Ceria-doped scandia-stabilized zirconia (10Sc2 O3 ·1CeO2 ·89ZrO2 ) as electrolyte for SOFCs: Sintering and ionic conductivity of thin, flat sheets (original) (raw)
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Samples of 6 mol% Sc2O3- 1 mol% CeO2 co-doped ZrO2 were fabricated by conventional ceramic processing methods and sintered at various temperatures from 1000 °C to 1650 °C in air. The sintering conditions on microstructure and phase content are investigated using various characterization methods, including pycnometry, diffraction, and spectroscopy. The electrical conductivity of samples was investigated using electrochemical impedance spectroscopy (EIS). The effect of inductive load (measured from room temperature to 800 °C) is discussed in low to high-temperature regimes. At T<400 °C since the arc is not a complete semicircle, the high-frequency arc could be fit using a constant phase element (CPE), while by subtraction of inductive load, a good fit is achieved using a capacitor element instead of CPE. The Arrhenius conductivity plot of samples reveals that the specimen sintered at 1600 °C for 6 hours exhibits the highest conductivity. The activation energy (Ea) and conductivity ...
Characterisation of Submicron-Grain Sized Yttria-Stabilised Zirconia Electrolyte for SOFCs
Journal of Materials Science and Engineering A
This paper investigates the effect of grain size within the nano to micron regime on ionic conductivity for yttria stabilised zirconia (YSZ) with various yttria levels. The samples were made using either slip casting or die pressing routes and were characterised via the use of 4-point electrical conductivity, AC impedance, high resolution transmission electron microscopy (HRTEM) and a field emission gun scanning electron microscope (FEGSEM). Little variation in ionic conductivity was noted over the range of grain sizes examined; rather the yttria content had the largest effect. The greatest variation was noted between the 3 mol% YSZ and 8 mol% YSZ where the conductivity was seen to vary by ~65% at 850 °C. This work forms part of an investigation into the potential use of fine grained zirconias as electrolytes in solid oxide fuel cell (SOFC) applications.
AIP Conference Proceedings, 2020
Solid oxide fuel cells (SOFCs) are considered an alternative electric power generation systems due to high energy conversion efficiency, fuel flexibility, and operation directly on natural gas. One important challenge in SOFC commercialization is to reduce its operating temperature to intermediate temperature (IT) range. Ceria based material has shown potential to enhance oxy ion conductivity by aliovalent doping. Co-doping approach is strategically applied as it gives more flexibility in a valence-size mismatch in host lattice of ceria and thus more degrees of freedom for materials behavior manipulation. In ceria for every two trivalent or one divalent dopant ions that replace Ce 4+ ions, one oxygen vacancy is generated to balance the charge. Sm and Sr as co-doping approach contribute to oxy-ion conductivity for functioning of SOFCs. In this attempt we focused on effect of sintering temperature on structural, microstructural and electrical properties of ceria based material for IT-SOFCs. With this motivation we have synthesized Sm and Sr based codoped ceria system (SSRDC) by hydrothermal synthesis route. We vary sintering temperature from 1100 and 1300 O C. The structural and microstructural changes with respect to increasing sintering temperature and its influence on formation of oxygen vacancies and hence on ionic conductivity studied systematically.
Doped zirconia and ceria-based electrolytes for solid oxide fuel cells: A review
Zirconia and ceria possess fl uorite-type structure and conduct electricity by means of oxide ion transport through the lattice. On doping, vacancies created at the oxygen site make way for the neighbouring oxygen atoms to ‘hop’ in the direction of electric fi eld. Among doped zirconia, 8 mol% yttria-stabilized zirconia and 9–11 mol% scandiastabilized zirconia exhibit the highest conductivity. Ceria electrolytes require lower operational temperature (~600–800°C) compared to that of zirconia electrolytes (800–1000°C). With improvement in the processing and fabrication techniques, researchers have developed thinner electrolytes to minimize ohmic polarization and enhance the ionic conductivity enabling operation at lower temperatures (~400–600°C). But such electrolytes are required to be supported on electrodes (anode or cathode) and in later times heterostructured bi-, tri- and multi-layered electrolyte films have been constructed. Since the last decade, development of submicron grain size electrolytes and ultimately two-phase materials with nanodimension grain size has shown improvement in ionic conductivity as well as low-temperature workability. The article reviews the turning points in the technological development of fl uorite-based solid oxide fuel cell electrolytes from single-phase micrometer dimension grain size to recently developed two-phase nanocomposites and nanowires, and the successful achievement of its workability at low temperatures (~450°C).
Solid State Ionics, 2009
The effects of cobalt addition (0.5 and 1 wt.%) on densification and ionic conductivity of Ce 0.9 Sm 0.1 O 1.95 (10SDC) and Ce 0.9 Sm 0.075 Y 0.025 O 1.95 (2.5Y-SDC) have been studied. X-ray diffraction (XRD) showed that Co had changed to Co 3 O 4 and Co 3 O 4 + CoO after firing at 900°C and 1300°C respectively. The addition of Co promoted densification to occur at lower temperatures with a more uniform grain growth and greatly improved both grain boundary and bulk conductivity for 10SDC. Significant improvement of grain boundary for the 2.5Y-SDC samples was obtained, even at 1300°C sintering, while bulk conductivity was slightly improved. Rapid grain growth along with improvement of ionic conductivity was observed when the samples were sintered further at higher temperature. Superior ionic conductivity of the 2.5Y-SDC samples with Co addition to that of the bare 10SDC suggested the potential use of Co as the co-dopant in this system to reduce the content of costly rare earth usage.
Processing and Application of Ceramics
Nanosized multi-doped ceria with composition Ce0.8Nd0.0025Sm0.0025Gd0.005Dy0.095Y0.095O2-? (CNSGDY) as perspective solid ionic conductor was obtained by modified glycine-nitrate procedure (MGNP) and room temperature self-propagating reaction (SPRT). The pressed pellets of both powders were sintered at 1550?C for 2 h in an air atmosphere. The obtained sintered samples were characterized by XRPD, Raman spectroscopy, FESEM, EDS and EIS methods. Despite a high temperature of sintering, XRPD and FESEM analyses of the samples confirmed appropriate dimensions of grains with fluorite structure. Overall concentration of introduced dopants (x = 0.2) in the structure of CeO2 after the sintering process was confirmed by EDS analysis. After sintering, Raman spectroscopy confirmed retention of the oxygen vacancies in the ceria lattice, which is in accordance with the improvement of ionic conductivity of solid ionic conductors. The highest value of total conductivity was obtained for the sintered ...
Scandia-stabilized-zirconia is a potential zirconia-based electrolyte for intermediate temperature solid oxide fuel cells (IT-SOFCs). In this study, the properties of zirconia co-doped with 10 mol% Sc and 1 mol% Ce (scandiaceria-stabilized-zirconia, 10Sc1CeSZ) electrolyte synthesized by the microwave-assisted glycine nitrate process (MW-GNP) were determined. The effects of microwave heating on the sintering temperature, microstructure, densification and ionic conductivity of the 10Sc1CeSZ electrolyte were evaluated. The phase identification, microstructure and specific surface area of the prepared powder were investigated using X-ray diffraction, transmission electron microscopy and the Brunauer-Emmett-Teller technique, respectively. Using microwave heating, a single cubic-phase powder was produced with nanosized crystallites (19.2 nm) and a high specific surface area (16 m 2 /g). It was found that the relative density, porosity and total ionic conductivity of the 10Sc1CeSZ electrolyte are remarkably influenced by the powder processing method and the sintering temperature. The pellet sintered at 1400°C exhibited a maximum ionic conductivity of 0.184 S/cm at 800°C. This is the highest conductivity value of a scandia-stabilized-zirconia based electrolyte reported in the literature for this electrolyte type. The corresponding value of the activation energy of electrical conductivity was found to be 0.94 eV in the temperature range of 500-800°C. Overall, the use of microwave heating has successfully improved the properties of the 10Sc1CeSZ electrolyte for application in an IT-SOFC. http://dx..my (M. Rao Somalu). Ceramics International xxx (xxxx) xxx-xxx 0272-8842/
Co-doping of scandia?zirconia electrolytes for SOFCs
Faraday Discussions, 2007
Scandia stabilised zirconias offer much better electrical performance than conventional yttria stabilised materials; however, the limited availability and high cost of scandia have generally limited interest in its application in fuel cells. Political and economic changes over the last decade have significantly enhanced scandia's availability, rendering it worth considering for commercial application, even though there is still some uncertainty about its ultimate market price. A small addition of 2 mol% yttria to scandia stabilised zirconia results in stabilisation of the cubic phase and so avoids the major phase changes that occur on thermal cycling of scandia substituted zirconias, which might be expected to be detrimental to long term electrolyte stability. This addition of yttria does slightly impair the electrical conductivity of the scandia stabilised zirconia, although this can be reversed by further addition of ceria. Samples which are cubic throughout the studied temperature range basically show two linear conductivity regions in Arrhenius conductivity plots. A key observation is that the low temperature activation energy decreases and the high temperature activation energy increases as yttrium content increases and scandium content decreases. This correlates with the strength of short-range order as indicated by neutron and electron diffraction studies. Although scandia substitution increases conductivity and decreases high temperature activation energy, it also increases the tendency to short-range ordering at lower temperatures, resulting in a significant increase in activation energy for conduction. This is attributed to the ionic size of the Sc ion which favours a lower coordination number than that associated with ideal fluorite phases. It should also be realised that Zr, which has a similar size to Sc, also prefers a lower coordination number than is ideal for fluorite hence driving the tendency for short-range order in zirconia fluorites.
Chemical Vapor Deposition, 2012
Dense, crack-free thin films (<5 mm) of the nanostructured scandia-zirconia system (Sc 2 O 3 :ZrO 2 ) stabilized in the cubic-fluorite phase (c-ZrO 2 ) are deposited through conventional low-pressure metal-organic(LP-MO) CVD by using b-diketonate metal complexes as precursors [(Zr(tmhd) and Sc(tmhd) 3 , with -tmhd ¼ 2,2,6,6-tetramethyl-3,5-heptanedionate]. The compositional (energy dispersive X-ray spectroscopy -EDX), structural (X-ray diffraction -XRD) and morphological (field emission gunenvironmental scanning electron microscopy -FEG-ESEM) analyses, confirmed the growth of dense partially and fully stabilized ZrO 2 , a suitable electrolyte for solid oxide fuel cells (SOFC). Results of impedance spectroscopy, which investigates the electrical conductivity of coating, deposited as thin as possible to guarantee the uniform covering of a porous substrate, are reported. Results of thin films of yttria-zirconia system (Y 2 O 3 :ZrO 2 ), deposited with the same method, are also reported for comparison.