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In the present paper, single-crystal PbMoO4 nanorods and nanowires were synthesized via a simple sonochemical process without any templates or surfactants for the first time. The samples were analyzed by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and electron diffraction (ED). Experimental results indicated that the obtained PbMoO4 nanowires were single-crystal in structure and the aspect ratio was about 200. The pH value and precursor were found to be critical factors to the controlled preparation of PbMoO4 nanorods and nanowires. The possible mechanism for the synthesis of PbMoO4 nanorods and nanowires was also discussed and other one-dimensional nanomaterials can also be successfully prepared by the present method. [ABSTRACT FROM AUTHOR]

The unreliable durability of high temperature proton exchange membrane fuel cells (HT-PEMFCs) is one of the restriction factors upon the commercialization process. In this paper, 600-h accelerated stress tests (ASTs) were performed on HT-PEMFCs to investigate the performance degradation under start/stop, load cycling (0.2–0.8 A cm−2 and 0.04–0.2 A cm−2) conditions. The activation, ohmic and mass transport polarization losses were determined in combination with the electrochemical impedance spectroscopy (EIS) and Tafel slope analysis, and the degradation modes such as carbon corrosion, catalyst degradation, acid loss and membrane degradation were analyzed by linear sweep voltammetry (LSV), cyclic voltammetry (CV) and transmission electron microscopy (TEM) characterization. The polarization curves of ASTs show that load cycling between 0.04 and 0.2 A cm−2 extensively aggravates performance degradation, indicating that high-potential operation has the greatest detrimental impact on the durability. By comparing the changes of the activation, ohmic and mass transport polarization losses, it can be found that the activation polarization is the dominant factor leading to performance degradation in the 600-h test, and the ohmic polarization has little effect on the performance degradation. After the test at load cycling between 0.2 and 0.8 A cm−2, the membrane is seriously degraded and the ohmic resistance increases significantly, and the severe acid loss becomes critical issue in the long-term durability of HT-PEMFC. • Activation, ohmic and mass transfer polarization losses are determined. • Activated polarization accounts for the largest proportion in the short term test. • Acid loss seriously affects the long term durability of HT-PEMFC. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we report the shape-controlled synthesis of MnWO4 nanocrystals by a simple hydrothermal method without any surfactants and templates. The as-prepared powders were characterized by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). It is found that MnWO4 nanofibers, nanorods, nanoflakes, and nanoparticles can be selectively prepared by tuning the experimental conditions such as the pH values and precursors. This green chemistry method is simple and highly reproducible, which can be extended to the shape-controlled synthesis of other metal oxide nanocrystals. [Copyright &y& Elsevier]

Abstract: PbWO4 dendrites have been successfully synthesized by a simple sonochemical method without any surfactants at room temperature. The as-prepared powders were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), electron diffraction (ED), and high-resolution transmission electron microscopy (HRTEM). The effect of pH value, molar ratio of [WO4 2−]/[Pb2+], reaction time, and the initial concentration of the starting solution on the formation of PbWO4 dendrites was investigated. Experimental results indicate that the molar ratio of [WO4 2−]/[Pb2+] played a crucial role in the formation of PbWO4 dendrites. A growth mechanism of PbWO4 dendrites was also discussed. The present process is proved to be environment-friendly, and can be extended to the controllable synthesis of other tungstates. [Copyright &y& Elsevier]

Abstract: In this paper, we report a simple hydrothermal method to synthesize barium strontium titanate (Ba1−x Sr x TiO3, x =0–1) dendrites without any templates. The obtained products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), electron diffraction (ED), and energy-dispersive X-ray spectroscopy (EDX), respectively. All the samples were identified as cubic perovskite phase by XRD and the obtained Ba1−x Sr x TiO3 (x =0–1) dendrites were single-crystal. The formation process of Ba1−x Sr x TiO3 dendritic structures was also investigated. It is rational to expect that dendritic structures of other perovskite oxides may also be synthesized by this simple method. [Copyright &y& Elsevier]

Abstract: Well-crystallized single-crystal BiFeO3 (BFO) nanoflakes have been successfully synthesized for the first time by the hydrothermal method assisted by KNO3. The as-prepared samples were characterized by X-ray powder diffraction (XRD), transmission electron microscope (TEM), high-resolution TEM (HRTEM), and physical property measurement system (PPMS). It was found that KNO3 played a key role in the formation of BFO nanoflakes. The as-prepared BFO nanoflakes were single-crystal in structure and showed super paramagnetic behavior at room temperature. It is expected that this process may be extended to the synthesis of other kinds of nanostructure materials, which will be beneficial to their detailed experimental investigation of the size- and morphology-dependent properties. [Copyright &y& Elsevier]

Abstract: In this paper, we report a simple hydrothermal method without any surfactants, for the first time, to synthesize single-crystal BaTiO3 dendrites. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron diffraction (ED), and high-resolution transmission electron microscopy (HRTEM). The KOH concentration was found to be vital to the final formation of BaTiO3 dendrites. An obvious morphology evolution from sphere-like shape to dendrite was observed when KOH concentration was decreased from 1 M to 0.1 M. It is rational to expect that dendritic structures of other perovskite oxides may also be synthesized by this simple method. [Copyright &y& Elsevier]

Abstract: Single-crystal PbTiO3 nanorods have been synthesized by phase transformation from Pb2Ti2O6 nanorods. In the process, single-crystal Pb2Ti2O6 nanorods were first prepared by hydrothermal method, and single-crystal PbTiO3 nanorods were obtained by phase transition from the resultant Pb2Ti2O6 nanorods. Various approaches including XRD, Raman, TEM, SAED, and HRTEM were used to investigate the as-prepared products. It was found that Pb2Ti2O6 nanorods played a key role in the formation of PbTiO3 nanorods. [Copyright &y& Elsevier]