A review on recent advances and trends in symmetrical electrodes for solid oxide cells

Abstract

Symmetrical solid oxide cells (SSOCs) with identical air and fuel electrodes have gained significant scientific interest in the last decade because they offer several advantages over conventional cell configurations. Among other features, simpler fabrication, better chemical and thermo-mechanical compatibility between cell layers, and electrode reversibility, make them attractive for electricity generation, H 2 production and CO 2 electroreduction. This review offers an overview of the most recent advances in the field of SSOCs, paying special attention to the relationship between electrode composition, crystal structure and properties. With that aim, symmetrical electrodes are classified in four groups according to their redox stability, i.e. single phases, composites, electrodes with exsolved metal particles and those that suffer a drastic phase transformation under reducing conditions, known in the literature as quasi-symmetrical electrodes. Furthermore, an outlook of other cell configurations with increased scientific interest are also discussed, i.e. symmetrical protonic fuel cells (H–SSOCs) and solid oxide electrolyzers for CO 2 electroreduction. With this overview in mind, the authors would like to highlight the challenge ahead of finding electrode materials that optimally work under both oxidizing and reducing conditions in terms of redox stability and electrochemical properties, and further conclude on the future development of SSOCs. • Symmetrical solid oxide fuel cells with identical air and fuel electrodes are reviewed. • The state-of-the-art and future perspectives of SSOFCs and SSOECs are provided. • Doping strategies, structure, microstructure and electrochemical properties of electrodes are discussed. • This review will be helpful for the development of new symmetrical electrodes.