Gas Adsorption‐Driven Electronic Modulation in WO ₃ @Cu ₃ (HHTP) ₂ Heterostructure: Mechanistic Origin of Selective Drift Resistance Room‐Temperature Formaldehyde Sensing

Formaldehyde is a ubiquitous indoor air pollutant whose carcinogenicity, high toxicity, and volatility pose severe health risks even at trace concentrations. Nevertheless, realizing ultra‐low detection limits with high selectivity under ambient‐temperature conditions using a single chemiresistive semiconductor remains an enduring challenge. A heterointerface‐engineered WO 3 @Cu 3 (HHTP) 2 nanocomposite is developed, integrating the high surface reactivity of WO 3 with the intrinsic conductivity and ordered π‐conjugated framework of the 2D conductive metal–organic framework (cMOF) Cu 3 (HHTP) 2 . Synergistic interfacial orbital hybridization between W 5 d (WO 3 ) and O 2 p π‐orbitals (cMOF) induces pronounced electronic structure modulation, promoting enhanced charge transport and gas–solid interfacial reaction kinetics. DFT calculations reveal that HCHO preferentially adsorbs at phenolic O sites in the cMOF and O‐vacancy sites on WO 3 , inducing localized charge redistribution and suppressing mid‐gap defect states. This adsorption‐driven Fermi level shift correlates directly with the experimentally observed resistance drop under HCHO exposure. The WO 3 @Cu 3 (HHTP) 2 sensor exhibits an ultralow detection limit (∼48 ppb), rapid response/recovery, minimal baseline drift, and exceptional selectivity under mixed gas environments at room temperature. These findings establish a clear mechanistic link between interfacial electronic structure tuning and enhanced sensing performance, offering a generalizable strategy for designing next‐generation VOC sensors via surface modification of metal oxides with cMOFs.