Illumination-boosted capacitance with NiFe2O4: design and performance of symmetric and asymmetric photo-powered supercapacitors with self-generated voltage

Abstract

The demand for renewable energy requires efficient methods of energy generation and storage. Photo-powered supercapacitors (PPSCs) store more charge when illuminated, supporting the sustainability of the energy supply. PPSCs require active materials capable of both charge separation and storage. This work describes symmetric and asymmetric PPSC configurations using nickel ferrite (NiFe₂O₄) as a photoelectrode. NiFe₂O₄ is a spinel oxide valued for its applications in photocatalysis and supercapacitors. NiFe₂O₄ nanoparticles, prepared by co-precipitation and calcined at different temperatures from 400 to 800 °C, exhibit temperature-dependent structure and morphology; higher calcination temperatures produce larger, more aggregated particles. Based on galvanostatic charge–discharge (GCD) measurements, the NF-600 electrode (calcined at 600 °C) exhibits the highest specific capacitance. Under illumination with a current density of 0.03 mA cm⁻², NF-600 achieves a specific capacity of 422.88 mA h g⁻¹, approximately 1.34 times the value obtained in the dark (314.96 mA h g⁻¹) at room temperature. The NF-600 photoelectrode was used to fabricate both symmetric and asymmetric photo-powered supercapacitors. The results indicate that the asymmetric device exhibited superior performance. Two of the devices generated a self-induced voltage without external bias. Under illumination, both devices showed improved electrochemical performance, including increased capacitance and energy density. The asymmetric device demonstrated better performance and enhanced cycling stability compared to the symmetric device. This work presents a simple PPSC fabrication method using nickel ferrite to enhance sustainable charge storage in future energy devices.