Optimization of strontium molybdate based composite anode for solid oxide fuel cells (original) (raw)
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The Journal of Physical Chemistry C, 2014
The suitability of double perovskite oxides of composition Sr 2 Mg 1−x Ni x MoO 6−δ (SMNM, x = 0−0.9) as anode materials for solid oxide fuel cells (SOFCs) was evaluated. Single double perovskite structures could be obtained up to x = 0.9 in syntheses at ambient atmosphere. However, after reduction at 800°C, trace amounts of impurities were detected in the sample with x = 0.9, suggesting that the upper limit for the Ni content (x) in SMNM is less than 0.9 under SOFC operating conditions. The electrical conductivity of SMNM increases with increasing Ni content because of the increase in the concentration of electronic defects, [Mo Mo 6+ 5+ ′], and the decreased band gap energy, as revealed by first-principles calculations. The substitution of Ni can facilitate the charge-transfer process of the electrode reaction, decrease the polarization resistance, and thus increase the power density of a single cell. Xray photoelectron spectroscopy and temperature-programmed reduction measurements were used to explain the reason for the performance improvement. SMNM showed good chemical compatibility with Ce 0.8 Sm 0.2 O 2−δ (SDC) but a slight reactivity with the electrolyte La 0.8 Sr 0.2 Ga 0.83 Mg 0.17 O 3−δ (LSGM) at 1300°C. The use of an SDC buffer layer could avoid the interface reaction between the SMNM anode and the LSGM electrolyte, resulting in better cell performance. The Sr 2 Mg 0.3 Ni 0.7 MoO 6−δ electrode exhibited a maximal power density of 160 mW cm −2 at 800°C with an electrolyte (LSGM, 400 μm)-supported cell configuration.
A series of Sr 0.8 La 0.2 TiO 3Àd (SLT)-Ce 0.8 Gd 0.2 O 2Àd (GDC) composite anodes with various volume ratios of SLT and GDC has been synthesized using a sucrose modified combustion technique. The percolation thresholds of Sr 0.8 La 0.2 TiO 3Àd and Ce 0.8 Gd 0.2 O 2Àd in the composite calculated based on the Kusy's percolation theory were 75.6 vol.% and 36.1 vol.%, respectively. While the rate of carbon deposition increased with an increase in the Ce 0.8 Gd 0.2 O 2Àd content, the total electrical conductivity decreased in humidified H 2 as well as in CH 4 . Based on the electrochemical performance measured using ACimpedance spectroscopy, the optimal anode composition was 65 vol.% Sr 0.8 La 0.2 TiO 3Àd -35 vol.% Ce 0.8 Gd 0.2 O 2Àd . This composite has polarization resistances of 2.80 U cm 2 and 4.60 U cm 2 in H 2 and CH 4 , respectively, measured at 800 C. Diffusion or concentration polarization was the rate determining steps for the fuel oxidation process in the Sr 0.8 La 0.2 TiO 3Àd -Ce 0.8 Gd 0.2 O 2Àd composite anode.
Properties and electrochemical performance of LSCM-LDC composite anodes for solid oxide fuel cells
Highly crystalline composite anodes composed of La 0.75 Sr 0.25 Cr 0.5 Mn 0.5 O 3Àd eLa 0.2 Ce 0.8 O 2Àd (LSCMeLDC) have been synthesized using a simple modified solegel method. LSCM is known for its superior redox stability. LDC acts both as an agent that blocks grain growth in LSCM, and reduces the area-specific resistance of the electrode, thereby enhancing the overall electrochemical performance of single cells. However, the carbon deposition rate of LSCMeLDC composite anodes increases with increasing LDC content. The optimal anode composition is 50 wt.% LSCMe50 wt.% LDC. This composite has a polarization resistance of 0.081 U cm 2 and 0.130 U cm 2 in H 2 and CH 4 , respectively, measured at 800 C.
Dependence of polarization in anode-supported solid oxide fuel cells on various cell parameters
Journal of Power Sources, 2005
The performance of solid oxide fuel cells (SOFCs) is affected by various polarization losses, namely, ohmic polarization, activation polarization and concentration polarization. Under given operating conditions, these polarization losses are largely dependent on cell materials, electrode microstructures, and cell geometric parameters. Solid oxide fuel cells (SOFC) with yttria-stabilized zirconia (YSZ) electrolyte, Ni-YSZ anode support, Ni-YSZ anode interlayer, strontium doped lanthanum manganate (LSM)-YSZ cathode interlayer, and LSM current collector, were fabricated. The effect of various parameters on cell performance was evaluated. The parameters investigated were: (1) YSZ electrolyte thickness, (2) cathode interlayer thickness, (3) anode support thickness, and (4) anode support porosity. Cells were tested over a range of temperatures between 600 and 800 • C with hydrogen as fuel, and air as oxidant. Ohmic contribution was determined using the current interruption technique. The effect of these cell parameters on ohmic polarization and on cell performance was experimentally measured. Dependence of cell performance on various parameters was rationalized on the basis of a simple analytical model. Based on the results of the cell parameter study, a cell with optimized parameters was fabricated and tested. The corresponding maximum power density at 800 • C was ∼1.8 W cm −2 .
Novel materials for solid oxide fuel cell technologies: A literature review
International Journal of Hydrogen Energy, 2017
This study aims to review novel materials for solid oxide fuel cell (SOFC) applications covered in literature. Thence, it was found that current SOFC operating conditions lead to issues, such as carbon surface deposition, sulfur poisoning and quick component degradation at high temperatures, which make it unsuitable for a few applications. Therefore, many researches are focused on cell performance enhancement through replacing the materials being used in order to improve properties and/or reduce operating temperatures. Most modifications in the anode aim to avoid some issues concerning conventionally used Ni-based materials, such as carbon deposition and sulfur poisoning, besides enhancing catalytic activity, once this component is directly exposed to the fuel. It was also found literature about the cathode with the aim of developing a material with enhanced properties in a wider temperature range, which has been compared to the currently used one: LSM perovskite (La 1-x Sr x MnO 3). Novel electrolyte materials can have ionic or protonic conductivity, thus performance degradation must be avoided at several operating conditions. In order to enhance its electrochemical performance, different materials for electrodes (cathode and anode) and electrolytes have been assessed herein.
Journal of Alloys and Compounds, 2000
In this paper we review a systematic study on the properties of the superior oxide-ion conductor Sr-and Mg-doped LaGaO (LSGM) 3 and its performance in a single fuel cell. The conductivity of the oxygen-deficient perovskite phase was shown to be purely ionic over a 222 wide range of oxygen partial pressures 10 #P #1 atm. The highest values of the oxide-ion conductivity, s 50.17, 0.08 and 0.03 O o 2 S / cm, were found for La Sr Ga Mg O at 800, 700 and 6008C, respectively; they remained stable over a weeklong test. The 0.8 0.2 0.83 0.17 2.815 reactivity of Ni and LSGM suggested use of a thin interlayer at the anode-electrolyte interface to prevent formation of lanthanum 2 nickelates; Ce Sm O (SDC) was selected for the interlayer. The peak power density of the interlayered cell is 100 mW/ cm higher 0.8 0.2 1.9
The Journal of Physical Chemistry C, 2012
Double-perovskite materials of composition Sr 2 Mg 1−x Co x MoO 6−δ (SMCMO, x = 0 to 0.7) were evaluated as potential SOFC anode materials. Their lattice structures, electrical and ionic conductivity, thermal expansion coefficient (TEC), and electrochemical performance were investigated as a function of Co content. Co doping was found to increase the TEC of the Sr 2 MgMoO 6−δ material; however, the TEC was within the range of the commonly used La 0.8 Sr 0.2 Ga 0.8 Mg 0.2 O 3-δ (LSGM) electrolyte. SMCMO also showed good chemical compatibility with the LSGM electrolyte at temperatures below 1300°C. Both the electronic and ionic conductivity increased with increasing Co doping. To investigate the effect of Co doping on the conduction properties of SMCMO, we performed first-principle calculations. From these results, the weak Co−O bond is considered to be responsible for the enhanced ionic conductivity of SMCMO materials. The substitution of Co was also found to increase the sinterability of SMCMO, resulting in a decrease in the polarization resistance of the SMMO electrode. Single-cell tests indicated the potential ability of the Co-doped SMMO to be used as SOFC anodes.
Synthesis and electrical properties of Al-doped Sr 2MgMoO 6-d as an anode material for solid oxide f
Fuel and Energy Abstracts, 2011
Aluminum doped Sr2MgMoO6-δ (SMMO) was synthesized via citrate-nitrate route. Dense samples of Sr2Mg1-xAlxMoO6−δ (0 ≤ x ≤ 0.05) were prepared by sintering the pellets at 1500 °C in air and then reducing at 1300 °C in 5%H2/Ar. The electrical conductivity strongly depended on the preparing atmosphere, samples reduced in 5%H2/Ar exhibited higher conductivity than those unreduced. Al-doping increased remarkably the electrical conductivity of Sr2Mg1-xAlxMoO6−δ. The reduced samples displayed a relatively stable electrical conductivity under oxygen partial pressure (Po2) from 10−19 to 10−14 atm at 800 °C, and exhibited an excellent recoverability in electrical conductivity when cycled in alternative air and 5%H2/Ar atmospheres. Sr2Mg0.95Al0.05MoO6−δ material showed a good chemical compatibility with LSGM and GDC electrolytes below 1000 °C, while there was an obvious reaction with YSZ. Al-doping improves the anode performance of SMMO in half-cell of Pt/Sr2Mg1-xAlxMoO6−δ∣GDC∣Pt in H2 fuel. The present results demonstrate that Sr2Mg1-xAlxMoO6−δ is a potential anode material for intermediate temperature-Solid Oxide Fuel Cells (IT-SOFCs).► Double perovskite Sr2Mg1-xAlxMoO6−δ (0 ≤ x ≤ 0.05) was prepared as anode materials for SOFC. ► The electrical conductivity of Sr2Mg1-xAlxMoO6−δ was enhanced by Al introduction. ► Al partial substitution for Mg increased the redox stability and improved the anode performance of Sr2Mg1-xAlxMoO6−δ materials. ► Sr2Mg0.95Al0.05MoO6−δ material showed a good chemical compatibility with LSGM and GDC electrolytes below 1000 °C, but an obvious reaction with YSZ electrolyte.
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