Activity enhancement of MgCO3/MgO for thermochemical energy storage by nitrate-promoted and morphology modification

Abstract

Thermochemical energy storage technology, with its ability to effectively solve the mismatch between energy supply and demand, holds considerable promise. Magnesium carbonate/magnesium oxide (MgCO3/MgO) in particular has shown broad prospects due to its high energy density and trans-regional storage capability. However, pure MgO has limited activity in the exothermic process, with a conversion rate of less than 2%. In this work, activity enhancement of MgCO3/MgO was investigated by combining chemical modification of alkali nitrates and physical morphology regulation. The results indicate that the activation effect of dopants on inert MgO depends on the electronegativity of the cation and the thermal stability of compound dopants. In particular, Na0.5K0.5NO3 with a molar ratio of 1:0.1 promotes MgO carbonation, resulting in a conversion rate of up to 67.5% and an exothermic density of 1964.25kJ/kg at 320°C. The enhanced activity is attributed to the melting of dopants that induces lattice distortion of the perfect crystal, hereby accelerating the chemical reaction. Additionally, the utilization of finely grained rod-like nanocrystalline magnesia precursor with a high specific surface area increased the adsorption capacity. Consequently, the synthesis of mesoporous MgO through the sol–gel method successfully broke through the CO2 adsorption of MgO carrier, achieving a conversion rate of 72.5% and a exothermic density of 2109.75kJ/kg MgO. During 20 release-storage cycles of the MgCO3/MgO TCES carrier, the conversion rate initially degraded significantly and eventually stabilized at approximately 25%. Overall, these methods provide a guiding principle for the preparation of thermochemical energy storage carriers in subsequent applications.