Catalysis across spectrum and time: Spectroscopic and electrochemical insights for material and mechanistic response

The transition toward sustainable energy systems has motivated extensive research into scalable routes for solar fuel generation. Silicon-based photoelectrodes are particularly promising due to their favorable optoelectronic properties, abundance, and compatibility with established microfabrication techniques. Nano-microstructuring silicon can enhance photoelectrochemical performance by improving light absorption, charge separation, and catalytic activity for hydrogen production from water. My PhD focused on developing scalable synthesis methods for silicon photoelectrodes and understanding the mechanisms governing their light-driven performance. In Paper I, I present a synthesis method for periodically arranged silicon microwires for photoelectrochemical hydrogen production. Compared with randomly distributed microwires prepared under similar conditions, the ordered structures show a 65% increase in activity, highlighting the importance of structural ordering for optimizing light–matter interactions and charge transport. In Paper II, this approach was extended to fabricate silicon microwires 100 – 200 nm in diameter to investigate optical effects like waveguiding and interactions between neighboring structures. The wavelength-dependent photocatalytic response reveals the role of waveguides in photocatalysis. By varying the thickness of a protective coating, we show a strong interplay between optical absorption, charge transfer, and catalytic activity. Another route to hydrogen production involves molecular catalysts for dehydrogenation of hydrogen carriers such as alcohols. In Paper III, in-situ X-ray absorption spectroscopy was used to study an iridium catalyst under operating conditions. The catalyst remains mainly in a stable oxidation state during the reaction cycle, avoiding common deactivation pathways and revealing the mechanism of thermal degradation. Together, these studies show how nanostructured photoelectrodes and mechanistic catalysis research contribute to the development of efficient and scalable hydrogen generation technologies.