Ba2NiMoO6-δ as a potential electrode for protonic ceramic electrochemical cells

A novel layered double perovskite-based electrode of composition Ba2NiMoO6-δ (BNMO) is proposed for application in Protonic Ceramic Electrochemical Cells (PCECs). Structural characterization by X-ray diffraction (XRD) revealed good chemical compatibility with a BaCe0.7Zr0.1Y0.2O3-δ (BCZY712) electrolyte and phase stability in oxidizing atmospheres. In this study, symmetrical cells of both the pure BNMO electrode and a composite electrode with 50 vol% of BCZY712 material were prepared by screen printing and sintering in air at 950 °C. Microstructural characterization by Scanning Electron Microscopy (SEM) showed good adhesion of the electrode films with the substrate, while Energy-dispersive Spectroscopy (EDS) revealed good percolation of both phases in the case of the composite electrode. Electrochemical studies made by Electrochemical Impedance Spectroscopy (EIS) on the pure BNMO electrode demonstrated that the total polarization resistance was lower in wet conditions in the case of N2 atmospheres, corroborating a potential protonic contribution, while in O2 atmospheres this term was similar between wet and dry conditions, due to dominant p-type electronic conductivity. Conversely, performance was aggravated by the addition of the BCZY712 composite phase; a result clarified to be due to an insufficient level of electronic conductivity in the composite electrode. To the best of our knowledge this is the first study of BNMO for proton conducting applications, providing important information on preparation, compatibility and electrochemical performance, as required for its further optimization.