Li and Na Adsorption on Graphene and Graphene Oxide Examined by Density Functional Theory, Quantum Theory of Atoms in Molecules, and Electron Localization Function

Abstract

Adsorption of Li and Na on pristine and defective graphene and graphene oxide (GO) is studied using density functional theory (DFT) structural and electronic calculations, quantum theory of atoms in molecules (QTAIM), and electron localization function (ELF) analyses. DFT calculations show that Li and Na adsorptions on pristine graphene are not stable at all metal coverages examined here. However, the presence of defects on graphene support stabilizes both Li and Na adsorptions. Increased Li and Na coverages cause metal nucleation and weaken adsorption. Defective graphene is associated with the presence of band gaps and, thus, Li and Na adsorptions can be used to tune these gaps. Electronic calculations show that Li– and Na–graphene interactions are Coulombic: as Li and Na coverages increase, the metal valences partially hybridize with the graphene bands and weaken metal–graphene support interactions. However, for Li adsorption on single vacancy graphene, QTAIM, ELF, and overlap populations calculations show that the Li-C bond has some covalent character. The Li and Na adsorptions on GO are significantly stronger than on graphene and strengthen upon increased coverages. This is due to Li and Na forming bonds with both carbon and oxygen GO atoms. QTAIM and ELF are used to analyze the metal–C and metal–metal bonds (when metal nucleation is present). The Li and Na clusters may contain both covalent and metallic intra metal–metal bonds: This effect is related to the adsorption support selection. ELF bifurcation diagrams show individual metal–C and metal–metal interactions, as Li and Na are adsorbed on graphene and GO, at the metal coverages examined here.

Dynamics of Li deposition on epitaxial graphene/Ru(0001) islands

“…Such would be the situation if the Li atoms were being intercalated at the graphene/Ru interface upon deposition already at room temperature. This is in agreement with calculations indi-cating that Li cannot reside on the surface of defect-free graphene 40,41 . The picture of Li atoms falling on top of the graphene islands, diffusing to the edges and from there onto the Ru terraces is consistent with the sharp decrease of the work function that takes place only after an appreciable Li coverage; the intercalation would then significantly proceed only after the Ru(0001) terraces have been covered by 0.3 ML -0.5 ML Li and by a mechanism of diffusion following a concentration gradient across the island edges into the interior of the islands.…”

Lithium doped graphene nanostructures for advanced energetic applications

“…Li graphene Вычисления по определению значения переноса металл-С для минимального расстояния между металлом, в данном случае литий, и атомом углерода, в случае поглощения адотома поверхностью графенового листа проводились с учетом дисперсионной поправки DFT-D3. В работе [17] показали, что использование поправки DFT-D2 дает следующие значения для величины переноса металл-С при минимальном расстоянии между литием и атомом углерода, при поглощении адатомов графеном: 0,040 e , 0,024 e и 0,022 e для LiC32, Li3C32 и Li5C32 соответственно. В указанной работе рассчитана данная величина с учетом поправки DFT-D2 для дефектной структуры графена 4x4 при наличии одной вакансии, которая составляет 0,138, однако количество значений металл-С, включенных в расчет, равно трем.…”

Hydrogen Storage Mechanism in Sodium-Based Graphene Nanoflakes: A Density Functional Theory Study

“…Dimakis et al investigated the multiple adsorption of Na onto a graphene surface using DFT calculations [21], which revealed that multiply adsorbed Na atoms are not stable on graphene at high coverages; however, the presence of defects on the graphene support was found to stabilize the adsorbed Na. Higher Na coverage results in metal nucleation that weakens adsorption.…”