The voltammetry of Pt(322) and Pt(111) electrodes in 0.5 M H2SO4 solution was studied in the presence and absence of hydrazine. The amount of hydrazine adsorbed was measured by its oxidation reaction. The effects of the adsorbed hydrazine on hydrogen adsorption-desorption behavior were investigated intensively. Hydrazine adsorbs on both step and terrace sites between 0.10 and 0.30 V (vs. RHE). The saturation amounts at these two sites differ depending on the electrode potential. The oxidation potential of hydrazine on step sites is 0.2 V more positive than that on terrace sites. Hydrazine adsorbs preferentially on step sites. The shapes of the hydrogen adsorption-desorption voltammograms are strongly affected by the adsorption of hydrazine on step sites. At potentials between 0.2 and 0.3 V hydrazine repels hydrogen atoms from step sites and is adsorbed itself instead. Hydrogen atoms can adsorb on step sites in the potential range where hydrazine does not adsorb. One hydrazine species (N2H4 or N2H5+) replaces about four hydrogen atoms on the step sites. Hydrazine adsorbs on terrace sites of Pt(322) and Pt(111) electrodes in the potential between 0.1 and 0.3 V. The behavior of hydrogen adsorption on Pt(322) terrace sites is not changed by the adsorbed hydrazine.
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