Enhanced hydrogen permeability and reverse water–gas shift reaction activity via magneli Ti4O7 doping into SrCe0.9Y0.1O3−δ hollow fiber membrane

Abstract

Hydrogen proton conducting perovskite-based hollow fiber membrane is an attractive hydrogen separation technology that shows higher stability relative to Pd-based membranes above 800 °C. One of the challenges towards high hydrogen (H2) permeability on such proton conducting membrane is enabling simultaneously high proton and electronic conductivities to be achieved in single phase membrane. This has been addressed by developing dual-phase membrane. Here, we showed another promising approach, i.e., exploitation of beneficial phase reactions to create new conductive phases along the grain boundaries. By doping up to 8 wt. % magneli Ti4O7 into SrCe0.9Y0.1O3-d (SCY), Ce-doped SrTiO3 and Y-doped CeO2 were created in-between SCY grains. Electrical conductivity tests confirmed higher conductivities for 5 and 8 wt. % Ti4O7-doped SCY relative to SCY between 750 and 950 °C. These higher conductivities manifested into higher H2 permeation fluxes for the doped SCY membranes. The highest flux of 0.17 mL min-1 cm-2 was observed for 5 wt. % Ti4O7-doped SCY at 900 °C when 50 vol. % H2/He and 100 vol. % N2 were used in the feed side and the permeate side, respectively. This is much higher than the flux of 0.05 mL min-1 cm-2 obtained from SrCe0.9Y0.1O3 membrane at identical condition. More essential is the fact that the doped SCY membranes displayed catalytic activity for the reverse water-gas shift (RWGS) reaction which consumed H2 in the permeate side; increasing the H2 flux up to 0.57 mL min-1 cm-2 at 900 °C. The 5 wt. % Ti4O7-doped SCY furthermore showed stable flux for more than 140 h at 850 °C despite the formation of minor amount of SrCO3 in H2-CO2-containing atmosphere; highlighting its potential application as membrane reactor for RWGS or dehydrogenation reaction.