Redox Poly-Counterion Doped Conducting Polymers for Pseudocapacitive Energy Storage

Conducting polymers (CPs) have been widely studied for electrochemical energy storage. However, the dopants in CPs are often electrochemically inactive, introducing "dead-weight" to the materials. Moreover, commercial-level electrode materials with high mass loadings (e.g., >10 mg cm(-2)) often encounter the problems of inferior electrical and ionic conductivity. Here, a redox-active poly-counterion doping concept is proposed to improve the electrochemical performance of CPs with ultra-high mass loadings. As a study prototype, heptamolybdate anion (Mo7O246-) doped polypyrrole (PPy) is synthesized by electro-polymerization. A 2 mm thick PPy electrode with mass loading of approximate to 192 mg cm(-2)reaches a record-high areal capacitance of approximate to 47 F cm(-2), competitive gravimetric capacitance of 235 F g(-1), and volumetric capacitance of 235 F cm(-3). With poly-counterion doping, the dopants also undergo redox reactions during charge/discharge processes, providing additional capacitance to the electrode. The interaction between polymer chains and the poly-counterions enhances the electrical conductivity of CPs. Besides, the poly-counterions with large steric hindrance could act as structural pillars and endow CPs with open structures for facile ion transport. The concept proposed in this work enriches the electrochemistry of CPs and promotes their practical applications.