Interface of Nickel Sulfides Optimizing Surface Reconstruction toward Efficient Bifunctional Oxygen Electrocatalysis in Rechargeable Zinc-Air Batteries

The air electrode of rechargeable zinc-air batteries (ZABs) suffers from four-electron sluggish kinetics of the oxygen evolution and reduction reactions (OER/ORR) and surface reconstruction caused by electro-oxidation of the OER process. Therefore, it is crucial to fabricate efficient bifunctional OER and ORR catalysts with optimized reconstruction. Herein, we synthesized double-layered core-shell spheres composed of nanoparticles ∼15 nm in size with NiCo₂S₄/Ni₉S₈ interfaces. Easily accessible to the inner and outer shells, the special porous structure endows a much enhanced specific surface area. The as-prepared catalytic material shows well-matched bifunctional catalytic activity toward the OER (η₁₀ = 286 mV) and ORR (E_1/2 = 0.85 V) with a lower oxygen potential gap of 0.7 V, better than its counterpart of commercial Pt/C + RuO₂ (0.8 V). The resulting ZAB also exhibits high peak power density (162 mW cm^-2) and charge-discharge durability (more than 260 h without attenuation). It was confirmed that the NiCo₂S₄/Ni₉S₈ interface can accelerate the OER surface reconstruction process, optimize the catalytic activity, and boost the charge-discharge kinetic rate. Especially, the redox pairs of Ni³⁺/Ni²⁺ and Co³⁺/Co²⁺ can provide extra battery capacity for ZAB besides the OER/ORR during charge-discharge processes.