Stability and Activity of Platinum/carbon Catalysts

Abstract

A platinum/carbon catalyst of the phosphoric acid fuel cell was evaluated to obtain high stability and activity. Among three carbons (Denka Black (acetylene black, Denkikagaku Kogyo), Regal 660 R, Vulcan XC-72 R (these two are furnace blacks, Cabot Corp. )), Denka Black had the lowest rate constant for the reaction with oxygen and steam (Figs.2, 4 and 7, Tables 2-4). Denka Black was considered to be stable for oxygen and steam, because the results of X-ray diffraction show that the spacing of graphitic layers is smaller and the crystallite size is larger than in the other carbons (Figs.3, 5 and 6).
The oxygen reduction was measured in about 98 wt% phosphoric acid at 190°C. Platinum/Denka Black also showed the highest activity from the polarization curves (Fig.8). Such activity seemed to be affected by the platinum particle dispersion, though the platinum crystallite (particle) sizes were similar in all the catalysts. Platinum particles supported on Denka Black were highly dispersed, as judged from the observation by transmission electron microscopy (Fig.9).