Evaluating oxygen diffusion, surface exchange and oxygen semi-permeation in Ln2NiO4+δ membranes (Ln=La, Pr and Nd)

To clearly identify the rate determining step (r.d.s.) in the oxygen semi-permeation of dense Ln2NiO4+δ membranes (with Ln=La, Pr and Nd), a specific apparatus was designed to measure the oxygen semi-permeation flux and activity gradient at both membrane surfaces. From these measurements, the coefficients for the oxygen diffusion and surface exchange at both membrane surfaces were determined. Their values were compared to the values reported in the literature for similar membrane materials. We concluded that the oxygen flux through these membranes was limited by the oxygen surface exchange at the oxygen-lean face and not oxygen volume diffusion, as previously claimed.