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

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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.

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