Over the past years, several studies have shown that the addition of certain amounts and types of carbon can maintain the negative active-material of lead–acid batteries in a healthy condition, even under the demanding application of high-rate partial state-of-charge cycling. Unfortunately, however, the presence of extra carbon can also degrade battery performance. A particular problem is increased water consumption due to higher hydrogen evolution at the negative electrode. Carbon usually exhibits a lower hydrogen overpotential than lead and additionally enlarges the specific surface-area of the electrode. Thus, during charging, an appreciable gassing current is generated on the carbon surface such that water in the electrolyte solution is consumed and the concentration of sulfuric acid is increased. This situation impedes proper charging and shortens battery life. A state-of-the-art method has therefore been developed to investigate the hydrogen evolution reaction (HER) on pure carbon additives in sulfuric acid solution. By employing a rotating disc electrode set-up together with drop cast carbon electrodes, it is possible to reduce the influence of binders and bubbles in order to obtain distinct Tafel behaviour. An initial attempt has been made to link the physical and chemical properties of carbon additives with the gassing current. Therefore, the on-set potentials and Tafel slopes of different carbon additives have been determined and compared. It is found that the specific surface-area of the carbonaceous material is an important parameter that correlates with the electrocatalytic activity. Some evidence has also been obtained to suggest that surface oxides might have a major impact on the gas evolution.
Fraunhofer Institute for Silicate Chemistry ISC - Center for Applied Electrochemistry
Biography: Jochen Settelein received his Master of Science in 2012 from the University of Wuerzburg with focus on surface and semiconductor physics. Since 2013, he has been studying for a PhD at the same University and also works as a research associate at the Center for Applied Electrochemistry at the Fraunhofer Institute for Silicate Research ISC.