Investigation on properties of BaZr0.6Hf0.2Y0.2O3-δ with sintering aids (ZnO, NiO, Li2O) and its application for hydrogen permeation

Abstract

BaZr0.8Y0.2O3-δ proton conductor has the characteristics of excellent chemical stability, but its impoverished sinterability and low conductivity hinder its applications in fuel cell and hydrogen separation. Hf doping in Zr site improves BaZr0.6Hf0.2Y0.2O3-δ sinterability and conductivity. To further enhance BaZr0.6Hf0.2Y0.2O3-δ properties, three kinds of sintering aids ZnO, NiO or Li2O were introduced and their effect on the sinterability, microstructure and conductivity of BaZr0.6Hf0.2Y0.2O3-δ were studied. The experimental results display that 4 mol% ZnO can enhance the sinterability and conductivity of BaZr0.6Hf0.2Y0.2O3-δ sample sintered at 1400 °C. Compared with BaZr0.6Hf0.2Y0.2O3-δ sintered at 1600 °C, BaZr0.6Hf0.2Y0.2O3-δ with 4 mol% ZnO is of larger grain size, higher relative density (95.5%) and lower sintering temperature (reducing by 200 °C). Meanwhile, the conductivity of BaZr0.6Hf0.2Y0.2O3-δ with 4 mol% ZnO reaches 4.17 × 10−3 S cm−1 in wet 5% H2/Ar at 700 °C, due to the reduction of the grain boundary resistance of sample. BaZr0.6Hf0.2Y0.2O3-δ with 4 mol% ZnO membrane for hydrogen separation via external short circuit was developed. The membrane with a thickness of 1.08 mm gives a hydrogen permeation flux of 0.098 mL min−1cm−2 at 800 °C with 50% H2/He as feed gas. The presence of water vapor significantly promotes the hydrogen permeability of the membrane. In addition, introduction of 3% CO2 or 100 ppm H2S into feed gas does not decrease the hydrogen permeation flux of the membrane.