Unraveling the Ionic Adsorption and Migration Mechanism of Inverse Opal Capacitive Deionization Electrode

Abstract

ABSTRACT Developing advanced capacitive deionization electrodes for desalination requires the concurrent enhancement of thermodynamic and kinetic properties. Despite extensive research on improving thermodynamic features represented by adsorption capacity, the investigation on the kinetics featuring ion migration is still insufficient. Herein, a two‐pronged strategy is proposed to resolve the adsorption‐migration trade‐off dilemma. A nature‐inspired inverse opal‐structured nitrogen‐doped carbon (IO‐NC) skeleton is developed to grow cobalt phosphide (CoP) quantum dots by a biomimetic mineralization method, denoted as IO‐NC/CoP. Benefiting from the robust, highly ordered porous IO‐NC skeleton and abundant adsorption sites of CoP quantum dots, the IO‐NC/CoP electrode yields a high salt adsorption capacity/rate (62.1 mg g −1 , 7.5 mg g −1 min −1 ) and 91.6% capacity retention after 60 cycles in 400 mg L −1 saline at 1.2 V. In addition, the adsorption kinetics and structural evolution of the IO‐NC/CoP electrode after long‐term cycles are thoroughly explored. Detailed theoretical calculations unveil the ion adsorption and migration mechanism. This study not only develops an advanced dechlorination electrode, but provides valuable guidelines to overcome the trade‐off between adsorption and migration, which is helpful for adsorption and separation applications.