(702c) Nanostructured TiN Supported Pt-Ru Catalysts for Direct Methanol Fuel Cells

Direct methanol fuel cells (DMFC) is one of the power sources that has gained attention in recent years for mobile and portable applications. The Pt-50at.% Ru alloy in particular has been identified as a most active catalyst for methanol electrooxidation in DMFC. However, the currently achieved power densities of DMFC are still significantly below those of proton exchange membrane (PEM) hydrogen fuel cells and other fuel cell types. One of the main issues relate to the relatively slow kinetics of the electrochemical reactions occurring at the electrodes. Therefore, an important objective in the development of high-performance DMFC will be to improve the reaction kinetics of the Pt-50at.% Ru based anode by synthesizing high surface area Pt- 50at.% Ru based catalysts. In order to obtain high surface area Pt-Ru based catalyst and the optimum catalyst utilization for methanol electrooxidation, the catalysts are generally dispersed in small conductive particles with high specific surface area known as catalyst supports. In the present work, highly conductive nanostructured titanium nitride has been used as a suitable support for Pt- 50at.% Ru catalyst to obtain high surface area Pt-Ru based catalyst with excellent catalytic activity. Nanostructured TiN with high specific surface area has been synthesized by the two-step halide approach. A novel complexation based sol-gel process has been developed to synthesize nanocrystalline Pt-50at.% Ru based anode catalysts in the presence of nanostructured TiN. Platinum (II) acetylacetonate and ruthenium (III) acetylacetonate were used as the sources for Pt and Ru. The Pt-Ru/TiN nanocomposite of nominal composition Pt50Ru50-30wt.% TiN possessing high specific surface area (~120m2/g) were successfully produced by controlled removal of carbonaceous species generated from the as-prepared precursor. The controlled removal of carbon related species has been successfully performed by controlled thermal treatment of the precursor using controlled oxidizing atmospheres such as 1% O2 balanced with ultrahigh purity (UHP) argon. The formation of nanocrystalline (~2-3nm) powders has been confirmed from XRD analysis and high resolution electron microscopy study. The electrochemical characterization was conducted on selected samples using a three-electrode cell. The Pt loading on the electrode was 0.3mg/1.5cm2. A solution containing 1 M methanol and 0.5 M sulfuric acid was used as an electrolyte as well as a source of the fuel. A Mercury/Mercurous sulfate electrode that has a potential of +0.658V with respect to standard hydrogen electrode (SHE) was used as the reference electrode. The Pt-Ru/TiN catalyst shows a current density 0.028A at ?0.10V which is about 24% better performance than pure Pt-Ru (0.02A at ?0.10V). The results clearly indicates that the Pt-Ru/TiN based nanocomposite catalyst, possessing high specific surface area, reveals an excellent catalytic activity, demonstrating the potential of the nanostructured TiN as a support for Pt-Ru based anode catalyst.