Department of Civil and Environmental Engineering, Vanderbilt University, Nashville, TN 37235-1831, USA.
Wetsus, European Centre of Excellence for Sustainable Water Technology, Oostergoweg 9, 8911 MA Leeuwarden, The Netherlands.
J Colloid Interface Sci. 2018 Feb 15;512:522-528. doi: 10.1016/j.jcis.2017.10.060. Epub 2017 Oct 17.
It is a widely accepted principle that a thermodynamically reversible desalination process should consume the Gibbs free energy of separation. This principle has been shown in reverse osmosis and has important practical implications in reducing its energy consumption. Capacitive deionization (CDI) with carbon electrodes, a desalination process based on electrical double layer (EDL) formation, should also follow such a principle when it operates in a thermodynamically reversible way. Inspired by a previous thermodynamic analysis on a three-stage reversible CDI process using the Gouy-Chapman-Stern model, we conducted a thermodynamic analysis of a four-stage reversible CDI cycle using the modified Donnan model. This analysis better reflects the cyclic nature of practical CDI operations and account for the significant EDL overlap in nanosized micropores of realistic CDI electrodes. Our analysis of CDI cycles with different separations and final discharge voltages shows that the electrical work to complete a four-stage cycles is numerically exactly identical to the Gibbs free energy of separation, as long as the cycle is operated in a thermodynamically reversible manner.
一个被广泛接受的原则是，热力学可逆脱盐过程应该消耗分离的吉布斯自由能。这个原则在反渗透中得到了证明，并在降低其能耗方面具有重要的实际意义。基于双电层（EDL）形成的电容去离子（CDI），在热力学可逆方式下运行时，也应该遵循这样的原则。受之前使用 Gouy-Chapman-Stern 模型对三阶段可逆 CDI 过程进行热力学分析的启发，我们使用改进的 Donnan 模型对四阶段可逆 CDI 循环进行了热力学分析。该分析更好地反映了实际 CDI 操作的循环性质，并考虑了实际 CDI 电极纳米级微孔中 EDL 的显著重叠。我们对不同分离和最终放电电压的 CDI 循环进行了分析，结果表明，只要在热力学可逆方式下运行，完成四阶段循环所需的电功在数值上与分离的吉布斯自由能完全相同。
