Effects of Li+, K+, and Ba2+ Cations on the ORR at Model and High Surface Area Pt and Au Surfaces in Alkaline Solutions

This Letter reveals new findings on the influence of noncovalent interactions on the electrochemical interface. Using surface X-ray scattering, we demonstrate that the barium cations are located at 3.4 A away from the surface, suggesting that they are partially hydrated, though not adsorbed at the surface. The effect of the cation on the oxygen reduction reaction (ORR) ranges from significant (Pt) to little (Au), depending on the nature of the metal and cation. Finally, we show that these results, as obtained on well-defined single-crystal surfaces, correlate well with observations on high surface area nanoparticle catalysts.