Orbital‐Level Electronic Modulation of MnO ₂ via Interfacial Built‐In Electric Fields: Breaking the Jahn–Teller Distortion Cycle for Ultra‐Durable Hybrid Capacitive Deionization

Abstract Manganese dioxide (MnO ₂ ) is widely recognized as a promising electrode material for hybrid capacitive deionization (HCDI) owing to its high theoretical specific capacity and low cost. However, its practical deployment is severely constrained by Mn ³⁺ ‐induced Jahn–Teller (J‐T) lattice distortions and associated disproportionation reactions, which lead to structural degradation and Mn dissolution. Here, these limitations are overcome by constructing a WS ₂ @MnO ₂ heterostructure, in which a built‐in electric field is introduced at the heterogeneous interface. Density functional theory (DFT) calculations reveal that this internal electric field facilitates directional charge transfer from the Mn d _z ² orbital, effectively lowering its electron occupancy and increasing the average Mn oxidation state. This electronic modulation significantly suppresses J‐T distortion and manganese dissolution, thereby enhancing structural stability. When tested in a 500 mg L ⁻¹ NaCl solution, the WS ₂ @MnO ₂ electrode exhibits improved HCDI performance, achieving a high initial salt adsorption capacity (SAC) of 91 mg g ⁻¹ and a salt adsorption rate of 9.75 mg g ⁻¹ min ⁻¹ . Notably, the electrode retains 87.88% of its SAC after 150 adsorption–desorption cycles, underscoring its excellent cycling durability. This work provides a novel and effective strategy for stabilizing MnO ₂ ‐based electrodes and introduces a broadly applicable approach for designing high‐performance electrochemical materials with intrinsic resistance to J‐T distortion.