Engineering the interfacial orientation of MoS 2 /Co 9 S 8 bidirectional catalysts with highly exposed active sites for reversible Li-CO 2 batteries.

Sluggish CO 2 reduction reaction (CO 2 RR) and evolution reaction (CO 2 ER) kinetics at cathodes seriously hamper the applications of Li-CO 2 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 CO 2 redox, but how to achieve a high exposure of dual active sites of TMDs with CO 2 RR/CO 2 ER activities remains a challenge. Herein, a bidirectional catalyst that vertically growing MoS 2 on Co 9 S 8 supported by carbon paper (V-MoS 2 /Co 9 S 8 @CP) has been designed with abundant edge as active sites for both CO 2 RR and CO 2 ER, 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-CO 2 batteries with V-MoS 2 /Co 9 S 8 @CP show superior performance compared with horizontally growing MoS 2 on Co 9 S 8 (H-MoS 2 /Co 9 S 8 @CP), MoS 2 @CP, and Co 9 S 8 @CP. Density functional theory calculations help reveal the relationship between performance and structure and demonstrate the synergistic effect between MoS 2 edge sites and Co 9 S 8 . 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-CO 2 batteries.