DOI: https://doi.org/10.29363/nanoge.interect.2022.013
Publication date: 11th October 2022
Alkaline water electrolysis is one of the simplest methods used for renewable hydrogen production [1]. In contrast to electrolyzers relying on acidic electrolytes, alkaline electrolyzers reach high conversion efficiency with abundant metals such as Ni-Fe alloys [2]. The outstanding properties can be mainly traced back to the host material Ni, which is both stable and electro-catalytically active in alkaline media. We demonstrate that this peculiarity can be related to its ability to form various compounds with hydrogen and oxygen (NiO, Ni(OH)2, NiOOH), which are known to stabilize Ni when in contact with electrolyte solutions as categorized in equilibrium Pourbaix diagrams. However, the surface is subject to a dynamic equilibrium, and the presence of specific phases depends on the presently applied conditions as well as on the history of the sample. We give a comprehensive overview of the evolution of the oxy-hydroxide surfaces from the ultrahigh vacuum clean Ni surface to water and oxygen gas exposure, liquid water contract, and under electrochemical conditions. Bridging these informations requires the use of APXPS setup at the Swiss Light Source [3] and a combination of soft- and hard x-ray photoelectron spectroscopy with electro-chemical impedance spectroscopy. Main outcome is that the high intrinsic electronic conductivity comes together with an increasing water intercalation into the oxy-hydroxide, which is experimental evidence for a water mediated OH- diffusion mechanism.
I would like to express my very great appreciation to Patrik Schmutz, Lars Jeurgens and Roland Hauert for the support provided as well as LightChEC for funding my research project.
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