Laser-processed electrodes consisting of amorphous nickel-niobium-platinum group metal surface alloys on niobium

Laser processing was applied to a specimen composed of a bulk niobium substrate covered by electrodeposited nickel and platinum group metals in order to form amorphous surface alloys having excellent electrocatalytic activities. The bulk niobium substrate acts as an electric conductor instead of thin amorphous alloys of a high electric resistance. Laser processing leads to alloying of electrodeposited metals with niobium, and hence the niobium content of the laser-processed layer is determined by the laser-processing conditions. A wide area is vitrified only when the niobium content was 35–40 at.% in spite of the fact that nickel-niobium alloys containing 25–65 at.% niobium become amorphous by conventional methods for preparation of amorphous alloys such as melt spinning. Vitrification of a wide area is performed by overlapped traverses by the laser beam and often results in crystallization in the heat-affected zone in the previously vitrified phase. Thus the laser processing must be carried out so as to form the surface alloy having a very high glass-forming ability, and the appropriate laser-processing conditions must be determined for each alloy family. The laser-processed amorphous alloy electrodes exhibit excellent electrocatalytic activities when their surfaces are activated chemically.