Induced-charge membrane capacitive deionization enables high-efficient desalination with polarized porous electrodes

초록

Exposure of a conducting porous material to an electric field in electrolytes induces an electric dipole, which results in capacitive charging of cations and anions at opposite poles. In this letter, we investigate a novel desalination method using this induced-charge capacitive deionization (IC–CDI). To do this, we devise a microscale IC–CDI platform that can visualize in situ ion concentrations, pH shifts, and fluid flows, and study ion transport dynamics and desalination performances compared to conventional CDI with unipolar / bipolar connections. Similar ion concentration and fluid flow characteristics were observed in Ohmic, limiting, and over-limiting regimes, but variations in desalination performance trends were noted based on the number of stacks. In a single cell, IC–CDI generates a higher electric field at the opposite poles of porous electrodes than simple conducted electrodes in CDIs with unipolar/bipolar connections, leading to superior salt removal and/or lower ionic current at a given applied voltage. This marks a clear contrast from CDI with bipolar connection, which lacks any advantage over CDI with unipolar connection in a single cell. These metrics of IC–CDI however deteriorated as the stack number increased, likely due to short-circuiting between the dipoles. As a result, IC–CDI in current form shows higher desalination efficient than conventional CDIs with low stack numbers (< 6), so we offer the scale-up module by repeating 4-stack IC–CDI units. Our study enhances comprehension of ion transport dynamics and desalination performance in IC–CDI, and the results could aid in the development of IC–CDI for energy/cost-efficient desalination.

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