A seawater battery with desalination capabilities enabling a dual-purpose aqueous energy storage system

Abstract Effectively storing electricity produced from renewable sources and increasing the supply of fresh water with a reduced carbon footprint are two pressing issues to sustainably and reliably provide electricity and clean water. In this study, a new aqueous rechargeable Na-ion battery system, which can store/release energy while operating in seawater and can also perform membrane-free seawater desalination, is developed enabling a dual-purpose energy storage system (ESS). The discharging cell of this system is composed of a sodiated NaTi2(PO4)3 electrode and a desodiated nickel hexacyanoferrate (NiHCF) electrode in 0.6 M NaCl, and generates an average output voltage of 1.19 V. The charging process is achieved in two separate cells that require low input voltages. In the first, a desodiated NaTi2(PO4)3 electrode is paired with Bi as a Cl-storage electrode, and this cell performs desalination during charging. In the second, a sodiated NiHCF electrode is paired with a chlorinated Bi electrode, and this cell performs salination during charging. The energy output generated by the discharging cell is ~94% of the combined energy inputs required by the two charging cells. As the energy consumed for the desalination and salination processes is not truly consumed but rather stored in the system through the charging process, and the majority of the energy stored during charging is recovered during discharging, the extra energy consumed for desalination is minimized. The high energy efficiency and desalination performance of the proof-of-concept dual-purpose ESS are reported with excellent cyclabilities of all component electrodes (> 1000 cycles).