Despite the excellent performance of Nb3O7(OH) in dye-sensitized solar cells and catalysis, its charge separation, transport, and structural properties remain poorly understood. Herein, the Nb3O7(OH) nanorods were prepared, and their structural characteristics, optoelectronic properties, and carrier mobility were also analyzed and investigated through a series of complex characterizations. Theoretical prediction suggested that the exciton binding energy of Nb3O7(OH) could be as high as 100.49 meV. The temperature-dependent photoluminescence (PL) of Nb3O7(OH) nanorods revealed two activation energies, and a higher proportion of long-lived components observed in the photoluminescence decay indicated effective electron trapping. That is, two energy states were present, hindering photogenerated charge recombination and promoting photocatalytic action. Current–voltage characteristics of the Nb3O7(OH) nanorod film were analyzed, revealing an ultrahigh carrier mobility of ∼310 cm2/V·s, ensuring fast and efficient electron transfer. Furthermore, Nb3O7(OH) nanorods were employed to reduce CO2, resulting in the effective production of CO and CH4. Overall, considering the presence of hydroxyl pairs on the surface of Nb3O7(OH), which facilitate the formation of the frustrated Lewis acid–base pairs and the activation of CO2, together with its effective electron trapping and charge transport, give Nb3O7(OH) nanorods a promising potential for CO2 reduction.
The mass of $^{27}$P was predicted to impact the X-ray burst (XRB) model predictions of burst light curves and the composition of the burst ashes. To address the uncertainties and inconsistencies in the reported $^{27}$P masses in literature, a wealth of information has been extracted from the $\beta$-decay spectroscopy of the drip-line nucleus $^{27}$S. We determine the most precise mass excess of $^{27}$P to date to be $-659(9)$~keV, which is 63~keV (2.3$\sigma$) higher than the AME2016 recommended value of $-722(26)$~keV. The experimentally unknown mass excess of $^{27}$S was estimated to be 17030(400)~keV in AME2016, and we constrain this mass to be 17678(77)~keV based on the measured $\beta$-delayed two-proton energy. In the temperature region of $(0.06-0.3)$~GK, the $^{26}$Si$(p,\gamma)^{27}$P reaction rate determined in this work is significantly lower than the rate recommended in the reaction rate libraries, up to two orders of magnitude around 0.1~GK. The impact of these newly determined masses and well-constrained rate on the modeling of the explosive astrophysical scenarios has been explored by hydrodynamic nova and post-processing XRB models. No substantial change was found in the nova contribution to the synthesis of galactic $^{26}$Al or in the XRB energy generation rate, but we found that the calculated abundances of $^{26}$Al and $^{26}$Si at the last stage of XRB are increased by a factor of 2.4. We also conclude that $^{27}$S is not a significant waiting point in the rapid proton capture process.
Li-O2 batteries are considered promising electrochemical energy storage devices due to their high specific capacity and low cost. However, this technology currently suffers from two serious problems: low round-trip efficiency and slow reaction dynamics at the cathode. Solving these problems requires designing novel catalysis materials. In this study, a bilayer tetragonal AlN nanosheet as the catalyst is theoretically designed for the Li-O2 electrochemical system, and the discharge/charge process is simulated by a first-principles approach. It is found that the reaction path leading to Li4O2 is energetically more favored than the path to form a Li4O4 cluster on an AlN nanosheet. The theoretical open-circuit voltage for Li4O2 is 2.70 V, which is only 0.14 V lower than the formation of Li4O4. Notably, the discharge overpotential for forming Li4O2 on the AlN nanosheet is only 0.57 V, and the corresponding charge overpotential is as low as 0.21 V. A low charge/discharge overpotential can effectively solve the problems of low round-trip efficiency and slow reaction kinetics. The decomposition pathways of the final discharge product Li4O2 and the intermediate product Li2O2 are also investigated, and the decomposition barriers are 1.41 eV and 1.45 eV, respectively. Our work shows that bilayer tetragonal AlN nanosheets are promising catalysts for Li-O2 batteries.
Abstract The regulation of electronic and optical properties with uniaxial and biaxial strain is computationally investigated for the monolayer thin film of a newly discovered quasi-layered MgGeN 2 phase. It is found that, under uniaxial compression in both [100] and [010] directions with the perpendicular lattice parameter relaxable, the band gap will first increases and then decreases, while under uniaxial tensile strain the band gap decreases monotonically and the light absorption in the visible region is strongly enhanced. When uniaxial compression was applied with the perpendicular lattice constant fixed, the band gap behaves like the first kind of uniaxial compression and the light absorption is enhanced in visible range by compression. When biaxial strain was applied, the band gap shows a monotonic decrease from the largest compression down to the largest tensile strain, while the light absorption behaves in the opposite way. Therefore, the band structure and light absorption of monolayer MgGeN 2 can be efficiently tuned with strain and stress, which can potentially be used for the MgGeN 2 film in device design, thus promoting its applications in optoelectronics and photocatalysis.
$\ensuremath{\beta}$-delayed one-proton emissions of $^{22}\mathrm{Si}$, the lightest nucleus with an isospin projection ${\mathrm{T}}_{z}=\ensuremath{-}3$, are studied with a silicon array surrounded by high-purity germanium detectors. Properties of $\ensuremath{\beta}$-decay branches and the reduced transition probabilities for the transitions to the low-lying states of $^{22}\mathrm{Al}$ are determined. Compared to the mirror $\ensuremath{\beta}$ decay of $^{22}\mathrm{O}$, the largest value of mirror asymmetry in low-lying states by far, with $\ensuremath{\delta}=209(96)$, is found in the transition to the first ${1}^{+}$ excited state. Shell-model calculation with isospin-nonconserving forces, including the $T=1$, $J=2$, 3 interaction related to the ${s}_{1/2}$ orbit that introduces explicitly the isospin-symmetry breaking force and describes the loosely bound nature of the wave functions of the ${s}_{1/2}$ orbit, can reproduce the observed data well and consistently explain the observation that a large $\ensuremath{\delta}$ value occurs for the first but not for the second ${1}^{+}$ excited state of $^{22}\mathrm{Al}$. Our results, while supporting the proton-halo structure in $^{22}\mathrm{Al}$, might provide another means to identify halo nuclei.
Nonaqueous alkali metal (AM)–O2 batteries are promising next-generation energy storage devices due to their outstanding specific capacity and energy density. However, the high charge–discharge overpotential and slow electrochemical reactions limit their development. Highly active cathode catalysts can solve this problem. Based on first-principles calculations, we theoretically explore the application potential of Si2Se2 and SiSe2 nanosheets as potential cathode electrocatalysts. Different electrochemical reduction paths are proposed for understanding the discharge process. For example, for Li–O2 battery, the main products on the electrocatalyst surface are LiO2 and Li2O2, and the charge/discharge overpotential of SiSe2 is less than 0.46 V. The main products are NaO2 and Na2O2 for Na–O2 battery, and the charge/discharge overpotentials are less than 0.73 V. There is only one catalytic product of K–O2 battery, which is KO2. Specially, the charge/discharge overpotential of Si2Se2 is significantly low, only 0.31 V for K–O2 battery. In addition, we found that neither Si2Se2 nor SiSe2 promoted the formation of the side product Li2CO3/Na2CO3 or caused the decomposition of the dimethyl sulfoxide electrolyte, suggesting that Si2Se2 and SiSe2 can effectively improve the reversible cycle life of AM–O2 batteries.
The $\ensuremath{\beta}$-delayed two-proton ($\ensuremath{\beta}2p$) decay of $^{27}\mathrm{S}$ was studied using a state-of-the-art silicon array and Clover-type HPGe detectors. An energy peak at 6372(15) keV with a branching ratio of 2.4(5)% in the decay-energy spectrum was identified as a two-proton transition via the isobaric-analog state in $^{27}\mathrm{P}$ to the ground state of $^{25}\mathrm{Al}$ in the $\ensuremath{\beta}$ decay of $^{27}\mathrm{S}$. Two-proton angular correlations were measured by the silicon array to study the mechanism of two-proton emission. Based on experimental results and Monte Carlo simulations, it was found that the main mechanism for the emission of $\ensuremath{\beta}2p$ by $^{27}\mathrm{S}$ is of sequential nature.
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