Polarization of Iron in H2S-NaHS Buffers

Abstract

Abstract Effects of H2S concentration, pH, and buffer capacity on the hydrogen evolution reaction are reported. Over-all electrode reaction in the presence of H2S is: The reaction is limited by H2S diffusion and by hydrogen overvoltage. Above the diffusion current, reaction is by decomposition of HS− or H2O. Expressions are derived for calculating the pH at the electrode surface at, above and below the diffusion current. After correcting for pH changes, Tafel slopes of 115 mv are found in 10−3 M HS− and 55–70 mv for higher concentrations of HS− below the diffusion current. Solutions of 10−1 and 10−2 M HS− develop protective films. Anodic polarization curves for these solutions show typical active-passive transitions, with very low residual currents in the passive region.