Hydrogen and oxygen evolution in sealed lead/acid 2 V cells. In situ gas measurement by Raman spectroscopy

Hydrogen, oxygen, nitrogen pressures inside five sealed lead/acid 2 V cells of 10 Ah are measured by Raman spectroscopy. Gas evolution is determined during short-term overcharge and rest periods. During the rest period, the oxygen reduction rate is in agreement with recently published data. Using qualitative data, it seemed that during overcharge, the oxygen reduction does not totally hinder the hydrogen evolution which is consequently much higher than expected. However, we observed that in our case hydrogen evolution is not correlated with the oxygen reduction rate assuming that the oxygen cycle is not fully accomplished, though oxygen reduction takes place. As a consequence and for evident balance of current, hydrogen evolution increased. Possible explanations are: mixed potential at the negative electrodes; grid corrosion, or oxidation of organic impurities at the positive electrodes.