Cuiling Zhang

Photocatalytic Activity of ZnWO4: Band Structure, Morphology and Surface Modification

Photocatalytic degradation of organic contaminants is an important application area in solar energy utilization. To improve material photocatalytic properties, understanding their photocatalytic mechanism is indispensable. Here, the photocatalytic performance of ZnWO4 nanocrystals was systematicly investigated by the photodegradation of tetraethylated rhodamine (RhB) under simulated sunlight irradiation, including the influence of morphology, AgO/ZnWO4 heterojunction and comparison with CoWO4 nanowires. The results show that the photocatalytic activity of ZnWO4 is higher than that of CoWO4, and the ZnWO4 nanorods exhibit better photocatalytic activity than that of ZnWO4 nanowires. In addition, the mechanism for the difference of the photocatalytic activity was also investigated by comparison of their photoluminescence and photocurrents. AgO nanoparticles were assembled uniformly on the surface of ZnWO4 nanowires to form a heterojunction that exhibited enhanced photocatalytic activity under irradiation at the initial stage. We found that a good photocatalyst should not only have an active structure for electrons directly to transfer from the valence band to the conduction band without the help of phonons but also a special electronic configuration for the high mobility, to ensure more excited electrons and holes in a catalytic reaction.

Hierarchical mesoporous NiFe2O4 nanocone forest directly growing on carbon textile for high performance flexible supercapacitors

Binary metal oxides have been considered as promising electrode materials for high performance pseudocapacitors because they offer higher electrochemical activity than mono metal oxides. The rational design of binder free electrode architecture is an efficient solution to the further enhancement of the performance of electrochemical supercapacitors. Herein, we report the synthesis of a hierarchical mesoporous NiFe2O4 (NFO) nanocone forest directly growing on carbon textile with ultra-high surface area by the hydrothermal method. The NiFe2O4 nanocone forest on carbon textile (NFO-CT) was used as a binder free electrode that exhibited the high capacitance of 697 F g−1 at a scan rate of 5 mV s−1 and was further used for the fabrication of a symmetric solid state supercapacitor. The open space between hierarchical nanocones allows easy diffusion for electrolyte ions and the carbon textile ensures fast electron transfer that leads to the remarkable electrochemical performance. The NFO-CT solid state supercapacitor exhibited the high capacitance of 584 F g−1 at a scan rate of 5 mV s−1 and 93.57% capacitance retention after 10 000 cycles with the advantages of being light weight, thin and having good flexibility. A high energy density of 54.9 W h kg−1 at a power density of 300 W kg−1 was achieved, indicating the excellent energy storage features. Furthermore, three charged supercapacitors in series can light 4 red colored LEDs (2 V, 15 mA) for 2 min.

Wind farm reactive power output optimization for loss reduction and voltage profile improvements

In recent years, the number of small size wind farms used as DG sources located within the distribution system are rapidly increasing. In this paper, wind farm made up with doubly fed induction generators (DFIG) is proposed as the continuous reactive power source to support system voltage control due to the reactive power control capability of DFIG. The particle swarm optimization (PSO) is utilized to find wind farm optimal reactive power output for distribution system losses reduction and voltage profiles improvement. Finally, the three feeder distribution system is used as a test case to evaluate the algorithm.