Interplay of H2, water vapor and oxygenat the surface of SnO2 based gas sensors – An operando investigation utilizing deuterated gases

The surface reactivity toward hydrogen and water vapor of three different (in grain size and amount of OH groups on the surface, different synthesis route) undoped tin dioxide materials (SnO2 Ac, SnO2Cl, SnO2 Cl K) was investigated at 300 °C by applying simultaneous resistance measurements and DRIFTS (diffuse reflectance infrared spectroscopy). The changes of the surface species, i.e. OH groups, were examined due to exposure to hydrogen H2/deuterium D2, watervapor H2O/deuterated water vaporD2O and carbon monoxide CO. A possibility to minimize IR related disturbing phenomena in the absorbance spectra is the use of deuterated gases (D2, D2O): everything which deals with OH groups/water related species is shifted in the IR spectrum. We were able to show that the reaction with those reducing gases can be traced back to the reaction with adsorbed oxygen. There was no evidence for a direct reaction of the test gas with OH groups or in case of H2, a direct reaction with (lattice) oxygen to hydroxyl groups.