Orbital-Level Electronic Modulation of MnO2 via Interfacial Built-In Electric Fields: Breaking the Jahn–Teller Distortion Cycle for Ultra-Durable Hybrid Capacitive Deionization

Manganese dioxide (MnO₂) 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 Mn³⁺-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 WS₂@MnO₂ 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_z² 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 WS₂@MnO₂ 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 MnO₂-based electrodes and introduces a broadly applicable approach for designing high-performance electrochemical materials with intrinsic resistance to J-T distortion.