Electrolytical production and properties of nickel-vanadium composite layers
Joanna Panek, Antoni Budniok Uniwersytet Śląski, Instytut Fizyki i Chemii Metali, ul. Bankowa 12, 40-007 Katowice
Annals 3 No. 6, 2003 pages 12-16
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abstract The subject of this study are nickel-based composite layers containing powdered vanadium. Electrolytic composite Ni+V layers were prepared by co-deposition of nickel and vanadium from a solution, in which metallic vanadium particles were suspended by stirring. The process of electrodeposition was carried out on a steel substrate, under galvanostatic conditions. The characterization of the layers included the investigation of surface morphology making use of stereoscopic microscope, structural investigation by X-ray diffraction method and the tests of chemical composition by X-ray fluorescence spectro-scopy. It was stated that the surface of Ni+Ti layers is more developed compared to nickel layer, and that surface enlargement increases with the increase in the amount of incorporated vanadium powder (Fig. 1). X-ray diffraction analysis of Ni+V layers showed their two-phased structure and confirmed their composite character (Fig. 2). It was stated, that chemical composition of obtained layers depends on amount of vanadium powder dispersed in galvanic bath as well as on the galvanic conditions under which they were obtained (Tab. 1). The percentage of vanadium in layers increases with the increase in the amount of vanadium powder in the bath, but diminishes with the increase in deposition current density. The percentage of vanadium varies from 6 to 45 wt.% in dependence on applied current density and the amount of vanadium powder in the bath. The obtained layers were applied as electrode materials for hydrogen evolution in alkaline environment. Electrochemical characterization of the layers was carried out by steady-state polarization method, making use of Tafel equation (Fig. 3, Tab. 2). It was ascertained, that investigated Ni+V composite layers are characterized by increased electrochemical activity for hydrogen evolution compared to nickel coatings, what is derived from lower values of Tafel equation parameters and lower values of hydrogen evolution overpotential at the current density of 100 mA/cm2 - η 100. Moreover, their activity in this process increases with an increase in the amount of vanadium in the layer. The increased activity of Ni+V layers may be attributed to the extended electrode surface arising from the character of composite layers as well as the hydrogen adsorption process occuring on the layers surface, which have catalytic influence on the hydrogen electroevolution. Key words: nickel, vanadium, electrolytic composite layers, hydrogen electroevolution