Improving phase compatibility between doped BaZrO3 and NiO in protonic ceramic cells via tuning composition and dopant

Y-doped BaZrO3 (BZY) is a promising electrolyte candidate in fuel cells and electrolysis cells due to its high proton conductivity and excellent chemical stability. Currently, the most common method for cell fabrication is the co-sintering process performed at high temperature (e. g., 1500 °C). However, the co-sintering process imposes negative effect on the performance of these electrochemical devices, since due to the complicated phase relationship of the BZY – NiO system, second phases form and Y doping level decreases at the high co-sintering temperature. In this work, two strategies were adopted to solve such problem. Firstly, based on the information of phase diagram in our recent work, electrolyte with the composition close to BaZr0.88Y0.12O3-δ was prepared, and showed positive effect on suppressing the formation of second phases after co-sintering. Secondly, the half cell with the BaZr0.8Yb0.2O3-δ (BZYb20) electrolyte was fabricated, and the electrolyte layer showed improved uniformity of elemental distribution, and the Yb content was close to the nominal value. These results indicate that the phase compatibility between the BaZrO3-based electrolyte and NiO electrode substrate can be improved by simply tuning the composition and selecting proper dopants. However, these two strategies showed no effect on suppressing the diffusion of Ni from the electrode substrate into the electrolyte layer, which is driven by the high temperature heat treatment during co-sintering. Further analysis on the bulk samples added with 2 wt% NiO revealed that such diffusion of Ni imposed negative effect on the hydration ability, ionic conductivity and transport number.