Enhanced ion diffusion induced by structural transition of Li-modified borophosphene.

Density functional theory (DFT) calculations have been carried out to investigate the performance of borophosphene in lithium-ion batteries. Our study has revealed the following: (1) the Dirac cone in the electronic structure demonstrates the metallic nature of borophosphene, implying the enhanced electronic conductivity of the anode electrodes; (2) borophosphene shows high adsorption of Li ions with binding energies in the range of -0.6 to -1.1 eV; (3) the theoretical storage capacity is significantly high, up to 1282.7 mA h g-1, and more interestingly, a structural transition is observed in the host borophosphene at a high density of Li ions; (4) at low concentrations, graphene-like borophosphene shows isotropic diffusion of Li atoms with a barrier around 0.5 eV, while at high density, the phosphorene-like borophosphene exhibits a reduced barrier in the range of 0.12-0.14 eV along the zigzag direction, suggesting strong promotion of Li-ion transportation; (5) meanwhile, owing to the structural transition, phosphorene-like borophosphene exhibits highly anisotropic migration of Li ions along the zigzag and armchair directions. These new findings present the great advantages of borophosphene as an anode material in lithium-ion batteries.

Programmable 3D Shape-Change Liquid Crystalline Elastomer Based on a Vertically Aligned Monodomain with Cross-link Gradient.

A liquid crystalline elastomer (LCE) as a kind of stimuli-responsive materials, which can be fabricated to present the three-dimensional (3D) change in shape, shows a wide range of applications. Herein, we propose a simple and robust way to prepare a 3D shape-change actuator based on gradient cross-linking of the vertically aligned monodomain of liquid crystals (LCs). First, gold nanoparticles grafted by liquid crystalline polymers (LCPs) are used to induce the homeotropic orientation of the LC monomer and cross-linkers. Then, photopolymerization under UV irradiation is carried out, which can result in the LCE film with a cross-link gradient. Different from the typical LCEs with homogenous alignment that usually show the shape change of extension/contraction, the obtained vertically aligned LCE film exhibits excellent bendability under a thermal stimulus. The nanoindentation experiment demonstrates that the deformation of LCE films comes from the difference in Young's modulus on two sides of the thin film. Simply scissoring the thin film can prepare the samples with different bending angles under the fixed length. Moreover, using a photomask to pattern the film during photopolymerization can realize the complex 3D deformation, such as bend, fold, and buckling. Further, the patterned LCE film doped with multiwalled carbon nanotubes modified by LCPs (CNT-PDB) can act as a light-fueled microwalker with fast crawl behavior.

Solid-State, Low-Cost, and Green Synthesis and Robust Photochemical Hydrogen Evolution Performance of Ternary TiO2/MgTiO3/C Photocatalysts.

Solar-driven photochemical hydrogen evolution is a promising route to sustainable hydrogen fuel production. Large-scale preparation of highly active photocatalysts using elementally abundant and less-expensive materials is urgently required for widespread practical application. Here, we report a highly efficient and low-cost TiO2/MgTiO3/C heterostructure photocatalyst for photochemical water splitting, which was synthesized on gram scale via a facile mechanochemical method. The heterostructure and carbon sensitization offer excellent photoconversion efficiency as well as good photostability. Under irradiation of one AM 1.5G sunlight, the optimal TiO2/MgTiO3/C photocatalyst can show a great solar-driven hydrogen evolution rate (33.3 mmol·h-1·g-1), which is much higher than the best yields ever reported for MgTiO3-related photocatalysts or pure TiO2 (P-25). We hope this work will attract more attention to inspire further work by others for the development of low-cost, efficient, and robust photocatalysts for producing hydrogen in artificial photosynthetic systems.

Strain-engineering tunable electron mobility of monolayer IV-V group compounds.

First-principles simulations demonstrate the anisotropic and high mobility in the new group monolayer IV-V semiconductors. The strain-engineered bandstructure reveals the conduction bands are sensitive to armchair-direction deformation. By applying strains, the electrical transportation in the armchair direction can be further improved or deteriorated. We use this important feature to achieve the tunable electron mobility in monolayer IV-V semiconductors. The controllable introduction of strain into semiconductors offers an important degree of flexibility in electrical transportation. Meanwhile, our works leads to a new approaches for research on mobility control in two-dimensional semiconductors. These will be useful for novel mechanical-electronic devices related to mobility switching.

Two-dimensional GeAsSe with high and unidirectional conductivity.

Prompted by the recent passion for researching two-dimensional materials, we investigate again the long-forgotten layered semiconductor material GeAsSe. A small cleavage energy (0.18 J m-2) and high thermal stability (1300 K) in monolayer structures were proved by employing density functional theory calculations. Additionally, the unusual electronic transport behaviors in GeAsSe make it more valuable for research. Our investigation proves unidirectional electronic transportation in GeAsSe. At room temperature (300 K), the transport ability of monolayer GeAsSe in the y direction is about 44 times larger than that in the x direction. Furthermore, through layer stacking, the conductivity of bilayer GeAsSe is improved to 192 cm2 V-1 s-1 in the y direction which is 200 times larger than that in the x direction (0.96 cm2 V-1 s-1), implying unidirectional conductivity. This work suggests that two-dimensional GeAsSe is a promising material for nano-electronic devices.

Novel elastic, lattice dynamics and thermodynamic properties of metallic single-layer transition metal phosphides: 2H-M 2P (Mo2P, W2P, Nb2P and Ta2P).

Recently, there has been a surge of interest in the research of two-dimensional (2D) phosphides due to their unique physical properties and wide applications. Transition metal phosphides 2H-M 2Ps (Mo2P, W2P, Nb2P and Ta2P) show considerable catalytic activity and energy storage potential. However, the electronic structure and mechanical properties of 2D 2H-M 2Ps are still unrevealed. Here, first-principles calculations are employed to investigate the lattice dynamics, elasticity and thermodynamic properties of 2H-M 2Ps. Results show that M 2Ps with lower stiffness exhibit remarkable lateral deformation under unidirectional loads. Due to the largest average Grüneisen parameter, single-layer Nb2P has the strongest anharmonic vibrations, resulting in the highest thermal expansion coefficient. The lattice thermal conductivities of Ta2P, W2P and Nb2P contradict classical theory, which would predict a smaller thermal conductivity due to the much heavier atom mass. Moreover, the calculations also demonstrate that the thermal conductivity of Ta2P is the highest as well as the lowest thermal expansion, owing to its weak anharmonic phonon scattering and the lowest average Grüneisen parameter. The insight provided by this study may be useful for future experimental and theoretical studies concerning 2D transition metal phosphide materials.

Strain engineering on transmission carriers of monolayer phosphorene.

The effects of uniaxial strain on the structure, band gap and transmission carriers of monolayer phosphorene were investigated by first-principles calculations. The strain induced semiconductor-metal as well as direct-indirect transitions were studied in monolayer phosphorene. The position of CBM which belonged to indirect gap shifts along the direction of the applied strain. We have concluded the change rules of the carrier effective mass when plane strains are applied. In band structure, the sudden decrease of band gap or the new formation of CBM (VBM) causes the unexpected change in carrier effective mass. The effects of zigzag and armchair strain on the effective electron mass in phosphorene are different. The strain along zigzag direction has effects on the electrons effective mass along both zigzag and armchair direction. By contrast, armchair-direction strain seems to affect only on the free electron mass along zigzag direction. For the holes, the effective masses along zigzag direction are largely affected by plane strains while the effective mass along armchair direction exhibits independence in strain processing. The carrier density of monolayer phosphorene at 300 K is calculated about [Formula: see text] cm-2, which is greatly influenced by the temperature and strain. Strain engineering is an efficient method to improve the carrier density in phosphorene.