Exploring the Influences of Nanoparticle Synthesis-Route and Electrolytic Ions on the Electrochemical Performance of MnFe2O4-Based Supercapacitors

Abstract

A facile and cost-effective synthesis of MnFe2O4 nanoparticles (MnF NPs) using solvothermal and co-precipitation method are explored. The structure, chemical coating, morphology, surface area, and pore size distribution of the NPs are characterized using XRD, FTIR, Raman, TGA, FESEM, EDAX, BET, and BJH analysis. This work investigates the supercapacitive performance of MnF NPs from two different perspectives; (i) influences of the synthesis methods, and (ii) the effect of solvated electrolytic ion size. The conclusion drawn from the morphological studies indicates that the co-precipitation method is more efficient in synthesizing nanoparticles with a smaller diameter and uniform distribution. The electrochemical performances of the NPs are evaluated using CV, GCD, and EIS techniques in 3.5 M KOH solution. NPs prepared by co-precipitation approach show higher specific capacitance of 1334 F/g at 2.5 A/g while the value for solvothermally synthesized sample is 786 F/g. These enhanced electrochemical properties are attributed to the smaller particle size, presence of an ample number of electro-active sites, better electronic conductivity of MnF, and multiple oxidation states of manganese and iron ions. Furthermore, the effect of electrolyte ionic radii on the electrochemical properties of the prepared samples is studied. The different aqueous electrolyte of alkaline nature is selected for the experiment. 3.5 M of LiOH, NaOH, and KOH are used to explore the effect of solvated ion size on the electrochemical performance of the MnF NPs. A rising trend of specific capacitance is observed according to the ionic mobility (K+ >Na+ >Li+) of the electrolytic cations. The capacitance of solvothermally synthesized MnF NPs is increased nearly twice with changing the cation from Li+ to K+ ions. The specific capacitance observed for MnF NPs synthesized by the co-precipitation approach are found to be 1002, 1125, and 1334 F/g at a current density of 2.5 A/g for LiOH, NaOH, and KOH, respectively. Among these, KOH-based electrolytes exhibit better activity, capacitance retention, rate performance, ionic conductivity, efficient charge or ion diffusion, and relaxation time. Apart from this, mechanistic studies using the Trasatti method and power-law are used to investigate the electrochemical behaviours of the prepared NPs. The study implies that the redox process of the NPs is diffusion controlled. The diffusion process contributes significantly to the overall charge storage properties of the NPs. This study infer that the co-precipitation approach is favorable in terms of time, cost, eco-friendliness and higher charge storage properties whereas KOH-based alkaline electrolyte is the best-suited to achieve better performance of supercapacitor. This suggests that the preparation method of NPs and the electrolytes play significant role on the performance of electrochemical capacitors.