The production of hydrogen by electrolysis of water is a key process for sustainable energy development. In line with the United Nations goals, there is an ongoing e˙ort to develop water splitting catalysts that are eÿcient, environmentally friendly and economically feasible. This requires understanding the properties of the electrodes and the adjacent electrolyte layers under reaction conditions. In this work the fundamental principles of light-matter interaction are utilised for the development of operando analytical techniques, which are adapted for probing hydrogen evolution reaction.
The first part of the work focuses on surface segregation phenomena taking place during electrocatalysis in high temperature electrolysis and fuel cells. The varying redox conditions alter the catalyst. The unique combination of hard and soft X-ray photoelectron spectroscopy confirmed the reversible Ni-exsolution in the high-temperature electrocatalyst La0.30Sr0.55Ti0.95Ni0.05O3− upon hydrogen exposure. In addition, the post mortem technique revealed the associated surface segregation of the other elements, in particular the debated surface enrichment of strontium.
In situ membrane X-ray absorption and photoelectron spectroscopies were de-veloped for and demonstrated on hydrogenation of molybdenum oxide. As the method relies on the permeation of hydrogen through membranes of palladium or palladium-silver alloys, their hydrogenation is examined in particular detail. Hydrogen-induced intermediate states and final products of oxide reduction show irreversible degradation by the formation of oxygen vacancies and water molecules.
The magneto-optical characterisation is a true in situ method to follow changes at electrochemical interfaces, and thus ideally suited to study the e˙ect of a magnetic field on the hydrogen and oxygen evolution reactions. This e˙ect is controversially debated, in particular the influence of the magnetic field on the electrode-electrolyte double layer. The developed magneto-optical set-up reveals that the enhancement of magnetocurrents is linked to the magnetic field e˙ects that occur within the di˙usion and electrochemical double layer. The results emphasize the importance of magnetic field gradients in the electrolyte in general.