Electrochemical behaviour of lead electrode in sulfuric acid solution containing citric acid

The electrochemical behaviour of a lead electrode as the positive electrode (in PbO2 form) and the negative electrode of a lead/acid battery in sulfuric acid solution containing different concentrations of citric acid has been studied by cyclic voltammetry. For the behaviour of lead as a positive electrode, a new layer of PbO2 is formed in the presence of citric acid. It is difficult for this layer to be reduced and, therefore, the conductivity between the positive grid and the positive active material will be greater than that in pure sulfuric acid solution. The peak currents attributed to the formation and reduction of PbO2, and to the evolution of oxygen, increase with the concentration of citric acid. The limits of the effects are reached at about 2 g/1 citric acid in 4.5 M H2SO4. For the behaviour of lead as a negative electrode, the peak currents attributed to the oxidation of lead to PbSO4 and to the evolution of hydrogen gas also increase with the concentration of citric acid. In 4.5 M H2SO4, the limits of these effects are reached at a citric acid concentration of 2 and 3 g/1, respectively. The observed behaviour is caused by the adsorption of citric acid on the PbO2, lead and PbSO4 surfaces.