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

Y.X. Xu,C.Y. Zhao

Thermochemical energy storage (TCES) is a pivotal technology for addressing the space-time mismatches in energy supply and demand. MgCO 3 /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 MgCO 3 /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 CO 2 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 MgCO 3 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 Na 0.5 K 0.5 NO 3 maintains at 50 % after 30 cycles, exhibiting no collapse or agglomeration due to its robust porous structure with strong thermal stability and permeability.