Impact of sintering procedures on the densification and conductivity of BaZr0.4Ce0.4Y0.1Yb0.1O3-δ electrolyte for protonic ceramic fuel cells

BaZr 0.4 Ce 0.4 Y 0.1 Yb 0.1 O 2.9 (BZCYYb4411), a promising proton-conducting electrolyte, requires high sintering temperatures, typically 1600 °C, to be densified to acceptable relative densities, greater than 90 %. This study explores three sintering strategies to reduce the sintering temperature to 1400 °C. The approaches include (1) external ZnO addition, (2) internal Zn doping, and (3) fluorite-phase Zr 0.4 Ce 0.4 Y 0.1 Yb 0.1 O 1.9 (ZCYYb4411) addition as a sintering aid. All methods yielded pure ceramics adopting the I 4/ mcm tetragonal perovskite phase, with Zn-based strategies achieving relative densities above 90 %. In contrast, the addition of the fluorite phase proved less effective, particularly at higher concentrations. In most cases, the conventional calcination step was avoided, and a relative density above 90 % was achieved through single-step sintering at 1400 °C, thereby improving energy efficiency and simplifying the process. The selected samples were subjected to SEM analysis and conductivity testing, revealing a high conductivity level: BaZr 0.4 Ce 0.4 Y 0.05 Yb 0.1 Zn 0.05 O 3-δ reached 0.9 × 10 −2 S cm −1 , while BZCYYb4411 with 0.5 wt% ZnO addition achieved 0.6 × 10 −2 S cm −1 at 700 °C in humidified N 2 underscoring the effectiveness of these approaches in enhancing the sintering of BZCYYb4411 while maintaining a high level of conductivity. • The proton-conducting BZCYYb4411 electrolyte was synthesized using the glycine nitrate process. • The I 4/ mcm space group was confirmed for the BZCYYb4411 structure based on neutron diffraction data. • Three sintering strategies were tested: internal Zn doping, external ZnO aid, and external ZCYYb4411 aid. • A single sintering step at 1400 °C for 10 h, without prior calcination, yields a relative density above 90 %. • In humidified N 2 at 700 °C, σ = 0.6-0.9 × 10 −2 S cm −1 for BZCYYb4411 + 0.5 wt % ZnO and BaZr 0.4 Ce 0.4 Y 0.05 Yb 0.1 Zn 0.05 O 3-δ .