Binary active sites of nickel–iron alloy bonded in nitrogen-doped carbon nanocage for robust durability and low polarization zinc-air batteries

The industrialization of rechargeable metal-air batteries, especially zinc-air batteries (ZABs), is greatly limited to the low efficiency, high polarization, and short lifetime of oxygen catalysts (both oxygen reduction reaction and oxygen evolution reaction), which still faces challenges. Herein, a novel efficient bifunctional electrocatalyst based on binary active sites engineering of NiFe alloy embedded in hierarchical nanoporous nitrogen-doped carbon nanocage (NiFe@NC) is successfully synthetized by pyrolysis of urea and Prussian blue analogues coated with polydopamine. Profiting from strong synergetic between NiFe alloy and nitrogen-doped carbon, abundant Fe/Ni–N–C bond, this unique hierarchical yolk-core-shell structure provides an integration of superior OER and ORR property, half-wave potential of 0.86 V for ORR and a small overpotential of 277 mV at 10 mA cm⁻² for OER in O₂-saturated 0.1 M KOH. Consequently, the liquid ZABs based on the electrocatalyst exhibits a high open-circuit voltage of 1.50 V, a low-polarization voltage of 0.68 V after 370 h at 10 mA cm⁻², as well as superior stability for up to 750 h (10 mA cm⁻²) and 450 h (20 mA cm⁻²). This work provides a reference significance to the research and development of high-performance rechargeable ZAB catalysts.