Proton exchange membrane water electrolysers are very promising renewable energy conversion devices to produce green hydrogen. These devices are strongly limited by the slow kinetics of the oxygen evolution reaction (OER) and the poor stability of the electrodes under the high potentials during operation. Although it has been demonstrated for several electrocatalytic reactions that the electrolyte composition and pH can critically affect the performance of the electrode, a fundamental understanding of the effect of the electrolyte is still needed. Chemical and structural analysis of the composition of the electrode-electrolyte interface can provide crucial information about the electrode evolution during the reaction, eventually transforming the as-grown catalyst into the actual active phase, and its dependence on the electrolyte composition and the applied potential.

Here we introduce our customized experimental set-up that provides structural, chemical and electrochemical characterization on exactly the same sample, by allowing the transfer of the catalyst from ultra-high vacuum (UHV) –compatible with surface science techniques- to an electrochemical cell in a controlled argon gas atmosphere. This optimized approach enables the direct correlation between the surface composition (X-Ray photoemission spectroscopy, XPS) and structure (Low energy electron diffraction, LEED, and Scanning tunneling microscopy, STM) at the atomic scale, and the macroscopic response of the catalyst (Electrochemical test). The correlation of cyclic voltammetry (CV) features with changes in the surface structure and chemical composition of the electrode is essential for a fundamental understanding of the operation of electrolysers to produce hydrogen from sustainable feedstocks.

Au is an interesting system to study because it is very stable over a large potential window and, therefore, can be used as a support material for more active OER materials. However, relatively little is known about the formation of Au hydroxides and oxides under operating conditions. Relevantly, the role of electrolyte composition in the activation/inhibition of the former processes is yet poorly understood. We applied the described experimental approach to study the potential-induced changes of Au(111) single crystals during electrochemical oxidation in H₂SO₄, HClO4 and NaOH. Combining ex-situ XPS and LEED characterization before and after potential steps, we monitored the surface changes within the electrochemical window up to formation of (hydro)oxides near the OER onset potential, and explored the effect of the electrolyte composition on the electro-oxidation of the Au(111) electrode.