Pt–TiO2 Nanocomposites as Catalysts for Proton Exchange Membrane Fuel Cell: Prominent Effects of Synthesis Medium pH

Pt-TiO2 nanocomposite catalysts in different Pt:Ti atomic ratios (1:1, 2:1 and 3:1) were synthesized in acidic (pH < 3) and basic (pH >10) medium for oxygen reduction reaction of proton exchange membrane fuel cells. The pH of synthesis medium significantly affected both physicochemical and catalytic properties of Pt-TiO2. Pt-TiO2 prepared in acidic medium exhibited smaller crystallite size, higher specific surface area and more non-stoichiometric titania with higher electrical conductivity as compared to that prepared in basic medium. The oxygen reduction reaction performance from fuel cell polarization curves showed that, Pt-TiO2 catalysts synthesized in acidic medium performed better than those prepared in basic medium. Among the catalysts with varying Pt:Ti atomic ratios, performance decreased in the order 3:1 > 2:1 > 1:1. Among all, Pt:Ti 3:1-A was found to exhibit better fuel cell performance as ORR catalyst (power density-530 mWcm-2; mass activity-123 mAmg-1Pt) compared to commercial Pt/C catalyst (power density-440 mWcm-2; mass activity-87 mAmg-1Pt), under identical conditions. The favourable conditions of synthesis of Pt-TiO2 catalyst achieved in acidic medium contribute to its enhanced properties.