Exfoliated 2D Layered and Nonlayered Metal Phosphorous Trichalcogenides Nanosheets as Promising Electrocatalysts for CO 2 Reduction.

Two-dimensional (2D) materials catalysts provide an atomic-scale view on a fascinating arena for understanding the mechanism of electrocatalytic carbon dioxide reduction (CO 2 ECR). Here, we successfully exfoliated both layered and nonlayered ultra-thin metal phosphorous trichalcogenides (MPCh 3 ) nanosheets via wet grinding exfoliation (WGE), and systematically investigated the mechanism of MPCh 3 as catalysts for CO 2 ECR. Unlike the layered CoPS 3 and NiPS 3 nanosheets, the active Sn atoms tend to be exposed on the surfaces of nonlayered SnPS 3 nanosheets. Correspondingly, the nonlayered SnPS 3 nanosheets exhibit clearly improved catalytic activity, showing formic acid selectivity up to 31.6 % with -7.51 mA cm -2 at -0.65 V vs. RHE. The enhanced catalytic performance can be attributed to the formation of HCOO* via the first proton-electron pair addition on the SnPS 3 surface. These results provide a new avenue to understand the novel CO 2 ECR mechanism of Sn-based and MPCh 3 -based catalysts.