Polyoxometalate as a Nature-Inspired Bifunctional Catalyst for Lithium-Oxygen Batteries

Abstract

Nature-inspired molecules present a family of affordable, environmentally friendly catalysts to enable and enhance next-generation energy storage systems. In this study, we report the use of cobalt-based polyoxometalates (Co-POMs) with an oxo-bridged tetracobalt active site, which is reminiscent of the natural oxygen-evolving complex, as an efficient and stable redox catalyst for Li-O2 batteries. Interestingly, Co-POMs exhibit catalytic activity for both oxygen evolution and reduction reactions (OER and ORR, respectively) under a certain condition when it forms a stable dispersion of molecular aggregates, which can be controlled by the types of electrolyte solvents and exposure to light. As a result of the optimized OER/ORR bifunctional activity, Li-O2 cells facilitated by Co-POM redox reactions successfully achieve improved efficiency and a longer cycle life in comparison to reference cells. The reversibility of the Li-O2 reactions in the presence of the bifunctional Co-POM catalysts is confirmed by ex situ characterizations.