Dr. Daniel Moreno
PAMS and Cooperative Engineering Program
Missouri State University
Abstract: Capacitive deionization (CDI) is an alternative desalination technology in which salt ions are stored within porous electrodes. Compared to reverse osmosis for lower concentration water streams, CDI has the potential to minimize energy demand and improve efficiency by operating and lower pressures and requiring less input energy. However, the structure of the electrode will limit the maximum amount of ions that can be stored, which can vary as a function of the initial temperature and concentration. Such variations can reveal important information about the mechanisms of the electrode’s desalination (electrosorption) process.
This work evaluates multiple types of CDI electrodes to determine their maximum storage capabilities as a function of their chemical composition. CDI processes are examined and compared for electrodes with no chemical charge, with fixed chemical charge, and redox-active electrodes with variable chemical charge. The main focal points from this research are: (1) evaluating ideal, equilibrium-based cycles to determine thermodynamically if Faradaic CDI (FaCDI) can attain higher thermodynamic efficiency, (2) evaluating short-term cycles in continuous mode as well as through a new means for predicting batch-mode performance, and (3) extending batch-mode performance over a range of porous electrodes to determine fitting isotherms as well as free energy, entropy, and enthalpy. From this study, we conclude that using a variable chemical charge via FaCDI can reduce energy consumption, improve efficiencies, and increase overall ion electrosorption. For all electrodes studied, new insight is highlighted into the computational analysis of predicted Gibbs free energy, entropy, and enthalpy of adsorption.