Optimization of electrolytes for enhanced performance of MnFe₂O₄ nanoparticles-based supercapacitor electrode

Abstract Fine-tuning both material design and electrolyte interactions is crucial in the race to develop next-generation supercapacitors. Here, we unveil a solvothermal route to engineer MnFe 2 O 4 nanoparticles (NPs) with tailored electrochemical properties. Structural and morphological analyses confirm the formation of well-defined MnFe 2 O 4 NPs, primed with abundant electroactive sites for superior charge storage. When tested in 3.5 M KOH, these NPs delivered a specific capacitance of 817 F g −1 at 2.5 A g −1 . Comparative studies with LiOH, NaOH, and KOH showed that ionic mobility strongly influences performance with K + enabling fastest ion transport and superior charge storage. XPS analysis confirmed Mn 2+ and Fe 3+ oxidation states, linking surface chemistry to electrochemical behavior. An asymmetric device with activated carbon as the negative electrode and MnFe 2 O 4 NPs as the positive electrode delivered 320 mF g −1 at 0.07 A g −1 , retained 185 mF g −1 at 0.13 A g −1 , and achieved an energy density of 87 mWh kg −1 at a power density of 363 W kg −1 . The device maintained ~72% of its capacitance after 7500 cycles. These results highlight the combined effect of controlled NP synthesis and electrolyte optimization in achieving stable, high-performance supercapacitors suitable for practical energy storage applications.