Antimony alloying electrode for high-performance sodium removal: how to use a battery material not stable in aqueous media for saline water remediation

Capacitive deionization (CDI) is based on ion electrosorption and has emerged as a promising desalination technology, for example, to obtain drinking water from brackish water. As a next-generation technology, battery desalination uses faradaic processes and, thereby, enables higher desalination capacities and remediation of feed water with high molar strength such as seawater. However, the full use of a large capacity of charge transfer processes is limited by the voltage window of water and the need to use electrode materials non-reactive towards the water. Using our multi-channel bi-electrolyte cell, we now introduce for the first time an alloying electrode for sodium removal in the context of water desalination. Separated by a ceramic sodium superionic conductor (NASICON) membrane, the antimony/carbon composite electrode accomplished sodium removal while chlorine removal is enabled via ion electrosorption with nanoporous carbon (activated carbon cloth). In a sodium-ion battery half-cell setup, the antimony/carbon composite electrode reaches an initial capacity of 714 mA h g−1 at a specific current of 200 mA g−1, which shows a slow but continuous degrading over the course of 80 cycles (426 mA h g−1 in 80th cycle). Our hybrid CDI cell provides a desalination capacity of an average of 294 mgNa gSb−1 (748 mgNaCl gSb−1) with a charge efficiency of ca. 74% in a 600 mM NaCl at a specific current of 200 mA g−1 and a voltage range of −2.0 V to +2.0 V.