Hydrogen Production by Water Dissociation in Surface-Modified BaCo x Fe y Zr

Dense perovskite membranes with mixed oxygen ion and electron conductivity have been intensively investigated as separator materials to produce pure oxygen from air or in membrane reactors for the partial oxidation of methane (POM) to synthesis gas, the oxidative dehydrogenation of light hydrocarbons (ODH) to olefins, or in the Ostwald process. It is accepted that oxygen permeation through a membrane involves 1) surface exchange between molecular oxygen and oxygen ions on the membrane surface and 2) bulk diffusion of the oxygen ion. The diffusion-controlled oxygen permeation flux can be increased by reducing the thickness of the membrane until its thickness reaches a critical value. Below the critical thickness, the surface exchange processes become rate limiting. In this case, the oxygen permeation flux can be enhanced by coating the membrane with materials that show a high exchange rate, such as cobalt-containing perovskites or noble-metal particles. It is worth noting that the surface reaction accelerated by the active materials in the above work is the oxygen ionization O2 + 4e Q2 O because only the inert gas He was used to sweep the permeated oxygen. Abstract: A porous perovskite BaCoxFeyZr0.9 x yPd0.1O3 d (BCFZ-Pd) coating was deposited onto the outer surface of a BaCoxFeyZr1 x yO3 d (BCFZ) perovskite hollow-fiber membrane. The surface morphology of the modified BCFZ fiber was characterized by scanning electron microscopy (SEM), indicating the formation of a BCFZ-Pd porous layer on the outer surface of a dense BCFZ hollow-fiber membrane. The oxygen permeation flux of the BCFZ membrane with a BCFZ-Pd porous layer increased 3.5 times more than that of the blank BCFZ membrane when feeding reactive CH4 onto the permeation side of the membrane. The blank BCFZ membrane and surface-modified BCFZ membrane were used as reactors to shift the equilibrium of thermal water dissociation for hydrogen production because they allow the selective removal of the produced oxygen from the water dissociation system. It was found that the hydrogen production rate increased from 0.7 to 2.1 mL H2 min 1 cm 2 at 950 8C after depositing a BCFZ-Pd porous layer onto the BCFZ membrane.