In situ synchrotron x-ray diffraction study of Zn/Bi 2 O 3 electrodes prior to and during discharge of Zn-air batteries: Influence on ZnO deposition

Abstract Zn-based electrodes containing different amount of Bi 2 O 3 have been analyzed by synchrotron XRD during the discharging process of a real Zn/air battery. Bi 2 O 3 is clearly detected for pristine Zn-Bi 2 O 3 based electrodes. However, immersion of Zn-Bi 2 O 3 electrodes in 6 M KOH solution before starting the discharge results in the disappearance of Bi 2 O 3 XRD signature in the pattern and the appearance of new peaks indicating the presence of metallic Bi, regardless of the amount of Bi 2 O 3 initially included in the Zn-Bi 2 O 3 electrodes. This behavior together with Open Circuit Voltage measurements points to a spontaneous reduction of Bi 3+ to metallic Bi by the oxidation of Zn to Zn 2+ . Irrespective of the amount of Bi 2 O 3 present in the negative electrodes, Zn XRD peaks diminish as the discharge proceeds. However, the initial amount of Bi 2 O 3 clearly affect to ZnO and Bi metal XRD peaks. ZnO peaks are observed only for electrodes without Bi 2 O 3 or those containing 6% of Bi 2 O 3 . Conversely, ZnO peaks do not appear in the XRD patterns obtained for higher quantities of Bi 2 O 3 electrodes. Besides, in this case metallic Bi peaks are observed during all discharging processes, indicating that Bi remained in the electrode. Finally, SEM and EDX studies support these conclusions.