SPECIAL THEME RESEARCH ARTICLE Effect of aqueous electrolytes on the supercapacitive performance of glycol-mediated CoFe 2 O 4 nanoparticles Barkha Rani 1,2 | Niroj Kumar Sahu 2 1 School of Electronics Engineering, Vellore Institute of Technology, Vellore, 632014, India 2 Centre for Nanotechnology Research, Vellore Institute of Technology, Vellore, 632014, India Correspondence Niroj Kumar Sahu, Centre for Nanotechnology Research, Vellore Institute of Technology, Vellore, Tamilnadu 632014, India. Email: nirojs@vit.ac.in; sniroj.phy@gmail. com Funding information CSIR, Government of India Abstract Glycol-mediated facile solvothermal process for synthesis of mesoporous cobalt ferrite (CoFe 2 O 4 ) nanoparticles (NPs) is reported. The structure, surface func- tionalization and morphology of the prepared sample are characterized by X- ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), ther- mogravimetric analysis (TGA) and field emission scanning electron micro- scope (FESEM). The role of the electrolyte on the charge-storage performance of the CoFe 2 O 4 NPs is investigated in detail by performing cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), electrochemical impedance spec- troscopy (EIS) and cyclic stability tests in neutral (3M Na 2 SO 4 ) and alkaline (3M KOH) aqueous electrolytes. The electrochemical activity of inverse spinel CoFe 2 O 4 can be tuned with the electrolytes. It possesses specific capacitance (C sp ) of 477 and 176 F/g in alkaline and neutral aqueous media respectively at a scan rate of 2 mV/s. The sample shows better performance in KOH electro- lyte because of the smaller size of solvated ions whereas possesses better rate capability in the neutral electrolyte. Significant Coulombic efficiency of 97% is observed in alkaline medium with a rise in C sp upto 5,000 cycles, which remains constant until 10,000 cycles. KEYWORDS aqueous electrolyte, CoFe 2 O 4 , ferrite, KOH, Na 2 SO 4 , supercapacitor 1 | INTRODUCTION Global economic progress, fossil fuel depletion and enhanced environmental pollution have increased the demand for highly efficient, clean and sustainable energy resources. However, fluctuations related to clean and renewable energy resources necessitate effi- cient energy-storage technology. In the modern age, the exponential growth in the requirement of electrical and electronic commodities has motivated researchers to focus on highly efficient energy-storage devices such as batteries and ultracapacitors. Ultracapacitors or supercapacitors have gained more attention compared with the battery over the past few years because of their well-known characteristics such as excellent reversibility, fairly long cycle life, high specific power density, rapid charging/discharging, eco-friendly nature and easy operation and packaging. 1–5 It is used for various applications such as smart devices, hybrid electrical vehicles, portable electronic devices and pace- makers where long cycle life and high-power density are desirable parameters. 3,6 However, it has disadvanta- geously lower energy densities compared with high- performance batteries. 7,8 Therefore, advanced capacitors with high C sp and energy density without compromis- ing cycle life and power delivery are required to meet the growing energy demands for practical application. 9,10 Received: 30 December 2019 Revised: 31 May 2020 Accepted: 12 July 2020 DOI: 10.1002/apj.2548 Asia-Pac J Chem Eng. 2020;e2548. wileyonlinelibrary.com/journal/apj © 2020 Curtin University and John Wiley & Sons, Ltd. 1 of 11 https://doi.org/10.1002/apj.2548