Single-Atom Platinum Sites with Asymmetric Coordination Environment on Fully Conjugated Covalent Organic Framework for Efficient Electrocatalysis

Abstract Two-dimensional (2D) covalent organic frameworks (COFs) and their derivatives have been applied as electrocatalysts towards a wide range of reactions owing to their unique nanoscale pore configurations, stable periodic structures, abundant coordination sites and high surface area. This work aims to construct the first non-thermodynamically stable Pt-N2 coordination active site through electrochemically modifying platinum (Pt) single atoms into fully conjugated 2D COF as conductive agent-free and pyrolysis-free electrocatalyst for hydrogen evolution reaction (HER). In addition to maximizing atomic utilization, single-atom catalysts with definite structures can be used to investigate catalytic mechanisms and structure-activity relationships. A series of physical characterizations, theoretical calculations and in-situ experiments demonstrate that NGA-COF not only provide favorable metal-support effect for Pt, but also enhance electron transport ability and structural stability. The former can adjust the binding energy between active sites to H* intermediate by forming unique Pt-N2 instead of the mainstream Pt-N4 coordination environment. The latter is ascribed to its unique stability in acidic environments.