Abstract
Ever-growing energy consumption in the world fosters the development of innovative energy technologies for sustainable energy production and storage. In this view, monolayer epitaxial graphene grown on 4H-SiC (MLEG/SiC) may be considered as a potential component of energy-related systems. The current paper deals with modelling of adsorption, diffusion and intercalation of hydrogen and lithium using MLEG/SiC model encompassing 2 × 2 graphene on √3 × √3R30° surface reconstructed nine-bilayer 4H-SiC. The obtained results demonstrate a strong and stable chemisorption of hydrogen on top site of epitaxial graphene with limited surface mobility, while lithiation process occurs via formation of LiC6 phase. The stages of hydrogen and lithium intercalation beneath graphene are studied in detail by performing potential energy scan. Energetic preferences for MLEG/SiC with intercalated hydrogen and lithium atoms versus MLEG/SiC with top-adsorbed H and Li are revealed. Li intercalant-induced complete decoupling of the buffer layer from the SiC substrate followed by the formation of bilayer graphene with inequivalent doping per layer is proposed as an explanation of experimentally observed Raman G peak splitting in electrochemically lithiated epitaxial graphene on 4H-SiC. This work provides deep insights into the nature of atomic-scale processes at epitaxial graphene, which is essential for improving performance of energy-related devices.
Highlights
Owing to its robustness, monolithic architecture and intriguing physical properties, device-quality monolayer epitaxial graphene grown on SiC through high-temperature Si sublimation is broadly recog nized as a key material component of sensing technologies [1,2,3,4,5,6,7,8], including Hall effect sensors [1], detector of terahertz waves [2] and sensor of toxic heavy metals [3,4,5,6]
The fundamental processes of neutral adatom adsorption, surface diffusion and intercalation at the mono layer epitaxial graphene supported by Si-face 4H-SiC substrate were investigated by means of first principles methods based on density functional theory (DFT)
Since hydrogen adsorption may be regarded as a rate-determining step for the hydrogen evolution reaction under alkaline conditions [63], it is first important to shed light on the adsorption of individual hydrogen atom on monolayer epitaxial graphene/4H-SiC
Summary
Monolithic architecture and intriguing physical properties, device-quality monolayer epitaxial graphene grown on SiC through high-temperature Si sublimation is broadly recog nized as a key material component of sensing technologies [1,2,3,4,5,6,7,8], including Hall effect sensors [1], detector of terahertz waves [2] and sensor of toxic heavy metals [3,4,5,6]. While the second possible application implies utilization of MLEG/SiC as an anode material un dergoing lithiation-delithiation during charge-discharge cycles [11,12,13,14]. For both considered cases, it is imperative to understand the nature of atomic-scale fundamental processes related to adsorption, surface diffusion and intercalation at the MLEG/SiC interface. Turning to the hydrogen case, it is worth noting that the interaction strength between H adsorbate and electrode surface is directly linked to the Gibbs free energy of H adsorption (Volmer reac tion) and to the resulting cathodic HER overpotential, which is the key descriptor for HER performance [16]. The knowledge on the interaction between freestanding graphene and hydrogen/lithium has been well documented
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