Recent progress on reduced graphene oxide and polypyrrole composites for high performance supercapacitors: A review

Supercapacitors have revolutionized energy storage technology significantly since their discovery. These devices play a crucial role in various applications, including hybrid electric vehicles and other systems reliant on elec-trical energy. Supercapacitors are considered indispensable energy storage devices due to their fast charging and discharging abilities, high power density, and long cycle life. The effectiveness of supercapacitors can be improved through the design and manufacture of electrode materials. Among the carbon derivatives widely employed as supercapacitor materials, reduced graphene oxide (rGO) has garnered considerable interest due to its superior properties for supercapacitor applications, such as strong mechanical stability, superior electrical conductivity, and large surface area. However, several drawbacks exist when using rGO alone as the electrode material. Therefore, further in-depth investigations are required to address several issues, such as low specific capacitance and slow ionic diffusion due to hydrophobicity and susceptibility to rGO restacking. Another promising conducting polymer, polypyrrole (PPy), has been extensively utilized for energy storage applications as a conducting agent or an electroactive material, thanks to its variable pseudocapacitive performance resulting from its multiple oxidation states. By combining the electrical double-layer capacitances of rGO and the pseu-docapacitances of PPy, rGO/PPy composites exhibit a synergistic effect, resulting in higher specific capacitance, longer cycle life, and higher energy density. This article provides a concise overview of several methods for producing rGO/PPy composites while elucidating the critical factors influencing their electrochemical capacitive performance. Several critical aspects of cell fabrication, such as electrode preparation technique, electrolyte, and current collector, are also discussed. Furthermore, this article summarizes the existing challenges and potential prospects of producing and using rGO/PPy composites, noble metal nanoparticles, metal oxides, and metal sulfides as supercapacitor electrodes.