Insight into the overpotentials of electrocatalytic hydrogen evolution on black phosphorus decorated with metal clusters

Abstract

Although the electrocatalytic hydrogen evolution reaction (HER) has great potential in energy conversion, the efficiency is limited by the reaction overpotential. Herein, the origin of thermodynamic overpotential in HER is studied systemically based on the proton-coupled electron transfer (PCET) theory. Metal clusters with different elements or sizes are combined with monolayer black phosphorus (BP@Mn) as model catalysts. The thermodynamic overpotentials in HER on BP@Mn originate from mainly electron transfer or concerted proton and electron transfer, which also constitutes the rate determining step. The redox potential of the rate determining step determines the efficiency of HER rather than the adsorption energy of H atoms, which also scales linearly with the LUMO state of the catalysts. In subsequent experiments, the turnover frequencies are observed to be in line with the activity trends derived theoretically. Among the different models, BP@Con exhibits the highest activity and smaller cluster exhibits higher catalytic ability. The results provide insights into the origin of thermodynamic overpotentials in HER and valuable guidance pertaining to the design of highly efficient electrocatalysts.