The increasingly severe energy crisis and environmental problems lead to the rapid development of renewable energies and their higher proportion in the energy-supply structure. The research and development of large-scale energy storage technologies are the keys to realize the wide utilization of renewable energies, because which have the unstable, discontinuous, and uncontrollable characteristics. Bromine-based flow batteries (Br-FBs) have been one of the most promising energy storage technologies with attracting advantages of low price, wide potential window, and long cycle life. However, Br-FBs suffer from the sluggish kinetics of Br2/Br- redox couple and serious self-discharge, which hinder the further commercialization and industrialization of Br-FBs. Electrode, one of the critical components in a Br-FB, provides the reaction sites for redox couples and exerts a significant effect on the performance of Br-FBs. In a research paper recently published in Energy Material Advances, Xianfeng Li et al. from Dalian Institute of Chemical Physics overviewed the properties, advantages, and disadvantages of different types of cathode materials for Br-FBs and summarized relevant modification approaches, providing comprehensive and available instructions to develop high-performance cathodes for high-power density and long-lifespan Br-FBs.
The authors first compared the commonly used cathode materials for Br-FBs, which were classified as metal-based compounds, such as Pt, and carbon-based materials, such as carbon felts (CFs) and graphite felts (GFs). In point of metal-based materials, except for some precious metals and oxides, most metals and metal oxides are unstable in the presence of highly corrosive bromine. So far, metal-based cathode materials currently available for Br-FBs are Pt, TiN, ZrOx, TiOx, WOx, etc. Carbon-based materials have been widely used as cathode materials of Br-FBs, because their electrochemical activity can be enhanced by regulating the internal structure and surface properties. At present, porous carbon fiber-based materials, especially CFs and GFs, are the most commonly used cathodes in Br-FBs due to their low price, good electronic conductivity, outstanding corrosion resistance as well as controllable surface properties.
Afterwards, the authors concentrated on the modification methods of CFs and GFs, including surface treatment and surface modification. The surface treatment is to construct intrinsically porous structures on the electrode surface by oxidizing etching, which can increase the specific surface area and introduce catalytic functional groups. However, surface treatment is used as a pretreatment method upon most occasions because of uncontrollable distribution of pores and deteriorated mechanical properties. Different from surface treatment, surface modification is to increase the electrochemical activity and hydrophilicity of the electrodes by introducing active materials. Based on the properties of introduced active materials, surface modifications can be classified as the metallic element modification, the nonmetallic element modification, and the structure decoration. Metallic element modification costs much and the modifier is not stable enough in Br-FBs. As for the nonmetallic element modification, although element doping contributes to improved activity and good wettability, the modified electrodes suffer from poor mechanical stability and nonuniform element distribution. Notably, the commonly used CF/GF-based electrode materials have good electronic conductivity and adjustable structure. As a result, to regulate the structures of the electrode by the structure decoration method is useful and has been commonly used to enhance the performance of cathodes of Br-FBs.
Finally, the authors summarized and prospected the future development directions of Br-FBs cathodes. The development of cathode materials with high activity, stability and bromine fixing/retention ability is significant to deal with the technical bottlenecks of low power density and serious self-discharge of Br-FBs. Thus, there still exists a huge potential for the development of advanced cathode materials of Br-FBs and further research on the mechanisms of Br2/Br- reactions. The further development directions are as follows:
(i). To continually develop advanced electrodes of Br-FBs with high activity and bromine retention capacity by enhancing their chemical surfaces and improving their physical structures.
(ii). The reaction mechanisms on the electrode are not clear and need in-depth investigations.
(iii) To improve the bromine fixing/retention capacity of electrodes by structural design, namely, to inhibit the diffusion and migration of bromine species to the negative side.
The National Natural Science Foundation of China (Grant No. 21206158), Key Project of Frontier Science, CAS (QYZDBSSW-JSC032), DICP funding (DICP I202026 and DICP I201928), and Liaoning Natural Science Foundation supported this work.
Reference
Authors: Luyin Tang,1,2Wenjing Lu,1 Huamin Zhang,1 and Xianfeng Li1
Title of original paper: Progress and Perspective of the Cathode Materials towards Bromine-Based Flow Batteries
Journal: Energy Material Advances
Affiliations:
1Division of Energy Storage, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Zhongshan Road 457, Dalian 116023, China
2University of Chinese Academy of Sciences, Beijing 100049, China
About the authors:
Dr. Luyin Tang received her BSc degree from Anhui University in 2019. She currently is a PhD student under the supervision of Prof. Xianfeng Li at Dalian Institute of Chemical Physics (DICP), Chinese Academy of Sciences (CAS). Her research focuses on composite electrodes for zinc-bromine flow batteries.
Dr. Wenjing Lu is an associate professor of Dalian Institute of Chemical Physics (DICP), Chinese Academy of Sciences (CAS). She mainly focuses on the research of the key materials of vanadium flow batteries and zinc-bromine flow batteries, including the membranes and the electrodes. Up to now, she has published many SCI papers in Chem. Soc. Rev、Energy Environ. Sci、Adv. Mater、ACS Energy Lett、Adv. Funct. Mater、Energy Storage Materials and so on.
Dr. Huamin Zhang currently serves as a full professor at Dalian Institute of Chemical Physics (DICP), Chinese Academy of Sciences (CAS). He was awarded "Ten Thousand Talent Program of the Organization Department of the Central Committee of the CPC". He is also CTO of Dalian Rongke Power Co., Ltd. He has received several awards including "Science &Technology for Development Award of the Chinese Academy of Sciences (Ranked First)", "2015 State Technological Invention Award (Ranking Third)" and Contribution Award of China Electrochemical. His research interests involve the topics of energy and energy storage, fuel cells, flow batteries, and batteries with a high specific energy density. He has co-authored more than 400 research papers published in peer-reviewed journals and more than 300 patents.
Prof. Dr. Xianfeng Li currently serves as Vice-Director of Dalian institute of Chemical Physics, Chinese Academy of Sciences and the Head of Energy Storage Division. He was awarded National Science Fund for Distinguished Young Scholars, "Technology Innovation Leading Talents" of Ten Thousand Talent Program of the Organization Department of the Central Committee of the CPC, etc. He has received several awards including "Science &Technology for Development Award of the Chinese Academy of Sciences (Ranked First)", "2015 State Technological Invention Award (Ranking Third)" and "Outstanding Science and Technology Achievement Prize of the Chinese Academy of Sciences (Ranked Second)". His research interests mainly focus on the electrochemical energy storage technologies, including vanadium flow batteries at generation side, zinc-based flow batteries at utilization side, and novel flow battery systems with high energy density and low cost. Up to now, he has published more than 250 SCI papers, among which, 100 papers with an IF of over 10 were published in Joule., J. Am. Chem. Soc., Energy Environ. Sci., Angew. Chem. Int. Ed., Nat. Commun. and so on. And the total citation times exceeded 10000 times. Now, his H-factor is 63. Furthermore, the applicant was authorized more than 200 patents including 8 international patents and 15 technology transfer licenses. He currently serves as the editorial member of J. Membr. Sci. Lett., Sci. Bull., J Energy Chem., Sustainable Energy & Fuels (RSC) and so on, together with the associate editor of Chinese Chem Lett., Adv. Membr.，and Renewables.
