Design of sample holder for in operando XAS of oxidation state changes in La1xSrxMnO3± electrodes

The design and construction of a sample holder for in operando X-ray absorption spectroscopy on solid oxide electrodes, like for instance the lanthanum strontium manganite electrodes, is explained. The sample holder is mounted in a test-cell, which is also described together with some preliminary test-results from temperature measurements and electrochemical characterisation performed on a “dummy” sample in the test cell. The test-cell is a modified version of a test-cell previously designed in our laboratory, and will in the future be used for X-ray absorption experiments on solid oxide electrodes. 1. Background The perovskite La1-xSrxMnO3±δ (LSM) has found application as electrode material in solid oxide electrochemical cells, like the solid oxide fuel cells (SOFCs), solid oxide electrolysis cells (SOECs) and cells for electrochemical gas purification. During several decades extensive research has been conducted on LSM, including work on electrical properties [1], defect chemistry [2] and the influence of electrical polarisation on segregation in LSM electrodes [3] An overall tendency today in the research on LSM electrodes and solid oxide electrodes in general, is an increased interest in studying the electrodes at realistic operating conditions, i. e. in operando, or at conditions close-to realistic operating conditions, i.e. in situ, with optical/spectroscopic methods. For in operando/in situ studies the use of X-ray absorption techniques has great advantages, as they in contrast to many other analytical methods do not require vacuum conditions. The challenge in performing in operando/in situ studies of solid oxide electrodes is the need for operating the electrodes at elevated temperatures (300900 °C), in controlled atmosphere and with electric contact, while still maintaining the optical access to the electrodes. To meet these requirements a careful design is necessary for any test-cell and sample holder for in operando studies of solid oxide electrodes. The design of a test-cell for in operando Xray absorption spectroscopy of solid oxide electrodes has been described by Hagen et al. together with preliminary test-results [4]. This paper describes the design of a new sample holder for a test-cell, which is a modified version of the test-cell described by Hagen et al. [4]. 22nd International Congress on X-Ray Optics and Microanalysis IOP Publishing Journal of Physics: Conference Series 499 (2014) 012010 doi:10.1088/1742-6596/499/1/012010 Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Published under licence by IOP Publishing Ltd 1 2. The design of the test-cell. The test-cell is intended for measurements in fluorescence mode, as both sample thickness and the mounting of the sample on a heat-stage make measurements in transmission mode impossible. In order to make it easy to transport the cell between different synchrotron facilities, the test-cell has a fairly compact design, with the dimensions of the main house being 8 cm x 12 cm x 12 cm. In the following the main house of the test-cell, the sample-holder and the sample, which in the future will be measured in the cell, will be described in more detail. 2.1 The main-house The main house is made of aluminium and has a removable front plate and back plate for easy access to the sample in the inner of the house. On the two opposite sides of the test-cell are X-ray windows, and a gas inlet and a gas-outlet made with standard fittings. The front plate is dominated by a large window, 9 cm in diameter, to allow for detection of the fluorescence signal from the sample. The small X-ray windows on the sides of the house and the big X-ray window in the front is made of Kapton® foil which is clamped between the front-plate/metal rings and the main-house together with O-rings to secure the sealing. Figure 1 shows a schematic drawing of the cell design, and a front view and a side view image of the cell. Figure 1. Illustrations of the test-cell for in operando X-ray absorption spectroscopy on solid oxide electrodes, a) schematic drawing, b) front view image and c) side view image. 120 mm 120 mm b) c)