The environmental chamber is devoted to perform in situ/operando ambient pressure X-ray absorption spectroscopy (AP-XAS) to investigate the physical-chemistry properties of materials employed in catalysis, absorption and energetic fields.
X-ray Absorption Spectroscopy (XAS) at APE-HE can be exploited to detect surface or buried atomic species displaying characteristic absorption edges in the relevant energy range (150-1600 eV). AP-XAS experiments are executed in total electron yield mode that are surface sensitive (few nm of probing depth). Three picoammeters are used during each XAS spectrum. One records the drain current at the entry of the end station (mesh) for intensity normalization, a second one measures the drain current of the sample, and a third one records the drain current of a reference sample, covering the whole range of energies, which is used as a reference of the photon energy.
The system is composed by a reactor cell for AP-XAS and an environmental chamber. The latest can be equipped with laser at different wavelength (375, 405 and 658 nm) to irradiate the sample mounted in the reactor cell. There is a gas-line that can flux in the reactor cell a mix of three gases at 1bar at different gas flow (between 2-55 ml/min ca.). An Agilent Micro-GC can be mounted at the output of the cell to detect and quantify the reagents and products gas. The cell has two independent electrical contacts, one on the sample and one on the membrane; this allows polarizing the membrane at positive bias voltage and recording the total electron yield (TEY) on the sample by measuring its drain current. In this way it is possible to record XAS spectra of the sample while keeping the sample at ambient pressure and/or expose it to a desired gas (or a mixture of gases) from RT to 400°C. The XAS spectroscopy provides a number of information on the electronic state of the material, starting from the oxidation state of each element and going in greater details like the symmetry of the ligands. In figure 4 is depicted the TEY spectrum of the Ce M4,5 absorption edge in Ceria/YSZ, using the fast data acquisition mode. The fast acquisition mode the XAS spectra allows the recording of XAS spectra with a great statistics in a time scale between seconds and few minutes. This allows to follow the evolution upon the reaction and/or to catch intermediate states.