Taking
into account the high conductivity and stability of carbon
materials, such as graphene, and the strong polar covalent bonding
character of main-group compounds, we explore potential 2D materials
in the C–S binary system through first-principles structure
search calculations. Herein, a hitherto unknown semiconducting C3S monolayer is identified, consisting of well-known n-biphenyl and S atom linked benzenes, exhibiting an obvious
direction-dependent atomic arrangement. Thus, it exhibits anisotropic
mechanical properties and carrier mobility. Its electron mobility
reaches 2.14 × 104 cm2 V–1 s–1 in the b direction,
along which n-biphenyl units are arranged, and is
much higher than that in the well-used MoS2 monolayer and
black phosphorus. Meanwhile, the C3S monolayer has high
optical absorption coefficients (105 cm–1), high thermal and dynamical stabilities, and a moderate ability
to split water. All these desirable properties make the C3S monolayer a promising candidate for applications in novel optoelectronic
devices.
An urgent and key problem in hydrogen evolution reaction (HER) is to prepare low-cost catalysts with activity comparable to that of platinum (Pt), an intrinsic large number of active sites, and high electrical conductivity.
Phosphorene
has offered an additional advantage for developing
new optoelectronic devices due to its anisotropic and high carrier
mobility. However, its instability in air causes a rapid degradation
of the performance of the device. Thus, improving the stability of
phosphorene while maintaining its original properties has become the
key to the development of high-performance electronic devices. Herein,
we propose that the formation of two-dimensional (2D) P-rich P–S
compounds could achieve this goal. First-principles swarm-structural
searches revealed two previously unkonwn P3S and P2S monolayers. The P3S monolayer, consisting of n-bicyclo-P6 units along the armchair direction,
exhibits anisotropic and wide band gap characteristics. Interestingly,
its carrier mobility reaches 1.11 × 104 cm2 V–1 s–1 and is much higher than
in phosphorene. Its electronic band gap and optical absorption coefficients
in the ultraviolet region reach 2.71 eV and 105 cm–1, respectively. Additionally, the P3S monolayer
has a high structural stability and resistance to air oxidation.
Investigations of the adsorptions of representative gases (NO2, NH3, H2S, SO2, CO, and HCHO) on different Ag-functionalized monolayer MoS2 surfaces were performed by first principles methods. The adsorption configurations, adsorption energies, electronic structure properties, and charge transfer were calculated, and the results show that the adsorption activities to gases of monolayer MoS2 are dramatically enhanced by the Ag-modification. The Ag-modified perfect MoS2 (Ag-P) and MoS2 with S-vacancy (Ag-Vs) substrates exhibit a more superior adsorption activity to NO2 than other gases, which is consistent with the experimental reports. The charge transfer processes of different molecules adsorbed on different surfaces exhibit various characteristics, with potential benefits to gas selectivity. For instance, the NO2 and SO2 obtain more electrons from both Ag-P and Ag-Vs substrates but the NH3 and H2S donate more electrons to materials than others. In addition, the CO and HCHO possess totally opposite charge transfer directs on both substrates, respectively. The BS and PDOS calculations show that semiconductor types of gas/Ag-MoS2 systems are more determined by the metal-functionalization of material, and the directs and numbers of charge transfer process between gases and adsorbents can cause the increase or decline of material resistance theoretically, which is helpful to gas detection and distinction. The further analysis indicates suitable co-operation between the gain-lost electron ability of gas and metallicity of featuring metal might adjust the resistivity of complex and contribute to new thought for metal-functionalization. Our works provide new valuable ideas and theoretical foundation for the potential improvement of MoS2-based gas sensor performances, such as sensitivity and selectivity.
Two-dimensional Mo2C materials (1T and 2H phases) have emerged as promising electrocatalysts for the hydrogen evolution reaction (HER) due to their low cost, inherent metallicity, and high stability. Unfortunately, the...
The rational design of low-cost electrocatalysts
with the desired
performance is the core of the large-scale hydrogen production from
water. Two-dimensional materials with high specific surface area and
excellent electron properties are ideal candidates for electrocatalytic
water splitting. Herein, we identify a hitherto unknown Mo2P3 monolayer with a Janus structure (i.e., out-of-plane asymmetry) through first-principle structure search
calculations. Its inherent metallicity ensures good electrical conductivity.
Notably, its catalytic activity is comparable to that of Pt and the
density of active sites is up to 2.65 × 1015 site/cm2 owing to the Mo → P charge transfer enhancing the
catalytic activity of P atoms and asymmetric structure exposing more
active sites to the surface. The Mo2P3 monolayer
can spontaneously produce hydrogen through the Volmer–Heyrovsky
pathway. These excellent performances can be well maintained under
strain. The coexistence of covalent and ionic bonds results in Mo2P3 having high stability. All these excellent properties
make the Mo2P3 monolayer a promising candidate
for electrocatalytic water splitting.
The exploration of novel intermetallic compounds is of great significance for basic research and practical application. Considering the interesting and diverse attributes of Na and Au, their large electronegative difference,...
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