Highly durable fuel cell electrocatalyst with low-loading Pt-Co nanoparticles dispersed over single-atom Pt-Co-N-Graphene nanofiber

Abstract The limited durability of Pt electrocatalysis toward cathodic oxygen reduction reaction is a remaining challenge, yet crucial for the development of Proton Exchange Membrane Fuel Cell. Here, we present a robust catalyst consisted of ~ 3 nm PtCo core-shell nanoparticles supported by porous Graphene-Nitrogen nanofiber decorated with single-atomic Pt and Co, termed PtCo@Pt-Co-GNF. The approach uses polymer-fiber containing Polyacrylonitrile and Cobalt-Metal-Organic-Framework as precursors to the Graphene-Nitrogen template where Pt clusters are in-situ reduced for high temperature synthesis. In a fuel cell with a total Pt loading (anode + cathode) of 0.083 mg cm-2, the new catalyst delivers unprecedented mass activity of 2.48 A mgPt-1 at 0.9 ViR-free, and a high Pt utilization of 11.9 kW gPt-1 at 150 kPaabs initially. Operando X-ray absorption spectroscopies (XAS) of PtCo@Pt-Co-GNF show that the structures of Co moieties under working and ex-situ condition are different, and Co moieties are modified during oxygen reduction reaction. Density Functional Theory combined with Operando XAS unveils that the synergistic effect of atomic neighboring Pt-Co dual center facilitates the oxygen-intermediates-adsorption strengthened on Co moieties and weakened on Pt sites, eventually enhancing the catalytic activity. Theoretical simulation further manifests that the enhanced curvature of the carbon substrate lowers the reaction thermodynamic barrier favoring the formation of H2O rather than H2O2 over Co-N4. This result along with the high carbon graphitization and the strong interaction between PtCo and Co-N-C may likely be responsible for the drastically enhanced durability of the catalyst which underwent 60,000 Accelerated-Stress-Test cycles including 30,000 cycles in H2-Air cell and a continued 30,000 cycles in H2-O2 cell with no obvious structure and composition changes.