Highly dispersed niobium catalyst on carbon black by polymerized complex method as PEFC cathode catalyst

Niobium catalysts with and without barium are dispersed on particulate carbon black by a polymerized complex method as a non-noble metal cathode for polymer electrolyte fuel cells (PEFCs). The barium-niobium composites were prepared by a polymerized complex method involving the addition of carbon black during the polymerization process, followed by nitridation under flowing ammonia. The material exhibits improved activity for oxygen reduction under acidic conditions, achieving an onset potential of 0.77 V vs normal hydrogen electrode (NHE). This onset potential is markedly higher than that for niobium composites prepared by conventional impregnation (0.52 V vs NHE). The production of H2 O2 by the two-electron reduction of oxygen was observed at potentials of less than 0.25 V vs NHE (approximately 5.4%). The onset potential of these catalysts is found to be dependent on the crystallinity and Nb5+ content on the surface and in the bulk, which can be controlled by the addition of barium and the conditions of pretreatment using an inert gas (nitrogen) before nitridation.