Yingying Gu

Facile electrodeposition of 3D concentration-gradient Ni-Co hydroxide nanostructures on nickel foam as high performance electrodes for asymmetric supercapacitors

Novel three-dimensional (3D) concentration-gradient Ni-Co hydroxide nanostructures (3DCGNC) have been directly grown on nickel foam by a facile stepwise electrochemical deposition method and intensively investigated as binder- and conductor-free electrode for supercapacitors. Based on a three-electrode electrochemical characterization technique, the obtained 3DCGNC electrodes demonstrated a high specific capacitance of 1,760 F·g−1 and a remarkable rate capability whereby more than 62.5% capacitance was retained when the current density was raised from 1 to 100 A·g−1. More importantly, asymmetric supercapacitors were assembled by using the obtained 3DCGNC as the cathode and Ketjenblack as a conventional activated carbon anode. The fabricated asymmetric supercapacitors exhibited very promising electrochemical performances with an excellent combination of high energy density of 103.0 Wh·kg−1 at a power density of 3.0 kW·kg−1, and excellent rate capability—energy densities of about 70.4 and 26.0 Wh·kg−1 were achieved when the average power densities were increased to 26.2 and 133.4 kW·kg−1, respectively. Moreover, an extremely stable cycling life with only 2.7% capacitance loss after 20,000 cycles at a current density of 5 A·g−1 was achieved, which compares very well with the traditional doublelayer supercapacitors.

General synthesis of LiLn(MO4)2:Eu3+ (Ln = La, Eu, Gd, Y; M = W, Mo) nanophosphors for near UV-type LEDs

A series of Eu3+-doped double tungstate and molybdate red phosphors, LiLn(MO4)2:Eu3+ (Ln = La, Eu, Gd, Y; M = W, Mo), have been successfully synthesized by a simple Pechini method. The procedure involves formation of homogeneous, and transparent, metal–citrate gel precursors using citric acid as a chelating ligand to form metal complexes and ethylene glycol as a cross-linker for polyesterification with the complexes, followed by calcination to promote thermal decomposition of the gel precursors to yield the final LiLn(MO4)2 nanoparticles. The as-synthesized nanoparticles were characterized by thermogravimetric/differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) as well as kinetic decay. The results indicate that the obtained LiLn(MO4)2:Eu3+ samples crystallize in the isostructure with tetragonal space group I41/a (no. 88). A room temperature PL spectrum shows that Eu3+-doped LiLn(MO4)2 powders exhibit an excellent luminescent properties under a near ultraviolet excitation wavelength of 395 nm, suitable for near UV type LEDs. By comparing with other counterparts, it is found that LiEu(WO4)2 and LiEu(MoO4)2 display the highest emission intensity. In addition, the phosphor of composition LiY0.95Eu0.05(WO4)2 shows promising application for white light emission with a decay time of 0.585 ms.

Binder-free hydrogenated NiO–CoO hybrid electrodes for high performance supercapacitors

Binder-free NiO–CoO hybrid electrodes were directly grown on nickel foam by electrodeposition and subsequent annealing in 5% H2/95% N2 gas at 300 °C. Crystal structure, elemental analysis, surface morphology and chemical compositions of the composites were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) equipped with an energy dispersive X-ray analysis system. The hydrogenated NiO–CoO hybrid electrodes were evaluated as electrodes for supercapacitors which demonstrated promising electrochemical performance with high specific capacitance, excellent rate capability, and stable cycling.

Facile synthesis of ultrathin MoS2/C nanosheets for use in sodium-ion batteries

We present a clean and simple method for the synthesis of MoS2/C hybrids. Commercial ion-exchange resins are used to absorb aqueous molybdate, followed by annealing with sulfur powder in an inert atmosphere. Even ultrathin MoS2 nanosheets with enlarged interlayers (0.63 nm) are homogeneously wrapped by mesoporous graphitic carbon. When evaluated as anodes for sodium-ion batteries, the MoS2/C nanocomposite exhibits good electrochemical performance. The first discharge/charge capacities at current density 50 mA g−1 are 784.3 and 590.0 mA h g−1, respectively, with initial coulombic efficiency of approximately 75%. It exhibits superior rate capabilities, with specific discharge capacities of 513.1, 467.3, 437.1, 399.2, 361.8, and 302.7 mA h g−1 at current densities of 50, 100, 200, 500, 1000, and 2000 mA g−1, respectively. This superior electrochemical performance is mainly due to the synergistic effect between the uniformly-distributed, ultrathin MoS2 nanosheets and the highly graphitized carbon. This not only mitigates mechanical stress during repeated cycling, but also provides good conductivity.

Encapsulated MnO in N-doping carbon nanofibers as efficient ORR electrocatalysts

Development of cheap, abundant and noble-metal-free materials as high efficient oxygen reduction electrocatalysts is crucial for future energy storage system. Here, one-dimensional (1D) MnO N-doped carbon nanofibers (MnO-NCNFs) were successfully developed by electrospinning combined with high temperature pyrolysis. The MnO-NCNFs exhibit promising electrochemical performance, methanol tolerance, and durability in alkaline medium. The outstanding electrocatalytic activity is mainly attributed to several issues. First of all, the uniform 1D fiber structure and the conductive network could facilitate the electron transport. Besides, the introduction of Mn into the precursor can catalyze the transformation of amorphous carbon to graphite carbon, while the improved graphitization means better conductivity, beneficial for the enhancement of catalytic activity for oxygen reduction reaction (ORR). Furthermore, the porous structure and high surface area can effectively decrease the mass transport resistance and increase the exposed ORR active sites, thus improve utilization efficiency and raise the quantity of exposed ORR active sites. The synergistic effect of MnO and NCNFs matrix, which enhances charge transfer, adsorbent transport, and delivers efficiency in the electrolyte solution, ensures the high ORR performance of MnO-NCNFs.摘要廉价、 储量丰富的非贵金属材料作为高效氧还原电催化剂是未来能量存储系统实际应用的关键. 基于此, 我们通过静电纺丝法并结合相应热处理制备了一维氮掺杂碳纳米纤维包覆一氧化锰(MnO-NCNFs). 该材料在碱性体系中表现出良好的电化学性能, 耐甲醇腐蚀性和稳定性. 其优异的电催化活性主要归结于以下几点: (1) 均一的一维纤维结构和导电网络能够促进反应过程中快速的电子转移; (2) 过渡金属锰的引入能够促进无定型碳向石墨碳的转变, 同时石墨化程度的提高意味着更好的导电性, 有利于氧还原活性的提高; (3) 多孔结构和高比表面积能够有效降低传质阻力并提高暴露的氧还原活性位点数量, 进而提高物质利用效率.