Seawater battery desalination with sodium-intercalation cathode for hypersaline water treatment

Abstract

The seawater battery desalination (SWB-D) system has a unique feature of storing energy while desalinating water. Contrary to other electrochemical processes, such as capacitive de-ionization or battery electrode deionization, SWB-D can be used to directly desalinate seawater owing to the high sodium uptake of the sodium metal composed anode. However, a relatively long time is required for desalination in this newly developed SWB-D because of the sluggish oxygen evolution reaction at the cathode, hindering the practical application of the SWB-D system for desalination. Hence, we propose using a sodium-intercalating cathode (nickel hex-acyanoferrate; NiHCF) instead of a capacitive material (carbon felt) in the SWB-D system to overcome this limitation. The redox reaction of NiHCF doubled the applied current from 1 to 2 mA (from 6.5 to 13.0 A m2) under an initial threshold voltage of 4.5 V, resulting in nearly twice the salt removal rate for the hypersaline water treatment (1.2 M NaCl). In addition, the energy efficiency of the system significantly increased from approximately 61% to 86%. Therefore, using an intercalation cathode in the SWB-D system can minimize the time required for hypersaline water treatment with a higher energy efficiency.