Temperature Dependence of Oxygen Reduction Reaction Activity at Stabilized Pt Skin-PtCo Alloy/Graphitized Carbon Black Catalysts Prepared by a Modified Nanocapsule Method

Abstract

We have developed a new catalyst supported on graphitized carbon black (GCB), which exhibits higher resistance to carbon corrosion than a conventional carbon black (CB), in order to favor both high mass activity for the oxygen reduction reaction (ORR) and high durability. To protect the underlying Pt(X)Co alloy from corrosion and maintain the modified electronic structure, two monolayers of Pt-skin layer (Pt(2ML)) were formed on the Pt(X)Co core-particles, which were of uniform size and composition. Characterization of the Pt(2ML)-PtCo(X = 1)/GCB, both by a scanning transmission electron microscope (STEM) with an energy dispersive X-ray (EDX) analyzer and by X-ray diffraction (XRD), indicated the formation of the Pt(2ML) on the PtCo alloy solid solution nanoparticles. The temperature dependence of the ORR activity of the Pt(2ML)-PtCo((2nm))/GCB catalyst was evaluated from the hydrodynamic voltammograms in O(2)-saturated 0.1 M HClO(4) solution at 30-90 °C by the channel flow double electrode (CFDE) technique. It was found that the Co dissolution from PtCo particles during the ORR was considerably suppressed by the stabilized Pt-skin structure. The kinetically controlled mass activity (MA(k)) for the ORR at the Pt(2ML)-PtCo((2nm))/GCB at E = 0.85 V vs reversible hydrogen electrode (RHE) was about two times larger than that for a standard commercial c-Pt/CB catalyst at 80-90 °C. The value of H(2)O(2) yield at the Pt(2ML)-PtCo((2nm))/GCB was found to be very low (0.2%), about one-half of that for c-Pt/CB, and it is thus better able to mitigate the degradation of the polymer electrolyte membrane and gasket material.