Catalysis of oxygen reduction on Au modified by Pd nanoislands in perchloric acid solution

Abstract

Oxygen reduction reaction (ORR) was studied on polycrystalline gold, Au(poly), modified by nanosized palladium islands in 0.1 M HClO4 solution using rotating disc electrode technique. Paladium was spontaneously deposited from 1 mM PdSO4 center dot 2H(2)O + 0.5 M H2SO4 solution for various deposition times at a submonolayer coverage. Topography of obtained Pd/Au(poly) surfaces was observed by tapping mode atomic force microscopy (AFM), while chemical surface composition changes were detected by simultaneously performed phase AFM. Deposited Pd islands were nonuniform in size and randomly distributed over the gold substrate. Size and number of Pd islands increase with the increase of the deposition time, and consequently surface coverage increases too. Deposited Pd was also identified by the changes in cyclic voltammetry (CV) profiles from which an active surface area was estimated. Obtained Pd/Au(poly) surfaces have shown a significant catalytic activity towards oxygen reduction reaction which increases with the increase of Pd islands coverage. The initial potential of ORR was shifted positively, while reaction pathway changes from 2e-reduction on pure gold to 4e-reduction on Pd modified gold. Additionally, obtained Pd/Au(poly) surfaces have shown a significant activity towards hydrogen peroxide reduction (HPRR), which appear as an intermediate during ORR. This supports the assumption that ORR on Pd/Au(poly) occurs partly through 4e-series reduction pathway, the fraction of which increases with the increase of Pd coverage.