Comprehensive evaluation of the photothermal conversion thermochemical energy storage composite materials: Material characterization, kinetics analysis and building heating application

To further promote the application of thermochemical energy storage below 120 °C, the thermochemical composite adsorbents prepared by combining graphite felt with MgCl₂/MgSO₄, SrBr₂ and LiOH, which are named F-M, F-S and F-L, respectively. Their performance is evaluated at the material characterization, kinetics analysis, photothermal conversion and practical application perspectives. The thermochemical energy storage density of the composites below 120 °C is relatively high, with 30 %wtSL F-M reaching 789.71 kJ/kg. Graphite felt effectively disperses hydrated salts and prevents agglomeration, and the activation energies of dehydration and hydration reactions are reduced. The activation energies of the dehydration and hydration reactions of 5 %wtSL F-L are 39.58 kJ/mol and 35.09 kJ/mol. The composites have high solar absorption capabilities and can directly absorb solar energy and store it as chemical energy. 5 %wtSL F-L has the highest energy storage power and solar-chemical energy conversion efficiency, reaching 1.65 W and 64.08 %. 12 %wtSL F-L and 30 %wtSL F-M reach high energy release temperature, which are suitable for public baths or building radiator heating. F-S achieves stable temperature output at 50.0°C for a long time and is suitable for building floor heating scenarios. Under the application temperature, the 60 %wtSL F-S reconverts 71.89 % of the stored chemical energy into usable thermal energy.