Electrochemical aspects of supercapacitors in perspective: From electrochemical configurations to electrode materials processing

Abstract

An electrochemical asymmetric capacitor is a device fabricated with a dissimilar electrode configuration possessing a pseudocapacitive (Faradaic process) or capacitive (non-Faradaic process) nature with different charge storage mechanisms leading to high power and long cycle life. However, the energy density and power density are improved by increasing the specific capacitance and the operating voltage of the device through novel materials processing. In this perspective, electrochemical techniques (in different cell configurations) will be analyzed to divulge the electrochemical aspects of supercapacitors (SCs). The two different active materials for cathode and anode in SCs using abundant, low-cost, environmentally friendly materials processed via facile experimental methods, exploiting green energy transition, are presented. In view of these facts, manganese dioxide (MnO₂) with the occurrence of a redox reaction (diffusion-controlled kinetics), and activated carbon (AC) with the electrostatic contribution (surface-controlled kinetics) are paired as positive and negative electrodes that can be principal electrode materials for SCs. MnO₂ can be synthesized using different techniques, the electrochemical technique yields the highly pure electrolytic manganese dioxide (EMD). On the other hand, AC is synthesized via the thermochemical conversion process of carbonization and activation. Here, a brief description of the procedures and schematics of the methods to produce EMD and AC in bulk has been summarised. The electrochemical analysis of materials processing inspires and enables simple modifications to the synthesis that could catalyze changes in storage properties.