Importance of pore structure control in porous substrate for high oxygen penetration in La_(0.6)Sr_(0.4)Ti_(0.3)Fe _(0.7)O_3 thin film for CH4_ partial oxidation

摘要

Effects of the pore structure of the support on the oxygen permeation rates of La_(0.6)Sr_(0.4)Ti_(0.3)Fe_(0.7)O _3 (LSTF) and La_(0.7)Sr_(0.3)Ga_(0.6)Fe _(0.4)O_3 (LSGF) films were investigated in this study. The pore structure of the support was an important factor for achieving a high oxygen permeation rate. Although LSGF membranes with the same thicknesses and compositions were used, the oxygen permeation rates increased with decreasing thickness of the substrate, suggesting a slow gas diffusion in substrate and so oxygen partial pressure on MIEC membrane may decrease comparing with that in gas phase. Oxygen permeation rates in LSGF membranes were also successfully simulated based on Fick's diffusion theory, and the model suggested that the gas diffusion in the porous substrate was highly important for achieving a high permeation rate in an asymmetric MIEC membrane. A laser manufacturing technique successfully prepared an LSTF substrate with straight pores, and the dense LSTF film with a 70 μm thickness was deposited on the prepared substrate. When the LSTF substrate with the straight pore structure was used for the LSTF film, the oxygen permeation rate was considerably improved and achieved a value as high as 15 cm~3/min cm~2 (three times higher than that for CH_4 fed to the substrate with random pores) under a CH_4 partial oxidation condition.