Towards Establishing Apparent Hydrogen Binding Energy as the Descriptor for Hydrogen Oxidation/Evolution Reactions

This perspective article formalizes our proposal that the apparent hydrogen binding energy (HBEapp), which takes into account of the water adsorption energy as well as the intrinsic hydrogen binding energy (HBE) on metal surfaces, is the descriptor for hydrogen oxidation/evolution reactions (HOR/HERs). We show that the HBEapp, not HBE, is pH dependent and can be determined from the underpotential-deposited hydrogen peaks in cyclic voltammograms for platinum group metals including Pt, Ir, Pd, and Rh, and the decrease of their HOR/HER activities with pH is the result of a strengthened HBEapp due to a weakened water adsorption. Also discussed are the needs of further experimental and theoretical work to prove this hypothesis. (C) The Author(s) 2018. Published by ECS.