A cobalt-free oxygen transport membrane, BaFe_(0.9)Zr_(0.1)O_(3-δ) and its application for producing hydrogen

摘要

Mixed ionic and electronic conductors are being explored for use as oxygen transport membrane (OTM) materials. An OTM material, BaFe_(0.9)Zr_(0.1)O_(3-δ) (BFZ), was fabricated by conventional solid-state synthesis, and its oxygen permeation flux was measured from 600 to 900 ℃. The BFZ is attractive for producing hydrogen because it is a cobalt-free material (resulting in low cost for fabrication) and has high oxygen permeation flux. The oxygen flux through a ≈ 0.45-mm-thick BFZ membrane exposed to flowing air and helium is ≈ 2.1 mL min~(-1) cm~(-2) at 900 ℃, and the activation energy for oxygen transport is 0.43 eV. With the results of the oxygen flux and the electrical conductivity for BFZ, its high oxygen permeability was explained. To show its potential application, the BFZ was tested in coal-gas-assisted water-splitting and ethanol (EtOH) reforming experiments. The hydrogen production rate of a 1.05-mm-thick BFZ tube was comparable to that of a much thinner ( ≈ 30 μm) La_(0.7)Sr_(0.3)Cu_(0.2)Fe_(0.8)O_(3-δ) thin-film tube. The EtOH reforming results also indicated significantly better performance of a BFZ disk compared with that of a Ba_(0.5)Sr_(0.5)Cu_(0.2)Fe_(0.8)O_(3-δ)/40 vol.% Ag disk. In addition, the crystal structure and the micro-structural behavior of BFZ fabricated in different conditions are discussed.