A sol-gel-based approach to synthesize high-surface-area Pt-Ru catalysts as anodes for DMFCs

A novel sol-gel based chemical process was developed to synthesize Pt-Ru catalysts possessing high specific surface area and good catalytic activity, for direct methanal fuel cells (DMFCs). In this process, tetramethylammonium hydroxide was used to hydrolyze platinum (II) acetylacetonate and ruthenium (III) acetylacetonate to form a homogeneous gel. Phase-pure powders possessing a high specific surface area as high as 136.9 m(2)/g were produced using controlled oxidizing atmospheres such as 1% O-2 balanced with N-2. The resultant powder consisted of nanocrystalline Pt-Ru particles (less than 10 nm) and also revealed an excellent catalytic activity in standard three-electrode half-cell tests (cell potential of 0.295 V at currents of ln(mA/g) of 8), demonstrating the potential of the sol-gel-based processes for synthesizing high-performance catalysts for DMFCs. The key factor in obtaining phase-pure powders with high specific surface area is the controlled removal of carbon species in the as-prepared precursors. The rapid kinetics of carbon removal in air caused the growth of particles as well as the formation of Ru oxide, thus leading to a low specific surface area powder, combined with the segregation of Ru oxide from the homogeneous Pt-Ru precursors. A limited oxidizing ability of the heat-treatment atmospheres used such as 0.1% O-2 also yielded a low specific surface area powder due to the insufficient removal of carbon. (C) 2003 The Electrochemical Society.