Switchable Local Ferroelectric Order Enables Reversible HER Modulation in Irradiated 2H-MoTe₂

Two-dimensional transition metal chalcogenides have attracted significant interest for advanced functional materials due to their tunable electronic structures and polymorphic phase transitions. However, achieving dynamically switchable room-temperature ferroelectricity remains a significant challenge. Here, we demonstrate that Ar⁺ ion beam irradiation induces controlled Te vacancies in monolayer 2H-MoTe₂, triggering robust out-of-plane ferroelectric polarization at 300 K. Through polarization-resolved second-harmonic generation (SHG) microscopy and low-temperature spectroscopic characterization, we verify the ion-beam-induced symmetry breaking and the formation of nonuniform ferroelectric domains with switchable polarization states. Comprehensive switching spectroscopy piezoresponse force microscopy (SS-PFM) with rigorous artifact mitigation reveals reversible 180° polarization switching, confirmed by characteristic phase hysteresis and symmetric amplitude butterfly loops. Crucially, polarity-dependent linear sweep voltammetry (LSV) demonstrates that hydrogen evolution reaction (HER) activity can be reversibly modulated by polarization switching: positive poling reduces the overpotential, while negative poling degrades it, establishing a direct causal link between ferroelectric state and catalytic performance. Remarkably, this defect-engineered ferroelectric polarization modifies the interfacial charge distribution, optimizing the hydrogen adsorption free energy (ΔG_H*) from 1.86 eV (pristine) to -0.27 eV (irradiated), thereby significantly enhancing the hydrogen evolution reaction (HER) activity. This work establishes ferroelectric polarization as a primary descriptor for electrocatalytic enhancement and provides a defect-engineering strategy for designing adaptive nanocatalysts.