Institute of Industrial Science, The University of Tokyo, 153-8505 Tokyo, Japan.
Institute of Industrial Science, The University of Tokyo, 153-8505 Tokyo, Japan;
Proc Natl Acad Sci U S A. 2018 Jul 31;115(31):7896-7900. doi: 10.1073/pnas.1800412115. Epub 2018 Jul 13.
Enhancement of hydrogen (H) absorption kinetics improves the performance of hydrogen-purifying membranes and hydrogen-storage materials, which is necessary for utilizing hydrogen as a carbon-free energy carrier. Pd-Au alloys are known to show higher hydrogen solubility than pure Pd. However, the effect of Au on the hydrogen penetration from the surface into the subsurface region has not been clarified so far. Here, we investigate the hydrogen absorption at Pd-Au surface alloys on Pd(110) by means of thermal desorption spectroscopy (TDS) and hydrogen depth profiling with nuclear reaction analysis (NRA). We demonstrate that alloying the Pd(110) surface with submonolayer amounts of Au dramatically accelerates the hydrogen absorption. The degree of acceleration shows a volcano-shaped form against Au coverage. This kinetic enhancement is explained by a reduced penetration barrier mainly caused by a destabilization of chemisorbed surface hydrogen, which is supported by density-functional-theory (DFT) calculations. The destabilization of chemisorbed surface hydrogen is attributed to the change of the surface electronic states as observed by angle-resolved photoemission spectroscopy (ARPES). If generalized, these discoveries may lead to improving and controlling the hydrogen transport across the surfaces of hydrogen-absorbing materials.
提高氢（H）吸收动力学可以改善氢气净化膜和储氢材料的性能，这对于将氢气作为无碳能源载体的利用是必要的。已知 Pd-Au 合金比纯 Pd 具有更高的氢溶解度。然而，目前还不清楚 Au 对氢从表面渗透到次表面区域的影响。在这里，我们通过热脱附光谱（TDS）和核反应分析（NRA）研究了 Pd(110)上 Pd-Au 表面合金的氢吸收。我们证明，在 Pd(110)表面合金化亚单层量的 Au 可显著加速氢的吸收。加速程度对 Au 覆盖率呈火山形。这种动力学增强可以通过主要由化学吸附表面氢的不稳定性引起的穿透势垒的降低来解释，这得到了密度泛函理论（DFT）计算的支持。化学吸附表面氢的不稳定性归因于表面电子态的变化，这可以通过角分辨光电子能谱（ARPES）观察到。如果能够推广，这些发现可能会改善和控制氢在吸氢材料表面的传输。
