Table of Content

18 December 2022, Volume 5 Issue S1

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Recent Progress in High Entropy Alloys for Electrocatalysts

Kun Wang, Jianhao Huang, Haixin Chen, Yi Wang, Wei Yan, Xianxia Yuan, Shuqin Song, Jiujun Zhang, Xueliang Sun

2022, 5(S1):  17.  doi:10.1007/s41918-022-00144-8

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High entropy alloys (HEAs), which can incorporate five or more constituents into a single phase stably, have received considerable attention in recent years. The composition/structure complexity and adjustability endow them with a huge design space to adjust electronic structure, geometric configuration as well as catalytic activity through constructing reaction active sites with optimal binding energies of different reaction intermediates. This paper reviews the recent progress on the preparation methods, characterization techniques, electrocatalytic applications and functional mechanisms of HEAs-based electrocatalysts for hydrogen evolution, oxygen evolution and oxygen reduction reactions. The synthesis approaches for HEAs from bottom-up (high-energy ball milling, cryo-milling, melt-spinning and dealloying) to top-down strategies (carbothermal shock, sputtering deposition and solvothermal) and the corresponding materials characterizations are discussed and analyzed. By summarizing and analyzing the electrocatalytic performance of HEAs for diverse electrocatalytic reactions in water electrolysis cells, metal-air batteries and fuel cells, the basic principle of their designs and the relevant mechanisms are discussed. The technical challenges and prospects of HEAs-based electrocatalysts are also summarized with the proposed further research directions. This review can provide a beneficial theoretical reserve and experimental guidance for developing high performance electrocatalytic materials via the paradigm of high entropy.



Engineering Gas–Solid–Liquid Triple-Phase Interfaces for Electrochemical Energy Conversion Reactions

Chen-Chen Weng, Xian-Wei Lv, Jin-Tao Ren, Tian-Yi Ma, Zhong-Yong Yuan

2022, 5(S1):  19.  doi:10.1007/s41918-022-00133-x

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The fundamental water cycle, carbon cycle and nitrogen cycle relying on heterogeneous gas-involving electrocatalytic processes have attracted extensive attention due to their critical contributions to clean, sustainable and energy-environmental electrochemical devices. The development of electrocatalytic materials has afforded gradually improved electrocatalytic reaction efficiency and increasingly promising implementation of electrochemical techniques. In gas-involving electrocatalytic reactions, apart from the intrinsic reaction kinetics, the microenvironment at the triple-phase interfaces of the solid catalyst, liquid electrolyte and gaseous reactant or product under reaction conditions can exert a significant effect on the eventual electrochemical performance since the key issues, including mass transport, electron conduction and accessibility of active sites, are highly sensitive to the electrocatalytic processes. Herein, we systematically summarize the up-to-date progress in energy-related electrocatalysts based on gas-liquid-solid triple-phase interface engineering in terms of an active-site-enriched surface, decent gas wettability and electrolyte infiltration and favorable electronic conductivity. To establish universal theory-structure-function relationships based on triple-phase interface engineering, the corresponding insightful understanding, architecture design/constituent regulation of electrocatalytic materials and admirable electrocatalytic activity are discussed, simultaneously revealing the practical energy-related applications in water electrolyzers, metal-based batteries and fuel cells. Finally, the remaining challenges, possible opportunities and future perspectives are highlighted.



Recent Progress in Surface Coatings for Sodium-Ion Battery Electrode Materials

Tyler Or, Storm W. D. Gourley, Karthikeyan Kaliyappan, Yun Zheng, Matthew Li, Zhongwei Chen

2022, 5(S1):  20.  doi:10.1007/s41918-022-00137-7

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Sodium-ion batteries (SIBs) are an emerging technology regarded as a promising alternative to lithium-ion batteries (LIBs), particularly for stationary energy storage. However, due to complications associated with the large size of the Na+ charge carrier, the cycling stability and rate performance of SIBs are generally inadequate for commercial applications. Due to their similar chemistry and operating mechanism to LIBs, many improvement strategies derived from extensive LIB research are directly translatable to SIBs. In addition to doping and tailoring of the particle morphology, applying coatings is a promising approach to improve the performance of existing electrode materials. Coatings can mitigate side reactions at the electrode-electrolyte interface, restrict active material dissolution, provide reinforcement against particle degradation, and/or enhance electrode kinetics. This review provides a comprehensive overview and comparison of coatings applied to SIB intercalation cathodes and anodes. Coatings are categorized based on their mechanism of action and deposition method. Key classes of SIB electrode materials are introduced, and promising coating strategies to improve the performance of each material are then discussed. These insights can help guide rational design of high-performance SIB electrodes.



Solid-State Electrochemistry and Solid Oxide Fuel Cells: Status and Future Prospects

San Ping Jiang

2022, 5(S1):  21.  doi:10.1007/s41918-022-00160-8

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Solid-state electrochemistry (SSE) is an interdisciplinary field bridging electrochemistry and solid-state ionics and deals primarily with the properties of solids that conduct ions in the case of ionic conducting solid electrolytes and electrons and/or electron holes in the case of mixed ionic and electronic conducting materials. However, in solid-state devices such as solid oxide fuel cells (SOFCs), there are unique electrochemical features due to the high operating temperature (600-1 000℃) and solid electrolytes and electrodes. The solid-to-solid contact at the electrode/electrolyte interface is one of the most distinguished features of SOFCs and is one of the fundamental reasons for the occurrence of most importance phenomena such as shift of the equipotential lines, the constriction effect, polarization-induced interface formation, etc. in SOFCs. The restriction in placing the reference electrode in solid electrolyte cells further complicates the SSE in SOFCs. In addition, the migration species at the solid electrode/electrolyte interface is oxygen ions, while in the case of the liquid electrolyte system, the migration species is electrons. The increased knowledge and understanding of SSE phenomena have guided the development of SOFC technologies in the last 30-40 years, but thus far, no up-to-date reviews on this important topic have appeared. The purpose of the current article is to review and update the progress and achievements in the SSE in SOFCs, largely based on the author's past few decades of research and understanding in the feld, and to serve as an introduction to the basics of the SSE in solid electrolyte devices such as SOFCs.



Molecular and Morphological Engineering of Organic Electrode Materials for Electrochemical Energy Storage

Zhenzhen Wu, Qirong Liu, Pan Yang, Hao Chen, Qichun Zhang, Sheng Li, Yongbing Tang, Shanqing Zhang

2022, 5(S1):  26.  doi:10.1007/s41918-022-00152-8

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Organic electrode materials (OEMs) can deliver remarkable battery performance for metal-ion batteries (MIBs) due to their unique molecular versatility, high flexibility, versatile structures, sustainable organic resources, and low environmental costs. Therefore, OEMs are promising, green alternatives to the traditional inorganic electrode materials used in state-of-the-art lithium-ion batteries. Before OEMs can be widely applied, some inherent issues, such as their low intrinsic electronic conductivity, significant solubility in electrolytes, and large volume change, must be addressed. In this review, the potential roles, energy storage mechanisms, existing challenges, and possible solutions to address these challenges by using molecular and morphological engineering are thoroughly summarized and discussed. Molecular engineering, such as grafting electron-withdrawing or electron-donating functional groups, increasing various redox-active sites, extending conductive networks, and increasing the degree of polymerization, can enhance the electrochemical performance, including its specific capacity (such as the voltage output and the charge transfer number), rate capability, and cycling stability. Morphological engineering facilitates the preparation of different dimensional OEMs (including 0D, 1D, 2D, and 3D OEMs) via bottom-up and top-down methods to enhance their electron/ion diffusion kinetics and stabilize their electrode structure. In summary, molecular and morphological engineering can offer practical paths for developing advanced OEMs that can be applied in next-generation rechargeable MIBs.



Catalyst Design for Electrolytic CO₂ Reduction Toward Low-Carbon Fuels and Chemicals

Yipeng Zang, Pengfei Wei, Hefei Li, Dunfeng Gao, Guoxiong Wang

2022, 5(S1):  29.  doi:10.1007/s41918-022-00140-y

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Electrocatalytic CO₂ reduction reaction (CO₂RR) is an attractive way to simultaneously convert CO₂ into value-added fuels and chemicals as well as to store intermittent electricity derived from renewable energy. However, this process involves multiple proton and electron transfer steps and is kinetically sluggish, thus leading to low conversion efficiency from electrical energy to chemical energy. Therefore, there is an urgent need to develop highly efficient CO₂RR catalysts with high activity, selectivity and stability. In this review, we firstly introduce the fundamentals of CO₂RR and then discuss the synthesis, characterization, catalytic performance and reaction mechanism of various catalysts based on specific CO₂RR products. The structure-performance relationships of some representative catalyst systems are highlighted, benefiting from advanced electrochemical in situ and operando spectroscopic characterizations. At the end, we illustrate existing challenges and emerging research directions, to design new generation of highly efficient catalysts and to advance both fundamental research and practical application of CO₂RR to low-carbon fuels and chemicals.



Atomic Layer Deposition for Electrochemical Energy: from Design to Industrialization

Zhe Zhao, Gaoshan Huang, Ye Kong, Jizhai Cui, Alexander A. Solovev, Xifei Li, Yongfeng Mei

2022, 5(S1):  31.  doi:10.1007/s41918-022-00146-6

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The demand for high-performance devices that are used in electrochemical energy conversion and storage has increased rapidly. Tremendous efforts, such as adopting new materials, modifying existing materials, and producing new structures, have been made in the field in recent years. Atomic layer deposition (ALD), as an effective technique for the deposition of conformal and thickness-controllable thin films, has been widely utilized in producing electrode materials for electrochemical energy devices. Recent strategies have emerged and been developed for ALD to construct nanostructured architectures and three-dimensional (3D) micro/nanostructures. These strategies emphasize the preparation of active materials for devices such as batteries and supercapacitors or as catalysts for hydrogen evolution. Additionally, ALD is considered to have great potential in practical industrial production. In this review, we focus on the recent breakthroughs of ALD for the design of advanced materials and structures in electrochemical energy devices. The function and merits of ALD will be discussed in detail from traditional thin film depositions for the coating and engineering/modification layers to complex 3D micro/nanostructures that are designed for active materials. Furthermore, recent works regarding metal-organic framework films and transition metal dichalcogenide films, which were prepared with the assistance of ALD oxide, will be highlighted, and typical examples will be demonstrated and analysed. Because it is within a rapidly developing field, we believe that ALD will become an industrial deposition method that is important, commercially available, and widely used in electrochemical energy devices.



Recycling and Upcycling Spent LIB Cathodes: A Comprehensive Review

Nianji Zhang, Zhixiao Xu, Wenjing Deng, Xiaolei Wang

2022, 5(S1):  33.  doi:10.1007/s41918-022-00154-6

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Worldwide demands for green energy have driven the ever-growing popularity of electric vehicles, resulting in demands for a million tons of lithium-ion batteries (LIBs). Such exigency will not only outstrip the current reserves of critical metals, such as Li, Co, Ni, and Mn, which are essential for LIB fabrication, but also necessitate the methods to properly, safely, and sustainably handle spent LIBs. Current LIB recycling infrastructure uses pyrometallurgical or hydrometallurgical methods and mainly focuses on cobalt recovery to maximize economic benefits. Despite being commercialized, these two methods are either energy-intensive or highly complicated, and their long-term economic feasibility is still uncertain, as the market trend is shifting towards cobalt-poor or even cobalt-free chemistry. Alternative non-destructive methods, including direct recycling and upcycling, have attracted much interest. Direct recycling, which is a non-destructive method, allows spent cathodes to be directly regenerated into new active materials for reuse, while upcycling, as an upgraded direct recycling method, transforms degraded cathode materials into materials with a better performance or applicability in other fields. This review mainly focuses on recent advances in techniques including pyro- and hydrometallurgy, direct recycling, and upcycling.