Preparation and evaluation of advanced electrocatalysts for phosphoric acid fuel cells. Final report

This research program details the preparation and characterization of platinum electrocatalysts supported on carbon substrates. In the first instance, the platinum electrocatalysts were characterized for their crystallite sizes and the degree of dispersion on the carbon supports. One application of these electrocatalysts was for anodic oxidation of hydrogen in hot phosphoric acid fuel cells, coupled with the influence of low concentrations of carbon monoxide in the fuel gas stream. In a similar way, these platinum on carbon electrocatalysts were evaluated for oxygen reduction in hot phosphoric acid. An extension of these catalyst preparation techniques involved the preparation of binary noble metal alloys for anodic oxidation of hydrogen and for the preparation of noble metal-refractory metal mixtures for oxygen reduction. An exemplar alloy of platinum and palladium (50/50 at. %) was discovered for anodic oxidation of hydrogen in the presence of carbon monoxide, and patent disclosures were submitted. For the cathode, platinum-vanadium alloys were prepared showing improved performances over pure platinum. Preliminary experiments on electrocatalyst utilization in electrode structures showed low utilization of the noble metal when the electrocatalyst loading exceeded one wt % on the carbon. Further gains are to be expected from improving the electrode structures.