RANEY-NICKEL ACTIVATED H-2-CATHODES .2. CORRELATION OF MORPHOLOGY AND EFFECTIVE CATALYTIC ACTIVITY OF RANEY-NICKEL COATED CATHODES

Raney nickel activated hydrogen-cathodes obtained by caustic leaching of cathodically deposited Ni/Zn precursor alloy coatings on nickel substrates were investigated with respect to their effective catalytic activity. Important factors influencing this activity are the surface specific amount of the inner surface of the Raney nickel coatings and, in particular, the tertiary structure of the catalyst coating. Coarse pores and cracks are developed during leaching of the Ni/Zn precursor which, due to unsteady deposition conditions, show a layered structure. These cracks are essential for a high catalytic activity, since micropores of Raney nickel coatings are utilized to pore depths of no more than 10 mum. The generation of layered structures of the coatings with changing zinc content, which is experienced by Ni/Zn codeposition from acidic solutions, is influenced by a number of process parameters. The most important parameter is the cathode potential which may fluctuate strongly during cathodic deposition of the Ni/Zn precursor coatings due to minute temperature and/or pH changes.