| Improved low temperature fuel cell catalyst compositions were pursued by constructing and screening thin film combinatorial libraries. The discrete composition combinatorial libraries were fabricated by plasma sputtering through shadow masks and then annealed in a vacuum furnace. Multichannel cyclic voltammetry was used to examine these libraries for short term catalytic activity. The oxidation of methanol and the reduction of oxygen were the reactions of interest. For the methanol oxidation reaction, compositions were ranked based on the potential defined at the onset of the reaction and the current density at the peak of the reaction. For the oxygen reduction reaction, compositions were ranked based on the onset potential of the oxygen reduction reaction.Results from the Pt-Ru, Pt-Ru-W, Pt-Ru-WC, Pt-Ru-(WC-Ta), Pt-Ta-WC, Pt-Ru-C, Pt-Ru-Cr, Pt-Ru-Ni, Pt-Ni-Cr, Pt-Ru-Co, Pt-Ti-Co, Pt-Co-Cr, Pd-Cr-Co, Pt-Co-Cu, Co-Cr-Cu, Pt-Ru-Cu, Pt-Ru-Mg4Ti, Pt-Fe-Ru, Pt-Fe-C and Pt-Fe-Cr systems are discussed. It was found that the optimum composition changed from initial to final tests. Cycling the potential at 60°C conditioned the libraries and altered the performance of most compositions. Usually the compositions that were initially active, were also unstable and would corrode away with the conditioning process.Systems that did not contain Pt (Pd-Cr-Co and Co-Cr-Cu) showed no activity for either methanol oxidation or oxygen reduction. Methanol oxidation testing revealed that the Pt-Ru-W, Pt-Ru-C, Pt-Ru-Ni and Pt-Ru-Co systems had compositions that could outperform the best Pt-Ru compositions. Overall the best methanol oxidation composition was Pt12Ru44Co44 with double the peak current density and an onset potential 142 mV lower than the average Pt response. The activity of this composition diminished in the presence of oxygen the best composition to reduce methanol in saturated oxygen was Pt44Ru12W44. Strong oxygen reduction responses were observed from compositions in the Pt-Ni-Cr, Pt-Ti-Co, Pt-Co-Cr and Pt-Fe-Cr systems. The best oxygen reducing composition was Pt27Co36 Cr37 with an onset potential of 0.673 V-SCE, 107 mV better than the standard, pure Pt. Another Pt-Co-Cr composition (Pt30Co 40Cr30) was the best oxygen reducing catalyst in the presence of methanol. Powder forms of these compositions may replace the current anode and cathode catalysts of all types of PEMFC in the near future. |
