Enhanced Local Electric Field for Efficient Water Splitting and Zn–Air Batteries Enabled by Ultrasmall CoNi-VN Derived from Polyoxovanadoborates

Abstract

Enhancing local electric fields (LEFs) near catalytic centers is a pivotal strategy to elevate electrocatalytic efficiency by accelerating electron transport and ion enrichment. Herein, a high-performance nanocomposite multifunctional electrocatalyst with high-curvature nanostructures was designed to generate strong LEFs, addressing slow reaction kinetics and high thermodynamic barriers. Ultrasmall vanadium nitride (VN) and cobalt–nickel alloy (CoNi) nanocomposite electrocatalyst systems were constructed by incorporating polyethylenimine (PEI) as a soft template and polyoxometalates (POMs) as precursors. This approach effectively prevents nanoparticle agglomeration and enhances active site exposure. Finite-element simulations revealed that the ultrasmall CoNi-VN nanoparticles generated strong LEFs, significantly enhancing electron transport and ion concentration around active sites. Meanwhile, the integrated ultrahigh-specific surface area, heteroatom doping, and effective mass transfer of the carbon nanotube structure endowed CoNi/VN/BNCNT with excellent HER (η₁₀, 109 mV), OER (η₅₀, 362 mV), and ORR (E_1/2, 0.85 V) activities. The rechargeable Zn–air batteries achieved a high specific capacity of 810 mAh g^–1, a peak power density of 220 mW cm^–2 at 350 mA cm^–2, a high open-circuit voltage of 1.51 V, and a low charging/discharging voltage gap of 0.89 V. Moreover, CoNi/VN/BNCNT requires cell voltages of 1.52 and 1.67 V to achieve current densities of 10 and 50 mA cm^–2 for water splitting. This work addresses the agglomeration of alloy and VN nanoparticles while regulating the intensity of the local electric field, providing a promising pathway for advanced energy conversion and storage technologies.