic SACs and their utility for applications as electrocat- alysts for ORR and other important electrochemical reactions.

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Layer-structure adjustable MoS2 catalysts for the slurry-phase hydrogenation of polycyclic aromatic hydrocarbons Donge Wang, Jiahe Li, Huaijun Ma, Chenggong Yang, Zhendong Pan, Wei Qu, Zhijian Tian 2021, 63(12): 294-304.  DOI: 10.1016/j.jechem.2021.08.053 Abstract ( 5 )   PDF (3210KB) ( 2 )   Slurry-phase hydrogenation technology is the frontier topic in the efficient conversion of heavy oils into light fractions around the world. Developing highly active dispersed MoS2 catalysts is the major obstacle to realize the industrial application of upgrading heavy oils. In this work, both top-down ball-milling method and bottom-up hydrothermal method were designed to synthesize MoS2 catalysts with control- lable layer structures. The stacking layers and lateral sizes for micro-scaled MoS2 catalysts by ball-milling method can be reduced to their limits and stabilize at 6 ~ 8 layers and lateral size of ca. 30 nm. The more flexible bottom-up hydrothermal method can construct MoS2 catalysts with much smaller lateral sizes and fewer stacking layers, especially, MoS2 catalyst fabricated with ammonium tetrathiomolybdate as Mo and S precursor possesses average stacking layers of 2 and lateral size of 5 ~ 10 nm. Polycyclic aro- matic hydrocarbons anthracene, phenanthrene and naphthalene were used as model compounds of heavy oils to investigate the catalytic hydrogenation performance of designed MoS2 catalysts. The cat- alytic activities of MoS2 catalysts can be well correlated with their stacking layers and lateral size. The edges of top and bottom S-Mo-S atomic layers for MoS2 sheets, named rim sites, are positively correlated with the exposure of active sites for catalytic hydrogenation of PAHs. The highest catalytic activity of MoS2 catalyst results from its layer structures of 100% rim sites and the smallest lateral size of 5 ~ 10 nm, which is beneficial to expose maximum active sites for catalytic hydrogenation reactions. This work can guide us to design the highly active hydrogenation catalysts, and promote the industrial application of upgrading heavy oils.

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Enabling stable sodium metal cycling by sodiophilic interphase in a polymer electrolyte system Xiaofei Hu, Edward Matios, Yiwen Zhang, Chuanlong Wang, Jianmin Luo, Weiyang Li 2021, 63(12): 305-311.  DOI: 10.1016/j.jechem.2021.06.026 Abstract ( 12 )   PDF (7703KB) ( 3 )   Enabling highly reversible sodium (Na) metal anodes in a polymer electrolyte (PE) system is critical for realizing next-generation batteries with lower cost, higher energy, and improved safety. However, the uneven Na deposition and high Na/PE interphase resistance lead to poor reversibility and short cycle life of Na metal anodes. To tackle these problems, here a variety of metal nanoparticles (M-np, M = Al, Sn, In or Au) are deposited onto copper (Cu) foils to synthesize binder-free M-np@Cu substrates for Na plating/ stripping. Notably, the Au-np@Cu substrate provides abundant preferential nucleation/growth sites, decreasing Na nucleation barrier and thus promoting uniform Na deposition. Accordingly, stable Na metal anodes are achieved with high reversible capacities, long cycle life, and high usage of Na. With the Au-np@Cu/Na anode and PE, the full cell using a commercial bulk sulfur cathode exhibits a reversible capacity of >400 mAh g-1 with near-100% Coulombic efficiency over 200 cycles.

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Enhancing LiNiO2 cathode materials by concentration-gradient yttrium modification for rechargeable lithium-ion batteries Yudong Zhang, Hang Li, Junxiang Liu, Jiuding Liu, Hua Ma, Fangyi Cheng 2021, 63(12): 312-319.  DOI: 10.1016/j.jechem.2021.07.029 Abstract ( 3 )   PDF (8620KB) ( 2 )   Lithium nickel oxide (LiNiO2) cathode materials are featured with high capacity and low cost for rechargeable lithium-ion batteries but suffer from severe interface and structure instability. Here we report that rationally designed LiNiO2 via concentration-gradient yttrium modification exhibits allevia- tive side reactions and improved electrochemical performance. The LiNiO2 cathode with LiYO2-Y2O3 coat- ing layer delivers a discharge capacity of 225 mAh g-1 with a high initial Coulombic efficiency of 93.4%. These improvements can be attributed to the formation of in-situ modified hybrid LiYO2-Y2O3 coating layer, which suppresses phase transformation, electrolyte oxidation and salt dissociation due to the for- mation of protective cathode electrolyte interface. The results indicate promising application of concentration-gradient yttrium coating as a facile approach to stabilize nickel-rich cathode materials.

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Sulfur-linked carbonyl polymer as a robust organic cathode for rapid and durable aluminum batteries Liang Fang, Limin Zhou, Lianmeng Cui, Peixin Jiao, Qinyou An, Kai Zhang 2021, 63(12): 320-327.  DOI: 10.1016/j.jechem.2021.06.034 Abstract ( 4 )   PDF (5595KB) ( 2 )   Rechargeable aluminum batteries are believed as a promising next-generation energy-storage system due to abundant low-cost Al sources and high volumetric specific capacity. The Al-storage cathodes, how- ever, are plagued by strong electrostatic interaction between host materials and carrier ions, leading to large overpotential and undesired cycling stability as well as sluggish ion diffusion kinetics. Herein, sulfur-linked carbonyl polymer based on perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) as the cathode materials for ABs is proposed, which demonstrates a small voltage polarization (135 mV), a reversible capacity of 110 mAh g-1 at 100 mA g-1 even after 1200 cycles, and rapid Al-storage kinetics. Compared with PTCDA, the sulfide polymer possesses higher working voltage because of its lower LUMO energy level according to theoretical calculation. The ordered carbonyl active sites in sulfide polymer contribute to the maximized material utilization and rapid ion coordination and dissociation, resulting in superior rate capability. Besides, the bridged thioether bonds endow the polysulfide with robust and flexible structure, which inhibits the dissolution of active materials and improves cycling stability. This work implies the importance of ordered arrangement of redox active moieties for organic electrode, which provides the theoretical direction for the structural design of organic materials applied in multivalent-ion batteries.

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Efficient CO2 electroreduction coupled with semi-dehydrogenation of tetrahydroisoquinoline by MOFs modified electrodes Zi-Hao Zhu, Ze-Long Liang, Sheng-Li Hou, Yao Xie, Yue Ma, Yan Zhang, Bin Zhao 2021, 63(12): 328-335.  DOI: 10.1016/j.jechem.2021.09.009 Abstract ( 7 )   PDF (6264KB) ( 3 )   Electroreduction of CO2 into formate catalyzed by metal-organic frameworks (MOFs) is a promising ave- nue to promote the carbon cycle, but the oxygen evolution reaction (OER) process in anode usually lim- ited the reaction efficiency. Here, a new framework {(Me2NH2)[Bi(L)]·4DMF·2H2O}n (V12) was constructed and structurally characterized (L = 5,5'-(1,3,6,8-tetraoxo-1,3,6,8-tetrahydrobenzo[lmn][3,8] phenanthroline-2,7-diyl) dibenzene-1,3-dicarboxylic acid; DMF = N,N-dimethylformamide). V12 pos- sesses large one-dimensional channels with the size of 1.5 × 0.7 nm and exhibits good stability in com- mon solvents. After V12 was modified on electrode via electrodeposition, as-synthesized sample exhibits impressive catalytic performance for the transformation of CO2 into formate with Faraday efficiency of 93.2% and current density of 11.78 mA cm-2 at -0.9 V (vs. RHE). Control experiments revealed that the MOFs electrodeposition strategy significantly improves the charge transfer rate and introduces more structural defects, which promotes the reaction activity. Moreover, tetrahydroisoquinoline is added as an accelerant in the anode to achieve the simultaneous generation of formate and dihydroisoquinoline. More importantly, the cell voltage is reduced from 2.79 to 2.52 V at 10 mA cm-2 in a two-electrode system due to more positive reaction kinetics. This work provides an enlightening strategy for using MOFs to estab- lish an effective system to achieve CO2 reduction while obtaining high value-added oxidation products.

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Conductive metal-organic frameworks promoting polysulfides transformation in lithium-sulfur batteries Shuai Wang, Fanyang Huang, Zhengfeng Zhang, Wenbin Cai, Yulin Jie, Shiyang Wang, Pengfei Yan, Shuhong Jiao, Ruiguo Cao 2021, 63(12): 336-343.  DOI: 10.1016/j.jechem.2021.08.037 Abstract ( 8 )   PDF (6040KB) ( 4 )   Metal organic frameworks (MOFs) have been extensively investigated in Li-S batteries owing to high sur- face area, adjustable structures and abundant catalytic sites. Nevertheless, the insulating nature of tradi- tional MOFs render retarded kinetics of polysulfides conversion, leading to insufficient utilization of sulfur. In comparison, conductive MOFs (c-MOFs) show great potential for promoting polysulfides trans- formation due to superb electronic conductivity. In this work, a nickel-catecholates based c-MOF, Ni- HHTP (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene), is designed to regulate surface chemistry of self-supported carbon paper for advanced Li-S batteries. Taking advantage of the porous structure and high conductivity, the as-prepared Ni-HHTP is conducive to synergising strengthening the chemisorption of polysulfides and accelerating the reaction kinetics in Li-S batteries, significantly mitigating the polysul- fides diffusion from the non-encapsulated sulfur cathode, therefore promoting polysulfides transforma- tion in Li-S batteries. This work points out a promising modification strategy for developing advanced sulfur cathode in Li-S batteries.

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CO activation by the heterobinuclear transition metal-iron clusters: A photoelectron spectroscopic and theoretical study Jumei Zhang, Zhiling Liu, Gang Li, Hongjun Fan, Ling Jiang, Hua Xie 2021, 63(12): 344-350.  DOI: 10.1016/j.jechem.2021.07.005 Abstract ( 7 )   PDF (2373KB) ( 3 )   Spectroscopic characterization of CO activation on multiple metal-containing catalysts remains an impor- tant and challenging goal for identifying the structure and nature of active site in many industrial pro- cesses such as Fischer-Tropsch chemistry and alcohol synthesis. Here, we use mass-selected photoelectron velocity-map imaging spectroscopy and quantum chemical calculations to study the reac- tions of CO molecules with several heterobinuclear transition metal-iron clusters M-Fe (M = Ti, V, Cr). The mass spectra reveal the favorable formation of MFe(CO)-4 with relatively high thermodynamic stability. The MFe(CO)-4 (M = Ti, V, Cr) complexes are established to have a metal-Fe bonded M-Fe(CO)4 structure with C3v geometry. While the positive charge and unpaired electrons are mainly located on the M atom, the natural charge of Fe(CO)4 is about 2e. The MFe(CO)-4 (M = Ti, V, Cr) can be seen as being formed via the interactions between the M+ fragment and the [Fe(CO)4]2- core, which satisfies the 18-electron rule. The CO molecules are remarkably activated in these MFe(CO)-4. These results shed insight into the structure-reactivity relationship of heterobinuclear transition metal carbonyls and would have important implications for understanding of CO activation on alloy surfaces.

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Ultralow-strain Ti substituted Mn-vacancy layered oxides with enhanced stability for sodium-ion batteries Yanchen Liu, Chenchen Wang, Meng Ren, Hengyi Fang, Zhuoliang Jiang, Fujun Li 2021, 63(12): 351-357.  DOI: 10.1016/j.jechem.2021.07.024 Abstract ( 24 )   PDF (3731KB) ( 9 )   Anionic redox reaction (ARR) in layered manganese-based oxide cathodes has been considered as an effective strategy to improve the energy density of sodium-ion batteries. Mn-vacancy layered oxides deli- ver a high ARR-related capacity with small voltage hysteresis, however, they are limited by rapid capacity degradation and poor rate capability, which arise from inferior structure changes due to repeated redox of lattice oxygen. Herein, redox-inactive Ti4+ is introduced to substitute partial Mn4+ to form Na2Ti0.5Mn2.5O7 (Na4/7[h1/7Ti1/7Mn5/7]O2, h for Mn vacancies), which can effectively restrain unfavorable interlayer gliding of Na2Mn3O7 at high charge voltages, as reflected by an ultralow-strain volume varia- tion of 0.11%. There is no irreversible O2 evolution observed in Na2Ti0.5Mn2.5O7 upon charging, which sta- bilizes the lattice oxygen and ensures the overall structural stability. It exhibits increased capacity retention of 79.1% after 60 cycles in Na2Ti0.5Mn2.5O7 (17.1% in Na2Mn3O7) and good rate capability (92.1 mAh g-1 at 0.5 A g-1). This investigation provides new insights into designing high-performance cathode materials with reversible ARR and structural stability for SIBs.

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Synthesis of perovskite BaTaO2N with low defect by Zn doping for boosted photocatalytic water reduction Yunfeng Bao, Hai Zou, Nengcong Yang, Gao Li, Fuxiang Zhang 2021, 63(12): 358-363.  DOI: 10.1016/j.jechem.2021.08.010 Abstract ( 7 )   PDF (2156KB) ( 3 )   Perovskite BaTaO2N (BTON) is one of the most promising photocatalysts for solar water splitting due to its wide visible-light absorption and suitable conduction/valence bands, but it still confronts the chal- lenge of high defect density causing decreased charge separation as well as photocatalytic activity. In this work, we develop a simple zinc doping strategy to greatly suppress its defect density and promote its water reduction performance. It is found that the defect formation on the nitrided Ba(Zn1/3-xTa2/3) O3-yNz (denoted as BZTON hereafter) will be greatly inhibited when the Zn-doped Ba(Zn1/3Ta2/3)O3 (BZTO) oxide is used as the nitridation precursor. The structural characterizations and discussion demon- strate that the effective inhibition of Ta5+ into Ta4+ defects in BZTON mainly results from the easy reduc- tion of zinc ions into metal and further the evaporation of zinc metal under the thermal ammonia flow. Interestingly, this simply doping methodology can be easily extended into the synthesis of SrTaO2N (STON) with extremely low defect density, demonstrating its generality. Benefiting from the successful control to the defect density, the as-obtained BZTON photocatalyst exhibits remarkably promoted charge separation as well as water reduction activity to produce hydrogen with respect to the pristine BTON. Our work may provide an alternative avenue to prepare oxynitride semiconductors with reduced defect den- sity for promoted solar energy conversion.

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Accurate machine learning models based on small dataset of energetic materials through spatial matrix featurization methods Chao Chen, Danyang Liu, Siyan Deng, Lixiang Zhong, Serene Hay Yee Chan, Shuzhou Li, Huey Hoon Hng 2021, 63(12): 364-375.  DOI: 10.1016/j.jechem.2021.08.031 Abstract ( 10 )   PDF (4626KB) ( 6 )   A large database is desired for machine learning (ML) technology to make accurate predictions of mate- rials physicochemical properties based on their molecular structure. When a large database is not avail- able, the development of proper featurization method based on physicochemical nature of target proprieties can improve the predictive power of ML models with a smaller database. In this work, we show that two new featurization methods, volume occupation spatial matrix and heat contribution spa- tial matrix, can improve the accuracy in predicting energetic materials' crystal density (qcrystal) and solid phase enthalpy of formation (Hf,solid) using a database containing 451 energetic molecules. Their mean absolute errors are reduced from 0.048 g/cm3 and 24.67 kcal/mol to 0.035 g/cm3 and 9.66 kcal/mol, respectively. By leave-one-out-cross-validation, the newly developed ML models can be used to deter- mine the performance of most kinds of energetic materials except cubanes. Our ML models are applied to predict qcrystal and Hf,solid of CHON-based molecules of the 150 million sized PubChem database, and screened out 56 candidates with competitive detonation performance and reasonable chemical struc- tures. With further improvement in future, spatial matrices have the potential of becoming multifunc- tional ML simulation tools that could provide even better predictions in wider fields of materials science.

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Three-dimensional Li-ion transportation in Li2MnO3-integrated LiNi0.8Co0.1Mn0.1O2 Xue Huang, Jianqing Zhao, Wenchang Zhu, Machuan Hou, Tong Zhou, Liangmin Bu, Lijun Gao, Wei Zhang 2021, 63(12): 376-384.  DOI: 10.1016/j.jechem.2021.08.012 Abstract ( 4 )   PDF (12756KB) ( 1 )   Ni-rich layered cathodes (LiNixCoyMnzO2) have recently drawn much attention due to their high specific capacities. However, the poor rate capability of LiNixCoyMnzO2, which is mainly originated from the two- dimensional diffusion of Li ions in the Li slab and Li+/Ni2+ cation mixing that hinder the Li+ diffusion, has limited their practical application where high power density is needed. Here we integrated Li2MnO3 nan- odomains into the layered structure of a typical Ni-rich LiNi0.8Co0.1Mn0.1O2 (NCM811) material, which minimized the Li+/Ni2+ cationic disordering, and more importantly, established grain boundaries within the NCM811 matrix, thus providing a three-dimensional diffusion channel for Li ions. Accordingly, an average Li-ion diffusion coefficient (DLi+) of the Li2MnO3-integrated LiNi0.8Co0.1Mn0.1O2 (NCM811-I) dur- ing charge/discharge was calculated to be approximately 6*10-10 cm2 S-1, two times of that in the bare NCM811 (3*10-10 cm2 S-1). The capacity delivered by the NCM811-I (154.5 mAh g-1) was higher than that of NCM811 (141.3 mAh g-1) at 2 C, and the capacity retention of NCM811-I increased by 13.6% after 100 cycles at 0.1 C and 13.4% after 500 cycles at 1 C compared to NCM811. This work provides a valuable routine to improve the rate capability of Ni-rich cathode materials, which may be applied to other oxide cathodes with sluggish Li-ion transportation.

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Development of Sn2+-based oxyfluoride photocatalyst with visible light response of ca. 650 nm via strengthened hybridization of Sn 5s and O 2p orbitals Yanpei Luo, Xin Zhou, Jiangwei Zhang, Yu Qi, Zheng Li, Fuxiang Zhang, Can Li 2021, 63(12): 385-390.  DOI: 10.1016/j.jechem.2021.07.028 Abstract ( 4 )   PDF (4156KB) ( 1 )   The hybridization between the outmost s orbitals of metal (Bi3+, Sn2+, Pb2+, Ag+) and O 2p orbitals has been widely employed to develop innovative semiconductors with upshift valence band as well as extended visible light response, but it is still challenging to obtain photocatalyst with absorption edge of above 550 nm. Here we report a novel Sn2+-based oxyfluoride Sn2TiNbO6F (STNOF) photocatalyst with a pyrochlore structure to exhibit an extended absorption edge to 650 nm and dual functionalities of both water reduction and oxidation. Density functional theory calculations suggest that the unprecedented broad-spectrum response of STNOF is mainly ascribed to the strengthened hybridization between O 2p and Sn 5s orbitals remarkably upshifting the valence band, which is caused by the distortion and com- pressive strain in the SnO6F2 dodecahedron with second-order Jahn-Teller effect due to partial fluorine substitution. The structural distortion and compressive strain are experimentally confirmed by the Fourier-transformed extended X-ray absorption fine spectra. As probe tests of the photocatalytic func-tionalities, water reduction and oxidation half reactions were examined to see obvious H2 and O2 evolu-tion under visible light irradiation. This work may provide an alternative strategy of developing extended visible light responsive semiconductors for promising solar energy conversion.

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A patterned titania nanorod array enables high fill factor in perovskite solar cells Jiupeng Cao, Yuanyuan Zhou, Feng Yan 2021, 63(12): 391-392.  DOI: 10.1016/j.jechem.2021.03.034 Abstract ( 4 )   PDF (785KB) ( 2 )

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Recent advances in phosphoric acid-based membranes for high-temperature proton exchange membrane fuel cells Zunmin Guo, Maria Perez-Page, Jianuo Chen, Zhaoqi Ji, Stuart M. Holmes 2021, 63(12): 393-429.  DOI: 10.1016/j.jechem.2021.06.024 Abstract ( 10 )   PDF (17601KB) ( 4 )   High-temperature proton exchange membrane fuel cells (HT-PEMFCs) are pursued worldwide as effi- cient energy conversion devices. Great efforts have been made in the area of designing and developing phosphoric acid (PA)-based proton exchange membrane (PEM) of HT-PEMFCs. This review focuses on recent advances in the limitations of acid-based PEM (acid leaching, oxidative degradation, and mechan- ical degradation) and the approaches mitigating the membrane degradation. Preparing multilayer or polymers with continuous network, adding hygroscopic inorganic materials, and introducing PA doping sites or covalent interactions with PA can effectively reduce acid leaching. Membrane oxidative degrada- tion can be alleviated by synthesizing crosslinked or branched polymers, and introducing antioxidative groups or highly oxidative stable materials. Crosslinking to get a compact structure, blending with stable polymers and inorganic materials, preparing polymer with high molecular weight, and fabricating the polymer with PA doping sites away from backbones, are recommended to improve the membrane mechanical strength. Also, by comparing the running hours and decay rate, three current approaches, 1. crosslinking via thermally curing or polymeric crosslinker, 2. incorporating hygroscopic inorganic materials, 3. increasing membrane layers or introducing strong basic groups and electron-withdrawing groups, have been concluded to be promising approaches to improve the durability of HT-PEMFCs. The overall aim of this review is to explore the existing degradation challenges and opportunities to serve as a solid basis for the deployment in the fuel cell market.

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Synthesis of ternary magnetic nanoparticles for enhanced catalytic conversion of biomass-derived methyl levulinate into γ-valerolactone Xueli Chen, Tingting Zhao, Xuesong Zhang, Yuxuan Zhang, Haitao Yu, Qian Lyu, Xiwen Jia, Lujia Han, Weihua Xiao 2021, 63(12): 430-441.  DOI: 10.1016/j.jechem.2021.07.013 Abstract ( 7 )   PDF (12547KB) ( 1 )   Conversion of levulinic acid and its esters into versatile c-valerolactone (GVL) is a pivotal and challenging step in biorefineries, limited by high catalyst cost, the use of hydrogen atmosphere, or tedious catalyst preparation and recycling process. Here we have successfully synthesized a ternary magnetic nanoparti-cle catalyst (Al2O3-ZrO2/Fe3O4(5)), over which biomass-derived methyl levulinate (ML) can be quanti- tively converted to GVL with an extremely high selectivity of > 99% and yield of ~98% in the absence of molecular hydrogen. Al2O3-ZrO2/Fe3O4(5) incorporates simultaneously inexpensive alumina and zirco-nia onto magnetite support by a facile coprecipitation method, giving rise to a core-shell structure, well- distributed acid-base sites, and strong magnetism, as evidenced by the X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron micro- scopy (TEM), high-angle annular dark-field scanning-TEM (HAADF-STEM), SEM-energy dispersive X-ray spectroscopy (SEM-EDX), temperature-programmed desorption of ammonia (NH3-TPD), temperature-programmed desorption of carbon dioxide (CO2-TPD), pyridine-adsorption infrared spectra (Py-IR), and vibrating sample magnetometry (VSM). Such characteristics enable it to be highly active and easily recycled by a magnet for at least five cycles with a slight loss of its catalytic activity, avoiding a time-consuming and energy-intensive reactivation process. It is found that there was a synergistic effect among the metal oxides, and the high efficiency and selectivity originating from such synergism are evi- denced by kinetic studies. Furthermore, a reaction mechanism regarding the hydrogenation of ML to GVL is proposed by these findings, coupled with gas chromatography-mass spectrometry (GC-MS) analysis. Accordingly, this readily synthesized and recovered magnetic nanocatalyst for conversion of biomass-derived ML into GVL can provide an eco-friendly and safe way for biomass valorization.

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Modification of compact TiO2 layer by TiCl4-TiCl3 mixture treatment and construction of high-efficiency carbon-based CsPbI2Br perovskite solar cells Wenran Wang, Yu Lin, Guizhi Zhang, Cuiting Kang, Zhenxiao Pan, Xinhua Zhong, Huashang Rao 2021, 63(12): 442-451.  DOI: 10.1016/j.jechem.2021.07.014 Abstract ( 6 )   PDF (4932KB) ( 2 )   In the construction of high performance planar perovskite solar cells (PSCs), the modification of compact TiO2 layer and engineering of perovskite/TiO2 interfaces are essential for efficient electron transfer and retarded charge recombination loss. In this work, a facile and effective strategy is developed to modify the surface of compact TiO2 layer by TiCl4-TiCl3 mixture treatment. Compared with conventional sole TiCl4, the TiCl4-TiCl3 treatment takes the advantage of accelerated and controlled hydrolysis of TiCl3, therefore TiO2 with dominating anatase phase and moderate roughness is obtained to facilitate the growth of CsPbI2Br perovskite layer with high quality. Furthermore, the oxidation-driven hydrolysis of TiCl3 component results in surface Cl doping that facilitates interfacial electron transfer with retarded recombination loss. The average power conversion efficiency (PCE) of carbon-based CsPbI2Br planar PSCs based on TiCl4-TiCl3 treatment increases to 14.18% from the intial 13.04% based on conventional sole TiCl4 treatment. The champion PSC exhibits a PCE of 14.46% (Voc = 1.28 V, Jsc = 14.21 mA/cm2, and FF = 0.794), which is one of the highest PCEs for carbon-based CsPbI2Br PSCs.

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Simultaneous passivation of bulk and interface defects through synergistic effect of anion and cation toward efficient and stable planar perovskite solar cells Cong Zhang, Huaxin Wang, Haiyun Li, Qixin Zhuang, Cheng Gong, Xiaofei Hu, Wensi Cai, Shuangyi Zhao, Jiangzhao Chen, Zhigang Zang 2021, 63(12): 452-460.  DOI: 10.1016/j.jechem.2021.07.011 Abstract ( 12 )   PDF (6137KB) ( 5 )   Bulk and interface carrier nonradiative recombination losses impede the further improvement of power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). It is highly necessary to develop multifunctional strategy to minimize surface and interface nonradiative recombination losses. Herein, we report a bulk and interface defect passivation strategy via the synergistic effect of anions and cations, where multifunctional potassium sulphate (K2SO4) is incorporated at SnO2/perovskite interface. We find that K+ ions in K2SO4 diffuse into perovskite layer and suppress the formation of bulk defects in per-ovskite films, and the SO42- ions remain located at interface via the strong chemical interaction with SnO2 layer and perovskite layer, respectively. Through this synergistic modification strategy, effective defect passivation and improved energy band alignment are achieved simultaneously. These beneficial effects are translated into an efficiency increase from 19.45% to 21.18% with a low voltage deficit of 0.53 V mainly as a result of boosted open-circuit voltage (Voc) after K2SO4 modification. In addition, the K2SO4 modification contributes to ameliorated stability. The present work provides a route to mini- mize bulk and interface nonradiative recombination losses for the simultaneous realization of PCE and stability enhancement by rational anion and cation synergistic engineering.

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Composite electron transport layer for efficient N-I-P type monolithic perovskite/silicon tandem solar cells with high open-circuit voltage Bingbing Chen, Pengyang Wang, Renjie Li, Ningyu Ren, Yongliang Chen, Wei Han, Lingling Yan, Qian Huang, Dekun Zhang, Ying Zhao, Xiaodan Zhang 2021, 63(12): 461-467.  DOI: 10.1016/j.jechem.2021.07.018 Abstract ( 7 )   PDF (3636KB) ( 1 )   Perovskite/silicon tandem solar cells (PSTSCs) have exhibited huge technological potential for breaking the Shockley-Queisser limit of single-junction solar cells. The efficiency of P-I-N type PSTSCs has sur- passed the single-junction limit, while the performance of N-I-P type PSTSCs is far below the theoretical value. Here, we developed a composite electron transport layer for N-I-P type monolithic PSTSCs with enhanced open-circuit voltage (VOC) and power conversion efficiency (PCE). Lithium chloride (LiCl) was added into the tin oxide (SnO2) precursor solution, which simultaneously passivated the defects and increased the electron injection driving force at the electron transfer layer (ETL)/perovskite interface. Eventually, we achieved monolithic PSTSCs with an efficiency of 25.42% and VOC of 1.92 V, which is the highest PCE and VOC in N-I-P type perovskite/Si tandem devices. This work on interface engineering for improving the PCE of monolithic PSTSCs may bring a new hot point about perovskite-based tandem devices.

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Coupled intramolecular/heterointerfacial electron transfer in polyelectrolyte-shielded Iso-type black phosphorus hetero-structure boosts oxygen reduction kinetics Zhongke Yuan, Jing Li, Zhengsong Fang, Meijia Yang, Kancheng Mai, Dingshan Yu 2021, 63(12): 468-476.  DOI: 10.1016/j.jechem.2021.07.032 Abstract ( 5 )   PDF (4974KB) ( 2 )   Searching new structured black phosphorus (BP) and exploring intriguing functions and applications have become a hot topic so far. Here, we introduce a novel Iso-type black phosphorus heterostructure guided by first principle calculation, which features unique heterointerface and electronic coupling inter- action via stacking assembly of exfoliated black phosphorus (EBP) and amine-functionalized EBP (N-EBP). Inspired by the theoretical results, we constructed the Iso-type heterostructure comprising of ultrathin exfoliated few-layered EBP and N-EBP, both of which were derived from identical bulk BP. The purposive amine-functionalization not only creates positively-charged P atoms on N-EBP as effective active sites via N-induced intramolecular electron transfer (IET) but also endows N-EBP with lower work function rela- tive to EBP, while the unique EBP/N-EBP Iso-type heterostructure engenders directional heterointerfacial electron transfer (HET). The coupled IET/HET effects optimize the charge redistribution to afford favorable O2 adsorption. In this case, our unique strategy for the first time exploits the inherent catalytic capability of BP toward the oxygen reduction reaction (ORR) and enables the first use of BP as metal-free ORR cat- alysts for Zn-air cells. The newly-designed heterostructure facilitates a 4-e- transfer ORR relative to inac- tive EBP or N-EBP. Importantly, the polymer-shielded heterostructure acts as efficient air electrodes to endow a primary Zn-air cell with high stability, large capacity and high energy density-superior to the commercial Pt/C-enabled cell. This study as the first report on metal-free BP-based ORR catalysts and air electrodes not only extends BP’s application scopes but also renders new insight toward design of electronically-coupled superstructures for energy-related applications.

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Technoeconomically competitive four-terminal perovskite/graphene- silicon tandem solar cells with over 20% efficiency Pengjie Hang, Jingkun Cong, Ge Li, Lijian Zuo, Chenxia Kan, Biao Li, Jiangsheng Xie, Yuxin Yao, Ying Wang, Hongzheng Chen, Deren Yang, Xuegong Yu 2021, 63(12): 477-483.  DOI: 10.1016/j.jechem.2021.07.031 Abstract ( 9 )   PDF (4688KB) ( 5 )   Perovskite/Silicon (PS) tandem solar cells have attracted much interest over recent years. However, the most popular crystalline silicon solar cells utilized in tandems require complicated fabrication processes mainly including texturization, diffusion, passivation and metallization, which takes up much cost in photovoltaic market. Here, we report a facile graphene/silicon (Gr/Si) solar cell featuring of low- temperature (≤200 °C) processing and an efficiency of 13.56%. For reducing the heat dissipation loss of high energy photon, the perovskite solar cell (PSC) with a wide band gap of 1.76 eV was adopted as the top cell for the tandem. To reduce the loss of parasitic absorption in hole transport layers (HTLs), thickness of Spiro-OMeTAD is re-optimized by compromising the efficiency and the optical transmittance of the devices. As a result, the semitransparent top perovskite solar cell yields a highest efficiency of 13.35%. Furthermore, we firstly achieved a low-temperature-processed four-terminal (4-T) perovskite/ graphene-silicon (PGS) heterojunction tandem solar cell with the efficiency of 20.37%. The levelized cost of electricity (LCOE) of PGS 4-T modules were estimated to a competitive price, exhibiting much greater potential for practical application compared to that of PS 4-T modules.

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Easy-to-fabricate high efficiency silicon nanowires solar cell modified by CdTe and zinc tetraphenyl porphyrin nanostructures Debanjan Maity, Saurabh Kumar Pathak, Melepurath Deepa 2021, 63(12): 484-497.  DOI: 10.1016/j.jechem.2021.08.009 Abstract ( 4 )   PDF (21495KB) ( 1 )   Liquid junction solar cell (LJSC) with vertically silicon nanowires (SiNWs) as the primary photosensitizer, co-sensitized with luminescent and narrow gap CdTe nanoparticles, and cuboidal microstructures of zinc tetraphenyl porphyrin (ZnTPP) dye offers broad and intense visible light absorption that translates into a maximum power conversion efficiency (PCE) of 9.09%, when combined with a polymeric gel of a I2/I- redox couple as the hole transport material and a counter electrode (CE) of poly(3,4-ethyelenedioxythio phene) doped with imide ions (PEDOT-N(CF3SO2)2), under 1 sun irradiance. The p-type CdTe efficiently scavenges holes from SiNWs and simultaneously allows the passage of photoexcited electrons from ZnTPP to SiNWs via electrical conduction thus imparting an enhanced solar cell performance. Co- sensitization also supresses back electron transfer effectively, as is inferred from a ~68% enhancement in PCE compared to SiNWs alone. Optimization of the CE entailed the evaluation of the effect of dopant anion: imide versus dicyanamide in PEDOT, and revealed that the presence of macro-cracks in the poly- mer surface, a deeper work function, and a lower electrical conductance are the shortcomings of the dicyanamide doped PEDOT and reduce the overall PCE, compared to imide. This study brings out how by judicious choice of photoanode and CE components, efficient, stable and easy-to-assemble LJSCs can be developed.

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Ink formulation, scalable applications and challenging perspectives of screen printing for emerging printed microelectronics Ying Zhang, Yuanyuan Zhu, Shuanghao Zheng, Liangzhu Zhang, Xiaoyu Shi, Jian He, Xiujian Chou, Zhong-Shuai Wu 2021, 63(12): 498-513.  DOI: 10.1016/j.jechem.2021.08.011 Abstract ( 12 )   PDF (8178KB) ( 5 )   Screen printing is regarded as a highly competitive manufacture technology for scalable and fast fabrica- tion of printed microelectronics, owing to its advanced merits of low-cost, facile operability and scalability. However, its large-scale application in printed microelectronics is still limited by screen printing functional ink. In this review, we summarize the recent advances of ink formation, typical scalable applications, and challenging perspectives of screen printing for emerging printed microelectronics. Firstly, we introduce the major mechanism of screen printing and the formation of different organic- and aqueous-based inks by various solvents and binders. Next, we review the most widely used applications of screen printing tech- nique in micro-batteries, micro-supercapacitors and micro-sensors, demonstrative of wide applicability. Finally, the perspectives and future challenges in the sight of screen printing are briefly discussed.

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Aqueous high-voltage all 3D-printed micro-supercapacitors with ultrahigh areal capacitance and energy density Yu Liu, Shuanghao Zheng, Jiaxin Ma, Yuanyuan Zhu, Jiemin Wang, Xinliang Feng, Zhong-Shuai Wu 2021, 63(12): 514-520.  DOI: 10.1016/j.jechem.2021.08.018 Abstract ( 4 )   PDF (8239KB) ( 2 )   With the rapid development of integrated and miniaturized electronics, the planar energy storage devices with high capacitance and energy density are in enormous demand. Hence, the advanced manufacture and fast fabrication of microscale planar energy units are of great significance. Herein, we develop aque- ous planar micro-supercapacitors (MSCs) with ultrahigh areal capacitance and energy density via an effi- cient all-3D-printing strategy, which can directly extrude the active material ink and gel electrolyte onto the substrate to prepare electrochemical energy storage devices. Both the printed active carbon/exfoli- ated graphene (AC/EG) electrode ink and electrolyte gel are highly processable with outstanding conduc- tivity (~97 S cm-1 of electrode; ~34.8 mS cm-1 of electrolyte), thus benefiting the corresponding shaping and electrochemical performances. Furthermore, the 3D-printed symmetric MSCs can be operated stably at a high voltage up to 2.0 V in water-in-salt gel electrolyte, displaying ultrahigh areal capacitance of 2381 mF cm-2 and exceptional energy density of 331 lWh cm-2, superior to previous printed micro energy units. In addition, we can further tailor the integrated 3D-printed MSCs in parallel and series with various voltage and current outputs, enabling metal-free interconnection. Therefore, our all-3D-printed MSCs place a great potential in developing high-power micro-electronics fabrication and integration.

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Pre-fixing defects in carbon framework for revealing the active sites of oxygen reduction reaction at nitrogen-doped carbon nanotubes Bing Huang, Kun Hou, Yang Liu, Rongtao Hu, Lunhui Guan 2021, 63(12): 521-527.  DOI: 10.1016/j.jechem.2021.08.024 Abstract ( 6 )   PDF (2857KB) ( 2 )   Nitrogen-doped carbon-based materials are promising non-platinum group metal electrocatalysts for the oxygen reduction reaction (ORR). Understanding their ORR active sites is vital for the rational design and development of nitrogen-doped carbon-based electrocatalysts with enhanced catalytic efficiency and selectivity. However, the conclusive analysis of the ORR mechanism of nitrogen-doped carbon-based electrocatalysts remains a grand challenge because the catalysts have a complex inhomogeneous struc- ture. Here, we elucidate this problem using nitrogen-doped carbon nanotubes framework catalysts with fixed defect concentrations prepared by pre-thermal treatment at a low temperature. The generation of defects under high-temperature treatment was effectively suppressed to enable a simple model for ORR mechanism study. A correlation between ORR pathways and the different nitrogen species in the nitrogen-doped carbon catalysts was revealed through a combination of structural and electrochemical properties investigations. Besides, our results also demonstrate the importance of defects for ORR. We believe that the results will provide instructive guidance for designing and developing novel carbon nanomaterials for ORR.

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Ion migration in halide perovskite solar cells: Mechanism, characterization, impact and suppression Huachao Zai, Yue Ma, Qi Chen, Huanping Zhou 2021, 63(12): 528-549.  DOI: 10.1016/j.jechem.2021.08.006 Abstract ( 50 )   PDF (28494KB) ( 33 )   Metal halide perovskites are emerging as the most promising candidate for the next-generation Photovoltaics (PV) materials, due to their superior optoelectronic properties and low cost. However, the resulting Perovskite solar cells (PSCs) suffer from poor stability. In particular, the temperature and light activated ionic defects within the perovskite lattice, as well as electric-field-induced migration of ionic defects, make the PSCs unstable at operating condition, even with device encapsulation. There is no doubt that the investigation of ion migration is crucial for the development of PSCs with high intrinsic stability. In this review, we first briefly introduce the origin and pathways of ion migration, and also the essential characterization methods to identify ion migration. Next, we discuss the impact of ion migration on the perovskite films and cells with respect to photoelectric properties and stability. Then, several rep- resentative strategies to suppress ion migration are systematically summarized in the context of compo- sition engineering, additive engineering and interface engineering, with an in-depth understanding on the underlying mechanisms which may provide more clues for further fabrication of PSCs with improved stability. Finally, a perspective with some suggestion on future research directions and chemical approaches are provided to alleviate ion migration in perovskite materials and the entire devices.

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High-performance Cu/ZnO/Al2O3 catalysts for methanol steam reforming with enhanced Cu-ZnO synergy effect via magnesium assisted strategy Zaizhe Cheng, Wenqiang Zhou, Guojun Lan, Xiucheng Sun, Xiaolong Wang, Chuan Jiang, Ying Li 2021, 63(12): 550-557.  DOI: 10.1016/j.jechem.2021.08.025 Abstract ( 7 )   PDF (6309KB) ( 4 )   Methanol steam reforming (MSR) is an attractive approach to produce hydrogen for fuel cells. Due to the limited catalyst loading volume and frequent start-ups and shut-downs on board, it is highly desired to develop an extremely active and robust catalyst. Herein, on the basis of industrial Cu/ZnO/Al2O3 catalysts, a series of CuZnAl-xMg catalysts with enhanced Cu-ZnO synergy were synthesized via magnesium assisted strategy. The incorporation of magnesium was found to be beneficial to the enhancement of cat- alytic activity and stability of catalyst. A combination of complementary characterizations (e.g. XRD, H2- TPR, N2O chemisorption, TEM, XPS analysis etc.) proves that isomorphous substitution of Cu2+ in mala- chite phase gives rise to more dispersive Cu and ZnO NPs, and the increased Cu+/Cu0 ratio indicates the strengthened Cu-ZnO synergy effect, which leads to the boosted stability during the thermal treatment.

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Secondary crystallization strategy for highly efficient inorganic CsPbI2Br perovskite solar cells with efficiency approaching 17% Jing Ma, Zhenhua Lin, Xing Guo, Long Zhou, Jian He, Zhou Yang, Jincheng Zhang, Yue Hao, Shengzhong Liu, Jingjing Chang 2021, 63(12): 558-565.  DOI: 10.1016/j.jechem.2021.08.021 Abstract ( 7 )   PDF (4317KB) ( 4 )   Inorganic CsPbI2Br perovskite solar cells (PSCs) have a tremendous development in last few years due to the trade-off between the excellent optoelectronic properties and the relatively outstanding stability. Herein, we demonstrated a strategy of secondary crystallization (SC) for CsPbI2Br film in a facile planar n-i-p structure (ITO/ZnO-SnO2/CsPbI2Br/Spiro-OMeTAD/Ag) at low-temperature (150 °C). It is achieved through the method of post-treatment with guanidinium bromine (GABr) atop annealed CsPbI2Br film. It was found that the secondary crystallization by GABr can not only regulate the crystal growth and pas- sivate defects, but also serve as a charge collection center to effectively collect photogenerated carriers. In addition, due to the excess Br ions in GABr, the formation of the Br-rich region at the CsPbI2Br perovskite surface can further lower the Fermi level, leading to more beneficial band alignment between the per- ovskite and the hole transport layer (HTL), while the phase stability was also improved. As a result, the champion cell shows a superb open-circuit voltage (Voc) of 1.31 V, a satisfactory power conversion efficiency (PCE) of 16.97% and outstanding stabilities. As far as we know, this should be one of the highest PCEs reported among all-inorganic CsPbI2Br based PSCs.

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Diethyl phenylphosphonite contributing to solid electrolyte interphase and cathode electrolyte interphase for lithium metal batteries Chunxia Miao, Shihan Qi, Kang Liang, Yanli Qi, Junda Huang, Mingguang Wu, Hongshun Zhao, Jiandong Liu, Yurong Ren, Jianmin Ma 2021, 63(12): 566-573.  DOI: 10.1016/j.jechem.2021.08.028 Abstract ( 9 )   PDF (10031KB) ( 2 )   Lithium metal batteries have obtained increasing interest due to their high specific capacity. Nonetheless, the growth of lithium dendrites brings safety risks to batteries and further deteriorates the performance. Herein, we explore diethyl phenylphosphonite (DEPP) as the electrolyte additive to alleviate this prob- lem. DEPP can be preferentially decomposed than carbonate solvents to form the stable interface between electrolyte and lithium anode for inhibiting the dendrite growth. As expected, the symmetrical LiIILi cells could achieve a stable cycling performance with 200 h at 1 mA cm-2. Moreover, DEPP can be preferentially oxidized on the surface of lithium cobalt oxides (LiCoO2) to form a dense cathode elec- trolyte interphase (CEI) film for suppressing the continuous oxidative decomposition of the electrolyte and eliminating the adverse effects of HF on the battery. This endows LiCoO2IILi full battery with the enhanced cycling and rate performance.

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Liquid-like adsorbent assembled by CNTs: Serving as renewable CO2 capture materials for indoor air Jae Won Lee, Minjae Kim, Han Sol Jung, Ronghuan Xu, Seonggon Kim, Yong Tae Kang 2021, 63(12): 574-584.  DOI: 10.1016/j.jechem.2021.08.027 Abstract ( 8 )   PDF (4611KB) ( 3 )   In this study, a CO2 capture material in the form of liquid-like adsorbents (LLAs) is developed to overcome the limitations of conventional types of adsorbents. The increase in indoor activities necessitates the cap- ture of CO2 in enclosed indoor spaces. Indoor spaces require safe and stable materials for CO2 capture because humans are present in these spaces. Solid adsorbents are mainly used because liquid absorbents are unsuitable owing to noise and scattering problems. In LLA, the liquid absorbent assembled by carbon nanotubes (CNTs) is solidified and prevented from flowing and scattering indoor. LLAs present to main- tain 95% of initial capacity after recycling 20 times, and have characteristics that can be regenerated in a low temperature heat source (80 to 120 ℃) and moisture resistance. This work not only provides indoor useable CO2 capture materials, but also offers a new prospect in the field of adsorbents.

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Confinement of sulfur-doped NiO nanoparticles into N-doped carbon nanotube/nanofiber-coupled hierarchical branched superstructures: Electronic modulation by anion doping boosts oxygen evolution electrocatalysis Tongfei Li, Jingwen Yin, Yu Li, Ziqi Tian, Yiwei Zhang, Lin Xu, Yanle Li, Yawen Tang, Huan Pang, Jun Yang 2021, 63(12): 585-593.  DOI: 10.1016/j.jechem.2021.08.035 Abstract ( 10 )   PDF (8368KB) ( 3 )   The search for non-precious and efficient electrocatalysts towards the oxygen evolution reaction (OER) is of vital importance for the future advancement of multifarious renewable energy conversion/storage technologies. Electronic modulation via heteroatom doping is recognized as one of the most forceful leverages to enhance the electrocatalytic activity. Herein, we demonstrate a delicate strategy for the in-situ confinement of S-doped NiO nanoparticles into N-doped carbon nanotube/nanofiber-coupled hier- archical branched superstructures (labeled as S-NiO@N-C NT/NFs). The developed strategy simultane- ously combines enhanced thermodynamics via electronic regulation with accelerated kinetics via nanoarchitectonics. The S-doping into NiO lattice and the 1D/1D-integrated hierarchical branched carbon substrate confer the resultant S-NiO@N-C NT/NFs with regulated electronic configuration, enriched oxy- gen vacancies, convenient mass diffusion pathways and superior architectural robustness. Thereby, the S- NiO@N-C NT/NFs display outstanding OER properties with an overpotential of 277 mV at 10 mA cm-2 and impressive long-term durability in KOH medium. Density functional theory (DFT) calculations further corroborate that introducing S-dopant significantly enhances the interaction with key oxygenate inter- mediates and narrow the band gap. More encouragingly, a rechargeable Zn-air battery using an air-cath- ode of Pt/C + S-NiO@N-C NT/NFs exhibits a lower charge voltage and preferable cycling stability in comparison with the commercial Pt/C + RuO2 counterpart. This study highlighting the concurrent consid- eration of electronic regulation, architectural design and nanocarbon hybridization may shed light on the future exploration of economical and efficient electrocatalysts.

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Size-refinement enhanced flexibility and electrochemical performance of MXene electrodes for flexible waterproof supercapacitors Jinkun Sun, Yingjian Liu, Jiayi Huang, Jiatian Li, Mengmeng Chen, Xiaoyu Hu, Yatao Liu, Run Wang, Yanan Shen, Jingjing Li, Xuecheng Chen, Dong Qian, Baigang An, Zunfeng Liu 2021, 63(12): 594-603.  DOI: 10.1016/j.jechem.2021.08.034 Abstract ( 5 )   PDF (6599KB) ( 1 )   Increasing mechanical flexibility without sacrificing electrochemical performance of the electrode mate- rial is highly desired in the design of flexible electrochemical energy storage devices. In metal-related materials science, decreasing the grain size introduces more grain boundaries; this stops dislocations and crack propagation under deformation, and results in increased strength and toughness. However, such a size refinement effect has not been considered in the mechanical properties, particle stacking, wet- ting, and electrochemical performances of flexible supercapacitor electrodes. In this paper, MXene was used as an electrode material to study the size refinement effect of flexible supercapacitors. Size refine- ment improved the strength and toughness of the MXene electrodes, and this resulted in increased flex- ibility. Finite elemental analysis provided a theoretical understanding of size refinement-increased flexibility. Moreover, the size refinement also improved the specific surface area, electric conductance, ion transportation, and water wetting properties of the electrode, and the size refinement provided highly increased energy density and power density of the MXene supercapacitors. A highly flexible, water-proof supercapacitor was fabricated using size-refined MXene. The current study provides a new viewpoint for designing tough and flexible energy storage electrodes. The size refinement effect may also be applicable for metal ion batteries and electronic and photo devices composed of MXene and other nanoparticles.

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Atomic level engineering of noble metal nanocrystals for energy conversion catalysis Yancai Yao, Shiqi Wang, Zhijun Li, Yuen Wu 2021, 63(12): 604-624.  DOI: 10.1016/j.jechem.2021.08.039 Abstract ( 5 )   PDF (12556KB) ( 1 )   It is commonly known that the performance of electrocatalysts is largely influenced by the size, morphol- ogy, composition, and crystalline phase of noble metal nanocrystals. However, the limited reserves and high cost of noble metals largely restrict their industrial applications. Along with the development of characterization techniques, theoretical calculations, and advanced material synthesis methods, modu- lating the electrocatalytic properties of noble metal nanocrystals at the atomic scale (e.g., monolayer/ sub-monolayer, single-atom alloy, ultrafine structure) has been flooding out. Engineering noble metal nanocrystals at the atomic level could not only immensely improve the noble metal atom utilization effi- ciency and lower the cost, but also boost the catalytic performance. In this review, we summarize the recent advanced progresses of regulating the noble metal nanocrystals at the atomic scale towards energy conversion application. Then, the challenges and perspectives of designing noble metal nanocrys- tals at the atomic scale in the future are discussed and considered. It is expected that this review will inspire scientists to further study precious metal-based materials for energy-oriented catalysis.

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Tuning the electron structure enables the NiZn alloy for CO2 electroreduction to formate Xiaodong Zhang, Yajiao Zhou, Hang Zhang, HuangJingWei Li, Kang Liu, Hongmei Li, Hao Pan, Junhua Hu, Junwei Fu, Shanyong Chen, Min Liu 2021, 63(12): 625-632.  DOI: 10.1016/j.jechem.2021.08.060 Abstract ( 6 )   PDF (7718KB) ( 2 )   Formate is an important liquid chemical, which can be produced by electrocatalytic carbon dioxide reduction reaction (CO2RR). Most of the metal catalysts for CO2RR to formate are toxic or noble metals, such as Cd, Hg, Pb and Pd, leading to the environmental pollution or increased production costs. Herein, we develop an environmentally friendly and low-cost NiZn alloy catalyst for CO2RR to formate. The X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron micro- scopy (TEM) confirm the alloy structure of the prepared NiZn catalyst. As for a catalyst for CO2RR, the NiZn alloy exhibits the FE- (Faraday efficiency of HCOO-) of 36 ± 0.7% at - 0.9 V vs. RHE in 0.1 M KHCO3, and remarkable stability for 40,000 s at - 0.8, -0.9, -1.0 and - 1.1 V vs. RHE, respectively. Theoretical calculation results indicate that the NiZn alloy exhibits the middle valence electron structure between the Zn and Ni metal, resulting in the favorable pathway for HCOOH formation but unfavorable for the hydrogen evolution reaction and CO production. The Ultraviolet Photoelectron Spectroscopy results verify the modulated valence electron structure for NiZn alloy as compared to Ni and Zn, consis- tent with the theoretical calculation results. This work provides new insights into design of alloy catalysts for CO2RR to formate.

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Chemical interaction motivated structure design of layered metal carbonate hydroxide/MXene composites for fast and durable lithium ion storage Huibin Guan, Hanna He, Tianbiao Zeng, Chuhong Zhang 2021, 63(12): 633-641.  DOI: 10.1016/j.jechem.2021.08.059 Abstract ( 5 )   PDF (11490KB) ( 2 )   Rational architecture design has turned out to be an effective strategy in improving the electrochemical performance of electrode materials for batteries. However, an elaborate structure that could simultane- ously endow active materials with promoted reaction reversibility, accelerated kinetic and restricted vol- ume change still remains a huge challenge. Herein, a novel chemical interaction motivated structure design strategy has been proposed, and a chemically bonded Co(CO3)0.5OH·0.11H2O@MXene (CoCH@MXene) layered-composite was fabricated for the first time. In such a composite, the chemical interaction between Co2+ and MXene drives the growth of smaller-sized CoCH crystals and the subse- quent formation of interwoven CoCH wires sandwiched in-between MXene nanosheets. This unique lay- ered structure not only encourages charge transfer for faster reaction dynamics, but buffers the volume change of CoCH during lithiation-delithiation process, owing to the confined crystal growth between con- ductive MXene layers with the help of chemical bonding. Besides, the sandwiched interwoven CoCH wires also prevent the stacking of MXene layers, further conducive to the electrochemical performance of the composite. As a result, the as-prepared CoCH@MXene anode demonstrates a high reversible capac- ity (903.1 mAh g-1 at 100 mA g-1) and excellent cycling stability (maintains 733.6 mAh g-1 at 1000 mA g-1 after 500 cycles) for lithium ion batteries. This work highlights a novel concept of layer- by-layer chemical interaction motivated architecture design for futuristic high performance electrode materials in energy storage systems.

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Activation of urchin-like Ni-doped W18O49/NF by electrochemical tuning for efficient water splitting Guojuan Hai, Jianfeng Huang, Liyun Cao, Koji Kajiyoshi, Long Wang, Liangliang Feng, Jun Chen 2021, 63(12): 642-650.  DOI: 10.1016/j.jechem.2021.08.056 Abstract ( 3 )   PDF (7834KB) ( 2 )   The electrochemical conversion is closely correlated with the electrocatalytic activities of the electrocatalyst. Herein, the urchin-like Ni-doped W18O49/NF with enriched active sites was prepared by solvothermal method followed by a low-temperature pyrolysis treatment was reported. Results demonstrate that the incorporation of Ni-doping triggers the lattice distortion of W18O49 for the increase- ment of oxygen defects. Further, high-valent W6+ are partially reduced to low-valent W4+, wherein the electrons originate from the oxidation process of Ni2+ to Ni3+. The Ni3+ ions show an enhanced orbital overlap with the OER reaction intermediates. The generated W4+ ions contribute to release oxygen vacan- cies, eventually reorganizing Ni-doped W18O49/NF to unique electrochemical active species with a special amorphous-crystalline interface (AM/NiWOx/NiOOH/NF). Simultaneously, the reconstruction results in an optimized valence band and conduction band. Eventually, the resultant AM/NiWOx/NiOOH/NF with abundant active sites and improved oxidation/reduction capability exhibits more superior catalytic per- formance compared with the Ni-doped W18O49/NF counterpart. This study gives more insights in the electrochemical evolution of the tungsten-based oxide and provides effective strategies for optimizing the catalytic activity of materials with inherent hydrogen evolution reaction limitations.

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Selenization triggers deep reconstruction to produce ultrathin γ-NiOOH toward the efficient water oxidation Kailu Guo, Hua Li, Junfeng Huang, Yantao Wang, Yong Peng, Siyu Lu, Cailing Xu 2021, 63(12): 651-658.  DOI: 10.1016/j.jechem.2021.08.055 Abstract ( 5 )   PDF (10966KB) ( 1 )   Transition metal chalcogenides will be in situ transformed into metal oxyhydroxides during oxygen evo-lution reaction (OER) process in alkaline medium. However, most of these compounds only undergo sur-face reconstruction under operating conditions, which contains a large percentage of inactive atoms in the core, thus limiting the exposure of the active sites. Here, we synthesize a Ni-Mo-Se precatalyst with three-dimensional hierarchical structure and develop a facile on-site electrochemical activation strategy for achieving deep reconstruction of the precatalyst. Using the combination of multiple spectroscopic characterizations and high resolution electron microscopy techniques, we unravel that the Ni-Mo-Se pre-catalyst is deeply reconstructed into γ-NiOOH with co-leaching of Mo and Se after the anodic oxidation. Such flower-like γ-NiOOH is constituted by distorted ultrathin nanosheets with a thickness of ~ 4.5 nm and contains abundant intercalated species such as water and OH- /CO32-, thus offering a large quantity of accessible active sites. To reach the current density of 10 mA cm-2, the derived electrode requires an overpotential of only 244 mV, outperforming almost all the reported analogues. This work highlights the reconstruction chemistry and provides a simple method for the preparation of efficient OER electrocatalyst.

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Comparing electrocatalytic hydrogen and oxygen evolution activities of first-row transition metal complexes with similar coordination environments Xiaotong Jin, Xialiang Li, Haitao Lei, Kai Guo, Bin Lv, Hongbo Guo, Dandan Chen, Wei Zhang, Rui Cao 2021, 63(12): 659-666.  DOI: 10.1016/j.jechem.2021.08.068 Abstract ( 6 )   PDF (6286KB) ( 2 )   Developing cheap and efficient electrocatalysts for water splitting is required for energy conversion tech- niques. Many first-row transition metal complexes have been shown to be active for the hydrogen evo- lution reaction (HER) and oxygen evolution reaction (OER). Metal ions play crucial roles in these catalytic processes, but the activity dependence on the nature of metal ions has been rarely studied due to the dif- ficulty to compare metal complexes with different coordination environments. We herein reported the synthesis of a series of metal complexes of azido-substituted porphyrin (1), in which metal ions have very similar coordination environments. By grafting 1-M (M = Mn, Fe, Co, Ni, and Cu) onto alkyne- functionalized carbon nanotubes (CNTs) through the same covalent connection, the resulted hybrids 1- M@CNT were all active and robust for both electrocatalytic HER and OER in alkaline aqueous solutions. Among these hybrids, 1-Fe@CNT displayed the highest electrocatalytic activity for HER, while 1- Co@CNT was the most active one for OER. Moreover, a two-electrode water electrolysis cell assembled with 1-Fe@CNT as the cathode and 1-Co@CNT as the anode required smaller applied bias potential by 210 mV to get 10 mA/cm2 current density as compared to that assembled with Pt/C and Ir/C with the same amount of metal loading. This work is significant to correlate HER and OER activity with the nature of first-row transition metal ions and to highlight promising potential applications of molecular electro- catalysis in water splitting.

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Degradation: A critical challenge for M-N-C electrocatalysts Yongchao Yang, Leo Lai, Li Wei, Yuan Chen 2021, 63(12): 667-674.  DOI: 10.1016/j.jechem.2021.10.012 Abstract ( 8 )   PDF (2951KB) ( 7 )   Atomically dispersed transition metal (M) and nitrogen (N) co-doped carbon (M-N-C) electrocatalysts hold excellent application potentials for several critical reactions required in electrochemical conversion processes and energy storage devices, including oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, carbon dioxide reduction reaction and nitrogen reduction reaction. Despite significant progress achieved in the past few decades, their commercialization is hindered by their fast degradation. This perspective article outlines the historical development of M-N-C electrocat- alysts, the current understanding of their active catalytic sites, and crucial degradation mechanisms. We highlight that many methods used to tailor M-N-C electrocatalysts likely cause contradictory effects on activity and stability. More emphasis is needed to address their degradation issues under industry- relevant working conditions.