On the oxygen reduction reaction catalyzed by Ti –Cu binary films in 0.5 M sulfuric acid solution

Abstract

Ti–Cu binary films co-sputtered in vacuum are catalytically active for the oxygen reduction in 0.5 M H 2SO 4. The activity for the oxygen reduction reaction (ORR) increased with increasing the Cu-content in the Ti–Cu films and it reached to a maximum with the copper composition up to 90 at.%. The constant Tafel slope of ~ 190 mV/decade which is comparable to that obtained on pure Cu films indicates that the active sites for oxygen reduction is copper sites. Through investigation of Tafel polarization, the Ti–Cu films revealed a constant Tafel slope (i.e., 190 mV/decade) similar to that of ORR on the pure Cu film. This infers that the electrochemical reduction of oxygen is predominated on the Cu-sites in the film. In the cyclic voltammograms, the strong broad peak should have arisen from the oxidation of Cu to Cu + and Cu 2+ ions. This oxidation indicated that the Ti–Cu films are unstable and the Cu-component is susceptible to dissolution in 0.5 M H 2SO 4. This dissolution caused a loss of catalytic activity in the films. Preparing the Ti–Cu films enriched in Ti will stabilize these films to prevent the Cu-dissolution.