A robust and double redox-active Prussian blue analogue with enhanced electronic density and reversible electrochemistry for efficient and sustainable capacitive deionization desalination.

Developing Prussian blue analogues that simultaneously achieve high structural robustness, rapid ion transport, and enhanced redox activity is pivotal for the practical implementation of Hybrid capacitive deionization (HCDI). Herein, we report a bimetallic VMnHCF synthesized via a green and low-carbon-footprint approach, in which the introduction of a tailored V-Mn coordination environment significantly increases the density of redox-active sites through the synergistic contribution of V/Mn and Fe-CN-centered dual redox couples. This bimetallic interaction drives the spin-state transition of Mn3+ from high spin to low spin, thereby suppressing Jahn-Teller distortion and enhancing lattice stability. The incorporation of V atomic orbitals reconstructs the electronic structure within the bimetallic coordination framework, leading to a reduced density of states near the Fermi level and lower unpaired electron occupation. In situ Raman spectroscopy directly captures the highly reversible and synchronous evolution of the dual redox centers, highlighting the critical role in enabling superior electrochemical reversibility and stability. When employed in HCDI, VMnHCF delivers an outstanding desalination capacity of 58.05 mg g-1 at an average desalination rate of 1.98 mg g-1 min-1 and retains 86.94% over 100 cycles. Furthermore, the engineered bimetallic coordination environment endows the VMnHCF electrode with exceptional Na+ selectivity over competing cations.