(694j) Synthesis of p-Doped Polypyrrole (PPy) and Poly (3,4,) Ethylene-Dioxythiophene (PEDOT) Composite Electrodes for Reversible Ion Exchange

Direct electrodeposition onto a carbon electrode substrate was used to create p-doped polypyrrole (PPY) and poly (3,4,) ethylene-dioxythiophene (PEDOT) composite electrodes for ion exchange. The effect of the dopant size and charge on ion exchange was examined in solutions containing sodium, calcium, magnesium or iron salts. While smaller dopant ions may leach from the polymer matrix; larger organic sulfonic acids are stably bound in the polymer structure. Test dopants included toluene sulfonic acid (TSH), ethylbenzene sulfonic acid (EBSH), naphthalene disulfonic acid (NDSH), and polystyrene sulfonic acid (PSS). Electrodes were made with three polypyrrole (PPy) to dopant molar ratios (1:1, 2:1, and 1:1.5), and 3 deposition times. The weight of polymer deposited was determined by weighing samples before and after, and by integration of the electrodeposition curves. The resulting electrode films were imaged via SEM with elemental analysis. Most of the PPY:PSS deposits show “cauliflower” type morphology, with a basic structure in the 3 to 8 micron range; however, when smaller dopants (EBSH) are used, unusual “cracked egg shell” structures are formed. This could be the result of a self-assembly process caused by the surfactant nature of the dopant. The electro-deposited PPy films are essentially 2-dimension, and adhere poorly to most surfaces, so creation of a substrate with good surface adhesion, high surface area, porosity, and conductivity is essential. These novel electrodes have been characterized electrochemically in several ionic solutions via Dual Electrode Cyclic Voltametry (DECV) to identify the ion insertion and removal voltages and currents, and via Cyclic Step ChronoAmperometry (CSCA) to determine the ionic capacities and charge/discharge rates of the electrodes. We propose a combined ion exchange and Electrical Double Layer (EDL) mechanism to explain the observed results. This combination permits higher ion removal capacities than CDI or conventional ion exchange materials alone. Sodium ion uptakes of greater than 50 mg per gram of polymer have been measured for some formulations, indicating a potential for desalination or water softening applications.