Spectroscopic analysis of Cu2+ dissolved in Y- and Yb-doped barium zirconates and its impact on sinterability and proton conduction

Abstract

Y- and Yb-doped barium zirconates are currently the most promising proton conductors for application in fuel cells and electrolyzers. To achieve a high density without sintering at a high temperature of approximately 1600 °C, the addition of sintering aids, such as NiO, CuO, or ZnO, is necessary. However, the sintering mechanism and influence of the incorporation of sintering aids into the lattice on proton conduction remain unclear. In this study, the sintering mechanism was investigated using model experiments with diffusion couples between CuO and BaCe_0.4Zr_0.4Y_0.1Yb_0.1O_3−δ (BCZYY441), and the dissolution state of Cu and its effect on proton conduction were analyzed using Raman and ESR spectroscopy. The results revealed that the formation of a liquid phase is crucial for the sintering effect. ESR spectroscopy revealed that the sintering aids dissolved at the interstitial sites adversely affecting the proton conduction, especially the proton transference number. Therefore, processes to remove dissolved sintering aids or explore new sintering aids are necessary.