Condensing Vapor Phase Polymerization (CVPP) of Electrochemically Capacitive and Stable Polypyrrole Microtubes

We introduce a novel condensing vapor phase polymerization (CVPP) strategy for depositing microtubes of the conducting polymer polypyrrole; these serve as one-dimensional hollow microstructures for storing electrochemical energy. In CVPP, water droplets are structure-directing templates for polypyrrole microtubes. Water vapor condensation and polymerization occur simultaneously - conformal coatings of microtubes deposit on porous substrates such as hard carbon fiber paper or glass fiber filter paper. A mechanistic evolution of the microtubular morphology is proposed and tested based on the mass transport of water and monomer vapors as well as on the reaction stoichiometry. A coating of PPy microtubes is characterized by a high reversible capacitance of 342 F g^-1 at 5 mV s^-1 throughout 5000 cycles of cyclic voltammetry and a low sheet resistance of 70.2 Ω □^-1. The open tubular structure is controlled in situ during synthesis and leads to electrodes that exhibit electrochemical stability at high scanning rates up to 250 mV s^-1 retaining all stored charge, even after extensive cycling at 25 mV s^-1.