A novel procedure in the galvanic deposition of Zn alloys for the preparation of large area Ni and Ni-Co surfaces

A new methodology for the electrodeposition of Ni-Zn and Ni-Co-Zn alloys that prevents zinc being in contact with the substrate and allows total elimination of this metal during alkaline leaching is fully described. This is achieved by a careful control of the plating bath composition during the electrolysis. The resulting coatings show a multilayer structure and the desirable concentration profile for all the metallic species involved, as revealed by SEM and EDX analyses. The electrochemical active area of the deposits after leaching of the zinc was measured by cyclic voltammetry. They were of the order of 1100 and 4400 times the geometric area for Ni and Ni-Co, respectively. These highly porous structures are very active for hydrogen evolution in alkaline solutions, showing extremely low overpotentials for relatively high current densities, as well as good stability for long term operation. Other possible applications for these structures are briefly discussed.