Tailoring chain-like NiFe2O4 through magnetic-field-assisted synthesis for enhanced pseudocapacitive behavior

Magnetic-field-assisted synthesis provides an effective route for regulating the microstructure and defect chemistry of ferrite-based electrode materials. However, the coupled effect of magnetic-field-induced assembly and defect evolution on the pseudocapacitive behavior of nickel ferrite (NiFe2O4) remains insufficiently clarified. Herein, NiFe2O4 samples were prepared by a magnetic-field-assisted hydrothermal method, and their structural evolution, surface chemical states, and electrochemical kinetics were systematically investigated under different magnetic-field conditions. The applied magnetic field promoted the chain-like self-assembly of NiFe2O4 nanoparticles, resulting in a more continuous conductive network, improved pore connectivity, and enhanced electrolyte accessibility. Meanwhile, the magnetic field increased the concentration of oxygen vacancies, which facilitated OH- adsorption/activation and strengthened the contribution of fast surface Faradaic reactions. Benefiting from the synergistic regulation of chain-like architecture and defect-rich surfaces, the optimized NFO-3 electrode exhibited markedly improved specific capacitance at 1.0 A g􀀀 1 and maintained a capacitance retention of 95.18% after cycling. Even at a high current density of 10 A g􀀀 1, NFO-3 still delivered a cycling stability of 90.59%. These results demonstrate that magnetic-field-assisted hydrothermal synthesis is a feasible strategy for tailoring the assembly behavior and defect structure of ferrite oxides, providing a useful approach for designing high-performance ceramic electrode materials for pseudocapacitive energy storage.