Fe–N–C Electrocatalyst with d-π Interaction Induced by Submicropore Vacancies for Durable Oxygen Reduction Reaction in Proton-Exchange Membrane Fuel Cells

Transition metal–nitrogen-carbon composites (M–N–C), which hold great promise as Pt-free oxygen reduction reaction (ORR) catalysts, still encounter issues such as low activity and insufficient durability in practical proton-exchange membrane fuel cells (PEMFCs). Herein, we present a specific design of Fe–N–C featuring rich submicropore vacancies (Fe–N–C-SMV). This was developed through a simple MgCl 2 ·6H 2 O-assisted pyrolysis process of the complexing compound consisting of 1,10-phenanthroline and FeCl 3 . The submicropore vacancies (<1.0 nm) generated by MgCl 2 ·6H 2 O break the molecular orbital symmetry of the FeN 4 moiety, inducing an additional d-π interaction between Fe and the N dopant. This interaction not only significantly reduces the oxygen adsorption energy but also regulates the spin polarization of Fe, thereby effectively inhibiting the demetalation of Fe. As a result, the Fe–N–C-SMV delivered a half-wave potential of 0.84 V in 0.5 M H 2 SO 4 and a minimal durability decay of 7.0 mV after 10,000 cycles. Moreover, it shows a high practical PEMFC performance, with a maximum power output of 822 mW cm –2 and a relatively low degradation rate of 0.665 mA cm –2 h –1 . The crucial role of submicropore vacancies in simultaneously enhancing Fe–N–C discovered in this work provides an inspiration for developing nonprecious metal electrocatalysts for ORR in PEMFCs.