Cathodes Raney-nickel coated

Cold rolling, Raney-nickel-coated cathodes, 40 114... 

Although at least four different technologies [cold rolling, flame spraying, Zn and A1 melt dipping, cathodic deposition of Ni/Zn precursor alloys (76)] have been described, only cold rolling and cathodic deposition of precursor alloys are used for commercial production of Raney-nickel-coated cathodes. 

Fig. 12. Morphology of Raney-nickel-coated cathodes for hydrogen evolution from caustic electrolytes (a) surface of Ni-Zn precursor coatings, (b) surface of Raney-nickel coating prepared by caustic leaching of the Zn content of the precursor, (c) cut through a Raney-nickel coating.

Obviously the contribution of the pore walls—according to the current density distribution—to cathodic hydrogen evolution becomes negligible beyond 10 fim pore depth so that for a perfect, undivided Raney-nickel coating of 100 fim thickness, only 7 to 8% utilization is anticipated. This is the reason why the fissures and cracks, the so-called tertiary structure of the catalyst, formed in Raney-nickel coatings by the leaching process are so important for improving its utilization. 

Fig. 14. Comparison of the current-voltage curves of a smooth nickel cathode and two different Raney-nickel-coated cathodes posessing comparable loading and effective surface (a) smooth nickel. Raney nickel prepared from two different precursors (b) plasma-sprayed NiAh, (c) NiAU cold rolled together with Mond nickel.

Microscopic and spectroscopic investigations (SEM and XPS) reveal the relatively fast change of the chemical composition of nickel sulfide coatings upon the onset of cathodic hydrogen evolution (74). Indeed, at 90°C all nickel sulfide phases are reduced to porous nickel within several days to a week s time. They lose some catalytic activity with time with an increase in overvoltage between 0.15 and 0.3 V after continuous operation for 1 year. It is clear that the catalyst after I week is already no longer nickel sulfide but some type of Raney nickel. Thus far the initial catalytic activity of the NiS, coating is of little relevance. The respective results and data are due to be published by the present authors (73). 

Reduction of several aliphatic and aromatic nitriles to the corresponding amines has also been reported. A palladium-coated nickel cathode, a carbon anode, and dilute hydrochloric acid have been used. A copper cathode, a graphite anode, and a promoter such as Raney nickel have been found satisfactory for the reduction of long-chain fatty nitriles. 

C. Welch, C.N. Hughes, R.A. Crawford, and D.W. DuBois, Electroarc-Produced Raney Nickel Alloy-Coated Cathodes for Chlor-Alkali cells. In M.M. Silver and E.M. Spore (eds). Proceedings of Symposium on Advances in the Chlor-Atkali and Chlorate Industry, Vol. 84-11, In The Electrochemical Society Inc., Princeton, NJ (1984), p. 192. 

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