Understanding of a Pt thin-film H₂ sensor under working conditions using AP-XPS and XAFS

The operating principle of a Pt thin-film H₂ gas sensor was investigated using a combination of surface sensitive ambient-pressure X-ray photoelectron spectroscopy and bulk sensitive X-ray absorption fine structure techniques, which provided chemical and structure information under working conditions, coupled with electric resistivity measurements. It is shown that the sensor response was in a linear relation with both coverages of H and O atoms on the Pt surface. Moreover, the bulk structure of Pt remains unchanged under H₂ exposure. These observations support that the resistivity change is associated with electron scattering in the near-surface region.