Composition and Morphology Changes and their Influence on Hydrogen Evolution on Ni-Mo and Fe-Mo Alloys Electrodeposited by DC and Pulsed Current

Published

June 1, 2002

Author(s)

V D. Jovic, B M. Jovic, Gery R. Stafford

Abstract

Ni-Mo and Fe-Mo alloys were electrodeposited using both DC and pulsed current from a phyrophosphate bath. Their composition and morphology were investigated by EDS and optical microscopy, respectively, in order to determine the influence of the deposition conditions on the morphology and composition of these alloys. It was shown that the electrodeposition parameters influenced both the composition of Fe-Mo alloys and the current efficiency of their deposition, while the macro-morphology did not change significantly with different applied current densities and waveforms. In the case of Ni-Mo alloys produced by pulse plating, the composition, morphology and current efficiency were all dependent on the applied current density. Compositions ranging from 28 at.% to 41 at.% Mo were obtained current efficiencies less than 10%. When the Mo 6+ concentration in the electrolyte was increased, the dependence of composition on current density was significantly reduced for both DC and pulsed plating. Even with the increased Mo 6+ concentration, the current efficiency for DC plating remained below 10%. The morphology was particularly sensitive to the co-generation of hydrogen and most deposits were micro-cracked.It was found that electrodeposited Fe-Mo alloys possess about 0.15V lower overvoltage than mild steel for hydrogen evolution in an electrolyte commonly used in commercial chlorate production. The hydrogen evolution overvoltage for electrodeposited Ni-Mo alloys in sodium hydroxide solution was dependent on both the electrode composition and roughness, both of which were dependent on the deposition parameters. Preliminary electrochemical impedance spectroscopy (EIS) results recorded during hydrogen evolution on freshly deposited samples indicate the cracks present in the Ni-Mo coatings do not create diffusion barriers and limit the hydrogen evolution reaction. The impedance data was fit to an equivalent circuit that has successfully been used for EIS analysis of cast Ni-Mo alloys.

Proceedings Title

AESF SUR/FIN 2002 (American Electroplaters and Surface Finishers Society)

Conference Dates

June 24-27, 2002

Conference Title

Surface Finishing

Pub Type

Conferences

Keywords

electrodeposited, Fe-Mo, Ni-Mo, pulsed current

Citation

Jovic, V. , Jovic, B. and Stafford, G. (2002), Composition and Morphology Changes and their Influence on Hydrogen Evolution on Ni-Mo and Fe-Mo Alloys Electrodeposited by DC and Pulsed Current, AESF SUR/FIN 2002 (American Electroplaters and Surface Finishers Society) (Accessed December 13, 2024)