Study on Diffusion Mechanism of CaO/Ca ( OH )2 Molecules During Thermochemical Energy Storage Process Based on Molecular Dynamics

In CaO/Ca ( OH )(2) energy storage process , the energy storage and mechanical performance are related to the structure of CaO grains. This work investigated the lattice structure and molecular motion of CaO/Ca ( OH) (2) grains during CaO/Ca ( OH )(2) energy storage process using molecular dynamics simulations. The result indicates that during the dehydration stage , the movement of Ca ( OH )(2) molecules is consistent with the bulk diffusion mechanism. The diffusion pre -exponential factor for O/H atoms is 7.9x10 -8 m( 2) /s , while that for Ca atom is only 4.7x10 (-8) m( 2) /s. The rapid diffusion of O/H destroys the original lattice structure , leading to a reduction in the crystallinity of CaO after dehydration. In the hydration stage , the diffusion pre -factor for outer molecules of CaO grains is 3.2x10( -8) m( 2) /s , which is 2.5 times higher than that of inner molecules. Consequently , the molecular motion of CaO molecule is consistent with the surface diffusion mechanism. The diffusion strength of CaO molecule is weak during the hydration stage , resulting in minimal impact on the CaO lattice structure. The simulation determines the diffusion mechanisms of CaO/ Ca ( OH )(2) molecules in the thermochemical energy storage process. This is crucial to understand the crystal structure evolution of CaO -based materials in CaO/Ca ( OH )(2) energy storage process.