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

Abstract

BaZr_0.4Ce_0.4Y_0.1Yb_0.1O_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_0.4Ce_0.4Y_0.1Yb_0.1O_1.9 (ZCYYb4411) addition as a sintering aid. All methods yielded pure ceramics adopting the I4/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_0.4Ce_0.4Y_0.05Yb_0.1Zn_0.05O_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 N₂ underscoring the effectiveness of these approaches in enhancing the sintering of BZCYYb4411 while maintaining a high level of conductivity.