- Email: [email protected]
03404 Novel applications for micro-SOFCs
06
estimate is based mainly on bidding information from competent manufacturers and suggests that the target purchase price of US$llOO per kW installed capacity is likely to be verified in the near future. Consequently, this permits IGCC generating costs significantly lower than those of a comparable advanced PCF steam power plant. In general, this strategy of stepwise replacement of existing PCF stations by advanced IGCC plants is still the most direct measure to reduce CO2 emissions from power generation which neither needs an extra amount of primary fuel nor leaves a CO2 utilization or disposal problem. It rather involves zero additional costs for the CO* avoided and, moreover, offers a power plant process best suited to prevent CO2 from being released into the atmosphere in the most efficient way, if such an extensive means becomes necessary in the future. 00103401 Modelling of olymer electrolyte membrane fuel cells with variable degrees o P water flooding Baschuk, J. J. and Li, X. Journal of Power Sources, 2000, 86, (l-2), 181-196. Polymer electrolyte membrane (PEM) fuel cells have received increasing attention from both the public and fuel cell community due to their great potential for transport applications. The phenomenon of water flooding in the PEM fuel cells is not well understood, and few modelling studies have included the effect of water flooding. On the other hand, water management is one of the critical issues to be resolved in the design and operation of PEM fuel cells. In the present study, a mathematical model has been formulated for the performance and operation of a single polymer electrolyte membrane fuel cell. This model incorporates all the essential fundamental physical and electrochemical processes occurring in the membrane electrolyte, cathode catalyst layer, electrode backing and flow channel. A special feature of the model is that it includes the effect of variable degree of water flooding in the cathode catalyst layer and/or cathode electrode backing region on the cell performance. The model predictions have been compared with the existing experimental results available in the literature and excellent agreement has been demonstrated between the model results and the measured data for the cell polarization curves. Hence, this model can be used for the optimization of PEM fuel cell design and operation, and can serve as a building block for the modelling and understanding of PEM fuel cell stacks and systems. 00103402 Modelling the integration of a compact plate steam reformer in a fuel .cell system Cunha, J. and Azevedo, J. L. T. Journrrl of Power Sources, 2000, 86, (l-2), 515-522. Fuel cell plant design requires an appropriate integration of components, especially with the fuel processing unit. The integration of a steam reformer for methanol with a polymer electrolyte membrane (PEM) fuel cell plant is examined here. The integration considers the use of the fuel ceil anode off gas (AOG) for combustion in order to supply the necessary heat for the reforming reaction. The whole fuel cell plant is considered with simple models for the components that allow sizing of the components and characterization of their operating conditions. A reformer, based on a plate heat exchanger, is considered with catalytic combustion of the AOG and methanol to supply the required energy. A detailed model for a plate heat exchanger, which considers reactions and heat transfer is used to predict temperature profiles. Modified nickel oxides as cathode materials for MCFC 00103403 Daza, L. er al. Journal ofPower Sources, 2000, 86, (l-2), 329-333. The preparation and subsequent oxidation of nickel cathodes modified by impregnation with cerium were evaluated by surface and bulk analysis. The cerium impregnated cathodes showed the same pore size distribution curve types and the same morphology as the reference nickel cathode. The measured nickel oxide dissolution rate in the molten carbonate mixture indicated that a minimum corrosion was evident for cathodes with 0.3-l wt% cerium oxide content. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed in the cathode characterization. As can be seen by SEM, the corrosion treatments produce marked modifications on the sample surfaces that appear more prominent for the cerium-free sample. The results also show that the lithiation process is a very significant factor that can improve the efficiency of the cell, but needs to be controlled because it can also produce very damaging effects such as the modification of the cathode volume by the formation on new compounds. 00/03404 Novel applications for micro-SOFCs Tompsett, G. A. ef al. Journal of Power Sources, 2000, 86, (I-2), 376-382. The application of micro-solid oxide fuels cells in small systems is discussed. Two types of application are examined, namely, leisure CHP systems and micro-hybrid vehicles. A unique triple layer catalyst-SOFC-catalyst system has been designed utilizing propane/butane fuel. The system consists of a co-generating gas burner with a pre-reforming catalyst, a micro-SOFC stack and an oxidation catalyst._ The pre-reforming catalyst comprising of ruthenium metal on Saffile” ceramic wool, was used to partially reform the propane/butane gas prior to entering the fuel cell, preventing carbon formation. The micro-SOFCs were YSZ tubes (Adelan, UK) with nickel/ YSZ cermet anodes on the outside and strontium-doped lanthanum manganite cathodes on the inside. Final oxidation was provided by a cordierite honeycomb coated with platinum combustion catalyst producing most of the heat for the fuel cell operation. Initial performance results were obtained and it was shown that a co-generating system could be achieved using a propane/butane fuel supply, piezoelectric ignition system and air
Necfrical
power supply and utilizatron (scientific, technical)
supply for the triple catalyst system. system for leisure and micro-hybrid power-assisted bicycles, is described.
The application of this micro-SOFC vehicles, such as golf trolleys and
00/03405 Optimisation of flow-field in polymer electrolyte membrane fuel cells using computational fluid dynamics techniques Hontafidn, E. et a/. Journal of Power Source.s, 2000, 86, (l-2), 363-368. The purpose of this work was the enhancement of performance of polymer electrolyte membrane fuel cells (PEMFC) by optimizing the gas flow distribution system. To achieve this, 3D numerical simulations of the gas flow in the assembly, consisting of the fuel side of the bipolar plate and the anode, were performed using a commercial computational fluid dynamics (CFD) software, the ‘FLUENT’ package. Two types of flow distributors were investigated: a grooved plate with parallel channels of the type commonly used in commercial fuel cells, and a porous material, The simulation showed that the permeability of the gas flow distributor is a key parameter affecting the consumption of reactant gas in the electrodes. Fuel utilization increased when decreasing the permeability of the flow distributor. In particular, fuel consumption increased significantly when the permeability of the porous material decreased to values below.that of the anode. This effect was not observed in the grooved plate, which permeability was higher than that of the anode. Even though the permeability of the grooved plate can be diminished by reducing the width of the channels, values lower than 1 mm are difficult to attain in practice. The simulation shows that porous materials are more advantageous than grooved plates in terms of reactant gas utilization. 00/03406 Optimisation of the cell shape for industrial MCFC stacks Arato, E. el ul. Journal of Power Sources, 2000, 86. (l-2), 302-308. This work aims to compare molten carbonate fuel cell (MCFC) stack behaviour when square and rectangular cells are used, and to discuss the optimization of their operating conditions. In particular, experimental data have been collected for a stack with square cells of 0.1 mz area to validate a stack simulation model; then, the effects of area increase of up to 0.75 mz have been predicted, proving the advantage of working with rectangular cells in order to obtain a better temperature and pressure drop management. Moreover, the operating conditions of a rectangular stack have been analysed and optimized when reformed natural gas, as well as coal gas, are used as fuel. The results presented and discussed have been used to guide design and operation of a rectangular slack constructed by Ansaldo Ricerche (ARI). 00103407 PAFC operating performance verified by Japanese gas utilities Kasahara, K. er al. Journal of Power Sources, 2000, 86, (l-2), 298-301, Japanese gas utilities have been conducting demonstration and field tests of on-site PAFC power generation plants for more than two decades since Tokyo Gas and Osaka Gas first participated in the TARGET Programme launched in the US in 1967. Total capacity of plants installed and tested to date has amounted to 15.56 MW. Cumulative number of installed plants has reached a total of 106. As of the end of August 1999, totalled 45 plants with a total capacity of 7800 kW are in operational. During the recent 2 years since the last Grove Symposium, 11 plants (,three for Tokyo Gas and eight for Osaka Gas) surpassed the 40,000 h durability target set as the R,D & D target for fuel cell technology. To date, two plants have logged an uninterrupted run of over a full year, the other target set as the reliability index. 00/03408 Phase relations in the system Sr-h-0 and thermodynamic measurements on SrlrOJ, SrzlrO, and Sr,lrO, using solid-state cells with buffer electrodes Jacob, K. T. ef al. J. Alloys Compd., 1999, 288, (l-2). 188-196. The standard Gibbs energies of formation of SrIrOS, SrzlrOl and Sr41r06 have been determined in the temperature range 975-1400 K using solidstate cells with (Y203) ZrOz as the electrolyte and pure oxygen gas at a pressure of 0.1 MPa as the reference electrode. For the design of appropriate working electrodes, phase relations in the ternary system Srlr-0 were investigated at 1350 K. The only stable oxide detected along the binary Ir-0 was IrOz. Three ternary oxides, SrlrO,, Sr21r04 and SrllrO,, compositions of which fall on the join SrO-IrOz, were found to be stable. Each of the oxides coexisted with pure metal iridium. Therefore, three working electrodes were prepared consisting of mixtures of lr + SrO + These Sr41r06, lr + Sr41r06 + Sr, - IrOd, and lr + Sr21r04 + Srlr03. mixtures unambiguously define unique oxygen chemical potentials under isothermal and isobaric conditions. A novel apparatus was used for the measurements, in which a buffer electrode was introduced between the reference and working electrodes to absorb the electrochemical flux of oxygen through the solid electrolyte. The buffer electrode prevented polarization of the measuring electrode and ensured accurate data. The standard Gibbs energies of formation of the compounds are represented. Chemical potential diagrams for the system Sr-lr-0 were developed based on the thermodynamic information. 00/03409 Planar solid oxide fuel cells: the Australian experience and outlook Godfrey, B. el a/. Journal of Power Sourct~.s, 2000. 86, (i-2), 68-73.
Fuel and Energy Abstracts
November 2000
383
estimate is based mainly on bidding information from competent manufacturers and suggests that the target purchase price of US$llOO per kW installed capacity is likely to be verified in the near future. Consequently, this permits IGCC generating costs significantly lower than those of a comparable advanced PCF steam power plant. In general, this strategy of stepwise replacement of existing PCF stations by advanced IGCC plants is still the most direct measure to reduce CO2 emissions from power generation which neither needs an extra amount of primary fuel nor leaves a CO2 utilization or disposal problem. It rather involves zero additional costs for the CO* avoided and, moreover, offers a power plant process best suited to prevent CO2 from being released into the atmosphere in the most efficient way, if such an extensive means becomes necessary in the future. 00103401 Modelling of olymer electrolyte membrane fuel cells with variable degrees o P water flooding Baschuk, J. J. and Li, X. Journal of Power Sources, 2000, 86, (l-2), 181-196. Polymer electrolyte membrane (PEM) fuel cells have received increasing attention from both the public and fuel cell community due to their great potential for transport applications. The phenomenon of water flooding in the PEM fuel cells is not well understood, and few modelling studies have included the effect of water flooding. On the other hand, water management is one of the critical issues to be resolved in the design and operation of PEM fuel cells. In the present study, a mathematical model has been formulated for the performance and operation of a single polymer electrolyte membrane fuel cell. This model incorporates all the essential fundamental physical and electrochemical processes occurring in the membrane electrolyte, cathode catalyst layer, electrode backing and flow channel. A special feature of the model is that it includes the effect of variable degree of water flooding in the cathode catalyst layer and/or cathode electrode backing region on the cell performance. The model predictions have been compared with the existing experimental results available in the literature and excellent agreement has been demonstrated between the model results and the measured data for the cell polarization curves. Hence, this model can be used for the optimization of PEM fuel cell design and operation, and can serve as a building block for the modelling and understanding of PEM fuel cell stacks and systems. 00103402 Modelling the integration of a compact plate steam reformer in a fuel .cell system Cunha, J. and Azevedo, J. L. T. Journrrl of Power Sources, 2000, 86, (l-2), 515-522. Fuel cell plant design requires an appropriate integration of components, especially with the fuel processing unit. The integration of a steam reformer for methanol with a polymer electrolyte membrane (PEM) fuel cell plant is examined here. The integration considers the use of the fuel ceil anode off gas (AOG) for combustion in order to supply the necessary heat for the reforming reaction. The whole fuel cell plant is considered with simple models for the components that allow sizing of the components and characterization of their operating conditions. A reformer, based on a plate heat exchanger, is considered with catalytic combustion of the AOG and methanol to supply the required energy. A detailed model for a plate heat exchanger, which considers reactions and heat transfer is used to predict temperature profiles. Modified nickel oxides as cathode materials for MCFC 00103403 Daza, L. er al. Journal ofPower Sources, 2000, 86, (l-2), 329-333. The preparation and subsequent oxidation of nickel cathodes modified by impregnation with cerium were evaluated by surface and bulk analysis. The cerium impregnated cathodes showed the same pore size distribution curve types and the same morphology as the reference nickel cathode. The measured nickel oxide dissolution rate in the molten carbonate mixture indicated that a minimum corrosion was evident for cathodes with 0.3-l wt% cerium oxide content. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed in the cathode characterization. As can be seen by SEM, the corrosion treatments produce marked modifications on the sample surfaces that appear more prominent for the cerium-free sample. The results also show that the lithiation process is a very significant factor that can improve the efficiency of the cell, but needs to be controlled because it can also produce very damaging effects such as the modification of the cathode volume by the formation on new compounds. 00/03404 Novel applications for micro-SOFCs Tompsett, G. A. ef al. Journal of Power Sources, 2000, 86, (I-2), 376-382. The application of micro-solid oxide fuels cells in small systems is discussed. Two types of application are examined, namely, leisure CHP systems and micro-hybrid vehicles. A unique triple layer catalyst-SOFC-catalyst system has been designed utilizing propane/butane fuel. The system consists of a co-generating gas burner with a pre-reforming catalyst, a micro-SOFC stack and an oxidation catalyst._ The pre-reforming catalyst comprising of ruthenium metal on Saffile” ceramic wool, was used to partially reform the propane/butane gas prior to entering the fuel cell, preventing carbon formation. The micro-SOFCs were YSZ tubes (Adelan, UK) with nickel/ YSZ cermet anodes on the outside and strontium-doped lanthanum manganite cathodes on the inside. Final oxidation was provided by a cordierite honeycomb coated with platinum combustion catalyst producing most of the heat for the fuel cell operation. Initial performance results were obtained and it was shown that a co-generating system could be achieved using a propane/butane fuel supply, piezoelectric ignition system and air
Necfrical
power supply and utilizatron (scientific, technical)
supply for the triple catalyst system. system for leisure and micro-hybrid power-assisted bicycles, is described.
The application of this micro-SOFC vehicles, such as golf trolleys and
00/03405 Optimisation of flow-field in polymer electrolyte membrane fuel cells using computational fluid dynamics techniques Hontafidn, E. et a/. Journal of Power Source.s, 2000, 86, (l-2), 363-368. The purpose of this work was the enhancement of performance of polymer electrolyte membrane fuel cells (PEMFC) by optimizing the gas flow distribution system. To achieve this, 3D numerical simulations of the gas flow in the assembly, consisting of the fuel side of the bipolar plate and the anode, were performed using a commercial computational fluid dynamics (CFD) software, the ‘FLUENT’ package. Two types of flow distributors were investigated: a grooved plate with parallel channels of the type commonly used in commercial fuel cells, and a porous material, The simulation showed that the permeability of the gas flow distributor is a key parameter affecting the consumption of reactant gas in the electrodes. Fuel utilization increased when decreasing the permeability of the flow distributor. In particular, fuel consumption increased significantly when the permeability of the porous material decreased to values below.that of the anode. This effect was not observed in the grooved plate, which permeability was higher than that of the anode. Even though the permeability of the grooved plate can be diminished by reducing the width of the channels, values lower than 1 mm are difficult to attain in practice. The simulation shows that porous materials are more advantageous than grooved plates in terms of reactant gas utilization. 00/03406 Optimisation of the cell shape for industrial MCFC stacks Arato, E. el ul. Journal of Power Sources, 2000, 86. (l-2), 302-308. This work aims to compare molten carbonate fuel cell (MCFC) stack behaviour when square and rectangular cells are used, and to discuss the optimization of their operating conditions. In particular, experimental data have been collected for a stack with square cells of 0.1 mz area to validate a stack simulation model; then, the effects of area increase of up to 0.75 mz have been predicted, proving the advantage of working with rectangular cells in order to obtain a better temperature and pressure drop management. Moreover, the operating conditions of a rectangular stack have been analysed and optimized when reformed natural gas, as well as coal gas, are used as fuel. The results presented and discussed have been used to guide design and operation of a rectangular slack constructed by Ansaldo Ricerche (ARI). 00103407 PAFC operating performance verified by Japanese gas utilities Kasahara, K. er al. Journal of Power Sources, 2000, 86, (l-2), 298-301, Japanese gas utilities have been conducting demonstration and field tests of on-site PAFC power generation plants for more than two decades since Tokyo Gas and Osaka Gas first participated in the TARGET Programme launched in the US in 1967. Total capacity of plants installed and tested to date has amounted to 15.56 MW. Cumulative number of installed plants has reached a total of 106. As of the end of August 1999, totalled 45 plants with a total capacity of 7800 kW are in operational. During the recent 2 years since the last Grove Symposium, 11 plants (,three for Tokyo Gas and eight for Osaka Gas) surpassed the 40,000 h durability target set as the R,D & D target for fuel cell technology. To date, two plants have logged an uninterrupted run of over a full year, the other target set as the reliability index. 00/03408 Phase relations in the system Sr-h-0 and thermodynamic measurements on SrlrOJ, SrzlrO, and Sr,lrO, using solid-state cells with buffer electrodes Jacob, K. T. ef al. J. Alloys Compd., 1999, 288, (l-2). 188-196. The standard Gibbs energies of formation of SrIrOS, SrzlrOl and Sr41r06 have been determined in the temperature range 975-1400 K using solidstate cells with (Y203) ZrOz as the electrolyte and pure oxygen gas at a pressure of 0.1 MPa as the reference electrode. For the design of appropriate working electrodes, phase relations in the ternary system Srlr-0 were investigated at 1350 K. The only stable oxide detected along the binary Ir-0 was IrOz. Three ternary oxides, SrlrO,, Sr21r04 and SrllrO,, compositions of which fall on the join SrO-IrOz, were found to be stable. Each of the oxides coexisted with pure metal iridium. Therefore, three working electrodes were prepared consisting of mixtures of lr + SrO + These Sr41r06, lr + Sr41r06 + Sr, - IrOd, and lr + Sr21r04 + Srlr03. mixtures unambiguously define unique oxygen chemical potentials under isothermal and isobaric conditions. A novel apparatus was used for the measurements, in which a buffer electrode was introduced between the reference and working electrodes to absorb the electrochemical flux of oxygen through the solid electrolyte. The buffer electrode prevented polarization of the measuring electrode and ensured accurate data. The standard Gibbs energies of formation of the compounds are represented. Chemical potential diagrams for the system Sr-lr-0 were developed based on the thermodynamic information. 00/03409 Planar solid oxide fuel cells: the Australian experience and outlook Godfrey, B. el a/. Journal of Power Sourct~.s, 2000. 86, (i-2), 68-73.
Fuel and Energy Abstracts
November 2000
383