Multi-scale dispersion in fuel cell anode catalysts:: Role of TiO2 towards achieving nanostructured materials

Multi-scale dispersion involving dispersion of catalyst particles on carbon support as well as intra-particle dispersion within the particles of a ternary Pt-Ru-Ti/C catalyst has been demonstrated. The presence of TiO2 can dramatically decreases the grain size of the obtained catalyst to about 1-2 nm when compared with similarly prepared Pt-Ru/C (3-4 nm) catalyst indicating that TiO2 can enhance the dispersion of the catalyst particles on carbon support. The structure and distribution of the Pt-Ru-Ti/C catalyst nanoparticles has been studied from high angle annular dark-field (HAADF) images combining with energy-dispersive X-ray spectroscopy (EDX). The composition of the Pt-Ru-Ti/C was found to be 50:34:16 (Pt:Ru:Ti, at%). The role of TiO2 in improving the intra-particle distribution has been investigated by X-ray absorption spectroscopy (XAS) at extended X-ray absorption fine structure region (EXAFS). The XAS parameters suggest that the Pt-Ru-Ti/C catalyst possess a structure in which the core is rich in Pt-Ru alloy and the shell is rich in Pt. In the shell, the Pt, Ru and TiO2 species are distributed homogenously. As a result of the improved multi-scale dispersion, the Pt-Ru-Ti/C catalyst exhibited enhanced activity towards methanol oxidation when compared to the commercial E-TEK 30 Pt-Ru/C catalyst and shows nearly similar performance when compared to the commercial JM 30 Pt-Ru/C catalyst with promising applications in fuel cells. (c) 2006 Elsevier B.V. All rights reserved.