| 1. |
- Ali, Amjad, et al.
(författare)
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A potential electrolyte (Ce1-x CaxO2-delta) for fuel cells:Theoretical andexperimental study
- 2018
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Ingår i: Ceramics International. - : ELSEVIER SCI LTD. - 0272-8842 .- 1873-3956. ; 44:11, s. 12676-12683
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Tidskriftsartikel (refereegranskat)abstract
- First-principles calculations are performed using density function theory to explore the effects of dopant Ca in ceria (Ce1-x CaxO2-delta). The impact of oxygen vacancy on band gap and density of states is examined in doped ceria using generalized gradient approximations. Vacancy association and vacancy formation energies of the doped ceria are calculated to reveal the effect of dopant on ion conduction. The experimental study of the sample Ce0.875Ca0.125O2-delta) was performed to compare with the theoretical results. The obtained results from theoretical calculation and experimental techniques show that oxygen vacancy increases the volume, lattice constant (5.47315 angstrom) but decrease the band gap (1.72 eV) and bulk modulus. The dopant radius (1.173 angstrom) and lattice constant (5.4718 angstrom) are also calculated by equations which is close to the DFT lattice parameter. The result shows that oxygen vacancy shifts the density of states to lower energy region. Band gap is decreased due to shifting of valence states to conduction band. Vacancy formation shows a significance increase in density of states near the Fermi level. Density of states at Fermi level is proportional to the conductivity, so an increase in density of states near the Fermi level increases the conductivity. The experimental measured ionic conductivity is found to 0.095 S cm(-1) at 600 degrees C. The microstructural studies is also reported in this work.
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| 2. |
- Rafique, Asia, et al.
(författare)
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Significance enhancement in the conductivity of core shell nanocomposite electrolytes
- 2015
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Ingår i: RSC Advances. - : Royal Society of Chemistry. - 2046-2069. ; 5:105, s. 86322-86329
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Tidskriftsartikel (refereegranskat)abstract
- Today, there is great demand of electrolytes with high ionic conductivities at low operating temperatures for solid-oxide fuel cells. Therefore, a co-doped technique was used to synthesize a highly ionically conductive two phase nanocomposite electrolyte Sr/Sm-ceria-carbonate by a co-precipitation method. A significant increase in conductivity was measured in this co-doped Sr/Sm-ceria-carbonate electrolyte at 550 degrees C as compared to the more commonly studied samarium doped ceria. The fuel cell power density was 900 mW cm(-2) at low temperature (400-580 degrees C). The composite electrolyte was found to have homogenous morphology with a core-shell structure using SEM and TEM. The two phase core-shell structure was confirmed using XRD analysis. The crystallite size was found to be 30-60 nm and is in good agreement with the SEM analysis. The thermal analysis was determined with DSC. The enhancement in conductivity is due to two effects; co-doping of Sr in samarium doped ceria and it's composite with carbonate which is responsible for the core-shell structure. This co-doped approach with the second phase gives promise in addressing the challenge to lower the operating temperature of solid oxide fuel cells (SOFC).
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| 3. |
- Ali, A., et al.
(författare)
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Alkaline earth metal and samarium co-doped ceria as efficient electrolytes
- 2018
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 112:4
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Tidskriftsartikel (refereegranskat)abstract
- Co-doped ceramic electrolytes M0.1Sm0.1Ce0.8O2-δ (M = Ba, Ca, Mg, and Sr) were synthesized via co-precipitation. The focus of this study was to highlight the effects of alkaline earth metals in doped ceria on the microstructure, densification, conductivity, and performance. The ionic conductivity comparisons of prepared electrolytes in the air atmosphere were studied. It has been observed that Ca0.1Sm0.1Ce0.8O2-δ shows the highest conductivity of 0.124 Scm-1 at 650 °C and a lower activation energy of 0.48 eV. The cell shows a maximum power density of 630 mW cm-2 at 650 °C using hydrogen fuel. The enhancement in conductivity and performance was due to increasing the oxygen vacancies in the ceria lattice with the increasing dopant concentration. The bandgap was calculated from UV-Vis data, which shows a red shift when compared with pure ceria. The average crystallite size is in the range of 37-49 nm. DFT was used to analyze the co-doping structure, and the calculated lattice parameter was compared with the experimental lattice parameter.
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| 4. |
- Ullah, Muhammad Kaleem, et al.
(författare)
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Tri-doped ceria (M0.2Ce0.8O2-δ, M= Sm0.1 Ca0.05 Gd0.05) electrolyte for hydrogen and ethanol-based fuel cells
- 2019
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388. ; 773, s. 548-554
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Tidskriftsartikel (refereegranskat)abstract
- In recent scientific research, an interest has been gained significantly by rare earth metals such as cerium (Ce), samarium (Sm) and gadolinium (Gd) due to their use in fuel cells as electrolyte and catalysts. When used in an electrolyte, these materials lower the fuel cell's operating temperature compared to a conventional electrolyte, for example, yittria-stabilized zirconia (YSZ) which operates at a high temperature (≥800 °C). In this paper, the tri-doped ceria, M0.2Ce0.8O2-δ(M = Sm0.1Ca0.05Gd0.05) electrolyte powders was synthesized using the co-precipitation method at 80 °C. These dopants were used for CeO2with a total molar ratio of 1 M. Dry-pressed powder technique was used to make fuel cell pellets from the powder and placed them in the furnace to sinter at 700 °C for 60 min. Electrical conductivity of such a pellet in air was 1.2 × 10−2S cm−1at 700 °C measured by the ProboStat-NorECs setup. The crystal structure was determined with the help of X-ray diffraction (XRD), which showed that all the dopants were successfully doped in CeO2. Raman spectroscopy and UV-VIS spectroscopy were also carried out to analyse the molecular vibrations and absorbance, respectively. The maximum open-circuit voltages (OCVs) for hydrogen and ethanol fuelled at 550 °C were observed to be 0.89 V and 0.71 V with power densities 314 mW cm−2and 52.8 mW cm−2, respectively.
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