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Electrolyte model for SOFC
RESEARCH TRENDS methanol oxidation on DMFC anodes than with carbon black support. The Pt particle size dispersed on the MCMBs is larger than catalyst on carbon black because of the MCMBs’ lower specific surface area. The lower anode polarization characteristic may be due to improved mass transport. Further work should reduce Pt particle size, and will study fuel cell performance using MCMB supported anode catalyst. Y.-C. Liu, X.-P. Qiu, Y.-Q. Huang and W.-T. Zhu: J. Power Sources 111(1) 160–164 (18 September 2002).
Low-temperature PEMFC activation The performance of a low-temperature PEM fuel cell can be greatly improved by first operating the cell at elevated temperature and pressure. Such a procedure is applicable to all kinds of MEAs whose electrodes are made using either supported or unsupported catalysts, and the effect achieved is permanent. Z. Qi and A. Kaufman: J. Power Sources 111(1) 181–184 (18 September 2002).
SOFCs utilizing DME fuel
significantly inhibited sintering, grain growth and agglomeration of the nickel phase in the cermet during high-temperature sintering and reducing, for enhanced Ni and YSZ phase distribution and significantly improved electrochemical activity and stability of Ni/YSZ anodes for H2 oxidation. S.P. Jiang, Y.Y. Duan and J.G. Love: J. Electrochem. Soc. 149(9) A1175–1183 (September 2002).
Effect of CO in fuel on PEMFC cathode performance The effect on both anode and cathode of CO in the anode fuel was studied using various PEM fuel cell MEAs. CO could poison the anode and also the cathode, and sometimes the cathode potential drop was larger. Fully hydrated membrane could reduce or even prevent CO crossover, especially for thicker membranes. It seems that CO transports to the cathode via diffusion through pinholes in the membrane. Z. Qi, C. He and A. Kaufman: J. Power Sources 111(2) 239–247 (23 September 2002).
DMFC heat and power management
The feasibility and benefits of using an oxygenated fuel for SOFCs were explored using dimethyl ether. Equal amounts of H2, CH4 and CO above about 675°C were observed in catalytic reactions on Nibased anodes, but the gases’ mole fractions were much higher at 550–650°C. Maximum power densities for DME-fed SOFCs were 0.10 and 0.21 W/cm2 at 600 and 700°C, respectively. No carbon deposition was observed in operation up to 700°C. E. Perry Murray, S.J. Harris and H. Jen: J. Electrochem. Soc. 149(9) A1127–1131 (September 2002).
This work describes heat and power management of a DMFC system including an anode feed loop with heat-exchanger and a compressor/expander on the cathode side. In particular, the influence of cathode water vaporization on DMFC heat management was investigated. Input parameters were stack temperature, cathode pressure and air flow rate. Especially at operating temperatures above 90°C, combinations of pressure and air flow rate are limited because of heat losses due to vaporization of water in the cathode. H. Dohle, J. Mergel and D. Stolten: J. Power Sources 111(2) 268–282 (23 September 2002).
Fabrication and testing of doped LSGM thin-film SOFC
Hydrogen through low-temperature methane reforming
A supported lanthanum gallate (LSGM) electrolyte thin-film SOFC with Ni-YSZ cermet anode and Sr-doped lanthanum manganite (LSM)-YSZ composite cathode was fabricated and tested. The severe high-temperature reaction between LSGM and NiO, required for full densification of LSGM film, can be avoided. An LSM-YSZ composite cathode was screen-printed on LSGM film, then fired at 1250°C. Electrolyte resistances of such SOFC single cells are much lower than thick LSGM film supported cells. J.W. Yan, Z.G. Lu, Y. Jiang, Y.L. Dong, C.Y. Yu and W.Z. Li: J. Electrochem. Soc. 149(9) A1132– 1135 (September 2002).
Hydrogen production for fuel cells by methane reforming at low temperatures was investigated. From thermodynamic equilibrium analysis, steam reforming (SRM) at low pressure and high steam: methane ratio can be achieved without significantly reduced hydrogen yield at only 550°C. A scheme is proposed for low-temperature hydrogen production by burning unconverted methane to supply heat for SRM. Experiments indicated that CH4 conversion increases significantly with increasing O2:CH4 or H2O: CH4 ratios, and the hydrogen content in dry tail gas increases with H2O:CH4 ratio. Z.-W. Liu, K.-W. Jun, H.-S. Roh and S.-E. Park: J. Power Sources 111(2) 283–287 (23 September 2002).
High-performance Ni/YSZ cermet SOFC anodes by ion impregnation Here the microstructure and performance of Ni/YSZ cermet SOFC electrodes were enhanced by ion impregnation. Impregnating very fine oxide particles into the Ni/YSZ cermet structure March 2003
Electrolyte model for SOFC This model describes the distribution of electron and electron hole concentrations and the potential along the electrolyte thickness. It
facilitates study of electrolyte materials and the effects of operating temperature, oxygen partial pressure and electrolyte thickness on oxygen semipermeability. For doped ZrO2 at 800°C in an SOFC, the thinner the electrolyte, the higher the energy efficiency and the output power density will be at intermediate current density due to the higher electrolyte ohmic loss. Thus, low O2 semipermeability for a thin electrolyte is desirable. S.H. Chan, X.J. Chen and K.A. Khor: J. Power Sources 111(2) 320–328 (23 September 2002).
Preparation of PtRu onto PEMs for DMFC anodes Impregnation–reduction was investigated for DMFC anode preparation. PtRu electrocatalysts were directly bonded onto a polymer electrolyte membrane by chemical reduction of a mixture of Pt and Ru complexes impregnated in the membrane. Deposited PtRu particles were embedded in the 3–4 µm membrane surface region to form a porous, hydrophilic layer. The PtRu layers are applicable to DMFC anodes, despite their small active surface area compared to conventional PtRu nanoparticles. N. Fujiwara, K. Yasuda, T. Ioroi, Z. Siroma and Y. Miyazaki: Electrochimica Acta 47(25) 4079– 4084 (25 September 2002).
Fine Pt catalyst supported on single-wall carbon nanohorns Single-wall carbon nanohorns (SWNHs) have a horn-shaped sheath of single-wall graphitic sheets, and a characteristic shape that supports fine Pt catalyst particles. Here Pt catalyst was supported on SWNHs to demonstrate their suitability for PEM fuel cell electrodes. Pt particles were homogeneously dispersed on the SWNHs, with a particle size of about 2 nm – less than half than when supported on conventional carbon black. A fuel cell using SWNHs had a higher current density than one using carbon black. T. Yoshitake, Y. Shimakawa, S. Kuroshima, H. Kimura, T. Ichihashi, Y. Kubo, D. Kasuya, K. Takahashi, F. Kokai, M. Yudasaka and S. Iijima: Physica B: Condensed Matter 323(1–4) 124–126 (October 2002).
Optimizing non-aqueous nickel slips in tape-casting MCFC electrodes The rheological behavior of non-aqueous carbonyl nickel slips for tape-casting, used in manufacturing MCFC electrodes, was investigated for different solvent and binder systems, by controling the total binder and plasticizer content and the binder/ plasticizer ratio. The content of glycerol trioleate dispersant in the slip was optimized. The densities, tensile strength and microstructure of green tapes obtained under different conditions were studied, and related to the slips’ rheological properties. F. Li, C.-M. Wang and K.-A. Hu: Materials Res. Bulletin 37(12) 1907–1921 (3 October 2002). Fuel Cells Bulletin
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Low-temperature PEMFC activation The performance of a low-temperature PEM fuel cell can be greatly improved by first operating the cell at elevated temperature and pressure. Such a procedure is applicable to all kinds of MEAs whose electrodes are made using either supported or unsupported catalysts, and the effect achieved is permanent. Z. Qi and A. Kaufman: J. Power Sources 111(1) 181–184 (18 September 2002).
SOFCs utilizing DME fuel
significantly inhibited sintering, grain growth and agglomeration of the nickel phase in the cermet during high-temperature sintering and reducing, for enhanced Ni and YSZ phase distribution and significantly improved electrochemical activity and stability of Ni/YSZ anodes for H2 oxidation. S.P. Jiang, Y.Y. Duan and J.G. Love: J. Electrochem. Soc. 149(9) A1175–1183 (September 2002).
Effect of CO in fuel on PEMFC cathode performance The effect on both anode and cathode of CO in the anode fuel was studied using various PEM fuel cell MEAs. CO could poison the anode and also the cathode, and sometimes the cathode potential drop was larger. Fully hydrated membrane could reduce or even prevent CO crossover, especially for thicker membranes. It seems that CO transports to the cathode via diffusion through pinholes in the membrane. Z. Qi, C. He and A. Kaufman: J. Power Sources 111(2) 239–247 (23 September 2002).
DMFC heat and power management
The feasibility and benefits of using an oxygenated fuel for SOFCs were explored using dimethyl ether. Equal amounts of H2, CH4 and CO above about 675°C were observed in catalytic reactions on Nibased anodes, but the gases’ mole fractions were much higher at 550–650°C. Maximum power densities for DME-fed SOFCs were 0.10 and 0.21 W/cm2 at 600 and 700°C, respectively. No carbon deposition was observed in operation up to 700°C. E. Perry Murray, S.J. Harris and H. Jen: J. Electrochem. Soc. 149(9) A1127–1131 (September 2002).
This work describes heat and power management of a DMFC system including an anode feed loop with heat-exchanger and a compressor/expander on the cathode side. In particular, the influence of cathode water vaporization on DMFC heat management was investigated. Input parameters were stack temperature, cathode pressure and air flow rate. Especially at operating temperatures above 90°C, combinations of pressure and air flow rate are limited because of heat losses due to vaporization of water in the cathode. H. Dohle, J. Mergel and D. Stolten: J. Power Sources 111(2) 268–282 (23 September 2002).
Fabrication and testing of doped LSGM thin-film SOFC
Hydrogen through low-temperature methane reforming
A supported lanthanum gallate (LSGM) electrolyte thin-film SOFC with Ni-YSZ cermet anode and Sr-doped lanthanum manganite (LSM)-YSZ composite cathode was fabricated and tested. The severe high-temperature reaction between LSGM and NiO, required for full densification of LSGM film, can be avoided. An LSM-YSZ composite cathode was screen-printed on LSGM film, then fired at 1250°C. Electrolyte resistances of such SOFC single cells are much lower than thick LSGM film supported cells. J.W. Yan, Z.G. Lu, Y. Jiang, Y.L. Dong, C.Y. Yu and W.Z. Li: J. Electrochem. Soc. 149(9) A1132– 1135 (September 2002).
Hydrogen production for fuel cells by methane reforming at low temperatures was investigated. From thermodynamic equilibrium analysis, steam reforming (SRM) at low pressure and high steam: methane ratio can be achieved without significantly reduced hydrogen yield at only 550°C. A scheme is proposed for low-temperature hydrogen production by burning unconverted methane to supply heat for SRM. Experiments indicated that CH4 conversion increases significantly with increasing O2:CH4 or H2O: CH4 ratios, and the hydrogen content in dry tail gas increases with H2O:CH4 ratio. Z.-W. Liu, K.-W. Jun, H.-S. Roh and S.-E. Park: J. Power Sources 111(2) 283–287 (23 September 2002).
High-performance Ni/YSZ cermet SOFC anodes by ion impregnation Here the microstructure and performance of Ni/YSZ cermet SOFC electrodes were enhanced by ion impregnation. Impregnating very fine oxide particles into the Ni/YSZ cermet structure March 2003
Electrolyte model for SOFC This model describes the distribution of electron and electron hole concentrations and the potential along the electrolyte thickness. It
facilitates study of electrolyte materials and the effects of operating temperature, oxygen partial pressure and electrolyte thickness on oxygen semipermeability. For doped ZrO2 at 800°C in an SOFC, the thinner the electrolyte, the higher the energy efficiency and the output power density will be at intermediate current density due to the higher electrolyte ohmic loss. Thus, low O2 semipermeability for a thin electrolyte is desirable. S.H. Chan, X.J. Chen and K.A. Khor: J. Power Sources 111(2) 320–328 (23 September 2002).
Preparation of PtRu onto PEMs for DMFC anodes Impregnation–reduction was investigated for DMFC anode preparation. PtRu electrocatalysts were directly bonded onto a polymer electrolyte membrane by chemical reduction of a mixture of Pt and Ru complexes impregnated in the membrane. Deposited PtRu particles were embedded in the 3–4 µm membrane surface region to form a porous, hydrophilic layer. The PtRu layers are applicable to DMFC anodes, despite their small active surface area compared to conventional PtRu nanoparticles. N. Fujiwara, K. Yasuda, T. Ioroi, Z. Siroma and Y. Miyazaki: Electrochimica Acta 47(25) 4079– 4084 (25 September 2002).
Fine Pt catalyst supported on single-wall carbon nanohorns Single-wall carbon nanohorns (SWNHs) have a horn-shaped sheath of single-wall graphitic sheets, and a characteristic shape that supports fine Pt catalyst particles. Here Pt catalyst was supported on SWNHs to demonstrate their suitability for PEM fuel cell electrodes. Pt particles were homogeneously dispersed on the SWNHs, with a particle size of about 2 nm – less than half than when supported on conventional carbon black. A fuel cell using SWNHs had a higher current density than one using carbon black. T. Yoshitake, Y. Shimakawa, S. Kuroshima, H. Kimura, T. Ichihashi, Y. Kubo, D. Kasuya, K. Takahashi, F. Kokai, M. Yudasaka and S. Iijima: Physica B: Condensed Matter 323(1–4) 124–126 (October 2002).
Optimizing non-aqueous nickel slips in tape-casting MCFC electrodes The rheological behavior of non-aqueous carbonyl nickel slips for tape-casting, used in manufacturing MCFC electrodes, was investigated for different solvent and binder systems, by controling the total binder and plasticizer content and the binder/ plasticizer ratio. The content of glycerol trioleate dispersant in the slip was optimized. The densities, tensile strength and microstructure of green tapes obtained under different conditions were studied, and related to the slips’ rheological properties. F. Li, C.-M. Wang and K.-A. Hu: Materials Res. Bulletin 37(12) 1907–1921 (3 October 2002). Fuel Cells Bulletin
13