Elongated Fe-N-C containing trace atomic Co dopants for high power density PEMFCs

Developing single-atom Fe-N4/C catalysts is crucial for the large-scale implementation of proton exchange membrane fuel cells (PEMFCs). While Fe-N4/C catalysts are inherently active in accelerating the slow ORR process, their performance is still inferior to that of Pt/C. Herein, a trace Co-doped Fe single-atom catalyst (Fe(tCo)-N-C) containing more active Fe2N8 sites has been synthesized. Interestingly, compared with typical FeN4 sites in Fe-N-C electrocatalyst, the Fe2N8 sites generate a larger Fe-N bond length due to Co-doped. The elongated Fe-N bond in Fe2N8 lowers the d-band center and charge density of the iron sites, enhancing ORR process by facilitating the formation of *OOH and the generation and desorption of *OH. Fe(tCo)-N-C manifested excellent acidic and alkaline ORR activity, with half-wave potential (E1/2) of 0.80 V in HClO4 solution and 0.89 V in KOH medium. More importantly, high peak power densities (Pmax) were realized by applying Fe(tCo)-N-C in PEMFCs, with the Pmax reaching 890 mW cm-2 in H2-O2 and 380 mW cm-2 in H2-air. Additionally, the trace Co dopants in the catalyst improved carbon graphitization and provided high ORR catalytic stability. This research introduces an innovative approach to engineer highly active Fe2N8 sites, providing valuable insights for the sustainable progress of PEMFC technology.