Catalytic Deposition of ZnO on Bi2O3 Surface Towards Prolonged Zn-Based Aqueous Rechargeable Battery

Tuesday, 31 May 2016: 14:00
Indigo Ballroom B (Hilton San Diego Bayfront)
J. Shin, R. Kumar, J. M. You (University of California, San Diego), J. Wang (UCSD), and Y. S. Meng (University of California, San Diego)
Recently, the demand for the large-scale power system has gained much interest due to the increase in energy demand. Scientists recognize load leveling as one of the most crucial aspect in making efficient large-scale power generation. Electrical energy storage (EES) system is most promising type of energy storage systems. Among number of criteria for the large-scale EES, low cost is one of the main focus. To achieve low cost of EES, Zn based aqueous battery should be utilized in the EES, due to the abundance and low cost of Zn and water. However, Zn based aqueous battery suffers from an intrinsic problem. When the Zn is oxidized to ZnO, Zn(OH)4-2 ion, intermediate phase is formed. This ion is soluble in aqueous electrolyte. When Zn is oxidized, most of the Zn2+ ion detaches from the current collector becoming inactive in the electrochemical process and the battery becomes non-rechargeable. There is a large number reports using Zn electrode in an electrochemical cell. Among them, numerous reports have suggested the use of Bi2O3 as an electrode additive. By simply mixing in the Bi2O3 to the Zn electrode, the electrochemical performance suddenly improves. Thus far in the literature, most explanation for such a phenomenon is improvement in the electrical conductivity. Due to the presence of Bi2O3, a better electrical connection is formed and thus the electrochemical performance is improved. However, electrical conductivity does not have an effect on the intrinsic chemical reaction of Zn oxidation. Here, we have conducted a series of characterizations to understand the mechanistic role of Bi2O3 in the Zn electrode. We have utilized electrochemistry, energy-dispersive X-ray spectroscopy mapping under scanning electron microscope, powder X-ray diffraction (PXRD), Raman spectroscopy, and X-ray photoelectron spectroscopy. Upon oxidizing the Zn electrode, the Bi2O3 surface was covered with ZnO. This ZnO had interactions with the Bi2O3 which was found in PXRD and Raman spectroscopy. We have discovered that the mechanism for the improved performance in the Zn based electrode with the presence of Bi2O3 is due to a surface catalytic deposition of ZnO. With the presence of Bi2O3, Zn oxidation reaction seems to skip the soluble Zn(OH)4-2 phase formation and directly deposits ZnO onto the surface of Bi2O3. This finding open the way for further optimizing the Zn based electrodes for rechargeable aqueous batteries