NiCo2O4/P,N-Doped Carbon with Engineered Interface to Improve the Rechargeability of Zn-Air Batteries at High Energy Demands

Abstract

The search for cost-effective, high-performance bifunctional catalysts for Zn-air batteries (ZABs) requires extensive research into precious-metal-free materials. This study provides insight into the synergy between nickel cobaltite and P,N-doped carbon modified through interface engineering by inducing oxygen vacancies in the spinel and non-metallic heteroatoms in the carbon material. NiCo₂O₄ with various oxygen vacancy levels was synthesized via an ethylene glycol-assisted solvothermal route. This resulted in significant changes in the structural and morphological properties, such as reduced crystallite size, lattice distortion, and increased oxygen vacancies, as observed from the physicochemical results. This was further verified by X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HR-TEM), which showed a homogeneous dispersion of nickel cobaltite nanorods on the carbonaceous matrix, along with an increased concentration of pyridinic nitrogen and the formation of P−N and P−C bonds, both of which enhance electrocatalytic activity. NiCo₂O₄DI/P,N−C exhibited superior discharge polarization behavior, achieving power and current densities of 124.4 mW cm⁻² and 215.8 mA cm⁻². Stability tests revealed that the catalyst had excellent performance, lasting up to 100 h, while Pt-IrO₂/C lasted only up to 21 h. These results demonstrate the great potential of tailoring surface defects and heteroatom doping via interface engineering, resulting in high-performance precious-metal-free electrocatalysts for long-lasting and high-efficiency ZABs.