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Existing proton exchange membranes have the disadvantages of low proton conductivity at high temperature, high cost, and poor barrier properties. Montmorillonite (MMT) materials have excellent thermal and chemical stability, and two-dimensional nanostructures formed by exfoliated MMT show excellent proton conductivity. Therefore, they are expected to become new proton exchange membrane materials. However, the existing exfoliation methods still lack a unified theoretical guidance. In this work, we systematically investigate the detailed swelling and exfoliation properties of MMT with different intercalation cations via extensive molecular dynamics simulations. We find that the swelling properties are determined by the hydration capacity of interlayer cations, and the exfoliation mainly occurs via a lateral sliding process between adjacent layers. The exfoliation energy barrier strongly depends on the interaction strength between interlayer cations and MMT nanosheets, swelling degree, and surface charge density. Lower interaction strength and a higher swelling degree together with larger surface charge density can result in an easy exfoliation process. Our work unveiled the detailed mechanism of the exfoliation process of MMT nanosheets and may contribute to the search for efficient MMT exfoliation methods. [ABSTRACT FROM AUTHOR]

Amino acids are considered effective additives for regulating the electric double layer (EDL) in zinc-ion battery (ZIB) electrolytes. In comparison to their polar counterparts, nonpolar amino acids have received less attention in research. We demonstrated that isoleucine (ILE), benefiting from its nonpolar alkyl chain, emerges as a highly suitable electrolyte additive for aqueous ZIBs. ILE molecules preferentially adsorb onto the anode surface of zinc metal, subsequently creating a locally hydrophobic EDL facilitated by the alkyl chain. On one hand, this enhances the thermodynamic stability at the anode, while on the other hand, it accelerates the desolvation process of zinc ions, thereby improving the kinetics. Benefiting from the unique properties of ILE molecules, Cu//Zn cells with the ILE additive ultimately achieved an extended cycle life of 2600 cycles with an average coulombic efficiency of 99.695%, significantly outperforming other amino acid additives reported in the literature.

Given the requirements for power and dimension scaling, modulating channel transport properties using high gate bias is unfavorable due to the introduction of severe leakages and large power dissipation. Hence, this work presents an ultrathin phototransistor with chemical-vapor-deposition-grown monolayer MoS 2 as the channel and a 10.2 nm thick Al:HfO 2 ferroelectric film as the dielectric. The proposed device is meticulously modulated utilizing an Al:HfO 2 nanofilm, which passivates traps and suppresses charge Coulomb scattering with Al doping, efficiently improving carrier transport and inhibiting leakage current. Furthermore, a bipolar pulses excitable polarization method is developed to induce a nonvolatile electrostatic field. The MoS 2 channel is fully depleted by the switchable and stable floating gate originating from remanent polarization, leading to a high detectivity of 2.05 × 10 11 Jones per nanometer of gating layer (Jones nm -1 ) and photocurrent on/off ratio >10 4 nm -1 , which are superior to the state-of-the-art phototransistors based on two-dimensional (2D) materials and ferroelectrics. The proposed polarizable nonvolatile ferroelectric gating in a monolayer MoS 2 phototransistor promises a potential route toward ultrasensitive photodetectors with low power consumption that boast of high levels of integration.

The rapid development of renewable energy systems, electric vehicles, and pulsed equipment requires energy storage media to have a high energy storage density and efficiency in a wide temperature range. The state-of-the-art biaxially oriented polypropylene (BOPP) film is insufficient to meet the growing demand for energy storage devices due to its low energy storage density and working temperature, which make it a research hotspot for developing dielectric energy storage materials. In this manuscript, based on the epoxy materials that have been shown as a potential energy storage medium, we aim to reduce the influence of the benzene ring delocalization structure on the energy storage losses and enhance the efficiency by gradually replacing them with cyclohexane structures to adjust the segment unsaturation of epoxy materials. The results show that by partially reducing the unsaturation of the curing agent, the epoxy material achieves an excellent high-temperature energy storage density of 2.21 J/cm 3 at 150 °C and 300 MV/m while maintaining an extremely high energy storage efficiency of 99.2%. Leakage current density and high-voltage dielectric spectroscopy tests confirm that a moderate reduction of the segment unsaturation of epoxy materials can greatly inhibit polarization loss at high temperatures, which may explain their high energy storage efficiency.

Herein, a new photocatalyst PdS@UiOS@CZS is successfully synthesized, where thiol-functionalized UiO-66 (UiOS), a metal-organic framework (MOF) material, is used as a host to encapsulate PdS quantum dots (QDs) in its cages, and Cd 0.5 Zn 0.5 S (CZS) solid solution nanoparticles (NPs) are anchored on its outer surface. The resultant PdS@UiOS@CZS with an optimal ratio between components displays an excellent photocatalytic H 2 evolution rate of 46.1 mmol h -1 g -1 under visible light irradiation (420∼780 nm), which is 512.0, 9.2, and 5.9 times that of pure UiOS, CZS, and UiOS@CZS, respectively. The reason for the significantly enhanced performance is that the encapsulated PdS QDs strongly attract the photogenerated holes into the pores of UiOS, while the photogenerated electrons are effectively migrated to CZS due to the heterojunction effect, thereby effectively suppressing the recombination of charge carriers for further high-efficiency hydrogen production. This work provides an idea for developing efficient photocatalysts induced by hole attraction.

Although substantial efforts have been made, controllable synthesis of p-type WS 2 remains a challenge. In this work, we employ NaCl as a seeding promoter to realize vapor-liquid-solid (VLS) growth of p-type WS 2 . Morphological evolution, including a one-dimensional (1D) nanowire to two-dimensional (2D) planar domain and 2D shape transition of WS 2 domains, can be well-controlled by the growth temperature and sulfur introduction time. A high growth temperature is required to enable planar growth of 2D WS 2 , and a sulfur-rich environment is found to facilitate the growth of high-quality WS 2 . Raman and photoluminescence (PL) mappings demonstrate uniform crystallinity and high quantum efficiency of VLS-grown WS 2 . Moreover, monolayer WS 2 -based field-effect transistors (FETs) are fabricated, showing p-type conducting behavior, which is different from previous reported n-type FETs from WS 2 grown by other methods. First-principles calculations show that the p-type behavior originates from the substitution of Na at the W site, which will form an additional acceptor level above the valence band maximum (VBM). This facile VLS growth method opens the avenue to realize the p-n WS 2 homojunctions and p/n-WS 2 -based heterojunctions for monolayer wearable electronic, photonic, optoelectronic, and biosensing devices and should also be a great benefit to the development of 2D complementary metal-oxide-semiconductor (CMOS) circuit applications.

Sodium ion batteries (SIBs) are expected to take the place of lithium ion batteries (LIBs) as next-generation electrochemical energy storage devices due to the cost advantages they offer. However, due to the larger ion radius, the reaction kinetics of Na + in anode materials is sluggish. SnS 2 is an attractive anode material for SIBs due to its large interlayer spacing and alloying reactions with high capacity. Calcination is usually employed to improve the crystallinity of SnS 2 , which could affect the Na + reaction kinetics, especially the pseudocapacitive storage. However, excessively high temperature could damage the well-designed nanostructure of SnS 2 . In this work, we uniformly grow SnS 2 nanosheets on a Zn-, N-, and S-doped carbon skeleton (SnS 2 @ZnNS). To explore the optimal calcination temperature, SnS 2 @ZnNS is calcined at three typical temperatures (300, 350, and 400 °C), and the electrochemical performance and Na + storage kinetics are investigated specifically. The results show that the sample calcined at 350 °C exhibited the best rate capacity and cycle performance, and the reaction kinetics analysis shows that the same sample exhibited a stronger pseudocapacitive response than the other two samples. This improved Na + storage capability can be attributed to the enhanced crystallinity and the intact nanostructure.

Designing electrical insulation materials with excellent surface flashover strength in a vacuum environment is crucial for high-power equipment and aerospace devices. In the present paper, the effect of two types of electronegative groups, the halogen-phenyl groups and the aromatic π-conjugated naphthyl groups, is used to greatly improve the vacuum flashover characteristics of polystyrene (PS), a commonly used polymer dielectric material in high-power devices. By polymerization of the monomers containing these electronegative groups, the bulk insulation material as a whole is modified expediently. In comparison to the base polymer PS, the electron affinity of the structures containing strong electronegative groups is studied with first-principles calculations based on the density functional theory. The nanosecond pulsed vacuum flashover testing results show that the vacuum flashover strength is increased by 10% after replacing the PS pendant phenyl groups with fluorophenyl groups and increased by 44% when replaced with the naphthyl groups. Furthermore, the thermally stimulated current and secondary electron emission yield spectroscopies are measured, to study the influence of strong electronegative groups on the trapping characteristics and further the electron-emitting features of the polymer dielectrics, which are closely related to the charged particle multiplication process during the vacuum flashover. The results prove that introducing strong electronegative groups can inhibit the triggering of vacuum flashover, suppress the electron emission, delay the flashover process, and thus greatly increase the vacuum flashover voltage. The study of this paper not only puts forward two groups of easily processable polymers with excellent vacuum flashover strength but also paves ways for the future material design of special insulation polymers.

Recently, a novel [2+2] cycloaddition between the classical I h -C 60 and a fluorenylideneallene complex has been achieved experimentally. In the fullerene-fluorene dyad product, stereo- and regio-selectivities were found in the experiment, but the reasons are still unknown. Our theoretical studies suggest that, based on a diradical pathway, the structural selectivity of the product strongly depends on the structural/electronic features of the fluorenylideneallene and C 60 complexes. When the R 1 group in fluorenylideneallene denotes the H atom, the E -type product is more stable than the Z -type one, whereas other bulkier R 1 groups lead to the reverse due to their steric hindrance. The π orbital conjugation between the fluorenyl group and the C β ═C γ bond in fluorenylideneallene is the main reason for the high selectivity of β,γ-cycloaddition. Analyses of both frontier orbitals and spin density for the intermediate structure suggest a diradical pathway of the reaction between fluorenylideneallene and C 60 and uncover a decisive role of the LUMO of C 60 toward regio-selectivity, which conduces to a high selectivity of the (6,6)-addition product.

The practical application of lithium-/sodium-metal batteries is currently hindered by severe safety issues caused by uncontrolled continuous dendrite growth. Semiconductive nanoporous g-C 3 N 4 film has been demonstrated to be an effective protection layer for lithium-/sodium-metal anode, which can suppress the growth of dendrite. However, the underlying mechanism of how this semiconductive flexible thin film works to suppress dendrite growth remains unclear. In this work, we investigate the detailed working mechanism of g-C 3 N 4 protection layer employing both density functional theory calculations and ab initio molecular dynamics simulations. The calculation results indicate that g-C 3 N 4 layers show strong adhesion toward the lithium-/sodium-metal surface. When contacting with lithium/sodium metal, the intrinsic triangular nanopores of g-C 3 N 4 will be quickly filled with lithium/sodium atoms, turning the semiconductive g-C 3 N 4 into a metallic material. Lithium/sodium atoms can migrate through the triangular nanopores of stacked g-C 3 N 4 layers via a vacancy-mediated approach with moderate energy barriers of 0.42 and 0.61 eV, respectively. With a low current density, the newly deposited lithium/sodium atoms can permeate through the g-C 3 N 4 protection layers, therefore resulting in a flat electrode surface with no dendrite; with a high current density, however, the newly deposited lithium/sodium atoms cannot transport across the protection layer timely, which will result in the aggregation of lithium/sodium atoms on the surface of the g-C 3 N 4 protection layer.

Recently, one η 1 -coordinated complex of endohedral metallofullerene (EMF) Y@ C 2 v (9)-C 82 [Re(CO) 5 ] has been synthesized and characterized with a highly efficient radical-coupling methodology by performing a photochemical reaction between Y@ C 2 v (9)-C 82 and [Re(CO) 5 ] 2 complexes. Theoretical investigations with the density functional theory reveal that this complex is stabilized by an ionic C-Re bond. The reactions of M@ C 2 v (9)-C 82 (M = Sc, Y, La) with [Re(CO) 5 ] 2 suggest that the reaction energies differ little because of similar single occupied molecular orbitals (SOMOs) of M@ C 2 v (9)-C 82 . In the reactions of Y@ C 2 v (9)-C 82 with various transition-metal complexes [M'L n ] 2 (M' = Mn, Tc, Re, Fe, Ru, Os, Co, Rh, Ir), the C-M' bonds with Mn, Tc, Re, Fe, Ru, and Os can stably exist, whereas those with Co, Rh, and Ir are unstable. Further analyses disclose that, in each element group, the stability of the C-M' bond is mainly determined by the bond energy of the M'-M' bond, which is related to the d σ orbital of the M'L n species. Moreover, the very-low-energy d σ orbitals and large geometrical distortions of M'(CO) 4 (M' = Co, Rh, Ir) lead to poor stabilities of the C-M' (M' = Co, Rh, Ir) bonds. As comparison, the reactions of Y@ C s (6)-C 82 and La@C 72 have been investigated. The Y@ C s (6)-C 82 structure is more reactive toward the [M'L n ] 2 complexes than Y@ C 2 v (9)-C 82 thanks to a lower SOMO of Y@ C s (6)-C 82 than that of Y@ C 2 v (9)-C 82 , which derives from position change of the Y atom in C s (6)-C 82 during the reactions. However, the formation of [Y@ C s (6)-C 82 ] 2 suppresses the formation of several C-M' bonds. The reactivity of La@C 72 is weak due to a high LUMO+1 of C 72 , which leads to a high SOMO of La@C 72 . We believe that this theoretical study provides primary principles of radical-coupling reactions of EMFs and will be valuable for future research of organometallic complexes of fullerene.

Using SCAN-rVV10+U, we show Cr 2 TiC 2 and Cr 2 TiC 2 T 2 (T = -F and -OH) MXenes are moderate band gap semiconductors mostly in the antiferromagnetic state. All investigated MXene structures show large Seebeck coefficients (>400 μV/K), especially Cr 2 TiC 2 (>800 μV/K) and Cr 2 TiC 2 F 2 (>700 μV/K). The hole relaxation time of p-type Cr 2 TiC 2 (OH) 2 is found to be ∼8 ps, ensuring its superior electron transport properties in comparison to other investigated MXenes. It is also discovered that the surface functionalization could decrease the phonon thermal conduction and that Cr 2 TiC 2 (OH) 2 has the smallest lattice thermal conductivity (∼6.5 W/m·K) and the largest electron thermal conduction (>50 W/m·K with n = 10 19 cm -3 ). We predict the ZT value of p-type Cr 2 TiC 2 (OH) 2 can reach 3.0 at 600 K with the maximum thermoelectric conversion efficiency of 20%. Overall, the thermoelectric property of Cr-based ordered double transition metal MXenes is far superior to that of any known two-dimensional structures in the MXene family.

A recent experimental study from Bruce's group demonstrated the feasibility of TiC as a cathode material for Li air battery. We investigate Li2O2 adsorption and deposition on TiC{111} surface by periodic density functional theory calculation. The results showed that, upon interaction with Ti-terminated TiC{111} surface, Li2O2 clusters reassembled into a saturated periodic two atomic layer coating in which each O atom was bonded to three Ti atoms to form a O layer equivalent to the layer formed by O2 surface oxidation, and the Li atoms sat on the top. The atomic arrangement of O and Li layers is the same as that of O2Li1 layers normal to ⟨0001⟩ direction in Li2O2 crystal structure. Interface models constructed based on this lead showed that the growth of Li2O2 can be continued through a surface conduction mechanism to form Li2O2 coating with lattice parameters almost identical to those of the standard Li2O2 unit cell. The results support the experimental discovery from Bruce's group.