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Mass-exchange between PEM cathode and anode channels
RESEARCH TRENDS environments was investigated. The corrosion rate is higher under 'outlet' conditions at 700°C compared to standard conditions at 650°C and 'inlet' conditions at 600°C. The corrosion potential increases with time when a protective corrosion layer is formed. Eventually it reaches a more positive potential, close to the cathode operating potential. On Thermax 4762 steel, the corrosion layer grows relatively quickly in the first 48 h, then slows down when a protective layer is formed. The corrosion layer consists of an Fe-rich outer layer and a protective AI- and Cr-rich inner layer. B. Zhu, G. Lindbergh: Electrocbimica Acta 46(17) 2593-2604 (15 May 2001).
Model electrodes of sprayed layers with a Pt precursor on glassy carbon substrates were used. The size and size distribution of the Pt nanoparticles were determined by highresolution transmission electron microscopy and X-ray line-shape analysis; the electrochemical activity of the catalyst layers was investigated by cyclic voltammetry. First results showed that an increase in catalytic activity is possible by applying pulsed electrodeposition (PED). M.-S. LSffler, B. Gross, H. Natter, R. Hempelmann, T. Krajewski, J. Divisek: Scripta Materialia 44(8/9) 2253-2257 (18 May 2001).
Kinetics of methanol decomposition Methanol steam reforming in supported Pd membrane reactor The supported Pd membrane is promising for the production of high-purity hydrogen from catalytic steam reforming of methanol. At the 350°C reaction temperature, the catalyst activity and stability are promoted by increasing the alumina content. Here a compact doublejacketed reactor has generated high-purity hydrogen directly from steam reforming of methanol, with no need for external purification and a much higher recovery yield. Y.-M. Lin, M.-H. Rei: Catalysis Today 67(1-3) 77-84 (15 May 2001).
Sulfonated PEEKcomposite membranes Here electrochemical properties of composite proton-exchange membranes prepared by incorporation of boron phosphate into a polymeric matrix of sulfonated polyether ether ketone (SPEEK) were studied. The composites' conductivity largely exceeded that of pure SPEEK polymer. However, it was lower than predicted by the effective medium theory for these mixtures. This is associated with formation of a capillary pore system in the membranes. Despite the developed porosity, the composite membranes were mechanically strong and unaffected by long-term storage in water. S.D. Mikhailenko, S.M.J. Zaidi, S. Kaliaguine: Catalysis Today 67(I-3) 225-236 (15 May 2001).
Nanostructured catalysts for PEM fuel cells A novel preparation technique for catalyst layers in PEM fuel cells is presented, which enables selective electrochemical deposition of Pt nanoparticles on those surface areas of the carbon support in contact with the protonand electron-conducting phases and simultaneously with the gaseous or liquid fuel.
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This work looks at the kinetics of methanol autothermal partial oxidation. The kinetics of methanol decomposition with a commercial copper on alumina catalyst were determined. Three other reactions were considered: dimethyl ether (DME) formation, steam reforming and water gas shift (WGS). Auxiliary experiments showed that the WGS reaction is negligible with this catalyst. The activation energies for DME formation, reforming and decomposition are comparable to values in the literature, while turnover frequencies were similar to a Pd/ZrO 2 catalyst from the literature. P. Mizsey, E. Newson, T.-B. Truong, P. Hottinger: Applied Catalysis A 213(2) 233-237 (30 May 2001).
Mass-exchange between PEM cathode and anode channels A numerical model is developed to predict the mass flow between channels in a PEM fuel cell with a serpentine flow path. The complete threedimensional Navier-Stokes equations with multi-species mixture are solved and electrochemical reactions are modeled as mass source/ sink terms in the control volumes. The results indicate that flow distributions in both anode and cathode channels are significantly affected by the mass consumption patterns on the membrane-electrode assembly. The water transport is governed by both electro-osmosis and diffusion processes. The overall pressure drop is less than that expected for a regular straight channel flow. S. Dutta, S. Shimpalee, J.W. Van Zee: Int. J. of Heat & Mass Transfer44(11) 2029-2042 (June 2001).
Oxygen reduction rate in PEM fuel cell The rates of oxygen reduction and generation of water vapour in a gas diffusion electrode and the active catalyst layer of a PEM fuel cell were
studied analytically. The model accounts for the diffusion of oxygen and water vapour, the reaction of oxygen and hydrogen ions in the liquid, and the effectiveness of a porous Pt catalyst on the cathode side. Calculations of cell polarization behaviour were compared with existing experimental data. There is a great possibility that the rate-limiting process is transport of oxygen and hydrogen ions in the Pt catalyst particle when the effective diameter of the Pt catalyst particle is greater than 2 pm. S. Fukada: Energy Conversion & Management 42(9) 1121-1131 (June 2001).
Fabrication of tubular SOFC electrolytes Long, straight, dense and evenly shaped tubular electrolytes (200-300 mm long, 2.4-2.5 mm inner diameter, 0.3-0.4 mm wall thickness) were fabricated from Sr- and Mg-doped LaGaO 3 materials by extrusion. An economic and practical process was developed to extrude the small tubes using water- and organic-based additives and optimized process parameters. The particle size distribution and specific surface area of the synthesized powder were modified by calcination and ball milling. Obtaining workable pastes played an important role in achieving smooth, linear, even and dense 'green' tubes. The final products showed a dense microstructure and improved mechanical strength over pressing routes.
Y. Du, N.M. Sammes: J. of European Ceramic Soc. 21(6) 727-735 (June 2001).
Modeling and analysis of transportation PEMFC An effective hydrogen fuel cell power system performance model for transportation applications has been developed. The baseline performance of an actual fuel cell system has been assessed with the model, and efficiencies and losses evaluated. Improvement measures for components and the overall system were identified, and assessed using the model. Significant benefits are found to be attainable through these improvement measures. R. Cownden, M. Nahon, M.A. Rosen: Int. J. of Hydrogen Energy 26(6) 615-623 (June 2001).
Dynamic behaviour of stationary PEMFC stack This PEM fuel cell stack can respond to fast load changes (<0.15 s). For maximum efficiency, the stack starts from ambient to reach its operating temperature of 75°C. Thus an algorithm was devised to start it and temporarily apply a load, so that after a few minutes the stack is ready to operate at full
FuelCellsBulletinNo.37
Model electrodes of sprayed layers with a Pt precursor on glassy carbon substrates were used. The size and size distribution of the Pt nanoparticles were determined by highresolution transmission electron microscopy and X-ray line-shape analysis; the electrochemical activity of the catalyst layers was investigated by cyclic voltammetry. First results showed that an increase in catalytic activity is possible by applying pulsed electrodeposition (PED). M.-S. LSffler, B. Gross, H. Natter, R. Hempelmann, T. Krajewski, J. Divisek: Scripta Materialia 44(8/9) 2253-2257 (18 May 2001).
Kinetics of methanol decomposition Methanol steam reforming in supported Pd membrane reactor The supported Pd membrane is promising for the production of high-purity hydrogen from catalytic steam reforming of methanol. At the 350°C reaction temperature, the catalyst activity and stability are promoted by increasing the alumina content. Here a compact doublejacketed reactor has generated high-purity hydrogen directly from steam reforming of methanol, with no need for external purification and a much higher recovery yield. Y.-M. Lin, M.-H. Rei: Catalysis Today 67(1-3) 77-84 (15 May 2001).
Sulfonated PEEKcomposite membranes Here electrochemical properties of composite proton-exchange membranes prepared by incorporation of boron phosphate into a polymeric matrix of sulfonated polyether ether ketone (SPEEK) were studied. The composites' conductivity largely exceeded that of pure SPEEK polymer. However, it was lower than predicted by the effective medium theory for these mixtures. This is associated with formation of a capillary pore system in the membranes. Despite the developed porosity, the composite membranes were mechanically strong and unaffected by long-term storage in water. S.D. Mikhailenko, S.M.J. Zaidi, S. Kaliaguine: Catalysis Today 67(I-3) 225-236 (15 May 2001).
Nanostructured catalysts for PEM fuel cells A novel preparation technique for catalyst layers in PEM fuel cells is presented, which enables selective electrochemical deposition of Pt nanoparticles on those surface areas of the carbon support in contact with the protonand electron-conducting phases and simultaneously with the gaseous or liquid fuel.
(~
This work looks at the kinetics of methanol autothermal partial oxidation. The kinetics of methanol decomposition with a commercial copper on alumina catalyst were determined. Three other reactions were considered: dimethyl ether (DME) formation, steam reforming and water gas shift (WGS). Auxiliary experiments showed that the WGS reaction is negligible with this catalyst. The activation energies for DME formation, reforming and decomposition are comparable to values in the literature, while turnover frequencies were similar to a Pd/ZrO 2 catalyst from the literature. P. Mizsey, E. Newson, T.-B. Truong, P. Hottinger: Applied Catalysis A 213(2) 233-237 (30 May 2001).
Mass-exchange between PEM cathode and anode channels A numerical model is developed to predict the mass flow between channels in a PEM fuel cell with a serpentine flow path. The complete threedimensional Navier-Stokes equations with multi-species mixture are solved and electrochemical reactions are modeled as mass source/ sink terms in the control volumes. The results indicate that flow distributions in both anode and cathode channels are significantly affected by the mass consumption patterns on the membrane-electrode assembly. The water transport is governed by both electro-osmosis and diffusion processes. The overall pressure drop is less than that expected for a regular straight channel flow. S. Dutta, S. Shimpalee, J.W. Van Zee: Int. J. of Heat & Mass Transfer44(11) 2029-2042 (June 2001).
Oxygen reduction rate in PEM fuel cell The rates of oxygen reduction and generation of water vapour in a gas diffusion electrode and the active catalyst layer of a PEM fuel cell were
studied analytically. The model accounts for the diffusion of oxygen and water vapour, the reaction of oxygen and hydrogen ions in the liquid, and the effectiveness of a porous Pt catalyst on the cathode side. Calculations of cell polarization behaviour were compared with existing experimental data. There is a great possibility that the rate-limiting process is transport of oxygen and hydrogen ions in the Pt catalyst particle when the effective diameter of the Pt catalyst particle is greater than 2 pm. S. Fukada: Energy Conversion & Management 42(9) 1121-1131 (June 2001).
Fabrication of tubular SOFC electrolytes Long, straight, dense and evenly shaped tubular electrolytes (200-300 mm long, 2.4-2.5 mm inner diameter, 0.3-0.4 mm wall thickness) were fabricated from Sr- and Mg-doped LaGaO 3 materials by extrusion. An economic and practical process was developed to extrude the small tubes using water- and organic-based additives and optimized process parameters. The particle size distribution and specific surface area of the synthesized powder were modified by calcination and ball milling. Obtaining workable pastes played an important role in achieving smooth, linear, even and dense 'green' tubes. The final products showed a dense microstructure and improved mechanical strength over pressing routes.
Y. Du, N.M. Sammes: J. of European Ceramic Soc. 21(6) 727-735 (June 2001).
Modeling and analysis of transportation PEMFC An effective hydrogen fuel cell power system performance model for transportation applications has been developed. The baseline performance of an actual fuel cell system has been assessed with the model, and efficiencies and losses evaluated. Improvement measures for components and the overall system were identified, and assessed using the model. Significant benefits are found to be attainable through these improvement measures. R. Cownden, M. Nahon, M.A. Rosen: Int. J. of Hydrogen Energy 26(6) 615-623 (June 2001).
Dynamic behaviour of stationary PEMFC stack This PEM fuel cell stack can respond to fast load changes (<0.15 s). For maximum efficiency, the stack starts from ambient to reach its operating temperature of 75°C. Thus an algorithm was devised to start it and temporarily apply a load, so that after a few minutes the stack is ready to operate at full
FuelCellsBulletinNo.37