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1.
The cathode reaction mechanism of porous Sm0.5Sr0.5CoO3−δ, a mixed ionic and electronic conductor (MIEC), is studied through a comparison with the composite cathode Sm0.5Sr0.5CoO3−δ/Sm0.2Ce0.8O1.9. First, the cathodic behaviour of porous Sm0.5Sr0.5CoO3−δ and Sm0.5Sr0.5CoO3−δ/Sm0.2Ce0.8O1.9 are observed for micro-structure and impedance spectra according to Sm0.2Ce0.8O1.9 addition, thermal cycling and long-term properties. The cathode reaction mechanism is discussed in terms of frequency response, activation energy, reaction order and electrode resistance for different oxygen partial pressures p(O2) at various temperatures. Three elementary steps are considered to be involved in the cathodic reaction: (i) oxygen ion transfer at the cathode-electrolyte interface; (ii) oxygen ion conduction in the bulk cathode; (iii) gas phase diffusion of oxygen. A reaction model based on the empirical equivalent circuit is introduced and analyzed using the impedance spectra. The electrode resistance at high frequency (Rc,HF) in the impedance spectra represents reaction steps (i), due to its fast reaction rate. The electrode resistance at high frequency is independent of p(O2) at a constant temperature because the semicircle of Rc,HF in the complex plane of the impedance spectra is held constant for different values of p(O2). Reaction steps (ii) and (iii) are the dominant processes for a MIEC cathode, according to the analysis results. The proposed cathode reaction model and results for a solid oxide fuel cell (SOFC) well describe a MIEC cathode with high ionic conductivity, and assist the understanding of the MIEC cathode reaction mechanism.  相似文献   

2.
The electrochemical properties of an Sm0.5Sr0.5CoO3−δ/Co3O4 (SSC/Co3O4) composite cathode were investigated as a function of the cathode-firing temperature, SSC/Co3O4 composition, oxygen partial pressure and CO2 treatment. The results showed that the composite cathodes had an optimal microstructure at a firing temperature of about 1100 °C, while the optimum Co3O4 content in the composite cathode was about 40 wt.%. A single cell with this optimized C40-1100 cathode exhibited a very low polarization resistance of 0.058 Ω cm2, and yielded a maximum power density of 1092 mW cm−2 with humidified hydrogen fuel and air oxidant at 600 °C. The maximum power density reached 1452 mW cm−2 when pure oxygen was used as the oxidant for a cell with a C30-1100 cathode operating at 600 °C due to the enhanced open-circuit voltage and accelerated oxygen surface-exchange rate. X-ray diffraction and thermogravimetric analyses, as well as the electrochemical properties of a CO2-treated cathode, also implied promising applications of such highly efficient SSC/Co3O4 composite cathodes in single-chamber fuel cells with direct hydrocarbon fuels operating at temperatures below 500 °C.  相似文献   

3.
Cobaltite-based perovskites based on Sm0.5Sr0.5CoO3−δ (SSC) are attractive as a cathode material with a barrier layer for solid oxide fuel cells (SOFC) due to their high electrochemical activity and electrical conductivity. SSC, synthesized by a complex method, is used as a cathode material in a composite cathode with Gd-doped ceria (GDC). A porous GDC layer is fabricated as a barrier to resist reactions of SSC with yttria-stabilized zirconia (YSZ). The effects of the ratio of SSC on GDC in composite cathodes and the thickness of the GDC barrier are characterized in this study. An SOFC with an SSC7–GDC3 composite cathode on a 4 μm GDC layer at 0.8 V yields the highest fuel cell performance: 1.24 W cm2 and 0.61 W cm2 at 780 °C and 680 °C, respectively. Impedance analysis indicates that the ohmic resistances are more dependent upon the GDC barrier thickness than the cathode composition. The polarization resistances at 780 °C and 730 °C exhibit similar values, but with decreasing temperature, the polarization resistances change dramatically according to the composition and barrier thickness. The ohmic and polarization resistances show different trends in different temperature ranges, due to the different charge transfer mechanisms of SSC and GDC within those temperature ranges. To obtain higher fuel cell performance, the addition of GDC into the porous SSC is effective, and the compositions of the composite cathode as well as the thickness of the barrier layer need to be optimized.  相似文献   

4.
A SSC deposit has been prepared by flame spraying using Sm0.7Sr0.3CoO3−δ (SSC) powder synthesized by a solid-state reaction. A post-spray annealing treatment of the SSC deposit has been performed. The coating characterization includes: the electrical conductivity of the SSC deposit along the lamellar direction measured by a four-electrode D.C. approach, the microstructures of SSC powders and deposits characterized using X-ray diffraction and scanning electron microscopy, the oxygen stoichiometry in both the as-sprayed and annealed deposits and starting powder determined by redox titration. The results show that a significant oxygen deficiency (12%) occurs in the sprayed powder particles during high temperature flame spraying, leading to reduction of the electrical conductivity of the as-sprayed SSC deposit. It is found that oxygen can be recovered through post-spray annealing treatment. After annealing at 900 °C for 5 h or at 1100 °C for 10 h, the electrical conductivity of annealed SSC reaches 433 S cm−1 or 510 S cm−1 at 600 °C due to a sharp recovery of deficient oxygen and microstructural change.  相似文献   

5.
The mixed ionic and electronic conductors (MIECs) of Sm0.5Sr0.5Co0.4Ni0.6O3−δ (SSCN)–Sm0.2Ce0.8O1.9 (SDC) were investigated for potential application as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs) based on an SDC electrolyte. Electrochemical impedance spectroscopy (EIS) technique was performed over the temperature range of 600–850 °C to determine the cathode polarization resistance which is represented by area specific resistance (ASR). To investigate the ORR mechanism, the impedance diagram for 70SSCN–30SDC was measured under applied cathodic voltage from E = 0.0 to E = −0.3 V. It indicated that the charge transfer dominated the rate-determining step at the temperature of 600 °C; whereas the diffusion or dissociative adsorption of oxygen dominated the rate-determining step at the temperature of 800 °C. In this study, the exchange current density (i0) for oxygen reduction reaction (ORR) was determined from the EIS data. The i0 value of 70SSCN–30SDC/SDC was 187.6 mA cm−2 which is larger than the i0 value of 160 mA cm−2 for traditional cathode/electrolyte, i.e. LSM/YSZ at 800 °C, indicating that the 70SSCN–30SDC composite cathode with a high catalytically active surface area could provide the oxygen reduction reaction areas not only at the triple-phase boundaries but also in the whole composite cathode.  相似文献   

6.
The Sm0.5Sr0.5CoO3−δ (SSC) with perovskite structure is synthesized by the glycine nitrate process (GNP). The phase evolution of SSC powder with different calcination temperatures is investigated by X-ray diffraction and thermogravimetric analyses. The XRD results show that the single perovskite phase of the SSC is completely formed above 1100 °C. The anode-supported single cell is constructed with a porous Ni-yttria-stabilized zirconia (YSZ) anode substrate, an airtight YSZ electrolyte, a Sm0.2Ce0.8O2−δ (SDC) barrier layer, and a screen-printed SSC-SDC composite cathode. The SEM results show that the dense YSZ electrolyte layer exhibits the good interfacial contact with both the Ni-YSZ and the SDC barrier layer. The porous SSC-SDC cathode shows an excellent adhesion with the SDC barrier layer. For the performance test, the maximum power densities are 464, 351 and 243 mW cm−2 at 800, 750 and 700 °C, respectively. According to the results of the electrochemical impedance spectroscopy (EIS), the charge-transfer resistances of the electrodes are 0.49 and 1.24 Ω cm2, and the non charge-transfer resistances are 0.48 and 0.51 Ω cm2 at 800 and 700 °C, respectively. The cathode material of SSC is compatible with the YSZ electrolyte via a delicate scheme employed in the fabrication process of unit cell.  相似文献   

7.
Cathode reaction models for solid oxide fuel cells with proton conducting electrolyte (H-SOFC) are proposed, and the reacting orders for each elementary step with respect to oxygen and water vapor partial pressure are calculated. The limiting steps of cathode reactions are investigated with Sm0.5Sr0.5CoO3−δ (SSC)-BaCe0.8Sm0.2O3−δ (BCS) composite cathodes. The results suggest that the migration of protons to TPBs and the surface diffusion of might be the limiting reactions for SSC-BCS composite cathodes in wet atmosphere, while the oxygen ions transferring into electrolyte, the reducing of Oad to , and surface diffusion of might be the limiting reactions for SSC-BCS composite cathode in dry atmosphere.  相似文献   

8.
In order to improve the electrical conductivity of the SrSc0.2Co0.8O3−δ (SrScCo) electrode, a composite of 70 wt% SrSc0.2Co0.8O3−δ and 30 wt% Sm0.5Sr0.5CoO3−δ (SrScCo + SmSrCo) was prepared and investigated for electrochemical oxygen reduction at intermediate temperatures. The phase reaction between SrScCo and SmSrCo and its effect on the electrical conductivity, oxygen vacancy concentration and oxygen mobility were examined by XRD, 4-probe DC conductivity measurement, iodometry titration and O2-TPD experiment, respectively. The results showed that the composite reached a maximum conductivity around 123 S cm−1 at 600 °C, nearly five times that of SrScCo. AC impedance results showed that the electron charge-transfer process was greatly improved by forming the composite electrode, while the oxygen-ion charge-transfer process was somewhat deteriorated. By firing at 1000 °C for 2 h, a SOFC with the SrScCo + SmSrCo cathode and thin-film SDC electrolyte delivered peak power densities of 1100 and 366 mW cm−2 at 600 and 500 °C, respectively, which were only modestly lower than those of a similar cell with a pure SrScCo cathode.  相似文献   

9.
A cobalt-free cubic perovskite oxide Sm0.5Sr0.5Fe0.8Cu0.2O3−δ (SSFCu) was investigated as a novel cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs). The thermal expansion coefficient (TEC) of SSFCu was close to that of Sm0.2Ce0.8O1.9(SDC) electrolyte and the electrical conductivity of SSFCu sample reached 72–82 S cm−1 in the commonly operated temperatures of IT-SOFCs (400–600 °C). Symmetrical electrochemical cell with the configuration of SSFCu/SDC/SSFCu was applied for the impedance study and area specific resistance (ASR) of SSFCu cathode material was as low as 0.085 Ω cm2 at 700 °C. Laboratory-sized tri-layer cells of NiO-SDC/SDC/SSFCu were operated from 450 to 700 °C with humidified hydrogen (∼3% H2O) as fuel and the static air as oxidant. A maximum power density of 808 mW cm2 was obtained at 700 °C for the single cell.  相似文献   

10.
Uniform nanopowders of La0.6Sr0.4CoO3−δ (LSC) were synthesized by the combined citrate–EDTA method. The precursor solution was prepared from nitrates of the constituent metal ion, citric acid and EDTA with a pH value controlled by ammonia. The obtained product was characterized by TG/DTA, XRD, SEM, and BET measurements. The single perovskite phase could form completely after sintering at the temperature of 900 °C. There was no significant effect of the precursor solution pH value on the perovskite phase formation temperature; however, LSC powders prepared from the precursors with different pH values showed specific shapes. The morphology of La0.6Sr0.4CoO3−δ powder was also optimized with proper surfactant addition. The sintered La0.6Sr0.4CoO3−δ bulk samples exhibited an electrical conductivity of 1867 S cm−1 in air at 800 °C. The impedance spectra of a symmetric LSC cathode on a GDC electrolyte substrate were measured and polarization resistance (Rp) values of 0.17 Ω cm2 at 700 °C and 0.07 Ω cm2 at 750 °C in air were obtained.  相似文献   

11.
A cobalt-free Sm0.5Sr0.5FeO3−δ–BaZr0.1Ce0.7Y0.2O3−δ (SSF–BZCY) was developed as a composite cathode material for proton-conducting solid oxide fuel cells (H-SOFC) based on proton-conducting electrolyte of stable BZCY. The button cells of Ni-BZCY/BZCY/SSF–BZCY were fabricated and tested from 550 to 700 °C with humidified H2 (~3% H2O) as a fuel and ambient oxygen as oxidant. An open-circuit potential of 1.024 V, maximum power density of 341 mW cm−2, and a low electrode polarization resistance of 0.1 Ω cm2 were achieved at 700 °C. The experimental results indicated that the SSF–BZCY composite cathode is a good candidate for cathode material.  相似文献   

12.
A cobalt-free Ba0.5Sr0.5Fe0.9Ni0.1O3−δ–Sm0.2Ce0.8O1.9 (BSFN–SDC) composite was employed as a cathode for proton-conducting solid oxide fuel cells (H-SOFCs) using BaZr0.1Ce0.7Y0.2O3−δ (BZCY) as the electrolyte. The chemical compatibility between BSFN and SDC was evaluated. The XRD results showed that BSFN was chemically compatible with SDC after co-fired at 1100 °C for 5 h. The thermal expansion coefficient (TEC) of BSFN–SDC, which showed a reasonably reduced value (16.08 × 10−6 K−1), was effectively decreased due to Ce0.8Sm0.2O1.9 (SDC) added. A single cell of Ni–BZCY/Ni–BZCY/BZCY/BSFN–SDC with a 25-μm-thick BZCY electrolyte membrane exhibited excellent power densities as high as 361.8 mW cm−2 at 700 °C with a low polarization resistance of 0.174 Ω cm2. The excellent performance implied that the cobalt-free BSFN–SDC composite was a promising alternative cathode for H-SOFCs.  相似文献   

13.
This study investigates the microstructure and electrochemical properties of Sm0.5Sr0.5Co0.8Cu0.2O3−δ (SSC-Cu) cathode infiltrated with Ce0.8Sm0.2O1.9 (SDC). The newly formed nanosized electrolyte material on the cathode surface, leading the increase in electrochemical performances is mainly attributed to the creation of electrolyte/cathode phase boundaries, which considerably increases the electrochemical sites for oxygen reduction reaction. Based on the experiment results, the 0.4 M SDC infiltration reveals the lowest cathode polarization resistance (RP), the cathode polarization resistances (Rp) are 0.117, 0.033, and 0.011 Ω cm2 at 650, 750, and 850 °C, and the highest peak power density, are 439, 659, and 532 mW cm−2 at 600, 700, and 800 °C, respectively. The cathode performance in SOFCs can be significantly improved by infiltrating nanoparticles of SDC into an SSC-Cu porous backbone. This study reveals that the infiltration approach may apply in SOFCs to improve their electrochemical properties.  相似文献   

14.
The properties and performance of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) + Sm0.2Ce0.8O1.9 (SDC) (70:30 in weight ratio) composite cathode for intermediate-temperature solid-oxide fuel cells were investigated. Mechanical mixing of BSCF with SDC resulted in the adhesion of fine SDC particles to the surface of coarse BSCF grains. XRD, SEM-EDX and O2-TPD results demonstrated that the phase reaction between BSCF and SDC was negligible, constricted only at the BSCF and SDC interface, and throughout the entire cathode with the formation of new (Ba,Sr,Sm,Ce)(Co,Fe)O3−δ perovskite phase at a firing temperature of 900, 1000, and ≥ 1050 °C, respectively. The BSCF + SDC electrode sintered at 1000 °C showed an area specific resistance of ∼0.064 Ω cm2 at 600 °C, which is a slight improvement over the BSCF (0.099 Ω cm2) owing to the enlarged cathode surface area contributed from the fine SDC particles. A peak power density of 1050 and ∼382 mW cm−2 was reached at 600 and 500 °C, respectively, for a thin-film electrolyte cell with the BSCF + SDC cathode fired from 1000 °C.  相似文献   

15.
In this study, a new oxygen-deficient cathode material, Sm0.5Sr0.5Co1−xCuxO3−δ (SSCCu) was developed. It is expected to enhance the efficiency of intermediate-temperature solid oxide fuel cells (IT-SOFCs). The structure, conductivity and electrochemical performance of SSCCu were examined as a function of copper content. The structure of Sm0.5Sr0.5Co0.9Cu0.1O3−δ and Sm0.5Sr0.5Co0.8Cu0.2O3−δ samples was a single orthorhombic perovskite phase. Second phase SrCoO2.8, however, formed in the Sm0.5Sr0.5Co0.7Cu0.3O3−δ and Sm0.5Sr0.5Co0.6Cu0.4O3−δ samples. The conductivity of the Sm0.5Sr0.5Co0.7Cu0.3O3−δ cathode was higher than that of other samples. However, the Sm0.5Sr0.5Co0.8Cu0.2O3−δ electrode exhibited the lowest overpotential of 25 mV at 400 mA cm−2 and the lowest area special resistance of 0.2 Ω cm2 at 700 °C.  相似文献   

16.
Sm0.5Sr0.5MO3−δ (M = Co and Mn) materials are synthesized, and their properties and performance as cathodes for solid oxide fuel cells (SOFCs) on Sm0.2Ce0.8O1.9 (SDC) and Y0.16Zr0.92O2.08 (YSZ) electrolytes are comparatively studied. The phase structure, thermal expansion behavior, oxygen mobility, oxygen vacancy concentration and electrical conductivity of the oxides are systematically investigated. Sm0.5Sr0.5CoO3−δ (SSC) has a much larger oxygen vacancy concentration, electrical conductivity and TEC than Sm0.5Sr0.5MnO3−δ (SSM). A powder reaction demonstrates that SSM is more chemically compatible with the YSZ electrolyte than SSC, while both are compatible with the SDC electrolyte. EIS results indicate that the performances of SSC and SSM electrodes depend on the electrolyte that they are deposited on. SSC is suitable for the SDC electrolyte, while SSM is preferred for the YSZ electrolyte. A peak power density as high as 690 mW cm−2 at 600 °C is observed for a thin-film SDC electrolyte with SSC cathode, while a similar cell with YSZ electrolyte performs poorly. However, SSM performs well on YSZ electrolyte at an operation temperature of higher than 700 °C, and a fuel cell with SSM cathode and a thin-film YSZ electrolyte delivers a peak power density of ∼590 mW cm−2 at 800 °C. The poor performances of SSM cathode on both YSZ and SDC electrolytes are obtained at a temperature of lower than 650 °C.  相似文献   

17.
Low-temperature solid oxide fuel cells with a La0.8Sr0.2MnO3 (LSM) interlayer between the Ce0.9Gd0.1O1.95 (GDC) electrolyte membrane (20 μm) and the Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF)–GDC composite cathode are fabricated by sintering the BSCF–GDC composite cathodes at 900, 950 and 1000 °C. The results of scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX) for a model LSM/BSCF bi-layer pellet suggest that Ba, Co and Fe in BSCF as well as La and Mn in LSM have diffused into their counter sides. The X-ray diffraction (XRD) results on the simulated cells also indicate the incorporation of La into the GDC electrolyte membrane and the mutual diffusion of elements between the LSM layer and the BSCF layer. Analysis of the impedance spectra and interfacial reaction activation energies shows that LSM interlayer accelerates the oxygen reduction. Considering a good cell performance and the highest open-circuit voltages (OCVs) at 600–500 °C, the optimum sintering temperature of BSCF–GDC composite cathode onto LSM interlayer is 900 °C.  相似文献   

18.
A palladium-impregnated La0.75Sr0.25Cr0.5Mn0.5O3−δ/yttria-stabilized zirconia (LSCM/YSZ) composite anode is investigated for the direct utilization of methane and ethanol fuels in solid oxide fuel cells (SOFCs). Impregnation of Pd nanoparticles significantly enhances the electrocatalytic activity of LSCM/YSZ composite anodes for the methane and ethanol electrooxidation reaction. At 800 °C, the maximum power density is increased by two and eight times with methane and ethanol fuels, respectively, for a cell with the Pd-impregnated LSCM/YSZ composite anode, as compared with that using a pure LSCM/YSZ anode. No carbon deposition is observed during the reaction of methane and ethanol fuels on the Pd-impregnated LSCM/YSZ composite anode. The results show the promises of nanostructured Pd-impregnated LSCM/YSZ composites as effective anodes for direct methane and ethanol SOFCs.  相似文献   

19.
A Sm0.5Sr0.5CoO3−δ-Ce0.8Sm0.2O2−δ (SSC-SDC) composite is employed as a cathode for proton-conducting solid oxide fuel cells (H-SOFCs). BaZr0.1Ce0.7Y0.2O3−δ (BZCY) is used as the electrolyte, and the system exhibits a relatively high performance. An extremely low electrode polarization resistance of 0.066 Ω cm2 is achieved at 700 °C. The maximum power densities are: 665, 504, 344, 214, and 118 mW cm−2 at 700, 650, 600, 550, and 500 °C, respectively. Moreover, the SSC-SDC cathode shows an essentially stable performance for 25 h at 600 °C with a constant output voltage of 0.5 V. This excellent performance implies that SSC-SDC, which is a typical cathode material for SOFCs based on oxide ionic conductor, is also a promising alternative cathode for H-SOFCs.  相似文献   

20.
In this study, we will report our investigation for La0.75Sr0.25Cr0.5Mn0.5O3−δ (LSCrM) based anodes impregnated with solutions of cobalt (Co) nitrate. A YSZ supported SOFC with pure LSCrM anode and La0.7Sr0.3MnO3 (LSM) cathode exhibits the maximum power density (Pmax) of 58.7 and 5.2 mW cm−2 at 850 °C in dry H2 and dry CH4. After the modification of anode with Co nitrate, the Pmax reaches 196.2 mW cm−2 in dry H2 and 28.5 mW cm−2 in dry CH4, about 3.34 times and 5.48 times increase, respectively. These results indicate that Co is also a potential catalyst for LSCrM anode. Moreover, the effect of impregnation amount of catalyst on the cell performance is also evaluated in this study.  相似文献   

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