Two-dimensional (2D) transition metal carbonitrides (MXene) have attracted growing interest in electrocatalytic hydrogen production due to its structural and electronic properties. In this work, the hydrogen evolution reaction (HER) activity of all 64 O-terminated ordered double transition metal carbonitrides in the form of M′2M″CNO2 (M′ = Ti, V, Cr, Zr, Nb, Mo, Hf, Ta; M″ = Ti, V, Cr, Zr, Nb, Mo, Hf, Ta) has been investigated by well-defined density functional theory (DFT) calculations. The results indicate that there are 11 M′2M″CNO2-MXene candidates whose HER performance is superior to that of Pt. Moreover, according to the stability screening, it is proved that Ti2NbCNO2, Mo2TiCNO2, and Ti2VCNO2 are more stable than other candidates. Especially, Ti2NbCNO2 have the potential to be perfect HER catalyst with the small Gibbs free energies of hydrogen adsorption (ΔGH) value of 0.02 eV, abundant catalytic sites on the C-side, and better stability. This work paves the way on designing excellent HER catalyst candidates based on M′2M″CNO2-MXenes.

The emergence of a two‐dimensional (2D) functionalized‐graphene structure, graphdiyne (GDY), promoting non‐metallic single atoms level to tailor its gas sensing performance. Herein, pristine, non‐metallic atom (N, B) doped 2D GDY is investigated for toxic and greenhouse gases sensing (CO, CO2, CH4, HCHO, H2S, SO2, SO3, NO2, NO, and NH3). The B‐doped GDY (B‐GDY) compared with pure or N doped GDY displays gas sensitivity, especially excellent sensitivity and selectivity toward NO, NO2, and NH3. Additionally, a humid environment has demonstrated no effect on the weakening selectivity of B‐GDY for the studied gases. Meanwhile, the effect of external electric field (E‐field) on sensing was calculated, indicating that the bandgap of NO‐adsorbed system reached the lowest 0.188 eV at −0.5 V Å−1 and the highest 0.363 eV at −0.1 V Å−1. This work paves the way on designing efficient and effective gas sensor toward toxic nitrogen‐based gases on GDY.

Ammonia (NH 3 ) detection at the early stage is an important precaution for human health and agricultural production. However, conventional sensing materials are difficult to achieve all the targeted operational performances such as low power consumption and high selectivity. MXenes are a type of graphene-like emergent material equipped with abundant surface sites benefiting gas-sensing applications. In the work, we discuss the sensing performance of Ti 3 C 2 O 2 to anticipate harmful and polluting NH 3 gases by density functional theory and nonequilibrium Green's function. The adsorption geometry, charge difference density, and partial density of states are discussed to understand the nature of interactions between gas molecules and Ti 3 C 2 O 2 . The theoretical results show that only NH 3 adsorbs onto the nanosheet through chemisorption. Then, a two-electrode Ti 3 C 2 O 2 -based gas sensor device is built to unravel the transport properties. Current under different bias voltages indicates the Ti 3 C 2 O 2 -based sensor could maintain extremely high sensitivity, demonstrating that Ti 3 C 2 O 2 has great potential for the NH 3 sensor with high selectivity, excellent sensitivity, and low energy consumption. Upon external electric fields, the adsorption energy and charge transfer can be tuned effectively, suggesting that Ti 3 C 2 O 2 is a versatile agent as an ammonia-sensing material.

The effects of pressure on the structural and electronic properties and the ionic configuration of ZIF-4 were investigated through the first-principles method based on the density functional theory. The elastic properties, including the isotropic bulk modulus K, shear modulus G, Young’s modulus E, and Poisson’s ratio ν of the orthorhombic-type structure ZIF-4 were determined using the Voigt–Reuss–Hill averaging scheme. The results show that the ZIF-4 phase is ductile according to the analysis of K/G and Cauchy pressure. The Debye temperatures obtained from the elastic stiffness constants increase with increasing pressure. Finally, the pressure-dependent behaviors of the density of states and ionic configuration are successfully calculated and discussed.