Design of a novel asymmetric capacitive deionization device with high desalination performance

Abstract

It is a serious challenge to develop a capacitive deionization device (CDI) with high electrosorption capacity, high desalination rate and low energy consumption. Herein, based on the difference of electromigration rate and anodic oxidation between Na⁺ and Cl⁻, a novel asymmetric capacitive deionization (A-CDI) system is developed, i.e., the mass loading of positive and negative electrode active material (sweet potato activated carbon) is different. The experimental results show that the A-CDI is more satisfactory than the conventional symmetric capacitive deionization electrode (S-CDI) in kinetics and thermodynamics. Furthermore, A-CDI has a high salt removal capacity, low energy consumption, fast regeneration and super cycle stability, and salt ions accumulate more in the A-CDI system. However, when the positive and negative electrodes exceed the optimal mass matching, the mass utilization rate of the active substances decreases with the increase of the negative mass loading. Moreover, potential analysis of zero charge (E_pzc) used anode material shows that the faradaic reactions at the electrode can be significantly prolonged in the A-CDI state, and the electrode voltage is closely related to the mass of the active substance loaded on the electrode. Overall, this study provides theoretical and experimental support for the efficient utilization of electrode active materials in the desalination process, and provides a reference for the design of high-performance CDI devices from the perspective of electrosorption desalination and energy storage. Finally, the adsorption mechanism of batch-mode CDI is analyzed.