Interfacial electronic coupling in carbon-engineered MoO2 for enhanced Pb2+ capture from wastewater via capacitive deionization.

Faradaic capacitive deionization (CDI) holds significant promise for selective ion separation, yet its practical deployment is fundamentally limited by sluggish ion-intercalation kinetics and incomplete structural reversibility arising from high interfacial energy barriers. Here, we engineer a graphene-confined MoO2-Mo electrode (MoO2-Mo@C) in which interfacial electronic coupling governs ion-storage kinetics at the atomic scale. The integration of metallic Mo0 with semiconducting MoO2 establishes a metal-semiconductor interface that induces interfacial charge redistribution and generates a built-in electric field. This internal field lowers the thermodynamic and kinetic barriers for Faradaic ion intercalation, thereby accelerating charge-transfer dynamics. Concurrently, confinement within a porous graphene framework constructs a continuous conductive network that facilitates electron transport and buffers lattice strain, enabling highly reversible structural reconstruction during cycling. Using Pb2+ as a model multivalent cation, the MoO2-Mo@C electrode achieves rapid and selective capture with a high adsorption capacity of 175 mg g-1 with 94.5% capacity retention over prolonged CDI operation. In-situ Raman spectroscopy directly visualizes the fully reversible lattice transformation, while density functional theory calculations reveal the interfacial electronic modulation and reduced diffusion energy barrier responsible for enhanced ion selectivity. By elucidating how interfacial electronic coupling modulates electronic polarization regulates Faradaic reaction kinetics, this work establishes a mechanism-driven design paradigm for constructing fast, selective, and structurally durable CDI electrodes, providing a scalable strategy for advanced electrochemical water purification and resource-efficient ion separation.