Storage of Hydrogen Adsorbed on Alkali Metal Doped Single-Layer All-Carbon Materials

Abstract

Controversial experimental results have suggested that the presence of alkali metals in graphitic adsorbents would intensify hydrogen adsorption. Mainly by use of density functional theory methods, several authors have confirmed this intensification, which has been explained by a significant charge transfer from dopand, located on top of the center of a ring (the hollow configuration), to substrate. However, in this work, it was found that, for each distance of the hollow configuration of the Li−graphene interaction, depending on the initial guess, not only one but two qualitatively different self-consistent field solutions would be possible. One of them would concentrate charge in the region between lithium and graphene. The other one would be just the opposite. At fully correlated second-order Möller−Plesset level, for each distance, the latter was found to be significantly more stable than the former. So, it seems that the charge transfer from lithium to graphene described by several authors would not take place. The set of results reported here would provide evidence that solutions for the interaction of alkali metals with single-layer all-carbon materials would be extremely sensitive to initial guesses and correlation treatments. It is concluded that, in the case of alkali metal doping being capable of significantly intensifying physisorption of molecular hydrogen on single-layer all-carbon materials, the postulated charge transfer from dopand (located on top of the center of a ring) to substrate would not be the mechanism.

Critical Insight into the Relentless Progression Toward Graphene and Graphene‐Containing Materials for Lithium‐Ion Battery Anodes

“…Singlelayer graphene behaved radically different instead and the intercalation stage "1", corresponding to the LiC 6 stoichio metry for the fully lithiated graphite, could not be reached. Based also on previous models developed few years before, [ 54,55 ] the authors proposed that the strong Coulombic repulsion of Li atoms facing opposite sides of the same graphene sheet results on lower binding energies, likely leading to a very low surface coverage equivalent only to a graphitic intercalation "stage 20" (i.e., stoichiometry of LiC 120 ). These fi ndings were further supported, few years later (i.e., in 2013), by a DFT study from B. I. Yakobson et al [ 56 ] showing that, in single-layer graphene, the formation of Li clusters is energetically favored with respect to any stable Li-graphene phase.…”

Surface diffusion and coverage effect of Li atom on graphene as studied by several density functional theory methods

“…Our results for Li adsorption on 4×4 graphene supercell are summarized in Table 1. For comparison, the adsorption of Li on graphene and graphite from the previous calculations (35)(36)(37)(38)(39)(40) is also M a n u s c r i p t given. From Table 1, we can see that the most stable adsorption site is Hol site, followed by less stable site, the Bri, with the OT site being the least stable.…”

Lithium adsorption on zigzag graphene nanoribbons

“…[25,26,27] The interaction between Li atoms and carbon-based materials has been a subject of intensive study motivated by their potential for more efficient Li-ion batteries and hydrogen storage media. While the detailed interaction mechanism is still controversial, [28,29] it is commonly accepted that it presents a mostly ionic character with a substantial electronic charge transfer from the Li atom to the graphitic surface. [30,31,32,33] In a recent work, Yoo et al presented experimental evidence of a higher Li storage capacity in graphene with respect to graphite.…”