A new energy conversion technology joining electrochemical and physical principles (original) (raw)
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Journal of Alloys and Compounds, 2019
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-stablized zirconia (YSZ) which operates at a high temperature (≥800 o C). In this paper, the tri-doped ceria, M 0.2 Ce 0.8 O 2-δ (M=Sm 0.1, Ca 0.05, Gd 0.05) electrolyte powders was synthesized using the co-precipitation method at 80 o C. These dopants were used for CeO 2 with a total molar ratio of 1M. Dry-pressed powder technique was used to make fuel cell pellets from the powder and placed them in the furnace to sinter at 700 o C for 60 minutes. Electrical conductivity of such a pellet in air was 1.2 × 10-2 S.cm-1 at 700 o C measured by the ProboStat-NorECs setup. The crystal structure was determined with the help of-ray diffraction (XRD), which showed that all the dopants were successfully doped in CeO 2. 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-2 and 52.8 mW.cm-2 , respectively.
Semiconductor-ionic Membrane of LaSrCoFe-oxide-doped Ceria Solid Oxide Fuel Cells
Electrochimica Acta
A novel fuel cell was constructed by using semiconductor La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) and ionic conductor Sm/Ca co-doped CeO 2 (SCDC) nanocomposite layer as a membrane, sandwiched by two thin semiconducting layers of Ni 0.8 Co 0.15 Al 0.05 Li-oxide (NCAL). Such device reached the output power density as high as 798 mW cm-2 at 550 o C in comparison to the fuel cell using the ionic SCDC electrolyte membrane, around 300 mW cm-2. The LSCF electronic conductor introduced into the membrane did not cause any short circuit but brought the significant enhancement on the power output. The physical semiconductor energy band alignment is proposed to prevent the internal electrons passing incorporated with the Schottky junction effect. The idea of combining semiconductor physics and ionic electrochemical FC process to employ the semiconductor-ionic membrane represents a new energy conversion technology, which is superior to the conventional fuel cell technologies.
Study of a solid oxide fuel cell with a ceria-based solid electrolyte
Solid State Ionics, 1989
The ionic conductivity of the ceria-samaria system is higher than that ofynria stabilized zirconia and other ceria-based oxides. The current density and power density of oxygen-hydrogen fuel cell with the ceria-samaria system was found to be high at 600-800 :C, because of its low internal cell resistance. However, the open circuit voltage of the cell for ceria-samaria system was lower than the theoretical value, because of reduction with H2 and resulting decrease in ionic transference number. To suppress the reduction, a thin film of yttria-stabilized zirconia was coated on the fuel side of ceria-samarium oxide disk by the ion plating method. The fuel cell with zirconia-coated ceria-samaria exhibited high durability of the cell output and stable open circuit voltage.
CURRENT-VOLTAGE CHARACTERISTICS OF FUEL CELLS WITH CERIA-BASED ELECTROLYTES
Dense electrolyte membranes with a thickness of 200 µm have been prepared from ceria solid solutions with Gd 2 O 3 , Sm 2 O 3 and CaO by tape casting. Electrochemical properties of CeO 2-based fuel cells have been studied in the temperature range from 600 to 800 °C. The electrolytes exhibit an ionic conductivity of 3-5 S/m at 700 °C and mechanical stability in oxidizing as well as in reducing atmospheres. Power densities exceeding 350 mW/cm 2 at 750°C are possible in CeO 2-based fuel cells with perovskite cathodes and Ni-cermet anodes. The mixed ionic/electronic conductivity of ceria electrolytes and its influence on current-voltage characteristics under fuel cell operating conditions are discussed.
Rsc Advances, 2012
Recently, a fuel cell device constructed with only one layer composited of ceria based nanocomposites (typically, lithium nickel oxide and gadolinium doped ceria (LiNiO2-GDC) composite materials), name electrolyte free fuel cell (EFFC) was realized for energy conversion by Zhu et al. 1-3 The maxium power density of this single component fuel cell is 450 mW cm −2 at 550 o C using hygrogen fuel. In this study, a model is developed to evaluate the performance of an EFFC. The kinetics of anodic and cathodic 10 reactions are modeled based on electrochemical impedance spectroscopy (EIS) measurement. The results show that both of the anodic and cathodic reactions are kinetically fast processes at 500 o C. The safety issues of an EFFC using oxidant and fuels at the same time without gas−tight separator is analyzed under open circuit and normal operation states, respectively. The reaction depth of anodic and cathodic processes dominates the competition between surface electrochemical and gas−phase reactions which are 15 effected by the catalytic activity and porosity of the materials. The voltage and power output of an EFFC are calculated based on the model and compared with the experimental results.
Journal of the American Ceramic Society, 2002
Cation-doped CeO 2 electrolyte has been evaluated in singlecell and short-stack tests in solid oxide fuel cell environments and applications. These results, along with conductivity measurements, indicate that an ionic transference number of ϳ0.75 can be expected at 800°C. Single cells have shown a power density >350 mW/cm 2. Multicell stacks have demonstrated a peak performance of >100 mW/cm 2 at 700°C using metallic separators.
Electrical properties of ceria-based oxides and their application to solid oxide fuel cells
Solid State Ionics, 1992
Ionic conductivities of ceria-alkaline-earth and -rare-earth oxide systems were investigated in relation to their structures, electrical conductivities, and reducibilities. Samaria and gadolinia-doped ceria samples exhibited the highest electrical conductivity in ceria-based oxides because of the close ionic radii of Sm 3 + and Gd 3 + to that of Ce 4+. The ionic conductivity of samariadoped ceria was also measured by an ac four-probe method with electron blocking electrodes. A solid oxide fuel cell with a samaria-doped ceria electrolyte produced high electric power, because of its highest oxygen ionic conductivity. The reduction of ceria electrolyte at the fuel side could be suppressed by a coating of stabilized zirconia thin film on the ceria surface. The anodic overvoltage of the doped ceria/anode interface was very small,
The role of ceria-based nanostructured materials in energy applications
Materials Today, 2014
Ceria (CeO 2 ) is enjoying increasing popularity in catalytic applications, and in some cases has established itself as an irreplaceable component. The reasons for such success stem from the intrinsic structural and redox properties of ceria. Reducing the ceria particles to the nanoscale has a profound impact on the catalytic behavior. The proliferation of improved synthetic methods that allow control over the final morphology and size of the nano-structures is opening new possibilities in terms of catalytic potential, particularly for energy-related applications.
Innovative solid carbonate–ceria composite electrolyte fuel cells
Electrochemistry Communications, 2001
An innovative solid carbonate–oxide composite and related fuel cell (FC) technology is reported. It was discovered that solid carbonate–ceria composite (SCC) electrolytes were highly conductive with the material conductivity level varying from 0.001 to between 400 and 600 °C, and related FCs reached a power density between 200 and at a current density of 300– in the same temperature region. The SCCs were discovered to possess both oxide-ion (originating from the ceria phase) and proton (from the carbonate phase) conduction. Being an all-solid ceramic FC, the SCC can effectively reduce the material corrosion problem that is serious for the molten carbonate fuel cells (MCFCs). On the other hand, the innovative FC technology based on the SCC electrolytes developed in this work is similar to solid oxide fuel cells (SOFCs) and different from the MCFCs based on their ionic transport and FC processes, which facilitates a development of new type of advanced FC technology.
ACS applied materials & interfaces, 2017
Samarium doped ceria-carbonate(SDC) has become an attractive electrolyte for low temperature fuel cells because of its impressive ionic conductivity and high performance. Different doped ceria-carbonate (SDC-single, SDC-binary, and SDC-ternary) electrolytes were synthesized by the co-precipitation/oxalate method, to optimize the electrochemical performance. The structure, morphology, and thermal, optical, and surface properties, have been studied using a variety of techniques. These include x-ray diffraction, scanning electron microscopy, thermogravimetric analysis, UV-visible absorption spectroscopy, and Fourier infrared spectroscopy. The x-ray diffraction results confirmed the successful incorporation of samarium into ceria as a crystalline and inclusion of carbonate is an amorphous nature. To analyze the conduction mechanism, dc conductivity was measured in a H2/O2 atmosphere. Doped ceria-binary carbonate (Li/Na)CO3-SDC) showed the highest ionic conductivity of 0.31 S cm-1, and p...