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1.
In this study, a conventional Ni/yttria‐stabilized zirconia (YSZ) anode and a new Cu‐CeO2‐YSZ anode structure were assembled in an attempt to combine the advantages of both structures for use in direct methane solid oxide fuel cells. For this purpose, only a limited region (≤20 μm) of NiO/YSZ was deposited at the boundary of the electrolyte to benefit from the superior catalytic activity of Ni in the cells, while the rest of the cell benefited from the Cu‐CeO2‐YSZ anode structure, which does not cause cracking reactions. First, the effects of different pore formers on the anode skeleton, as well as the interactions of the Ni‐Cu species in the anode skeleton, are discussed. Then, the NiO/YSZ‐interlayer‐containing button cells with different thicknesses (≤20) and different ratios of NiO (40 wt%, 50 wt%, and 60 wt%) were studied. After the examination of the cells, 2 model cells with outstanding performance and 2 additional internal reference cells, conventional Ni/YSZ and Cu‐CeO2‐YSZ, were scaled up, and performance analysis and long‐term stability studies were carried out. As a result, for solid oxide fuel cells with increased carbonization resistance (around 6% performance loss due to carbonization after 100‐hour stability testing) and 86.1% of the initial performance of the conventional Ni/YSZ anode structure, a 15‐μm‐thick 40 wt% NiO/60 wt% YSZ interlayer with a dual layer anode structure is proposed.  相似文献   

2.
Microstructural features and physical properties of the anodes crucially affect the electrochemical performance of anode-supported solid oxide fuel cells (SOFCs). This paper evaluated the microstructural characteristics and properties including porosity, pore size distribution, sintering shrinkage, mechanical strength, and electrical conductivity of the SOFC anode using carbon microspheres (CMSs) as the pore-former in the fabrication of Ni/YSZ ceramic anode. CMSs with different average particle sizes (CMS1: 11.54 μm, CMS2: 4.39 μm, and CMS3: 0.27 μm) were synthesized, and then incorporated into NiO/YSZ at various volumetric blend ratios ranging from 4.4 to 44.6 vol.%. SOFC anode cermets with a desirable range of porosity (30–40%), shrinkage (15.9–17.3%), flexural strength (75.4–157.8 N), and electrical conductivity (253.5–510.7 S/cm) were obtained using approximately 4–10 vol% of CMS1, 4–20 vol.% of CMS2, and 10–34 vol.% of CMS3. In addition, the use of CMS as the pore former reduced the amount of closed pores in the anode disks from 2.05% to <1%.  相似文献   

3.
A novel approach of fabricating SOFC anode comprising graded compositions in constituent phases having layer wise microstructural variation is reported. Such anode encompasses conventional NiO–YSZ (40 vol% Ni) with higher porosity at the fuel inlet side and Ni–YSZ electroless cermet (28–32 vol% Ni) with less porosity toward the electrolyte. Microstructures and thicknesses of the bilayer anodes (BLA) are varied sequentially from 50 to 250 μm for better thermal compatibility and cell performance. Significant augmentation in performance (3.5 A cm−2 at 800 °C, 0.7 V) is obtained with engineered trilayer anode (TLA) having conventional anode support in conjunction with layers of electroless cermet each of 50 μm having 28 and 32 vol% Ni. Engineered TLA accounts for substantial reduction both in cell polarization (ohmic ASR: 78 mΩ cm2 versus 2835 mΩ cm2; cell impedance: 0.35 Ω cm2 versus 0.9 Ω cm2) and degradation rate (76 μV h−1 versus 219 μV h−1) compared to cells fabricated with conventional cermet.  相似文献   

4.
Tape casting is conventionally used to prepare individual, relatively thick components (i.e., the anode or electrolyte supporting layer) for solid oxide fuel cells (SOFCs). In this research, a multilayer ceramic structure is prepared by sequentially tape casting ceramic slurries of different compositions onto a Mylar carrier followed by co-sintering at 1400 °C. The resulting half-cells contains a 300 μm thick NiO–yttria-stabilized zirconia (YSZ) anode support, a 20 μm NiO–YSZ anode functional layer, and an 8 μm YSZ electrolyte membrane. Complete SOFCs are obtained after applying a Gd0.1Ce0.9O2 (GDC) barrier layer and a Sm0.5Sr0.5CoO3 (SSC) -GDC cathode by using a wet-slurry spray method. The 50 mm × 50 mm SOFCs produce peak power densities of 337, 554, 772, and 923 mW/cm2 at 600, 650, 700, and 750 °C, respectively, on hydrogen fuel. A short stack including four 100 mm × 150 mm cells is assembled and tested. Each stack repeat unit (one cell and one interconnect) generates around 28.5 W of electrical power at a 300 mA/cm2 current density and 700 °C.  相似文献   

5.
《Journal of power sources》2006,162(2):1036-1042
To protect the ceria electrolyte from reduction at the anode side, a thin film of yttria-stabilized zirconia (YSZ) is introduced as an electronic blocking layer to anode-supported gadolinia-doped ceria (GDC) electrolyte solid oxide fuel cells (SOFCs). Thin films of YSZ/GDC bilayer electrolyte are deposited onto anode substrates using a simple and cost-effective wet ceramic co-sintering process. A single cell, consisting of a YSZ (∼3 μm)/GDC (∼7 μm) bilayer electrolyte, a La0.8Sr0.2Co0.2Fe0.8O3–GDC composite cathode and a Ni–YSZ cermet anode is tested in humidified hydrogen and air. The cell exhibited an open-circuit voltage (OCV) of 1.05 V at 800 °C, compared with 0.59 V for a single cell with a 10-μm GDC film but without a YSZ film. This indicates that the electronic conduction through the GDC electrolyte is successfully blocked by the deposited YSZ film. In spite of the desirable OCVs, the present YSZ/GDC bilayer electrolyte cell achieved a relatively low peak power density of 678 mW cm−2 at 800 °C. This is attributed to severe mass transport limitations in the thick and low-porosity anode substrate at high current densities.  相似文献   

6.
A simple and cost-effective gel-casting technique is developed and optimized to fabricate NiO/stabilized yttria–zirconia (YSZ) anode-supported solid oxide fuel cells (SOFCs). The effect of ammonium poly-(methacrylate) (PMAA) dispersant and pH on the zeta potential of YSZ and NiO particles and the viscosity of the NiO/YSZ slurries is studied in detail. The results show that the absolute zeta potential of YSZ and NiO particles reaches a maximum value at pH value ∼10 and the viscosity of the NiO/YSZ slurry is lowest when the PMAA dispersant content is 1.5 wt.%. A gel-cast NiO/YSZ anode-supported button cell with a spin-coated, thin, YSZ electrolyte film (∼9 μm) and a La0.72Sr0.18MnO3−δ (LSM)/YSZ composite cathode gives a peak power output of 1.07 and 0.65 W cm−2 at 900 and 800 °C under humidified hydrogen and air. The effect of a graphite pore-former in the gelation and microstructure of NiO/YSZ anode substrates is investigated.  相似文献   

7.
A low pressure injection molding (LPIM) technique is successfully developed to fabricate porous NiO–YSZ anode substrates for cone-shaped tubular anode-supported solid oxide fuel cells (SOFCs). The porosity and microstructure of the anode samples prepared with different amount of pore formers are investigated through the Archimedes method and SEM analysis. Experimental results show that with 15 wt.% paraffin as plasticizer, porosity of the NiO–YSZ substrates sintered at 1400 °C is proportional to the amount of graphite as pore former, and proper porosities can be obtained with or without 5 wt.% graphite. NiO–YSZ/YSZ/LSM–YSZ single cells are assembled and tested to demonstrate the feasibility of the LPIM technique. At 800 °C, with moist hydrogen (75 ml min−1) as fuel and ambient air as oxidant, the cell with the anode substrate fabricated with 5 wt.% pore former shows a maximum power density of 531 mW cm−2, while the cell without any pore former, 491 mW cm−2. Two of the single cells (without graphite) are applied to assemble a two-cell-stack which gives an open circuit voltage of 1.75 V and a maximum output power of 5.32 W, at operating temperature of 800 °C.  相似文献   

8.
Various anode-supported solid oxide fuel cells (SOFC), based on 10 mol% Dy-doped La2Mo2O9 (LDM) electrolyte, are prepared analytically and operated under single chamber conditions to explore the connections between electrode and power performance. The cathode of tested SOFCs is compositionally graded with three composites of samarium strontium cobaltite and Gd-doped ceria (GDC) to relax the thermal stress, because of sizable thermal expansion differences above 400 °C. We focus the research attention on varying the anode pore structure and composition to promote the power performance in methane/air mixture at 700 °C. For the one-layer support of GDC+NiO+LDM anode, addition of 10 wt% graphite minimizes its mass transport resistance through creating 8–5 μm long and ∼1 μm wide slit-shaped pores. The graphite pore former raises the peak power value by 80 mW cm−2. Adopting a more porous and active outer layer, the double-layer support further enhances the cell power. The peak power was first raised by 48 mW cm−2, using an outer layer that was prepared with 63 wt% NiO. Dosing 3% Pd on this outer layer uplifts another 59 mW cm−2. In this study, with an improved anode, the peak power value reaches 437 mW cm−2.  相似文献   

9.
In this study, solid oxide fuel cells (SOFCs) consisting of a NiO-YSZ anode, a NiO/YSZ-YSZ functional layer, YSZ electrolyte and a (La0.8Sr0.2)MnO3 + yttria-stabilized zirconia (LSM-YSZ) cathode were fabricated by tape-casting, lamination, and a co-firing process. NiO/YSZ-YSZ nano-composite powder was synthesized for the anode functional layer via the Pechini process in order to improve cell performance. After optimization of the slurries for the anode functional anode, electrolyte and cathode, all components were casted so as to fabricate the monolithic laminate. The co-firing temperature was optimized to minimize second phase formation between the (La0.8Sr0.2)MnO3 (LSM) and yttria-stabilized zirconia (YSZ) and to increase the sinterability of the YSZ electrolyte. The YSZ electrolyte was fully sintered with the addition of 0.5 wt% CuO, and the second phases of La2Zr2O7 and SrZrO3 did not form at 1350 °C. Ni-YSZ anode-supported unit cells were fabricated by co-firing at 1250-1400 °C. The unit cells co-fired at 1250 °C, 1300 °C, 1325 °C, 1350 °C and 1400 °C had maximum power densities of 0.18, 0.18, 0.30, 0.46 and 0.036 W/cm2, respectively, in humidified hydrogen (∼3% H2O) and air at 800 °C.  相似文献   

10.
A Ni/ yttria-stabilized zirconia (YSZ) cermet anode was modified by coating with samaria-doped ceria (SDC, Sm0.2Ce0.8O2) 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.The maximum power density of an anode-supported cell (electrolyte; 8 mol% YSZ and thickness of 30 μm, and cathode; La0.85Sr0.15MnO3) with the modified anode was about 0.3 W/cm2 at 700 °C in the mixture of methane (25%) and air (75%) as the fuel and air as the oxidant. The cell was operated for 500 h without significant degradation of cell performance.  相似文献   

11.
The main drawback of Ni/YSZ anode supports for solid oxide fuel cell application is their low tolerance to reducing and oxidizing (RedOx) atmosphere changes, owing to the Ni/NiO volume variation. This work describes a structured approach based on design of experiments for optimizing the microstructure for RedOx stability enhancement. A full factorial hypercube design and the response surface methodology are applied with the variables and their variation range defined as: (1) NiO proportion (40-60 wt% of the ceramic powders), (2) pore-former proportion (0-30 wt% corresponding to 0-64 vol.%), (3) NiO particle size (0.5-8 μm) and (4) 8YSZ particle size (0.6-9 μm).To obtain quadratic response models, 25 different compositions were prepared forming a central composite design. The measured responses are (i) shrinkage during firing, (ii) surface quality, (iii) as-sintered porosity, (iv) electrical conductivity after reduction and (v) expansion after re-oxidation. This approach quantifies the effect of all factors and their interactions. From the quadratic models, optimal compositions for high surface quality, electrical conductivity (>500 S cm−1 at room temperature) and RedOx expansion (<0.2% upon re-oxidation) are defined. Results show that expansion after re-oxidation is directly influenced by the sample porosity whereas, surprisingly, the NiO content, varied between 40 and 60 wt%, does not show any impact on this response.  相似文献   

12.
8Y2O3-ZrO2 (8YSZ)/NiO cermet anode-supported symmetric cell is introduced and fabricated using a tape casting process to analyze the anodic behavior of an anode-supported cell. An anode-supported symmetric cell helps us understand the complex anode structure of cermets. The anodic behavior of 8YSZ/NiO is compared to a MIEC electrode of Sm0.2Ce0.8O1.9 (SDC)/NiO. The anodic behavior of a 8YSZ/NiO cermet electrode is investigated and discussed with respect to the hydrogen partial pressure (p(H2)), water partial pressure (p(H2O)), area specific resistance (ASR), activation energy (Ea), thermal cycle, and redox process. Based on these studies, an empirical reaction model of 8YSZ/NiO is established, and the related reaction processes are discussed. On impedance spectra diagram, high and medium frequency arcs are associated with the charge transfer process and the H2O formation reaction, while the low frequency arc corresponds to the dissociative adsorption and the surface diffusion/gas phase diffusion process. Changes in microstructure by redox and thermal cycling have a significant effect on the electrochemical properties and structural stability of a thick anode-supported cermet structure.  相似文献   

13.
A novel design of solid oxide fuel cell (SOFC) which utilizes a thick film (<20 μm) as an electrolyte support is developed and tested. The sintered 16 μm-thick yttria-stabilized zirconia (YSZ) electrolyte film is mounted on a 1-mm thick YSZ ring by sintering the two pieces together. With this new configuration, it is possible to fabricate a thick (<20 μm) electrolyte-supported SOFC and measure the power density of the unit cell. With LSCF (La0.6Sr0.4Co0.2Fe0.8O3−δ) as a cathode and Ni–YSZ as a composite anode, the cell with a 16 μm-thick YSZ electrolyte achieves a high performance, i.e., a maximum power density of 590 mW cm−2 at 800 °C. This value is comparable with that of most anode-supported SOFCs using YSZ electrolytes.  相似文献   

14.
A Ni–YSZ (Y2O3-stabilized ZrO2) composite is commonly used as a solid oxide fuel cell anode. The composite powders are usually synthesized by mixing NiO and YSZ powders. The particle size and distribution of the two phases generally determine the performance of the anode. Two different milling methods are used to prepare the composite anode powders, namely, high-energy milling and ball-milling that reduce the particle size. The particle size and the Ni distribution of the two composite powders are examined. The effects of milling on the performance are evaluated by using both an electrolyte-supported, symmetric Ni–YSZ/YSZ/Ni–YSZ cell and an anode-supported, asymmetric cell. The performance is examined at 800 °C by impedance analysis and current-voltage measurements.  相似文献   

15.
Nickel oxide-yttria stabilized zirconia (NiO-YSZ) thin films were reactively sputter-deposited by pulsed direct current magnetron sputtering from the Ni and ZrY targets onto heated commercial NiO-YSZ substrates. The microstructure and composition of the deposited films were investigated with regard to application as thin anode functional layers (AFLs) for solid oxide fuel cells (SOFCs). The pore size, microstructure and phase composition of both as-deposited and annealed at 1200 °C for 2 h AFLs were studied by scanning electron microscopy and X-ray diffractometry and controlled by changing the deposition process parameters. The results show that annealing in air at 1200 °C is required to improve structural homogeneity of the films. NiO-YSZ films have pores and grains of several hundred nanometers in size after reduction in hydrogen. Adhesion of deposited films was evaluated by scratch test. Anode-supported solid oxide fuel cells with the magnetron sputtered anode functional layer, YSZ electrolyte and La0.6Sr0.4Co0.2Fe0.8O3/Ce0.9Gd0.1O2 (LSCF/CGO) cathode were fabricated and tested. Influence of thin anode functional layer on performance of anode-supported SOFCs was studied. It was shown that electrochemical properties of the single fuel cells depend on the NiO volume content in the NiO-YSZ anode functional layer. Microstructural changes of NiO-YSZ layers after nickel reduction-oxidation (redox) cycling were studied. After nine redox cycles at 750 °C in partial oxidation conditions, the cell with the anode NiO-YSZ layer showed stable open circuit voltage values with the power density decrease by 11% only.  相似文献   

16.
《Journal of power sources》2006,162(2):1053-1059
Fabrication of YSZ films deposited on NiO–samaria-doped ceria (SDC) substrate was studied by the chemical vapor infiltration method (CVI). A NiO–SDC substrate was used as oxygen source. The main mechanism of YSZ growth was electrochemical vapor deposition (EVD), while the contribution of oxygen in the carrier gas increased with increasing NiO content of the substrate above 60.6 mol%. The YSZ film on SDC used as the anode proved effective in obtaining high cell performance. In particular, a YSZ film thickness of 1 μm yielded the highest cell performance in the temperature range from 973 to 1073 K. The CVI method was useful for preparing a dense and strong YSZ film on the complex-shaped NiO–SDC substrate.  相似文献   

17.
In the present study, the anode-supported micro-tubular solid oxide fuel cells (MT-SOFCs) with an electrolyte thin interlayer were manufactured. The anode support tubes consisting of 56 wt% nickel oxide and 44 wt% YSZ (8 mol% yttria (Y2O3) stabilized zirconia (ZrO2)) were produced by using the thermo-extrusion method, whereas the electrolyte and cathode layers were manufactured using the dip-coating method. The half-cells consisting of anode and electrolyte were manufactured by using two different methods. In the first method, the anode-support tubes were pre-sintered at 1200 °C, then covered with the electrolyte layer by using the dip-coating method and then exposed to second sintering at 1400 °C. In the second method, the anode and electrolyte layers were sintered together at 1400 °C (co-sintering) in order to produce the half-cells. The half-cells that were produced and then coated with cathode solutions by using the dip-coating method and the final cells were successfully produced at the end of the sintering at 1150 °C. The porosity and shrinkage percentage values of these MT-SOFCs differed from each other. The power densities of these cells were tested at 700 °C, 750 °C, and 800 °C by using H2 gas as fuel and the results of the microstructural and cost analyses were compared.  相似文献   

18.
To improve the performance of anode-supported solid oxide fuel cells (SOFCs), various types of single cells are manufactured using a thin-film electrolyte of Yttria stabilized zirconia (YSZ) and an anode functional layer composed of a NiO–YSZ nano-composite powder. Microstructural/electrochemical analyses are conducted. Single-cell performances are highly dependent on electrolyte thickness, to the degree that the maximum power density increases from 0.74 to 1.12 W cm−2 according to a decrease in electrolyte thickness from 10.5 to 6.5 μm at 800 °C. The anode functional layer reduced the polarization resistance of a single cell from 1.07 to 0.48 Ω cm2 at 800 °C. This is attributed to the provision by the anode layer of a highly reactive and uniform electrode microstructure. It is concluded that optimization of the thickness and homogeneity of component microstructure improves single-cell performances.  相似文献   

19.
Solid oxide fuel cells (SOFCs) represent an option to provide a bridging technology for energy conversion (coal syngas) as well as a long-term technology (hydrogen from biomass). Whether the fuel is coal syngas or hydrogen from biomass, the effect of impurities on the performance of the anode is a vital question. The anode resistivity during SOFC operation with phosphine-contaminated syngas was studied using the in situ Van der Pauw method. Commercial anode-supported solid oxide fuel cells (Ni/YSZ composite anodes, YSZ electrolytes) were exposed to a synthetic coal syngas mixture (H2, H2O, CO, and CO2) at a constant current and their performance evaluated periodically with electrochemical methods (cyclic voltammetry, impedance spectroscopy, and polarization curves). In one test, after 170 h of phosphine exposure, a significant degradation of cell performance (loss of cell voltage, increase of series resistance and increase of polarization resistance) was evident. The rate of voltage loss was 1.4 mV h−1. The resistivity measurements on Ni/YSZ anode by the in situ Van der Pauw method showed that there were no significant changes in anode resistivity both under clean syngas and syngas with 10 ppm PH3. XRD analysis suggested that Ni5P2 and P2O5 are two compounds accumulated on the anode. XPS studies provided support for the presence of two phosphorus phases with different oxidation states on the external anode surface. Phosphorus, in a positive oxidation state, was observed in the anode active layer. Based on these observations, the effect of 10 ppm phosphine impurity (or its reaction products with coal syngas) is assigned to the loss of performance of the Ni/YSZ active layer next to the electrolyte, and not to any changes in the thick Ni/YSZ support layer.  相似文献   

20.
In this study the fabrication and characterization of Ni/10ScSZ (Ni/10 mol% Sc2O3-90 mol% ZrO2) and Ni/10Sc1CeSZ (Ni/10 mol% Sc2O3-1 mol% CeO2-89 mol% ZrO2) cermet anode films was studied and compared. Both 10ScSZ and 10Sc1CeSZ electrolyte powders showed tetragonal and cubic phases at room temperature, respectively. The NiO/10ScSZ and NiO/10Sc1CeSZ composites with 10-60 vol% of Ni content were prepared by mixing as-received commercial powders of NiO, 10ScSZ and 10Sc1CeSZ followed by ink preparation. Samples were sintered for 1 h at temperatures of 1250-1350 °C. All the cermet films were then reduced under a mixture of hydrogen (10%) and nitrogen (90%) at 800 °C for 2 h. The effect of Ni content and sinter temperature on the DC electrical conductivity were investigated, and the results showed a sharp change in conductivity at around 30 vol% Ni, corresponding to continuity/discontinuity of the Ni-Ni contact network, and the conductivity increased as the sinter temperature increased from 1250 to 1350 °C. An acceptable electrical conductivity at 700 °C for these cermet films was obtained at >40 vol% Ni, consistent with behaviour reported for more conventional Ni/YSZ cermets. The effect of sinter temperature on the microstructure and porosity of Ni/10Sc1CeSZ and Ni/10ScSZ cermet films was also investigated. This revealed that the porosity of the cermet films with the same Ni content decreased as the sinter temperature increased and that, for a given sinter temperature, the porosity of the cermet films increased with Ni content. The porosities of 40Ni/60ScCeSZ (40 vol% Ni/60 vol% 10Sc1CeSZ) and 40Ni/60ScSZ (40 vol% Ni/60 vol% 10ScSZ) anodes sintered at 1250, 1300 and 1350 °C for 1 h were in the range of 30-45%. Electrochemical measurement of symmetrical cells using an 8YSZ electrolyte at 700 °C revealed that the lowest electrode polarization resistance of 40Ni/60ScCeSZ and 40Ni/60ScSZ anodes was obtained at sinter temperatures of 1350 °C and 1300 °C respectively. Carbon deposition over 40Ni/60ScCeSZ, 40Ni/60ScSZ and 40Ni/60YSZ catalysts was evaluated at 700 °C for 1 h at S/C = 0.8 and the results showed that the ratio of deposited carbon was lower in the case of Ni/10ScSZ and Ni/10Sc1CeSZ compared to Ni/YSZ (0.35). Overall, Ni/10Sc1CeSZ and Ni/10ScSZ cermets having 40 vol% Ni were found to be optimum, with the 40Ni/60ScCeSZ cermet proving to be better than 40Ni/60ScSZ cermet in terms of both electronic conductivity and electrode polarization resistance, with both materials exhibiting improved tolerance towards carbon deposition compared to Ni/YSZ.  相似文献   

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