Impact of nickel substitution on supercapacitor and photocatalytic performances of cobalt-ferrites nanoparticles

Abstract

Ni_xCo_1-xFe₂O₄ nanoparticles were synthesized by precipitation method and developed as bifunctional nanoparticles for photocatalytic and supercapacitor applications. The crystalline structure and gradual changing of the cell parameters by substituting Ni²⁺ ions into the Co-ferrite lattice were confirmed by XRD. Raman analysis shows that the Co²⁺ ions partially substitute Fe³⁺ ions in tetrahedral sites, and the substitution with Ni²⁺ ions lead to a rearrangement of cations on octahedral sites. The samples have a mixture of spherical and rectangular shapes with an average size between 4 and 14 nm for Ni-ferrite and Co-ferrite, respectively. All the samples are ferromagnetic at room temperature; both magnetic phases were evidenced by EPR spectroscopy. In substituted Co ferrite, 80 % Ni was identified as the optimum amount, ensuring the best photocatalytic activity against RhB solution under visible irradiation. The photocatalytic mechanism was explained, considering that the samples generate only superoxide radicals under visible light. The sample with the best photocatalytic performance was combined with PVDF membrane to enhance its hydrophilicity and self-cleaning properties. Additionally, Ni-Co ferrite nanoparticles were studied as electrode materials in symmetrical supercapacitor devices. Electrochemical characteristics indicate good performance and cycling stability and confirmed an appreciable increase in specific capacitance by substituting Co²⁺ with Ni²⁺ ions.