Potential oscillation during electrolysis of water in acidic solutions under numerous conditions

We have revealed that a novel potential oscillation occurs in hydrogen evolution reaction (HER) during water electrolysis, not only when H2SO4 solutions are used as electrolytes as has been reported in our earlier papers (Mukouyama et al., 2008; 2013), but also when a large variety of acid solutions are used as electrolytes. When the acid concentration is lower than ca. 0.1 M, the electrode potential oscillates spontaneously under current controlled conditions in a high overpotential region, e.g. more negative than ca. −1.0 V vs. SHE. The oscillation appears by addition of a small amount of salts, such as LiClO4, Na2SO4, K2SO4 and MgSO4, even when the acid concentration is higher than ca. 0.1 M. We have also found that the oscillation occurs not only when Pt, Au or Cu is used as a working electrode as has been reported in the papers but also when various metal substrates such as Rh, Ag, Fe, Ni, W, Zn, Sn and In are used. It was revealed that the local pH at the electrode surface oscillates between acidic and basic synchronously with the potential oscillation. The mechanism of the oscillation can be explained by an autocatalytic bubble evolution and the changes in the local pH and in the concentration of dissolved hydrogen at the electrode surface due to the bubble evolution.