Electrochemical performance of crystalline Ni-Co-Mo-Fe electrodes obtained by mechanical alloying on the oxygen evolution reaction

Electro-active Co₃₀ Ni₇₀, Co₃₀ Mo₇₀, Ni₃₀ Mo₇₀, Co₁₀ Ni₂₀ Mo₇₀, Fe₁₀ Co₃₀ Ni₆₀ and Co₁₀ Fe₃₀ Ni₆₀ wt% alloys have been prepared by mechanical alloying. The electrocatalytic behavior of obtained electrodes has been evaluated in 30 wt% KOH aqueous solutions as a function of different temperatures (298, 323 and 343 K) and overvoltages (η = 200, 300, 400 mV). The effect of Fe contamination during mechanical milling was also analyzed. The electrode performance was studied by cyclic voltammetry, ac-impedance and steady-state polarization techniques. Appreciable current values for oxygen evolution reactions (OER) were measured at Ni-Co-Mo-Fe electrodes produced by this technique. It was also found that the electrochemically formed Co and Fe oxides and/or hydroxides did not show an activity for OER as good as reported on hydrogen evolution reaction (HER). Tafel plots of preoxidized at 1 cycle and prolonged cycled (50 cycles) for Co₃₀ Ni₇₀, Co₃₀ Mo₇₀, Ni₃₀ Mo₇₀, Co₁₀ Ni₂₀ Mo₇₀, Fe₁₀ Co₃₀ Ni₆₀ and Co₁₀ Fe₃₀ Ni₆₀ crystalline electrodes were very different, which might be related to changes in the surface enrichment of one or two of the alloy constituents. The Mo electrocatalytic effects seem to be more important on the OER at higher temperatures than those showed previously for HER. Molybdenum containing crystalline Co and Ni powders (Co₁₀ Ni₂₀ Mo₇₀) showed the best catalytic behavior for the OER.