Local and Nonlocal Functions of Cs Promoter in the O₂-Oxidation of Graphite

Abstract

The O 2 oxidation reaction of graphite was studied by preparing Cs promoters in two different states: Cs adsorbed on a surface [Cs(ad)] and Cs trapped underneath a surface carbon plane [Cs(tr)]. Reactive ion scattering spectrometry (RIS) and scanning tunneling microscopy (STM) were used to identify the reaction intermediates and to measure the spatial range of the Cs promoter effect. Cs(ad) promotes the oxidation reaction in a localized region through formation of CsO and CsO 2 intermediates. On the other hand, Cs(tr) promotes the reaction over a long range, such that a large number (∼10 3 ) of O 2 molecules are chemisorbed at a graphite surface and etch away the surface carbons.

A comparison between physically and chemically driven etching in the oxidation of graphite surfaces

“…It has been shown that Ar, C or Cs atoms implanted on graphite usually lead to the appearance of recognizable features in the STM images, in the form of protruding dome-like structures a few nm in lateral size with unperturbed atomic-scale pattern and atomically smooth edges [15,37,40]. We have occasionally observed such type of protruding feature in the STM images of DBD air plasma-treated graphite (images not shown), which we attribute to implanted Ar or C atoms, but never in the STM images of samples oxidized by UVO, consistent with a lack of ion bombardment in the latter case.…”

“…To the best of our knowledge, no general rule has been reported in the literature that can tell us which types of implanted species will lead to a depression or to a protruding structure. In the case of implanted Ar, C or Cs, their protruding appearance by STM was attributed to an upward deformation of the surface graphene due to the presence of the interstitial atom and/or to an increase of the local density of electronic states near the Fermi level for the surface graphene as a result of charge donation from the implanted species [15,37,40]. Along the same lines, the depression can be tentatively ascribed to an area of reduced local density of states near the Fermi level due to charge donation from the surface graphene to the implanted species.…”

Theory of genus reduction in alkali-induced graphitization of nanoporous carbon

“…Either the alkali atom alone is sufficient to lower the barrier through direct charge transfer to the reaction intermediate or it acts in concert with a cofactor already present in the structure, such as hydrogen, hydroxyl, water, or oxygen groups, which must also be mobile and so able to follow the advancing reaction edge. 9 Reaction pathway calculations in the presence of alkali metal can help answer this question.…”

“…Cs is already known to promote the O 2 oxidation of graphite, even when ensconced below the surface of graphite. 9 A gentler oxidizing agent than O 2 may be unable to destroy the carbon network, instead promoting its conversion to graphite.…”

Hydrogen storage properties of nanocrystalline Pt dispersed multi-walled carbon nanotubes

“…The presence of dangling bonds at the defect sites leads to the atomic storage of hydrogen. Among the different methods of creating defects in carbon materials like mechanical milling [17,18], oxidation by O 2 at high temperatures above 800 K [23,24] and oxidation by alkali-metal addition [25][26][27]. Chemical oxidation using HNO 3 , HCl and H 2 O 2 [28][29][30] has drawn great attention due to its high efficiency and simplicity.…”