Volmer/Heyrovsky-Dominated Hydrogen Evolution on Pt–N–C Single Sites Triggered by Negatively Charged Adsorbed Hydrogen: A Theoretical Insight

Pt–N–C single-site catalysts (SSCs) have presented extraordinary hydrogen evolution reaction (HER) activity with 100% Pt utilization, but the origin of activity remains unclear due to the diversity of their configurations, hydrogen adsorption modes, and HER routes thereof. Herein, the HER thermodynamics and kinetics on up to 19 typical Pt–N–C sites were systematically examined by a constant electrode potential (CEP) first-principles method with the multi-H atom adsorption modes, in association with the working conditions of the electrode potential and acidic aqueous environment. The negatively charged H atom (Hδ−) with near-zero adsorption energy is found to be the key to achieving fast HER kinetics, and four highly active sites were screened out. The Hδ− is formed on the para position of C or H ligands and stabilized by N ligands. Moreover, our study indicates the Volmer/Heyrovsky-dominated HER mechanism for Pt–N–C SSCs, different from the generally accepted Tafel-dominated mechanism. This study demonstrates the impact of unique adsorption modes of SSCs on the mechanism and activity of HER, and it offers an indicator of Hδ− to design highly active SSCs.