Design and Modular Optimization of Components in Molecular Solar Thermal (MOST) Systems
This doctoral thesis focuses on advancing Molecular Solar Thermal (MOST) energy storage systems, a technology based on molecular photoswitches capable of capturing solar energy and storing it as chemical bond strain energy. The work specifically addresses the challenges associated with the norbornadiene/quadricyclane (NBD/QC) couple, focusing on the optimization of the back-conversion reaction through heterogeneous catalysis and the improvement of the system's sustainability. In the first stage of the research, a lack of standardized methods for evaluating the efficiency of heat release processes was identified. To address this, a protocol based on UV-Vis spectroscopy was developed. This method enabled a systematic screening of an extensive library of commercial catalysts, evaluating critical parameters such as reaction rate and catalyst stability in solution. Thanks to this protocol, it was determined that noble metal-based materials, particularly platinum on carbon supports, exhibit superior activity compared to other traditional systems. Subsequently, the thesis explores the molecular engineering of photoswitches to overcome the dependence on volatile and highly toxic organic solvents, such as toluene. New norbornadiene derivatives functionalized with symmetric amide groups were designed and synthesized. These compounds demonstrated not only excellent energy storage capacity and thermal stability but also significantly improved solubility in polar solvents such as ethanol. Irradiation and characterization studies confirmed that these systems maintain their functionality in more sustainable media, bringing MOST technology closer to safer operating conditions. Finally, the design and characterization of noble metal heterogeneous catalysts (Pt, Pd, Rh, Au) supported on carbon and alumina were investigated in depth. Using advanced techniques such as transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), the catalyst structure was correlated with its activity. It was concluded that a low metal loading and the maintenance of the metallic (reduced) oxidation state are fundamental to maximizing reaction efficiency. These findings establish a technical foundation for the implementation of MOST devices using recoverable catalysts and low-environmental-impact solvents.
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