Phosphorus-doped iron-nitrogen-carbon catalyst with penta-coordinated single atom sites for efficient oxygen reduction

Single-atomic Fe-N₄ is the well-acknowledged active site in iron-nitrogen-carbon (Fe-N-C) material for oxygen reduction reaction (ORR). The adjusting of the electronic distribution of Fe-N₄ is promising for further enhancing the performance of the Fe-N-C catalyst. Herein, a phosphorus (P)-doped Fe-N-C catalyst with penta-coordinated single atom sites (FeNPC) is reported for efficient oxygen reduction. Fe K-edge X-ray absorption spectroscopy (XAS) verifies the coordination environment of single Fe atom, while density functional theory (DFT) calculations reveal that the penta-coordination and neighboring doped P atoms can simultaneously change the electronic distribution of Fe-N₄ and its adsorption strength of key intermediates, reducing the reaction-free energy of the potential-limiting step. Electrochemical tests validate the remarkable intrinsic ORR activity of FeNPC in alkaline media (a half-wave potential (E_1/2) of 0.904 V vs. reversible hydrogen electrode (RHE) and limited current density (J_L) of 6.23 mA·cm⁻²) and an enhanced ORR performance in neutral (E_1/2 = 0.751 V, J_L = 5.27 mA·cm⁻²) and acidic media (E_1/2 = 0.735 V, J_L = 5.82 mA·cm⁻²) with excellent stability, highlighting the benefits of optimizing the local environment of single-atomic Fe-N₄.