Thin-Film Non-Precious Metal Model Catalysts for Oxygen Reduction Reaction

Non-precious metal catalysts (NPMCs) synthesized from earth-abundant elements, nitrogen and carbon, have been identified as potential alternatives to more scarce Pt-based catalysts currently used in the cathode oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs). Nevertheless, understanding the role of each component of state-of-the-art NPMCs remains a significant challenge due to their highly heterogeneous structure. This understanding is necessary for the development of next-generation NPMCs with improved catalytic activity and durability that could ultimately replace Pt-based ORR catalysts. In this work, a bottom-up systematic approach, starting from model graphene-based precursors, has been applied to eliminate the complexity of NPMCs and better understand the role of each component. 

Graphene and graphene-oxide (GO) thin-films transferred onto glassy carbon electrodes were used as starting materials. Nitrogen heteroatoms were incorporated into the thin-film substrates either by chemical modification in high-temperature ammonia treatments or by direct chemical activation using a unique high-flux energetic nitrogen atom beam technology, which overcomes thermal activation reaction barriers. Identification and speciation of doped nitrogen heteroatoms was performed via XPS. By varying reaction conditions, different nitrogen contents and species were obtained. Chemical-structure-to-activity relationships were then attempted through detailed physical and electrochemical characterization of the synthesis process to provide detailed information about the importance of each component addition for the formation of active and selective NPMCs.

Acknowledgment

Financial support from the Los Alamos National Laboratory Laboratory-Directed Research and Development (LDRD) Program is gratefully acknowledged.