Enhanced hybrid capacitive performance for efficient and selective potassium extraction from wastewater: Insights...

Prussian blue analogues hold great promise for directly extracting potassium resource from wastewater via hybrid capacitive deionization (HCDI). However, there remain unresolved scientific issues regarding low efficiency and selectivity arising from asymmetric potential distribution induced by spontaneous charge matching. This work systematically investigated the underlying mechanisms for enhancing the storage capacity and specific affinity of representative Berlin Green towards K⁺ through precise regulation of insertion potential during HCDI operation. Empowered by controlling electrochemical intercalation behaviors, the compatibility between ionic and electronic kinetics was significantly enhanced. Impressive values of 160.12 mg/g, 61.27 %, and 0.07 kWh/mol were achieved under potentiostatic mode (0.1 V vs. Ag/AgCl) for insertion capacity, charge efficiency, and energy consumption, respectively. These results significantly outperformed the optimal levels obtained under constant cell voltage (0.9 V), which were 128.52 mg/g, 47.50 %, and 0.12 kWh/mol, respectively. In both aqueous solution with binary components and urine, the results emphasized the potential of the synergy effect between lattice hindrance and insertion chemistry in promoting intercalation selectivity, with the highest selectivity coefficients of 28.35 (K⁺/Na⁺), 76.22 (K⁺/Ca²⁺) and 175.12 (K⁺/Mg²⁺), respectively. The presented concept-to-proof offers a versatile approach for the advancement of high-performance HCDI and paves the way towards its sustainable application in nutrient recycling from natural waters or wastewaters.