First-principles study of hydrogen storage application of Ti3C2Tx monolayer MXene

MXene, with its high aspect ratio and adjustable surface properties, has garnered significant attention in the realm of hydrogen storage research. For the first time, considering a ternary/quaternary mixed terminated MXene surface, the authors have investigated comprehensively the hydrogen storage potential of two-dimensional (2D) titanium carbide Ti3C2Tx monolayer MXene using density functional theory (DFT). By considering mixed terminated surfaces, this study indicated the locally induced dipole due to the mixed termination is beneficial in facilitating hydrogen adsorption with stronger average adsorption energies than that of the uniform F-/O-/OH-/H-terminated surfaces. The authors estimated a compelling average H2 surface adsorption energy on the ternary mixed termination and total surface storage capacity to be −0.14 eV/H2 and ∼2 wt% H2, which is comparable to that of the metal-organic frameworks (MOFs). This study also reveals the importance of the local surface chemistry effects on hydrogen adsorption

First-principles studies of boron nanostructures

Boron is an \u27electron deficient\u27 element which has a rather fascinating chemical versatility. In the solid state, the elemental boron has neither a pure covalent nor a pure metallic character. As a result, its vast structural dimensionally and peculiar bonding features hold a unique place among other elements in the periodic table. In order to understand and properly describe these unusual bonding features, a detailed and systematic theoretical study is needed. In this work, I will show that some of the qualitative features of boron nanostructures, including clusters, sheets and nanotubes can easily be extracted from the results of first principles calculations based on density functional theory. Specifically, the size-dependent evolution of topological structures and bonding characteristics of boron clusters, Bn will be discussed. Based on the scenario observed in the boron clusters, the unique properties of boron sheets and boron nanotubes will be described. Moreover, the ballistic electron transport in single-walled carbon nanotubes will be considered. It is expected that the theoretical results obtained in the present thesis will initiate further studies on boron nanostructures, which will be helpful in understanding, designing and realizing boron-based nanoscale devices

Theoretical study of electron transport in boron nanotubes

The electron transport in single-walled boron nanotube (BNT) is studied using the Landauer-Büttiker [R. Landauer, J. Phys.: Condens: Matter 1, 8099 (1989); M. Büttiker, Phys. Rev. Lett. 57, 1761 (1986)] multichannel approach in conjunction with the tight-binding method. In the range of the calculated length (1-5.0 nm) of the tubes, the calculations predict a ballistic transport in BNT and find a relatively low resistance for BNTs as compared to that of the single-walled carbon nanotubes (CNTs) of comparable length. A lower resistance in the case of BNT than the CNT may be attributed to electron-deficient nature of boron characterized by the presence of two-center, and multicenter bonds in the former

A XANES study of lithium polysulfide solids: A first-principles study

X-ray absorption spectroscopy (XAS) is used for capturing the reaction mechanisms at the molecular level via the determination of local electronic configurations inside Li-S batteries. In this paper, a comprehensive investigation of the S K-edge X-ray absorption near-edge structure (XANES) of a series of stoichiometric lithium polysulfide solids was performed, assuming that these polysulfide solids are formed during the battery cycling process. The results based on density functional theory show that the pre-edge peak in the S K-edge XANES spectra is not a common feature in the solid phase in contrast to the case of pristine polysulfide molecules where the pre-edge peak constitutes a unique signature when dissolved in liquid electrolytes. A general redshift in the S K-edge XANES peak is found when a Li vacancy is introduced in these lithium polysulfide solids. Furthermore, the first peak positions of the S K-edge XANES spectra of the lithium polysulfide solids appear within a small range (2471-2473 eV) overlapping with the white line of the α-S8 bulk (∼2472 eV). Therefore, the results suggest that the use of additional characterization methods might be necessary for accurately identifying the elusive solid phase lithium polysulfides in Li-S batteries instead of relying only on S K-edge XANES spectroscopy. This journal i

First-principles study of MXene properties with varying hydrofluoric acid concentration

With varying hydrofluoric acid (HF) concentrations under three etching conditions, we presented a comparative study of the effects of both the ordered and randomly ternary mixed terminated Ti3C2Tx surfaces with a wide variation of O/OH/F stoichiometry on the thermodynamic stability and electronic properties. Regardless of the HF concentration, an OH-rich surface is found to be thermodynamically stable and the electrical conductivity of Ti3C2Tx is substantially affected by the OH concentration. The charge density difference and electron localization function demonstrated a significant electron localization at the hydroxyl group on the O/OH/F mixed terminated surface, which could yield a locally induced dipole on the surface that renders favorable reaction sites on the functionalized surface. In addition, a large tunability in the work function (ΔΦ ∼ 3.5 eV) is predicted for Ti3C2Tx. These findings provide a pathway for strategically tuning the electronic and structural properties of Ti3C2 MXenes etched with HF

Geometric, electronic properties and the thermodynamics of pure and Al--doped Li clusters

The first--principles density functional molecular dynamics simulations have been carried out to investigate the geometric, the electronic, and the finite temperature properties of pure Li clusters (Li$_{10}$, Li$_{12}$) and Al--doped Li clusters (Li$_{10}$Al, Li$_{10}$Al$_2$). We find that addition of two Al impurities in Li$_{10}$ results in a substantial structural change, while the addition of one Al impurity causes a rearrangement of atoms. Introduction of Al--impurities in Li$_{10}$ establishes a polar bond between Li and nearby Al atom(s), leading to a multicentered bonding, which weakens the Li--Li metallic bonds in the system. These weakened Li--Li bonds lead to a premelting feature to occur at lower temperatures in Al--doped clusters. In Li$_{10}$Al$_2$, Al atoms also form a weak covalent bond, resulting into their dimer like behavior. This causes Al atoms not to `melt' till 800 K, in contrast to the Li atoms which show a complete diffusive behavior above 400 K. Thus, although one Al impurity in Li$_{10}$ cluster does not change its melting characteristics significantly, two impurities results in `surface melting' of Li atoms whose motions are confined around Al dimer.Comment: 9 pages, 7 figure

Impact of cardiac arrest centers on the survival of patients with nontraumatic out‐of‐hospital cardiac arrest : a systematic review and meta‐analysis

Background The role of cardiac arrest centers (CACs) in out‐of‐hospital cardiac arrest care systems is continuously evolving. Interpretation of existing literature is limited by heterogeneity in CAC characteristics and types of patients transported to CACs. This study assesses the impact of CACs on survival in out‐of‐hospital cardiac arrest according to varying definitions of CAC and prespecified subgroups. Methods and Results Electronic databases were searched from inception to March 9, 2021 for relevant studies. Centers were considered CACs if self‐declared by study authors and capable of relevant interventions. Main outcomes were survival and neurologically favorable survival at hospital discharge or 30 days. Meta‐analyses were performed for adjusted odds ratio (aOR) and crude odds ratios. Thirty‐six studies were analyzed. Survival with favorable neurological outcome significantly improved with treatment at CACs (aOR, 1.85 [95% CI, 1.52–2.26]), even when including high‐volume centers (aOR, 1.50 [95% CI, 1.18–1.91]) or including improved‐care centers (aOR, 2.13 [95% CI, 1.75–2.59]) as CACs. Survival significantly increased with treatment at CACs (aOR, 1.92 [95% CI, 1.59–2.32]), even when including high‐volume centers (aOR, 1.74 [95% CI, 1.38–2.18]) or when including improved‐care centers (aOR, 1.97 [95% CI, 1.71–2.26]) as CACs. The treatment effect was more pronounced among patients with shockable rhythm ( P =0.006) and without prehospital return of spontaneous circulation ( P =0.005). Conclusions were robust to sensitivity analyses, with no publication bias detected. Conclusions Care at CACs was associated with improved survival and neurological outcomes for patients with nontraumatic out‐of‐hospital cardiac arrest regardless of varying CAC definitions. Patients with shockable rhythms and those without prehospital return of spontaneous circulation benefited more from CACs. Evidence for bypassing hospitals or interhospital transfer remains inconclusive

The Physics of the B Factories

This work is on the Physics of the B Factories. Part A of this book contains a brief description of the SLAC and KEK B Factories as well as their detectors, BaBar and Belle, and data taking related issues. Part B discusses tools and methods used by the experiments in order to obtain results. The results themselves can be found in Part C