EAGER: Polymer Sponge Electrodes for Energy-Efficient Desalination

Current seawater desalination technology is energy-intensive and costly, limiting our ability to generate clean water for an increasing global population. In recent years, researchers have explored a new concept based on the removal of salt from seawater using a battery-like device where salt water flows into the device, salt ions bind to electrodes within the device, and fresh water flows out.

One would expect this technology, called capacitive deionization (CDI), to maximize the energy efficiency of desalination by recovering input energy through discharge of the electrodes—similar to charging and discharging a battery. However, the performance of CDI devices has not yet been competitive for seawater desalination. Researchers at the University of Missouri will work to understand the origins of the poor performance of CDI electrodes for seawater desalination and overcome these limitations to boost the energy efficiency of CDI.

The investigators will decouple and independently study the two main factors thought to drive CDI inefficiency – low ion uptake capacity and slow ion transport within CDI electrodes. Electrically conductive coatings that bind large amounts of ions will be used to control the ion uptake capacity of electrodes, while a soft, compressible electrode matrix will be used to control the rate of ion transport within the electrodes using mechanical compression during charging.

This work will fill a critical gap in understanding how electrode design aspects are coupled with physical processes to drive CDI performance. The outcomes of this project will define the most promising avenues for investigation in pursuit of the next generation of desalination technology.

This project will establish a new modality of CDI electrode that integrates high-rate, faradaic surface reactions for rapid ion uptake within a soft, compressible sponge substrate for rapid ion transport within the CDI electrode through mechanical compression of the sponge. To generate these electrodes, researchers will employ established molecular layer deposition (MLD) chemistry using sequential reaction of gas-phase precursors to impregnate microporous polyurethane (PU) foams with electrically-conductive and redox-active polyethylenedioxythiophene (PEDOT) coatings.

The project will (1) study key synthesis aspects enabling the fabrication of compressible CDI electrodes and (2) benchmark what level of CDI efficiency can be delivered from compressible electrodes. Researchers will study the impact of PEDOT thickness, foam void volume, and compression rate on the energy efficiency of ion uptake. This work will help researchers understand and overcome the barriers limiting the performance of existing CDI electrodes, potentially enabling CDI to outperform current seawater desalination technology and providing low-cost, clean water to help address global water scarcity.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.