A nanostructured Pd-Cr catalyst was deposited on a supported carbon surface using the modified borohydride reduction method for the oxygen reduction reaction (ORR) to be utilized as an efficient catalyst in the proton-exchange membrane fuel cell. The crystal structure and feature nanostructure of the Pd-Cr@carbon were established through the use of X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). Meanwhile, its catalytic activity was studied using the cyclic voltammetry and electrochemical polarization techniques. Based on the XRD analysis, it was observed that the Pd phase with the fcc crystal structure was dominant, while the Pd-Cr phase with tetragonal crystal structure was detected only for the as-prepared sample and samples calcined at 573 K. The estimated average crystallite size of the Pd phase increased from 9.66 to 37.54 nm as the calcination temperature increased to 973 K, and the calcination time had a slight effect on the crystallite size. On the other side, the average crystallite size for the formed Pd-Cr phase slightly increased from 43.74 nm for the as-prepared sample to 44.90 nm for the sample calcined at 573 K for 3 h. The TEM examination revealed the uniform distribution of the Pd and Pd-Cr nanoparticles upon the carbon surface. The calcination temperature and time played an important role in controlling the structural and morphology parameters of Pd-Cr@carbon. The adsorption/desorption potentials were found to be dependent on the calcination temperature and time and hence the particle and crystallite sizes. The optimum ORR activity and chemical stability were observed for samples calcined at 773 K for 3 h.
相似文献In the present work, gallium oxide nanoparticles (nGa2O3) are synthesized via the thermal microwave combustion method, while nanocomposites of polyvinyl alcohol (PVA) polymer with various concentrations (0, 1, 2, 3, 4, and 5 wt%) of nGa2O3 are prepared by the casting technique. The structural characterization of nGa2O3, PVA, and films of PVA-Ga2O3 nanocomposites are studied using X-ray diffraction (XRD), High-resolution transmission electron microscopy (HRTEM), and Fourier-transform infrared (FTIR) spectroscopy. The HRTEM and XRD examinations showed that the prepared nGa2O3 has an average crystallite size of?~?5.6 nm and particle size of?~?0.9 µm. The FTIR analysis reveals the occurrence of some interactions between nGa2O3 and the functional groups of the PVA structure. On another side, the refractive index, absorption coefficient, and optical bandgap (Eg) were determined using the Wemple-DiDomenico single oscillator model. It was shown that Eg slightly reduced from 3.61 to 3.55 eV with increasing the Ga2O3 content to 3 wt%, while raised again up to 3.58 eV for 5 wt% Ga2O3. Other optical characteristics such as the optical density, extinction coefficient, optical susceptibility, thermal emissivity, optical sheet resistance for the PVA?Ga2O3 nanocomposites are investigated. The linear and nonlinear optical parameters together with their dependencies on the doping ratio reveals the qualification of PVA?Ga2O3 nanocomposites for nonlinear optical applications.
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