Oxygen transport kinetics of the oxygen interstitial system lanthanum praseodymium nickel oxide and cation ordered double perovskite-Ln barium cobalt oxide (Ln = praseodymium and neodymium) oxides

The main purpose of this dissertation is the development of the new cathode materials for intermediate temperature solid oxide fuel cells (SOFC).; The oxygen transport kinetics of the oxygen interstitial system La xPr2-xNiO4+delta and cation ordered double perovskite---LnBaCo2O5+delta (Ln = Pr and Nd) by electrical conductivity relaxation (ECR), DC conductivity, and AC impedance spectroscopy were studied. The measured values were compared with those obtained from isotope exchange and depth profiling (IEDP).; The ECR experiment gave the oxygen transport kinetics parameters---oxygen diffusion coefficients ( DO2- ) and surface exchange coefficients (kex) for bulk dense samples. Assuming the ALS model which contains DO2- and kex, the cathode performance of La xPr2-xNiO4+delta was estimated by AC impedance spectroscopy for porous samples. The oxygen transport kinetics from different techniques had a good agreement. It was found that both values of DO2- and kex for PrBaCo2O5+delta (PBCO) and NdBaCo2O5+delta (NBCO) measured by ECR were remarkably high at low temperatures (300 ∼ 500 °C).; The dense thin films with well-defined microstructures and geometry were studied for La2NiO4+delta (LNO) and PBCO by ECR and IEDP. The ECR and isotope measurements agree well, though the ECR data indicate the presence of two distinct kinetics pathways. The oxygen surface exchange kinetics of PBCO thin film is much faster than those of disordered perovskite LaSrCo2O6-delta.; The oxygen transport studies by AC impedance for LNO and PBCO polycrystalline thin film on YSZ single crystal substrates suggested the rate determining step of the oxygen reduction reaction. Two different oxygen reduction models were proposed for PBCO.