Synergistic Effect of Ni ₂ P/Co ₂ P Heterojunctions and Phosphorus Vacancies for High-Performance Bifunctional Oxygen Catalysis in Zinc–Air Batteries

The activity and durability of bifunctional oxygen electrocatalysts are critical determinants for the energy efficiency and economics of fuel cells and metal–air batteries. Herein, we introduce a heterojunction–vacancy coengineering strategy that couples Ni 2 P/Co 2 P heterojunctions with phosphorus vacancies (V P ) within mesoporous N,P-doped carbon nanospheres (Ni 2 P/Co 2 P-V P -NPCs). This catalyst is synthesized by converting mesoporous polydopamine nanospheres via high-temperature phosphidation and H 2 reduction. The resulting structure exhibits outstanding bifunctional oxygen catalytic performance. For the oxygen reduction reaction (ORR), the half-wave potential ( E 1/2 ) is 0.85 V (vs RHE) with a limiting diffusion current density ( j d ) of 5.87 mA cm –2 and 96.67% current retention over 24 h in 0.1 M KOH. For the oxygen evolution reaction (OER), an overpotential of 277 mV (@10 mA cm –2 ) is achieved with 94.57% current retention over 24 h in 1.0 M KOH. In a rechargeable zinc–air battery, Ni 2 P/Co 2 P-V p -NPCs delivers a peak power density of 141.9 mW cm –2, excellent specific capacity (797.3 mAh g –1 ), and high energy density (1004.6 Wh·kg Zn –1 ), sustaining 600 h cycling at 10 mA cm –2 . Density functional theory (DFT) calculations reveal that the Ni 2 P/Co 2 P heterojunction downshifts the d-band center of Co cites, lowering the Gibbs free energy (Δ G ) for the potential-determining steps (*OH → OH – in ORR and *O → *OOH in OER), while phosphorus vacancies increase charge density of adjacent Co sites, facilitating interfacial charge transfer and boosting durability. This cooperative modulation precisely tunes the local electronic structure, providing a practical route to high-performance transition-metal catalysts for rechargeable zinc–air batteries.