Highly dense barium cerate-zirconate electrolytes through a practical two-step sintering route for proton-conducting fuel cells

Proton-Conducting Fuel Cells nowadays represent the most promising technology for intermediate to low-temperature operating Solid Oxide Fuel Cells. One of the key requirements in the manufacturing of Proton-Conducting Fuel Cell, due to the high refractory nature of the materials, is the production of homogenous and high-density ceramic electrolytes to effectively separate the fuel and oxidizing gases. A variety of technologies are currently used to produce ceramic electrolytes, each characterized by specific advantages and limitations. In this study, dense Ba 1.1 Ce 0.6 Zr 0.2 M 0.2 O 3-δ (M = Y, Gd) ceramics were prepared to investigate the sintering process by introducing a two-step sintering optimization to obtain dense and defect-free electrolytes without the use of sintering aids. The optimized two-step method was compared with the conventional sintering route, using both in-house synthetized Ba 1.1 Ce 0.6 Zr 0.2 M 0.2 O 3-δ (M = Y, Gd) perovskite powders and a commercially available reference. The sintering optimization resulted in highly dense electrolyte (> 94%) showing reduced cracks and porosity, and greater grains dimension, 1.43 μm and 1.86 μm for Y and Gd doped structures, respectively. Conductivities studies on as-sintered electrolytes were carried out in different environments to assess how the sintering procedures affect proton conduction. Conductivities as high as 0.73·10 -2 S/cm and 1.30·10 -2 S/cm at 600 °C were obtained in wet hydrogen atmosphere for the two-step sintered Ba 1.1 Ce 0.6 Zr 0.2 M 0.2 O 3-δ (M = Y, Gd), confirming the optimized two-step sintering method as a reliable alternative to both conventional sintering and innovative sintering procedures such as microwave heating or cold sintering.