Polymers for Charge Storage

Abstract

Current and emerging electronic devices have exacerbated the need for improvements in highperformance charge storage devices (CSDs). While traditional CSDs have relied on inorganic materials, such as metals and metal oxides [1], researchers are turning more and more to organic polymers for their charge storage ability [2]. Electroactive polymers (EAPs) rely on oxidation and reduction (redox) processes to store and release charge. These polymers can be used to store energy in batteries as well as in electrochemical capacitors. The advantages of EAPs in CSDs include high conductivity, mechanical flexibility, chemical stability, rawmaterial availability, ease of manufacturing, low cost, and reduced environmental impact [2]. There have been several recent reviews on the use of EAPs for charge storage applications [1–11]. Electroactive polymers, also known as inherently or intrinsically conductive polymers, consist of alternating double and single bonds. The removal of an electron (oxidation, also known as p-doping) results in a resonance-stabilized, positively charged polymer (Fig. 1). Conversely, the addition of an electron (reduction, also known as n-doping) results in a resonance-stabilized, negatively charged polymer (Fig. 1). The resonance delocalization of the resultant positive or negative charge results in conductivities as high as 10 S cm 1 [3], although values of 10 to 10 S cm 1 are more readily achievable. Both oxidation and reduction processes are theoretically reversible, so that the redox processes can be used repeatedly to store/release electrons. In practice, the reversibility of these processes depends on numerous factors, including polymer structure, device design, and solvent/ electrolyte choice [2]. Redox processes in EAPs result in remarkable changes in properties of EAPs, including conductivity, color, volume, permeability, and reactivity. These redox-controllable properties have led to investigation of EAPs for use in a wide range of applications including electrochromics, sensors, actuators, and charge storage [3].