Chemical and mechanical stability of BCZY-GDC membranes for hydrogen separation

This work investigates, for the first time, the hydrogen permeation of BaCe0.65Zr0.20Y0.15O3-δ-Ce0.8Gd0.2O2-δ (BCZY-GDC) asymmetric membranes for 100 h, using wet 15% CO2 in Ar as sweep gas. In the same frame, ex-situ aging tests were performed for 100 h exposure at 750 ◦C in different atmospheres (H2, CO2, H2 + CO2), to evaluate the phase, microstructure, and mechanical long-term stability of this system. The thermal aging in H2-atmosphere leads to lower flexural strength caused by a microstructure embrittlement of the BCZY-GDC asymmetric membrane, due to chemical expansion/contraction of the GDC cell after the aging cycle. Indeed, microcracking of GDC grains, that decreases the composite hardness, is observed in symmetric (pressed pellet) membranes. The aging in CO2 causes a slightly increase in flexural strength values due to the formation of submicrometric Zr-doped ceria-BaCO3 phases at the expense of the perovskite. Higher hardness values related to the emerging of BaCO3 islands on the symmetric membrane surface were also recorded. In H2 + CO2 atmosphere (real testing condition), the membrane shows a slight decrease in flexural strength and hardness while no evident morphological or structural changes (except the BaCO3 formation in traces) were observed. This study highlights that promising and stable hydrogen permeation flux values can be recorded using the asymmetric configuration for 100 h, using wet 15% CO2 in Ar as sweep gas. Neither structural nor morphological modification of the membrane were detected after the testing.