Zn-based electrodes containing different amount of Bi2O3 have been analyzed by synchrotron XRD during the discharging process of a real Zn/air battery. Bi2O3 is clearly detected for pristine Zn-Bi2O3 based electrodes. However, immersion of Zn-Bi2O3 electrodes in 6 M KOH solution before starting the discharge results in the disappearance of Bi2O3 XRD signature in the pattern and the appearance of new peaks indicating the presence of metallic Bi, regardless of the amount of Bi2O3 initially included in the Zn-Bi2O3 electrodes. This behavior together with Open Circuit Voltage measurements points to a spontaneous reduction of Bi3+ to metallic Bi by the oxidation of Zn to Zn2+. Irrespective of the amount of Bi2O3 present in the negative electrodes, Zn XRD peaks diminish as the discharge proceeds. However, the initial amount of Bi2O3 clearly affect to ZnO and Bi metal XRD peaks. ZnO peaks are observed only for electrodes without Bi2O3 or those containing 6% of Bi2O3. Conversely, ZnO peaks do not appear in the XRD patterns obtained for higher quantities of Bi2O3 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.