Thangadurai, VenkataramanKan, Wang Hay2014-05-142014-06-162014-05-142014Kan, W. H. (2014). Development of mixed ion-electron conducting metal oxides for solid oxide fuel cells (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/25682http://hdl.handle.net/11023/1519A solid oxide fuel cell (SOFC) is an energy conversion device, which directly converts chemical fuels (e.g., H2, CxHy) into electricity and heat with high efficiency up to 90%. The byproduct of CO2 can be safely sequestrated or subsequently chemically transformed back into fuels(e.g., CO, CH4) by electrolysis using renewable energy sources such as solar and wind. The stateof-the-art Ni-YSZ anode is de-activated in the presence of ppm level of H2S and forming coke in hydrocarbons. Currently, mixed ion and electron conductors (MIECs) are considered as alternatives for Ni-YSZ in SOFCs. The key goal of the research was to develop mixed ion-electron conducting metal oxides based on B-site disordered perovskite-type Ba(Ca,Nb)1-xMxO3-δ (M = Mn, Fe, Co), the B-site 1:1 ordered perovskite-type (M = Mn, Fe, Co) and the Sr2PbO4-type Sr2Ce1-xPrxO4 for SOFCs. Ba2(Ca,Nb)2-xMxO6-δ was chemically stable in 30 ppm levels of H2S at 600 °C for 24 h and in pure CO2 at 800 °C for 24 h. The thermal expansion coefficients (TEC) of the as-prepared ordered perovskites was found to be comparable to Zr0.84Y0.16O1.92 (YSZ). The near-surface concentration of Fe2+ in Ba2Ca0.67Fe0.33NbO6-δ was found to be about 3 times higher than that in the bulk sample. The electrochemical performance of Ba2Ca0.67M0.33NbO6-δ was assessed by ac impedance spectroscopy using a YSZ supported half-cell. The area specific polarization resistance (ASR) of all samples was found to decrease with increasing temperature. The ASR for H2 gas oxidation can be correlated to the higher concentration of low valence Fe2+ species near-surface (nano-scale). BaCa0.335M0.165Nb0.5O3-δ crystallizes in the B-site disordered primitive perovskite (space group Pm-3m) at 900 °C in air, which can be converted into the B-site 1:2 ordered perovskite (space group P-3m1) at 1200 °C and the B-site 1:1 ordered double perovskite phase (space groupFm-3m) at 1300 °C. The chemical stability of the perovskites in CO2 and H2 highly depends on the B-site cations ordering. The B-site disordered primitive perovskite phase is more readily reduced in dry and 3% H2O in 10% H2 balanced with 90% N2, and is less stable in CO2 at elevated temperatures, compared to the B-site 1:1 ordered double perovskite phase. The thermal decomposition is highly suppressed in Sr2Ce1−xPrxO4 compounds for Pr > 0, suggesting that Pr improves the thermal stability of the compounds. Rietveld analysis of PXRD and SAED supported that both Pr and Ce ions are located on the 2a site in Pbam. Conductivity increases with Pr content in Sr2Ce1−xPrxO4. The highest total conductivity of 1.24 x 10−1 S cm−1 was observed for Sr2Ce0.2Pr0.8O4 at 663 °C in air.engUniversity of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission.Chemistry--Inorganicmixed ion and electron conductors (MIECs)solid oxide fuel cells (SOFCs)perovskitebarium calcium niobate (BCN)Sr2PbO4-typedoctoral thesis10.11575/PRISM/25682