Tortoza Mariana S, Humphries Terry D, Sheppard Drew A, Paskevicius Mark, Rowles Matthew R, Sofianos M Veronica, Aguey-Zinsou Kondo-Francois, Buckley Craig E
Department of Physics and Astronomy, Fuels and Energy Technology Institute, Curtin University, GPO Box U1987, Perth, WA 6845, Australia.
Phys Chem Chem Phys. 2018 Jan 24;20(4):2274-2283. doi: 10.1039/c7cp07433f.
Magnesium hydride (MgH) is a hydrogen storage material that operates at temperatures above 300 °C. Unfortunately, magnesium sintering occurs above 420 °C, inhibiting its application as a thermal energy storage material. In this study, the substitution of fluorine for hydrogen in MgH to form a range of Mg(HF) (x = 1, 0.95, 0.85, 0.70, 0.50, 0) composites has been utilised to thermodynamically stabilise the material, so it can be used as a thermochemical energy storage material that can replace molten salts in concentrating solar thermal plants. These materials have been studied by in situ synchrotron X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, temperature-programmed-desorption mass spectrometry and Pressure-Composition-Isothermal (PCI) analysis. Thermal analysis has determined that the thermal stability of Mg-H-F solid solutions increases proportionally with fluorine content, with Mg(HF) having a maximum rate of H desorption at 434 °C, with a practical hydrogen capacity of 4.6 ± 0.2 wt% H (theoretical 5.4 wt% H). An extremely stable Mg(HF) phase is formed upon the decomposition of each Mg-H-F composition of which the remaining H is not released until above 505 °C. PCI measurements of Mg(HF) have determined the enthalpy (ΔH) to be 73.6 ± 0.2 kJ mol H and entropy (ΔS) to be 131.2 ± 0.2 J K mol H, which is slightly lower than MgH with ΔH of 74.06 kJ mol H and ΔS = 133.4 J K mol H. Cycling studies of Mg(HF) over six absorption/desorption cycles between 425 and 480 °C show an increased usable cycling temperature of ∼80 °C compared to bulk MgH, increasing the thermal operating temperatures for technological applications.
氢化镁（MgH）是一种在300°C以上温度下运行的储氢材料。不幸的是，在420°C以上会发生镁烧结，这限制了其作为热能储存材料的应用。在本研究中，通过用氟取代MgH中的氢以形成一系列Mg(HF)ₓ（x = 1、0.95、0.85、0.70、0.50、0）复合材料，从而在热力学上稳定该材料，使其能够用作可替代聚光太阳能热电厂中熔盐的热化学储能材料。已通过原位同步加速器X射线衍射、差示扫描量热法、热重分析、程序升温脱附质谱法以及压力-组成-等温（PCI）分析对这些材料进行了研究。热分析确定，Mg-H-F固溶体的热稳定性随氟含量成比例增加，Mg(HF)在434°C时具有最大的氢解吸速率，实际储氢容量为4.6±0.2 wt% H（理论值为5.4 wt% H）。每种Mg-H-F组合物分解时都会形成一种极其稳定的Mg(HF)相，其剩余的氢直到505°C以上才会释放。Mg(HF)的PCI测量确定其焓（ΔH）为73.6±0.2 kJ mol⁻¹ H，熵（ΔS）为131.2±0.2 J K⁻¹ mol⁻¹ H，略低于MgH，MgH的ΔH为74.06 kJ mol⁻¹ H，ΔS = 133.4 J K⁻¹ mol⁻¹ H。在425至480°C之间对Mg(HF)进行六个吸收/解吸循环的循环研究表明，与块状MgH相比，其可用循环温度提高了约80°C，提高了技术应用的热运行温度。
