Electrochemical Desalination Using Intercalating Electrode Materials: A Comparison of Energy Demands

Abstract

One approach for desalinating brackish water is to use electrode materials that electrochemically remove salt ions from water. Recent studies found that sodium-intercalating electrode materials (i.e., materials that reversibly insert Na+ ions into their structures) have higher specific salt storage capacities (mgsalt/gmaterial) than carbon-based electrode materials over smaller or similar voltage windows. These observations have led to the hypothesis that energy demands of electrochemical desalination systems can be decreased by replacing carbon-based electrodes with intercalating electrodes. To test this hypothesis and directly compare intercalation materials, we examined nine electrode materials thought to be capable of sodium intercalation in an electrochemical flow cell with respect to volumetric energy demands (W·h·L–1) and thermodynamic efficiencies as a function of productivity (i.e., the rate of water desalination, L·m–2·h–1). We also examined how the materials’ charge-storage capacities changed over 50 cycles. Intercalation materials desalinated brackish water more efficiently than carbon-based electrodes when we assumed that no energy recovery occurred (i.e., no energy was recovered when the cell produced electrical power during cycling) and exhibited similar efficiencies when we assumed complete energy recovery. Nickel hexacyanoferrate exhibited the lowest energy demand among all of the materials and exhibited the highest stability over 50 cycles.

Electrochemical ion insertion from the atomic to the device scale

“…Ion-insertion materials have higher storage capacity than traditional carbon aerogel electrodes used in CDI, since they store ions in bulk volumes rather than in surface double layers. If ion-insertion reactions and solid diffusion are fast 140 , then these systems can be designed to achieve comparable or better energy efficiency compared to carbon-based CDI 141,142 , and a recent technology comparison shows that the PBA NiHCF is emerging as one of the most promising sodium extraction materials in this class 143 . An important means to achieve high efficiency is to recover some of the undissipated free energy extracted from composition differences during portions of the cycle when the system produces power [141][142][143][144] , thus further blurring the distinction among hybrid systems acting as both a rechargeable battery and an electro-sorption system.…”

Crystallographic design of intercalation materials

“…This reversible insertion is often accompanied by a simultaneous change to the host materials' lattice structure and/or its physical properties (i.e., optical, thermal, electronic) [1]. This intrinsic coupling between ionic (or molecular) insertion and physical properties makes intercalation materials well-suited for next-generation applications, such as electrodes in lithium batteries [2], electrochromic materials in smart windows [3,4], and ion-exchange membranes in water desalination devices [5]. Despite the technological relevance of intercalation materials, their widespread use is plagued by chemo-mechanical challenges that limit material performance and lifespans [6,7,8].…”

Porous evaporators with special wettability for low-grade heat-driven water desalination

“…[4][5][6][7][8] Currently, Reversible electrochemical desalination technologies that based on the compensation of electric charge by ionic species are promising technologies for saline water treatment because of their cyclic efficiency and reversibility, but most of them are suffered from Iow-removal capacity, efficiency and rate. 9,10 Capacitive deionization (CDI) worked on electrostatic adsorption via electrochemical doublelayer capacitance theory and Faraday Redox reaction are also prosperously developed to treat industrial saline water, desalinate seawater and water-soluble radioactive wastewater, but the high concentration of total dissolved solids (TDS) and high fouling potential of industrial saline wastewater are two major challenges in CDI process, especially when desalination of high saline wastewater. 11,12 Besides, reverse osmosis (RO) membrane technology is also regarded as the most energy-efficient desalination technology, accounting for 60% of global desalination capacity, because the liquid water does not undergo a phase transition with low energy consumption.…”