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 MgCl2·6H2O-assisted pyrolysis process of the complexing compound consisting of 1,10-phenanthroline and FeCl3. The submicropore vacancies (<1.0 nm) generated by MgCl2·6H2O break the molecular orbital symmetry of the FeN4 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 H2SO4 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.