Narrow Results

Differences in average voltages for the alkali ion intercalation (Li, Na) in a variety of electrode materials are investigated. The average Li and Na insertion potentials in the cavities of ◻ReO₃-perovskite, ramsdellite-◻Ti₂O₄, layered-◻₂A₂Ti₃O₇ (A = Li, Na) and NASICON-◻Na₃Ti₂(PO₄)₃ have been calculated by first principles calculations at the density functional theory level. The results identify the type of site occupied by the inserted ion as the relevant structural parameter. Occupation of large sites (c.n. = 12, 8) might yield Na insertion voltages higher than Li ones. On the other extreme, occupation of tetrahedral sites raises the Li insertion voltage as much as 0.8 V above the Na one. For octahedral sites the higher polarizing character of Li ions vs. Na ions acts as a key-factor to bring the Li intercalation voltage above that of Na intercalation.

Beryllium (Be)-decorated graphene with 585 double carbon vacancy defect and nitrogen-doped porphyrin defect are investigated for hydrogen storage applications using the first principle calculation based on density functional theory. It is found that the Be atom disperses well in the defective sites of graphene and prevents clustering. For the case of Be-decorated 585 double vacancy graphene, only two H₂ molecules are adsorbed via Kubas interaction with the stretched H–H bond length of 0.8 Å. In Be-decorated porphyrin defect graphene system, four H₂ molecules are molecularly chemisorbed with the H–H bond length of 0.77 Å. The chemisorptions are due to the hybridization between Be-p orbital and the H-$\sigma$ orbital. The average binding energy of H₂ molecule is found to be 0.43eV/H₂ which lies within the required range that can permit recycling of H₂ molecules under ambient conditions.

Nd₂CuO${}_{4\pm \delta }$ is known to possess either oxygen vacancies or interstitial oxygen defects, depending on the synthesis route, as well as may exhibit the A-site deficiency. In this work, insight into physicochemical properties of Nd₂CuO${}_{4\pm \delta }$ and Nd${}_{1.9}$CuO${}_{4\pm \delta }$ layered oxides is given, focusing on the crystal structure, electrical conductivity, and oxygen permeation, as well as on numerical density functional theory (DFT) simulations concerning ionic defects formation and their possible movement in the crystal structure. The results indicate that in oxidizing conditions at low temperatures, interstitial oxygen defects are stable, but with the increase of temperature, the release of oxygen is observed, leading to formation of the oxygen vacancies. Both materials are stable at elevated temperatures in air and Ar. Larger oxygen nonstoichiometry and improved electrical conductivity at high temperatures for Nd${}_{1.9}$CuO${}_{4\pm \delta }$ compound are accompanied by the recorded oxygen flux of ca. 0.2mLcm${}^{-2}$min${}^{-1}$ at 880^∘C for 0.8mm thick ceramic membrane.

Herein, we report a novel layered lead bromide, (CH₃CH${}_2{)}_3$N${}^{+}$Br${}^{-}$(CH${}_2{)}_2$NH${}_3^{+})$PbBr₃, where bulky organic cations, (CH₃CH${}_2{)}_3$N${}^{+}$Br${}^{-}$(CH${}_2{)}_2$NH${}_3^{+})$, amino-ethyl triethyl ammonium [aetriea] were not only incorporated between the inorganic layers but also sandwiched within the inorganic [PbBr₆]${}^{4-}$ octahedral layered structure. The UV-Visible, photoluminescence spectroscopy (PL), X-ray diffraction (XRD) and a field-emission scanning electron microscope (FE-SEM) result show that the new perovskitoid has a microrod shape with an estimated bandgap of $\sim$3.05 eV. The structural and optoelectronic properties of the [aetriea]PbBr₃perovskitoid were further corroborated by first-principles density functional theory (DFT) calculations. Thermogravimetric analysis (TGA) data show good stability of the [aetriea]PbBr₃perovskitoid. Time-resolved photoluminescence (TRPL) decays from new [aetriea]PbBr₃perovskitoid showing 6 ns average lifetime. These results suggest that doubly charged cation hybrid perovskite materials are potential candidates for optoelectronic applications.

Based on the first-principles calculation method of density functional theory, the influence of different directions and concentrations of Sn doping on V₂O₅ was discussed. The doping formation energy, electronic density of states, and isosurface charge density of different Sn doping directions and doping concentration structures are calculated. The calculation results of five different crystal orientation doping models show that the doped structure along the [111] crystal orientation has a smaller doping formation energy of 1.879 eV, which has the best electrical properties and the largest charge density. And the charge distribution is the most concentrated. It is most conducive to the formation of conductive filaments. In addition, as the doping concentration increases, the charge density gradually increases. When the doping concentration is 3.174%, the peak impurity energy level is the highest and the band gap is the smallest. At the same time, there is a tendency to form conductive filaments in the direction of charge extension [111], and the resistance change characteristics of vanadium pentoxide are best improved. The research results of this paper can provide certain theoretical guidance for improving the performance of resistive random access memory based on vanadium pentoxide.

MXenes are a family of two-dimensional materials that could be attractive for use as electrodes in lithium batteries due to their high specific capacity. For this purpose, it is necessary to evaluate magnitudes such as the lithium adsorption energy and the magnitude of the open-circuit voltage for different lithium concentrations. In this paper, we show through first-principles calculations that in a V₂C monolayer, we must consider the high correlation between the electrons belonging to vanadium to obtain correct results of these quantities. We include this correlation employing the Hubbard coupling parameter obtained by a linear response method. We found that the system is antiferromagnetic and that the quantities studied depend on the magnetic phase considered. Indirectly, experimental results could validate the theoretical value of the Hubbard parameter.

The electronic, the thermal, and the optical properties of hexagonal MgX monolayers (where $X$ = $C$, $N$, and $O$) are investigated via first principles studies. Ab-initio molecular dynamic, AIMD, simulations using NVT ensembles are performed to check the thermodynamic stability of the monolayers. We find that an MgO monolayer has semiconductor properties with a good thermodynamic stability, while the MgC and the MgN monolayers have metallic characters. The calculated phonon band structures of all the three considered monolayers show no imaginary nonphysical frequencies, thus indicating that they all have excellent dynamic stability. The MgO monolayer has a larger heat capacity then the MgC and the MgN monolayers. The metallic monolayers demonstrate optical response in the IR as a consequence of the metal properties, whereas the semiconducting MgO monolayer demonstrates an active optical response in the near-UV region. The optical response in the near-UV is beneficial for nanoelectronics and photoelectric applications. A semiconducting monolayer is a great choice for thermal management applications since its thermal properties are more attractive than those of the metallic monolayer in terms of heat capacity, which is related to the change in the internal energy of the system.

Lithium–carbon dioxide (Li–CO₂) batteries are novel high energy density energy storage devices that can simultaneously enrich and convert CO₂, but their widespread implementation is hindered by the continuous accumulation of lithium carbonate at the cathode. Herein, we developed non-precious metal cobalt-based nitride matrix composite Co${}_{5.47}$N@C based on metal-organic frameworks precursor for the catalytic cathode of advanced Li–CO₂ batteries. The highly stable Co${}_{5.47}$N achieves favorable adsorption and catalysis of CO₂ molecules by virtue of the excellent electronic structure on the surface, while the nanoscale high dispersion also effectively promotes interfacial electron transfer. As expected, the assembled Li–CO₂ battery exhibits excellent electrochemical performance in the discharge capacity of 10,000 mAh g${}^{-1}$ and a cycling capability of about 400 h. Further density functional theory (DFT) calculations explored the relationship between electronic structure and electrochemical activity. This work promotes the development of catalytic materials for Li–CO₂ batteries cathode.