Zn-Stabilized Manganese Phosphate via Electrodeposition: A Cation-Adaptive Cathode for High-Performance Hybrid Capacitive Deionization

To address the persistent challenge of manganese dissolution and structural instability in manganese-based electrodes for aqueous desalination, we devised an integrated strategy that merges targeted material design with controllable synthesis. We in situ fabricated a Zn2+-doped Na–Zn–Mn phosphate/oxide composite (SZMP) on three-dimensional porous carbon felt using a simple one-step potentiostatic coelectrodeposition method. This approach sidesteps the complexities of traditional high-temperature solid-state methods, allowing for uniform and adherent growth of the active material, which optimizes ion and electron transport pathways. The Zn2+ dopant stabilizes the NASICON-type framework by modulating the local electronic structure at the atomic level, effectively suppressing the Jahn–Teller distortion of Mn3+ and significantly enhancing structural integrity. The resulting SZMP electrode features a unique “cation-adaptive” charge storage mechanism, showing high and stable electrochemical responses to Na+, K+, Mg2+, and Ca2+ ions. As a SZMP//AC hybrid capacitive deionization (HCDI) cathode, the device achieves outstanding desalination performance, with a maximum specific desalination capacity of 675 mg/g in NaCl solutions (500–1500 mg/L) and a high capacity retention of 96% after 10 000 cycles in complex simulated seawater. This work offers a scalable synthesis route and introduces a novel material design paradigm for creating durable, high-performance desalination systems capable of treating complex real-world water.