Engineering the interfacial orientation of MoS₂/Co₉S₈ bidirectional catalysts with highly exposed active sites for reversible Li-CO₂ batteries.

Abstract

Sluggish CO₂ reduction reaction (CO₂RR) and evolution reaction (CO₂ER) kinetics at cathodes seriously hamper the applications of Li-CO₂ batteries, which have attracted vast attention as one kind of promising carbon-neutral technology. Two-dimensional transition metal dichalcogenides (TMDs) have shown great potential as the bidirectional catalysts for CO₂ redox, but how to achieve a high exposure of dual active sites of TMDs with CO₂RR/CO₂ER activities remains a challenge. Herein, a bidirectional catalyst that vertically growing MoS₂ on Co₉S₈ supported by carbon paper (V-MoS₂/Co₉S₈@CP) has been designed with abundant edge as active sites for both CO₂RR and CO₂ER, improves the interfacial conductivity, and modulates the electron transportation pathway along the basal planes. As evidenced by the outstanding energy efficiency of 81.2% and ultra-small voltage gap of 0.68 V at 20 μA cm^-2, Li-CO₂ batteries with V-MoS₂/Co₉S₈@CP show superior performance compared with horizontally growing MoS₂ on Co₉S₈ (H-MoS₂/Co₉S₈@CP), MoS₂@CP, and Co₉S₈@CP. Density functional theory calculations help reveal the relationship between performance and structure and demonstrate the synergistic effect between MoS₂ edge sites and Co₉S₈. This work provides an avenue to understand and realize rationally designed electronic contact of TMDs with specified crystal facets, but more importantly, provides a feasible guide for the design of high-performance cathodic catalyst materials in Li-CO₂ batteries.