Unlocking the capacity of Mn-based Prussian blue cathodes in capacitive deionization

Manganese (Mn)-based Prussian blue analogs (PBAs) typically exhibit suboptimal electrochemical performance due to their inherent Jahn-Teller effect distortion and low electrical conductivity. Here, a potassium substitution and high entropy strategy is proposed to synergistically construct K2(FeMnCoNiCu)[Fe(CN)6] (K-HEHCF) cathode to address the aforementioned issues. K-HEHCF exhibits excellent capacitive deionization (CDI) performance, with a high adsorption capacity of 104.92 mg g−1 at 1.4 V, and capacity retention close to 100% after 200 cycles. Under optimized conditions, the K-HEHCF electrode exhibits a significant removal effect on the cations in the simulated circulating cooling water sample, demonstrating certain practicality. By comprehensively characterizing various physical and chemical properties, it was found that the synergistic effect of high entropy and K substitution enhanced the electronic conductivity, constructed a charge compensation network, inhibited phase transformation, and due to the incomplete exchange of Na+ and K+ during the reaction process, some residual K+ served as the backbone to stabilize the framework structure. Additionally, the assembled CDI cell can drive LED as a desalination battery, enabling energy recovery. This work further exploits the potential of manganese-based PBAs cathodes and provides a ideas for the design of PBAs electrodes with both capacity and stability. Freshwater scarcity drives the need for better desalination. Here, authors develop a potassium-substituted, high-entropy manganese-based Prussian blue cathode that achieves high capacity, stability, and energy recovery in capacitive deionization.