DAMIAN, SERENA (2025) Innovative biomimetic systems for photocatalytic hydrogen evolution. [Tesi di dottorato]

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Abstract

Light-driven processes are increasingly recognized as key strategies for sustainable solar-to-fuel conversion, with the hydrogen evolution reaction (HER) offering one of the most promising routes for renewable hydrogen production. Inspired by the efficiency of natural hydrogenases, considerable research efforts have been devoted to the development of artificial photosystems that combine molecular photosensitizers, sacrificial electron donors, and redox-active catalyst. Within this field, cobalt-based hydrogenase functional mimics have emerged as particularly attractive due to their earth abundance and versatility. Among these, Mimochrome VI*a (CoMC6a), is a rationally designed porphyrin-peptide conjugate that has demonstrated remarkable catalytic activity, longevity, and stability for electrochemical and photoinduced HER under mild conditions. While extensive studies on cobalt-based catalysts have established their potential as efficient and stable hydrogenase mimics, the role of the photosensitizer–donor pair in governing photosensitizer regeneration, electron-transfer pathways, and catalyst stability remains underexplored. Building on this background, the present thesis focuses on the optimization of photochemical systems evaluating the effect of different ruthenium sensitizers and sacrificial donors in combination with CoMC6*a as redox catalyst. The study focuses on how modifications in the ligand framework of the photosensitizer influence photophysical behaviour and electron-transfer efficiency, while also assessing the impact of different electron donors, including both one- and two-electron reductants, on catalytic performance and stability. Furthermore, the use of dimethylformamide (DMF) as a reaction medium provides a controlled environment in which photoinduced electron transfer can be decoupled from proton transfer, offering clearer mechanistic insights than those obtainable in aqueous solutions. Mechanistic insights were obtained through complementary techniques, including gas chromatography (GC) for quantifying H₂, UV–Vis absorption and fluorescence spectroscopy for monitoring electronic states, and cyclic voltammetry (CV) for redox characterization of the catalytic cycle. By integrating these approaches, the thesis contributes to a deeper understanding of the fundamental factors governing light-driven hydrogen evolution in artificial systems. The results highlight how the synergy between sensitizer design, donor selection, and solvent environment shapes the efficiency and selectivity of HER. More broadly, this work establishes design principles that can inform the rational development of robust, tunable, and sustainable photocatalytic architectures, bridging the gap between homogeneous molecular systems and complex bioinspired assemblies for solar hydrogen production.

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