Electrochemical Energy Reviews

Interfaces in Sulfide Solid Electrolyte-Based All-Solid-State Lithium Batteries: Characterization, Mechanism and Strategy

Zhan Wu, Xiaohan Li, Chao Zheng, Zheng Fan, Wenkui Zhang, Hui Huang, Yongping Gan, Yang Xia, Xinping He, Xinyong Tao, Jun Zhang

2023, 6(2): 10. doi:10.1007/s41918-022-00176-0

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Owing to the advantages of high energy density and environmental friendliness, lithium-ion batteries (LIBs) have been widely used as power sources in electric vehicles, energy storage systems and other devices. Conventional LIBs composed of liquid electrolytes (LEs) have potential safety hazards; thermal runaway easily leads to battery explosion and spontaneous combustion. To realize a large-scale energy storage system with higher safety and higher energy density, replacing LEs with solid-state electrolytes (SSEs) has been pursued. Among the many SSEs, sulfide SSEs are attractive because of their high ionic conductivities, easy processabilities and high thermostabilities. However, interfacial issues (interfacial reactions, chemomechanical failure, lithium dendrite formation, etc.) between sulfide SSEs and electrodes are factors limiting widespread application. In addition, the intrinsic interfacial issues of sulfide SSEs (electrochemical windows, diffusion mechanisms of Li⁺, etc.) should not be ignored. In this review, the behaviors, properties and mechanisms of interfaces in all-solid-state lithium batteries with a variety of sulfide SSEs are comprehensively summarized. Additionally, recent research progress on advanced characterization methods and designs used to stabilize interfaces is discussed. Finally, outlooks, challenges and possible interface engineering strategies are analyzed and proposed.

Carbon-Based Electrodes for Advanced Zinc-Air Batteries: Oxygen-Catalytic Site Regulation and Nanostructure Design

Wenjie Shao, Rui Yan, Mi Zhou, Lang Ma, Christina Roth, Tian Ma, Sujiao Cao, Chong Cheng, Bo Yin, Shuang Li

2023, 6(2): 11. doi:10.1007/s41918-023-00181-x

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Zn-air batteries are highly attractive for direct chemical-to-electrical energy conversion and for solving the energy crisis and environmental problems. Designing efficient oxygen electrodes has been considered one of the most critical steps in the development of advanced Zn-air batteries because of the sluggish kinetics of the oxygen reduction reaction and the oxygen evolution reaction. In recent years, nanostructured carbon-based electrodes with large surface areas, efficient oxygen-catalytic centers, and hierarchically porous matrices have provided significant opportunities to optimize the performance of the oxygen electrodes in both primary and rechargeable Zn-air batteries. In this review, we provide a comprehensive summary of the reported nanostructured carbon-based electrodes for advanced Zn-air batteries in terms of tailoring the oxygen-catalytic sites and designing carbon supports. The versatile synthetic strategies, characterization methods, and in-depth understanding of the relationships between the oxygen-catalytic sites/nanostructures and the oxygen electrode performance are systematically summarized. Furthermore, we also briefly outline recent progress in engineering flexible and high-power Zn-air batteries. Ultimately, a thorough discussion of current primary challenges and future perspectives on the rational design of nanostructured carbon-based oxygen electrodes is given, thus providing inspiration for the future prosperity of fast-kinetic and efficient Zn-air batteries in a broad range of energy fields.

Structure, Property, and Performance of Catalyst Layers in Proton Exchange Membrane Fuel Cells

Jian Zhao, Huiyuan Liu, Xianguo Li

2023, 6(2): 13. doi:10.1007/s41918-022-00175-1

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Catalyst layer (CL) is the core component of proton exchange membrane (PEM) fuel cells, which determines the performance, durability, and cost. However, difficulties remain for a thorough understanding of the CLs’ inhomogeneous structure, and its impact on the physicochemical and electrochemical properties, operating performance, and durability. The inhomogeneous structure of the CLs is formed during the manufacturing process, which is sensitive to the associated materials, composition, fabrication methods, procedures, and conditions. The state-of-the-art visualization and characterization techniques are crucial to examine the CL structure. The structure-dependent physicochemical and electrochemical properties are then thoroughly scrutinized in terms of fundamental concepts, theories, and recent progress in advanced experimental techniques. The relation between the CL structure and the associated effective properties is also examined based on experimental and theoretical findings. Recent studies indicated that the CL inhomogeneous structure also strongly affects the performance and degradation of the whole fuel cell, and thus, the interconnection between the fuel cell performance, failure modes, and CL structure is comprehensively reviewed. An analytical model is established to understand the effect of the CL structure on the effective properties, performance, and durability of the PEM fuel cells. Finally, the challenges and prospects of the CL structure-associated studies are highlighted for the development of high-performing PEM fuel cells.

Recent Advancements in Photoelectrochemical Water Splitting for Hydrogen Production

Yibo Zhao, Zhenjie Niu, Jiwu Zhao, Lan Xue, Xianzhi Fu, Jinlin Long

2023, 6(2): 14. doi:10.1007/s41918-022-00153-7

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Sunlight is the most abundant and inexhaustible energy source on earth. However, its low energy density, dispersibility and intermittent nature make its direct utilization with industrial relevance challenging, suggesting that converting sunlight into chemical energy and storing it is a valuable measure to achieve global sustainable development. Carbon–neutral, clean and secondary pollution-free solar-driven water splitting to produce hydrogen is one of the most attractive avenues among all the current options and is expected to realize the transformation from dependence on fossil fuels to zero-pollution hydrogen. Artificial photosynthetic systems (APSs) based on photoelectrochemical (PEC) devices appear to be an ideal avenue to efficiently achieve solar-to-hydrogen conversion. In this review, we comprehensively highlight the recent developments in photocathodes, including architectures, semiconductor photoabsorbers and performance optimization strategies. In particular, frontier research cases of organic semiconductors, dye sensitization and surface grafted molecular catalysts applied to APSs based on frontier (molecular) orbital theory and semiconductor energy band theory are discussed. Moreover, research advances in typical photoelectrodes with the metal–insulator–semiconductor (MIS) architecture based on quantum tunnelling are also introduced. Finally, we discuss the benchmarks and protocols for designing integrated tandem photoelectrodes and PEC systems that conform to the solar spectrum to achieve high-efficiency and cost-effective solar-to-hydrogen conversion at an industrial scale in the near future.

Interfacial Modification, Electrode/Solid-Electrolyte Engineering, and Monolithic Construction of Solid-State Batteries

Qirong Liu, Qiqi Chen, Yongbing Tang, Hui-Ming Cheng

2023, 6(2): 15. doi:10.1007/s41918-022-00167-1

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Solid-state lithium-metal batteries (SLMBs) have been regarded as one of the most promising next-generation devices because of their potential high safety, high energy density, and simple packing procedure. However, the practical applications of SLMBs are restricted by a series of static and dynamic interfacial issues, including poor interfacial contact, (electro-)chemical incompatibility, dynamic Li dendrite penetration, etc. In recent years, considerable attempts have been made to obtain mechanistic insight into interfacial failures and to develop possible strategies towards excellent interfacial properties for SLMBs. The static and dynamic failure mechanisms at interfaces between solid electrolytes (SEs) and electrodes are comprehensively summarized, and design strategies involving interfacial modification, electrode/SE engineering, and the monolithic construction of SLMBs are discussed in detail. Finally, possible research methodologies such as theoretical calculations, advanced characterization techniques, and versatile design strategies are provided to tackle these interfacial problems.

Overcoming the Electrode Challenges of High-Temperature Proton Exchange Membrane Fuel Cells

Quentin Meyer, Chujie Yang, Yi Cheng, Chuan Zhao

2023, 6(2): 16. doi:10.1007/s41918-023-00180-y

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Proton exchange membrane fuel cells (PEMFCs) are becoming a major part of a greener and more sustainable future. However, the costs of high-purity hydrogen and noble metal catalysts alongside the complexity of the PEMFC system severely hamper their commercialization. Operating PEMFCs at high temperatures (HT-PEMFCs, above 120 °C) brings several advantages, such as increased tolerance to contaminants, more affordable catalysts, and operations without liquid water, hence considerably simplifying the system. While recent progresses in proton exchange membranes for HT-PEMFCs have made this technology more viable, the HT-PEMFC viscous acid electrolyte lowers the active site utilization by unevenly diffusing into the catalyst layer while it acutely poisons the catalytic sites. In recent years, the synthesis of platinum group metal (PGM) and PGM-free catalysts with higher acid tolerance and phosphate-promoted oxygen reduction reaction, in conjunction with the design of catalyst layers with improved acid distribution and more triple-phase boundaries, has provided great opportunities for more efficient HT-PEMFCs. The progress in these two interconnected fields is reviewed here, with recommendations for the most promising routes worthy of further investigation. Using these approaches, the performance and durability of HT-PEMFCs will be significantly improved.

Recent Progress in and Perspectives on Emerging Halide Superionic Conductors for All-Solid-State Batteries

Kaiyong Tuo, Chunwen Sun, Shuqin Liu

2023, 6(2): 17. doi:10.1007/s41918-023-00179-5

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Rechargeable all-solid-state batteries (ASSBs) are considered to be the next generation of devices for electrochemical energy storage. The development of solid-state electrolytes (SSEs) is one of the most crucial subjects in the field of energy storage chemistry. The newly emerging halide SSEs have recently been intensively studied for application in ASSBs due to their favorable combination of high ionic conductivity, exceptional chemical and electrochemical stability, and superior mechanical deformability. In this review, a critical overview of the development, synthesis, chemical stability and remaining challenges of halide SSEs is given. The design strategies for optimizing the ionic conductivity of halide SSEs, such as element substitution and crystal structure design, are summarized in detail. Moreover, the associated chemical stability issues in terms of solvent compatibility, humid air stability and corresponding degradation mechanisms are discussed. In particular, advanced in situ/operando characterization techniques applied to halide-based ASSBs are highlighted. In addition, a comprehensive understanding of the interface issues, cost issues, and scalable processing challenges faced by halide-based ASSBs for practical application is provided. Finally, future perspectives on how to design high-performance electrode/electrolyte materials are given, which are instructive for guiding the development of halide-based ASSBs for energy conversion and storage.

Addressing Transport Issues in Non-Aqueous Li–air Batteries to Achieving High Electrochemical Performance

Zhuojun Zhang, Xu Xiao, Xingbao Zhu, Peng Tan

2023, 6(2): 18. doi:10.1007/s41918-022-00157-3

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Li–air batteries are a promising type of energy storage technology because of the ultra-high theoretical specific energy. Great advances are made in recent years, including the illustration of reaction mechanisms, development of effective catalyst materials, and design of battery structures accelerating species transport. However, the application still suffers from low rate capability, poor round-trip efficiency, and unsatisfactory cycling life. Herein, we mainly focus on the species transport issues of non-aqueous Li–air batteries, including Li⁺ across the solid surfaces and the electrolyte, O₂ solubility and diffusivity, distribution of intermediates and products, and side reactions by other components from the air. Besides, considerable emphasis is paid to expound the approaches for enhancing species transport and accelerating reactions, among which the realization of well-designed electrode structures and flowing electrolytes is of great significance for the rapid migration of O₂ and Li⁺ and mitigating the negative effects by solid insoluble Li₂O₂. Moreover, optimizing reaction interfaces and operating conditions is an attractive alternative to promote reaction rates. This work aims to identify the mechanism of transport issues and corresponding challenges and perspectives, guiding the structure design and material selection to achieve high-performance Li–air batteries.

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