20BaO·5MnO2·5NiO·70V2O5 glass was synthesized by melting the mixture composed of BaCO3, MnO2, NiO, and V2O5 at 1100 °C for 2 hours. The vanadate glass was annealed at 450 °C for various times (0, 30, 60, and 300 min.). Pulverized vanadate glass was utilized for the preparation of the air electrode by mixing the powder with 7.5 mass% of poly (tetrafluoroethylene) (PTFE), which was hot-pressed on a gas diffusion layer over a Ni metal mesh.
The electrode connected to a Cu wire was mounted onto the window of Teflon-made cell. 8M KOH aqueous solution and a Pt mesh were placed inside the Teflon cell as the electrolyte and the counter electrode, respectively. The temperature of the Teflon cell was held constant by soaking it into a water tank kept at 60 °C. Anodic and cathodic polarization measurements were carried out using a potentiostat. An Hg/HgO electrode was used as the reference electrode.
The electrical conductivity of the as-prepared vanadate glass was 5.4 × 10 -6 S cm-1 at RT. After the annealing at 450 oC for 300 min, it increased to 1.1 × 10 -2 S cm-1. Figure shows the anodic and cathodic polarization curves of 20BaO·5MnO2·5NiO·70V2O5 glass electrodes. The vanadate electrode showed an excellent bifunctional oxygen reduction/evolution activity, being comparable to that of the materials reported in the literature, like polycrystalline LaNiO3 . This vanadate glass could be a highly potential candidate for the bifunctional catalytic material for the rechargeable metal-air battery.
1) K. Matsuda, S. Kubuki, and T. Nishida, AIP Conf. Proc. (msms2014) 1622, 3-7 (2014).