engleski

Effect of the nanoparticles size on the catalytic activity of sputter deposited nickel films

The mechanical, electrical, corrosion and catalytic properties of nanomaterials are mostly governed by their microstructure– grainsize, primary intercrystalline defects like grain boundaries and triple junctions, secondary effects like porosity, residual amorphous regions, lattice dislocations, vacancies etc. Therefore, the insight into the structure of nanomaterial is essential for understanding their physical properties. Nanocrystalline nickel (nc-Ni) thin films were deposited onto fused silica substrates using dc magnetron sputtering in a wide range of working gas pressure (0.33-1.33 Pa) and substrate temperatures (35^o C – 300^o C). The film structure was investigated using Grazing incidence small angle X-ray scattering (GISAX) and XRD analysis. It was found that the isotrophic/spherical particles prevail at temperatures up to 100^o C, while the platelet-like particles predominate at higher temperatures. These inhomogeneities are ascribed to the intergranular matter/grain boundaries since the grain size was found to increase from 11.7 nm at 35^o C to about 76 nm at 150^o C. We investigated the catalytic properties of sputter deposited nc-Ni films for the hydrogen evolution reaction (HER) in 1.0 M NaOH solution at 25^o C. The kinetic parameters for the HER were deduced from the electrochemical impedance spectroscopy measurements. The performance toward the HER was correlated with the grain size, d as well as with the volume fraction of the intercrystalline mater/grain boundaries (the spherical particles of inhomogeneites, RG ) inside sputter deposited Ni-films. An improved catalytic activity for the HER of nc-Ni in comparison with polycrystalline Ni strongly reflects nano-structural effects at the solid-liquid interface.

nickel; nickel-alloys; hydrogen evolution; linear polarization; electrochemical impedance spectroscopy

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