Searching for alkali acetates and their mixtures for closed-loop reverse electrodialysis with high cell potential difference and high Gibbs free energy of mixing by thermodynamic modeling

The application of non-conventional salt in closed-loop reverse electrodialysis has attracted much attention. The search for such salt solution is an important first step. In the present work, the activity coefficients, the values of ideal potential difference and Gibbs free energy of mixing of alkali acetates and their mixtures are systematically predicted by electrolyte molecular interaction volume model, and the prediction results are analyzed from the perspective of the variation law of activity coefficients to search the most promising systems. In contrast to the NaCl system and under the same concentration conditions (m = 0.1-3.5 mol kg(-1)), the ideal potential difference and Gibbs free energy of mixing of the KAc, RbAc and CsAc systems are increased obviously among the pure salt systems, with increases of about 12%-14% and 16%-18%, respectively; while the ideal potential difference and Gibbs free energy of mixing of the KAc + RbAc, KAc + CsAc, and RbAc + CsAc systems are improved obviously among the mixed systems, with increases of about 13% and 17%-18%, respectively. By further comparison, the ideal potential difference and Gibbs free energy of mixing of the mixture are found to be included in the range between the two pure salt cases. Finally, from the thermodynamic modeling point of view, there is no benefit from using the alkali acetate mixtures. The performance of the pure salt2 (a mixture consists of the pure salt1 and the pure salt2) is always superior to that of the mixture, and the pure CsAc system provides almost the maximum values of ideal cell potential difference and Gibbs free energy of mixing.