Enhanced Capacitive Deionization using Carbon Electrodes Conformally Coated with Metal Oxides by Atomic Layer Deposition

Access to clean water is a global problem that has led to the development of multiple desalination techniques. All techniques strive to reduce the cost of desalinating water to provide clean water in a cost effective manner. Capacitive deionization (CDI) is a new technique that can reduce the cost of ownership by ~85% compared with reverse osmosis for brackish water. This project will further improve the cost effectiveness of CDI by significantly improving the capacitance of the carbon electrodes used for CDI. The cost of these carbon electrodes accounts for ~50% of the capital cost of a CDI system. Higher capacitance is derived from adding metal oxide coatings to the carbon electrodes that are employed for CDI. Metal oxide coatings are electrochemically active and store additional ions on their surface. These extra stored ions add to the capacitance obtained from the electric double layer effect. This extra capacitance is known as pseudocapacitance. Poor metal oxide coating techniques have demonstrated increasing the electrode capacitance by more than two times. Estimates indicate that the capacitance could be increased by more than a factor of 10 if the metal oxide coating could be conformal on the entire surface area of the electrode. This project will use atomic layer deposition (ALD) to obtain larger capacitances on CDI carbon electrodes. ALD NanoSolutions and the University of Colorado will demonstrate that TiO 2 ALD coatings can significantly improve the capacitance of carbon electrodes. They will also work with a commercial partner to evaluate TiO 2 ALD coatings on carbon electrodes used for CDI. Various TiO2 film thicknesses and coating conditions will be evaluated to optimize the capacitance enhancement. Commercial Applications and Other Benefits: Cost effective water purification technologies can be applied to desalinate seawater and brackish water or purify wastewater. If successful, this proposed technology could significantly reduce the capital and maintenance costs of CDI systems. Cost reduction is possible by significantly reducing the surface area of the carbon electrodes needed for desalination.