Multi-interfacial heterojunctions Fe₃O₄@NiCo₂O₄/NiCoP as efficient electrocatalysts for urea-assisted rechargeable Zn-air batteries

The development of Zn-air batteries (ZABs) is crucial to alleviate conventional fossil energy shortages and environmental problems. However, the slow thermodynamic process of the oxygen evolution reaction (OER) impedes its application. Urea oxidation reaction (UOR), substituting for OER, offers a thermodynamically favorable alternative and is useful for treating urea waste streams. However, both reactions suffer from slow kinetics and catalysts are urgently required to accelerate the reaction. In this study, a bifunctional sea urchin-shaped catalyst Fe₃O₄@NiCo₂O₄/NiCoP synthesis involved a two-step hydrothermal and phosphatization. Its heterogeneous structure and defects produced by the introduction of P enhance the catalytic performance of both OER and UOR. The catalyst can produce 10 mA cm⁻² with an OER reaction potential of only 1.47 V, which outperforms commercial RuO₂, and a UOR reaction potential of 1.344 V. ZAB and urea-assisted ZAB (uZAB) assembled by this catalyst have low charging/discharging voltage gaps of 0.69 V and 0.50 V, respectively. In addition, uZAB has a long cycle life (600 cycles) and high energy conversion efficiency (70.8 %). This work presents a uncomplicated and practical way to fabricate new OER and UOR electrocatalysts with good performance and simultaneously deepens the research on Zn-air batteries.