Application of solid electrolytes in electrochemical reduction of CO₂ or O₂

Electrochemical conversion of abundant CO₂/O₂ into value-added products and fuels holds great promise to achieve sustainable energy systems. In most cases, aqueous electrolyte containing salts are used, inevitably suffering subsequent purification if pure products needed for further purpose. Instead, the application of solid electrolyte has seen a booming and that thought to be commercially attractive. Nevertheless, there is a scarcity of comprehensive reviews focusing exclusively on the application of solid electrolytes in electrochemical CO₂/O₂ reduction, in contrast to the more readily available reviews on battery technologies. In this manner, we review recent advance and challenges in the understanding electrochemical reduction of CO₂/O₂ using solid electrolytes to produce high valuable chemicals like H₂O₂, formic acid, etc. It begins with a brief introduction of historical development of solid electrolyte and their properties. Then it followed with summarizing of its application used in oxygen reduction reaction (ORR) by power consuming mode (2e^--ORR), or by power generating mode in fuel-cell. Afterward, diverse type of solid electrolytes has been systemically reviewed, including the corresponding cells, the production rate along with different roles in electrochemical CO₂ reduction. Finally, challenges and prospects of solid electrolytes are discussed, aiming to guide a promising direction for directly producing high-value chemicals in near future.