1,721,142 research outputs found
Surface and in-depth chemistry of sulfuric and perchloric acid intercalated graphite explored through secondary ion mass spectrometry (SIMS) and atomic force microscopy (AFM)
No full textGraphite can be considered one of the most studied materials for technological application in batteries, energy, electronics, catalysis, and water purification. The intercalation of ions and molecules is often the fundamental mechanism behind these technological applications.
Thirty years after the publication of the model, there are still several unclear mechanisms related to the intercalation of solvated anions into graphite that deserve to be more deeply investigated.
In this article, we describe how ToF-SIMS can be combined with in situ and ex-situ AFM to correlate changes in the topographical features with changes in the surface and in-depth chemistry of GIC samples obtained from HOPG electrochemically intercalated in sulfuric and perchloric acid aqueous solution. Thanks to this combined approach, the interpretative model of intercalation mechanism was revised demonstrating that graphite structural defects are areas of preferential access for the solvated electrolytes. EGO formation, gas evolution, and blister growth can take place at the subsurface as well as in the bulk of the electrode by penetration through rifts or diffused step edges. Finally, the reduction of the intercalated carbon lattice is not usually accompanied by complete ejection of the intercalated electrolyte anions
Blister evolution time invariance at very low electrolyte pH: H 2 SO 4 /graphite system investigated by electrochemical atomic force microscopy
No full textTemporal analysis of blister evolution during anion intercalation in graphite
No full textIn the currently accepted picture, when graphite is immersed and polarized in a diluted sulfuric acid electrolyte, the surface undergoes an invasive process due to the intercalation of solvated sulphate anions inside the crystal. The following evolution of CO, CO2 and O2 promotes the surface swelling and the growth of blisters. Here, we give evidence that the appearance of blisters affects the graphite surface as soon as the oxygen potential is reached, i.e. before the traditionally accepted anion intercalation stage, which instead is demonstrated slowing the blister development. These results suggest a new picture of the solvated anion intercalation in graphite with respect to the current interpretative model
Temperature Effects on the HOPG Intercalation Process
Full text linkGraphite intercalation via chemical strategies is a common procedure to delaminate
stratified crystals and obtain a suspension of graphene flakes. The intercalation mechanism at the
molecular level is still under investigation in view of enhancing graphene production and reducing
damage to the original pristine crystal. The latter, in particular, can undergo surface detriment due to
both blister evolution and carbon dissolution. The role of the electrolyte temperature in this process
has never been investigated. Here, by using an in-situ atomic force microscopy (AFM) apparatus,
we explore surface morphology changes after the application of fast cyclic-voltammetries at 343 K,
in view of de-coupling the crystal swelling phenomenon from the other electrochemical processes.
We find that blisters do not evolve as a consequence of the increasing temperature, while the quality of
the graphite surface becomes significantly worse, due to the formation of some adsorbates on possible
defect sites of the electrode surface. Our results suggest that the chemical baths used in graphite
delamination must be carefully monitored in temperature for avoiding undesired electrode detriment
Physical confinement versus adsorption driven reconstruction: The case of sulfate anion interaction with vicinal Cu(111) surfaces
No full textNano-electrochemistry, i.e., the research of the properties of nano-(structured) electrodes and their influence on
electrochemical processes when immersed inside an electrolyte, represents a hot topic in view of applications in
nano-electronics, electro-catalysis and energy storage devices. The role of physical confinement in the electrochemical fabrication and performances of the respective systems have been recently addressed in the context of
metal-organic networks on surfaces, but rarely of nano-structured bare metal surfaces, for instance, regularly
stepped (vicinal) surfaces. In this work we investigate the interplay between physical confinement and adsorbate
induced restructuring by the electrochemical adsorption of sulfate anions on the flat and two distinctly different
vicinal Cu(111) surfaces. Sulfate adsorption on the flat Cu(111) surface is known to create a long-range ordered
Moir ́e-superstructure with lattice parameters in the 2–4 nm range due to an expansion of the topmost layer of
copper atoms with respect to the underlying crystal planes. This restructuring is also observed on a vicinal Cu
(111) surface whose original terrace width is considerably smaller than the lattice vectors of the sulfate induced
Moir ́e-structure. The results clearly indicate not only that the Moir ́e formation lifts the physical confinement
imposed by the initial terrace width, but also shine more light on the Moir ́e formation process itself. Such
adsorbate induced restructuring, of course, depends on the respective adsorbate – electrode combination, but
must, in principle, always be taken into account in order to understand electrochemical processes at nanostructured (and nano-sized) electrode surfaces
A microprocessor-aided platform enabling surface differential reflectivity and reflectance anisotropy spectroscopy
Full text linkSurface differential reflectivity (SDR) and reflectance anisotropy spectroscopy (RAS) [sometimes known as reflectance difference spectroscopy] are two well-known optical spectroscopies used in the investigation of surfaces and interfaces. Their adaptability on different experimental conditions (vacuum, controlled atmosphere and liquid environment) allows for the investigation not only of surface states and/or ultra-thin films but also of more complex interfaces. In these circumstances, the analysis of the sample with both techniques is decisive in view of obtaining a correct picture of the sample optical properties. In this work, we show a microelectronic hardware solution useful to control both a SDR and a RAS apparatus. We describe an electronic architecture that can be easily replicated, and we applied it to a representative sample where the interpretation of the optical properties requires an analysis by both SDR and RAS
Astronomical silicate nanoparticle analogues produced by pulsed laser ablation on olivine single crystals
Full text linkSilicate nanoparticles, otherwise referred to as very small grains (VSGs) [1], occur in various
astrophysical environments. These grains experience substantial processing (e.g., amorphization)
during their lifetime in the diffuse interstellar medium due to events such as grain-grain collisions
and irradiation [2]. Moreover, several studies have pointed out that the main building blocks of
these silicates are O, Si, Fe, Mg, Al and Ca, all elements that are among the principal constituents of
the Earth’s surface [3], thus leading to the name “astronomical silicates”. However, the structure
and chemical evolution together with the origin of these grains are still poorly understood and
intensively debated [4,5].
The aim of this study is the simulation of space weathering processes on olivine single
crystals by liquid phase pulsed laser ablation (LP-PLA). The study of the resulting structure of both
the target and the ablated material together with their chemical evolution has been carried out by a
multiple technique characterization. In particular, spectroscopy and dynamic light scattering
measurements, analyses of the electrostatic properties and reactivity to acids and bases on the
obtained colloidal solutions of the ablated nanoproducts have been performed and coupled with highresolution transmission electron microscopy (HR-TEM).
Selected olivine target crystals (Fo87) from the São Miguel island (Azores) were analyzed
by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray spectroscopy (EDX). LP-PLA
experiments were performed with a Nd:YAG laser focused via a singlet lens onto the surface of the
target, which was fixed at the bottom of a polystyrene box filled with 4 ml of deionized water (type
1) to immerge it completely. Laser pulses of 5 ns and 100 mJ simulate the timeframe and energy
exchange occurring during grain-grain interstellar collisions [6] and they generate a plasma plume
at the crystal/liquid interface. The rapid cooling induced by the confining liquid layer brings about
the condensation of the chemical vapor it contains with production of a colloidal solution of
nanoparticles. These solutions were analyzed by dynamic light scattering techniques and optical
absorption spectroscopy in the range from 200 nm to 1100 nm (6.20 eV - 1.13 eV). Absorption
measurements on the colloidal solutions have been compared against reference colloidal solutions
dispersed in deionized water (i.e. mesoporous silica [SiO2] nanoparticles, brucite [Mg(OH)2]
nanoparticles, aluminum hydroxide [Al(OH)3] nanoparticles, chrysotile [Mg3Si2O5(OH)4] nanotubes,
and synthetic forsterite [Mg2SiO4] nanoparticles). Moreover, additional absorption analyses have
been carried out as a function of the addition of known aliquots of sulfuric acid and sodium
hydroxide solutions. TEM/EDS analyses were then performed on the ablated nanoparticles deposited
via electrophoresis on C-coated Cu grids and compositional variations of the ablated target were
determined by X-ray photo-emission spectroscopy analyses.
The size distribution of LP-PLA synthesized nanoparticles is typically multimodal due to
aggregation phenomena. Aggregation is consistent with the measured ζ-potential, which is negative
with a relatively low absolute value, within the range 30-50 mV. Nonetheless, a recurrent mode is
centered at about 2 nm (hydrodynamic diameter) and it is consistent with the measured size
distribution obtained by transmission electron microscopy analysis (average nanoparticles diameter
around 3-5 nm). Optical absorption measurements on the ejected material show a main band
around 215 nm. This feature is very similar to the “B2 band” reported in several studies on silica
glass [7] and ascribed to oxygen vacancies, but its nature is still far to be fully understood. We also
found that this feature at 215 nm is very common among both Si and Mg compounds (e.g., Sioxide, Mg-hydroxide, chrysotile). Moreover, additional absorption bands in the range 240-350nm are
observed suggesting the formation of new space weathering products as result of the ablation
process.
Therefore, these results suggest that substantial chemical processing might be expected
during space weathering of “typical” interstellar grains into VSGs. Moreover, coupling these
experimental results with remote sensing datasets will provide fundamental information about the
origin and evolution of these silicate grains
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