Co-adsorption of cations causes the apparent pH dependence of hydrogen adsorption on a stepped platinum single-crystal electrode
Xiaoting Chen, Ian McCrum, Kathleen A. Schwarz, Michael Janik, Marc Koper
The successful deployment of advanced energy-conversion systems depends critically on our understanding of the fundamental interactions of the key intermediates (hydrogen and hydroxyl) at electrified metal-aqueous electrolyte interfaces. Herein, the effect of alkali metal cations (Li+, Na+, K+ and Cs+) on the non-Nernstian pH shift of the step-related voltammetric peak of the Pt(553) electrode is investigated over a wide pH window (1~13) by means of experimental and computational methods. Our results show that the co-adsorbed alkali cations along the step weaken the OH adsorption at the step sites, causing a positive shift of the potential of the step- related peak on Pt(553). Density functional theory calculations explain our observations on the identity and concentration of alkali cations on the non-Nernstian pH shift, and provide definite proof that cation-hydroxyl co-adsorption causes the apparent pH dependence of hydrogen adsorption in the step sites of platinum electrodes.