Solid oxide fuel cell bi-layer anode with gadolinia-doped ceria for utilization of solid carbon fuel (original) (raw)
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Journal of Power Sources, 2004
A Ni/ yttria-stabilized zirconia (YSZ) cermet anode was modified by coating with samaria-doped ceria (SDC, Sm 0.2 Ce 0.8 O 2 ) sol within the pores of the anode for a solid oxide fuel cell (SOFC) running on hydrocarbon fuel. The surface modification of Ni/YSZ anode resulted in an increase of structural stability and enlargement of the triple phase boundary (TPB), which can serve as a catalytic reaction site for oxidation of carbon or carbon monoxide. Consequently, the SDC coating on the pores of anode made it possible to have good stability for long-term operation due to low carbon deposition and nickel sintering.
Asian journal of engineering and applied technology, 2012
Solution combustion technique was used for the preparation of NiO-CGO (Ceria Gadolinia Oxide) composites-a precursor to SOFC anode by mixing cerium nitrate, gadolinium nitrate and nickel nitrate in stoichiometric ratio to form a precursor of composition Ce0. 90 Gd0. 10 O 1.95-0.40 NiO. The concentration of oxidant i.e. glycine, was varied between 0.5 to 1.6 mole% and its effect was studied on the crystallite size and agglomerate of resulting NiO-CGO composite. The products formed were characterized by X-Ray Diffraction, Scanning Electron Microscope and Particle Size Analyzer. The results showed that the composite precursor varied in combustion characteristics, crystallite size and agglomerated particle size depending on the concentration of the fuel.
Yttria-doped ceria anode for carbon-fueled solid oxide fuel cell
Journal of Solid State Electrochemistry, 2014
Direct carbon fuel cells offer twice the efficiency compared with conventional coal-fired power plants and the highest efficiency among various fuel cells. However, the delivery of solid fuel to electrode/electrolyte interface is a critical issue and hinders the long-term performance of the fuel cell. The use of mixed ionic electronic conducting anodes has the potential to reduce the problem by shifting the fuel oxidation reaction from anode/electrolyte to anode/solid carbon interface. In search for a better anode material, Y 2 O 3doped ceria has been investigated as a suitable anode material for use in direct carbon fuel cells and the performance compared with Gd 2 O 3-doped ceria. These materials have high ionic conductivity in oxidizing environments and are also known to have reasonable mixed ionic and electronic conductivity in reducing environments. In this manuscript, the stability of the anode materials in fuel cell operating environments has been investigated with X-ray diffraction (XRD) and scanning electron microscopy. Electrochemical impedance spectroscopy, in pure N 2 and CO 2 /N 2 anode chamber atmospheres, has been used to deconvolute the contribution of various fuel cell components to voltage losses and to elucidate the reaction mechanism. No precious metals were used on the anode side, neither as a catalyst nor as a current collector.
Advanced Inorganic Materials for Solid Oxide Fuel Cells
Energy Materials
SSC-Sm 1-x Sr x CoO 2 MIEC-Mixed ionic-electronic conductor SOFC-Solid oxide fuel cell TEM-Transmission electron microscopy HRTEM-High resolution transmission electron microscopy SAED-Selected area electron diffraction SIMS-Secondary ion mass spectrometry XRD-X-ray diffraction TEC-Thermal expansion coefficient ' 2 3 3 ZrO x Zr O O Y O Y V O (1.3) One significant disadvantage with the ZrO 2 based SOFCs is the temperature of operation at which ionic conductivity is sufficiently high support a device which for 8YSZ is typically 800-1000 o C, depending upon the thickness of the electrolyte. This leads to a further consideration for fuel cell operation-that of electrolyte supported or electrode supported designs. Again each design has advantages, but to increase performance it is generally accepted that lower operating temperatures are required would typically be of Ni-YSZ composite type 27, 28. These composites are often referred to as "cermets". Similarly for CGO and LSGM based cells the composite materials are of the Ni-CGO and Ni-LSGM type. Preparation of the anode structure is usually achieved through the mixing of NiO with the appropriate electrolyte component, followed by a reduction step to produce the Ni cermet. Volume changes associated with the reduction step do not appear to be detrimental to the overall durability of the cell, but there have been observations of serious degradation of the anode when reoxidation occurs. These are significant concerns for thermal cycling and it is clear that over relatively modest timescales there is a significant degradation rate of 10m cm-2 per 1000 hours at 1000 o C for YSZ based devices 29. Clearly these degradation rates and the evolution of reaction products is too great for long term operation. Redox stability of the electrode structure is therefore a common problem for Ni based anodes, and significant volume changes upon oxidation of Ni to NiO have been demonstrated to significantly impact upon the mechanical integrity of the cell 30. One further limitation of the anode component in these devices is the degradation of performance with the increase of sulphur content in the fuel stream and also with the risk of coking if carbon rich fuel streams are used, such as with natural gas 31. Evidently if a pure hydrogen fuel were used in the SOFC these issues of anode operation would not arise, however one of the advantages of the SOFC is the potential fuel flexibility offered by the use of oxide anodes, such as the reforming of natural gas in the anode. 1.3 Conventional cathodes Cathode materials for SOFCs based on any of the electrolytes described in section 1.1 are of the perovskite structure type, generally La-based with transition metals located on the B site. Several authors 4, 5, 32-35 have summarised the range of
Solid oxide fuel cell with NiCo–YSZ cermet anode for oxidation of CO/H2 fuel mixtures
Journal of Power Sources, 2012
The suggestion has been made in the literature that solid oxide fuel cells (SOFCs) operated with syngas as fuel may be viable in certain gas ratio regimes. We have explored this hypothesis with a promising bimetallic anode material. SOFCs with Ni 0.7 Co 0.3 -YSZ cermet anodes were operated with CO/H 2 mixtures in the full concentration range. Electrochemical impedance spectroscopy and voltammetry measurements were employed to measure the exchange current density (i 0 ) values of each fuel mixture. The fuel mixtures of CO/H 2 ratios corresponding to the range 20/80 and 30/70 were found to have i 0 values larger than that of pure H 2 with the same cell. For these two fuel ratios, an improvement of 5-8 times, respectively, in the exchange current density has been observed. Higher CO/H 2 fuel ratios in the range of 60/40-80/20 produced i 0 values lower than H 2 , as carbon poisoning is operational in this region. Continuous running of a cell with fuel ratio 25/75 CO/H 2 for 7 days produced i 0 values above the values for pure H 2 as has been recently suggested.
Analysing carbon deposition on Ni/YSZ anode tested in an Solid Oxide Fuel Cell (SOFC)
Journal of New Materials for Electrochemical Systems
Integrated Planar Solid Oxide Fuel Cells (IP-SOFC), which utilise a Ni/YSZ based anode, have been operated under direct hydrogen-methane mixture fuel injection at 900 oC. This process has shown some disadvantages in fuelling to the IP-SOFC; producing carbon deposition from the methane in the fuel mixture, causing direct structural damage to the IP-SOFC surface and blocking the area of activation for reaction processes and reducing the performances. These factors were shown to adversely affect the performance of the IP-SOFC over time. The aim of this paper is to calculate the amount of carbon deposited through the use of temperature programmed oxidation (TPO). In addition, the distribution of carbon is studied and analysed on all parts of the IP-SOFC cells. The results show that both amorphous and graphitic carbon were formed causing microstructural damage thereby reducing the cell performance. Furthermore, the reaction temperature was demonstrated to increase the total amount of car...
Preparation of NiO-YSZ/YSZ bi-layers for solid oxide fuel cells by electrophoretic deposition
Journal of Power Sources, 2006
A simple and cost-effective method, starting with electrophoretic deposition (EPD) on a carbon sheet, has been developed for preparation of a NiO-YSZ anode and thin, gas-tight YSZ electrolyte layer on it for use in solid oxide fuel cells (SOFCs). The innovative feature of this approach enables the deposition of anode materials as well as the YSZ electrolyte, which were subsequently co-fired in air at high temperatures to remove the carbon and form an anode-supported dense YSZ electrolyte. A functional SOFC constructed by brush painting a layer of mixed cathode consisting of La 0.8 Sr 0.2 MnO 3 (LSM) and YSZ on the electrolyte layer followed by firing at 1250 • C, displayed a peak power density of 434 mW cm −2 at 800 • C when tested with H 2 as fuel and ambient air as oxidant.