The characteristics of some organic expanders used in the negative active mass of the lead acid batteries can be studied by means of different electrochemical techniques, including electrochemical impedance, cyclic voltammetry and potentiostatic transients. Flat electrodes made from pure lead have been used in laboratory cells. The evaluation of the expanders performance carried out on the basis of the results of such techniques takes into account different important actions of the organic additives such as adsorption on lead and the kinetics of electrochemical reactions, which are all very important for the practical behaviour of the expanders in the negative plate of the lead-acid battery. Hydrogen evolution tests on negative plates can add useful information for the comparison of the results of laboratory electrochemical techniques with data which are closer to the practical operation of the system. Techniques for the chemical characterization of the expanders have also been considered and a tentative to compare the chemical properties to the electrochemical characteristics of the organic substances is presented. The need for clarifying possible correlations between chemical characterization and electrochemical tests is shortly discussed. This last point is mainly focused on the understanding of the action of the functional groups which are present in the organic molecules.
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