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

摘要

The enhancement of oxygen reduction reaction (ORR) on platinum nanoparticles (Pt NPs) was examined by changing transition metal oxide support for Pt NPs. In order to use transition metal oxide having low electron conductivity as electrocatalyst support materials, thin the transition metal oxides were formed on cup-stacked carbon nanotube (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. 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 TiNbO_x (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.