Electrochemical and x-ray photoelectron spectroscopy characterization of surface films on MmNi(3.5)Al(0.8)Co(0.7)

MmNi(3.5)Al(0.8)Co(0.07) has been characterized using electrochemical techniques and x-ray photoelectron spectroscopy. The stability and rapid hydriding and dehydriding kinetics that it exhibits in KOH have been attributed to the proper-ties of a surface film. A hypothetical model of this film has been proposed in which stability results hom an inner, dense barrier region that protects the thermodynamically unstable alloy from the electrolyte. Rapid reaction rates are attributed to the high concentrations of metallic cobalt and nickel present in the film. A continuous electron-conducting network composed of these two metals is proposed that allows electron transfer between the bulk intermetallic and the outer regions of the film where solution species participating in the reactions are readily available.