New Strategies for Electrochemical Water Desalination Using Bi as a Cl-Storage Electrode

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Population growth has increased demand for freshwater to critical levels. Desalination of seawater has the potential to address this issue. However, current technology does not have the efficiency needed for sustainable operation. The goal of this project is to develop two types of novel electrochemical desalination cells for highly efficient desalination of brackish and seawater. The novel desalination technology manages energy, water, and dissolved salts different from existing desalination methods. If successful, this technology has the potential to provide efficient desalination to sustainably meet the increasing demands for freshwater in the Nation.The proposed research will use bismuth (Bi) as a new chloride (Cl)-storage electrode in two novel desalination strategies. The first strategy is to create a membrane-free desalination battery by combining Bi as a Cl-storage electrode with a sodium (Na)-storage electrode. This battery can store and release salt ions while simultaneously storing and releasing energy, thus minimizing the net energy requirement for desalination. The second strategy is to construct an electrodialysis (ED) cell composed of Bi and BiOCl electrodes. Compared to conventional ED cells, the operating voltage of the Bi/BiOCl ED cell can be markedly lowered because the forward Bi chlorination and reverse BiOCl dechlorination redox reactions are used as the electrode reactions. The operation of the proposed desalination cells is based on electrochemical redox reactions involving simultaneous electron and ion transfer, ion storage, and phase transformations. This is a highly novel approach compared to conventional desalination methods. The proposed research will establish atomic level mechanistic understanding of kinetics, cyclability, and capacity of Cl-storage/release on the Bi and BiOCl electrodes. This knowledge is essential to enhance desalination efficiency with a minimum energy input. If successful, the electrochemical desalination processes can be easily integrated with various other electrochemical processes, including electrochemical water disinfection and electrochemical production of fuels and other chemicals.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.