Oxygen transport in La2NiO4 + δ: Assessment of surface limitations and multilayer membrane architectures

The steady-state oxygen permeation through dense La2NiO4 + δ ceramics, limited by both surface exchange and bulk ambipolar conduction, can be increased by deposition of porous layers onto the membrane surfaces. This makes it possible, in particular, to analyze the interfacial exchange kinetics by numerical modelling using experimental data on the oxygen fluxes and equilibrium relationships between the oxygen chemical potential, nonstoichiometry and total conductivity. The simulations showed that the role of exchange limitations increases on reducing oxygen pressure, and becomes critical at relatively large chemical potential gradients important for practical applications. The calculated oxygen diffusion coefficients in La2NiO4 + δ are in a good agreement with literature. In order to enhance membrane performance, the multilayer ceramics with different architecture combining dense and porous components were prepared via tape-casting and tested. The maximum oxygen fluxes were observed in the case when one dense layer, ~ 60 μm in thickness, is sandwiched between relatively thin (< 150 μm) porous layers. Whilst the permeability of such membranes is still affected by surface-exchange kinetics, increasing thickness of the porous supporting components leads to gas diffusion limitations.