Xiaobiao Liu

Strain-Modulated Electronic Structure and Infrared Light Adsorption in Palladium Diselenide Monolayer.

Two-dimensional (2D) transition-metal dichalcogenides (TMDs) exhibit intriguing properties for both fundamental research and potential application in fields ranging from electronic devices to catalysis. Based on first-principles calculations, we proposed a stable form of palladium diselenide (PdSe2) monolayer that can be synthesized by selenizing Pd(111) surface. It has a moderate band gap of about 1.10 eV, a small in-plane stiffness, and electron mobility larger than that of monolayer black phosphorus by more than one order. Additionally, tensile strain can modulate the band gap of PdSe2 monolayer and consequently enhance the infrared light adsorption ability. These interesting properties are quite promising for application in electronic and optoelectronic devices.

Forming heterojunction: an effective strategy to enhance the photocatalytic efficiency of a new metal-free organic photocatalyst for water splitting

Photocatalytic water splitting is a new technology for the conversion and utilization of solar energy and has a potential prospect. One important aspect of enhancing the photocatalytic efficiency is how to improve the electron-hole separation. Up to now, there is still no ideal strategy to improve the electron-hole separation. In this article, for metal-free organic photocatalysts, we propose a good strategy- forming heterojunction, which can effectively improve the electron-hole separation. We provide a metal-free organic photocatalyst g-C12N7H3 for water splitting. The stability of g-C12N7H3 has been investigated, the X-ray diffraction spectra has been simulated. Using first-principles calculations, we have systematically studied the electronic structure, band edge alignment, and optical properties for the g-C12N7H3. The results demonstrated that g-C12N7H3 is a new organocatalyst material for water splitting. In order to enhance the photocatalytic efficiency, we provided four strategies, i.e., multilayer stacking, raising N atoms, forming g-C9N10/g-C12N7H3 heterojunction, and forming graphene/g-C12N7H3 heterojunction. Our research is expected to stimulate experimentalists to further study novel 2D metal-free organic materials as visible light photocatalysts. Our strategies, especially forming heterojunction, will substantially help to enhance the photocatalytic efficiency of metal-free organic photocatalyst.

Cu3N and its analogs: a new class of electrodes for lithium ion batteries

Electrode materials with low diffusion energy barriers and high storage capacity of lithium are crucial for high performance rechargeable lithium-ion batteries (LIBs). Based on first-principles calculations, we demonstrate a new class of electrode materials. Taking advantage of the large voids in Cu3N crystals, high lithium mobility and storage capacity can be achieved. The diffusion of Li on Cu3N nanosheets experiences an energy barrier of about 0.09 eV, which is much lower than those of presently proposed electrode materials. The maximum Li capacity of Cu3N nanosheets can reach 1008 mA h g−1. In view of a large number of crystals sharing the same lattice structure as Cu3N, this work opens an avenue for developing electrode materials for high performance LIBs.

Half-metallic TiF3: a potential anode material for Li-ion spin batteries

As a key component of spintronic devices, spin batteries that can generate spin-polarized current are drawing increasing interests. Herein, we propose a simple strategy for spin batteries by introducing a half-metallic anode material in the conventional Li-ion batteries. Using first-principles calculations, we demonstrate a potential half-metallic anode material, TiF3 crystal, which has stable ferromagnetism and half-metallicity under Li insertion. Low Li diffusion barriers (0.16–0.37 eV) and moderate Li storage capacity (256 mA h g−1) are revealed in the TiF3 crystal. The combination of half-metals and Li-ion battery offers a new solution for spin batteries.

Novel Conductive Metal–Organic Framework for a High-Performance Lithium–Sulfur Battery Host: 2D Cu-Benzenehexathial (BHT)

Despite the high theoretical capacity of lithium-sulfur (Li-S) batteries, their commercialization is severely hindered by low cycle stability and low efficiency, stemming from the dissolution and diffusion of lithium polysulfides (LiPSs) in the electrolyte. In this study, we propose a novel two-dimensional conductive metal-organic framework, namely, Cu-benzenehexathial (BHT), as a promising sulfur host material for high-performance Li-S batteries. The conductivity of Cu-BHT eliminates the insulating nature of most S-based electrodes. The dissolution of LiPSs into the electrolyte is largely prevented by the strong interaction between Cu-BHT and LiPSs. In addition, orientated deposition of Li2S on Cu-BHT facilitates the kinetics of the LiPS redox reaction. Therefore, the use of Cu-BHT for Li-S battery cathodes is expected to suppress the LiPS shuttle effect and to improve the overall performance, which is ideal for practical application of Li-S batteries.

Tunable Dirac cones in two-dimensional covalent organic materials: C2N6S3 and its analogs

Two-dimensional covalent organic frameworks (2D-COFs) are drawing increasing interest due to the unique configurations and exotic properties. Here, using density-functional theory calculations, we prove the stability of C2N6S3 monolayer by an imagery-frequency-free phonon spectrum, and demonstrate a new ternary 2D-COF: C2N6O3, C2N6Se3 and C2N6Te3 monolayers. The sawtooth-like linkages make the C2N6S3 is soft, and sustain a biaxial tensile strain up to 24% which is as much as graphene. The electronic band structure exhibits linear dispersion near the Fermi level with a flat band right above the Dirac bands, which is unlike the other hexagonal organic monolayers with Dirac cone. The Fermi velocity is comparable to that in graphene and can be tuned by applying biaxial tensile strain. Similar results are also found in its analogs, such as C2N6O3, C2N6Se3 and C2N6Te3 monolayers. This opens an avenue for the design of 2D Dirac materials.

Electron spin-polarization and spin-gapless states in an oxidized carbon nitride monolayer

Electron spin-polarization in metal-free organic materials is currently drawing considerable attention due to their applications in organic electronics. Using first-principles calculations, we propose a stable two-dimensional (2D) honeycomb lattice oxidized carbon nitride material, C2NO. The energetic favorability, phonon spectrum and molecular dynamics simulation confirm the stability and plausibility of the C2NO material. The electronic structure of the metal-free organic material is spin-polarized, yielding magnetic moments of 1.0 μB in one primitive cell. More interestingly, the spin-polarized electronic band lines have a zero band gap at the Fermi level, exhibiting spin-gapless features. These unique properties are promising for spin detectors and generators for electromagnetic radiation over a wide range of wavelengths based on the spin photoconductivity.