Development of Novel Pt-Co Catalysts for Pem Fuel Cells
Lingyun Liu1, Hector R. Colon-Mercado2, Jong-Won Lee1, and Branko Popov1. (1) Department of Chemical Engineering, University of South Carolina, 301 Main Street, Swearingen Engineering Center, Columbia, SC 29208, (2) Savannah River National Laboratory, Aiken, SC 29808
Highly dispersed Pt crystallites on a porous carbon support is used as electrocatalysts for the oxygen reduction reaction (ORR) in PEMFC. At the cathode, the overpotential caused by slow kinetics is in excess of 300 mV from the thermodynamic potential for ORR, even when pure Pt is used. The search for more active and less expensive ORR catalysts with better stability than Pt has led to the development of Pt-based binary or ternary alloys. Our previous study  showed that highly active Co-chelate catalysts can be prepared by supporting Co-N complexes on a carbon black followed by a heat-treatment at elevated temperatures. Oxygen functional groups introduced on carbon surface with an acid treatment improved the dispersion of Co-N complexes, resulting in improved activity and selectivity towards four-electron reduction of molecular oxygen. In this work, a novel procedure was developed to synthesize Pt-Co electrocatalyst with high activity and stability, using Co-dispersed carbon as a support for the Pt catalyst. The Co/C was previously treated in an acidic medium to remove excess Co and to decrease the Co particle sizes. Rotating disk electrode and fuel cell experiments indicated that the Pt-Co catalyst prepared by using the USC procedure shows higher catalytic activity and better ORR kinetics, as compared with the commercially available Pt-Co catalyst. Post heat-treatment of the Pt-Co catalyst in an inert atmosphere decreased the electrochemical active surface area due to the agglomeration of Pt particles, but increased the stability of the catalyst.
 N.P. Subramanian, S.P. Kumaraguru, H.R. Colon-Mercado, H. Kim, B.N. Popov, T. Black, D.A. Chen, J. Power Sources, in press.