Moaaed Motlak

Cobalt/Chromium Nanoparticles-Incorporated Carbon Nanofibers as Effective Nonprecious Catalyst for Methanol Electrooxidation in Alkaline Medium

Cobalt-Chrome nanoparticles-incorporated carbon nanofibers (CNFs) are proposed as an effective nonprecious electrocatalyst for methanol oxidation in the alkaline media. The introduced nanofibers were prepared by simple technique, electrospinning. Carbonization of as-spun mat composed of chromium acetate, cobalt acetate and poly(vinyl alcohol) (PVA) at high temperature (900∘C) leads to production of the introduced nanofibers. The physicochemical characteristics were investigated by X-ray diffractometer (XRD), scanning electron microscope (SEM), field emission scanning electron microscope (FESEM), transmission electron microscope (TEM) equipped with EDX and TEM mapping. The exploited analyses confirmed that the final product is in the form of CNFs decorated by Co/Cr nanoparticles. Based on the results obtained from the cyclic voltammetry (CV) measurements, the proposed Co/Cr-incorporated CNFs possess high electrocatalytic activity toward methanol electrooxidation as a clear peak of methanol oxidation appeared with corresponding current density of 56mA/cm2. Moreover, the current density increased by increasing methanol concentration up to 4.0M. Overall, the proposed nanofibers open new avenue for platinum-free and stable nanostructural catalysts for fuel cell technology.

Super effective Zn-Fe-doped TiO2 nanofibers as photocatalyst for ammonia borane hydrolysis

ABSTRACT In this study, the photocatalytic activity of TiO2 nanofibers toward ammonia borane hydrolysis has been strongly modified by doping the nanostructure by ZnO and Fe2O3 oxides. Due to the differences in the work function and band gap energy among the three semiconductors (TiO2, ZnO and Fe2O3), illumination of TiO2 leads to accumulate the electrons and holes on the conduction and valance bands of Fe2O3 and ZnO, respectively. Accordingly, the experimental results indicated that the surface of the obtained nanofibers is very active which results in an instant hydrolysis of ammonia borane molecules reaching the active zone surrounding the nanofibers. Moreover, negative activation energy was determined as increasing the temperature led to decrease the photocatalytic performance. Furthermore, kinetic studies indicated that the heterogeneous catalytic reaction describing the ammonia borane hydrolysis process is zero order which additionally supports the super activity of the introduced nanofibers. It was also observed that Fe2O3 content in the introduced nanofibers has distinct influence as the best performance was obtained at 1 wt%. The modified TiO2 nanofibers were prepared by calcination of electrospun nanofibers composed of titanium isopropoxide, zinc acetate and iron acetate in air at 700 °C for 1 h. Overall, the present study opens a new avenue to overcome the fast electrons/holes recombination dilemma facing TiO2-based nanostructures.

Surface reconstruction at the initial Ge adsorption stage on Si(114)-2 × 1

By combined investigation of scanning tunneling microscopy and synchrotron core-level photoemission spectroscopy on the structural and chemical evolution at the initial stage of Ge adsorption on Si(114)-2 × 1, it has been observed that one-dimensional (1D) sawtooth-like nanostructures composed of (113) and (117) facets and 1D trenches adjacent to the (113) facets are readily formed without any wetting layer. Due to the absence of chain structures on the reconstructed Si(114)-2 × 1, enhanced Ge interdiffusion detected from Ge/Si(5 5 12)-2 × 1 has not been found. Instead, Si atoms originating from etched surfaces and arriving Ge atoms form the alloy facets with Ge-rich surfaces. These experimental results prove that, if the direction of the Ge overlayer corresponding to that of the substrate is unstable like the present case, the arriving atoms prefer to form facets covered with the species of lower surface free energies rather than a uniform wetting layer.