Papers by Keyword: IT-SOFC

Abstract: Active roles of carbon species in solid oxide fuel cell (SOFC) cathode was simulated by adding graphene oxide (GO) into Ba_0.5Sr_0.5Co_0.2Fe_0.8 (BSCF) materials prepared by sol-gel method. The mixture was heated up to intermediate temperature SOFC range (650 - 850°C) for a period of 5 hours. A depth-profiling measurement by x-ray photoelectron spectroscopy (XPS) technique was carried out to analyse the carbon species activities at near surface of BSCF cathode. A depth-profiling analysis indicated that the graphene oxide bond components are retained under the cathode surface and does not affected the formation of carbonate phases in BSCF cathode.

Abstract: OAbstract. One of the approaches that has been done to produce a better performance of an intermediate temperature solid oxide fuel cell (IT-SOFC) is by varying the synthesis methods. This paper focused on the proton conducting electrolyte in particularly barium cerate and barium zirconate system namely BaCe_0.9Y_0.1O_3-δ (BCY) and BaZr_0.9Y_0.1O_3-δ (BZY). Supercritical ethanol processing technique is one of the alternative synthesis routes that able to produce ceramics powder at lower calcination temperature. The samples were synthesized in High-Pressure-High-Temperature (HP-HT) Batch Wise reactor system using ethanol as reaction medium. XRD was used to study the structure of both samples and all the data were refined using Rietveld refinement method by X’pert Highscore software. VESTA software is used to observe the crystal structure for both BCY and BZY samples. Both BCY and BZY have 98.16% and 96.55% purity after being calcined at 700°C and 1100°C, respectively. This study showed that BCY has orthorhombic structure with lattice parameter a=8.76Å, b=6.24Å and c=6.21Å and BZY exhibited cubic structure with a=b=c, and a=4.194Å. It was observed that BCY synthesized by supercritical fluid (SCF) method at reduced calcination temperature exhibited an acceptable value of lattice paramter as compared to other method that used higher processing temperature.

Abstract: Abstract. Solid oxide fuel cell (SOFC) is an electrochemical conversion device that undergoes a thermal cycling at various operating temperature where lead to the degradation of its mechanical properties. Electrolyte among the main component in SOFC plays a crucial part in defined the overall performance which facing a lattice expansion event when exposed to heating. Thus, in this paper BaCe0.54Zr0.36Y0.1O3-δ (BCZY) was selected as potential electrolyte for intermediate temperature solid oxide fuel cell (IT-SOFC) to investigate its lattice expansion as a function of temperature. The sample was prepared via a sol gel method and calcined at 1100°C for 10 hours to form a powder and then pressed to become a pellet. To ensure a good densification in such pellet, two-steps sintering processes was indicated at 1500°C and ground to a powder form prior to the lattice expansion measurements. High temperature X-ray diffraction (HT-XRD) was used to study the lattice expansion of sample in the temperature range of 25°C to 700°C with interval 100°C under air atmosphere. HT-XRD analysis was done using X’pert Highscore Plus software and Visual for Electronic and Structural Analysis (VESTA) software was used to observe the crystal structure. Phase and structural analysis of BCZY electrolyte materials were discussed. Apparently, the BCZY shows an average of 97% phase purity from room temperature to 700°C. Rietveld refinement analysis revealed that the BaCe0.54Zr0.36Y0.1O3-δ exhibits cubic symmetrical structure with unit cell, a=b=c that varied from 4.3440Å - 4.3731Å for all the temperature studied. Thus, the expansion percentage for the lattice expansion from room temperature to 700°C was about 12.6 %.

Abstract: A “cobalt free” cathode material with stoichiometric composition La_0.8Sr_0.2Fe_0.8Cu_0.2O₃ (LSFCu) was specifically developed for La_0.8Sr_0.2Ga_0.8Mg_0.2O₃ (LSGM) electrolyte. The chemical stability with LSGM electrolyte was investigated by structural and morphological analysis. The electrochemical properties of LSFCu dense pellets were investigated in the temperature range 600–750°C by electrochemical impedance spectroscopy (EIS). LSFCu/LSGM/LSFCu symmetrical cells were prepared and Area Specific Resistance (ASR) values, directly depending on the rate limiting step of the oxygen reduction reaction, were evaluated. Fuel cells were prepared using LSFCu as cathode material on LSGM pellet and electrochemical tests were performed and compared to similar fuel cells prepared by using commercial La_0.6Sr_0.4Fe_0.8Co_0.2O₃(LSFCo). The maximum current density and power density recorded for LSFCu and LSFCo were comparable demonstrating that Cu can be used as substitutes Co.

Abstract: The development of electrochemical devices towards clean energy generation has been intensified in the last years. In this context, fuel cells, and especially intermediate temperature solid oxide fuel cells (IT-SOFC) have received much attention. Perovskite type materials of composition Ba_1-xSr_xCo_1-yFe_yO_3-δ, doped or not with rare earth ions, have been quite promising because they have good ionic conductivity and operate at relatively low temperatures (500 750 °C). In this study, powders of compositions (BaSr)_0.5Sm_0.5Co_0.8Fe_0.2O_3-δ (BSSCF) and (BaSr)_0.5Nd_0.5Co_0.8Fe_0.2O_3-δ (BSNCF) were prepared using commercial gelatin powder as a polymerizing agent for its use as cathode. The as-prepared powders were calcined at 1000 oC and characterized by X-ray diffraction and scanning electron microscopy. Screen-printed symmetrical cells were sintered 1150 °C and studied by electrochemical impedance spectroscopy in order to assess the cathode kinetics for the oxygen reduction reaction. The best area specific resistance was found for the BSSCF cathode sintered at 1150 °C for 4 h (0.157 Ω.cm² at 750 °C), demonstrating that this novel composition is suitable for application as SOFC cathode material. key words: Cathode, microstructure, impedance spectroscopy, IT-SOFC.

Abstract: The LSCM (La_0.7Sr_0.3Cr_0.5Mn_0.5O_3-δ) powders were synthesized by glycine-nitrate process (GNP). An anode functional layer (AFL) LSCM was fabricated on an porous NiO-LSCM anode substrate by slurry spin coating. The effect of pore-former, sintering temperature and sintering time on the quality of thin film was investigated. The film with good apparent morphology was obtained when the operating parameters were fixed as follows: the pore-former is ethyl cellulose, the content of ethyl cellulose is 5 wt.%, the sintering temperature is 1000 °C and the sintering time is 4 h.

Abstract: The Gd substituted BaCe_0.8Y_0.1O_3-δ nanocomposites were prepared by a modified Pechini route and then the prepared material was subjected to conventional sintering at 1400°C. The powder XRD results show that the material exhibit orthorhombic crystalline structure and the mean particle size were calculated to be ~40 nm. SEM micrographs indicate that the particle sizes were observed in the nanometer range with dense microstructure, which leads to increase in the densification of the material. FT-IR result confirms the presence of metal bondings in the material. DTA peaks observed at 725°C and 880°C show the crystallization of the material and the corresponding weight loss was recorded in the TG spectrum. I-V & I-P results show that the maximum open cell voltage (OCV) was measured at 1.1V and the maximum power density of about 801mWcm² was observed which may be due to the substitution of Gd ions into the BaCeYO₃ sites showing an improved electrochemical performance of IT-SOFC electrolytes.

Abstract: Perovskite-structure La0.7Sr0.3Cr0.5Mn0.5O3-δanode powder was prepared by glycine nitrate process. The result of characterization indicated that the pore morphology and mechanical property of anode support pellets using starch as pore-forming agent are superior to that of using activated carbon. The maximum value of porosity and specific surface area are 40%, 1.256m2/mg at 10MPa, respectively. The conductive mechanism is small-polaron conductive mechanism at low temperature, but it is metalloid conductive mechanism at high temperature.

Abstract: To develop novel cathode materials with high electrical performances for intermediate temperature solid oxide fuel cells (IT-SOFCs) and optimize the preparation process, perovskite-type oxides Pr_1-x-ySr_xCa_yCo_1-zFe_zO_3-δ (x=0.1, 0.2; y=0.1, 0.2; z=0.2, 0.3, 0.4; denoted as PSCCF-81182, PSCCF-72173 and PSCCF-62264) were prepared by solid state reaction. The formation process, phase structure and microstructure of the prepared samples were measured using TG-DTA, FT/IR, XRD and SEM techniques. The mixed conductivity of the samples was measured using DC four-terminal method in the range of 150-950 °C. Chemical state of the elements was measured by XPS experiments. The results show that the prepared samples PSCCF-81182, PSCCF-72173 and PSCCF-62264 exhibit a single phase with cubic perovskite structure after sintered at 1200 °C for 6 h. The mixed conductivity of the samples increases with temperature up to a maximum value, and then decreases. At lower temperature, the conductivity follows small polaron hopping mechanism. The negative temperature dependence occurring at higher temperature is due to the creation of oxygen vacancies for charge balance. At intermediate temperature (600-800 °C), the mixed conductivity values of the prepared samples are all much higher than 100 S•cm^-1，and can meet the demand of cathode materials for IT-SOFC. XPS tests show that Co and Fe elements in PSCCF-72173 are all of + 3 and + 4 valence. Absorbed oxygen can also be found from the XPS patterns, which is related to the concentration of oxygen vacancies in the perovskite-type oxides.

Abstract: Pr_1.2Sr_0.8NiO₄ (PSNO) and Sm_0.2Ce_0.8O_1.9 (SCO) powders were synthesized by a glycine-nitrate process and a gel-casting process, respectively. Pr_1.2Sr_0.8NiO₄-x Sm_0.2Ce_0.8O_1.9 (x=0, 25, 50) composite cathode materials were prepared by mechanically mixing the two powders. The particle size of the synthesized PSNO and SCO powders is about 100nm and 50nm, respectively. PSNO and SCO have a good chemical compatibility. Area specific resistance value for the Pr_1.2Sr_0.8NiO₄-x Sm_0.2Ce_0.8O_1.9 (x=25, 50) composite cathode on SCO electrolyte is 0.087 and 0.076Ωcm² at 750°C, which indicates Pr_1.2Sr_0.8NiO₄-Sm_0.2Ce_0.8O_1.9 composite materials may be a promising cathode material for intermediate temperature solid oxide fuel cell (IT-SOFC).