Chloride ion, the majority salt in nature, is ∼52% faster than sodium ion (D[subscript Na+] = 1.33, D[subscript Cl−] = 2.03[10[superscript −9]m[superscript 2]s[superscript −1]]). Yet, current electrochemical desalination technologies (e.g. electrodialysis) rely on bipolar ion conduction, removing one pair of the cation and the anion simultaneously. Here, we demonstrate that novel ion concentration polarization desalination can enhance salt removal under a given current by implementing unipolar ion conduction: conducting only cations (or anions) with the unipolar ion exchange membrane stack. Combining theoretical analysis, experiment, and numerical modeling, we elucidate that this enhanced salt removal can shift current utilization (ratio between desalted ions and ions conducted through electrodes) and corresponding energy efficiency by the factor ∼(D[subscript −] − D[subscript +])/(D[subscript −] + D[subscript +]). Specifically for desalting NaCl, this enhancement of unipolar cation conduction saves power consumption by ∼50% in overlimiting regime, compared with conventional electrodialysis. Recognizing and utilizing differences between unipolar and bipolar ion conductions have significant implications not only on electromembrane desalination, but also energy harvesting applications (e.g. reverse electrodialysis).
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机译:氯离子是自然界中的多数盐,比钠离子快52%(D [下标Na +] = 1.33,D [下标Cl-] = 2.03 [10 [上标-9] m [上标2] s [上标- 1]])。然而,当前的电化学脱盐技术(例如电渗析)依赖于双极离子传导,同时去除一对阳离子和阴离子。在这里,我们证明了新颖的离子浓缩极化脱盐技术可以通过实现单极性离子传导在给定电流下增强除盐能力:与单极性离子交换膜叠层仅传导阳离子(或阴离子)。结合理论分析,实验和数值模型,我们阐明了这种增强的除盐效果可以使电流利用率(脱盐离子与通过电极传导的离子之间的比率)和相应的能量效率以〜(D [subscript-]-D [subscript] +])/(D [下标−] + D [下标+])。与传统的电渗析相比,单极性阳离子传导的这种增强特别适合于NaCl脱盐,在超限条件下可节省约50%的功耗。认识和利用单极性和双极性离子传导之间的差异不仅对电膜脱盐有重要意义,而且对能量收集应用(例如反向电渗析)也有重要意义。
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