• Ni doping in FeVO4 nanoparticles successfully tunes both magnetic and electrochemical properties, with Fe0.95Ni0.05VO4 achieving the highest specific capacitance of 334.05 F·g−1 at 1 A·g−1.
• Increasing Ni content reduces nanoparticle size and enhances specific surface area and magnetization, while XANES confirms Ni2+ substitution at Fe3+ sites.
• Ni-doped FeVO4 exhibits weak ferromagnetic behavior at room temperature, contrasting with the antiferromagnetic nature of undoped FeVO4.
• The Fe0.8Ni0.2VO4 electrode shows outstanding cyclic stability due to its enhanced specific surface area, highlighting the potential of Ni doping for supercapacitor applications.