MOF/LDH cross composites derived heterojunction nanospheres as highly efficient catalysts for ORR-OER and rechargeable Zn-air batteries

Exploiting high-stability and cost-effective cathode catalysts is still one of the most important issues in promoting the practical application of Zn-air batteries (ZABs). Herein, the MOF/LDH crossed composites are utilized as templates to construct the N-doped carbon framework carrying the CoFe/Fe3C heterojunction as highly efficient electrocatalysts for ORR-OER and ZABs. During pyrolysis, the Co-Fe-LDH transforms into the CoFe alloy nanoparticle, while the MOFs convert to the Fe3C phase, thus leading to the formation of the CoFe/Fe3C heterojunction. Owing to the strong interactions between the heterogeneous interface of MOF and LDH, more active sites can be obtained on the surface of the contact interface. Moreover, more oxygen vacancies are generated in the catalysts after the formation of heterojunction. The optimal CoFe/Fe3C@CN-900 catalysts exhibit excellent ORR-OER performance with a potential gap between ORR and OER of 0.713 V at 0.1 M KOH electrolyte. DFT calculations demonstrate that the electron redistributes and accumulates at the heterojunction interface between CoFe and Fe3C, resulting in a stronger electron-donating capacity and faster electron conductivity. The CoFe/Fe3C@CN-900-based aqueous and solid-state ZABs also display good battery performance with high power density, strong discharge stability, large capacity, and good charge–discharge cycling durability.