Improving the Oxygen Reduction Reaction Activity of FeN₄–Graphene via Tuning Electronic Characteristics

Developing transition-metal–nitrogen–carbon (TM–N–C) catalysts to replace platinum in the oxygen reduction reaction (ORR) is very important but remains a grand challenge. Here, we investigate the ORR behavior of FeN4 embedded graphene. Our first-principles results show that the adsorption and dissociation of O2, which are elementary reactions of ORR, are largely dependent on the FeN4 concentration, although the architecture and the magnetic moment of the material are unaltered, distinct from the previous comprehension that the magnetic moment of TM–N–C plays a dominant role in the ORR. It is revealed that FeN4–graphene can alter from semimetallicity to metallicity and to half-metallicity, depending on the concentration, and the half-metallic FeN4–graphene exhibits the highest catalytic performance in the ORR. Because O2 exhibits a triplet ground state with unpaired electrons, it tends to interact with low energy states of catalysts. The half-metallic FeN4–graphene possesses highly active partially filled energy bands (PFEBs) and more easily donates electrons to the half-occupied πp* orbital of O2 than other systems, giving rise to the high catalytic activity. Our findings provide new insight into spin catalysis and should be useful in developing high-performance catalysts for ORR.