Appearance of new potential oscillation during hydrogen evolution reaction by addition of Na2SO4 and K2SO4

We have found that the hydrogen evolution reaction (HER) on platinum and gold electrodes in the 0.10 M or 0.14 M H2SO4 solution is anomalously affected only by the addition of Na2SO4 or K2SO4. In the absence of these salts, with a decreasing potential, the reduction current on the Pt electrode in the 0.10 M H2SO4 solution exponentially increases (in absolute value) below the hydrogen reversible potential, ca. −0.05 V vs. SHE, and almost linearly increases below ca. –0.15 V. In the presence of 0.03 M Na2SO4 or K2SO4, however, the reduction current hardly changes in the potential region between ca. −0.9 and −1.7 V. When the current is controlled, a new potential oscillation appears in this potential region. Almost the same behavior is also observed on the Au electrode. When the potential of the Pt electrode is controlled in the 0.14 M H2SO4 solution, the potential region where the reduction current hardly changes appears by the addition of 0.05 M Na2SO4, which is higher than that for 0.10 M H2SO4. We postulate that the decrease in the current by the addition of these salts is due to the decrease in the electromigration transport of hydrogen ions from the bulk solution to the electrode surface.