Enhanced electrocatalytic hydrogen evolution from nitrogen plasma-tailored MoS nanostructures.

Two-dimensional (2D) layered transition metal dichalcogenides such as MoS have been viewed as the most favorable candidates for replacing noble metals in catalyzing the hydrogen evolution reaction in water splitting owing to their earth abundance, superb chemical stability, and appropriate Gibbs free energy. However, due to its low number of catalytic sites and basal catalytic inertia, the pristine MoS displayed intrinsically unsatisfactory HER catalytic activity. Here, the hydrogen evolution catalytic activities of nanostructured MoS powder before and after plasma modification with nitrogen doping were experimentally compared, and the influence of treatment parameters on the hydrogen evolution catalytic performance of MoS has been studied.

Tailoring the Microstructure of Porous Carbon Spheres as High Rate Performance Anodes for Lithium-Ion Batteries.

Benefiting from their high surface areas, excellent conductivity, and environmental-friendliness, porous carbon nanospheres (PCSs) are of particular attraction for the anodes of lithium-ion batteries (LIBs). However, the regulation of carbon nanospheres with controlled pore distribution and graphitization for delivering high Li storage behavior is still under investigation. Here, we provide a facile approach to obtain PCSs with different microstructures via modulating the carbonization temperatures.

Second-order Jahn-Teller effect induced high-temperature ferroelectricity in two-dimensional NbOX (X = I, Br).

Based on the first-principles calculations, we investigated the ferroelectric properties of two-dimensional (2D) materials NbOX (X = I, Br). Our cleavage energy analysis shows that exfoliating one NbOI monolayer from its existing bulk counterpart is feasible. The phonon spectrum and molecular dynamics simulations confirm the dynamic and thermal stability of the monolayer structures for both NbOI and NbOBr.

Exploring the catalytic activity of graphene-based TM-NC single atom catalysts for the oxygen reduction reaction density functional theory calculation.

Electrocatalysts for the oxygen reduction reaction (ORR) are extremely crucial for advanced energy conversion technologies, such as fuel cell batteries. A promising ORR catalyst usually should have low overpotentials, rich catalytic sites and low cost. In the past decade, single-atom catalyst (SAC) TM-N (TM = Fe, Co, ) embedded graphene matrixes have been widely studied for their promising performance and low cost for ORR catalysis, but the effect of coordination on the ORR activity is not fully understood.

Optimized Pinecone-Squama-Structure MoS-Coated CNT and Graphene Framework as Binder-Free Anode for Li-Ion Battery with High Capacity and Cycling Stability.

Extensive research has been conducted on the development of high-rate and cyclic stability anodes for lithium batteries (LIBs) due to their high energy density. Molybdenum disulfide (MoS) with layered structure has garnered significant interest due to its exceptional theoretic Li storage behavior as anodes (670 mA h g). However, achieving a high rate and long cyclic life of anode materials remains a challenge.

Two-dimensional metal-free boron chalcogenides BX (X = Se and Te) as photocatalysts for water splitting under visible light.

Finding photocatalysts that fully utilize the visible solar light to split water into hydrogen and oxygen has been a challenging problem for a long time. In this regard, compared to traditional three-dimensional materials, graphene-like two-dimensional materials offer many advantages such as ultra-high surface area for photochemical reactions and minimal migration distance for carriers. Herein, using density functional theory (DFT), we examine the potential of a new series of two-dimensional boron chalcogenides, BX (X = S, Se, Te) as candidates for such photocatalysts.

Polymeric heptazine imide by O doping and constructing van der Waals heterostructures for photocatalytic water splitting: a theoretical perspective from transition dipole moment analyses.

Semiconductor-based photocatalysts have received extensive attention for their promising capacity in confronting global energy and environmental issues. In photocatalysis, a large band gap with suitable edge-position is necessary to warrant enough driving force for reaction, whereas a much smaller band gap is needed for visible-light response and high solar energy conversion efficiency. This paradox hinders the development of photocatalysts.

Ultra-High-Temperature Ferromagnetism in Intrinsic Tetrahedral Semiconductors.

Ferromagnetic semiconductors exhibit novel spin-dependent optical, electrical, and transport properties, which are promising for next-generation highly functional spintronic devices. However, the possibility of practical applications is hindered by their low Curie temperature. Currently, whether semiconducting ferromagnetism can exist at room temperature is still unclear because of the absence of a solid physical mechanism.

Toward Intrinsic Room-Temperature Ferromagnetism in Two-Dimensional Semiconductors.

Two-dimensional (2D) ferromagnetic semiconductors have been recognized as the cornerstone for next-generation electric devices, but the development is highly limited by the weak ferromagnetic coupling and low Curie temperature ( T). Here, we reported a general mechanism which can significantly enhance the ferromagnetic coupling in 2D semiconductors without introducing carriers. On the basis of a double-orbital model, we revealed that the superexchange-driven ferromagnetism is closely related to the virtual exchange gap, and lowering this gap by isovalent alloying can significantly enhance the ferromagnetic (FM) coupling.

Confinement boosts CO oxidation on an Ni atom embedded inside boron nitride nanotubes.

To date, most studies of heterogeneous catalysis have focused on metal particles supported on the surface of substrates. However, studies of the catalytic properties of metallic nanoparticles supported on the interior surface of nanotubes are rare. Using first-principles calculations based on density functional theory, we have studied the CO oxidation on a single nickel atom confined in a nitrogen vacancy on the inside surface of boron nitride nanotubes (BNNT).

Prediction of Intrinsic Ferromagnetic Ferroelectricity in a Transition-Metal Halide Monolayer.

The realization of multiferroics in nanostructures, combined with a large electric dipole and ferromagnetic ordering, could lead to new applications, such as high-density multistate data storage. Although multiferroics have been broadly studied for decades, ferromagnetic ferroelectricity is rarely explored, especially in two-dimensional (2D) systems. Here we report the discovery of 2D ferromagnetic ferroelectricity in layered transition-metal halide systems.

Effect of Coulomb Correlation on the Magnetic Properties of Mn Clusters.

In spite of decades of research, a fundamental understanding of the unusual magnetic behavior of small Mn clusters remains a challenge. Experiments show that Mn is antiferromagnetic while small clusters containing up to five Mn atoms are ferromagnetic with magnetic moments of 5 μ/atom and become ferrimagnetic as they grow further. Theoretical studies based on density functional theory (DFT), however, find Mn to be ferromagnetic, with ferrimagnetic order setting in at different sizes that depend upon the computational methods used.

Diverse carrier mobility of monolayer BNC : a combined density functional theory and Boltzmann transport theory study.

BNC monolayer as a kind of two-dimensional material has numerous chemical atomic ratios and arrangements with different electronic structures. Via calculations on the basis of density functional theory and Boltzmann transport theory under deformation potential approximation, the band structures and carrier mobilities of BNC (x  =  1,2,3,4) nanosheets are systematically investigated. The calculated results show that BNC-1 is a material with very small band gap (0.

Ca-Embedded CN: an efficient adsorbent for CO capture.

Carbon dioxide as a greenhouse gas causes severe impacts on the environment, whereas it is also a necessary chemical feedstock that can be converted into carbon-based fuels via electrochemical reduction. To efficiently and reversibly capture CO, it is important to find novel materials for a good balance between adsorption and desorption. In this study, we performed first-principles calculations and grand canonical Monte Carlo (GCMC) simulations, to systematically study metal-embedded carbon nitride (CN) nanosheets for CO capture.

Nanoporous MoS monolayer as a promising membrane for purifying hydrogen and enriching methane.

We present a theoretical prediction of a highly efficient membrane for hydrogen purification and natural gas upgrading, i.e. laminar MoS material with triangular sulfur-edged nanopores.

Stabilization of the Metastable Lead Iodide Perovskite Phase via Surface Functionalization.

Metastable structural polymorphs can have superior properties and applications to their thermodynamically stable phases, but the rational synthesis of metastable phases is a challenge. Here, a new strategy for stabilizing metastable phases using surface functionalization is demonstrated using the example of formamidinium lead iodide (FAPbI) perovskite, which is metastable at room temperature (RT) but holds great promises in solar and light-emitting applications. We show that, through surface ligand functionalization during direct solution growth at RT, pure FAPbI in the cubic perovskite phase can be stabilized in nanostructures and thin films at RT without cation or anion alloying.

Carrier mobility in double-helix DNA and RNA: A quantum chemistry study with Marcus-Hush theory.

Charge mobilities of six DNAs and RNAs have been computed using quantum chemistry calculation combined with the Marcus-Hush theory. Based on this simulation model, we obtained quite reasonable results when compared with the experiment, and the obtained charge mobility strongly depends on the molecular reorganization and electronic coupling. Besides, we find that hole mobilities are larger than electron mobilities no matter in DNAs or in RNAs, and the hole mobility of 2L8I can reach 1.

New Ferroelectric Phase in Atomic-Thick Phosphorene Nanoribbons: Existence of in-Plane Electric Polarization.

Ferroelectrics have many significant applications in electric devices, such as capacitor or random-access memory, tuning the efficiency of solar cell. Although atomic-thick ferroelectrics are the necessary components for high-density electric devices or nanoscale devices, the development of such materials still faces a big challenge because of the limitation of intrinsic mechanism. Here, we reported that in-plane atomic-thick ferroelectricity can be induced by vertical electric field in phosphorene nanoribbons (PNRs).

Superhalogens as building blocks of two-dimensional organic-inorganic hybrid perovskites for optoelectronics applications.

Organic-inorganic hybrid perovskites, well known for their potential as the next generation solar cells, have found another niche application in optoelectronics. This was demonstrated in a recent experiment (L. Dou, et al.

Graphdiyne as a High-Efficiency Membrane for Separating Oxygen from Harmful Gases: A First-Principles Study.

We theoretically explored the adsorption and diffusion properties of oxygen and several harmful gases penetrating the graphdiyne monolayer. According to our first-principles calculations, the oxidation of the acetylenic bond in graphdiyne needs to surmount an energy barrier of ca. 1.

Realizing half-metallicity in K2CoF4 exfoliated nanosheets via defect engineering.

Two-dimensional (2D) materials with intriguing electronic characteristics open up tremendous opportunities for application in future nanoelectronic devices, and have become one of the hot subjects of today's research. Here, we firstly predict the possibility of realizing a 2D exfoliated ionic bonding nanosheet, namely the K2CoF4 nanosheet, based on first-principles calculations. Through analysis of the cleavage energy, in-plane stiffness and stability, the free-standing K2CoF4 nanosheet can be exfoliated in experiments.

Quantum Phase Transition in Germanene and Stanene Bilayer: From Normal Metal to Topological Insulator.

Two-dimensional (2D) topological insulators (TIs) that exhibit quantum spin Hall effects are a new class of materials with conducting edge and insulating bulk. The conducting edge bands are spin-polarized, free of back scattering, and protected by time-reversal symmetry with potential for high-efficiency applications in spintronics. On the basis of first-principles calculations, we show that under external pressure recently synthesized stanene and germanene buckled bilayers can automatically convert into a new dynamically stable phase with flat honeycomb meshes.

Atomically Thin Transition-Metal Dinitrides: High-Temperature Ferromagnetism and Half-Metallicity.

High-temperature ferromagnetic two-dimensional (2D) materials with flat surfaces have been a long-sought goal due to their potential in spintronics applications. Through comprehensive first-principles calculations, we show that the recently synthesized MoN2 monolayer is such a material; it is ferromagnetic with a Curie temperature of nearly 420 K, which is higher than that of any flat 2D magnetic materials studied to date. This novel property, made possible by the electron-deficient nitrogen ions, render transition-metal dinitrides monolayers with unique electronic properties which can be switched from the ferromagnetic metals in MoN2, ZrN2, and TcN2 to half-metallic ones in YN2.

Two-dimensional silicon monolayers generated on c-BN(111) substrate.

Silicene, a buckled two-dimensional honeycomb structure of silicon, has been experimentally synthesized on very few substrates. Furthermore, synthesizing silicene with a Dirac point is another hot research area. However, only silicene grown on Ag(111) has been reported to have a Dirac point, which has lowered the expectations of researchers.

Coexistence of metallic and insulating-like states in graphene.

Since graphene has been taken as the potential host material for next-generation electric devices, coexistence of high carrier mobility and an energy gap has the determining role in its real applications. However, in conventional methods of band-gap engineering, the energy gap and carrier mobility in graphene are seemed to be the two terminals of a seesaw, which limit its rapid development in electronic devices. Here we demonstrated the realization of insulating-like state in graphene without breaking Dirac cone.