Universal Dependence of Hydrogen Oxidation/Evolution Reaction Activity on pH and Hydrogen Binding Energy

Hydrogen oxidation/evolution reactions (HOR/HER) are among the most important and most studied reactions for a wide range of applications including H₂-fueled low temperature fuel cells, electrolyzers and photoelectrochemical cells. In particular, the sluggish HOR/HER reaction kinetics on Pt in base - two orders of magnitude slower than that in acid - is a substantial challenge for the development of hydroxide exchange membrane fuel cells (HEMFCs).  To this end, a fundamental understanding of key factors that determine the electrocatalytic performance is essential to the rational design of efficient HOR/HER catalysts in base. We systematically investigate the pH-dependence of HBE and HOR/HER activity on carbon supported platinum group metals (supported Pt, Ir, Pd and Rh nanoparticles), and quantitatively correlate the exchange current density with the HBE of the corresponding metal in electrolyte with different pH. A universal linear correlation of HBE, determined by cyclic voltammograms (CVs) in a broad pH range, indicating that the influence of pH on HBE is independent of catalytic materials.