CATALYTIC ACTIVITY AND STABILITY OF HEAT-TREATED IRON PHTHALOCYANINESFOR THE ELECTROREDUCTION OF OXYGEN IN POLYMER ELECTROLYTE FUEL-CELLS

Iron phthalocyanine (FePc) and tetracarboxylic iron phthalocyanine (Fe PcTc) have been adsorbed on carbon black (C). The resulting FePc/C and FePcTc/C have been heat-treated in Ar at various temperatures ranging from 100 to 1100 degrees C to obtain catalysts for the electroreducti on of oxygen. The electrochemical properties of these materials have b een measured by rotating disk electrode and in polymer electrolyte fue l cells. These properties have been correlated with the bulk and surfa ce characterizations of the catalysts. The most active catalyst is unp yrolyzed FePcTc/C but it is also the least stable one. The only cataly sts which are active and stable are those obtained at high pyrolysis t emperatures (greater than or equal to 900 degrees C). At those tempera tures there is no Fe-N bond anymore, and Fe is-mainly observed as a me tal surrounded by a graphitic envelope. After 10 h in a fuel cell at 5 0 degrees C, 0.5 V Versus reversible hydrogen electrode (RHE), FePcTc/ C and FePc/C pyrolyzed at 1000 degrees C yielded currents 37 and 40% t hat of a commercial Pt catalyst containing the same metalloading (2 wt .%), respectively.