Identification of Active Species and Mechanisms in Non-Precious Metal Oxygen Reduction Catalysts By Poisoning and Magnetic Measurements

This talk addresses the Oxygen Reduction Reaction (ORR) utilizing Fe- and Co-based non precious metal (NPM) catalysts. There has long been uncertainty as to the active site for ORR in these materials due to the heterogeneity of the as-prepared catalyst. We have developed several methods with which to interrogate these materials. First, by using a purification scheme which removes and then remetallates the active site we substantially reduce catalyst heterogeneity. Second, we have developed a method by which to poison some of these active sites. Third, we use magnetic measurements to probe those sites affected by poisoning. We show as well that there is a minimum metal requirement for high ORR activity and that the metal must be arranged in certain critical configurations.