Boron engineering enables enhanced ORR/OER activity of Ni2P/Co2P heterojunctions anchored on hierarchical carbon for Zn-air batteries

Developing bifunctional oxygen electrocatalysts with excellent activity and durability is critical for scaling rechargeable zinc–air batteries (ZABs). Herein, we propose an integrated “etching–doping–phosphorization/carbonization” route to synthesize Ni 2 P/Co 2 P heterojunctions anchored on B,N,P co-doped carbon (Ni 2 P/Co 2 P-NPBC). Firstly, boric acid etching of the ZIF(Zn, Co, Ni) generates a bird-nest-like porous framework and simultaneously introduces boron; subsequent phosphorization/carbonization at 1000 °C yields Ni 2 P/Co 2 P nanocrystals uniformly anchored on the B, N, P co-doped carbon. It is confirmed that the carbon framework exhibits abundant defects and contains B, N, and P atoms chemically bonded to the matrix. This structure possesses a high surface area and a through-pore network, which ensure the exposure of active sites and facilitate rapid mass transport. Density functional theory (DFT) calculations show that boron doping markedly decreases charge density and upshifts the d-band center of Co sites in the Ni 2 P/Co 2 P heterojunction (from −1.26 to −0.87 eV), thereby raising the oxygen reduction reaction (ORR) limiting potential (from 0.34 to 0.69 V) and lowering the oxygen evolution reaction (OER) theoretical overpotential (from 0.89 to 0.54 V). Benefiting from these features, Ni 2 P/Co 2 P-NPBC in alkaline media delivers an ORR half-wave potential of 0.88 V (vs. 0.85 V for 20% Pt/C) and an OER overpotential of 264 mV at 10 mA cm −2 (vs. 308 mV for RuO 2 ). A lab-fabricated ZAB achieves an open-circuit voltage of 1.586 V, a peak power density of 180.8 mW cm −2 , a specific capacity of 816.2 mAh g −1 , an energy density of 1159.0 Wh kg Zn −1 , and 600 h stable cycling.