Probing Lattice-Oxygen Redox in Pt-WO3 Nanocrystals by Operando Spectroscopy: Bridging Surface Chemistry and Ethanol Sensing.

Understanding how lattice oxygen participates in gas sensing remains a challenge in metal-oxide chemistry. Here, we combine operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), operando Raman spectroscopy, ex situ electron paramagnetic resonance (EPR), in situ X-ray diffraction, electrical measurements, and density functional theory (DFT) calculations to elucidate the ethanol-sensing mechanism of Pt-loaded WO3 nanocrystals. Among the compositions, 1Pt-WO3 exhibits the highest ethanol response (S = 98.8 at 350°C), sixfold higher than pristine WO3. Reversible changes in the W-O vibrational region, together with an EtOH-induced EPR signal at g = 2.007 and DRIFTS results, support the formation of reduced W species and oxygen-vacancies during ethanol exposure and reoxidation of reduced W species and oxygen vacancy healing by O2. In situ XRD showed no bulk phase transformation, consistent with a redox process occurring at the surface or near-surface region. Under oxygen-containing atmospheres, vacancy healing restores lattice integrity and stabilizes sensor performance. Pt acts as a catalytic mediator that facilitates O2 activation and promotes oxidation of partial-oxidation intermediates toward CO2, thereby amplifying sensor response. These results establish a near-surface lattice-oxygen redox cycle as a key mechanistic feature of ethanol sensing and provide a basis for the design of high-performance metal-oxide gas sensors.