Gorte, Raymond J
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Publication Analysis of the Performance of the Electrodes in a Natural Gas Assisted Steam Electrolysis Cell(2008-02-01) Gorte, Raymond J; Wang, Wensheng; Vohs, John MThe performance of solid oxide electrolysis (SOE) cells while operating in the natural gas assisted steam electrolysis (NGASE) mode was evaluated. The SOE cells used yttria-stabilized-zirconia (YSZ) as the oxygen ion conducting electrolyte, Co–CeO2–YSZ as the H2–H2O electrode, and Pd-doped CeO2 YSZ source as the CH4-oxidation electrode. The cell electrochemical performance was evaluated as a function of the H2O/H2 ratio and the extent of conversion of CH4. The results of this study provide insight into the factors that control electrode performance and further demonstrate the viability of an NGASE cell for the production of H2.Publication An Examination of SOFC Anode Functional Layers Based on Ceria in YSZ(2007-08-21) Vohs, John M; Gross, Michael D; Gorte, Raymond JThe properties of solid oxide fuel cell (SOFC) anode functional layers prepared by impregnation of ceria and catalytic metals into porous yttria-stabilized zirconia (YSZ) have been examined for operation at 973 K. By varying the thickness of the functional layer, the conductivity of the ceria-YSZ composite was determined to be only 0.015–0.02 S/cm. The initial performance of anodes made with ceria loadings of 40 or 60 wt % were similar but the anodes with lower loadings lost conductivity above 1073 K due to sintering of the ceria. The addition of dopant levels of catalytic metals was found to be critical. The addition of 1 wt % Pd or Ni decreased the anode impedances in humidified H2 dramatically, while the improvement with 5 wt % Cu was significant but more modest. Pd doping also decreased the anode impedance in dry CH4 much more than did Cu doping; however, addition of either Pd or Cu led to similar improvements for operation in n-butane. Based on these results, suggestions are made for ways to improve SOFC anode functional layers.Publication SOFC Anodes Based on Infiltration of La0.3Sr0.7TiO3(2008-09-22) Lee, Shiwoo; Vohs, John M; Gorte, Raymond J; Kim, GuntaeComposites formed by infiltration of 45 wt % La0.3Sr0.7TiO3 (LST) into 65% porous yttria-stabilized zirconia (YSZ) were examined for application as solid oxide fuel cell (SOFC) anodes. Although LST does not react with YSZ, the structure of the LST deposits was strongly affected by the calcination temperature. At 1373 K, the LST formed loosely packed, 0.1 µm particles that filled the YSZ pores. The conductivity of this composite depended strongly on the pretreatment conditions but was greater than 0.4 S/cm after heating to 1173 K in humidified (3% H,2O) H2. Following calcination at 1573 K, the LST had sintered significantly, decreasing the conductivity of the composite by a factor of approximately 5. The addition of a catalyst was critical for achieving reasonable electrochemical performance, with the addition of 0.5 wt % Pd and 5 wt % ceria increasing the power density of otherwise identical cells from less than 20 to 780 mW/cm2 for operation in humidified (3% H2O) H2 at 1073 K. Electrodes prepared from LST deposits calcined at 1373 K were found to exhibit a much better performance than those prepared from LST deposits calcined at 1573 K, demonstrating that the structure of the composite is critical for achieving high performance.Publication Preparation of SOFC Anodes by Electrodeposition(2007-10-11) Vohs, John M; Jung, Sukwon; Gorte, Raymond JAnodes for solid oxide fuel cells (SOFCs) have been prepared by electrodeposition of either Co or Ni into a layer of porous yttria-stabilized zirconia (YSZ), 60 µm thick. The YSZ, having 65% porosity, was prepared by tape casting with graphite pore formers and was attached to the dense YSZ electrolyte. After adding 10 vol % CeO2 by impregnation of aqueous solutions of CeNO3)3, followed by calcination at 723 K, the porous YSZ was made conductive by exposing it to n-butane at 1123 K to form a coating of carbon. As much as 40 vol % metal could be added to the porous layers, while the carbon could then be removed by exposing the anode to humidified H2 at SOFC operating temperatures. The ohmic losses in cells containing 40 vol % Co or 30 vol % Ni were unaffected by heating to 1173 K. Finally, a cell with 15 vol % Cu and 15 vol % Co was prepared by electrodeposition of Cu onto electrodeposited Co. No carbon formation was observed on the Cu–Co anode following exposure to dry methane at 1073 K.Publication Engineering Composite Oxide SOFC Anodes for Efficient Oxidation of Methane(2008-02-14) Kim, Guntae; Corre, G.; Vohs, John M; Irvine, J. T. S.; Gorte, Raymond JCeramic anodes for solid oxide fuel cells SOFCs were prepared by aqueous impregnation of nitrate salts to produce composites with 45 wt % La0.8Sr0.2Cr0.5Mn0.5O3 (LCSM)in a 65% porous yttria-stabilized zirconia (YSZ) scaffold. Scanning electron micrographs indicate that the LSCM coats the YSZ pores following calcination at 1473 K. Composites produced in this manner exhibit conductivities at 1073 K of approximately 1 S/cm in air and 0.1 S/cm in humidified H2. A SOFC with a composite anode composed of 45 wt % LSCM, 0.5 wt % Pd, and 5 wt % ceria exhibited maximum power densities at 1073 K of 1.1 and 0.71 W cm−2 in humidified (3% H2O) H2 and methane, respectively.Publication The Effect of Oxide Dopants in Ceria on n-Butane Oxidation(2003-08-08) Zhao, S.; Gorte, Raymond JSolid solutions of CeO2 with Yb2O3, Y2O3, Sm2O3, Gd2O3, La2O3, Nb2O5, Ta2O5, and Pr6O11 were prepared by sol-gel methods. All of the samples exhibited a single, cubic phase in x-ray diffraction and the lattice parameters were consistent with formation of the solid solutions. Surprisingly, all of the mixed oxides exhibited a much lower catalytic activity for n-butane oxidation than that of pure CeO2 at 650 K, with Sm0.2Ce0.8O1.9, Gd0.2Ce0.8O1.9, La0.2Ce0.8O1.9, Nb0.1Ce0.9O2.05, and Ta0.1Ce0.9O2.05 showing rates less than 10-2 that of pure ceria. Lower dopant levels with Sm+3 and Gd+3 affected the rates proportionately less. The implications of these results for use of ceria as an oxidation catalyst are discussed.Publication Characterization of YSZ-YST Composites for SOFC Anodes(2004-11-30) He, Hongpeng; Vohs, John M; Huang, Yingyi; Gorte, Raymond JPorous composites of Sr0.88Y0.08TiO3-δ (YST) and yttria-stabilized zirconia (YSZ) were formed by tape-casting methods and examined as potential anodes for SOFC. Even after calcination to 1773 K, the YSZ and YST crystallites remain as separate phases, as demonstrated by XRD and SEM with EDX analysis. Furthermore, it was possible to fabricate anode-supported electrolytes by calcination of a bilayer tape formed by casting a thin YSZ tape over the green, YSZ-YST tape. Cells with anodes having 50-wt% YST and 80-wt% YST were tested and shown to yield good open-circuit voltages, although the power densities in H2 and CH4 between 973 and 1173 K were modest. Impedance spectra of the cells suggest that the conductivity of the YST-YSZ composites is insufficient for high performance.Publication An Investigation of LSF-YSZ Conductive Scaffolds for Infiltrated SOFC Cathodes(2017-01-01) Cheng, Yuan; Oh, Tae-Sik; Gorte, Raymond J; Wilson, Rachel; Vohs, John MPorous compostites of Sr-doped LaFeO3 (LSF and yttria-stabilized zirconia (YSZ) were investigated as conductive scaffolds for infiltrated SOFC cathodes with the goal of producing scaffolds for which only a few perovskite infiltration steps are required to achieve sufficient conductivity. While no new phases form when LSF-YSZ composites are calcined to 1623 K, shifts in the lattice parameters indicate Zr can enter the perovskite phase. Measurements on dense, LSF-YSZ composites show that the level of Zr doping depends on the Sr:La ration. Because conductivity of undoped LSF increases with Sr content while both the iconic and electronic conductivities of Zr-doped LSF decrease with the level of Zr in the perovskite phase, there is an optimum initial Sr content corresponding to La0.9Sr0.1FeO3 (LSF91). Although schaffolds made with 100% LSF had a higher conductivity then scaffolds made with 50:50 LSF-YSZ mixtures, the 50:50 mixture provides the optimal interfacial structure with the electrolyte and sufficient conductivity, providing the best cathode performance upon infiltration of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF).Publication Recent Developments on Anodes for Direct Fuel Utilization in SOFC(2004-11-30) Gorte, Raymond J; Vohs, John M; McIntosh, StevenThis paper reviews recent work on SOFC anode fabrication at the University of Pennsylvania. In this work, anode fabrication is based on the preparation of a porous YSZ matrix, into which electronic and catalytic components are added by impregnation of the appropriate metal salts. First, the methods used to prepare porous YSZ are described, along with a description of the structures that are obtained. Next, it is demonstrated that cell performance is strongly affected by the methods used to impregnate and pretreat ceria that is added to the porous YSZ. Third, the role of carbonaceous deposits within the anode is discussed. These deposits can lead to improved electronic conductivity that results in improved performance. Finally, the effect of precious-metal dopants, added to ceria to improve the catalytic properties of the anode, is discussed. Pd, Pt, and Rh are shown to give large increases in the performance of the cells, particularly in CH4.Publication Zirconia-Based Electrolyte Stability in Direct-Carbon Fuel Cells with Molten Sb Anodes(2015-01-01) Zhou, Xiaoliang; Vohs, John M; Oh, Tae-Sik; Gorte, Raymond JDirect carbon fuel cells (DCFC) that use zirconia-based electrolytes and molten Sb anodes have much promise for the efficient conversion of carbonaceous solid fuels into electricity. However, etching of the electrolyte, and ultimately cell failure, has been observed during operation. In this study, we have investigated this etching phenomenon as a function of the electrolyte composition and cell operating conditions and demonstrated that it is not electrochemical in nature, but rather results from reaction between the electrolyte and Sb2O3.