Synergistic energy harvesting and storage in stoichiometry-engineered CoxFe3-xO4 spinel ferrites nanoparticles

Spinel ferrites are increasingly recognized as multifunctional materials for energy technologies owing to their tunable cation distribution, defect density, and adaptable electronic structures. In this work, Co x Fe 3-x O 4 (x = 0.5–1.1) nanomaterials were synthesized by sol–gel auto-combustion route to investigate composition-dependent structural and functional evolution. Variation in the Co:Fe ratio induced marked changes in cation valence states and oxygen-vacancy concentrations, directly governing electrical and electrochemical responses. Increasing Co content transformed a mixed CoFe 2 O 4 /α-Fe 2 O 3 system into a phase-pure spinel, enhancing crystallinity and redox uniformity. The optimized Co 0.7 Fe 2.3 O 4 composition demonstrated outstanding dual performance. In hydroelectric cell, it produced 0.97 V and 14.7 mW output, continuously powering LEDs for more than 3.5 h with a power density of 3.68 mW cm −2 . As a supercapacitor electrode in 3 M MgSO 4 , it delivered an ultrahigh capacitance of 2916 F g −1 , energy density of 328 Wh kg −1 , power density of 1010 W kg −1 , and anomalous >250 % retention after 5000 cycles. Electrochemical impedance spectroscopy revealed minimized charge-transfer resistance and accelerated ion/electron transport, arising from balanced Co 2+ /Co 3+ and Fe 2+ /Fe 3+ redox centers, oxygen-vacancy conduction, and heterointerfaces with residual α-Fe 2 O 3 . These results establish stoichiometric engineering as a powerful pathway to integrate energy harvesting and storage in scalable ferrite systems. • Co 0.7 Fe 2.3 O 4 delivers superior multifunctional energy performance. • Hydroelectric cell output of 0.97 V and 14.7 mW continuous power. • Supercapacitor capacitance of 2916 F g −1 with excellent cycling stability. • Stoichiometric tuning yields phase-pure spinel with enhanced properties.