Engineering iron-group bimetallic nanotubes as efficient bifunctional oxygen electrocatalysts for flexible Zn–air batteries

Air cathode performance is essential for rechargeable zinc–air batteries (ZABs). In this study, we develop a self-templated synthesis technique for fabricating bimetallic alloys (FeNi3), bimetallic nitrides (FeNi3N) and heterostructured FeNi3/FeNi3N hollow nanotubes. Owing to its structural and compositional advantages, FeNi3/FeNi3N exhibits remarkable bifunctional oxygen electrocatalytic performance with an extremely small potential gap of 0.68 ​V between the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Theoretical calculations reveal reduced Gibbs free energy for the rate-limiting O–O bond formation during OER due to the self-adaptive surface reconfiguration, which induces a synergistic effect between Fe(Ni)OOH developed in situ on the surface and the inner FeNi3/FeNi3N. ZAB fabricated using the FeNi3/FeNi3N catalyst shows high power density, small charge/discharge voltage gap and excellent cycling stability. In addition to its excellent battery performance, the corresponding quasi-solid-state ZAB shows robust flexibility and integrability. The synthesis method is extended to prepare a CoFe/CoFeN oxygen electrocatalyst, demonstrating its applicability to other iron-group elements.