以第一原理計算探討缺陷石墨烯與硼摻雜石墨烯對氫化鎂之脫氫行為和機制的影響

Abstract

氫能儲存的實際應用長期受限於材料的脫氫動力學遲滯與高能障問題。鎂氫化物(MgH2)因具備高氫含量與良好可逆性而被視為具潛力的儲氫材料，然而其強烈的鎂氫鍵結導致氫釋放困難，嚴重限制其脫氫效率。

本研究透過第一原理密度泛函理論，系統性探討石墨烯–氫化鎂異質接面對脫氫行為的影響，並比較完整石墨烯、含結構缺陷石墨烯以及硼摻雜石墨烯所形成之異質界面。藉由分析結構穩定性、氫空缺形成能、電子結構特性與反應路徑，釐清界面交互作用在氫釋放過程中的關鍵角色。

計算結果顯示，相較於純氫化鎂表面，石墨烯–氫化鎂異質接面可顯著降低氫空缺形成所需的能量；其中，缺陷與硼摻雜石墨烯界面能進一步穩定二配位氫空缺構型，顯示空缺能量行為高度依賴於界面原子結構。電子結構分析指出，異質界面產生明顯的電荷重新分佈，促進電子由氫化鎂向石墨烯轉移，進而降低氫移除相關能障。

反應路徑分析進一步顯示，完整石墨烯主要促進單階段脫氫機制，而缺陷與硼摻雜石墨烯則引入具較低能障的雙階段脫氫途徑。上述結果證實，石墨烯修飾不僅能提升氫化鎂的脫氫動力學，也會改變其脫氫反應機制。

本研究從原子尺度提供缺陷與摻雜石墨烯界面調控氫化鎂脫氫行為的關鍵見解，並為高效石墨烯基儲氫觸媒的設計提供理論依據。

Hydrogen storage remains constrained by slow kinetics and high activation barriers in magnesium-based hydrides, limiting their practical deployment. Magnesium hydride (MgH2) is attractive due to its high hydrogen capacity and reversibility; however, its dehydrogenation performance is hindered by strong Mg–H bonding and sluggish hydrogen release.

Density functional theory–based first-principles calculations were used to explore how pristine graphene, defect-engineered graphene, and boron-doped graphene modify the dehydrogenation behavior of MgH2. Structural stability, hydrogen vacancy formation energetics, electronic structure characteristics, and reaction pathways are analyzed to clarify the role of graphene–MgH2 interfacial interactions.

The calculated results demonstrate that graphene–MgH2 heterojunctions substantially reduce the energetic cost associated with hydrogen vacancy formation compared with bare MgH2 surfaces. Defective and boron-doped graphene further enhance this effect by stabilizing twofold-coordinated hydrogen vacancy configurations. Electronic structure analyses indicate pronounced charge redistribution at the heterointerface, facilitating electron transfer from MgH2 to graphene and lowering the energy cost of vacancy formation.

Reaction pathway calculations demonstrate that pristine graphene primarily promotes a one-stage hydrogen desorption mechanism, whereas defective and boron-doped graphene introduce an alternative two-stage pathway with reduced activation barriers. These findings confirm that graphene modification not only accelerates hydrogen release kinetics but also alters the underlying dehydrogenation mechanism of MgH2.

This study provides atomistic-level insight into defect- and dopant-assisted graphene interfaces and offers practical design guidelines for graphene-based catalysts aimed at improving hydrogen storage performance.