Electrochemically regenerable MXene/high-entropy prussian blue analogue cathodes for U(VI) capture in hybrid capacitive deionization

Regenerable cathodes that integrate efficient charge transfer with abundant binding sites are essential for electrochemical U(VI) capture in hybrid capacitive deionization (HCDI) systems. Herein, Ti 3 C 2 T x MXene (MXene), a two-dimensional transition metal carbide, a high-entropy Prussian blue analogue (HEPBA), and their composite, MXene-HEPBA, were evaluated as cathode materials for electro-assisted U(VI) removal. MXene mainly exhibited electric double-layer capacitive behavior, whereas HEPBA and MXene-HEPBA showed pronounced Faradaic redox characteristics. By coupling the conductive MXene scaffold with the multimetal coordination-active HEPBA framework, MXene-HEPBA delivered specific capacitances of 87 F/g at 1.25 A/g and 67 F/g at 6.25 A/g. In synthetic U(VI)-containing solutions, MXene-HEPBA achieved a U(VI) uptake capacity of 56 mg/g under optimized HCDI conditions and exhibited efficient regeneration, with a desorption efficiency of 92% using 0.5 mol/L HNO 3 under a reverse voltage of 0.8 V. In actual uranium-bearing groundwater, MXene-HEPBA achieved approximately 59% U(VI) removal, corresponding to an uptake capacity of 47.612 mg/g after pH and flow-rate optimization. Mechanistic analyses revealed that U(VI) was mainly immobilized as coordinated uranyl-like species through coupled electrosorption, surface complexation, and multisite coordination involving MXene surface terminations and HEPBA coordination sites. These results demonstrate its potential as a regenerable HCDI cathode for electrochemical purification of uranium-contaminated groundwater.