Tuning the electronic state of CoFe alloy via in-situ partial Co nitridation for enhanced oxygen electrocatalysis in zinc-air battery.

The low catalytic activity and high susceptibility to corrosion of CoFe alloys limit their efficiency and stability in oxygen evolution and reduction reactions (OER/ORR). Here, via a partial nitridation strategy, CoN is in-situ formed adjacent to CoFe alloy to construct a well-defined heterointerface within N-doped bamboo-like carbon nanotube (CoN-CoFe/NCNT). As indicated by computational calculations, the interfacial electrons are transferred from Fe atom to CoN in the CoN-CoFe heterojunction, optimizing the adsorption of O-intermediates and accelerating the rate-determining steps (*O to *OH in ORR and *O to *OOH in OER). X-ray absorption spectra confirm that Fe atom loses electrons, increasing its oxidation state. The Fe site in the heterojunction is identified as the primary active site for both ORR and OER, while the Co site in CoN plays an auxiliary role. Thus, CoN-CoFe/NCNT exhibits promising bifunctional activity with a very-low potential difference between ORR and OER (ΔE = 0.645 V). Interestingly, hydroxyl radical primarily induces corrosion of active species (FeOOH/CoOOH) and the structural framework during OER. CoN-CoFe/NCNT-based zinc-air battery shows excellent open-circuit potential (1.56 V) and charge/discharge stability (500 h). This study provides a new strategy to overcome the challenges posed by alloy-based catalysts and pave the way for highly-efficient energy conversion.