A Universal Electrolyte Formulation for the Electrodeposition of Pristine Carbon and Polypyrrole Composites for Supercapacitors

Electrodeposition of conducting polymer-carbon composites from an electrolyte precursor solution is a facile one-step approach to fabricate device-ready electrodes for energy storage. A key challenge in this approach is the dispersion of the carbon nanomaterials with the aqueous precursor solution with previous approaches either heavily oxidizing the carbon nanomaterials or using high concentrations of anionic surfactants as dopants. However, the former reduces the electrical conductivity of carbon, while the latter reduces the ionic mobility of the conducting polymer due to the large anion size. Herein, for the first time we present a quaternary electrolyte formulation for the fabrication of pristine carbon and polypyrrole (PPy) composites that does not sacrifice either electron or ion mobility. The electrolyte uses lithium perchlorate (20 mM) as a supporting electrolyte and dopant, sodium dodecylbenzenesulfonate at a very low concentration (1.43 mM) as a surfactant, together with pristine carbon nanomaterials and pyrrole monomers. The order of magnitude difference between the concentration of the dopant and surfactant ion allows the as-deposited PPy to be doped predominantly by small-sized and mobile perchlorate anions. Composites of PPy with carbon black, carbon nanotubes, and electrochemical exfoliated graphene (EEG) have been successfully prepared using this new quaternary electrolyte. The as-fabricated PPy/EEG composite electrodes showed a specific capacitance of 348.8 F g^-1 with a high rate capability (190.7 F g^-1 at 71 A g^-1). Supercapacitor devices based on the PPy/EEG composite electrodes exhibit a high rate behavior up to 500 mV s^-1 and a long cycle life of 5000 cycles.