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Composite Ni+Mo coatings were obtained by electrodeposition of Ni with Mo particles on
a steel substrate from the nickel bath in which metallic powder was suspended by stirring. The
deposition was conducted under galvanostatic conditions. Deposits were characterized by the
presence of Mo microsize particles embedded into the nanocrystalline nickel matrix. The influence
of the metal powder amount in the bath, as well as the deposition current density on the chemical
composition of the coatings was investigated. The content of incorporated Mo increases with the
increase in the amount of metal powder in the bath, and diminishes with the increase in the
deposition current density. The mechanism of metallic particles embedding is explained on the
base of Ni2+ ions adsorption process. Incorporation of Mo particles into electrolytic nickel
matrix causes an increase in the real surface area of deposits.
Thermal treatment of deposited coatings leads to chemical reactions in the solid state and in a consequence exerts significant influence on their phase composition and surface morphology. As a result of the interaction between the nickel matrix and incorporated Mo particles Ni3Mo intermetallic phase and Ni-Mo solid solution are arising. The obtained composite coatings were tested as electrode materials for hydrogen evolution in alkaline environment. Electrochemical characterization of the composites was carried out by steady-state polarization method. It was ascertained, that as-deposited Ni+Mo coatings are characterized by enhanced electrochemical activity for this process, which was confirmed by considerable decrease in the hydrogen evolution overpotential, by a nearly 170-260 mV compared to nickel electrode. Thermal treatment decreases the electrochemical activity of the investigated materials, as the values of hydrogen evolution overpotential on heated coatings are much higher. |
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