Enhanced Electrocatalysis of Oxygen Reduction on Pt/TaOx/GC

Here we demonstrate a remarkable enhancement of oxygen reduction reaction (ORR) activity on a novel Pt/TaOx/GC electrocatalyst where at first tantalum oxide (TaOx) and next Pt were deposited electrochemically on a glassy carbon (GC) surface. An excellent electrocatalytic activity of the Pt/TaOx/GC electrocatalyst for ORR was found to be more than 12 times that of the unmodified Pt/GC one as evaluated from the kinetic currents at 0.80 V. SEM images showed no significant differences in the size and distribution of Pt nanoparticles between these two electrocatalysts, indicating that these are not factors causing the observed ORR activity. The spillover of oxygen-containing species resulting from the electronic interaction between Pt and TaOx, which is evidently demonstrated from the XPS analysis, is strongly suggested as the crucial factor for the ORR enhancement. Interestingly, the spillover effect also results in a remarkable increase in the electrochemically active "apparent" surface area of Pt on the Pt/TaOx/GC electrocatalyst. Moreover, the rotating ring-disk electrode voltammetric measurements obviously showed the increase in limiting current as well as the decrease in ring current on this novel electrocatalyst relative to the unmodified one, confirming a complete four-electron reduction pathway. On the basis of these findings a plausible mechanism has been proposed for the observed enhancement in ORR where the role of TaOx is to reduce the formation of OH on the Pt surface by spillover effect and to promote d orbital vacancy of Pt for oxygen adsorption by electron donation to Ta.