Abstract:

In this paper, the MgO/Mg(OH)₂ heat storage system is taken as the research topic. Based on microscopic heat storage mechanism, the molecular crystal structure model of corresponding heat storage materials is established. The first principle density functional theory was used to analyze the effects of adsorption distance and configuration on adsorption stability, and the influence of doping on heat storage was further studied. It was found that for different adsorption distances, physical adsorption and chemical adsorption work together resulting in different adsorption energy, and the optimal adsorption distance was 0.15 nm. Mg atom has a strong ability to lose electrons at the highly symmetrical Mg-top position, i.e., the magnesium atom in the center of the first layer of the supercell. Thus, it loses the most electrons, and the chemical bonds and molecular force on the surface are also stronger here. Therefore, this is the most stable adsorption site. Apart from this, doping Li, Na and K atoms is beneficial to heat storage of magnesium oxide. This study partly reveals the microscopic mechanism of the thermochemical heat storage system, which has very good reference value for the subsequent research, especially in the improvement of material performance and multi-component adsorption, such as the influence of doped atomic crystal itself and two-component adsorption.

Key words: thermodynamic properties, thermochemical heat storage, micro-mechanism of reaction, Mg-based heat storage material, computational chemistry

摘要：

以MgO/Mg(OH)₂储热系统为研究对象，以微观储热机理为切入点，建立相应储热材料的分子晶体结构模型，采用第一性原理密度泛函理论，分析不同吸附距离和吸附构型对吸附稳定性的影响，并进一步研究了掺杂对储热的影响。研究发现，对于不同吸附距离，因为物理吸附和化学吸附共同作用，导致吸附能不同，最佳吸附距离为0.15 nm；Mg原子在高对称的镁顶位，即超晶胞第一层中央的镁原子，具有很强的失电子能力，所以失去的电子数最多，存在更强的化学键，分子与表面的作用力更强，是最稳定的吸附位点；掺杂Li、Na、K原子有利于氧化镁储热。本研究某种程度上揭示了热化学储热系统的微观机理，这对后续研究双组分吸附、掺杂的原子对晶体本身的影响等改性处理改善反应物性质的方法研究有很好的参考价值。

关键词: 热力学性质, 热化学储热, 微观反应机理, 镁基储热材料, 计算化学