Iron-Based Atomically Dispersed Fe-N-C Catalysts for the Oxygen Reduction Reaction Within PEMFCs

Since the cathode oxygen reduction reaction (ORR) of proton-exchange membrane fuel cells (PEMFC) depends on sluggish reaction kinetics and is greatly dependent on costly Pt-based catalysts, it hinders the large-scale commercialization. As a result, atomically isolated Fe-N-C materials are highly promising non-precious-metal ORR catalysts for PEMFCs because of their low cost, high atomic efficiency and intrinsic catalytic activity coming from Fe-N 4 binding sites. However, Fe-N-C systems also have some shortcomings compared to Pt-based systems in terms of intrinsic activity, active site concentration and long term stability in acidic environment. Taking these aforementioned constraints into account, this review thoroughly introduces two types of enhancement tactics, namely, coordination environment adjustment and dual atom site assembly. Coordination-environment modification is achieved by heteroatom doping, axial coordination and spin-state regulation to change the electronic framework of Fe centers. Synergistic interaction between the homonuclear or heteronuclear metal active sites in dual atom catalyst promotes the O-O bond dissociation and 4-electron transfer selectivity. In this survey, the progress of these approaches in investigations is systematically analyzed. Future research needs to include operando characterization and theory-based design, along with testing of membrane-electrode-assemblies.