Structure-activity relationship between pore morphology and thermochemical energy storage properties based on MgCO3/MgO

Abstract

Thermochemical energy storage (TCES) is a pivotal technology for addressing the space-time mismatches in energy supply and demand. MgCO3/MgO carrier offers the advantages of high energy density, seasonal storage capability, and abundant nontoxic reserves. However, it is encumbered by poor exothermic activity and kinetic irreversibility. In this study, innovative preparation approaches for MgCO3/MgO have been developed, involving the regulation of physical morphology, so as to reveal the structure-activity relationship between pore morphology and TCES properties. The results indicate that SD-cotton-MgO (MgO prepared by structure-directing agent, cotton) could carbonate up to 76.98 %, facilitated by its mesopores that aid in the transport of reactants. SGSC-MgO (MgO prepared by sol-gel self-combustion method) exhibits the fastest reaction rate at the initial stage, with a rate of 593.1 μmol/min/g adsorbent because distributed macropores expose the other nanopores. As for SD-CPM-MgO (MgO prepared by structure-directing agent, carboniferous polysaccharide microsphere), owning to long pore distance of micropores hindering CO2 diffusion, its kinetics gradually decreases as the CPM size decreases. Porous media with mixed aperture could exhibit strong kinetic performance. Furthermore, the heat storage density and maximum power of SD-cotton-MgO increase as the endothermic temperature rises, achieving a peak energy density of 1385.7 kJ/kg MgCO3 at 400 °C. Still, its heat release density increases and then decreases with exothermic temperature, reaching 1964.3 kJ/kg MgO at 320 °C. Finally, the cycle stability is contingent on the activation of the chemical modification for the first heat release and antidegradation of the physical structure for subsequent cycles. SD-cotton-MgO doped with Na0.5K0.5NO3 maintains at 50 % after 30 cycles, exhibiting no collapse or agglomeration due to its robust porous structure with strong thermal stability and permeability.