Molecular Solar Thermal Energy Storage System: Evaluation of Different Candidates

Doctoral thesis, 2019

The development of solar energy can potentially meet the growing requirements for a global energy system beyond fossil fuels, however necessitates new scalable technologies for solar energy storage. One approach is the development of energy storage systems based on molecular photoswitches, so-called molecular solar thermal energy storage (MOST). By using organic photoswitchable compounds, the material can absorb sunlight thus photoisomerized to a metastable high energy photoisomer for ideally a long period of storage time, in such way, solar energy can be transformed to chemical bond strength of the molecule. When energy is needed, the converted molecule can be passed through a catalytic fixed bed reactor to release efficiently the stored energy in the form of heat, which could be used for, in this instance, domestic heating and low-temperature industrial heating purposes. Various candidates have been proposed for MOST applications, however a systematic evaluation and comparison of the proposed candidates is still scare. Here in this thesis, three candidates with difference photoswitching mechanisms including a norbornadiene derivative, an azobenzene derivative, and a dihydroazulene derivative have been characterized in detail for their availability of MOST purposes. Some modifications of tested norbornadiene has been tried as a further effort to improve the molecules’ properties. Later, all three candidates have been integrated into either indoor or outdoor devices for real application evaluations. Moreover, for stored energy release part, suitable catalysts for each candidate has been discovered, more discussion about future catalyst perspective have been performed in the context. Results show in a clear way how far this technology can be industrialized and the direction of next generation of MOST candidates.