Self-grown layered double hydroxide nanosheets on bimetal-organic frameworks-derived N-doped CoOx carbon polyhedra for flexible all-solid-state rechargeable Zn-air batteries

The synthesis of non-precious metal electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is essential for flexible rechargeable metal-air batteries. Herein, a novel LDH@N-CoOx@C bifunctional electrocatalyst was synthesized by a straightforward solution reaction, annealing process, and hydrothermal reaction. The material consisted of two-dimensional (2D) NiFe layered double hydroxide (LDH) nanosheets self-grown on N-doped CoOx carbon polyhedra derived from bimetal-organic frameworks. The outer LDH nanosheets effectively maintained the catalytic activity and long-term stability of the inner N-CoOx@C. The heterostructure formed by the LDH self-growth on N-CoOx@C and the strong electronic interaction between N-CoOx@C and LDH greatly promoted the OER and ORR activities. The LDH@N-CoOx@C exhibited a low overpotential of 273 mV at 10 mA cm(-2) for OER and a half-wave potential (E-1/2) close to the commercial Pt/C catalyst for ORR, demonstrating its excellent bifunctional catalytic performance. In addition, the LDH@N-CoOx@C catalyst showed a higher energy density and extraordinary stability in liquid Zn-air batteries (ZABs) compared with the commercial Pt/C + RuO2 catalyst, having good prospect in flexible all-solid-state ZABs.