Investigating the Role of Operating Parameters and Surface Treatments of Carbon Based Electrodes in Capacitive Deionization

This research focused on studying salt ion removal behavior and regeneration of electrodes used in capacitive deionization (CDI). CDI is a novel deionization technology that utilizes electrochemical processes to extract ions from water and either hold them electrostatically on the electrode surface or trap them in a double layer formed next to surface of electrodes. The use of porous carbon materials as electrodes in CDI enhances ion removal capacity because of availability of high surface area, conductivity, porosity, non-corrosive behavior, and other favorable properties. Experiments were conducted with a synthetic NaCl solution prepared in the laboratory. The first part of this dissertation focused on studying the adsorption and desorption behavior of CDI electrodes under various operating parameters. The effects of applied voltage, ambient temperature, flow rate, and initial concentration of solution on the salt removal behavior of CDI electrodes during the adsorption stage were studied. An isotherm study was conducted to model the data obtained during adsorption stage. Regeneration of saturated/exhausted CDI electrodes was achieved through desorption with observed variables being applied reverse potential, duration of applied reverse potential, ambient temperature, and flow rate. The second part of this research focused on studying salt removal behavior of CDI electrodes before and after surface treatment. Two types of surface treatments were studied – nitric acid treatment and gold deposition on electrode surface. This is the first study to use novel gold deposited carbon/aerogel fiber paper-based electrodes in CDI experiments. The salt removal behavior of treated electrodes was studied for two symmetric (same electrode on both sides as positive and negative) and two asymmetric (treated electrode on one side and untreated on the other side) electrode configurations. The results from these configurations were compared with symmetric configuration of untreated electrodes (both positive and negative electrodes are untreated). The characteristics of the electrodes before and after surface treatment were assessed based on scanning electron microscopy (SEM), three-dimensional laser confocal microscopy, cyclic voltammetry (CV), Fourier transform spectroscopy (FTIR), and surface area and porosity measurement from BET isotherm analysis. The highest salt removal capacity achieved was 8.0 mg/g of NaCl when a gold-deposited electrode was used as an anode and an untreated electrode was used as a cathode