Electropolymerized poly(3,4-ethylenedioxythiophene) coatings on porous carbon electrodes for electrochemical separation of metals

Electrode-assisted techniques are well suited for separation of ions from solutions with reduced energy and chemical consumption. This emerging platform can benefit greatly from the convection enhanced and zero-gap reactor designs unlocked by macroporous electrodes, but immobilizing ion-selective layers on such complex 3D architectures is challenging. We propose electropolymerization of conductive polymers as a coating methodology to fabricate highly conformal coatings with electrochemically-switchable ion-exchange functionality. To demonstrate this, we study the synthetic parameters, resulting morphology and ionic separation performance of poly(3,4-ethylenedioxythiophene) (PEDOT) on commercially available carbon paper electrodes. Electropolymerization of PEDOT in organic solvents results in rougher morphologies with high sensitivity to electrochemical protocols employed. When polymerized in aqueous solutions of poly(4-styrenesulfonate) (PSS-), the resulting PEDOT/PSS blend polymer forms smooth coatings with a controllable thickness down to 0.1 µm. With appropriate voltage bias, PEDOT/PSS coated electrodes can take up and release Ni2+ in the presence of excess Na+. Increasing the coating thickness decreases the adsorption capacity due to mass transfer limitations, and the maximum adsorption capacity for Ni2+ is reached for the thinnest coatings at 228 mg g-1. Through a systematic study of PEDOT/PSS coated carbon paper, we hope to establish electropolymerization as a promising avenue for porous electrode functionalization.