Humphries Terry D, Matsuo Motoaki, Li Guanqiao, Orimo Shin-Ichi
WPI-Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
Phys Chem Chem Phys. 2015 Mar 28;17(12):8276-82. doi: 10.1039/c5cp00258c.
Complex transition metal hydrides have potential technological application as hydrogen storage materials, smart windows and sensors. Recent exploration of these materials has revealed that the incorporation of anionic hydrogen into these systems expands the potential number of viable complexes, while varying the countercation allows for optimisation of their thermodynamic stability. In this study, the optimised synthesis of Na2Mg2TH8 (T = Fe, Ru) has been achieved and their thermal decomposition properties studied by ex situ Powder X-ray Diffraction, Gas Chromatography and Pressure-Composition Isotherm measurements. The temperature and pathway of decomposition of these isostructural compounds differs considerably, with Na2Mg2FeH8 proceeding via NaMgH3 in a three-step process, while Na2Mg2RuH8 decomposes via Mg2RuH4 in a two-step process. The first desorption maxima of Na2Mg2FeH8 occurs at ca. 400 °C, while Na2Mg2RuH8 has its first maxima at 420 °C. The enthalpy and entropy of desorption for Na2Mg2TH8 (T = Fe, Ru) has been established by PCI measurements, with the ΔHdes for Na2Mg2FeH8 being 94.5 kJ mol(-1) H2 and 125 kJ mol(-1) H2 for Na2Mg2RuH8.
复杂过渡金属氢化物作为储氢材料、智能窗和传感器具有潜在的技术应用价值。最近对这些材料的探索表明，将阴离子氢引入这些体系会增加可行配合物的潜在数量，同时改变抗衡阳离子可优化其热力学稳定性。在本研究中，已实现了Na2Mg2TH8（T = Fe，Ru）的优化合成，并通过非原位粉末X射线衍射、气相色谱和压力-组成等温线测量研究了它们的热分解性质。这些同构化合物的分解温度和途径有很大差异，Na2Mg2FeH8通过NaMgH3以三步过程进行分解，而Na2Mg2RuH8通过Mg2RuH4以两步过程进行分解。Na2Mg2FeH8的第一个解吸最大值出现在约400°C，而Na2Mg2RuH8的第一个最大值出现在420°C。通过PCI测量确定了Na2Mg2TH8（T = Fe，Ru）的解吸焓和熵，Na2Mg2FeH8的ΔHdes为94.5 kJ mol(-1) H2，Na2Mg2RuH8的ΔHdes为125 kJ mol(-1) H2。
