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Revealing the Chemical State of Palladium in Operating In2O3 Gas Sensors: Metallic Pd Enhances Sensing Response and Intermetallic InxPdy Compound Blocks It

Ovsianytskyi, Oleksandr; Bekheet, Maged F.; Gili, Albert; Gurlo, Aleksander

The sensing response of metal oxides activated with noble metal nanoparticles is significantly influenced by changes to the chemical state of corresponding elements under operating conditions. Here, a PdO/rh-In2O3 consisting of PdO nanoparticles loaded onto rhombohedral In2O3 was studied as a gas sensor for H2 gas (100–40000 ppm in an oxygen-free atmosphere) in the temperature range of 25–450 °C. The phase composition and chemical state of elements were examined by resistance measurements combined with synchrotron-based in situ X-ray diffraction and ex situ X-ray photoelectron spectroscopy. As found, PdO/rh-In2O3 undergoes a series of structural and chemical transformations during operation: from PdO to Pd/PdHx and finally to the intermetallic InxPdy phase. The maximal sensing response (RN2/RH2) of ∼5 ⋅ 107 towards 40000 ppm (4 vol %) H2 at 70 °C is correlated with the formation of PdH0.706/Pd. The InxPdy intermetallic compounds formed around 250 °C significantly decrease the sensing response.
Published in: ChemPhysChem, 10.1002/cphc.202200775, Wiley-VCH