Triode fuel cells (original) (raw)
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Acta Materialia, 2003
Fuel cells offer the possibility of zero-emissions electricity generation and increased energy security. We review here the current status of solid oxide (SOFC) and polymer electrolyte membrane (PEMFC) fuel cells. Such solid electrolyte systems obviate the need to contain corrosive liquids and are thus preferred by many developers over alkali, phosphoric acid or molten carbonate fuel cells. Dramatic improvements in power densities have been achieved in both SOFC and PEMFC systems through reduction of the electrolyte thickness and architectural control of the composite electrodes. Current efforts are aimed at reducing SOFC costs by lowering operating temperatures to 500-800°C, and reducing PEMFC system complexity be developing 'water-free' membranes which can also be operated at temperatures slightly above 100°C.
Triode Solid Oxide Fuel Cells: A New Approach to Enhanced Anodic and Cathodic Electrocatalysis
ECS Proceedings Volumes, 2005
The introduction of a third electrode is described for enhancing the performance of fuel cells. The new device and method introduces a new controllable variable in fuel cell and battery operation and has been found to cause up to 700% enhancement in SOFC fuel cell power output but also enhancement in overall thermodynamic efficiency. This significant enhancement of SOFC performance results from the minimization of anodic and cathodic overpotential. Thus the triode fuel cell operation is quite advantageous under high Wagner number conditions. A mathematical model has been developed describing the observed enhanced performance and identifying the critical parameters for successful operation of triode SOFCs with paste and state of the art SOFC electrodes. The model is compared with experimental results of triode SOFC operation.
Polarization measurements on single-step co-fired solid oxide fuel cells (SOFCs
Journal of Power Sources, 2007
Anode-supported planar solid oxide fuel cells (SOFC) were successfully fabricated by a single step co-firing process. The cells comprised of a Ni + yttria-stabilized zirconia (YSZ) anode, a YSZ or scandia-stabilized zirconia (ScSZ) electrolyte, a (La 0.85 Ca 0.15 ) 0.97 MnO 3 (LCM) + YSZ cathode active layer, and an LCM cathode current collector layer. The fabrication process involved tape casting of the anode, screen printing of the electrolyte and the cathode, and single step co-firing of the green-state cells in the temperature range of 1300-1330 • C for 2 h. Cells were tested in the temperature range of 700-800 • C with humidified hydrogen as fuel and air as oxidant. Cell test results and polarization modeling showed that the polarization losses were dominated by the ohmic loss associated with the electrodes and the activation polarization of the cathode, and that the ohmic loss due to the ionic resistance of the electrolyte and the activation polarization of the anode were relatively insignificant. Ohmic resistance associated with the electrode was lowered by improving the electrical contact between the electrode and the current collector. Activation polarization of the cathode was reduced by the improvement of the microstructure of the cathode active layer and lowering the cell sintering temperature. The cell performance was further improved by increasing the porosity in the anode. As a result, the maximum power density of 1.5 W cm −2 was achieved at 800 • C with humidified hydrogen and air.
Chemical Industry and Chemical Engineering Quarterly, 2011
In this study, a single polymer electrolyte membrane fuel cell (PEMFC) in H2/O2 form with an effective dimension of 5?5 cm as well as a single direct methanol fuel cell (DMFC) with a dimension of 10?10 cm were fabricated. In an existing test station, the voltage-current density performances of the fabricated PEMFC and DMFC were examined under various operating conditions. As was expected DMFC showed a lower electrical performance which can be attributed to the slower methanol oxidation rate in comparison to the hydrogen oxidation. The results obtained from the cell operation indicated that the temperature has a great effect on the cell performance. At 60?C, the best power output was obtained for PEMFC. There was a drop in the cell voltage beyond 60?C which can be attributed to the reduction of water content inside the membrane. For DMFC, maximum power output was resulted at 64oC. Increasing oxygen stoichiometry and total cell pressure had a marginal effect on the cell performance. T...
The paper deals with the testing of performances of SOFC planar cells having as mechanical support either the anode or the electrolyte. Polarization traces at different temperature and hydrogen flow have been drawn to assess the electrochemical behavior and the limiting polarization factors of anode-supported and electrolyte-supported cells. The experimental data from polarization tests has then been summarized and analyzed through a parameter estimation technique, which allowed us to compare the performances of each cell throughout some defined macroscopic parameters, each one being referred and distinctive of a certain polarization overvoltage occurring during a SOFC operation. SEM and optical micrographs have been also collected in order to characterize the fine microstructure of the tested cells, and to discuss the macroscopic polarization results with reference to the microstructure.
A power generation system based on integrated methane fed solid oxide fuel cell (SOFC) and organic Rankin cycle (ORC) was modeled and validated against experimental results available in the literature. A comprehensive comparative analysis was conducted on the system performance based the oxygen ion-conducting electrolyte SOFC (SOFC-O 2−) and proton-conducting electrolyte SOFC (SOFC-H +) electrolyte. The comparative analysis was conducted from viewpoints of energy, exergy, economic, and environmental. Current density and stack temperature were considered as the input variables. The multi-objective optimization procedure based on an evolutionary algorithm was conducted in the presence of exergy efficiency and sum of the unit cost of the products (SUCP) as the objective functions. The performance of the SOFC-O 2− and the SOFC-H + based power generation systems were compared at their optimum conditions. The system based the SOFC-O 2− had a better performance compared to the system based the SOFC-H + from the objective functions viewpoints. The system based the SOFC-O 2− had a higher exergy efficiency (60.20% compared to 54.06%) and lower SUCP (48.24 /GJcomparedto48.75/GJ compared to 48.75 /GJcomparedto48.75/GJ) than the system based the SOFC-H + at their optimum conditions. The SOFC-O 2− produced 18 kW power higher than the SOFC-H +. This led to increase the system power from 147.9 kW in the case of the SOFC-H + to 156.4 kW for the SOFC-O 2− .
A novel approach to study the structure versus performance relationship of SOFC electrodes
Journal of Power Sources, 2006
The aim of this work is to develop a new rigorous model to study the structure performance relationship of solid oxide fuel cell (SOFC) electrodes. A new two-dimensional, geometrical model which captures the inhomogeneous nature of the location of electrochemical reactions based on random packing of electronic and ionic conducting particles has been developed. The results show that the concentration of oxygen inside the cathode in the 2D model is not only a function of the electrode depth but also changes along the width of the electrode. Furthermore the effect of composition of the electrode on the length of active three-phase boundary (TBP) and total polarization resistance has been demonstrated. A parametric study of the effect of the conductivity of ionic conductor and diffusion coefficient on the performance of the electrode has been given.
International Journal of Energy and Environmental Engineering, 2016
In the presented work, a model is created in order to investigate the effect of different material parameters and operating conditions on the anode diffusion overpotential, which influence the exergy and energy efficiency of the solid oxide fuel cell (SOFC). In this research, it was demonstrated that the anode material parameters and operating conditions of the device components such as porosity, tortuosity, pore diameter, temperature, pressure and current density of the anode have various effects on the anode diffusion overpotential, which consequently affect the exergy and energy efficiency of the SOFC. The model has provided a strong direction on how to optimize the SOFC exergy and energy efficiency, by reducing the anode diffusion overpotential, which is affected by various material parameters and operating conditions. Keywords Diffusion polarization Á Efficiency Á Porosity Á Tortuosity Á SOFC List of symbols A Area (cm 2) A f The thermodynamic factor c v The oxygen concentration vacancy C gas Capacitance associated the with gas-phase diffusion polarization (F/cm 2) D AB The binary diffusion coefficient (cm 2 /s)
Effect of Anode Stoichiometry and Back Pressure on the Performance of PEMFCs
In this study, the performance of polymer electrolyte membrane fuel cells was investigated. Two important operating conditions, namely the anode stoichiometry ratio and cell's back pressure were considered, whereby their effect on the cell performance was analyzed in isolation and relative to each other. Polarization curves showed that when operating the cell at low back pressure, an increase in the anode stoichiometry resulted in an increase in the cell performance due to enhanced fuel cell thermodynamics. However, upon increasing the back pressure, an increase in the anodic stoichiometry resulted in a poorer performing cell due to an increase in the hydrogen crossover rate and an increase in membrane resistance. From this work it became evident that the relationship between back pressure increment and anodic fuel stoichiometry was not linear, and requires optimization.