Abstract
High cost of the platinum-based catalysts for the sluggish oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cell (PEMFC) is delaying wide-spread commercialization of fuel cell electric vehicles (FCEVs). It is crucial to develop highly-active and cost-effective materials to reduce amount of platinum usage and eventually to replace the platinum-based catalysts. In this respect, nitrogen-doped carbon incorporated with atomically-dispersed metal and/or metal nanoclusters (M-N-C) has attracted tremendous attention owing to their high catalytic activity towards ORR. By atomically dispersing Pt or forming Pt nanoclusters in the nitrogen-doped carbon, utilization of Pt can be maximized, resulting in ultralow usage of Pt catalyst. Fe incorporated in the nitrogen-doped carbon (Fe-N-C) has been reported as the best candidate to attain high ORR activity among the non-precious catalysts. In applying these catalysts for PEMFC, it is still required to improve activity and durability of those M-N-C catalysts in the harsh acidic environment of PEMFC.
Herein, we present Pt-N-C and Fe-N-C as highly-active ORR catalysts prepared through a facile method. To enhance ORR activity of those M-N-C catalysts, a hetero-atom is doped into the M-N-C catalyst. In addition, effects of formation of metal nanoclusters on the ORR activity are investigated with respect to the size of the nanoclusters. DFT calculation study explores active sites for the ORR in M-N-C catalysts by examining the oxygen adsorption energy of reaction intermediates towards benefiting ORR.