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1.
A theoretical study of a solid oxide fuel cell (SOFC) fed by ethanol is presented in this study. The previous studies mostly investigated the performance of ethanol-fuelled fuel cells based on a thermodynamic analysis and neglected the presence of actual losses encountered in a real SOFC operation. Therefore, the real performance of an anode-supported SOFC with direct-internal reforming operation is investigated here using a one-dimensional isothermal model coupled with a detailed electrochemical model for computing ohmic, activation, and concentration overpotentials. Effects of design and operating parameters, i.e., anode thickness, temperature, pressure, and degree of ethanol pre-reforming, on fuel cell performance are analyzed. The simulation results show that when SOFC is operated at the standard conditions (V = 0.65 V, T = 1023 K, and P = 1 atm), the average power density of 0.51 W cm−2 is obtained and the activation overpotentials represent a major loss in the fuel cell, followed by the ohmic and concentration losses. An increase in the thickness of anode decreases fuel cell efficiency due to increased anode concentration overpotential. The performance of the anode-supported SOFC fuelled by ethanol can be improved by either increasing temperature, pressure, degree of pre-reforming of ethanol, and steam to ethanol molar ratio or decreasing the anode thickness and fuel flow rate at inlet. It is suggested that the anode thickness and operating conditions should be carefully determined to optimize fuel cell efficiency and fuel utilization.  相似文献   

2.
This paper presents a performance analysis of a planar solid oxide fuel cell (SOFC) with different support structures, i.e., electrode (anode and cathode) and electrolyte supports. An electrochemical model, taking into account structural and operational parameters and gas diffusion at the electrodes, is used to analyze the characteristics of the planar SOFC. Simulation results demonstrate that under cell operation at an intermediate temperature (1073 K), an anode-supported SOFC is superior to an electrolyte- and cathode-supported SOFC. Analysis of individual cell voltage loss indicates that ohmic loss dominates the performance of an electrolyte-supported SOFC whereas activation and ohmic overpotentials constitute the major loss in an electrode-supported counterpart. Sensitivity analyses of the anode-supported SOFC show that decreasing the electrolyte and anode thickness can improve cell performance. A decrease in operating temperature causes the cell to operate at a lower range of current density due to an increase in ohmic and activation overpotentials. Further, increasing the operating pressure and degree of pre-reforming reduces the concentration overpotential and thereby enhances cell performance.  相似文献   

3.
An electrochemical model was developed to study the methane (CH4) fed solid oxide fuel cell (SOFC) using proton conducting electrolyte (SOFC-H) and oxygen ion conducting electrolyte (SOFC-O). Both the internal methane steam reforming (MSR) and water gas shift (WGS) reactions are considered in the model. Previous study has shown that the CH4 fed SOFC-H had significantly better performance than the SOFC-O. However, the present study reveals that the actual performance of the CH4 fed SOFC-H is considerably lower than the SOFC-O, partly due to higher ohmic overpotential of SOFC-H. It is also found that the CH4 fed SOFC-H has considerably higher cathode concentration overpotential and lower anode concentration overpotential than the SOFC-O. The anode concentration overpotentials of the CH4 fed SOFC-H and SOFC-O are found to decrease with increasing temperature, which is different from previous analyses on the H2 fed SOFC. Therefore, high temperature is desirable for increasing the potential of the CH4 fed SOFC. It is also found that there exist optimal electrode porosities that minimize the electrode total overpotentials. The analyses provided in this paper signify the difference between the CH4 fed SOFC-H and SOFC-O. The model developed in this paper can be extended to 2D or 3D models to study the performance of practical SOFC systems.  相似文献   

4.
An electrochemical model was developed to study the ammonia (NH3)-fed solid oxide fuel cells with proton-conducting electrolyte (SOFC-H) and oxygen ion-conducting electrolyte (SOFC-O). Different from previous thermodynamic analysis, the present study reveals that the actual performance of the NH3-fed SOFC-H is considerably lower than the SOFC-O, mainly due to higher ohmic overpotential of the SOFC-H electrolyte. More analyses have been performed to study the separate overpotentials of the NH3-fed SOFC-H and SOFC-O. Compared with the NH3-fed SOFC-H, the SOFC-O has higher anode concentration overpotential and lower cathode concentration overpotential. The effects of temperature and electrode porosity on concentration overpotentials have also been studied in order to identify possible methods for improvement of SOFC performance. This study reveals that the use of different electrolytes not only causes different ion conduction characteristics at the electrolyte, but also significantly influences the concentration overpotentials at the electrodes. The model developed in this article can be extended to 2D and 3D models for further design optimization.  相似文献   

5.
A general electrode–electrolyte-assembly (EEA) model has been developed, which is valid for different designs of solid oxide fuel cells (SOFCs) operating at different temperatures. In this study, it is applied to analyze the performance characteristics of planar anode-supported SOFCs. One of the novel features of the present model is its treatment of electrodes. An electrode in the present model is composed of two distinct layers referred to as the backing layer and the reaction zone layer. The other important feature of the present model is its flexibility in fuel, having taking into account the reforming and water–gas shift reactions in the anode. The coupled governing equations of species, charge and energy along with the constitutive equations in different layers of the cell are solved using finite volume method. The model can predict all forms of overpotentials and the predicted concentration overpotential is validated with measured data available in literature. It is found that in an anode-supported SOFC, the cathode overpotential is still the largest cell potential loss mechanism, followed by the anode overpotential at low current densities; however, the anode overpotential becomes dominant at high current densities. The cathode and electrolyte overpotentials are not negligible even though their thicknesses are negligible relative to the anode thickness. Even at low fuel utilizations, the anode concentration overpotential becomes significant when chemical reactions (reforming and water–gas shift) in the anode are not considered. A parametric study has also been carried out to examine the effect of various key operating and design parameters on the performance of an anode-supported planar SOFCs.  相似文献   

6.
In this study, a numerical framework for microstructure design of functionally graded (FG) electrodes of solid oxide fuel cells (SOFCs) is developed using a number of mesoscale numerical simulations. The “multi-sphere” discrete element method, kinetic Monte Carlo method and lattice Boltzmann method are used sequentially to model the powder packing, powder sintering, and electrochemical reaction in the cathode. In the current FG electrode concept, porosity gradients with linear and nonlinear profiles are considered for La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) FG-cathodes. It is shown that in a porosity graded cathode, the concentration overpotential can be mitigated by improving the gas transport. However, when the porosity of the cathode is higher than approximately 0.40, the porosity gradient design contributes little to reduce the concentration overpotential but it rather increases the activation and ohmic overpotentials. In all cases, the porosity gradient design can suppress sintering, hence the thermal stability of the cathode can be improved. For cathode with an initial thickness of 25 μm and density range of 0.40–0.65, an optimal exponential factor of P = 1.5 is found for the best performance of the cathode.  相似文献   

7.
In this work, solid oxide fuel cells (SOFCs) based on different electrolytes, i.e., the yttria-stabilized zirconia (YSZ) and the samaria-doped ceria (SDC), were investigated to study their performances at low-temperature operation. The predicted performance of both SOFCs was validated with the experimental results. The verified models were implemented to study the impact of operating conditions, i.e., cell temperature, pressure, thicknesses of cathode, anode, and electrolyte, on their performances. The decrease in the operating temperature from intermediate range (800–900 °C) to low range (550–650 °C) has a considerable effect on the performance of the YSZ-based SOFC as conventional type, which dropped from 0.67–1.40 W/cm2 to 0.027–0.13 W/cm2. Under the low operating temperature range, the performance of SDC-based SOFC was superior to that of the YSZ-based SOFC, due to the lower ohmic loss. Nevertheless, the SDC-based SOFC has higher concentration overpotentials than the YSZ-based SOFC. The concentration overpotentials of the SDC-based SOFC can be reduced by the thinner anode and cathode thicknesses. In addition, the SDC-based SOFC at low operating temperature with the pressurized operation could significantly improve its power density, about 20% at 2 bar, which was close to that of YSZ-based SOFC at intermediate temperature of 800 °C.  相似文献   

8.
In this study, the use of metal foam as a flow distributor at cathode is evaluated numerically by a comprehensive three-dimensional solid oxide fuel cell (SOFC) model. The results show that the adoption of metal foam improves the power density by 13.74% at current density of 5000 A m−2 in comparison with conventional straight channel design. It is found that electronic overpotential, oxygen concentration and reaction rates distribute more uniformly without the restriction of ribs. The effects of cathode thickness on the two different flow distributors are compared. Compared with conventional straight channel, the metal foam is found to be more suitable as a distributor for anode supported SOFC with thin cathode gas diffusion layer. Moreover, when metal foam is applied to the fuel cell with a larger reaction area, a more uniform velocity distribution and a lower temperature distribution can be achieved. It is also found that an appropriate permeability coefficient should offer a reasonable pressure drop, which is beneficial for the fuel cell system performance improvement.  相似文献   

9.
An electrochemical model was developed to study the NH3-fed and H2-fed solid oxide fuel cells based on proton conducting electrolyte (SOFC-H). The modeling results were consistent with experimental data in literature. It is found that there is little difference in working voltage and power density between the NH3-fed and the H2-fed SOFC-H with an electrolyte-support configuration due to an extremely high ohmic overpotential in the SOFC-H. With an anode-supported configuration, especially when a thin film electrolyte is used, the H2-fed SOFC-H shows significantly higher voltage and power density than the NH3-fed SOFC-H due to the significant difference in concentration overpotentials. The anode concentration overpotential of the NH3-fed SOFC-H is found much higher than the H2-fed SOFC-H, as the presence of N2 gas dilutes the H2 concentration and slows down the transport of H2. More importantly, the cathode concentration overpotential is found very significant despite of the thin cathode used in the anode-supported configuration. In the SOFC-H, H2O is produced in the cathode, which enables complete fuel utilization on one hand, but dilutes the concentration of O2 and impedes the diffusion of O2 to the reaction sites on the other hand. Thus, the cathode concentration overpotential is the limiting factor for the H2-fed SOFC-H and an important voltage loss in the NH3-fed SOFC-H. How to reduce the concentration overpotentials at both electrodes is identified crucial to develop high performance SOFC-H.  相似文献   

10.
We propose a novel interconnector design, termed bi-layer interconnector, for solid oxide fuel cells (SOFCs). It can disturb the fuel gas and air on the planes normal to the SOFC three-phase-boundary (TPB) layer. In this paper, a two-dimensional half-cell model is developed to study the concentration overpotentials in the fuel side of the SOFC stack with conventional and novel bi-layer interconnectors. The numerical results show that the novel bi-layer interconnector can increase the velocity of the fuel gas in the porous anode. The results of mole fraction distribution illustrate that the novel bi-layer interconnector can effectively disturb the fuel flow. The average H2 mole fraction in the porous anode of SOFC with bi-layer interconnector is about 4.7% higher than that of conventional SOFC. The average H2 mole fraction at TPB interface is about 9.2% higher. The concentration overpotential of the novel SOFC design is lower than that of the conventional SOFC design by 5%. It can enhance the mass transfer in porous electrode and improve the performance of SOFC.  相似文献   

11.
Symmetrical solid oxide fuel cell (SOFC) adopting the same material at both electrodes is potentially capable of promoting thermomechanical compatibility between near components and lowering stack costs. In this paper, MnCr2O4–Gd0.1Ce0.9O2-δ (MCO-GDC) composite electrodes prepared by co-infiltration method for symmetrical electrolyte supported and anode supported solid oxide fuel cells are evaluated at a temperature range of 650–800 °C in wet (3% H2O) hydrogen and air atmospheres. Without any alkaline earth elements and cobalt, the co-infiltrated MCO-GDC composite electrode shows excellent activity for oxygen reduction reaction but mediocre activity for hydrogen oxidation reaction. With MCO-GDC as the cathode, the Ni-YSZ (Y2O3 stabilized ZrO2) anode supported asymmetrical cell demonstrates a peak power density of 665 mW cm−2 at 800 °C. The above results suggest MCO-GDC is a promising candidate cathode material for solid oxide fuel cells.  相似文献   

12.
Solid oxide fuel cell technology is the technology which can be driving force to change the course of action of the modern era due to its optimal power generation features with maximum electrical efficiency for automobiles and household devices. Fuel cells can be best described as electrochemical devices that make use of fuel oxidation to convert chemical energy into electrical energy and also lower the amount of oxidant simultaneously.A typical SOFC consists of a cathode, anode and an electrolyte constituting a single cell. These single cells are stacked together for a bigger assembly to produce higher degree of power. The solid electrolyte fills the gap between the cathode and anode transporting O2− ions only. This leaves out electrons as transporting medium, which then pass through the cell via external circuit. Out of the two electrodes, oxidation of fuel takes place at the anode and reduction of oxygen takes place at the cathode. The SOFCs operate at higher temperatures of 600–1200°C producing heat as a byproduct of high quality, actively encouraging quick electrocatalysis utilizing non-precious metals and allowing internal restructuration. The SOFC can also work with high purity hydrogen for proton transport other than O2− ion transport. There are many ceramic materials which have been engineered to act as efficient electrolyte materials. Yttria-stabilized zirconia (YSZ) is the most widely used material as solid electrolyte in SOFC.The present review presents a detailed overview of the SOFC related materials and devices and is an effort to present various reported works in a concise manner.  相似文献   

13.
Valuable, “green” H2 can be produced with a microbial electrolysis cell (MEC). To achieve a high volumetric production rate of high purity H2, a continuous flow MEC with an anion exchange membrane, a flow through bioanode and a flow through Ni foam cathode was constructed. At an electrical energy input of 2.6 kWh m−3 H2 (applied cell voltage: 1.00 V), this MEC was able to produce over 50 m3 H2 m−3 MEC d−1 (22.8 ± 0.1 A m−2). The MEC had a low cathode overpotential compared to an MEC with Pt-based cathode, because of the high specific surface area of Ni foam (128 m2 m−2 projected area). The MEC performance however, decreased during 32 days of operation due to an increase in anode and cathode overpotentials. Scaling likely caused the increase in anode overpotential, but it remained unclear what caused the increase in cathode overpotential.  相似文献   

14.
A three‐dimensional (3D) nonisothermal model is developed and applied for anode‐supported planar solid oxide fuel cell (SOFC). The mass and momentum, species, ion, electric, and heat transport equations are solved simultaneously by implementing the electrochemical kinetics and electrochemical reaction as volumetric source terms. The interconnect land limits the O2 transport under the land and lowers the local current density under the land. The effects of interconnect land width and cathode substrate thickness on SOFC cell performance are quantified in this study. Cathode stoichiometry is found to have a large effect on the SOFC cell temperature distribution. Under low‐cathode stoichiometry, significant temperature gradients are seen in the SOFC cell. Higher‐cathode stoichiometry is beneficial for lower temperature and more uniform current density distribution in SOFC cell. Co‐flow and counter‐flow arrangements are investigated and discussed with the model. Counter‐flow arrangement is found to induce a high temperature and high current density region near the H2 inlet. On the other hand, co‐flow arrangement leads high temperature and high current density to occur relatively downstream, a slightly lower maximum temperature on cell and considerably more uniform current density distribution. A 67.2‐cm2 SOFC cell is simulated considering the side cooling effect. The side cooling effectively lowers the cell temperature, at the same time, causes temperature, current density, and fuel utilization nonuniformity in the across multichannel direction. Because of the strong coupling of the in‐plane current density distribution and temperature distribution, limiting the locally high temperature and temperature gradient is critical for achieving a more uniform current density distribution in anode‐supported planar SOFC.  相似文献   

15.
This work investigates the reaction characteristics of the anode and cathode by overpotential analyses in 100 cm2 class planar anode-supported SOFCs. The reactant gas addition (RA) technique was applied to analyse the overpotential, which uses the reactant gas flow rate and partial pressure as parameters due to their variation upon adding a reactant species to an electrode. The anodic overpotential was determined to be made up of mass transfer-induced overpotentials of H2 and H2O species. The H2O species account for the majority of the anodic overpotential at the measured current range i.e., 0–150 mA cm?2. Thus, the anodic reaction is under an extreme H2O-induced mass-transfer resistance compared with H2. The RA method showed that the cathodic overpotential was mainly due to a deficiency of O2 species in the mass transfer through the gas phase rather than the solid phase. Furthermore, both cathodic and anodic overpotentials depended on gas flow rate and utilisation, indicating a significant gas-phase mass transfer effect.  相似文献   

16.
A nanocrystalline powder with a lanthanum based iron- and cobalt-containing perovskite, La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF), is investigated for solid oxide fuel cell (SOFC) applications at a relatively low operating temperature (600-800 °C). A LSCF powder with a high surface area of 88 m2 g−1, which is synthesized via a complex method with using inorganic nano dispersants, is printed onto an anode supported cell as a cathode electrode. A LSCF cathode without a sintering process (in situ sintered cathode) is characterized and compared with that of a sintering process at 780 °C (ex situ sintered cathode). The in situ sintered SOFC shows 0.51 A cm−2 at 0.9 V and 730 °C, which is comparable with that of the ex situ sintered SOFC. The conventional process for SOFCs, the ex situ sintered SOFC, including a heat treatment process after printing the cathodes, is time consuming and costly. The in situ sinterable nanocrystalline LSCF cathode may be effective for making the process simple and cost effective.  相似文献   

17.
Solid oxide fuel cell (SOFC) has experienced a growing interest in the last few decades because of generating energy more efficiently than the conventional combustion of fossil fuels. By using the same material as anode and cathode of SOFC (symmetric fuel cell), the production of reliable and repeatable cells would be simpler. In this work, La0.4Sr0.6Co0.2Fe0.7Nb0.1O3−δ (LSCFN) perovskite has been prepared and evaluated as both cathode and anode material of symmetric fuel cell. The results of symmetric fuel cell show that a maximum peak power density of 500 mW cm−2 has been achieved and the total electrode polarization resistances of the cell is only 0.22 Ω cm2 at 850 °C which is much lower than that of typical symmetric fuel cell with La0.75Sr0.25Cr0.5Mn0.5O3−δ as electrode material. All of these results indicate that LSCFN can potentially be a promising candidate for the electrode material of symmetric fuel cell.  相似文献   

18.
A PdPt (10 wt% Pt) catalyst is used to replace platinum at the cathode of a proton exchange membrane fuel cell membrane electrode assembly (PEMFC MEA) whereas pure palladium is used as the anode catalyst. The catalysts are deposited on commercial carbon woven web and carbon paper GDLs by plasma sputtering. The relations between the depth density profiles, the electrode support and the fuel cell performances are discussed. It is shown that the catalyst gradient is an important parameter which can be controlled by the catalyst depth density profile and/or the choice of electrode support. An optimised electrode structure has been obtained, which allows limiting the platinum requirement. Under suitable conditions of a working PEMFC (80 °C and 3 bar absolute pressure), very high catalysts utilization is obtained at both electrodes, leading to 250 kW gPt−1 and 12.5 kW gPd−1 with a monocell fitted with a PdPt (10:1 weight ratio) cathode and a pure Pd anode.  相似文献   

19.
Phosphine (PH3) as a contaminant in coal syngas has been shown to cause permanent degradation on solid oxide fuel cell (SOFC) anode performance. Previous studies on the performance degradation have been performed at constant current or constant voltage over the entire experiment. In this work, the effect of overpotential (difference between the open circuit voltage and the applied voltage) on rates of degradation of SOFC performance is examined. A commercial SOFC from MSRI is exposed in sequence to first hydrogen, then coal syngas and then coal syngas with 10 ppm PH3. The rates of cell power density loss rates are monitored for three overpotentials (0.1, 0.2 and 0.3 V). There is no apparent correlation between the degradation rates and overpotential values. Post-mortem studies including SEM, XRD and XPS confirm the migration of nickel to the anode surface and the formation of a nickel phosphide phase.  相似文献   

20.
While the desired microstructure of the state-of-the-art Ni-YSZ anode for a solid oxide fuel cell (SOFC) based on YSZ is well known, the anode microstructure for a SOFC based on a proton conductor is yet to be optimized. In this study, we examined the effect of anode porosity on the performance of a SOFC based on BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb), a mixed ion (proton and oxygen anion) conductor with high ionic conductivity at intermediate temperatures. Three cells with Ni-BZCYYb cermet anodes of different porosities (37%, 42%, and 50%) and identical electrolytes and cathode components were fabricated and tested. Under typical fuel cell operating conditions, the cell with anode of the lowest porosity (37%), prepared without pore former, achieved the highest performance, demonstrating a peak power density of 1.2 W/cm2 at 750 °C. This is radically different from the results of Ni-YSZ anodes for YSZ based cells, where high anode porosity (∼55%) is necessary to achieve high performance. The observed increase in performance (or electrocatalytic activity for anode reactions) is attributed primarily to the unique microstructure of the anode fabricated without the use of pore forming precursors.  相似文献   

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