A Comparative Study of Cathodic Electrodeposited Nickel Hydroxide Films Electrocatalysts

This paper describes the cathodic electrodeposition of Ni hydroxides from NiCl2 at const. potentials. In a single compartment electrochem. cell, the procedure yields black films that have the appearance of glassy C. XPS analyses reveal that the films consist of a mixt. of Ni(OH)2 and NiOOH in a proportion that depends on the deposition potential; also, SIMS analyses indicate that the coatings are richer in NiOOH in the inner regions towards the support. The electrochem. behavior was compared with data obtained on electrodes based on pure Ni(OH)2 prepd. by cathodic electrodeposition from Ni(NO3)2, following literature procedures. This comparison confirms the composite nature of black Ni hydroxide (BN) coatings, adding that Ni(OH)2 and NiOOH are present in nearly equal amts. The electrocatalytic activity of BN electrodes was tested in the oxidn. of MeOH in alk. solns. Exptl. results are consistent with a mechanism previously proposed in literature for the oxidn. of org. compds. on Ni electrodes. Comparison with electrodes based on pure Ni(OH)2 shows that, in the low potentials region, the presence of a high amt. of NiOOH causes a decrease of activity, while an opposite effect is obsd. when the potential is increased. The black Ni electrodes show a remarkable stability in repeated cycles of oxidn. of MeOH and O2 evolution; under similar conditions, conventional Ni(OH)2 films show an appreciable decrease in thickness, as evidenced by the decrease of peak charge in cyclic voltammetry expts