Boron, a nearest-neighbor of carbon, is possibly the second element that can possess free-standing flat monolayer structures, evidenced by recent successful synthesis of single-walled and multiwalled boron nanotubes (MWBNTs). From an extensive structural search using the first-principles particle-swarm optimization (PSO) global algorithm, two boron monolayers (α(1)- and β(1)-sheet) are predicted to be the most stable α- and β-types of boron sheets, respectively. Both boron sheets possess greater cohesive energies than the state-of-the-art two-dimensional boron structures (by more than 60 meV/atom based on density functional theory calculation using PBE0 hybrid functional), that is, the α-sheet previously predicted by Tang and Ismail-Beigi and the g(1/8)- and g(2/15)-sheets (both belonging to the β-type) recently reported by Yakobson and co-workers. Moreover, the PBE0 calculation predicts that the α-sheet is a semiconductor, while the α(1)-, β(1)-, g(1/8)-, and g(2/15)-sheets are all metals. When two α(1) monolayers are stacked on top each other, the bilayer α(1)-sheet remains flat with an optimal interlayer distance of ~3.62 Å, which is close to the measured interlayer distance (~3.2 Å) in MWBNTs.

Urea electrooxidation with favorable thermodynamic potential offers great promise for decoupling H2/O2 evolution from sluggish water splitting, and simultaneously mitigating the problem of urea‐rich water pollution. However, the intrinsically slow kinetics of the six‐electron transfer process impels one to explore efficient catalysts in order to enable widespread use of this catalytic system. In response, taking CoS2/MoS2 Schottky heterojunctions as the proof‐of‐concept paradigm, a catalytic model to modulate the surface charge distribution for synergistically facilitating the adsorption and fracture of chemical group in urea molecule is proposed and the mechanism of urea electrooxidation at the molecular level is elucidated. Based on density functional calculations, the self‐driven charge transfer across CoS2/MoS2 heterointerface would induce the formation of local electrophilic/nucleophilic region, which will intelligently adsorb electron‐donating/electron‐withdrawing groups in urea molecule, activate the chemical bonds, and thus trigger the decomposition of urea. Benefiting from the regulation of local charge distribution, the constructed Schottky catalyst of CoS2‐MoS2 exhibits superior urea catalytic activities with a potential of 1.29 V (only 0.06 V higher than the thermodynamic voltage of water decomposition) to attain 10 mA cm−2 as well as robust durability over 60 h. This innovational manipulation of charge distribution via Schottky heterojunction provides a model in exploring other highly efficient electrocatalysts.

Searching experimental feasible two-dimensional (2D) ferromagnetic crystals with large spin-polarization ratio, high Curie temperature and large magnetic anisotropic energy is one key to develop next-generation spintronic nanodevices. Here, 2D FeSi nanosheet, one counterpart of Hapkeite mineral discovered in meteorite with novel magnetism is proposed on the basis of first-principles calculations. The 2D FeSi crystal has a slightly buckled triangular lattice with planar hexacoordinated Si and Fe atoms. The spin-polarized calculations with hybrid HSE06 function method indicate that 2D FeSi is a ferromagnetic half metal at its ground state with 100% spin-polarization ratio at Fermi energy level. The phonon spectrum calculation and ab initio molecular dynamic simulation shows that 2D FeSi crystal has a high thermodynamic stability and its 2D lattice can be retained at the temperature up to 1200 K. Monte Carlo simulations based on the Ising model predict a Curie temperature over 780 K in 2D FeSi crystal, which can be further tuned by applying a biaxial strain. Moreover, 2D structure and strong in-plane Fe-Fe interaction endow FeSi nanosheet sizable magnetocrystalline anisotropy energy with the magnitude of at least two orders larger than those of Fe, Co and Ni bulks. These novel magnetic properties render the 2D FeSi crystal a very promising material for developing practical spintronic nanodevices.