Browsing by Author "Kan, Wang Hay"

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    Development of mixed ion-electron conducting metal oxides for solid oxide fuel cells
    (2014-05-14) Kan, Wang Hay; Thangadurai, Venkataraman
    A 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.
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    Effect of V-doping on the structure and conductivity of garnet-type Li5La3Nb2O12
    (Springer, 2015) Kan, Wang Hay; Truong, Lina; Thangadurai, Venkataraman
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    Probing Surface Valence, Magnetic Property, and Oxide Ion Diffusion Pathways in B-Site Ordered Perovskite-type Ba2Ca0.67M0.33NbO6-d (M = Mn, Fe, Co)
    (Elsevier, 2016) Kan, Wang Hay; Dong, Pengcheng; Bae, Jong-Seong; Adams, Stefan; Thangadurai, Venkataraman
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    Surface and bulk study of strontium-rich chromium ferrite oxide as a robust solid oxide fuel cell cathode
    (Royal Society of Chemistry, 2015) Chen, Min; Paulson, Scott; Kan, Wang Hay; Thangadurai, Venkataraman; Birss, Viola
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    Trends in electrode development for next generation solid oxide fuel cells
    (Royal Society of Chemistry (RSC), 2016-11-10) Kan, Wang Hay; Samson, Alfred Junio; Thangadurai, Venkataraman
    High temperature electrochemical devices, such as solid oxide fuel cells (SOFCs), will play a vital role in the future green and sustainable energy industries due to direct utilization of carbon-based fuels and their ability to couple with renewable energies to convert by-products into valuable fuels using solid oxide electrolysis cells (SOECs). All-solid-state design provides a great opportunity toward the optimization of durability, cost, efficiency and robustness. Electrodes, one of the most important components that facilitate the electrochemical redox reactions, have been actively investigated for several decades to optimize a matrix of chemical composition, microstructure, and performance. Although some mixed ionic electronic conductors (MIECs) can provide electrochemically active surface with excellent chemical tolerance comparing to the composite electrodes made of conventional ceramic electrolyte and metal (cermet), their electrochemical activities may not be high enough to obtain a desirable power, even at moderate temperature operation. This shortage could be improved by engineering the microstructure of the electrodes, which control electrochemically active sites in SOFCs and SOECs. In this article, the current trends in electrode-engineering techniques for advanced SOFCs are reviewed.