Xi'an Chen

3D hierarchical nitrogen-doped carbon nanoflower derived from chitosan for efficient electrocatalytic oxygen reduction and high performance lithium–sulfur batteries

Despite diverse carbon materials being intensively applied in energy storage and conversion, efficient optimization of the carbon structure to further improve its performance is still a great challenge. Herein, we design and fabricate a highly uniform 3D hierarchical N-doped carbon nanoflower (NCNF) using low-cost chitosan as the nitrogen and carbon source by a silica template method. The as-prepared NCNF with abundant meso-porous channels displays a high surface area (907 m2 g−1) and large pore volume (1.85 cm3 g−1), thereby demonstrating high performance as a bifunctional material for the electrocatalytic oxygen reduction reaction (ORR) and in lithium–sulfur batteries. As a metal-free ORR electrocatalyst, the NCNF exhibits excellent electrochemical activity comparable to that of commercial Pt/C (20 wt%), and much better methanol tolerance and durability. As sulfur accommodation for a Li–S battery cathode, the NCNF high loading content of sulfur (80 wt%) achieves an extremely high capacity (1633 mA h g−1 at 0.2C), excellent rate capability (916 mA h g−1 at 5C) and good cycling performance with a capacity decay of 0.07% per cycle over 500 cycles at 1C. Even when the area density is improved to 4.5 mgsulfur cm−2, the battery delivers a high areal capacity of ∼5.5 mA h cm−2 (0.37 mA cm−2) and still maintains ∼3 mA h cm−2 after 200 cycles with a smaller capacity decay of 0.07% per cycle at a high area current density of 3.77 mA cm−2. Significantly, the carbon materials recycled from the Li–S cathode after 500 cycles are reused as ORR electrocatalysts, displaying more excellent electrocatalytic activity than Pt/C (20 wt%).

Nano-TiO2: An Efficient and Reusable Heterogeneous Catalyst for Ring Opening of Epoxides Under Solvent-Free Conditions

Abstract Nano-TiO2 is an effective heterogeneous catalyst for the ring opening of epoxides with aromatic amines to afford β-amino alcohols in good to excellent yields at room temperature under solvent-free conditions. It was found that the catalyst is recyclable, and the activity of the catalyst was not weakened markedly even after several reaction cycles. In addition, the catalytic activity of TiO2 strongly depends on particle size or surface area. GRAPHICAL ABSTRACT

Gallium Trichloride–Promoted Highly Regioselective Ring Opening of Epoxides with NH4SCN and NaN3 in Water

Abstract β‐Hydroxy thiocyanates and β‐azidoalchols were obtained in excellent yields via GaCl3‐promoted highly regioselective ring opening of epoxides with ammonium thiocyanate or sodium azide in water. The present method is very rapid and equally compatible for both ammonium thiocyanate and sodium azide.

Controllable synthesis of highly uniform flower-like hierarchical carbon nanospheres and their application in high performance lithium–sulfur batteries

Elemental sulfur cathodes for lithium/sulfur batteries are receiving intense interest owing to their high theoretical capacity and energy density. However, they still suffer from severe capacity fading and moderate rate capability. Herein, we provide rational design and controllable fabrication of highly uniform flower-like hierarchical carbon nanospheres (FCNS) for sulfur accommodation for lithium/sulfur battery cathodes. The as-prepared three dimension FCNS with a size of around 200 nm seem to be assembled by petal-like carbon nanosheets with a thickness of about 4 nm, forming many mesoporous channels, which lead to their high surface area and large pore volume. With such a tailor-made structure, FCNS/sulfur composite cathodes with high sulfur-loading (81 wt%) deliver high specific capacity, long cycling life and excellent rate capability. Particularly, N-doped flower-like carbon nanospheres (NFCNS) with higher surface area (1223 m2 g−1) and larger pore volume (2.33 cm3 g−1) are also fabricated by treating with NH3 and used to host sulfur in lithium–sulfur battery cathodes, exhibiting more excellent rate capability (829 mA h g−1 at 5C) and cycling stability with a decay of 0.03% per cycle over 200 cycles at 1C. Even though the area density is improved to 2.5 mg sulfur per cm2, the battery still has a decay of 0.056% per cycle over 200 cycles.

B2O3/Al2O3 as an Efficient and Recyclable Catalyst for the Synthesis of β-Amino Alcohols under Solvent-Free Conditions

Abstract A convenient and efficient procedure for the solvent-free synthesis of β-amino alcohols has been achieved via B2O3/Al2O3-promoted highly regioselective ring opening of epoxides with aromatic amines in good to excellent yields at room temperature. Additionally, the catalyst can be recycled without affecting the catalytic property.

Molybdenum Carbide Nanoparticles Coated into the Graphene Wrapping N‐Doped Porous Carbon Microspheres for Highly Efficient Electrocatalytic Hydrogen Evolution Both in Acidic and Alkaline Media

Abstract Molybdenum carbide (Mo2C) is recognized as an alternative electrocatalyst to noble metal for the hydrogen evolution reaction (HER). Herein, a facile, low cost, and scalable method is provided for the fabrication of Mo2C‐based eletrocatalyst (Mo2C/G‐NCS) by a spray‐drying, and followed by annealing. As‐prepared Mo2C/G‐NCS electrocatalyst displays that ultrafine Mo2C nanopartilces are uniformly embedded into graphene wrapping N‐doped porous carbon microspheres derived from chitosan. Such designed structure offer several favorable features for hydrogen evolution application: 1) the ultrasmall size of Mo2C affords a large exposed active sites; 2) graphene‐wrapping ensures great electrical conductivity; 3) porous structure increases the electrolyte–electrode contact points and lowers the charge transfer resistance; 4) N‐dopant interacts with H+ better than C atoms and favorably modifies the electronic structures of adjacent Mo and C atoms. As a result, the Mo2C/G‐NCS demonstrates superior HER activity with a very low overpotential of 70 or 66 mV to achieve current density of 10 mA cm−2, small Tafel slope of 39 or 37 mV dec−1, respectively, in acidic and alkaline media, and high stability, indicating that it is a great potential candidate as HER electrocatalyst.

Active metallic indium-mediated ring-opening of epoxides with diphenyl diselenides: a novel one-pot synthesis of β-hydroxy selenides in aqueous media

An efficient and simple one-pot procedure for the synthesis of β-hydroxy selenides in aqueous media through highly regioselective ring-opening of epoxides with diphenyl diselenide in the presence of active metallic indium is described.

Low-temperature construction of MoS2 quantum dots/ZnO spheres and their photocatalytic activity under natural sunlight

Zinc oxide (ZnO) nanophotocatalyst is a promising candidate for degrading organic pollutants but has an extremely low photocatalytic activity under nature sunlight. In this work, flower-like MoS2 quantum dots/ZnO (MQ/ZnO) nanospheres with the size of approximately 1.26 μm are prepared at low temperature. The resultant flower-like MQ/ZnO nanospheres displayed higher photocatalytic activity than pure ZnO nanospheres under natural sunlight and without stirring, with the decomposition rate of the MQ/ZnO composites approximately 3.3 times higher than that of the pure ZnO nanospheres. Furthermore, the introduction of MoS2 QDs endowed ZnO nanospheres with optical memory ability. The enhanced sunlight-driven photocatalytic activity is dependent on the unique electrical properties of MoS2 QDs and the synergistic effect between ZnO and MoS2 QDs.

3D CNTs/Graphene-S-Al3Ni2 Cathodes for High-Sulfur-Loading and Long-Life Lithium-Sulfur Batteries

Abstract Lithium–sulfur batteries suffer from poor cycling stability at high areal sulfur loadings (ASLs) mainly because of the infamous shuttle problem and the increasing diffusion distance for ions to diffuse along the vertical direction of the cathode plane. Here, a carbon nanotube (CNT)/graphene (Gra)‐S‐Al3Ni2 cathode with 3D network structure is designed and prepared. The 3D network configuration and the Al in the Al3Ni2 provide an efficient channel for fast electron and ion transfer in the three dimensions, especially along the vertical direction of the cathode. The introduction of Ni in the Al3Ni2 is able to suppress the shuttle effect via accelerating reaction kinetics of lithium polysulfide species conversion reactions. The CNT/Gra‐S‐Al3Ni2 cathode exhibits ultrahigh cycle‐ability at 1 C over 800 cycles, with a capacity degradation rate of 0.055% per cycle. Additionally, having high ASLs of 3.3 mg cm−2, the electrode delivers a high reversible areal capacity of 2.05 mA h cm−2 (622 mA h g−1) over 200 cycles at a higher current density of 2.76 mA cm−2 with high capacity retention of 85.9%. The outstanding discharge performance indicates that the design offers a promising avenue to develop long‐life cycle and high‐sulfur‐loading Li–S batteries.