| 1. |
- Parbey, Joseph, et al.
(författare)
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Electrospun fabrication of nanofibers as high-performance cathodes of solid oxide fuel cells
- 2020
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Ingår i: Ceramics International. - : Elsevier BV. - 0272-8842. ; 46:5, s. 6969-6972
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Tidskriftsartikel (refereegranskat)abstract
- The oxygen reduction reaction (ORR) activity can strongly affect the performance of solid oxide fuel cells (SOFCs). To improve the electron transfer and enhance active sites for reactions in cathode, La0.8Sr0.2MnO3 mixed with Y2O3-stabilized ZrO2 (LSM/YSZ) nanofibers were co-fabricated by the electrospinning method. The fibers were well characterized and the electrochemical properties were evaluated by preparing a symmetrical sample with yttria-stabilized Zirconia (YSZ) pellet as electrolyte. The electrochemical impedance spectra reveal that appropriate grinding time can benefit an improved electrical conductivity and this nanostructure also has a porosity of up to 50%, which is expected to reduce the resistance of mass transfer and enhance the electron and ion transportation.
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| 2. |
- Parbey, Joseph, et al.
(författare)
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High-performance solid oxide fuel cells with fiber-based cathodes for low-temperature operation
- 2020
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Ingår i: International Journal of Hydrogen Energy. - : Elsevier BV. - 0360-3199. ; 45:11, s. 6949-6957
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Tidskriftsartikel (refereegranskat)abstract
- Low-temperature operation of solid oxide fuel cells (SOFCs) results in deterioration in electrochemical performance due to sluggish oxygen reduction reaction (ORR) at the cathode. To enhance the reaction pathway for ORR, La0.8Sr0.2MnO3 (LSM) nanofibers were fabricated by electrospinning and used for low-temperature solid oxide fuel cells operated at 600–700 °C. The morphological and structural characteristics show that the electrospun LSM nanofiber has a highly crystallized perovskite structure with a uniform elemental distribution. The average diameter of the LSM nanofiber after sintering is 380 nm. A symmetric cell of nanofiber-based LSM cathode on scandia-stabilized zirconia (SSZ) electrolyte pellet exhibits much lower area specific resistances compared to commercial LSM powder-based cathode. A single cell based on the nanofiber LSM cathode on yttrium-doped barium cerate-zirconia (BCZY) electrolyte exhibits a power density of 0.35 Wcm−2 at 600 °C, which increases to 0.85 Wcm−2 at 700 °C. The cell has an area specific resistance (ASR) of 0.46 Ωcm2 at 600 °C, which decreases to 0.07 Ωcm2 at 700 °C. The results indicate that the LSM electrode fabricated by the electrospinning process produces a nanostructured porous electrode which optimizes the microstructure and significantly enhances the ORR at the cathode of SOFCs.
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| 3. |
- Parbey, Joseph, et al.
(författare)
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Progress in the use of electrospun nanofiber electrodes for solid oxide fuel cells : A review
- 2019
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Ingår i: Reviews in Chemical Engineering. - : Walter de Gruyter GmbH. - 2191-0235 .- 0167-8299. ; 36:8, s. 879-931
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Tidskriftsartikel (refereegranskat)abstract
- The application of one-dimensional nanofibers in the fabrication of an electrode greatly improves the performance of solid oxide fuel cells (SOFCs) due to its advantages on electron transfer and mass transport. Various mixed ionic-electronic conducting materials with perovskites and Ruddlesden-Popper-type metal oxide structures are successfully electrospun into nanofibers in recent years mostly in solvent solution and some in melt forms, which are used as anode and cathode electrodes for SOFCs. This paper presents a comprehensive review of the structure, electrochemical performance, and development of anode and cathode nanofiber electrodes including processing, structure, and property characterization. The focuses are first on the precursor, applied voltage, and polymer in the material electrospinning process, the performance of the fiber, potential limitation and drawbacks, and factors affecting fiber morphology, and sintering temperature for impurity-free fibers. Information on relevant methodologies for cell fabrication and stability issues, polarization resistances, area specific resistance, conductivity, and power densities are summarized in the paper, and technology limitations, research challenges, and future trends are also discussed. The concluded information benefits improvement of the material properties and optimization of microstructure of the electrodes for SOFCs.
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| 4. |
- Yu, Guangsen, et al.
(författare)
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Fabrication of Nickel-YSZ cermet nanofibers via electrospinning
- 2017
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388. ; 693, s. 1214-1219
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Tidskriftsartikel (refereegranskat)abstract
- Abstract The Ni-YSZ cerment as a promising anode for solid oxide fuel cells and its performance strongly depends on its miscrocture. This work focused on fabrication of Ni-8YSZ nanofibers via an electrospinning technique using yttria and zirconia nanoparticles as precussors. The effects of viscosity on the quality of fibers were assessed by adjusting the polymer and solid contents in slurry. The fibers sintered at different temperatures showed varying morphologies and a bead-like chain at temperatures higher than 800 °C was obtained. Crystalization of the YSZ was completed above 1400 °C and NiO was above 800 °C. The porosity of the fiber structure can reach high up to 45% before NiO reducation. The nanocrystallization of an anode for SOFCs was beneficial to enhance the electrochemical reaction sites and also to reduce the difficulties for gas diffusion.
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| 5. |
- Zeng, Shumao, et al.
(författare)
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Effect of the electrochemical active site on thermal stress in solid oxide fuel cells
- 2018
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 165:2, s. 105-113
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Tidskriftsartikel (refereegranskat)abstract
- A 3D model is developed by coupling the equations for momentum, gas-phase species, heat, electron and ion transport to analyze cell polarization, current density and temperature in solid oxide fuel cells (SOFCs). The increase of active sites is beneficial to improve efficiency of electrochemical reactions, but it can be also detrimental to SOFCs’ stability as it will induce changes in strength and distribution of the thermal stresses. The variation of thermal stresses is systematically studied by grading the active site along the main flow direction. The results indicate that the first principle stress increases with the active site at the interface of electrolyte and electrode, but the shear stress mainly appears in the vicinity of gas inlets, which both suffer from a dramatic change when the active site is enhanced from the initial state to 1.5 times. Moreover, the electrolyte is subjected to large contrary tensile stresses, and the first principle stress is responsible for crack possibly occurring to the electrolyte. We also confirm that the sharp fluctuation of stress caused by the active sites can be relieved through adjusting thickness of the anode active layer.
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| 6. |
- Zeng, Shumao, et al.
(författare)
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Thermal stress analysis of a planar anode-supported solid oxide fuel cell : Effects of anode porosity
- 2017
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Ingår i: International Journal of Hydrogen Energy. - : Elsevier BV. - 0360-3199. ; 42:31, s. 20239-20248
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Tidskriftsartikel (refereegranskat)abstract
- A Fuel cell is a highly efficient device for converting chemical energy in fuels to electrical energy and the electrical efficiency is strongly affected by the porosity in electrodes due to its close couplings with mass transfer and active sites for the electrochemical reactions, which will also cause changes in distribution of thermal stresses inside the electrodes. A three-dimensional computational fluid dynamics (CFD) approach based on the finite element method (FEM) is used to investigate the effects of porosity on polarizations, temperatures and thermal stresses by coupling equations for gas-phase species, heat, momentum, ion and electron transport. It was found that the porosity in the anode remarkably affected the exchange current density and electrical current density, but it had an opposite effect on the anodic activation polarization compared to that in cathode. The first principle stress was enhanced from 0 to 2 MPa to 6-8 MPa by an increased anode porosity from 25% to 40%, and the increased porosity resulted in a decrease of the von mises stress along the main flow direction as well. The conclusions could be used to lay foundations for an improved performance and stabilization by optimizing electrode microstructures and by eliminating the stresses in electrodes.
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| 7. |
- Zeng, Shumao, et al.
(författare)
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Thermal stress analysis of sulfur deactivated solid oxide fuel cells
- 2018
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 379, s. 134-143
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen sulfide in fuels can deactivate catalyst for solid oxide fuel cells, which has become one of the most critical challenges to stability. The reactions between sulfur and catalyst will cause phase changes, leading to increase in cell polarization and mechanical mismatch. A three-dimensional computational fluid dynamics (CFD) approach based on the finite element method (FEM) is thus used to investigate the polarization, temperature and thermal stress in a sulfur deactivated SOFC by coupling equations for gas-phase species, heat, momentum, ion and electron transport. The results indicate that sulfur in fuels can strongly affect the cell polarization and thermal stresses, which shows a sharp decrease in the vicinity of electrolyte when 10% nickel in the functional layer is poisoned, but they remain almost unchanged even when the poisoned Ni content was increased to 90%. This investigation is helpful to deeply understand the sulfur poisoning effects and also benefit the material design and optimization of electrode structure to enhance cell performance and lifetimes in various hydrocarbon fuels containing impurities.
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| 8. |
- Zhang, Xiaoqiang, et al.
(författare)
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Mechanism of chromium poisoning the conventional cathode material for solid oxide fuel cells
- 2018
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 381, s. 26-29
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Tidskriftsartikel (refereegranskat)abstract
- Chromium poisoning the La0.875Sr0.125MnO3 (LSM) cathode for solid oxide fuel cells is a critical issue that can strongly affect the stability. In this study, we evaluate the temperature distribution in a SOFC based on a 3D model and then combine conductivity test and material computation to reveal the effects of chromium in SUS430 stainless steels on LSM conductivities. The starch concentration in LSM pellets and the applied pressure on the contact with interconnect materials show close relationships with the chromium poisoning behavior. The density functional theory (DFT) computing results indicate that chromium atoms preferably adsorb on the MnO2-terminated and La (Sr)-O-terminated (001) surfaces. The resulting conclusions are expected to deeply understand mechanism of chromium deactivating conventional cathodes at some typical operational conditions, and offer crucial information to optimize the structure to avoid the poisoning effect.
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| 9. |
- Zhang, Xiaoqiang, et al.
(författare)
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Thermal stress analysis at the interface of cathode and electrolyte in solid oxide fuel cells
- 2020
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Ingår i: International Communications in Heat and Mass Transfer. - : Elsevier BV. - 0735-1933. ; 118
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Tidskriftsartikel (refereegranskat)abstract
- A benign thermal stress in solid oxide fuel cell is of great importance for its stability and the interfaces between different components suffer from unexpected risks of instability such as electrode delamination and crack due to varying thermal expansion coefficients. Besides, chromium poisoning cathode materials leads to phase changes, which possibly induces thermal stresses at the interface of electrolyte and cathode. A three dimensional model at the microscale level is thus developed to unravel the effect of thermal stress on the interface. The model is constructed by governing equations including heat, species, momentum, ion and electronic transportation. The contact modes between the active cathode and electrolyte are studied to reveal the cell performance and thermal stresses, which are strongly related to the number of contact sites and the contact area. Moreover, chromium poisoning the contact causes the disordered distribution of thermal stresses with the increase of the contact sites, worsening the cell current density and durability. The resulting conclusions are expected to offer a solution to avoid possible fatal mechanical failure due to unfavorable interface design and chromium attack.
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| 10. |
- Zhang, Xiaoqiang, et al.
(författare)
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Thermal stress analysis of solid oxide fuel cells with chromium poisoning cathodes
- 2018
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 165:14, s. 1224-1231
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Tidskriftsartikel (refereegranskat)abstract
- Chromium(Cr) poisoning of the traditional LSM cathode is one of the most critical issues that accounts for instability of solid oxide fuel cells (SOFCs). The poisoning course will introduce alien species in the cathode active regions and it causes phase change and structure deformation, reducing the sites for electrochemical reactions. A 3D model is thus developed by coupling the computational fluid dynamics (CFD) approach with the finite element method to unravel the involved electrochemical processes in chromium poisoning of SOFCs. A function is proposed based on the experimental results to describe the distribution of Cr-related compounds in cathode. The results indicate that chromium poisoning can induce a dramatic decrease in the electric current density, which can also lead to increase of activation polarizations and lower the temperature. Three kinds of thermal stresses are strongly affected by the invasion of chromium into cathodes, which are all significantly reduced with the poisoning extent. The resulting conclusions are beneficial to deeply understand the Cr poisoning of SOFCs and also to material design to prevent cathodes from Cr-based interconnect attack.
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