Phthalo-carbonitride nanosheets as excellent N2 reduction reaction electrocatalysts: a first-principles study

Based on density functional theory computation, a series of transition metal atoms anchored on phthalo-carbonitride (pc-C₃N₂) nanosheets have been investigated for the nitrogen reduction reaction (NRR). The results show that Mo and W atoms anchored on the large holes of pc-C₃N₂ exhibit excellent performance in the NRR with low limiting potentials of -0.24 V and -0.23 V, respectively. Moreover, W@pc-C₃N₂ can effectively suppress the hydrogen evolution reaction. We predict that the porous carbon-nitrogen catalyst W@pc-C₃N₂ has a promising future to explore more favorable applications for the NRR.

A general strategy for the functionalization of two-dimensional metal chalcogenides

Two-dimensional (2D) metal chalcogenides (MC) such as MoS₂ have been recognized as promising materials for near future applications. However, general strategies to functionalize them are still scarce, while the nature of functionalization still remains unclear. Herein, we demonstrate a simple and universal functionalization route through complexation reaction between the amino-containing organic agents and MCs. Degrees of functionalization are tunable by adjusting the organic group types and ratios. No further defects are introduced and the functionalized 2D MCs are dispersible in corresponding typical solvents. Both experimental results and geometry optimization calculations indicate that the grafting of functional groups through the coordination effect truly exist, while the surface properties and resulting photoelectric properties of 2D MCs are greatly altered. More intriguingly, our proposed functionalization process is demonstrated to be universal and can be applied to different MCs, thus opening new avenues for the application of 2D MCs.

Two-dimensional thio- and seleno-cyanates of Mo and W

The stability of two-dimensional (2D) transition metal di-chalcogenides (TMDC) is controlled by the fact that sulfur or selenium atoms can cap the 2D layers without exposing highly reactive bonds. Here we use first-principles calculations to show that a similar structural motif can stabilize Mo- and W-based 2D materials with thio- or seleno-cyanate groups. In particular, we show that the formation of Mo(SeCN)₂, W(SCN)₂ and W(SeCN)₂ sheets is energetically favorable and can lead to various configurations that resemble the well-known polymorphs of TMDCs. The lowest-energy structures are small-gap semiconductors, while certain polytypes bear Dirac-like cones close to the Fermi energy, demonstrating the potential of these new 2D materials for applications in modern electronic devices.

Two-dimensional Mo(SCN)2: a novel MoS2-variant

Transition metal dichalcogenides (TMDC) are currently among the most studied two-dimensional (2D) materials. Based on first-principles calculations we propose a new family of 2D materials which resemble TMDC's, but contain more complex chemical groups instead of elemental chalcogen atoms. In particular, we identify various stable 2D polymorphs of molybdenum di-thiocyanate, Mo(SCN)₂, with structures akin to those of MoS₂. The most stable Mo(SCN)₂ polymorphs are semiconductors with small energy band gaps, whereas a higher-energy structure is metallic. Since the calculated formation energies of MoS₂ and Mo(SCN)₂ are comparable, the synthesis of the latter should be feasible.

Ca- and Sc-based ternary AlB2-like crystals: a first-principles study

The aluminum diboride (AlB₂) crystal structure comprises intercalated metal atoms between honeycomb sheets. In addition to metal diborides, which represent the most common family of AlB₂-like structures, many more materials are known to crystallize in this geometry. Here we use first-principles calculations to probe the structural and electronic properties of several such systems. Specifically, we investigate the stability of various polymorphs of CaAuAs, CaAuP, CaCuP, ScAuGe, ScAuSi, Ca₂AgSi₃ and Ca₂AuGe₃ and find lattice parameters in excellent agreement with available experimental data. The analysis of densities of states and band structure diagrams show that all materials are metallic. However, the details of band dispersion vary significantly, from typical metals such as CaAuP, to almost semi-metallic behaviour in CaCuP.

Magnetic two-dimensional C3N2 carbonitrides: semiconductors, metals and half-metals

Using density-functional theory (DFT) calculations we probe the spin polarization of functionalized two-dimensional (2D) phthalo-carbonitrides (pc-C₃N₂), i.e., 2D polymers of tetra-cyanoethylene.