This work demonstrates that it is possible to follow the surface chemistry of oxygen on SnO 2 based gas sensing materials using operando Diffuse Reflectance Infrared Fourier-Transform Spectroscopy (DRIFTS). The inherent difficulties, due to the intrinsic properties of the studied oxide and the limitations of the method, were overcome by comparing the results obtained for two different materials and by using of isotopically labeled gases together with the simultaneous measurement of the sensor signals. In spite of the differences in the surface composition and reactivity between the different materials, the experimental results show that the reactive oxygen species are similar in nature and the gas recognition takes place by the interplay of surface reduction and (re-)oxidation.

Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and first-principles calculations are performed to investigate the different ways in which water reacts with a SnO 2 surfaces and to evaluate the cross interference of humidity on the detection of CO. Two different materials, chosen because of their very different properties, were investigated. The experimental results were interpreted with the help of theoretical modelling of two clean and defective surfaces, namely (110) and (101). The experimental results show, and the theoretical calculations confirm, that water vapor can interfere with the CO detection in different ways depending on the active surface and the concentration of oxygen vacancies. This is related to the different ways in 2 which the water vapor reacts with tin oxide; on the one hand it can reduce the (101) surface, on the other hand it can heal the oxygen vacancies of the defective (110) surface.

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The impact of Pt doping on the surface reactions between tin dioxide, water vapour, CO and H2 was investigated by a combination of simultaneously performed operando DRIFT (Diffuse Reflectance Infrared Fourier Transform) spectroscopy, DC resistance measurements and analysis of the reaction products by using a MS (Mass Spectrometer). Both undoped and Pt doped tin dioxide sensors were exposed to different test gases in synthetic air or in N2 backgrounds. The approach made it possible to identify the differences between the two materials with respect to their surface chemistry and their impact on the gas sensing performance. The main finding is that the presence of Pt changes the reaction partners' nature for water vapour and H2 on the one hand, and CO on the other hand when the sensors are operated in air. In this way the cross interference effect of humidity, which is responsible for the loss of CO sensing performance for the sensors based on undoped SnO2, is reversed.

NaInS(2) , a H(2) -evolving photocatalyst, is synthesized as single-crystalline hexagonal plates by coupling a molten salt synthesis with ultrasonic spray pyrolysis (USP) for the first time. USP NaInS(2) films are used as a new photoanode material and have an initial photocurrent of ≈37 μA/cm(2) upon illumination and activities 25 times greater than films made from a standard non-aerosol NaInS(2) sample.