The charge-discharge characteristics and the aging mechanism of PbO 2 layers in contact with sulfuric acid solutions of different concentrations (1.5-5.0 M) were studied by using combined cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) techniques. For this purpose, thick lead dioxide layers were electrodeposited on gold substrate from aqueous solutions of Pb(NO 3) 2 dissolved in nitric acid. Based on the electrochemical and the mass change responses, it was found that in more concentrated solutions of H 2 SO 4 , the main reduction reaction was the transformation of lead dioxide to lead sulfate. However, in less concentrated sulfuric acid media, the transformation of lead dioxide to lead(II) ion became the main reaction. These Pb 2+ ions transformed into lead sulfate crystals later by a chemical reaction. Because the electrochemical oxidation of lead sulfate is less favourable in sulfuric acid medium of higher concentrations, thus, PbO 2 layers cannot be tested by continuous cyclization, which is necessary to study their aging parameters. Therefore, a delay step before each cyclic voltammogram was applied while the nonconductive lead sulfate dissolves or alternatively, by applying a pre-oxidation step prior to each cyclic voltammetry experiment to produce electrochemically significant amount of lead dioxide which can be reduced during the following negative potential sweep.

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<p class="PaperAbstract"><span lang="EN-GB">In recent decades, more and more electronic systems (start-stop, drive-by-wire, brake-by-wire) have been developed in the automotive industry therefore reliable power sources are necessary. It is essential to understand thoroughly the detailed behavior of the battery to increase its efficiency, stability and monitorability which is the most popular field nowadays. Over-discharge plays an important role in aging because it increases the probability of initiation of grid corrosion, sulfation and loss of active mass. In this work, the effects of over-discharge of lead-acid battery have been investigated via internal resistance increase and temperature change separately for both the negative and the positive electrode. Most of the measurements were carried out in a prepared test cell (which contained a negative and a positive plate, an Ag│Ag₂SO₄ reference electrode, a shunt for measuring current accurately) connected to a dummy battery and an electronic load.</span></p>

The charge-discharge characteristics and the aging mechanism of PbO 2 layers doped with bismuth in contact with sulfuric acid solutions were studied by using combined cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM) techniques. For this purpose, thick lead dioxide layers (non-doped and doped with Bi) were electrodeposited on gold substrate from aqueous solutions of Pb(NO 3 ) 2 dissolved in nitric acid and they were investigated in sulfuric acid media. Based on the electrochemical and the mass change responses, it is concluded that during the electrodeposition, bismuth influences the structure of the PbO 2 formed. Bi(III) also inhibits the oxidation of lead sulfate and affects the reduction kinetics of lead dioxide. During successive cyclization (aging), the presence of bismuth accelerates the hydration of PbO 2 .