Effect of the d-Band Center on the Oxygen Reduction Reaction Activity of Electrochemically Dealloyed Ordered Intermetallic Platinum–Lead (PtPb) Nanoparticles Supported on TiO2-Deposited Cup-Stacked Carbon Nanotubes

The electrocatalysis of PtPb ordered intermetallic nanoparticles (NPs)-deposited TiO2/cup-stacked carbon nanotube (PtPb NPs/TiO2/CS) catalysts for oxygen reduction reaction (ORR) was examined in 0.1 M HClO4 aqueous solution. The as-prepared catalyst exhibited only a low activity for the ORR, but its ORR activity was found to be largely enhanced by the electrochemical dealloying, i.e., by the dissolution of Pb via a repeating potential scan cycling between 0.05 and 1.1 V vs RHE at 100 mVs–1 in N2-saturated 0.1 M HClO4 aqueous solution, and to change drastically via a surface structural change of the PtPb NPs from the PtPb ordered intermetallic structure to the Pt3Pb ordered intermetallic structure and further to the Pt3Pb(core)–Pt(shell) structure with an increase in the potential scan cycling. We also found that changing the number of the potential scan cycling leads to a change in the d-band center of the resulting catalyst, and consequently, a so-called volcano-type corelationship between ORR activity and the d-band center was found to hold for a series of the electrochemically dealloyed PtPb NPs/TiO2/CS catalysts. The maximum ORR activity was obtained for the Pt3Pb catalyst prepared by the 200 cycles of potential scan cycling, the d-band center value of which is ca. 0.2 and 0.3 eV lower than those of the Pt NPs deposited on TiO2/CS (Pt NPs/TiO2/CS) and the Pt NPs deposited on carbon black (Pt NPs/CB), respectively, being in agreement with the expectation for the ORR electrocatalysis of Pt-based catalysts ( Angew. Chem., Int. Ed. 2006, 45, 2897？2901)