Spectroscopic and spectroelectrochemical study of metal oxide/electrolyte interfaces for electrodes used in energy conversion

Metal oxides play a major role in the development of processes capable of converting energy from renewable sources into key reagents for the chemical industry, such as hydrogen. Indeed, H2 is the fundamental reagent in the Haber-Bosch process for the production of ammonia, and hence fertilizers, and is also expected to play a key role in the decarbonization of the steel industry. Metal oxides are used as electrocatalysts in the anodes of water electrolyzers. These devices consist of an electrochemical cell in which electric current from a renewable energy source is used to split the H2O molecule, producing H2 at the cathode and O2 at the anode. In alkaline electrolyzers (AWE), the most widespread technology, the anode is a nickel oxide including some amount of iron[1].

Studying the behavior of metal oxides under electrocatalytic conditions or after they have been irreversibly degraded (post-mortem analysis) is an area of intense research at present[2], given the important role this class of materials will play in the energy transition. In this competitive context, the aims of the thesis project will be: 1) to develop an original methodology to study spectroscopically and under unconventional conditions the metal oxide/aqueous electrolyte interface during the electrocatalysis process, and 2) to reveal which intermediate species are created at the oxide surface and the role they play in the material's activity and deactivation pathways.

The methodology to be developed will rely on the application of cryo-electrochemical methods, i.e. the combination of electrochemical and spectroscopic methods at low temperatures[3,4]. This strategy has a dual benefit. On the one hand, lowering the temperature slows down chemical processes, making it easier to detect reaction intermediates, which have a very short lifetime at room temperature. Secondly, the experimental system developed will be compatible with spectroscopic methods requiring ultra-high vacuum (< 1.10-9 mbar). In this regard, particular emphasis will be placed on developing an experimental system enabling spectroelectrochemical measurements using  X-ray photoelectron spectroscopy (XPS). Furthermore, Raman spectroelectrochemistry at ambient and low temperatures will be explored.

To carry out this work, the PhD student will benefit from access to state-of-the-art experimental equipment at ICB. For example, an XPS instrument equipped with a conventional X-ray source, Al Kα, and a high-energy X-ray source, Cr Kα, which allows for increasing the sampling depth of surface analysis. At present, this equipment is only available in two laboratories in France. The PhD student may also need to travel nationally to carry out measurements as part of the XPS research federation: SPE FR 2050 CNRS, supported by the laboratory, and internationally to laboratories with which collaboration already exists (e.g. the Autonomous University of Barcelona). Finally, measurements on large synchrotron facilities (e.g. SOLEIL) could be envisaged.

-References :

(1)         Chatenet, M.; Pollet, B. G.; Dekel, D. R.; Dionigi, F.; Deseure, J.; Millet, P.; Braatz, R. D.; Bazant, M. Z.; Eikerling, M.; Staffell, I.; Balcombe, P.; Shao-Horn, Y.; Schäfer, H. Water Electrolysis: From Textbook Knowledge to the Latest Scientific Strategies and Industrial Developments. Chem. Soc. Rev.2022, 51 (11), 4583–4762.

(2)         Da Silva, E. S.; Macili, A.; Bofill, R.; García-Antón, J.; Sala, X.; Francàs Forcada, L. Boosting the Oxygen Evolution Activity of FeNi Oxides/Hydroxides by Molecular and Atomic Engineering. Chemistry – A European Journal2023, 30 (4), e202302251.

(3)         López, I.; Le Poul, N. Low-Temperature Electrochemistry and Spectroelectrochemistry for Coordination Compounds. Coordination Chemistry Reviews2021, 436, 213823.

(4)         López, I.; Le Poul, N. Theoretical Aspects of Electrochemistry at Low Temperature. Journal of Electroanalytical Chemistry2021, 887, 115160.