Effect of silver coating and doping of iron and cobalt on the oxygen permeability of la2nio4

Ion transport membrane (ITM) based reactor is one of the developing technologies for carbon dioxide capture and sequestration which integrates air separation and fuel conversion. These ITM reactors use mixed conducting oxygen permeable ceramic membranes which can simultaneously transport both oxygen ions and electrons without the requirement of an external circuit. However, the oxygen permeability of these membranes is relatively low which still hinders their use in industrial applications. One of the potential materials for oxygen permeability is the La2NiO4 (LNO), which is known for its high temperature stability.;In this study, LNO powders were synthesized by sol-gel method from nitrate solutions. These powders were compacted to obtain LNO membranes and characterized using Xray diffraction (XRD) and scanning electron microscopy (SEM). A gas permeation system was built for the oxygen flux measurement. This system was connected to a gas chromatograph for quantitative analysis. Thick membranes (1mm) were used for permeability measurements at temperature of 700°C.;The oxygen permeability of the LNO membrane was measured with different ratios of oxygen and nitrogen in the feed gas. The permeability increased with the increase in oxygen concentration on the feed side. The oxygen permeability was also tested with respect to temperature and the flux was found to increase with increasing temperature. A maximum oxygen flux of 0.064 imol cm -2s-1 (0.099ml min-1 cm-2) was obtained at temperature of 800°C. The activation energy was calculated to be 0.67eV.;A long term stability test was performed on the LNO membrane and the flux was found to decrease sharply at the starting and then stabilize. In order to further enhance the permeability, the LNO membrane was coated with silver paste on the feed side. Results showed an enhancement of upto 40% in the flux values as compared to the pure LNO membrane suggesting that silver acts as a catalyst for the surface reactions on the feed side. However, for the membranes coated with silver by using an ion sputtering instrument a decrease in the flux value was observed as compared to the pure LNO membrane. The reason could be attributed to the disintegration of the dense silver coating into small particles of silver distributed all over the membrane which reduced the effective surface area of the membrane exposed for permeation.;The LNO membrane was also doped with iron and cobalt so as to increase the bulk diffusion in the membrane. The doping of the LNO membrane with 20% iron decreased the flux values by about 25%. However, doping the LNO with 20% cobalt increased the permeation flux by 25% as compared to the pure LNO membrane. A maximum flux of 0.1 imol cm-2s-1 was obtained for the La2Ni0.75Co0.25O 4 membrane and the La2Ni0.70Co0.30O 4 membrane. Increasing the cobalt content further increased the amount of leakage in the system.