OPERANDO X-RAY ABSORPTION SPECTROSCOPY STUDIES OF (PHOTO)ELECTRODE MATERIALS FOR H2 PRODUCTION/CONVERSION

The field of hydrogen economy has emerged due to energy scarcity and environmental pollution. As a result, there is a growing emphasis on the development of efficient generation and storage solutions for hydrogen, along with its utilization as a clean, renewable fuel source to generate electricity to meet human activities. In this sense, it involves various electrochemical reactions, and one of the main tasks is understanding the reaction mechanisms in the reaction process to rationally design high-efficiency electrodes. Therefore, this thesis is focused on this topic. In this thesis, the works mainly contain 3 parts: (1) Transition metals (Fe, Cu, Mn) are used to dilute or alternate expensive electrode materials for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and photoelectrochemical water splitting. The prepared electrodes were characterized by a series of advanced techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS), X-ray diffraction (XRD), and Brunauer–Emmett–Teller (BET) analysis. (2) The electrochemical performance, reaction mechanism, charge transfer kinetics, and overpotential of the synthesized electrodes were rigorously evaluated by cyclic voltammetry (CV), Linear sweep voltammetry (LSV), and Tafel slope. (3) Operando X-ray absorption spectroscopy (XAS), as an elemental selective and powerful technique, was utilized to obtain specific elemental electronic structure information (such as the oxidation state, and coordination number) and illustrate the reaction mechanisms over electrodes during above mentioned reaction. At the same time, the pump and probe XAS technique was applied to illustrate the photoinduced electron transfer path during the photoelectrochemical water splitting process. Finally, operando XAS stands as a cornerstone in this investigation, offering a deeper understanding of the electronic structures of the electrodes in real time. It provides insights into the rational design or regeneration strategies for electrodes in the development of efficient and sustainable energy production and conversion technologies