2, ICPEES UMR 7515, Strasbourg, , France
Water electrolysis is considered as a promising means for converting renewable electricity into hydrogen for storage and on-demand utilization. The sluggish oxygen evolution reaction (OER) at the anode results in considerable energy losses and calls for the development of more efficient electrocatalysts. To guide the catalyst search it is critically important to understand key steps of the OER. In this presentation we will discuss how application of Near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and soft X-ray spectroscopy can contribute to advancing the understanding of the oxygen electrocatalysis on metal oxide surfaces. In the first part of the presentation we will consider OER electrocatalysis on Ir- and Ru-based anodes to shed light on the reaction mechanism, on the structure-activity relations and on the nature of degradation processes. We will see that combining NAP-XPS with the complementary soft X-ray spectroscopy (NEXAFS) at the oxygen K-edge allows one to detect reaction intermediates on the electrode surface . We will also discuss the controversial issue related to the formation of Ir(V), and consider metal-support interactions in Ir/SnO2 supported anode catalysts. We will compare IrOx anodes with RuOx and Ir-stabilized RuOx anodes, where transformation of Ru(IV) into higher oxides may be conveniently followed with NAP-XPS, and discuss the origin of electrochemical instability of Ru-based anodes during the oxygen evolution reaction .
The second part of the talk will be devoted to the noble metal-free transition metal (Mn, Co) oxides as promising anode materials for anion-exchange membrane fuel and electrolysis cells. We will touch upon such issues as beam damage in the presence and in the absence of water, structural and compositional transformations under polarization, and relevance of the spectroscopic information obtained in model systems operating at mbar pressures for practical systems.
The author is indebted to V. A. Saveleva and S. Zafeiratos (Strasbourg, France), L. Wang, A.S. Gago and K.A. Friedrich (Stuttgart, Germany), D. Techner, M. Haevecker, A. Knop-Gericke and R. Schloegl (Berlin, Germany), J.-J. Gallet and F. Bournel (Paris, France), A. S. Ryabova, D. Antipin, I. Filimonenkov, S. Ya. Istomin, E. V. Antipov, G. A. Tsirlina and K. Stevenson (Moscow, Russia). The research leading to the presented results has received funding within ERA.NET.RUS.PLUS (project #270 NANOMorf), and the European Union's Seventh Framework Programme (FP7/2007-2013) for Fuel Cell and Hydrogen Joint Technology Initiative under Grant No. 621237 (INSIDE).
 V. A. Saveleva, L. Wang, D. Teschner, T. Jones, A. S. Gago, K. A. Friedrich, R. Schloegl, S. Zafeiratos, E. R. Savinova, in preparation.
 V. A. Saveleva, L. Wang, W. Luo, S. Zafeiratos, C. Ulhaq-Bouillet, A. S. Gago, K. A. Friedrich, E. R. Savinova, J.Phys.Chem.Lett. 7 (2016) 3240.