Hydrogen Adsorption on Nearly Zigzag-Edged Nanoribbons: A Density Functional Theory Study

Michael Rivera Mananghaya,Catherine Stampfl,Gil Nonato Santos,Dennis Yu

doi:10.1038/s41598-017-14189-z

Michael Rivera Mananghaya, Catherine Stampfl + Show 2 more

Open Access

https://doi.org/10.1038/s41598-017-14189-z

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Abstract

The realistic shapes of N doped graphene nanoribbons (GNRs) can be realized by considering nearly zigzag-edged (NZE) imperfections and pyridine defects (3NV). The paper focuses on NZE-GNRs with 3NV that is populated by Scandium abbreviated as Sc/NZE-3NVGNRs. Systematic calculations have clarified roles of the nano-shapes of NZE-3NVGNRs in its formation, energetics, stability and electron states functionalized with Sc using density functional theory (DFT) formalisms. According to DFT calculations, the magnitude of the spin that is attributed to the rise of magnetic order is closely linked to the altered shape of the ribbon edges. Also, calculations show that the stability of Sc functionalization at the 3NV and NZE site is thermodynamically stable and is dictated by a strong binding energy (BE). The magnitude of the BE is enhanced when the zigzag edge is short or the ribbon width is narrow, suggesting a reduced clustering of Sc atoms over the Sc-doped NZE-3NVGNRs. Results also show that as the length of the zigzag edge in Sc/NZE-3NVGNRs increases it creates considerable distortion on the appearance of the structure. Finally, the Sc/NZE-3NVGNRs as a potential candidate for hydrogen storage was evaluated and it was found that it could adsorb multiple hydrogen molecules.

Highlights

An ideal substitute for fossil fuel-coal, natural gas and oil is H2 as it is non-toxic and environmentally friendly
The calculated Eedge for various configurations of the nearly zigzag-edged (NZE)-3NVGNRs shown in Fig. 1 is tabulated in Table 1 as a function of nzig
The calculation shows that the existence of short-range magnetic order and magnetism is closely linked to the structure of the zigzag edges of the ribbon

Summary

Introduction

An ideal substitute for fossil fuel-coal, natural gas and oil is H2 as it is non-toxic and environmentally friendly. The storage capacity or operating conditions fall below the standard set by the Department of Energy (DOE) of >6 wt.% It is recommended by the U.S DOE that for room temperature application of hydrogen energy, the optimal adsorption enthalpy should be within ~0.1–0.2 eV per H2 at ~30 bar[15,16,17]. Pyridine vacancies (3NV) are found in the zigzag edges because of the unzipping process of N doped carbon nanotubes (CNTs). The TM decorated systems tend to form clusters rather than spreading over the adsorbent, resulting in metal aggregation and reduced hydrogen storage capacity. For the number of H2 to be adsorbed on each Sc-decorated ideal zigzag-edged (IZE) nanoribbons with 3NV defects, rigorous calculation shows that it is around five[17]. The purpose of the present paper is to clarify the intricate roles of Nano shapes of the edges in Sc functionalized

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