Hydrogen separation by Pd–CaZr0.9Y0.1O3−δ cermet composite membranes

A cermet composite membrane composed of a hydrogen-transporting metal (Pd) embedded in a thermodynamically stable, proton-conducting, ceramic matrix (CaZr0.9Y0.1O3−δ) was proposed to achieve the successful combination of high permeability and chemical stability in a CO2-containing atmosphere at elevated temperatures (>600 °C). The influence of both applied hydrogen chemical potential gradient and temperature on the hydrogen permeation properties of 0.5-mm-thick, Pd–CZY cermet membranes were studied using dry feed gases with 20–80% H2. The hydrogen permeation flux increased from 1.3 to 2.3 cm3(STP)/min-cm2 with increasing temperature and pH2pH2 gradient. The effect of the ceramic matrix on the permeability of the Pd–cermet membranes was also compared. The proton-conducting ceramic matrix exhibited the maximum hydrogen permeation flux, which was attributed to the additional ambipolar hydrogen permeation through the cermet membrane. Finally, the hydrogen permeability in CO2-containing gas streams was investigated using a dry feed gas stream comprised of 30% CO2, 20% H2 and 50% He. The decrease in hydrogen permeation flux with increasing temperature was ascribed to the decrease in the H2 content in the feed gas stream as calculated using the Gibbs energy minimization method.

Graphical abstractAll hydrogen permeation flux values were normalized to a thickness of 0.46 mm. The highest hydrogen permeation flux of Pd–CZY may be ascribed to the effect of ambipolar diffusion of the proton-conducting matrix. The ambipolar oxygen flux may plausibly have occurred against hydrogen permeation due to the simultaneous application of the oxygen potential gradient while maintaining the hydrogen partial pressure gradient.Figure optionsDownload full-size imageDownload as PowerPoint slide