Conjugated Polyelectrolytes: Underexplored Materials for Pseudocapacitive Energy Storage

Abstract

Conjugated polyelectrolytes (CPEs) are characterized by an electronically delocalized backbone bearing ionic functionalities. These features lead to properties relevant for use in energy‐storing pseudocapacitor devices, including ionic conductivity, water processability, gel‐formation, and formation of polaronic species stabilized by electrostatic interactions. In this Perspective, the basis for evaluating the figures of merit for pseudocapacitors is provided, together with the techniques used for their evaluation. The general utility and challenges encountered with neutral conjugated polymers are then discussed. Finally, recent advances on the use of CPEs in pseudocapacitor devices are reviewed. The article is concluded by discussing how their miscibility in aqueous media permits the incorporation of CPEs in living materials that are capable of switching function from extraction of energy from bacterial metabolic pathways to pseudocapacitor energy storage.

Pseudocapacitive Conjugated Polyelectrolyte/2D Electrolyte Hydrogels with Enhanced Physico‐Electrochemical Properties

“…[ 29 ] This class of materials is gaining increasing interests for applications in energy storage. [ 30 ] CPE‐K is a self‐ p ‐doped conjugated polyelectrolyte that is characterized by a redox‐active conjugated poly(cyclopentadithiophene‐ alt ‐​benzothiadiazole) backbone and sulfonate pendant groups, see Figure a. It has been reported to self‐assemble into a hierarchical hydrogel structure primarily through ionic cross‐links.…”

Conjugated Polyelectrolyte/Bacteria Living Composites in Carbon Paper for Biocurrent Generation

“…[ 36 ] In all cases, the specific capacitance obtained for the CPE‐K/ S. oneidensis MR‐1 biocomposite was ≈70 F g −1 , matching literature precedents using gold electrodes. [ 7,36,42 ] However, a higher cycling stability for the biocomposite was obtained with carbon electrodes relative to their gold counterparts. Specifically, 70% of the initial specific capacitance was retained for the biocomposite atop carbon after 200 cycles compared to only 10% specific capacitance retention atop gold electrodes.…”

“…The porous structure may offer additional structural support to prevent swelling volumetric changes within the biocomposite upon cycling. [ 42 ]…”

Polypyrrole Polyethylene Composite for Controllable Linear Actuators in Different Organic Electrolytes

“…The reason why such anions stay inside the PPy network is the changing of sigma-bonds (cross-linkage) during reversible redox cycles keeping former mobile anions immobile [16] or in other cases the anions having a nonspherical form such as triflate anions (CF 3 ) not being able to diffuse out at reduction, shown especially on PEDOT linear films [17] where the porosity is greater than in PPy films. The ion mobility inside PPy films can be enhanced by increasing the overall conductivity of the films, for example by adding additional conductive particles as in ion gold implementation [18] or including polyelectrolytes to enhance ion conductivities [19,20]. PEO is known to be a polyelectrolyte often applied in Nafion membranes to increase ion mobility for lithium battery applications [21] but is also applied in bending actuators that contain an IPN membrane with PEO, sandwiched between conducting polymer electrodes [22].…”