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.
Conformality of the coating on carbon fibers verified via EDX, potentials of the reference electrodes, segmentation procedure, AAS calibration, electropolymerization data, coating verification of thin and thick layers via EDX, capacitance voltammograms, electrochemical adsorption & desorption data, table with best sample of this work compared against various electrode-assisted ion-exchange systems