Increasing Pt oxygen reduction reaction activity and durability with a carbon-doped TiO2 nanocoating catalyst support

Abstract

We report a conductive TiO₂ nanocoating on carbon nanotubes (CNTs) as a Pt electrocatalyst support that shows a significant enhancement in Pt catalyst activity and durability for the oxygen reduction reaction. By using CNTs as the substrate for TiO₂ nanocoating, the nanoscale morphology of the oxide was retained during heat treatment. After carbon doping of the TiO₂ nanocoating, X-ray photoelectron spectroscopy suggests a shift in the binding energy of Ti 2p, implying a suboxide formation. The X-ray absorption near-edge structure showed the mid-edge and post-edge up to 5010 eV, which are attributed to a 1s → 4p transition and promotion of a photoelectron to higher vacant orbitals of Ti and Ti–O anti-bonding states. The observed smaller coordination number implies that a suboxide was formed with substitutional carbon. On the other hand, the extended X-ray absorption fine structure showed that carbon also exists in interstitial positions. Electrochemical studies showed that the carbon-doped TiO₂/CNT support has a much greater electrical conductivity than that of undoped TiO₂/CNT, demonstrating that carbon doping is an effective way to achieve electrical conductivity in the oxide. Pt supported on the carbon-doped TiO₂/CNTs (Pt/c-TiO₂/CNTs) showed a better oxygen reduction activity than a commercial Pt/C catalyst. The catalyst only has a less than 3% loss in activity after electrochemical cycling 5000 times, as compared to an activity loss of about 55% for the Pt/C catalyst. The much better activity and durability of the TiO₂ nanocoating supported Pt was attributed to the oxygen deficient oxide support surfaces and strong metal–support interactions.