CHANGES IN CATHODE CATALYST STRUCTURE AND ACTIVITY IN PHOSPHORIC-ACIDFUEL-CELL OPERATION

Changes in the cathode catalyst structure and activity obtained from a small size phosphoric acid fuel cell (PAFC) operated for various time s up to 12000 h, were examined. It was confirmed that the platinum sur face oxide reduction potential in cyclic voltammograms (CV) shifted in the positive direction with cell operation. This may be one of the ma nifestations of the activity enhancement for the oxygen reduction reac tion (ORR). It was assumed that this activity increase for the ORR was caused by an increase in the surface roughness, due to the dissolutio n of the alloyed base metals. Changes in the platinum chemical state o f the alloy surface, from PtO to Pt, and growth of the Pt (110) plane would also contribute to this effect.