A New Strategy of Using Cation Intercalation Electrodes for Water Desalination

Water desalination is a promising technological solution to water scarcity. While several technologies are currently utilized to produce freshwater from saline water sources, there are remaining challenges including intensive energy usage (e.g., thermal distillation), fouling (e.g., reverse osmosis), and high material costs (e.g., electrodialysis). The use of cation intercalation electrodes allows for electrochemically driven capture and release of ions, thus effectively desalinating water using inexpensive electrode materials that require low voltage without producing byproducts. To date, previous approaches using cation intercalation electrodes have focused on intercalation and deintercalation of Na+ in order to directly capture Na+ that is abundant in saline water. This approach has limited the choice of electrode materials and electrochemical properties, which are crucial for efficient water desalination. To overcome this challenge, we demonstrated a new strategy for water desalination using cation intercalation electrodes that interact with K+. Water desalination was achieved in a 4-channel electrochemical flow cell separated by an alternative array of anion and cation exchange membranes with copper hexacyanoferrate (CuHCF) as a model electrode material. Deintercalation of K+ upon oxidation of CuHCF enabled the transport of Cl− through an anion exchange membrane from the adjacent channel that produces desalinated water. Intercalation of K+ upon reduction of CuHCF enabled the transport of Cl− through an anion exchange membrane to the adjacent channel that produces concentrated water. A cation exchange membrane located between desalinated and concentrated water channels allowed for separating Na+. Using the new concept of utilizing K+, several performance parameters were evaluated including electrochemical properties, salt separation, and energy consumption. Collectively, we show that the use of K+ as an intercalant for cation intercalation electrodes can represent a new strategy for electrochemical water desalination.