Interplay of H_2, water vapor and oxygenat the surface of SnO_2 based gas sensors - An operando investigation utilizing deuterated gases

摘要

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 (SnO_2 Ac, SnO_2Cl, SnO_2 Cl K) was investigated at 300℃ 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 H_2/deuterium D_2, watervapor H_2O/deuterated water vaporD_2O 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 H_2, a direct reaction with (lattice) oxygen to hydroxyl groups.