Tailoring of active nickel alloy cathodes for hydrogen evolution in a hot concentrated hydroxide solution was attempted by electrodeposition. Electrodeposited iron is naturally more active for hydrogen evolution than nickel, but Ni-Fe alloys show further high activity for hydrogen evolution, although the rate-determining step being assumed as proton discharge is not changed. The carbon addition to iron or nickel remarkably enhances the activity for hydrogen evolution and changes the mechanism of hydrogen evolution. Ternary Ni-Fe-C alloys show the highest activity for hydrogen evolution, and the Tafel slope of hydrogen evolution is about 33 mV/dec, suggesting the rate-determining step of desorption of adsorbed hydrogen by recombination. XPS analysis reveals that the charge transfer occurs from nickel to iron in alloys and the carbon addition particularly enhances the charge transfer. Accelerated proton discharge due to enhanced charge transfer from nickel to iron seems responsible for the high activity of the Ni-Fe-C alloys for hydrogen evolution.
Carbon addition to electrodeposited Co-Mo alloys was made to enhance electrolytic hydrogen evolution activity and to prevent open-circuit corrosion in 8 M NaOH at 90°C. Co-30 atom % Mo alloy showed the highest activity for hydrogen evolution among the binary Co-Mo alloys, but open-circuit immersion resulted in dissolution of molybdenum as molybdate, with a consequent decrease in the hydrogen evolution activity. Addition of carbon to electrodeposited Co-Mo alloys by adding lysine in the deposition electrolytes further enhanced hydrogen evolution activity and slowed dissolution of molybdenum during open-circuit immersion, although complete prevention of dissolution of molybdenum was not attained.
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