Hydrogen-Bond Gating of Interfacial Capacitance in Amine-Rich Hybrid Interfaces for Redox-Free Ionic Recognition

Continuous, selective ion detection in aqueous media without redox mediation remains an outstanding challenge in electrochemical sensing. Here, we introduce a hydrogen-bond-gated, nonfaradaic charge-transduction mechanism that enables real-time selective halide detection (F⁻ ion) under ambient conditions. The amine-rich electroactive interface, constructed by integrating polyethylenimine (PEI) onto UiO-66-NH₂ MOF (metal-organic framework), functions as a redox-inactive yet ion-responsive hybrid platform. Under applied bias, F⁻···H interactions at the interface modulate interfacial capacitance, producing a distinct, reversible signal that allows continuous monitoring at pH 7. The optimized hybrid achieves a detection limit of 0.2 ppm with exceptional selectivity for F⁻ over competing anions (Cl⁻, Br⁻, I⁻, NO₃⁻, CO₃²⁻, CH₃COO⁻), supported by DFT-derived charge-polarization analysis, confirming H-bond-driven stabilization. The system maintains stable operation over >25 h (250 cycles) and accurately quantifies F⁻ ions in real water samples (real-time detection of F⁻ ions in tap and drinking water down to ∼1 ppm). This study establishes H-bond-mediated modulation of interfacial capacitance as a design principle for redox-free amperometric electrochemical sensing, offering a versatile platform for responsive hybrid materials and adaptive ionic interfaces.