Effect of growth-time on electrochemical performance of birnessite manganese oxide (δ-MnO2) as electrodes for supercapacitors: An insight into neutral aqueous electrolytes

Abstract

This study demonstrates successful synthesis of nanoflower-like birnessite δ-MnO2 materials through a simple and effective hydrothermal technique. Characterization of the flower-like materials grown at various dwell times were carried out by employing scanning electron microscopy (SEM), X-ray diffractometry (XRD), Brunauer-Emmett-Teller (BET) and Barrett–Joyner–Halenda (BJH) models, and electrochemical analysis to understand the effect of different growth time on their morphological, structural, surface area along with pore size distribution and electrochemical characteristics as electrodes for electrochemical capacitors. Attention is mainly based on electrochemical assessment of the as-synthesized materials with an insight into some neutral aqueous electrolytes, mainly lithium sulphate (1 M Li2SO4) and sodium sulphate (1 M Na2SO4) solutions as potential medium owing to their non-corrosive nature, cost-effectiveness, electrochemical stability and environmentally friendliness. Significant charge propagation, with a high specific capacitance of 387.1 F g-1 was achieved for the half-cell electrode in 1 M Li2SO4 alongside excellent cycling stability for up to 5 000 cycles performed at 3 A g-1 specific current. A comprehensive electrochemical assessment is performed to understanding the relationship between solvated and diffused ions of the neutral electrolytes that could result in fast charge storage kinetics as well as high specific capacitance.