Tuning of D-Band Center of Platinum Nanoparticles By Changing Transition Metal Oxide Support Materials for Enhancement of Oxygen Reduction Reaction (2)

Abstract

The enhancement of oxygen reduction reaction (ORR) on platinum nanoparticles (Pt NPs) was examined by changing transition metal oxide as a support material for Pt NPs. In order to use transition metal oxide having low electron conductivity as electrocatalyst support materials, thin transition metal oxide supports were formed on cup-stacked carbon nanotubes (CSCNT). In addition, mixed transition metal oxides having various ratios of two transition metal ions were prepared to produce continuous changes in the electron state (d-band center) of Pt NPs that was interacted electrically with the mixed transition metal oxides. The ORR activity measured in an acidic aqueous solution depended on the kinds of the metal oxide supports. The plot of the d-band center of Pt NPs deposited on the metal oxides vs. their ORR activity showed a volcano shape. That is, the volcano plot could be drawn by changing the support materials for the first time and maximum ORR activity could be observed at an optimized level of the d-band center. The metal oxide of TiNbOx (Ti:Nb = 1:6.6) could produce the optimized d-band level and could reach the ORR activity to the maximum activity. It was made clear from X-ray photoelectron spectroscopy (XPS) measurements that the d-band center could be down-shifted moderately by donation of electron from the metal oxide supports to Pt NPs for enhancing the ORR. Figure 1. Schematic illustrations of (A-E) preparation of Pt NPs/metal oxide/CSCNT samples and possible positions of Pt NPs deposited on metal oxides and contacted with metal oxides. Figure 1