Uniformly dispersed ternary nanoporous carbon-MgO-LiCl composites for medium-temperature thermochemical energy storage: Thermodynamic properties and dehydration kinetics

Mg(OH)2/MgO thermochemical energy storage, with its high energy storage density and long-term storage capability, provides the ability to regulate solar energy across time periods and enhances the continuity of energy supply. Lithium doping can adjust the Mg(OH)2 dehydration temperature, enabling broader applications and facilitating its use in cascaded thermal energy storage systems. However, the materials agglomeration remains an issue, slowing the dehydration/hydration kinetics. In this study, novel ternary nanoporous carbon (NC)-MgO-LiCl composites were constructed via a calcination method. NC was used to disperse the MgO/LiCl particles and LiCl was employed to adjust the dehydration temperature. The thermodynamic properties of the composite were investigated using thermogravimetric analysis. The influence of NC and LiCl modifications on the dehydration kinetic mechanism of the composite was analyzed by comparing it with pure Mg(OH)2/MgO and binary NC-MgO composite. Results revealed that NC matrix effectively supported uniformly dispersed MgO/LiCl nanoparticles. Both hydration and dehydration rates of the ternary composite were significantly accelerated. At a 5 % LiCl-to-MgO mass ratio, the dehydration temperature dropped by 45 °C (onset) and 53 °C (peak). Incorporating NC and LiCl progressively reduced the dehydration activation energy. Master plots showed that pure Mg(OH)2, binary, and ternary composites all followed a nucleation-growth mechanism, where the defects generated by reduced particle size and LiCl doping might lower activation energy. The derived kinetic models effectively characterized the dehydration process. These findings highlight the potential of matrix/salts/Mg(OH)2/MgO materials with wider thermal energy storage temperature ranges and provide modification references to enhance reaction kinetics based on kinetic mechanisms.