The effect of rhodium nanoislands on the electrocatalytic activity of gold for oxygen reduction in perchloric acid solution

The effect of spontaneously deposited rhodium nanoislands on the electrocatalytic activity of polycrystalline gold, Au(poly), for oxygen reduction reaction (ORR) was studied using rotating disc electrode technique in 0.1 M HClO4 solution. Surface topography atomic force microscopy (AFM) images of obtained Rh/Au(poly) surfaces revealed that both the size and coverage of rhodium nanoislands increase with the deposition time, for a given depositing conditions. The exact values of rhodium coverage ranging from 50% to the full coverage, and the qualitative changes in the surface chemical composition with respect to bare gold were estimated from phase AFM images. Deposited Rh was also identified by the changes in cyclic voltammetry (CV) profiles from which potential limits for ORR were determined. Obtained Rh/Au(poly) surfaces have shown a significant shift of the initial potential for ORR to the more positive potentials with respect to pure gold already for 50% Rh coverage, indicating that a pronounced electronic effect is responsible for the lowering of the activation energy for oxygen adsorption. The initial potential increases only slightly with the further increase of Rh coverage. Reaction pathway changes from 2e− reduction at lower overpotentials to a partial 4e− reduction at higher overpotentials. The later is attributed to the increased activity of obtained Rh/Au(poly) surfaces towards hydrogen peroxide reduction (HPRR), which appear as an intermediate during ORR. The fraction of 4e− reduction slightly increases with the increase of Rh coverage.