Composition tuning and heterostructure construction of Fe-doped Co-Ni hydroxide nanosheets for boosting oxygen electrocatalysis in rechargeable Zn-air batteries

Development of highly efficient bifunctional catalysts for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is essential for enhancing the performance of rechargeable metal-air batteries. Herein, Fe-doped Co-Ni hydroxide nanosheets with mixed tetrahedral and octahedral coordination (CoNiFe LDH_Td/Oh) were explored as bifunctional electrocatalyst for rechargeable Zn-air batteries (ZABs). A high cobalt content in LDH_Td/Oh was crucial for outstanding ORR performance, while small amounts of Ni and Fe were beneficial in enhancing the OER activity. Furthermore, superlattice-like structures of LDH_Td/Oh hetero-assembled with reduced graphene oxide (rGO), RuO_2.1 or Ti₃C₂, were constructed, respectively, and comparatively studied. Experimental results confirmed significant enhancement of both OER and ORR catalytic activities in LDH_Td/Oh/rGO and LDH_Td/Oh/RuO_2.1 due to improved electrical conductivity as well as substantial interfacial electronic coupling effect. Theoretical calculations further revealed that the heterostructure with RuO_2.1 can effectively reduce the reaction barrier of OER, while the combination with rGO may enhance the electronic density of Co near the Fermi level, thereby increasing the availability of electronic states for ORR. As an air electrode catalyst for ZAB, LDH_Td/Oh/rGO stood out with a high peak power density (149 mW cm⁻²), a high specific capacity (775 mAh g⁻¹) and long cycling stability (over 180h) at a current density of 10 mA cm⁻², outperforming precious metal electrocatalysts (Pt/C + RuO₂ mixture).