Constructing Synergistic Triazine and Acetylene Cores in Fully Conjugated Covalent Organic Frameworks for Cascade Photocatalytic H2O2 Production

Covalent organic frameworks (COFs) are an ideal template for photocatalytic H2O2 synthesis because of the tunable chemical structures and semiconductor properties. However, the photoactivity for COFs is still under-improved due to the inefficient intrinsic charge generation, fast recombination of photogenerated charges, and limited electron transport along the frameworks. Herein, spatially separated and synergistic triazine and acetylene units are first integrated into COFs (EBA-COF and BTEA-COF) for photocatalytic H2O2 production. The spatial separation of triazine and acetylene cores leads to efficient charge separation and suppressed charge recombination, and C═C linkage facilitates electrons transport over the skeletons. Both experimental and computational results suggested that triazine and acetylene units synergistically promote H2O2 synthesis in a two-electron pathway. The EBA-COF showed an attractive activity with a H2O2 production rate of 1830 μmol h-1 gcat-1, superior to that of most other COF-based catalysts. This study provides a method for designing photocatalysts with synergistic photocatalytic active sites based on vinylene-linked COFs

Carbon coated ultrasmall anatase TiO2 nanocrystal anchored on N,S-RGO as high-performance anode for sodium ion batteries

Anatase TiO2 has been investigated as one of the most promising anode materials for sodium ion batteries (SIBs) with low cost and high theoretical capacity. Herein, a composite material of TiO2/N,S-RGO@C with carbon coated ultrasmall anatase TiO2 anchored on nitrogen and sulfur co-doped RGO matrix was successfully prepared by a rational designed process. The composite structure exhibited ultrasmall crystal size, rich porous structure, homogeneous heteroatoms doping and thin carbon coating, which synergistically resulted in elevated electron and ion transfer. The anode exhibited high rate capacities with good reversibility under high rate cycling. The carbon coating was investigated to be effective to prevent active material falling and lead to long term cycling performance with a high capacity retention of 181 mAh g−1 after 2000 cycles at 2 C. Kinetic studies were carried out and the results revealed that the superior performance of the composite material were derived from the decreased charge transfer resistance and elevated ion diffusion. Results suggested that the TiO2/N,S-RGO@C composite is a promising anode material for sodium ion batteries. Keywords: Titanium dioxide, Nitrogen/sulfur doping RGO, Sodium ion battery, Long cycle lif

Fcc -> bcc -> hcp successive phase transformations in the strained ultrathin copper film: A molecular dynamic simulation study

The phase transformation behaviors of ultrathin Cu film under uniaxial tensile stress are investigated using molecular dynamic simulation. With the stress increasing, Cu film undergoes a successive phase transformation, i.e. firstly fcc -> bcc, then bcc -> hcp. The phase transformation process is very fast and thorough, i.e., all parents phase can transit into the new phase almost instantaneously. The crystallography mechanisms of two martensitic transformations are exactly corresponding to Bain and Burgers mechanism, respectively. By examining the formation conditions of such phase transformation in Cu film, we reveal that this fcc -> bcc -> hcp successive phase transformation will be subject to the very strict simulation conditions, namely stretching along [100] ( or [010], [001] ) direction, definitive tensile speed (1 x 10(10)/s), appropriate film thickness (0.7230-18.08 nm), low temperature (T <= 10 K), and continuous stretching process without any relaxation procedure

Recent Progress on the Alloy-Based Anode for Sodium-Ion Batteries and Potassium-Ion Batteries

High-energy batteries with low cost are urgently needed in the field of large-scale energy storage, such as grid systems and renewable energy sources. Sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) with alloy-based anodes provide huge potential due to their earth abundance, high capacity, and suitable working potential, and are recognized as attractive alternatives for next-generation batteries system. Although some important breakthroughs have been reported, more significant improvements are still required for long lifetime and high energy density. Herein, the latest progress for alloy-based anodes for SIBs and PIBs is summarized, mainly including Sn, Sb, Ge, Bi, Si, P, and their oxides, sulfides, selenides, and phosphides. Specifically, the material designs for the desired Na+/K+ storage performance, phase transform, ionic/electronic transport kinetics, and specific chemical interactions are discussed. Typical structural features and research strategies of alloy-based anodes, which are used to facilitate processes in battery development for SIBs and PIBs, are also summarized. The perspective of future research of SIBs and PIBs is outlined

Formation of Moire superstructure of epitaxial graphene on Pt(111): A molecular dynamic simulation investigation

The moire superstructures formed in the graphene on Pt (111) surface have been studied employing classical molecular dynamics (CMD) simulation. We have shown that the 20 moire superstructures, whose positions and periodicities are the same as the prediction of the geometric model proposed by Merino, can be obtained via the rotation of graphene. This observation demonstrates that molecular dynamics simulation is an effective method for searching for moire superstructure formed in the graphene on transition metal surface. The characteristics of moire superstructures, such as fluctuation of the graphene layer, C-C bond length and stress of carbon atoms, are investigated. For the superstructures with large periodicity, the graphene layer is fluctuant. In the region of the maximal height of the superstructure, there is a strong attraction between the graphene and Pt substrate, so that the carbon atoms are concave, and the C-C bonds are stretched by 0.0004 angstrom. In the region of the minimal height of the superstructure, the C-C bond lengths are the same as those in freestanding graphene. Additionally, a moire superstructure with an ultra-long periodicity (L = 60.1 angstrom) is observed, and its formation mechanism is discussed