We have built an end-station for near ambient pressure x-ray photoelectron spectroscopy (NAP-XPS) at the Photon Factory. This NAP-XPS end-station has been applied to operando measurements for functional material surfaces to understand the mechanisms of the functional surface processes under working conditions. Here we introduce two application studies concerning NAP-XPS based operando observations for functional material surfaces : (1) Rh catalyst for NO conversion and (2) PtRh thin-film sensor for selective detection of H2 under coexistence of NH3. In the former study, the catalytic reaction rates measured by mass spectrometry are directly correlated to coverages of surface species under working conditions, which enables to perform kinetic analyses to understand the mechanisms behind the catalytic reactions. In the latter study, the resistivity changes of the thin film under gas exposure were measured and correlated to surface chemical states of the sensor, which unveils the mechanisms for the selective detection of H2.
