‘Ladder-doped’ polypyrrole: a possible electrode material for inclusion in electrochemical supercapacitors?

Polypyrrole (pPy) electrodes containing polysulfonated aromatic anions are investigated by cyclic voltammetry as electrodes for use in electrochemical supercapacitors. These ‘ladder-doped’ materials are deposited as thick films (ca. 10 μm) having open structures that permit the rapid insertion/ejection (up to 300 mV s−1) of cations and anions from aqueous solution, and give an effective or ‘geometric’ capacitance of up to 0.40 F cm−2. The ‘dual mode’ doping behaviour seems essential for good capacitive response. These electrodes show a remarkable tendency to perform better at high cycling rates, an effect attributed to the way the structure ‘self-organises’ during the self-doping process. Good electrode response depends on protecting the open structure containing hydrophilic ion-conducting channels.