Engineering Cu-enhanced Mn-based Prussian blue analogue with boosted dual-redox activity for efficient and fast capacitive deionization

Prussian Blue analogs (PBAs) have emerged as one of the promising materials for capacitive deionization (CDI) due to their excellent specific capacity and outstanding ion adsorption capability. However, Mn-based hexacyanoferrate Prussian Blue (MnHCF) suffers from insufficient utilization of active sites and poor ion kinetics during the electrochemical process, resulting in weak ion adsorption capacity and easy destruction of its stable structure. In this work, CuMnHCF was synthesized by incorporating Cu into the MnHCF framework via an in situ solvothermal approach. The appropriate introduction of Cu effectively occupied the interstitial sites of the MnHCF structure, optimized its electronic configuration, and successfully activated both the metal–N bonds and the Fe–CN dual redox-active sites within the framework (evidenced by in situ Raman measurements). These merits collectively led to a significant enhancement in the electrosorption capacity of CuMnHCF toward Na ions. The CuMnHCF electrode exhibits excellent cycling stability in aqueous NaCl electrolyte. After 5000 cycles, the specific capacitance decay is minimal, with a capacity retention rate of approximately 61.5% (5 A g −1 ). As applied in electrochemical desalination experiment at a voltage of 1.2 V for 50 cycles, the retention rate of CuMnHCF electrode reached as high as 82.2%. Additionally, it not only exhibits a high salt removal capacity of 58.4 mg g −1 (salt removal rate: 1.95 mg g −1 min −1 ), but also a peak salt removal rate of 15.7 mg g −1 min −1 . As an application extension, the CuMnHCF electrode also shows excellent desalination performance for K + , Ca 2＋ , and Mg 2 + .