Pathak A D, Tranca I, Nedea S V, Zondag H A, Rindt C C M, Smeulders D M J
Energy Technology, Department of Mechanical Engineering, Eindhoven University of Technology, Eindhoven 5612 AZ, The Netherlands.
J Phys Chem C Nanomater Interfaces. 2017 Sep 28;121(38):20576-20590. doi: 10.1021/acs.jpcc.7b05245. Epub 2017 Aug 28.
Chloride-based salt hydrates form a promising class of thermochemical materials (TCMs), having high storage capacity and fast kinetics. In the charging cycles of these hydrates however hydrolysis might appear along with dehydration. The HCl produced during the hydrolysis degrades and corrodes the storage system. Our GGA-DFT results show that the enthalpy charge during proton formation (an important step in hydrolysis) is much higher for CaCl·2HO (33.75 kcal/mol) than for MgCl·2HO (19.55 kcal/mol). This is a strong indicator that hydrolysis can be minimized by appropriate chemical mixing of CaCl and Mg Cl hydrates, which is also confirmed by recent experimental studies. GGA-DFT calculations were performed to obtain and analyze the optimized structures, charge distributions, bonding indicators and harmonic frequencies of various chemical mixtures hydrates and compared them to their elementary salts hydrates. We have further assessed the equilibrium products concentration of dehydration/hydrolysis of the chemical mixtures under a wide range of operating conditions. We observed that chemical mixing leads to an increase of the onset hydrolysis temperature with a maximum value of 79 K, thus increasing the resistance against hydrolysis with respect to the elementary salt hydrates. We also found that the chemical mixing of CaCl and MgCl hydrates widens the operating dehydration temperature range by a maximum value of 182 K (CaMgCl·2HO) and lowers the binding enthalpy with respect to the physical mixture by ≈65 kcal/mol for TCM based heat storage systems.
基于氯化物的盐水合物构成了一类很有前景的热化学材料（TCMs），具有高存储容量和快速动力学。然而，在这些水合物的充电循环中，水解可能会与脱水同时出现。水解过程中产生的HCl会降解并腐蚀存储系统。我们的广义梯度近似密度泛函理论（GGA-DFT）结果表明，对于CaCl·2HO（33.75千卡/摩尔），质子形成过程（水解中的一个重要步骤）中的焓变比MgCl·2HO（19.55千卡/摩尔）高得多。这有力地表明，通过CaCl和MgCl水合物的适当化学混合可以将水解降至最低，最近的实验研究也证实了这一点。进行GGA-DFT计算以获得并分析各种化学混合物水合物的优化结构、电荷分布、键合指标和谐波频率，并将它们与其单质盐水合物进行比较。我们还评估了在广泛的操作条件下化学混合物脱水/水解的平衡产物浓度。我们观察到化学混合导致起始水解温度升高，最大值为79 K，从而相对于单质盐水合物提高了抗水解能力。我们还发现，CaCl和MgCl水合物的化学混合使操作脱水温度范围最大拓宽了182 K（CaMgCl·2HO），并且对于基于TCM的储热系统，相对于物理混合物降低了约65千卡/摩尔的结合焓。
