Fluorine-doped barium cobaltite perovskite membrane for oxygen separation and syngas production

Chemical bonds created between cations and oxygen ions perform a critical role in the oxygen permeability of perovskite oxides. Here, fluorine was doped into the O-sites of perovskite to weaken metal-oxygen bonds and successfully synthesize Ba_0.5Sr_0.5Co_0.8Fe_0.17Y_0.03O_3-δF_0.09 oxides. The crystal structure, morphology, and oxygen permeability of the Ba_0.5Sr_0.5Co_0.8Fe_0.17Y_0.03O_3-δF_0.09 oxides were investigated. The results indicated that partial substitution of oxygen ions with those of fluorine greatly enhanced the oxygen permeation flux. Both thermogravimetric analysis and O₂-TPD results indicated that more O₂ escaped from F-doped perovskite and more oxygen vacancies were generated. The O 1s XPS spectra showed that the lower metal-oxygen bond energy was responsible for the improved oxygen permeability of F-doped perovskite. Oxygen permeation flux reached 3.15 ml min⁻¹ cm⁻² at 900 °C and was maintained at approximately 3 ml min⁻¹ cm⁻² for 1300 h in the oxygen permeation test. A membrane reactor equipped with an F-doped disc membrane was constructed to produce syngas, reaching 99% methane conversion and an 88% carbon monoxide selectivity at 900 °C.