Vermeulen Paul, van Thiel Emile F M J, Notten Peter H L
Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, Den Dolech 2, Eindhoven, The Netherlands.
Chemistry. 2007;13(35):9892-8. doi: 10.1002/chem.200700747.
In the search for hydrogen-storage materials with a high gravimetric capacity, Mg(y)Ti((1-y)) alloys, which exhibit excellent kinetic properties, form the basis for more advanced compounds. The plateau pressure of the Mg--Ti--H system is very low (approximately 10(-6) bar at room temperature). A way to increase this pressure is by destabilizing the metal hydride. The foremost effect of incorporating an additional element in the binary Mg--Ti system is, therefore, to decrease the stability of the metal hydride. A model to calculate the effect on the thermodynamic stability of alloying metals was developed by Miedema and co-workers. Adopting this model offers the possibility to select promising elements beforehand. Thin films consisting of Mg and Ti with Al or Si were prepared by means of e-beam deposition. The electrochemical galvanostatic intermittent titration technique was used to obtain pressure-composition isotherms for these ternary materials and these isotherms reveal a reversible hydrogen-storage capacity of more than 6 wt. %. In line with the calculations, substitution of Mg and Ti by Al or Si indeed shifts the plateau pressure of a significant part of the isotherms to higher pressures, while remaining at room temperature. It has been proven that, by controlling the chemistry of the metal alloy, the thermodynamic properties of Mg-based hydrides can be regulated over a wide range. Hence, the possibility to increase the partial hydrogen pressure, while maintaining a high gravimetric capacity creates promising opportunities in the field of hydrogen-storage materials, which are essential for the future of the hydrogen economy.
在寻找具有高重量储氢容量的储氢材料时，表现出优异动力学性能的Mg(y)Ti((1 - y))合金构成了更先进化合物的基础。Mg - Ti - H体系的平台压力非常低（室温下约为10^(-6)巴）。提高该压力的一种方法是使金属氢化物失稳。因此，在二元Mg - Ti体系中加入额外元素的首要作用是降低金属氢化物的稳定性。Miedema及其同事开发了一个计算合金化金属对热力学稳定性影响的模型。采用该模型能够预先筛选出有前景的元素。通过电子束沉积制备了由Mg和Ti与Al或Si组成的薄膜。利用电化学恒电流间歇滴定技术获得了这些三元材料的压力 - 组成等温线，这些等温线显示出超过6 wt.%的可逆储氢容量。与计算结果一致，用Al或Si替代Mg和Ti确实使等温线的很大一部分平台压力移向更高压力，同时保持在室温下。已经证明，通过控制金属合金的化学组成，可以在很宽的范围内调节Mg基氢化物的热力学性质。因此，在保持高重量储氢容量的同时提高氢分压的可能性为储氢材料领域创造了有前景的机会，这对氢经济的未来至关重要。
