Pd/Pt embedded CN monolayers as efficient catalysts for CO oxidation.

Single atom catalysts (SACs) based on 2D materials have been identified to be efficient in many catalytic reactions. In this work, the catalytic performance of Pd/Pt embedded planar carbon nitride (CN) for CO oxidation has been investigated via spin-polarized density functional theory calculations. We find that Pd/Pt can be firmly anchored in the porous CN monolayer due to the strong hybridization between Pd/Pt-d orbitals and adjacent N-2p orbitals. The resulting high adsorption energy and large diffusion barrier of Pd/Pt ensures the remarkable stability of the catalyst Pd/Pt@CN during the CO oxidation reaction. The three distinct CO reaction mechanisms, namely, Eley-Rideal (ER), Langmuir-Hinshelwood (LH), and tri-molecular Eley-Rideal (TER), are taken into consideration comparatively. Intriguingly, the oxidation reaction on Pd@CN prefers to proceed through the less common TER mechanism, where two CO molecules and one O2 molecule need to cross a small reaction barrier of 0.48 eV, and finally dissociate into two CO2 molecules. However, the LH mechanism is the most relevant one on Pt@CN with a rate-limiting reaction barrier of 0.68 eV. Moreover, the origin of the SAC's reactivity enhancement is the electronic "acceptance-donation" interaction caused by orbital hybridization between Pd/Pt and preadsorbed O2/CO. Our findings are expected to widen the catalytic application of carbon-based 2D materials.

C2N: an excellent catalyst for the hydrogen evolution reaction.

Based on first-principles calculations, we study the hydrogen evolution reaction (HER) on metal-free C2N and make efforts to improve its catalytic performance. At H* coverages (θ) of 3/6 and 4/6, the free energy of hydrogen adsorption (ΔGH*) is 0.10 eV and 0.07 eV, respectively, which is competitive with the precious catalyst Pt. Moreover, ΔGH* can be modulated to zero under a tensile strain, and the strength of the strain depends on the H concentration. Experimentally, it is possible to achieve a strain of around 2% through coupling C2N with graphene, and the HER performance of the hybrids would be generally enhanced. Moreover, the catalytic activity of the hybrids is tunable via electron and hole doping of graphene. In the strong H binding cases (θ = 1/6), anchoring Mn atoms into C2N exhibits a perfect catalytic property with ΔGH* of -0.04 eV. Therefore, C2N-based catalysts are expected to be easily synthesized and highly active catalysts for the HER. These findings may shed light on replacing Pt by metal-free or/and non-precious metal counterparts.

Modulation of electronic and magnetic properties of edge hydrogenated armchair phosphorene nanoribbons by transition metal adsorption.

Based on first-principles calculations, we present a systematic investigation of the electronic and magnetic properties of armchair phosphorene nanoribbons (APNRs) functionalized by 3d transition metal (TM) atoms. We found that the central hollow site is the most favorable adsorption site for Mn, Co and Ni, while Fe preferentially occupies the edge hollow site. All of the TM atoms bind to the adjacent P and their adsorption energies are in the range of -4.29 eV to -1.59 eV. Meanwhile, the large ratio of the adsorption energy to the cohesive energy of the metal bulk phase indicates that TM atoms have a preferred 2D growth mode on the edge hydrogenated armchair phosphorene nanoribbons (H-APNRs). The magnetic moments reduce by about 2-4 µB, relative to their free atom states, depending on whether the TM atom is in the high-spin or low-spin state. This reduction is mainly attributed to the electrons transferring from the high-level TM 4s shell to the low-lying 3d shell. Our results demonstrate that TM atom adsorption is a feasible approach to functionalizing the H-APNRs chemically, which results in peculiar electronic and magnetic properties for potential applications in nano-electronics and spintronics.

Electrical and optical behaviors of SiC(GeC)/MoS2 heterostructures: a first principles study.

Hybrid structures have attracted a great deal of attention because of their excellent properties, which can open up a way we could not foresee in materials science and device physics. Here, we investigate the electrical and optical behaviors of SiC(GeC)/MoS2 heterostructures, using first principles calculations based on density functional theory. Non-covalent bonding exists between the junctions due to the weak orbital coupling. Both junctions have optically active band gaps, smaller than that of the SiC or GeC and MoS2 layers, which result in enhanced optical adsorption under visible-light irradiation. A small number of electrons transfer from SiC/GeC to MoS2 causing its n-doping. Furthermore, the charge density states of the valence band maximum and the conduction band minimum are localized at different sides, and thus the electron-hole pairs are spatially separated. Our results provide a potential scheme for photovoltaic materials.