Relationship Between ORR Catalytic Activity and D-Band Center of Pt Nanoparticle Deposited on Metal Oxide Support Materials

Abstract

Platinum nanoparticles (Pt NPs) have been selectively anchored by photodeposition on titanium oxide (TiO2) matrix which is formed by hydrolysis of titanium isopropoxide on cup–stacked carbon nanotubes (CSCNT) in isopropanol, producing the composite Pt catalyst useful for oxygen reduction reaction (ORR) in acidic media, i.e., Pt NPs/TiO2/CSCNT. Using scanning transmission electron microscopy (STEM) with a high–angle annular–dark–field (HAADF) detector it has been clarified that Pt NPs are sunk into the TiO2 moieties and have the unique polyhedral shape surrounded mainly by the Pt (1 1 1) and Pt (1 0 0) facets. X–ray photoelectron spectroscopy (XPS) allowed us to confirm changes in electronic properties of both Pt NPs and TiO2 support, induced by the so-called strong metal–support interactions (SMSI) and the significantly increased ORR activity was attained in 0.1 M HClO4, compared with the Pt NPs deposited on CB (Vulcan carbon) and CSCNT. The surface structure of the Pt NPs was characterized by transmission electron microscopy (TEM), indicating the improved durability of the Pt NPs deposited on the TiO2/CSCNT, i.e., the only slight increase in the particle size after the durability test (typically 2000 times’ potential cycling at 10 mV s-1 in the potential ranges of 0.05 to 1.1 V and 1.0 to 1.5 V vs. RHE in 0.1 M HClO4). The results obtained demonstrate that the anchoring of Pt NPs on the TiO2 support material deposited on CSCNT is an effective way to enhance the ORR activity of Pt NPs by the SMSI as well as to prohibit Pt NPs from aggregating, i.e., the degradation of the ORR activity of Pt NPs.