Differential capacity curves of iron in perchloric acid in the presence of anions

Abstract

Influences of inorganic anions on the differential capacity ( C) vs. electrode potential ( E) curves of iron in perchloric acid solution system have been measured by the single pulse method. Three capacity maxima for HClO 4 alone are interpreted as being due to: (1) OH −1 desorption or, alternatively, reorientation of water dipole molecules; (2) adsorption of ClO 4 poststaggered−; and (3) adsorption of hydrogen evolution precursors. Heights of the capacity maxima and potentials at which they take place depend greatly on the perchloric acid concentration. Addition of Cl −, Br −, or SO 4 poststaggered− to the HClO 4 solution shifted the peaks and suppressed the curve over the entire potential region. Furthermore, new peaks attributable to the adsorption or desorption of added ions were observed. With l − the peaks were lacking and the curves were depressed, implying less reversible sorption of iodide ion than for the other halide ions. Adsorb ability of inorganic anions examined in these experiments was in the order: F − < SO 4 poststaggered−2 < Cl − < Br − < I −.