Creation of a Highly Active Pt/Pd/C Core-Shell-Structured Catalyst by Synergistic Combination of Intrinsically High Activity and Surface Decoration with Melamine or Tetra-(tert-butyl)-tetraazaporphyrin

A Pt/Pd/C core-shell-structured catalyst with an extraordinarily high activity of 3625 A g(-1)-Pt at 0.9 V versus a reversible hydrogen electrode (RHE) for the oxygen reduction reaction (ORR) was created by a synergistic combination of intrinsically high activity and surface decoration with melamine or tetra-(tert-butyl)-tetraazaporphyrin (tBuTAP). The intrinsically highly active Pt/Pd/C catalyst with an ORR mass activity of ca. 1000 A g(-1)-Pt at 0.9 V versus RHE was synthesized by a direct displacement reaction method, and the activity was activated to ca. 1500 A g(-1)-Pt via a high activation protocol (HAP) (a rectangular potential cycling of 0.05-1.0 V vs an RHE conducted in 0.1 mol dm(-3) HClO4 under an Ar atmosphere at 80 degrees C). The ORR activities of the Pt/Pd/C catalysts were further increased by surface decoration with melamine or tBuTAP, and the mass activity of ORR of the catalyst activated by an HAP was enhanced to 3625 A g(-1)-Pt at 0.9 V versus RHE via the melamine decoration, which is about 11-fold that of a reference Pt/C catalyst (320 A g(-1)-Pt). Cyclic voltammograms, linear sweep voltammograms, and CO stripping voltammograms indicated that the surface decoration further destabilized the OH species (OHad) adsorbed on the Pt shell and suppressed the formation of oxide on the Pt shell, which could explain the extraordinary enhancement of ORR activity. We present guidelines for creating Pt-based catalysts with extraordinarily high activity for the ORR by the synergistic combination of the intrinsically active Pt-based catalyst [improvement from the inside of Pt nanoparticles (NPs)] and surface decoration (improvement from the outside of Pt NPs).