Electrochemical behaviour of bismuth in sulfuric acid solution

Bismuth is considered to be a detrimental element to lead–acid batteries because it has lower hydrogen evolution overpotential than lead. On the other hand, bismuth can improve the performances of negative or positive active-materials. It is necessary to understand the performance of bismuth in sulfuric acid solution in order to reduce its detrimental effect on lead–acid batteries and make good use of its beneficial aspects. In this paper, the electrochemical behaviour of bismuth in sulfuric acid solution is studied by cyclic voltammetry (CV), chronoamperometry (CA), electrochemical impedance spectroscopy (EIS), scanning electronic spectroscopy (SEM), and X-ray diffraction (XRD). At potentials near close to the open-circuit value bismuth dissolves actively when it is anodized. As the potential increases, two oxidation peaks are observed. The first peak corresponds to the formation of bismuth sulfate, that follows a dissolution–precipitation mechanism and suppresses the dissolution of bismuth. The second peak due to secondary oxidation of bismuth under the bismuth sulfate film. There is a large current plateau at higher potentials this involves the dissolution of bismuth sulfate into solution, the formation of bismuth sulfate from bismuth oxide, and the formation of bismuth oxide from matrix bismuth. Hydrogen evolution takes place on bismuth just after the potential where the reduction of lead sulfate is completed. Oxygen evolution cannot occur on bismuth covered with bismuth sulfate.