Abstract: Photocatalytic overall water splitting (OWS) is widely recognized as the ideal route for producing green hydrogen, a key component of the global transition to sustainable energy. This thesis focuses on exploring the photophysical differences between Rh and Pt cocatalysts in photocatalytic OWS for hydrogen production. By employing advanced spectroscopic techniques, this work aims to elucidate the underlying mechanisms that contribute to the distinct performances of these noble metal cocatalysts. The study not only highlights their comparative behavior in photocatalytic OWS systems but also leverages operando spectroscopic analysis to provide detailed insights into their photophysical properties under working conditions. This research bridges material science and spectroscopy to advance our understanding of catalyst behavior in sustainable hydrogen production. The work is organized into four chapters, each addressing a specific aspect of this multidisciplinary research.

The first chapter introduces the importance of hydrogen in the global energy transition, examining production pathways and emphasizing the significance of electrochemical and photocatalytic OWS for sustainable energy solutions. Additionally, this chapter highlights the importance of operando studies for advancing the understanding of materials used in these processes. Special focus is placed on spectroelectrochemical techniques, such as Attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR–SEIRAS), which provide real-time insights into material behaviors and reaction mechanisms at electrode-electrolyte interfaces.