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First-principles studies of hydrogen interaction with ultrathin Mg and Mg-based alloy films

机译:氢与超薄Mg和Mg基合金膜相互作用的第一性原理研究

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The search for technologically and economically viable storage solutions for hydrogen fuel would benefit greatly from research strategies that involve systematic property tuning of potential storage materials via atomic-level modification. Here, we use first-principles density-functional theory to investigate theoretically the structural and electronic properties of ultrathin Mg films and Mg-based alloy films and their interaction with atomic hydrogen. Additional delocalized charges are distributed over the Mg films upon alloying them with 11.1 % of Al or Na atoms. These extra charges contribute to enhance the hydrogen binding strength to the films. We calculated the chemical potential of hydrogen in Mg films for different dopant species and film thickness, and we included the vibrational degrees of freedom. By comparing the chemical potential with that of free hydrogen gas at finite temperature (7) and pressure (P), we construct a hydrogenation phase diagram and identify the conditions for hydrogen absorption or desorption. The formation enthalpies of metal hydrides are greatly increased in thin films, and in stark contrast to its bulk phase, the hydride state can only be stabilized at high P and T (where the chemical potential of free H_2 is very high). Metal doping increases the thermodynamic stabilities of the hydride films and thus significantly helps to reduce the required pressure condition for hydrogen absorption from H_2 gas. In particular, with Na alloying, hydrogen can be absorbed and/or desorbed at experimentally accessible T and P conditions.
机译:寻求氢燃料的技术上和经济上可行的存储解决方案的方法将从研究策略中受益匪浅,这些策略涉及通过原子级修饰对潜在存储材料进行系统性调整。在这里,我们使用第一原理密度泛函理论从理论上研究超薄Mg膜和Mg基合金膜的结构和电子性能以及它们与原子氢的相互作用。在将Mg薄膜与11.1%的Al或Na原子合金化后,会在Mg薄膜上分配其他离域电荷。这些额外的电荷有助于增强氢与膜的结合强度。我们计算了不同掺杂物种类和膜厚的Mg膜中氢的化学势,并包括了振动自由度。通过在有限温度(7)和压力(P)下与自由氢气的化学势进行比较,我们构建了氢化相图并确定了氢吸收或解吸的条件。薄膜中金属氢化物的形成焓大大增加,并且与它的体相形成鲜明对比的是,氢化物状态只能在高P和T(游离H_2的化学势很高)时才稳定。金属掺杂增加了氢化物膜的热力学稳定性,因此大大有助于降低从H_2气体吸收氢所需的压力条件。特别地,通过钠合金化,可以在实验上可接近的T和P条件下吸收和/或解吸氢。

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