Studies of fibrous carbons for high-temperature thermal energy storage

In this thesis, fibrous carbons of renewable or synthetic origin in the form of flexible or rigid porous structures were investigated in-depth in order to evaluate their future use as hosts of phase change materials for thermal energy storage applications. Various commercial fibrous carbons were sorted, their morphological, physical and structural properties were thoroughly characterised, and their chemical stability was tested in molten lithium salts, before and after chemical vapour deposition of pyrocarbon. Either traditional or novel methodologies were proposed to characterise the fibrous carbons properties with respect to their effect on the preparation and performances of a hybrid material: carbon / phase change material. The use of different empirical and analytical models was also presented in order to determine characteristic quantities that are not directly measurable, such as elastic modulus of soft felts and tortuosity, and to validate the accuracy of the experimental results, all having an excellent predictive character. The materials’ attractiveness is due to the examined: (i) lightweight and highly porous structure with remarkable physical properties; (ii) resistance to oxidation; (iii) ability of being modified. Indeed, it appears that fibrous carbons with improved characteristics in terms of heat transfer, mechanical strength and chemical stability can be obtained and should produce, without significant loss of porosity and thus of stored thermal energy density, better hybrid materials. Finally, while the work presented here has a direct impact on the future implementation of fibrous carbons in thermal energy storage applications, the results obtained might also be used for many other end-uses.