Department of Civil and Environmental Engineering , Vanderbilt University , Nashville , Tennessee 37235-1831 , United States.
Department of Chemical and Biomolecular Engineering , Vanderbilt University , Nashville , Tennessee 37235-1831 , United States.
Environ Sci Technol. 2018 Apr 3;52(7):4051-4060. doi: 10.1021/acs.est.7b06064. Epub 2018 Mar 22.
Membrane capacitive deionization (MCDI) can be typically operated with constant voltage (CV) or constant current (CC) mode in the charging stage. While a series of previous studies have compared both charging modes to identify the better operating mode, neither their performance evaluation protocols were consistent, nor did their conclusions unanimously converge. This study presents a new framework to evaluate and compare MCDI performance, considering the kinetic efficiency, the energetic efficiency, and the intrinsic trade-off between the two. A key prerequisite for making rational comparison of performance between MCDI operations is that the operations being compared should all result in the same target adsorption. With this key prerequisite and the new evaluation framework based on the trade-off curve between kinetic and energetic efficiencies, our experimental assessment and theoretical analysis suggest that whether CC or CV charging is more efficient is strongly dependent on the target adsorption and, to a less extent, on the kinetic rate of charging. However, the advantage in energy or kinetic efficiency of one charging mode over that of the other is relatively small in all cases. Our study also reveals that, for a given MCDI system, there exist regimes of target adsorptions and kinetic rates that can only be achieved by either CC or CV charging, or even regimes that can be achieved by neither charging mode. In summary, this study revises our current understanding regarding the comparison of the two typical charging modes in MCDI, and introduces a new framework for comparing the performance of different MCDI and CDI operations.
膜电容去离子（MCDI）在充电阶段通常可以采用恒压（CV）或恒流（CC）模式进行操作。虽然之前有一系列研究比较了这两种充电模式以确定更好的操作模式，但它们的性能评估协议不一致，结论也不一致。本研究提出了一种新的框架来评估和比较 MCDI 的性能，同时考虑了动力学效率、能量效率以及两者之间的内在权衡。在对 MCDI 操作的性能进行合理比较的关键前提是，被比较的操作都应导致相同的目标吸附。基于动力学和能量效率之间的权衡曲线的这个关键前提和新的评估框架，我们的实验评估和理论分析表明，CC 或 CV 充电哪种更有效率强烈取决于目标吸附，在较小程度上取决于充电的动力学速率。然而，在所有情况下，一种充电模式相对于另一种充电模式在能量或动力学效率方面的优势都相对较小。我们的研究还表明，对于给定的 MCDI 系统，存在仅可通过 CC 或 CV 充电实现的目标吸附和动力学速率的区域，甚至存在两种充电模式都无法实现的区域。总之，本研究修正了我们对 MCDI 中两种典型充电模式比较的现有理解，并引入了一种用于比较不同 MCDI 和 CDI 操作性能的新框架。
