Feng Yexin, Chen Ji, Fang Wei, Wang En-Ge, Michaelides Angelos, Li Xin-Zheng
School of Physics and Electronics, Hunan University , Changsha 410082, P. R. China.
Thomas Young Centre, University College London , London WC1E 6BT, United Kingdom.
J Phys Chem Lett. 2017 Dec 21;8(24):6009-6014. doi: 10.1021/acs.jpclett.7b02820. Epub 2017 Dec 4.
Recent experiments have triggered a debate about the ability of protons to transfer easily through individual layers of graphene and hexagonal boron nitride (h-BN). However, state-of-the-art computer calculations have shown that the barriers to proton penetration can, at >3 eV, be excessively high. Despite considerable interest the origin of this apparent anomaly between experiment and simulation remains unclear. We offer a new perspective on this debate and show on the basis of first-principles calculations that the barrier for proton penetration is significantly reduced, to <1 eV, upon hydrogenation, even in the absence of pinholes in the lattice. Although hydrogenation has not been offered as an explanation before, analysis reveals that the barrier is reduced because hydrogenation destabilizes the initial state (a deep-lying chemisorption state) and expands the honeycomb lattice through which the protons penetrate. This study offers a rationalization of the fast proton transfer observed in experiments and highlights the ability of proton transport through single-layer materials in hydrogen-rich solutions.
最近的实验引发了一场关于质子能否轻松穿过单层石墨烯和六方氮化硼（h-BN）的争论。然而，最新的计算机计算表明，质子穿透的势垒可能过高，超过3电子伏特。尽管人们对此兴趣浓厚，但实验与模拟之间这种明显异常现象的根源仍不清楚。我们为这场争论提供了一个新视角，并基于第一性原理计算表明，即使晶格中没有针孔，氢化后质子穿透的势垒也会显著降低至1电子伏特以下。尽管之前没有人将氢化作为一种解释，但分析表明，势垒降低是因为氢化使初始状态（一种深埋的化学吸附状态）不稳定，并使质子穿透的蜂窝晶格膨胀。这项研究为实验中观察到的快速质子转移提供了一种合理的解释，并突出了质子在富氢溶液中通过单层材料的传输能力。
