Distribution of sulphur and electrochemical properties of nickel sulphur coatings electrodeposited on the nickel foam as hydrogen evolution reaction cathodes

Nickel sulfur electrode was prepared on the nickel foam by electrodeposition method in a modified Watts bath into which thiourea, citric acid and a small amount of saccharin were added. The micrographs of various layers of nickel sulphur coatings were investigated by SEM. The distributions and mass contents of sulphur in nickel sulphur coatings were measured by EDX. The phase constitutions of the first layer of nickel sulphur coating were determined by XRD. The influence of current density on coating structures was studied. The hydrogen evolution potentials of various electrodes, including nickel sulphur coatings on foam and net nickel substrates, pure nickel foam and nickel net were measured. Results indicated that the distributions of sulphur contents in various layers are gradient and not homogeneous, the sizes of fine particles in various layers are not the same. XRD examinations show that the structure of the nickel sulphur coating is amorphous. With increase of current density the amorphous structures gradually increase and the crystal ones gradually decrease. In the range of sulphur contents from 18% to 18.8% the electrochemical activities of Ni-S coating electrodes are the highest. The hydrogen evolution reaction activity of amorphous Ni-S coatings on the nickel foam substrate is much higher than that on the nickel net substrate. (C) 2005 Elsevier B.V. All rights reserved.