Soft x-rays spectroscopies in liquids at BACH
We have developed suitable cells to perform soft x-ray spectroscopy in the presence of liquids and reagent gases at ambient pressure: two types of static cells working in transmission or in fluorescence modes, and an electrochemical flow cell which allows to carry out cyclic voltammetry in situ, electrochemical deposition on a working electrode and to study chemical reactions in-operando conditions.
Rev. Sci. Instrum. 92, 015115 (2021)
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Spectroscopic techniques based on synchrotron radiation are fundamental to provide significant insights into the behaviour of electrocatalysts under operating conditions. In particular, an exhaustive comprehension of the electronic properties of materials in ambient pressure gas or in liquid environment is required, as well as mechanistic understanding of the electronic evolution occurring at the solid/liquid or solid/gas interfaces during catalytic or electrochemical reactions. In order to characterize such interfaces in situ, one would need a probe, that can penetrate the solid and/or the liquid layer, while generating collectable signals from the interface layer (typically several nanometers thick) or from the bulk region of the solution. Therefore, there is an increasing demand to develop techniques or to implement the existing ones to study phenomena at the interfaces and to design cells for in situ measurements. We designed, fabricated and tested static and microfluidic cells for soft x-ray spectroscopy in the presence of fluids on the basis of already existing cells which revealed a good reliability and versatility. Examples of experiments performed on BACH beamline are reported. O K-edge XAS spectra of different samples in aqueous solution and air were performed in the static cell. The design of the microfluidic cell equipped with the three-electrodes system allows to perform cyclic voltammetry, electrochemical deposition and chemical reactions in operando conditions.As a demonstration of its possibilities, we reported the cathodic electrodeposition of NiOOH layers with variable thickness. The morphology of the deposited films was characterized by SEM evidencing the typical porous structure of the material. Ni L-edge XAS measurements revealed the co-existence of 2+, 3+ oxidation states in the electronic structure of NiOOH. A similar material FexNiOOH, with higher electrocatalyic performances due the presence of Fe, was used to test the cell for XAS in operando conditions. The XAS spectra recorded on the Ni L-edge at applied potentials above the oxidation and below the reduction potentials show the expected change in Ni oxidation state. We expect that the availability of these cells on BACH beamline will raise a large interest in the users community for in operando experiments on a variety of catalysts. |
This work was supported by IOM-CNR start up project 2010, EUROFEL project (RoadMap Esfri), MIUR project FIRB Futuro in Ricerca 2012 N. RBFR128BEC, CNR-STM (Short Term Mobility) projects (2015, 2016), Swedish Research Council (grant n. 2019-00663) and from the EU‐H2020 Research and Innovation programme under grant agreement n. 654360 Nanoscience Foundries and Fine Analysis- Europe Soft X-ray spectroscopies in liquids at CNR-IOM BACH beamline at Elettra
S. Nappini, L. D'Amario, M. Favaro, S. Dal Zilio, F. Salvador, E. Betz-Güttner, A. Fondacaro, Igor Píš,, L. Romanzin, A. Gambitta, F. Bondino, M. Lazzarino, and E. Magnano*
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