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

摘要

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_xCo alloy from corrosion and maintain the modified electronic structure, two monolayers of Pt-skin layer (Pt_(2 ML)) were formed on the Pt_xCo core-particles, which were of uniform size and composition. Characterization of the Pt_(2 ML)-PtCo(X = l)/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_(2 ml) on the PtCo alloy solid solution nanoparticles. The temperature dependence of the ORR activity of the Pt_(2 ML)-PtCo_(2 nm)/GCB catalyst was evaluated from the hydrodynamic voltammograms in Cysaturated 0.1 M HClO4 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_(2 ML)-PtCo_(2 nm)/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 H2O2 yield at the Pt2 ml-PtCo_(2 nm)/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.