Poly(arylene alkylene)-Based Ion-Exchange Polymers for Enhancing Capacitive Desalination Capacity and Electrode Stability

Membrane capacitive deionization (MCDI) has emerged as a promising technique for desalination due to the merits of high capacity, low energy consumption, and high energy efficiency. However, normal free-standing ion-exchange membranes are used in MCDI, and they usually have the drawbacks of high thickness and cost, limiting their large-scale application in industrial promotion. Here, we report a scalable, continuous processing strategy to produce MCDI electrodes for enhancing capacitive desalination capacity and electrode stability, in which the carbon electrodes are coated using poly(arylene alkylene)-based ion-exchange polymers. The MCDI based on integrated ion-exchange polymer-coated membrane electrodes (C-MCDI) delivered a high salt adsorption capacity of up to 23.7 mg g(-1) and an excellent charge efficiency of up to 98%, far higher than that of membrane-free CDI with bare carbon electrodes and MCDI with free-standing membrane-based carbon electrodes (FS-MCDI). The COMSOL simulation demonstrated that the coated ion-exchange membrane in C-MCDI was more effective for reducing the interface contact resistance between the carbon and ionexchange membrane and enhancing the ion transportation. Furthermore, the C-MCDI device showed a long lifespan with a stable desalination capacity of around 18.6 mg g(-1) after 500 cycles; instead, the capacity continuously attenuated to near zero in CDI with bare carbon electrodes. Hence, this work proposed two novel polymer-based ion-exchange materials for scalable fabrication of high-performance MCDI electrodes via an environmentally friendly, cost-effective, and process-integrated method.

Automated summary

A scalable, continuous processing strategy for producing high-performance MCDI electrodes was reported, in which carbon electrodes were coated with poly(arylene alkylene)-based ion-exchange polymers. The resulting C-MCDI showed higher salt adsorption capacity and charge efficiency compared to CDI with bare carbon electrodes and FS-MCDI. COMSOL simulation revealed that the coated ion-exchange membrane in C-MCDI effectively reduced interface contact resistance and enhanced ion transportation.