The Effect of Noncovalent Interactions on the HOR, ORR, and HER on Ru, Ir, and Ru0.50Ir0.50 Metal Surfaces in Alkaline Environments

Abstract

The role of noncovalent interactions in the hydrogen oxidation reaction (HOR), oxygen reduction reaction (ORR), and hydrogen evolution reaction (HER) on Ru, Ir, and Ru0.5Ir0.5 electrodes is studied in alkaline solution containing K+, Li+, and Ba2+ cations. We found that noncovalent interaction between hydrated cations and covalently bonded OHad increases in the same order as specific charge density of the corresponding cation (K+ < Li+ < Ba2+). This interaction is also found to cause an increase in the density of OHad·····Mn+(H2O)x clusters in the compact part of double layer. The trend in interaction strengths is inversely proportional to the activity of the HOR and ORR, which suggests that the clusters “block” the metal active sites necessary for the adsorption of H2 and O2. In the case of the HER, however, we demonstrate that the activity is directly proportional to the strength of these noncovalent interactions. To explain this behavior, we suggest that the hydrated cations affect the rate of the water dissociation step which increases in the order K+ < Li+ < Ba2+.