Electrolyte pH-dependent hydrogen binding energies and coverages on platinum, iridium, rhodium, and ruthenium surfaces

Abstract

The strong pH-dependent hydrogen evolution and oxidation reaction kinetics on platinum-group metal surfaces has persisted as an unsolved enigma for several decades. To better understand this issue, we apply surface-enhanced infrared absorption spectroscopy to directly monitor the vibrational wavenumbers and band areas of adsorbed H atoms on platinum, iridium, rhodium, and ruthenium surfaces in both strong acidic and alkaline media. It is reported for the first time that the H binding strength and its coverage decreases and increases, respectively, from acidic to alkaline environments on all four metals, which are important factors in determining the hydrogen electrocatalysis kinetics. This work supplements molecular-level information of H adsorption behavior in different electrolyte environments that is of great importance to further understanding the hydrogen electrocatalysis mechanisms.