A review on the advances in electrochemical capacitive charge storage in transition metal oxide electrodes for pseudocapacitors

With the remarkable growth in renewable energy and zero-commission commitments, the requirement for energy storage has driven the research by a storm. The supercapacitor is one of the energy storage technologies that have seen significant contributions in recent applications. With the aim of increasing the specific capacitance and the energy density, extensive research is carried out to improve the electrode characteristics. Although recent work has shown great progress in improving the performance of these electrodes, the practicality and scalability of the presented synthesis or fabrication methods seem near impossible. Electric double-layer capacitors are already commercialized and have had great success, pseudocapacitors on the other hand are yet to make it into the industry due to various manufacturing challenges and tremendous complexity involved. In this comprehensive review, a summary of various nanosynthesis methods with their advantages and drawbacks is presented. It proceeds by briefly highlighting various supercapacitors followed by emphasizing the characteristics of electrodes as well as a few objectives that need to be considered during the fabrication. Also reviewed in this paper is much research that demonstrates remarkable performance but also brings to highlight the drawbacks during electrode preparation. In addition, a significant emphasis is placed on green synthesis, an economical approach for the development of the supercapacitor electrode.