Recent trends in hierarchical electrode materials in supercapacitor: Synthesis, electrochemical measurements, performance and their charge-storage mechanism

Abstract

Supercapacitors are energy storage devices that getting significant research interest among global researchers due to their features such as high specific capacitance, quick charge/discharge, high power density, prolonged cycle life, and safety that contribute to applications in portable electronic devices. Electrode materials are key constituents of supercapacitors and they control their electrochemical performances. There are various structures of electrode materials have been developed for supercapacitors such as core-shell structures, hetero-structures, and hierarchical structures. Among the structures, hierarchical electrode materials (HEMs) are low-cost, easy to synthesize, have high surface area, high active sites, and high electrochemical performances. Thus, this review focuses on the recent synthesis of hierarchical-type electrode materials, electrochemical setup, and characterization, analyses three- and two-electrode system performances in the use of supercapacitors, and charge-storage mechanisms, and summarizes critical viewpoints for future research. The performance of HEMs-based supercapacitors is shown to be high when compared to a single type of electrode. In supercapacitors, porous carbons, metal-organic frameworks, and transition metal sulfides-based HEMs have exceptional electrochemical capabilities across all parameters, including specific capacitance, cycle stability, energy density, and capacitance retention, as found in this review. This review may be helpful to the primary researchers who are working on the preparation and measurement of HEMs for supercapacitor applications. Further, the hierarchical structure-based electrode material is promising for future research in advanced supercapacitor research and could be of interest in technology transfer.