Water adsorption kinetics and thermal storage performance of MgSO4/MWCNT/Al-based MOF composite materials for energy storage

•It’s found that high salt content is a key factor for high heat storage capacity.•33% optimized mass ratio of MgSO4 solution to AF-CNT composite matrix is obtained.•The increase on λ of AF-0.5 wt% MWCNT compared to AF is 36.8%.•The ESD of AF-CNT-Mg3 at 232.89 kW·h·m−3 is superior to common adsorbents. Thermochemical energy storage technology stands as a promising avenue to address the intermittent and fluctuating nature of solar energy. However, it poses significant challenges due to the inadequate adsorption performance of adsorbents and limited heat and mass transfer capacity. In this research, a composite adsorption heat storage material, denoted as AF-CNT-Mg, was successfully synthesized, demonstrating high water adsorption and excellent heat transfer capacity. This material was developed using aluminum fumarate (AF) and multiwalled carbon nanotubes (CNT) as a composite matrix, with magnesium sulfate acting as impregnated hygroscopic salt. The influence of CNT content and magnesium sulfate mass fraction on thermal conductivity and water adsorption properties was thoroughly investigated. Results indicate that increasing CNT concentration enhances heat storage performance while diminishing water adsorption performance. Consequently, an AF-CNT matrix with a CNT mass fraction of 0.2 wt% was chosen as the composite matrix. The texture and thermal properties of AF-CNT-Mg composites were analyzed through automated specific surface area and pore size analysis, scanning electron microscopy, thermogravimetry, and differential scanning calorimetry. Furthermore, the effects of varying concentrations of impregnated metal ions on water adsorption properties were explored. Interestingly, a significant enhancement in the water adsorption performance and heat storage capacity was observed. The energy storage density could reach 838.4 kJ·kg−1, with a maximum water adsorption amount of 0.53 kgH2O·kg−1. Overall, these findings demonstrate that incorporating CNT expansion and hygroscopic salt magnesium sulfate into the al-based metal–organic framework substantially improves the heat storage performance of the composite adsorption heat storage material. Such advancements hold promising implications for applications in solar thermal power generation systems.