Electrolytical production and properties of nickel-molybdenum composite layers
Antoni Budniok, Joanna Panek Uniwersytet Śląski, Instytut Fizyki i Chemii Metali, ul. Bankowa 12, 40-007 Katowice
Annals 3 No. 6, 2003 pages 30-34
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abstract The aim of this investigation was to obtain Ni+Mo composite layers differing in Mo content, to carry out their characterization and to estimate their suitability as electrode materials for hydrogen evolution in alkaline environment. Ni+Mo composite layers were obtained on a steel substrate by electrolytic codeposition of nickel and molybdenum powder from an electrolyte containing Mo powder suspension. Surface morphology of obtained layers as well as the phase and chemical composition were determined. It was ascertained that surface morphology of Ni+Mo composite layers is influenced by the amount of metallic powder in the bath (and Mo content in the layers deriving from it) as well as by the applied deposition current density. It was stated that the surface of Ni+Mo layers is more developed compared to nickel layer, and that surface enlargement increases with the increase in the amount of incorporated molybdenum powder and also with the increase in deposition current density (Fig. 1). Structural investigation of deposited layers showed the presence of nickel and molybdenum crystalline phases (Fig. 2). Chemical composition of obtained layers depends on amount of molybdenum powder dispersed in galvanic bath as well as on the galvanic conditions under which they were obtained (Tab. 1). The percentage of molybdenum in the layers lies within the limits 22÷56 wt.% and increases with the increase in the amount of molybdenum powder in the bath, but diminishes with the increase in deposition current density. The obtained layers were tested as electrode materials for hydrogen evolution in alkaline environment. Electrochemical characterization of the layer was carried out by steady-state polarization method. Basing on recorded η = f(log j) dependences the Tafel equation parameters for this process were determined (Fig. 3, Tab. 2). It was ascertained, that investigated Ni+Mo 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 for these layers. Their greater activity in this process may be attributed to the developed electrode surface arising from the incorporation of Mo powder into the nickel matrix. Key words: nickel, molybdenum, electrolytic composite layers, hydrogen electroevolution