High Performance Energy Efficient Bi-Functional NASICON Electrode for Continuous Cation-Selective Capacitive Deionization
Effective ion intercalation nanomaterials offer tremendous opportunities to various deionization systems such as capacitive deionization (CDI) to significantly improve the removal capacity for brackish water desalination. However, the asymmetric design of CDI devices causes a low removal rate due to the indispensable regeneration half-cycle. Furthermore, the choices of chloride selective electrodes for such devices are limited. This imposes a big challenge on further improvement of CDI systems. Herein, we report a cation-selective CDI system using a single bi-functional Na2VTi(PO4)3 @ Carbon nanomaterial with redox couples of V4+/V3+ and Ti3+/Ti4+ as an advanced symmetric electrode. The as-prepared continuous desalination set-up shows a superior removal rate of 0.029 mg g-1 sec-1 (1.74 mg g-1 min-1) with a high half-cycle removal capacity of 45 mg g-1. In addition, an extremely high cycle-stability of at least 50 cycles and extremely low energy consumption of 0.048 Wh g-1 per cycle is achieved. The bi-functional intercalation mechanism is investigated by in-situ XRD and ex-situ XPS. The symmetric device yields a simplified and low-cost configuration with improved energy efficiency and high removal capacity. This opens a new horizon towards the commercialization of CDI technologies.