STUDY BY POTENTIAL-MODULATED REFLECTANCE SPECTROSCOPY OF THE REACTIVITY OF ETHANOL WITH THE PASSIVATING LAYER ON NI AND FE

The influence of ethanol on the passivating films on Ni and Fe electro des in 1 M NaOH was studied by cyclic voltammetry and potential-modula ted reflectance (PMR) spectroscopy over a wide potential range. The de crease in the PMR maximum attributed to NiOOH which occurs when ethano l is added clearly shows that ethanol produces a decrease in the thick ness of the NiOOH layer on the Ni electrode; this effect increases in a nearly exponential way with the potential, reaching near saturation at an ethanol concentration of 1 M. A similar, but much smaller, decre ase in the FeOOH layer on iron is also produced by ethanol. In contras t, neither the passivating NiO on Ni nor the passivating Fe(III) oxide s on Fe are attacked by ethanol. Since only the Fe and Ni oxyhydroxide s are attacked by ethanol, while the passivating oxides are not, it is concluded that in order to react with ethanol the anodic oxides of Fe and Ni must have hydroxyl groups.