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Microfuel processor for miniature power supply
FCBSeptember
8/28/02
9:34 AM
Page 11
RESEARCH TRENDS
Research Trends Characterization of composite SOFC cathodes The performance of Pt/YSZ and LSM/YSZ composite SOFC electrodes as a function of the electrode composition is investigated experimentally. The qualitative features of the impedance spectra are similar for both cathodes; in particular, in both the electrode performance shows a dome-shaped curve as a function of the electrode composition. Nevertheless, the quantitative aspects are very different; in particular, the electrode performance is much higher for the LSM/YSZ electrode than for Pt/YSZ. Also, the composition which gives the maximum performance and the experimental values of the percolation thresholds are different. The reasons for the discrepancies are analysed and discussed. A. Barbucci, R. Bozzo, G. Cerisola and P. Costamagna: Electrochimica Acta 47(13/14) 2183–2188 (25 May 2002).
Phenyl phosphonic acid functionalized poly[aryloxyphosphazenes] for DMFCs The synthesis of phenyl phosphonic acid functionalized poly[aryloxyphosphazene] membranes is described, for use in DMFCs. Polymer membranes with ion-exchange capacities between 1.17 and 1.43 meq/g were cast from N,N-dimethyl-formamide and found to have proton conductivities between 10–2 and 10–1 S/cm. Equilibrium water swelling values were between 11% and 32%, depending on the polymer structure. Methanol diffusion coefficients for both radiation cross-linked and noncross-linked membranes in 3M aqueous methanol at 80°C and 2.8 bar were at least 12 times lower than for Nafion 117, and six times lower than for a radiation cross-linked sulfonated polyphosphazene membrane. H.R. Allcock, M.A. Hofmann, C.M. Ambler, S.N. Lvov, X.Y. Zhou, E. Chalkova and J. Weston: J. of Membrane Science 201(1/2) 47–54 (31 May 2002).
Fuel cell APUs for heavy-duty trucks Fuel cells are promising for auxiliary power units (APUs) in heavy-duty diesel-engined trucks, which presently suffer from heavy fuel consumption, pollution and greenhouse gas emissions. This work estimates costs and benefits of fuel cell APUs, and calculates the payback period to be about 2.6–4.5 years. This estimate is uncertain since future fuel cell costs are unknown, and cost savings from idling vary greatly. The
September 2002
payback period is particularly sensitive to diesel fuel consumption at idle. Given the large potential environmental and economic benefits of fuel cell APUs, the first major commercial application of fuel cells may be as truck APUs. C.-J. Brodrick, T.E. Lipman, M. Farshchi, N.P. Lutsey, H.A. Dwyer, D. Sperling, S.W. Gouse, D.B. Harris and F.G. King: Transportation Research Part D: Transport & Environment 7(4) 303–315 (June 2002).
optimize startup. The stack/compressor model is proposed to solve the problem, by varying external conditions. To perform system startup under stable conditions, the air relative humidity and temperature are maintained in a proper range. This approach has been utilized to define the power module characteristics and layout of a mid-sized hybrid city bus within an EU project. M. De Francesco and E. Arato: J. of Power Sources 108(1/2) 41–52 (1 June 2002).
Microfuel processor for miniature power supply
Diffusion layer pore-size distribution and mass-transport in PEMFCs
A microscale fuel reformer for use with a miniature fuel cell was built and operated at efficiencies attractive for use as a miniature power supply for microelectronics. The processor comprises two vaporizer/preheaters, a heat-exchanger, combustor and steam reformer. A proprietary catalyst processed a 1:1 methanol: water mixture into a hydrogen-rich stream (73–74 vol% H2, 25–26 vol% CO2, 0.6–1.2 vol% CO on a dry basis). An integrated fuel processor using proprietary catalyst in the reformer and catalytic combustion was built. When 100 mWe of hydrogen was produced, a thermal efficiency of 9% (estimated 4.5% net efficiency) was achieved. J.D. Holladay, E.O. Jones, M. Phelps and J. Hu: J. of Power Sources 108(1/2) 21–27 (1 June 2002).
The influence of the diffusion layer pore-size distribution on mass-transport problems in PEMFCs is investigated using electrodes with hydrophobic diffusion layers for which the poresize distribution is designed by pore-former and heat treatment. The pore-size distribution of the diffusion layer is found to be a more critical parameter for mass-transport processes within the electrode and for cell performance characteristics than the total porosity. Experimental data indicate that the performance loss due to mass-transport limitations can be reduced by enlarging the macropore volume in the diffusion layer. The water flooding problem is discussed in terms of condensation phenomena dependent on pore-size. C.S. Kong, D.-Y. Kim, H.-K. Lee, Y.-G. Shul and T.-H. Lee: J. of Power Sources 108(1/2) 185–191 (1 June 2002).
Soldier-portable fuel cell power A 15 We portable power system is being developed for the US Army, comprising a hydrogengenerating fuel reformer coupled to a PEMFC. The project’s first phase, reported here, developed and demonstrated a methanol steam reformer system. The reformer included a combustor, two vaporizers and a steam reforming reactor. Assuming a 14-day mission life and an ultimate 1 kg processor/fuel cell assembly, then operating at 13 We the system yielded a fuel processor efficiency of 45% and an estimated net efficiency of 22%. The resulting energy density of 720 Wh/kg is several times the energy density of Li-ion batteries. D.R. Palo, J.D. Holladay, R.T. Rozmiarek, C.E. Guzman-Leong, Y. Wang, J. Hu, Y.-H. Chin, R.A. Dagle and E.G. Baker: J. of Power Sources 108(1/2) 28–34 (1 June 2002).
Start-up analysis for automotive PEM fuel cell systems A problem in developing a power generation module adaptable to a wide range of cars is the definition of the compressor system for air feeding. Here the transient response of the system (fuel cell and compressor) is investigated to
Thermodynamically favourable reformer operating conditions The characteristics of steam-methane reforming (SMR), partial oxidation (POX) and autothermal reforming (ATR) are investigated, with favourable operating conditions identified for each process. The optimum SMR reactor steam:carbon (S:C) ratio is 1.9. The optimum POX reactor air ratio is 0.3 at a preheat temperature of 312°C. The ATR reactor’s optimum air ratio and S:C ratio are 0.29 and 0.35, respectively, at a preheat of 400°C. Simulated material and energy balances give the CH4 flow rates required to generate 1 mol/s of hydrogen as 0.364 mol/s for POX, 0.367 mol/s for ATR and 0.385 mol/s for SMR. Thus POX has the lowest energy cost to produce the same amount of hydrogen from CH4. Y.-S. Seo, A. Shirley and S.T. Kolaczkowski: J. of Power Sources 108(1/2) 213–225 (1 June 2002).
Co–W alloys as anode materials for methanol fuel cells Co–W alloys are developed by electroplating using a bath solution containing triammonium citrate and dimethyl sulfoxide. The alloys are
Fuel Cells Bulletin
11
8/28/02
9:34 AM
Page 11
RESEARCH TRENDS
Research Trends Characterization of composite SOFC cathodes The performance of Pt/YSZ and LSM/YSZ composite SOFC electrodes as a function of the electrode composition is investigated experimentally. The qualitative features of the impedance spectra are similar for both cathodes; in particular, in both the electrode performance shows a dome-shaped curve as a function of the electrode composition. Nevertheless, the quantitative aspects are very different; in particular, the electrode performance is much higher for the LSM/YSZ electrode than for Pt/YSZ. Also, the composition which gives the maximum performance and the experimental values of the percolation thresholds are different. The reasons for the discrepancies are analysed and discussed. A. Barbucci, R. Bozzo, G. Cerisola and P. Costamagna: Electrochimica Acta 47(13/14) 2183–2188 (25 May 2002).
Phenyl phosphonic acid functionalized poly[aryloxyphosphazenes] for DMFCs The synthesis of phenyl phosphonic acid functionalized poly[aryloxyphosphazene] membranes is described, for use in DMFCs. Polymer membranes with ion-exchange capacities between 1.17 and 1.43 meq/g were cast from N,N-dimethyl-formamide and found to have proton conductivities between 10–2 and 10–1 S/cm. Equilibrium water swelling values were between 11% and 32%, depending on the polymer structure. Methanol diffusion coefficients for both radiation cross-linked and noncross-linked membranes in 3M aqueous methanol at 80°C and 2.8 bar were at least 12 times lower than for Nafion 117, and six times lower than for a radiation cross-linked sulfonated polyphosphazene membrane. H.R. Allcock, M.A. Hofmann, C.M. Ambler, S.N. Lvov, X.Y. Zhou, E. Chalkova and J. Weston: J. of Membrane Science 201(1/2) 47–54 (31 May 2002).
Fuel cell APUs for heavy-duty trucks Fuel cells are promising for auxiliary power units (APUs) in heavy-duty diesel-engined trucks, which presently suffer from heavy fuel consumption, pollution and greenhouse gas emissions. This work estimates costs and benefits of fuel cell APUs, and calculates the payback period to be about 2.6–4.5 years. This estimate is uncertain since future fuel cell costs are unknown, and cost savings from idling vary greatly. The
September 2002
payback period is particularly sensitive to diesel fuel consumption at idle. Given the large potential environmental and economic benefits of fuel cell APUs, the first major commercial application of fuel cells may be as truck APUs. C.-J. Brodrick, T.E. Lipman, M. Farshchi, N.P. Lutsey, H.A. Dwyer, D. Sperling, S.W. Gouse, D.B. Harris and F.G. King: Transportation Research Part D: Transport & Environment 7(4) 303–315 (June 2002).
optimize startup. The stack/compressor model is proposed to solve the problem, by varying external conditions. To perform system startup under stable conditions, the air relative humidity and temperature are maintained in a proper range. This approach has been utilized to define the power module characteristics and layout of a mid-sized hybrid city bus within an EU project. M. De Francesco and E. Arato: J. of Power Sources 108(1/2) 41–52 (1 June 2002).
Microfuel processor for miniature power supply
Diffusion layer pore-size distribution and mass-transport in PEMFCs
A microscale fuel reformer for use with a miniature fuel cell was built and operated at efficiencies attractive for use as a miniature power supply for microelectronics. The processor comprises two vaporizer/preheaters, a heat-exchanger, combustor and steam reformer. A proprietary catalyst processed a 1:1 methanol: water mixture into a hydrogen-rich stream (73–74 vol% H2, 25–26 vol% CO2, 0.6–1.2 vol% CO on a dry basis). An integrated fuel processor using proprietary catalyst in the reformer and catalytic combustion was built. When 100 mWe of hydrogen was produced, a thermal efficiency of 9% (estimated 4.5% net efficiency) was achieved. J.D. Holladay, E.O. Jones, M. Phelps and J. Hu: J. of Power Sources 108(1/2) 21–27 (1 June 2002).
The influence of the diffusion layer pore-size distribution on mass-transport problems in PEMFCs is investigated using electrodes with hydrophobic diffusion layers for which the poresize distribution is designed by pore-former and heat treatment. The pore-size distribution of the diffusion layer is found to be a more critical parameter for mass-transport processes within the electrode and for cell performance characteristics than the total porosity. Experimental data indicate that the performance loss due to mass-transport limitations can be reduced by enlarging the macropore volume in the diffusion layer. The water flooding problem is discussed in terms of condensation phenomena dependent on pore-size. C.S. Kong, D.-Y. Kim, H.-K. Lee, Y.-G. Shul and T.-H. Lee: J. of Power Sources 108(1/2) 185–191 (1 June 2002).
Soldier-portable fuel cell power A 15 We portable power system is being developed for the US Army, comprising a hydrogengenerating fuel reformer coupled to a PEMFC. The project’s first phase, reported here, developed and demonstrated a methanol steam reformer system. The reformer included a combustor, two vaporizers and a steam reforming reactor. Assuming a 14-day mission life and an ultimate 1 kg processor/fuel cell assembly, then operating at 13 We the system yielded a fuel processor efficiency of 45% and an estimated net efficiency of 22%. The resulting energy density of 720 Wh/kg is several times the energy density of Li-ion batteries. D.R. Palo, J.D. Holladay, R.T. Rozmiarek, C.E. Guzman-Leong, Y. Wang, J. Hu, Y.-H. Chin, R.A. Dagle and E.G. Baker: J. of Power Sources 108(1/2) 28–34 (1 June 2002).
Start-up analysis for automotive PEM fuel cell systems A problem in developing a power generation module adaptable to a wide range of cars is the definition of the compressor system for air feeding. Here the transient response of the system (fuel cell and compressor) is investigated to
Thermodynamically favourable reformer operating conditions The characteristics of steam-methane reforming (SMR), partial oxidation (POX) and autothermal reforming (ATR) are investigated, with favourable operating conditions identified for each process. The optimum SMR reactor steam:carbon (S:C) ratio is 1.9. The optimum POX reactor air ratio is 0.3 at a preheat temperature of 312°C. The ATR reactor’s optimum air ratio and S:C ratio are 0.29 and 0.35, respectively, at a preheat of 400°C. Simulated material and energy balances give the CH4 flow rates required to generate 1 mol/s of hydrogen as 0.364 mol/s for POX, 0.367 mol/s for ATR and 0.385 mol/s for SMR. Thus POX has the lowest energy cost to produce the same amount of hydrogen from CH4. Y.-S. Seo, A. Shirley and S.T. Kolaczkowski: J. of Power Sources 108(1/2) 213–225 (1 June 2002).
Co–W alloys as anode materials for methanol fuel cells Co–W alloys are developed by electroplating using a bath solution containing triammonium citrate and dimethyl sulfoxide. The alloys are
Fuel Cells Bulletin
11