Gaber A.M. Mersal

Reduced graphene oxide nanosheets decorated with Au, Pd and Au–Pd bimetallic nanoparticles as highly efficient catalysts for electrochemical hydrogen generation

Reduced graphene oxide (rGO) nanosheets decorated with gold nanoparticles (Au NPs/rGO), palladium nanoparticles (Pd NPs/rGO), and gold–palladium bimetallic nanoparticles (Au–Pd NPs)/rGO are synthesized by a simple solution chemistry approach using ascorbic acid as an eco-friendly reducing agent. These materials are characterized by high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-angle annular diffraction field-scanning transmission electron microscopy (HAADF-STEM) and thermogravimetric analysis (TGA). The as-prepared nanocomposites are tested as electrocatalysts for efficient hydrogen evolution in deaerated 0.5 M H2SO4 aqueous solution using polarization and impedance measurements. Experimental findings show that the tested catalysts exhibit fast hydrogen evolution kinetics with onset potentials as low as −17, −7.2, and −0.8 mV vs. RHE for Au NPs/rGO, Pd NPs/rGO, and Au–Pd NPs/rGO, respectively. In addition, Tafel slopes of 39.2, 33.7 and 29.0 mV dec−1 and exchange current densities of 0.09, 0.11, and 0.47 mA cm−2 are measured for Au NPs/rGO, Pd NPs/rGO, and Au–Pd NPs/rGO, respectively. The tested materials not only maintain their high performance after 5000 sweep cycles, but their activity is simultaneously enhanced after this aging process. These findings reveal that the tested catalysts, particularly Au–Pd NPs/rGO, are promising candidates among other noble metal catalysts for hydrogen evolution, approaching the commercial Pt/C catalyst (onset potential: 0.0 mV, Tafel slope: 31 mV dec−1, and exchange current density: 0.78 mA cm−2). The high hydrogen evolution reaction (HER) activity of such materials is likely due to the abundance of active catalytic sites, the increased electrochemically accessible surface area and significantly improved electrochemical conductivity.

Spectroscopic, electrochemical, and alkylation reactions: tert-Butyl N-(2-mercaptoethyl)carbamate copper(II) and nickel(II) complexes as structural mimics for the active site of thiolate-alkylating enzymes

Two new dithiolate copper(II) and nickel(II) complexes with the ligand tert-butyl N-(2-mercaptoethyl)-carbamate (Boc-SH) were prepared. Their structures were established to be [(Boc-S)2M], where M=Cu (1) and Ni (2) by using elemental analysis, thermal analysis, molar conductivity, FT-IR, Raman, UV/VIS, and ESR as well as EI-mass spectroscopic methods. The X-ray structure of the ligand Boc-SH was also determined. Spectral data showed that the carbamate ligand act as anioinic bidentate through one immine nitrogen and one thiolate sulfur donor atoms. The spectral techniques suggest that both complexes appear to have square planar geometries. The very low electrical conductance of the two complexes supports their neutral nature. The redox behaviors of the obtained complexes were also investigated by cyclic voltammetry. The monomeric nature of both complexes was assessed from their magnetic susceptibility values. The thermoanalytical data evidence that complex (2) is stable up to 165°C and undergo complete decomposition, resulting in NiO as a residual product. The TEM image of the obtained oxide residue showed its nanosize cluster, suggesting that complex (2) may be used as a precursor for the formation of nanooxide. The methylation reactions of the two dithiolate complexes (1) and (2) with methyl iodide appear to occur intramolecularly at the metal(II)-bound dithiolates, forming the metal(II)-bound dithioether complexes [M(Boc-SCH3)2]I2 with clean second-order constants of 7.95×10(-2) and 10.59×10(-2) M(-1) s(-1), respectively.