Mengmeng Zhen

Well-distributed TiO2 nanocrystals on reduced graphene oxides as high-performance anode materials for lithium ion batteries

Ultra small TiO2 nanocrystals were well dispersed on reduced graphene oxide nanosheets through two-step hydrothermal treatments without any surfactants and high-temperature calcinations. Profiting from small TiO2 nanoparticles, high electronic conductivity and low carbon content, the nanocomposites presented excellent reversible capacity and high-rate performance for lithium storage.

Efficient NiSe-Ni3Se2/Graphene Electrocatalyst in Dye-Sensitized Solar Cells: The Role of Hollow Hybrid Nanostructure

Hollow and hybrid nanomaterials are excellent electrocatalysts on account of their novel electrocatalytic properties compared with homogeneous solid nanostructures. In this report, NiSe-Ni3Se2 hybrid nanostructure with morphology of hollow hexagonal nanodisk was synthesized in situ on graphene. A series of NiSe-Ni3Se2/RGO with different phase constitutions and nanostructures were obtained by controlling the durations of solvothermal treatment. Because of their unique hollow and hybrid structure, NiSe-Ni3Se2/RGO hollow nanodisks exhibited higher electrocatalytic performance than NiSe/RGO and solid NiSe-Ni3Se2/RGO nanostructure for reducing I3(-) as counter cell (CE) of dye-sensitized solar cells (DSSCs). Additionally, NiSe-Ni3Se2/RGO hollow nanodisks achieved much lower charge transfer resistance (Rct = 0.68 Ω) and higher power conversion efficiency (PCE) (7.87%) than those of Pt (Rct = 1.41 Ω, PCE = 7.28%).

Synthesis of Mesoporous Wall‐Structured TiO2 on Reduced Graphene Oxide Nanosheets with High Rate Performance for Lithium‐Ion Batteries

Mesoporous wall-structured TiO2 on reduced graphene oxide (RGO) nanosheets were successfully fabricated through a simple hydrothermal process without any surfactants and annealed at 400 °C for 2 h under argon. The obtained mesoporous structured TiO2 -RGO composites had a high surface area (99 0307 m(2)  g(-1)) and exhibited excellent electrochemical cycling (a reversible capacity of 260 mAh g(-1) at 1.2 C and 180 mAh g(-1) at 5 C after 400 cycles), demonstrating it to be a promising method for the development of high-performance Li-ion batteries.

Controlled fabrication of hierarchical WO3·H2O hollow microspheres for enhanced visible light photocatalysis

WO3·H2O nanostructures have been prepared through a facile hydrothermal route by controlling their morphology during synthesis. WO3·H2O nanoplates with a thickness of ∼45 nm and hierarchical hollow microspheres (HMSs) structures could be obtained by introducing different amounts of citric acid. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were employed to understand the structure and morphology of the two types of WO3·H2O. The formation mechanisms for WO3·H2O nanoplates and WO3·H2O HMSs were investigated. The photocatalytic activities, determined by rhodamine B (RhB) degradation under visible light irradiation of WO3·H2O HMSs photocatalysts, were significantly improved as compared with WO3·H2O nanoplates. The higher efficiency of photocatalytic activity in WO3·H2O HMSs was attributed to its higher surface-to-volume ratio and stability against aggregation. In addition, we investigated the toxicity of WO3·H2O HMSs against an important model fungus, yeast (Saccharomyces cerevisiae). The results indicate that the as-synthesized hierarchical WO3·H2O HMSs could be used as a green and efficient photocatalyst.

BiOBr–BiOI microsphere assembled with atom-thick ultrathin nanosheets and its high photocatalytic activity

BiOBr–BiOI composite microspheres assembled with atom-thick ultrathin nanosheets have been synthesized via a simple solvothermal route with the surfactant polyvinylpyrrolidone (PVP). The structure was characterized with AFM, which confirmed the 0.9 nm thickness of the single-layered nanosheets. The ultrathin structure with atomic thickness mainly relies on its lamellar structure and the reason for the formation of the few- or even single-layered structure is the strong intra-layer chemical bonding and weak inter-layer interaction. The 3D BiOBr–BiOI exhibits excellent photocatalytic activity for BPA degradation under visible light irradiation. Nearly 80% of BPA was degraded in 2 h irradiation, and over 90% after 5 h. Based on these findings, the photodegradation mechanism was investigated and O2− was suggested to be the main active oxidant in the BPA-removal processes. Our investigation showed that the electron–hole pairs on ultrathin nanosheets can be separated effectively which resulted in significantly promoted solar-driven photocatalytic activity for extremely low photocatalyst loading.

Reduced Graphene Oxide‐Supported TiO2 Fiber Bundles with Mesostructures as Anode Materials for Lithium‐Ion Batteries

Although the synthesis of mesoporous materials is well established, the preparation of TiO2 fiber bundles with mesostructures, highly crystalline walls, and good thermal stability on the RGO nanosheets remains a challenge. Herein, a low-cost and environmentally friendly hydrothermal route for the synthesis of RGO nanosheet-supported anatase TiO2 fiber bundles with dense mesostructures is used. These mesostructured TiO2 -RGO materials are used for investigation of Li-ion insertion properties, which show a reversible capacity of 235 mA h g(-1) at 200 mA g(-1) and 150 mA h g(-1) at 1000 mA g(-1) after 1000 cycles. The higher specific surface area of the new mesostructures and high conductive substrate (RGO nanosheets) result in excellent lithium storage performance, high-rate performance, and strong cycling stability of the TiO2 -RGO composites.

MnO2 nanotubes with graphene-assistance as low-cost counter-electrode materials in dye-sensitized solar cells

MnO2 nanotubes were synthesized via hydrothermal conditions. We investigated their catalytic activities with a counter electrode (CE) in DSSCs by photocurrent–voltage (J–V) curves and measured conversion efficiency. To enhance their power conversion efficiency (PCE), different amounts of reduced graphene were added by simple physical mixing. With the addition of 6 wt% reduced graphene (rGO), the short-circuit current density, open-circuit voltage, and fill factor (FF) were Jsc = 15.97 mA, Voc = 0.71 V, and FF = 0.51. Furthermore, the conversion efficiency achieved 5.77%, which was slightly better than the commercial Pt CE (PCE = 5.40%). Compared to the traditional Pt CE of DSSCs, this material has the advantages of low cost, simple synthesis, and high conversion efficiency with graphene assistance.

Ultrathin Ni–Ni3Se2 nanosheets on graphene as a high-performance counter electrode for dye-sensitized solar cells

Ultrathin nanostructures of metal chalcogenides have exhibited excellent electrocatalytic activity due to the high percentage of surface atoms and many exposed interior atoms, which inevitably induce the formation of defects serving as highly efficient active sites. Here we report for the first time a high-performance electrocatalyst of ultrathin Ni–Ni3Se2 nanosheets on graphene nanosheets. Specifically, the thickness of the obtained nanosheets is in the range of 1.5–2.5 nm. Furthermore, the specific surface area of the ultrathin Ni–Ni3Se2/graphene nanosheets was as much as ∼162.5 m2 g−1. The electrocatalytic activity of Ni–Ni3Se2/graphene nanosheets was measured as a counter cell of dye-sensitized solar cells. Ni–Ni3Se2/graphene nanosheets exhibited high performance for the reduction of I3− to I−, and achieved higher power conversion efficiency (7.76%) compared with that of the Pt-based reference electrode (7.42%).

Synthesis of hierarchical ZnO/ZnCo2O4 nanosheets with mesostructures for lithium-ion anodes

Novel bi-component-active hierarchical ZnO/ZnCo2O4 (ZZCO) nanosheets with mesostructures are successfully prepared through a convenient and practical hydrothermal route followed by a calcination process. When evaluated as anode materials for lithium-ion batteries (LIBs), the bi-component-active hierarchical ZZCO nanosheets with mesostructures exhibit highly reversible lithium storage capacity, and strong cycling stability at the 500 mA g−1 rate for 150 cycles. More significantly, the hybrid ZZCO presents an exceptionally high rate capability up to the 2 A g−1 rate.

Facile Preparation and Lithium Storage Properties of TiO2 @Graphene Composite Electrodes with Low Carbon Content.

Over the past decade, TiO2 /graphene composites as electrodes for lithium ion batteries have attracted a great deal of attention for reasons of safety and environmental friendliness. However, most of the TiO2 /graphene electrodes have large graphene content (9-40 %), which is bound to increase the cost of the battery. Logically, reducing the amount of graphene is a necessary part to achieve a green battery. The synthesis of TiO2 nanosheets under solvothermal conditions without additives is now demonstrated. Through mechanical mixing TiO2 nanosheets with different amount of reduced graphene (rGO), a series of TiO2 @graphene composites was prepared with low graphene content (rGO content 1, 2, 3, and 5 wt %). When these composites were evaluated as anodes for lithium ion batteries, it was found that TiO2 +3 wt % rGO manifested excellent cycling stability and a high specific capacity (243.7 mAh g(-1) at 1 C; 1 C=167.5 mA g(-1) ), and demonstrated superior high-rate discharge/charge capability at 20 C.