BaCe_0.5Zr_0.3Y_0.2–xYb_xO_3–δ proton-conducting electrolytes for intermediate-temperature solid oxide fuel cells

Highlights: •BaCe_0.5Zr_0.3Y_0.2–xYb_xO_3–δ proton conductors were prepared and characterized. •The ceramic with x = 0.1 (BCZYYb) exhibited largest grains and highest conductivity. •SOFC based on 25 μm-thick BCZYYb was successfully prepared and tested. •BCZYYb is conductive and stable electrolyte candidate for IT-SOFCs. -- Abstract: This work describes new findings concerning the preparation of Y- and Yb- co-doped BaCeO₃–BaZrO₃ materials, their structural, microstructural, electrical characterization and application as electrolytes for solid oxide fuel cell. The BaCe_0.5Zr_0.3Y_0.2–xYb_xO_3–δ (x = 0–0.2, Δx = 0.05) materials are successfully synthesized using a citrate-nitrate combustion method and then sintered at 1450 °C to form single-phase and highly dense ceramic samples. The sample with the BaCe_0.5Zr_0.3Y_0.1Yb_0.1O_3–δ (BCZYYb) composition is found to possess the largest grains coupled with the highest ionic conductivity. This ceramic material is used as an electrolyte for the fabrication an electrochemical cell designed as NiO–BCZYYb|BCZYYb (25 μm)|NBFC (where NBFC = Nd_0.5Ba_0.5Fe_1.9Cu_0.1O_3–δ), which demonstrates as maximal power density as 140 and 290 mW cm⁻² at 600 and 700 °C with open circuit voltages higher than 1.01–1.04 V, respectively. The separation of the total resistance of the cell in its ohmic and polarization components allows the film electrolyte conductivity to be calculated, which attains quite high level (2.4 and 3.8 mS cm⁻¹, respectively). This study shows that BaCe_0.5Zr_0.3Y_0.1Yb_0.1O_3–δ can be used instead of electrolytes with a lower Zr-concentration (for example, BaCe_0.7Zr_0.1Y_0.1Yb_0.1O_3–δ) with no significant deterioration of the transport properties.