NEW ZINC AND IRON ELECTRODES OF THE 2ND KIND IN SULFURIC-ACID, HYDROFLUORIC-ACID AND (CYCLO)ALKYLAMMONIUM HYDROGEN SULFATES

New zinc and iron electrodes of the second kind have been examined in solutions of low pH. The electrolytes are 5 - 14 M H2SO4, 40 - 60% H2F2 and 3 - 5 M (cyclo)alkylammonium hydrogen sulphates in water, methanol or acetonitrile. The cyclic behaviour of the metals (as a layer on glassy carbon) under galvanostatic conditions (j = 1 - 10 mA cm-2) has been investigated in detail. Optimum results are found with some of the amine salt systems. Morpholinium hydrogen sulphate allows smooth cycling of zinc up to 60 cycles. No passivation in the anodic halfcycle is observed. The corrosion current density is only 10 μA cm-2. Current efficiency for the electroplating of zinc in the cathodic halfcycle is high. A potential difference of about 300 mV between charge and discharge indicates the presence of a protective layer. Tendency for passivation is a general problem, especially for iron, and it has been studied in greater detail. The results are interpreted in terms of a salt-like layer rather than an oxide film. © 1990.