Elucidating the nexus between Fe coordination and N-doped carbon matrix for efficient oxygen reduction catalysts

Abstract In the pursuit of inexpensive and efficient oxygen reduction catalysts, Fe–N–C catalysts have garnered significant attention as a viable alternative to scarce platinum-based materials. Nevertheless, the intricate interaction between the carbon matrix and Fe active sites, along with the mechanism by which such synergies modulate catalytic activity, remains elusive. Herein, a programmed temperature pyrolysis strategy is developed to optimize both the carbon matrix properties and coordination environments of Fe sites. Systematic characterizations uncover the correlations between key parameters of Fe sites (the oxidation state, coordination number, and density of state), as well as the carbon matrix (the functional groups, nitrogen species and content, and the degree of graphitization), with the resultant catalytic activity. The optimized catalyst exhibits a high half-wave potential of 0.935 V and good stability, and the assembled zinc–air battery delivers a high peak power density and long-term cycling durability. Theoretical calculations reveal that Fe–N4 coordination more effectively reduces the energy barrier for *OH release compared to Fe–N3 coordination. Additionally, adjacent graphitic nitrogen species further lower the energy barrier of the rate-determining step, thereby accelerating oxygen reduction kinetics. This work highlights the critical role of the carbon support and Fe site properties in synergistically boosting the catalytic performance.