Abstract: https://reurl.cc/Vm8Am5
Chemical reactions at surfaces play a crucial role in various chemical processes, including catalytic synthesis, energy conversion, environmental remediation, and gas sensing. Surface science techniques allow us to investigate the fundamental physicochemical processes occurring at surfaces. We have developed several in situ and operando experimental methods to observe surface reactions at gas/solid and solid/liquid interfaces. So far, our research is focusing on the development and characterization of gas sensing materials capable of detecting small molecules such as hydrogen, using ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and X-ray absorption spectroscopy (XAFS).
Recently, we developed a sensor material which detects hydrogen gas in air and human breath with high sensitivity (1 ppm), using nanometer-thick platinum-based thin films, such as Pt-Rh alloys. The Pt-Rh sensor detects atmospheric hydrogen concentrations through changes in electrical resistivity. We performed operando AP-XPS measurements in conjunction with resistivity monitoring to study the sensing behavior of the Pt-Rh thin-film sensor. The results show that the resistivity decreases upon exposure to H2 gas, whereas it increases when exposed to O2 gas. Corresponding changes were observed in the Rh 3d and Pt 4f XPS spectra depending on the background gas conditions. Prior to gas exposure, the surface was dominated by Rh oxide. Upon exposure to H2 gas, the chemical state shifted markedly, with Rh oxide being fully reduced to its metallic state. Conversely, exposure to O2 gas led to the reformation of oxygen-induced species. These findings demonstrate that the surface chemical state is closely correlated with the functional properties of the material.