14 research outputs found
Modification of the electronic structure in a carbon nanotube with the charge dopant encapsulation
We present the first-principles study of effects of the charge dopants such
as Cesium and Iodine encapsulated on the electronic structure of carbon
nanotubes. An encapsulated cesium atom donates an electron to the nanotube and
produces donor-like states below the conduction bands. In contrast, an iodine
trimer (I) accepts an electron from the nanotube and produces an
acceptor-like state above the valance band maximum. We find that a Cs atom
inside a metallic armchair carbon nanotube gives rise to spatial oscillations
of the density of states near the Fermi level.Comment: Applied Physics Letters (in press), 3 color figure
Reduction of Activation Energy Barrier of Stone-Wales Transformation in Endohedral Metallofullerenes
We examine effects of encapsulated metal atoms inside a C molecule on
the activation energy barrier to the Stone-Wales transformation using {\it ab
initio} calculations. The encapsulated metal atoms we study are K, Ca and La
which nominally donate one, two and three electrons to the C cage,
respectively. We find that isomerization of the endohedral metallofullerene via
the Stone-Wales transformation can occur more easily than that of the empty
fullerene owing to the charge transfer. When K, Ca and La atoms are
encapsulated inside the fullerene, the activation energy barriers are lowered
by 0.30, 0.55 and 0.80 eV, respectively compared with that of the empty
C (7.16 eV). The lower activation energy barrier of the Stone-Wales
transformation implies the higher probability of isomerization and coalescence
of metallofullerenes, which require a series of Stone-Wales transformations.Comment: 13 pages, 3 figures, 1 tabl
Hydrogen-Bond Dynamics of Water at the Interface with InP/GaP(001) and the Implications for Photoelectrochemistry
We investigate the structure, topology,
and dynamics of liquid
water at the interface with natively hydroxylated (001) surfaces of
InP and GaP photoelectrodes. Using <i>ab initio</i> molecular
dynamics simulations, we show that contact with the semiconductor
surface enhances the water hydrogen-bond strength at the interface.
This leads to the formation of an ice-like structure, within which
dynamically driven water dissociation and local proton hopping are
amplified. Nevertheless, the structurally similar and isovalent InP
and GaP surfaces generate qualitatively different interfacial water
dynamics. This can be traced to slightly more covalent-like character
in the binding of surface adsorbates to GaP, which results in a more
rigid hydrogen-bond network that limits the explored topological phase
space. As a consequence, local proton hopping can give rise to long-range
surface proton transport on InP, whereas the process is kinetically
limited on GaP. This allows for spatial separation of individual stages
of hydrogen-evolving, multistep reactions on InP(001). Possible implications
for the mechanisms of cathodic water splitting and photocorrosion
on the two surfaces are considered in light of available experimental
evidence
Band-gap sensitive adsorption of fluorine molecules on sidewalls of carbon nanotubes: an ab initio study
We report from ab initio calculations that the band-gap sensitive side-wall functionalization of a carbon nanotube is feasible with the fluorine molecule (F2), which can provide a route to the extraction of semiconducting nanotubes by etching away metallic ones. In the small diameter cases like (11, 0) and (12, 0), the nanotubes are easily functionalized with F2 regardless of their electronic properties. As the diameter becomes larger, however, the fluorination is favoured on metallic CNTs with smaller activation barriers than those of semiconducting ones. Our results suggest that low-temperature exposure to F2 molecules in the gas phase can make a dominant portion of fluorinated metallic nanotubes and unfluorinated semiconducting ones. This is consistent with recent experimental reports.close5
Controlling Gas Generation of Li-Ion Battery through Divinyl Sulfone Electrolyte Additive
The focus of mainstream lithium-ion battery (LIB) research is on increasing the battery’s capacity and performance; however, more effort should be invested in LIB safety for widespread use. One aspect of major concern for LIB cells is the gas generation phenomenon. Following conventional battery engineering practices with electrolyte additives, we examined the potential usage of electrolyte additives to address this specific issue and found a feasible candidate in divinyl sulfone (DVSF). We manufactured four identical battery cells and employed an electrolyte mixture with four different DVSF concentrations (0%, 0.5%, 1.0%, and 2.0%). By measuring the generated gas volume from each battery cell, we demonstrated the potential of DVSF additives as an effective approach for reducing the gas generation in LIB cells. We found that a DVSF concentration of only 1% was necessary to reduce the gas generation by approximately 50% while simultaneously experiencing a negligible impact on the cycle life. To better understand this effect on a molecular level, we examined possible electrochemical reactions through ab initio molecular dynamics (AIMD) based on the density functional theory (DFT). From the electrolyte mixture’s exposure to either an electrochemically reductive or an oxidative environment, we determined the reaction pathways for the generation of CO2 gas and the mechanism by which DVSF additives effectively blocked the gas’s generation. The key reaction was merging DVSF with cyclic carbonates, such as FEC. Therefore, we concluded that DVSF additives could offer a relatively simplistic and effective approach for controlling the gas generation in lithium-ion batteries