Electrochemical Characterization of Activated Carbon Cloth for Capacitive Deionization

The global water demand continues to increase as population growth, urbanization, and industrialization intensify. The resulting pressure on limited water resources and environmental concerns about current treatment methods have inspired research and development of alternative separation approaches including electrochemical separations, such as capacitive deionization (CDI). CDI is a low cost and low energy electrochemical separation technology that works by applying a potential of ~1.2 V to a system to remove ions from water. Activated carbon cloth (ACC) is a promising electrode material for CDI because of its electrical conductivity, porosity, and large surface area. However, previous studies show that oxidation of ACC is leading to decreased performance over a long period of time. This work aims to connect CDI performance with quantitative electrochemical properties. Various CDI experiments were performed by cycling an electrochemical cell more than 1,000 times. Using a three-electrode electrochemical cell, cyclic voltammetry was performed to calculate the specific capacitance of pristine ACC in comparison to the post-CDI ACC. Additionally, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were performed, and the results are consistent with carbon oxidation. This work shows that cyclic voltammetry is a valuable tool for investigating and understanding the electrochemical properties of ACC electrodes and their connection to CDI performance. Oxidation was not observed following 1,000 CDI cycles with an inorganic salt solution (sodium chloride). However, due to successive voltage cycling and prolonged voltage application in the presence of an organic salt solution (sodium butyrate), a decrease in specific capacitance and an increase in oxygen content were observed. More tests need to be performed to fully understand the conditions that lead to oxidation and the extent of its damage.