Masashi Shiota

Combined in situ EC-AFM and CV measurement study on lead electrode for lead–acid batteries

Abstract An electrochemical atomic force microscope (EC-AFM) was used to study the reaction of a lead electrode in sulfuric acid electrolyte, when the reaction corresponding to what occurs at the negative electrode of a lead–acid battery took place. At first, the AFM was applied to observation of the lead electrode during cyclic-voltammetry (CV) measurement, and was found to be useful to obtaining continuous in situ images of the surface morphology. These AFM images dynamically showed the surface morphology change during the oxidation/reduction cycle. From these observation results, it was visually confirmed that the quick deposition of lead sulfate crystals occurs after super-saturation phenomena at the oxidation peak on CV, and that the slow dissolving of the lead sulfate crystals occurs after the reduction peak. AFM images of the lead sulfate morphology after oxidation were then compared with those in a different potential sweeping rate and electrolyte concentration at CV. It was clearly found that the crystal size becomes smaller when the potential sweeping rate is fast or the electrolyte concentration is high. We also compared the difference in AFM images and SEM images that were observed on the same electrode sample.

In situ analysis of electrochemical reactions at a lead surface in sulfuric acid solution

Abstract An Atomic Force Microscope (AFM) was used to analyze the surface of a lead plate when the reaction corresponding to what occurs at the negative electrode of a lead acid battery, Pb+SO 4 2− ⇄PbSO 4 +2e, took place. At the beginning, when the lead plate, on the surface of which lead oxide already existed, was in contact with sulfuric acid, lead sulfate crystals were formed and gradually grew with time without applying any potential. In situ AFM observation of the formation and the growth of lead sulfate at the potential corresponding to the discharge reaction was attempted. And it was possible along with the reduction of the lead sulfate, which formed in discharging process. The results also showed that the chemically formed lead sulfate crystals were clearly different in appearance from the electrochemically formed ones. These results were also applied to a study of the mechanism of the sulfation process that often occurs in the active material of the negative electrode of a lead acid battery.

Study of charge acceptance for the lead-acid battery through in situ EC-AFM observation — influence of the open-circuit standing time on the negative electrode

An influence of the open-circuit standing time after oxidation of the lead electrode was investigated for understanding charge acceptance of the negative electrode of a lead-acid battery. It was confirmed by a potentiostatic transient experiment that charge acceptance of the lead electrode heavily depended on the standing time before charging, and charge acceptance decreased if the standing time was longer. This tendency was conspicuous at the initial period of the reduction process in particular. When the behavior of the lead electrode surface during the open-circuit standing after oxidation was observed by in situ electrochemical atomic force microscope (EC-AFM), it was found that some lead sulfate crystals gradually grow with time to bigger crystals having a smooth surface, retaining basically its morphology of previous one. We have concluded that the standing time dependence of the charge acceptance is caused by this behavior of the crystals. Also, it was confirmed that charge acceptance of a valve regulated lead-acid (VRLA) battery with different standing times can be explained by result of the potentiostatic transient test and the EC-AFM observation.

Reaction between lead oxide and lignin in aqueous solution

The reaction between lignin and the surface oxide layer on Pb plates was studied by dipping experiments in ultra pure water with lignin, anodic polarograms in sulfuric acid solution with or without lignin and also scanning electron microscopy (SEM) observations of the sample surface after anodic polarization. It is found that the lignin reacts with the surface oxide on the Pb plates in ultra pure water with lignin to reaction products containing Pb and the lignin and they grew preferentially at the interface between Pb and the surface oxide. The deposits formed on the surface suppress to passivate the Pb surface under sulfuric acid solution.

In Situ EC‐AFM Observation on Pb Electrodes in Sulfuric Acid Solution with or without Lignin

Surface morphologies of Pb electrodes in sulfuric acid solution with or without lignin at −20°C during anodic oxidation have been investigated by using in situ EC‐AFM combined with cyclic voltammetry (CV). Whether the lignin is added or not in the solution, it was found at −20°C that the precipitation of lead sulfate crystals occurs immediately after supersaturation of dissolved Pb2+ ions at the anodic oxidation peak on CV. It was also found that the number of lead sulfate crystals formed on the Pb electrode after anodic oxidation decreases and the crystal size becomes larger when the lignin is added in the solution.