Green Synthesis of Metal Oxide-Based Electrode Materials for Supercapacitor Electrode

Renewable energy sources have gained attention as promising, economically viable, and environmentally friendly alternatives to address the concerns surrounding climate change and the eventual depletion of non-renewable fossil fuel resources ( Figure 1 ). It is important to note that significant portions of renewable energy sources are intermittent or variable. Therefore, there is a need to develop effective storage techniques to ensure a constant and reliable supply of energy. The most common kind of storage system in use right now is a secondary battery ( Dubal et al. 2017 ). The power density of batteries is modest despite their high-energy density. The chemical nature of energy storage in batteries leads to physicochemical changes in the electrolytes and electrodes during charging and discharging. Unfortunately, these changes have a negative impact on both the battery life and cyclability. Because of this, their employment in energy storage is limited. However, supercapacitors are superior to batteries in terms of power density and cycle stability ( Latha et al. 2021 , Palanisamy et al. 2019 ). Despite their potential benefits, batteries are often deemed impractical for energy storage due to their low energy density, high effective series resistance, and relatively high cost. According to a comparison of energy density between supercapacitors, lead-acid batteries, and lithium-ion batteries, the energy density of supercapacitors is lower than that of lead-acid and lithium-ion batteries, but they outperform secondary batteries in terms of power density, life cycle, cyclability, and safety. They are getting a lot of buzz for their potential as a novel energy storage ( Simon and Gogotsi 2008 ).