Fabrication methods, pseudocapacitance characteristics, and integration of conjugated conducting polymers in electrochemical energy storage devices

Among the diverse range of modern renewable energy storage technologies, electrochemical energy storage devices have been rapidly adopted across various applications owing to their superior characteristics, including high coulombic efficiency, elevated energy and power densities, scalability, modularity, and rapid response capabilities. Conjugated conducting polymers have recently attracted significant attention in electrochemical energy storage devices due to their unique pseudocapacitive behavior, hybrid ionic/electronic conduction, rapid doping/de-doping dynamics, bulk intercalation of ionic species, high specific capacity, and exceptional structural and thermal stability. Conducting polymers exhibit pseudocapacitance through reversible redox reactions coupled with doping/de-doping processes, facilitating the movement of counterion dopants and ionic species between the polymer matrix and the electrolyte. The size and nature of counterion dopants significantly influence the electrochemical performance of these polymers. Small counterion dopants like chloride enhance redox exchange with the electrolyte and broaden the electrochemical potential window, which is advantageous for electrochemical energy storage devices. The pseudocapacitive properties can be further enhanced by increasing the semi-crystalline characteristics and attaining longer polymer chains. This review article focuses on the fabrication methods, fundamental aspects of ionic and electrical conductivity, and pseudocapacitance characteristics of conjugated conducting polymers, as well as their applications in Li–ion batteries, supercapacitors, and redox flow batteries.