Single Mo Atom Supported on Defective Boron Nitride Monolayer as an Efficient Electrocatalyst for Nitrogen Fixation: A Computational Study

The production of ammonia (NH₃) from molecular dinitrogen (N₂) under mild conditions is one of the most attractive and challenging processes in chemistry. Here by means of density functional theory (DFT) computations, we systematically investigated the potential of single transition metal atoms (Sc to Zn, Mo, Ru, Rh, Pd, and Ag) supported on the experimentally available defective boron nitride (TM–BN) monolayer with a boron monovacancy as a N₂ fixation electrocatalyst. Our computations revealed that the single Mo atom supported by a defective BN nanosheet exhibits the highest catalytic activity for N₂ fixation at room temperature through an enzymatic mechanism with a quite low overpotential of 0.19 V. The high spin-polarization, selective stabilization of N₂H* species, or destabilizing NH₂* species are responsible for the high activity of the Mo-embedded BN nanosheet for N₂ fixation. This finding opens a new avenue of NH₃ production by single-atom electrocatalysts under ambient conditions

XH/π (X = C, Si) Interactions in Graphene and Silicene: Weak in Strength, Strong in Tuning Band Structures

The lack of a band gap has greatly hindered the applications of graphene in electronic devices. By means of dispersion-corrected density functional theory computations, we demonstrated that considerable CH/π interactions exist between graphene and its fully (graphane) or patterned partially (C₄H) hydrogenated derivatives. Due to the equivalence breaking of two sublattices of graphene, a 90 meV band gap is opened in the graphene/C₄H bilayer. The band gap can be further increased to 270 meV by sandwiching graphene between two C₄H layers. By taking advantage of the similar SiH/π interactions, a 120 meV band gap also can be opened for silicene. Interestingly, the high carrier mobility of graphene/silicene can be well-preserved. Our theoretical results suggest a rather practical solution for gap opening of graphene and silicene, which would allow them to serve as field effect transistors and other nanodevices

Carbon-Doped Boron Nitride Nanosheet: An Efficient Metal-Free Electrocatalyst for the Oxygen Reduction Reaction

Replacing precious Pt-based catalysts with cheap and earth-abundant materials to facilitate the sluggish oxygen reduction reaction (ORR) at the cathode is critical to realize the commercialization of fuel cells. In this work, we explored the potential of utilizing the experimentally available carbon (C)-doped boron nitride (BN) nanosheet as an ORR electrocatalyst by means of comprehensive density functional theory (DFT) computations. Our computations revealed that C-singly doping into <i>h</i>-BN nanosheets can cause high spin density and charge density and reduce the energy gap, resulting in the enhancement of O₂ adsorption. In particular, the C_N sheet (substituting N by C atom) exhibits appropriate chemical reactivity toward O₂ activation and promotes the subsequent ORR steps to take place though a four-electron OOH hydrogenation pathway with the largest activation barrier of 0.61 eV, which is lower than that of the Pt-based catalyst (0.79 eV). Therefore, the C_N-based BN sheet is a promising metal-free ORR catalyst for fuel cells

Patterned Partially Hydrogenated Graphene (C₄H) and Its One-Dimensional Analogues: A Computational Study

By means of density functional theory (DFT) computations, we systematically studied the structural and electronic properties of the experimentally just achieved new two-dimensional (2D) hydrocarbon  the patterned partially hydrogenated graphene with formula C₄H (Adv. Mater 2011, 23, 4497), and in particular its one-dimensional (1D) analogues. The C₄H layer is a stable 2D crystal featured with periodic Clar sextet aromatic rings and is semiconducting with a wide band gap; however, this single-sided patterned partially hydrogenated C₄H layer can only be obtained when the possibility of double-sided hydrogenation is excluded, since the double-sided graphane-embedded structure is energetically more favorable. The 1D C₄H nanotubes, rolled up by the C₄H layer, exhibit excellent thermodynamic properties and all have a wide band gap regardless of the tube diameter and chirality. In contrast, cutting the C₄H layer into 1D C₄H nanoribbons can result in rich electronic characteristics: they can be metallic or semiconducting depending on the chirality and edge configuration

Tuning Electronic Properties of Germanane Layers by External Electric Field and Biaxial Tensile Strain: A Computational Study

Comprehensive density functional theory computations with van der Waals (vdW) correction demonstrated that there exists strong hydrogen bonding between two-dimensional (2D) germanane layers. Especially, germanane layers all have a direct band gap, irrespective of stacking pattern and thickness. The band gap of germanane bilayer can be flexibly reduced by applying an external electronic field (E-field), leading to a semiconducting-metallic transition, whereas the band gap of germanane monolayer is rather robust in response to E-field. In contrast, the band gaps of both germanane monolayer and bilayer can be reduced to zero when subjected to a biaxial tensile strain. These results provide many useful insights for the wide applications of germanane layers in electronics and optoelectronics

Single-Layer [Cu₂Br(IN)₂]_<i>n</i> Coordination Polymer (CP): Electronic and Magnetic Properties, and Implication for Molecular Sensors

Inspired by the recent breakthrough in synthesizing the two-dimensional (2D) [Cu₂Br­(IN)₂]_<i>n</i> (IN = isonicotinato) single-layer coordination polymer (CP) (<i>Chem. Commun.</i> <b>2010</b>, <i>46</i>, 3262), we systematically investigated the structural, electronic, and magnetic properties of this periodic monolayer [Cu₂Br­(IN)₂]_<i>n</i> CP, as well as its possible application as molecular sensors by means of density functional theory computations. The pristine monolayer [Cu₂Br­(IN)₂]_<i>n</i> CP is ground-state antiferromagnetic with a band gap of 0.47 eV. Among various gas molecules (H₂, O₂, CO, CO₂, NO, NO₂, N₂, and NH₃), NO and NO₂ have strong interactions with the metal centers and can effectively modify the electronic structure of this monolayer [Cu₂Br­(IN)₂]_<i>n</i> CP, suggesting the feasibility of designing 2D CP-based molecular sensors to detect NO and NO₂ molecules

Frustrated Lewis Pair Catalysts in Two Dimensions: B/Al-Doped Phosphorenes as Promising Catalysts for Hydrogenation of Small Unsaturated Molecules

Using comprehensive density functional theory (DFT) computations, we designed two promising two-dimensional (2D) metal-free heterogeneous frustrated Lewis pair (FLP) catalysts for the hydrogenation of small unsaturated molecules (such as ketone, nitrile, and ethylene). The catalyst consists of a phosphorene monolayer that is doped with B or Al impurity to form a frustrated B/P or Al/P Lewis pair without the need for steric hindrance. The hydrogenations of ketones, nitrile, and ethylene on the B- or Al-doped phosphorene prefer to proceed through a two-step mechanism: the heterolytic dissociation of H₂ molecule, followed by the concerted hydrogen transfer. This study not only identifies two promising catalysts, namely B/Al-doped phosphorenes, for the hydrogenations of small unsaturated molecules, but also provides a useful strategy to develop FLP catalysts in 2D materials

Fe-Anchored Graphene Oxide: A Low-Cost and Easily Accessible Catalyst for Low-Temperature CO Oxidation

By means of first-principles computations, we investigated the catalytic capability of the Fe-anchored graphene oxide (Fe–GO) for CO oxidation with O₂. The high-energy barrier of Fe atom diffusion on GO and the strong binding strength of Fe anchored on GO exclude the metal clustering problem and enhance the stability of the Fe–GO system. The Fe-anchored GO exhibits good catalytic activity for CO oxidation via the favorable Eley–Rideal (ER) mechanism with a two-step route, while the Langmuir–Hinshelwood (LH) mechanism is not kinetically favorable. The low-cost Fe-anchored GO system can be easily synthesized and serves as a promising green catalyst for low-temperature CO oxidation

Graphane/Fluorographene Bilayer: Considerable C–H···F–C Hydrogen Bonding and Effective Band Structure Engineering

Systematic density functional theory (DFT) computations revealed the existence of considerable C–H···F–C bonding between the experimentally realized graphane and fluorographene layers. The unique C–H···F–C bonds define the conformation of graphane/fluorographene (G/FG) bilayer and contribute to its stability. Interestingly, G/FG bilayer has an energy gap (0.5 eV) much lower than those of individual graphane and fluorographene. The binding strength of G/FG bilayer can be significantly enhanced by applying appropriate external electric field (E-field). Especially, changing the direction and strength of E-field can effectively modulate the energy gap of G/FG bilayer, and correspondingly causes a semiconductor–metal transition. These findings open new opportunities in fabricating new electronics and opto-electronics devices based on G/FG bilayer, and call for more efforts in using weak interactions for band structure engineering

Self-Modulated Band Structure Engineering in C₄F Nanosheets: First-Principles Insights

Density functional theory (DFT) computations with van der Waals (vdw) correction revealed the existence of considerable C^δ+F^δ−···C^δ+F^δ− dipole–dipole interactions between two experimentally realized C₄F monolayers. The dipole–dipole interactions induce a subtle interlayer polarization, which results in a significantly reduced band gap for C₄F bilayer as compared to the individual C₄F monolayer. With increasing the number of stacked layers, the band gap of C₄F nanosheets can be further reduced, leading to a semiconducting–metallic transition. Moreover, the band gap of C₄F nanosheets can be feasibly modulated by applying an external electric field. Our results provide new insights on taking advantage of nonbonding interactions to tune the electronic properties of graphene materials