电化学析氢反应中单层MoSe_2氢吸附机理第一性原理研究

Hydrogen adsorption mechanism on single-layer MoSe_2 for hydrogen evolution reaction:First-principles study

基于密度泛函理论的第一性原理方法,本文计算了单层2H相MoSe_2纳米材料表面及两种边缘(Mo原子边缘、Se原子边缘)不同活性位点、不同氢原子吸附率下的氢吸附吉布斯自由能(Gibbs free energy,用?G_H^0表示),并且将对应的微观结构进行了系统分析比较,得出?G0H最接近于0 eV的吸附位点及相应的吸附率.同时,结合差分电荷密度和电负性理论,分析了单层MoSe_2两种边缘氢吸附的电荷转移及成键特性,进一步解释了不同吸附位点呈现的结构与能量趋势.最后,通过基于密度泛函理论的第一性原理分子动力学模拟,研究了高温热运动对两种边缘氢吸附的影响,获得了氢原子发生脱附的临界温度及对应的微观动态过程.该理论研究从原子尺度揭示了单层2H相MoSe_2纳米材料边缘不同位点在不同温度下对氢原子吸附和脱附的微观机理,证实了Mo原子边缘的畸变和重构行为,加深了对实验中单层2H相MoSe_2边缘在不同温度下氢吸附机理的理解,为实验中通过控制MoSe_2边缘设计廉价高效的析氢催化剂提供理论参考.

Based on the first-principles of the density functional theory, the Gibbs free energies（ΔGH^0） of the hydrogen adsorption on the 2H-phase molybdenum diselenide monolayer（MoSe2） with different active sites and hydrogen coverage rates are calculated. The calculated results reveal that several ideal adsorbed rates and sites are very close to those at thermoneutral state（ΔGH^0～0）. To compare their catalytic ability in the hydrogen evolution reaction（HER）, the exchange current density（i0） as a function of ΔGH^0 is calculated as a volcano curve. Two sites located at the top of volcano curve present higher exchange current densities than that of Pt catalyst. The charge transfers and the bonding details of the two edge-hydrogen-adsorptions（Mo edge and Se edge） are analyzed by the charge density difference and electronegativity as the associated structures and relative ΔGH^0 are further explained. It is found that the localized charge transfer distributed uniformly between the hydrogen atoms and the adsorption sites can facilitate the catalytic ability of HER. For this reason, the catalytic ability of HER for the Se edge is more stable than that of Mo edge with less sensitivity to the absorption sites and hydrogen coverage rates. Based on the first-principles molecular dynamics（MD）simulation, finally, the influences of the thermal motion on the two kinds of structures of hydrogen adsorption at the higher temperature are explored, with the critical temperature for the hydrogen desorption as well as the atomistic dynamics discovered. It is worth mentioning that during the structure optimization and MD simulation, the edge deformation and reconstruction are discovered, respectively, which indicates that the ideal edge of MoSe2 may not be the most stable structure, which will change with the external conditions. This theoretic study reveals the atomistic mechanisms of the hydrogen adsorption and desorption of the single-layer 2H-phase MoSe2 at different temperatures, with the edge lattice deformation and reconstruction discovered, which can deepen our insights into the HER mechanisms near the edges of the 2H-phase MoSe2 at different temperatures and provide theoretic guidelines for designing the high-efficient and low-cost catalyst in the HER through tuning the MoSe2 edges.