Predicting and Enhancing the Ion Selectivity in Multi-Ion Capacitive Deionization

Abstract

Lack of potable water in communities across the globe is a serious humanitarian problem promoting the desalination of saline water (seawater and brackish water) to meet the growing demands of human civilization. Multiple ionic species can be present in natural water sources in addition to sodium chloride, and capacitive deionization (CDI) is an upcoming technology with the potential to address these challenges because of its efficacy in removing charged species from water by electro-adsorption. In this work, we have investigated the effect of device operation on the preferential removal of different ionic species. A dynamic Langmuir (DL) model has been a starting point for deriving the theory, and the model predictions have been validated using data from reports in the literature. Crucially, we derive a simple relationship between the adsorption of different ionic species for short and long adsorption periods. This is leveraged to directly predict and enhance the selective ion removal in CDI. Furthermore, we demonstrate an example of how this selectivity could reduce excess removal of ions to avoid remineralization needs. In conclusion, the method could be valuable for predicting the impact of improved device operation on capacitive deionization with multi-ion compositions prevalent in natural water sources.

Langmuir-Based Modeling Produces Steady Two-Dimensional Simulations of Capacitive Deionization via Relaxed Adsorption-Flow Coupling

“…During desalination, an applied potential precisely extracts salt ions from the water to adsorb them inside the spacious electrodes (Figure ). The process is strongly susceptible to changes in operational and structural conditions, such as the voltage, − ion concentration − and composition, − flow rate, , electrode material, − electrode modifications, , device structure, − flow mode, , and presence of ion-selective membranes. ,, Also, the ion-concentration dependency makes the intracellular dynamics important . Thus, researchers have developed models that capture some of this spatial information, such as in 1D, − partial 2D, or full 2D. , …”

Sodium to cesium ions: a general ladder mechanism of ion diffusion in prussian blue analogs

“…This makes them effective for energy storage 3 and desalination by capacitive deionization (CDI), among many potential applications. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] The versatile nature of PBAs further enables applications in carbon capture, 19 Fenton reactions, 20 sensing, 21 and biomedicine. 22,23 At the extreme end, it can even be applied for cesium decontamination [24][25][26][27][28] because the huge Cs + ions can passively replace K + ions in the matrix formed by the host structure.…”

A new automated model brings stability to finite‐element simulations of capacitive deionization

“…Different modeling approaches has been built to describe the CDI processes including molecular dynamics, [53] transmission line, [29,54,55] dynamic Langmuir, [40,41,[56][57][58][59][60] and modified Donnan (mD) [2,11,23,61,62] models. While some macroscopic studies simplify treating the entire cell as a single 0D entity, [63] others consider spatiotemporal information through spatially resolved finite-element modeling (FEM) using software packages like COMSOL.…”