Routes to Bidirectional Cathodes for Reversible Aprotic Alkali Metal-CO Batteries.

Aprotic alkali metal-CO batteries (AAMCBs) have garnered significant interest owing to fixing CO and providing large energy storage capacity. The practical implementation of AAMCBs is constrained by the sluggish kinetics of the CO reduction reaction (CORR) and the CO evolution reaction (COER). Because the COER and CORR take place on the cathode, which connects the internal catalyst with the external environment. Building a bidirectional cathode with excellent COER and CORR kinetics by optimizing the cathode's internal catalyst and environment has attracted most of the attention to improving the electrochemical performance of AAMCBs. However, there remains a lack of comprehensive understanding. This review aims to give a route to bidirectional cathodes for reversible AAMCBs, by systematically discussing engineering strategies of both the internal catalyst (atomic, nanoscopic, and macroscopic levels) and the external environment (photo, photo-thermal, and force field). The COER and CORR mechanisms and the "engineering strategies from internal catalyst to the external environment-cathode properties-CORR and COER kinetics and mechanisms-batteries performance" relationship are elucidated by combining computational and experimental approaches. This review establishes a fundamental understanding for designing bidirectional cathodes and gives a route for developing reversible AAMCBs and similar metal-gas battery systems.