In Situ Spectroscopic Characterization of Surface-Isolated Water Oxidation Catalysts
Green plants convert sunlight into chemical energy in the process of photosynthesis. Key step of this process is water oxidation, which generates four protons, four electrons and dioxygen, and it requires a catalyst. Replicating this process would enable widespread use of solar energy. Ruthenium-based complexes were the first artificial water oxidation catalyst discovered. They have been extensively studied in solution under water oxidation conditions modeled by chemical oxidation. However, chemical oxidation requires extremely oxidizing conditions and may lead to catalyst degradation. Practical applications of ruthenium catalysts for water oxidation require more controlled conditions via isolation of a studied catalyst on an electrode surface. In this work, two catalytic systems have been studied by in situ X-ray absorption and Electron Paramagnetic Resonance spectroscopic methods. The first system is a single-site catalyst incorporated into a metal-organic framework, which is deposited onto electrode surface as a thin film. The effect of the sample preparation on the catalytic behavior in the water oxidation process was studied. The second system of studies is a ruthenium catalyst that was proposed to function via an unusual 7-coordinate intermediate. This intermediate was impossible to detect in solution due to its high reactivity. In this work, the catalyst anchored to an electrode surface was studied using spectroscopic techniques, which allowed to detect and characterize this intermediate.
Pushkar, Purdue University.
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