New Developments in Low-carbon Supercapacitors for Emerging Applications: A Critical Review

Abstract

Despite offering huge potential, the current commercial usage of supercapacitors has critical shortcomings in essential electrochemical performance metrics. Also, there are concerns in terms of safety, sustainability, economics, and environmental issues. The performance of a supercapacitor can be largely influenced by appropriate materials design and synthesis protocol for electrodes and electrolytes. Green and sustainable supercapacitor electrodes based on biomass have attracted much attention in developing high-power and energy-dense applications due to their abundance in nature, biodegradability, renewability, negligible toxicity, etc. Metal and metal oxide (RuO2, TiO2, MnO2, NiO, Fe3O4, Co3O4, and V2O5) composites may turn out to be very interesting candidate materials for electrodes and are covered in detail. However, the metal nitrides, sulfides, and carbide-based composites should not be ignored since they also offer some other benefits. Electrolytes play a pivotal role in supercapacitors. Therefore, water-in-salt, aqueous, nonaqueous, solid-state/quasisolid-state, and redox-active electrolytes are discussed at length. Binders as well as conductive materials are also adequately covered. The use cases of green supercapacitors in emerging applications such as automotive, renewable energy, medical, and electrical/electronic appliances are discussed. We conclude by outlining the future perspectives of the usages of supercapacitors in the pursuit of sustainable development of modern civilization.