Prussian blue analogue based integrated membrane electrodes for desalination and selective removal of ammonium ions in a rocking-chair capacitive deionization

Capacitive deionization (CDI) technology has shown significant promise in selective removal of nutrients from wastewater. In this study, a novel inorganic integrated membrane electrodes (i-IMEs) were developed with Prussian blue analogues (PBAs), cation insertion materials, as a coating on activated carbon (AC) electrode to replace cation exchange membrane. When the i-IMEs were operated in a rocking-chair CDI (RCDI) system for continuous desalination, a high specific adsorption capacity (SAC) of 42.7 mg/g and an impressive charge efficiency of 71.6 % were obtained. Moreover, taking advantage of PBAs' ion-selective properties for monovalent cations especially NH4+, this IME-RCDI achieved highly selective removal of cations compared to a RCDI with bare AC electrodes. The selectivity coefficients (Si/j) of NH4+ to divalent cations (such as Ca2+) and monovalent cations (such as Na+) were determined to be 2.15 and 1.95, respectively. These values are much higher than those obtained for AC electrodes, which were 0.3 and 1.07, respectively. Overall, this work demonstrates that the incorporation of PBAs in the i-IME-RCDI configuration offers superior desalination performance and selective removal capabilities for specific ions such as NH4+.