Chemical Process and Energy Resources Institute CERTH

Thessaloníki, Greece

Chemical Process and Energy Resources Institute CERTH

Thessaloníki, Greece
SEARCH FILTERS
Time filter
Source Type

Paloukis F.,CNRS The Institute of Chemistry and Processes for Energy, Environment and Health | Papazisi K.M.,Chemical Process and Energy Resources Institute CERTH | Dintzer T.,CNRS The Institute of Chemistry and Processes for Energy, Environment and Health | Papaefthimiou V.,CNRS The Institute of Chemistry and Processes for Energy, Environment and Health | And 9 more authors.
ACS Applied Materials and Interfaces | Year: 2017

Understanding the surface chemistry of electrode materials under gas environments is important in order to control their performance during electrochemical and catalytic applications. This work compares the surface reactivity of Ni/YSZ and La0.75Sr0.25Cr0.9Fe0.1O3, which are commonly used types of electrodes in solid oxide electrochemical devices. In situ synchrotron-based near-ambient pressure photoemission and absorption spectroscopy experiments, assisted by theoretical spectral simulations and combined with microscopy and electrochemical measurements, are used to monitor the effect of the gas atmosphere on the chemical state, the morphology, and the electrical conductivity of the electrodes. It is shown that the surface of both electrode types readjusts fast to the reactive gas atmosphere and their surface composition is notably modified. In the case of Ni/YSZ, this is followed by evident changes in the oxidation state of nickel, while for La0.75Sr0.25Cr0.9Fe0.1O3, a fine adjustment of the Cr valence and strong Sr segregation is observed. An important difference between the two electrodes is their capacity to maintain adsorbed hydroxyl groups on their surface, which is expected to be critical for the electrocatalytic properties of the materials. The insight gained from the surface analysis may serve as a paradigm for understanding the effect of the gas environment on the electrochemical performance and the electrical conductivity of the electrodes. © 2017 American Chemical Society.


Paloukis F.,CNRS The Institute of Chemistry and Processes for Energy, Environment and Health | Papazisi K.M.,Chemical Process and Energy Resources Institute CERTH | Balomenou S.P.,Chemical Process and Energy Resources Institute CERTH | Tsiplakides D.,Chemical Process and Energy Resources Institute CERTH | And 6 more authors.
Applied Surface Science | Year: 2017

For several decades an open question in many X-ray photoelectron spectroscopy (XPS) studies was whether or not the results obtained in ultra-high vacuum conditions (UHV) were representative of the sample state in gas atmospheres. As a consequence, near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) was received by surface scientists as an important tool for in situ characterization of the gas-solid interactions. However, it is not yet clear how, if at all, the surface state formed in contact with the gas is modified when this gas is evacuated. In this work we compare synchrotron-based XPS results recorded at 300 °C on Ni/yttria- stabilized zirconia cermet and La0.75Sr0.25Cr0.9Fe0.1O3 perovskite, under 3.5 mbar O2 and UHV environments. We found that the surface state formed in O2 is maintained to a large extent under vacuum. In addition, we demonstrate that the correlation of XPS spectra recorded in the two conditions can provide information regarding the electrical conductivity of the specific surface sites of these complex oxides. Our findings suggest that comparison of XPS measurements in gas and in vacuum environments might be particularly useful in applications where the electronic conductivity at the surface plays a crucial role, as for example in solid oxide electrochemical devices. © 2017 Elsevier B.V.

Loading Chemical Process and Energy Resources Institute CERTH collaborators
Loading Chemical Process and Energy Resources Institute CERTH collaborators