Electrochemical Desalination of Seawater and Hypersaline Brines with Coupled Electricity Storage

Abstract

We present a zinc|ferricyanide hybrid flow battery that achieves extensive first-pass desalination while simultaneously supplying electrical energy (10 Wh/L). We demonstrate 85% salt removal from simulated seawater (35 g/L NaCl) and 86% from hypersaline brine (100 g/L NaCl), together with reversible battery operation over 100 h with high round-trip efficiency (84.8%). The system has a high operating voltage (E 0 = +1.25 V), low specific energy consumption (2.11 Wh/L for 85% salt removal), and a desalination flux (4.7 mol/m 2 •h) on par with that of reverse osmosis membranes. Salt removal was similarly effective at higher feed salinities, for which reverse osmosis becomes physically impossible because of the pressure required. The results have positive implications for regions that rely on desalination for their freshwater needs, especially where sea salinity is high. Alternatively, the battery may also be useful in minimal liquid discharge wastewater treatment if operated as a brine concentrator.

Dual‐Zinc Electrode Electrochemical Desalination

“…This technology can be used to achieve an ion capture capacity that is up to six times higher than conventional CDI . Various deionization designs based on the faradaic electrode reaction have been proposed, including rocking‐chair desalination, redox‐flow battery desalination, and some novel design desalination . These desalination devices operate by the use of individual capture/release of ions by two separate electrode materials.…”

Integrated Saltwater Desalination and Energy Storage through a pH Neutral Aqueous Organic Redox Flow Battery

“…To more directly compare this cell's performance to other reported systems, the cell was also cycled at slower current density (charge at 2.5 mA cm −2 , discharge at 1.33 mA cm −2 ) to more directly compare its energy efficiency to literature examples (Table 1, Figure S2, Supporting Information). Among reported desalination flow batteries (Zn/K 4 [Fe(CN) 6 ], [ 16 ] VCl 3 /NaI, [ 17 ] and FMN‐Na/4‐HO‐TEMPO [ 18 ] ), the Zn/K 4 [Fe(CN) 6 ] desalination RFB represents the most efficient system truly capable of providing both power and near completely desalinated water (Table 1). Slowing the current to still twice that of the previously reported Zn system, the MV system achieves a deeper level of salt removal at a much more comparable energy cost.…”

“…Slowing the current to still twice that of the previously reported Zn system, the MV system achieves a deeper level of salt removal at a much more comparable energy cost. The combination of higher current density and larger cell capacity delivered a nearly ninefold increase in the freshwater production rate compared to the zinc system, [ 16 ] while maintaining a competitive energy efficiency compared to reverse osmosis. The slower applied current allowed for a deeper level of desalination.…”

“…[ 16–18 ] These first attempts show promising ability as desalinators, with energy efficiency of <15 KJ mol −1 of salt removed. [ 16–18 ] However, simple metal salts (ZnCl 2 , VCl 2 , and NaI) used as charge storage materials in these reported desalination RFBs are subject to the issue of membrane crossover which causes irreversible capacity loss, thus reducing the cycling life of these desalination RFBs. In addition, high cell resistance of these systems limits the current density available to <2 mA cm −2 .…”

Vertically aligned carbon nanotubes: production and applications for environmental sustainability

“…Ion sorption is the fundamental property that enables heavy metal removal, electrochemical desalination, supercapacitors, and batteries; that is, most of the energy storage applications rely on this property of CNTs. The nanoporous structure, enormous number of available adsorption sites, and high conductivity enable CNTs to act as the active component in devices for both water treatment and energy storage, potentially tackling the water scarcity and energy crises (and some have proposed that this could be done simultaneously 155,156 ). The available heavy metal ion adsorption investigations are mostly confined to randomly oriented and solution-dispersed CNTs, and several studies have claimed that surface functional group density is the key control factor to enhance heavy metal adsorption capacity.…”