Characterization and activity correlations of Pt bimetallic catalysts for low temperature fuel cells

Pt bimetallic catalysts were prepared by impregnating a commercial Pt/C with various transition metals (Pt/M = 3, M: V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Ag and W) and sintering at 900 °C. All the freshly prepared catalysts show, except PtW, enrichment of the base metal on the PtM particle surface, and the degree of enrichment can be correlated with the surface energy of the base metal. Upon potential excursion in sulfuric acid solution, about 10–30% increases in the Pt surface area were observed when the scan limit was increased from 1.0 V to 1.5 V, except PtFe, PtCr and PtAg which showed 70%, 80%, and 270% increase, respectively, due to the surface roughening that was caused by leaching of the base metal. reduction tests using a half cell in phosphoric acid solution at 190 °C show monotonic decreases of electrode activity as time elapses for pure Pt, PtW, PtCu, PtZr and PtMn, whereas the rest show an initial increase that is followed by monotonic decrease over time. More pertinent increase at the initial stage was observed for PtCr, PtFe and PtAg catalysts due to the surface roughening effect. Among many parameters tested, a good correlation was found between the mass activity (A/g Pt) and the Pt surface area (SCV) obtained from the coulombic charge of the strongly adsorbed hydrogen. The specific activity (μA/cm2 Pt) based on SCV (m2/g Pt) was within the range of 2.12 ± 0.14 for all the tested PtM bimetallic catalysts.