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DMFC cell performance and cathode research
RESEARCH TRENDS
Research Trends Fracture energy and crack growth in surface-treated YSZ for SOFCs The SOFC electrolyte, yttria-stabilized zirconia (YSZ), was coated and co-sintered with different electrode coatings. Two energy release rates – for crack initiation and arrest – characterized the cracking behavior. A 30–50% improvement in fracture resistance compared with untreated YSZ was due to coating effects. Interdiffusion of Mn and Ni from coatings into the YSZ lattice during sintering appears to introduce residual stresses, for improved fracture energy. Crack bridging appears to contribute to improved fracture toughness in surface-treated YSZ. A.N. Kumar and B.F. Sørensen: Materials Science & Engineering A 333(1/2) 380–389 (August 2002).
Carbon deposition in Ni-YSZ anodesupported SOFC with methane An anode-supported planar SOFC was fabricated with LSM (La0.78Sr0.22MnxO3), 8YSZ and Ni/YSZ. A single cell was tested with hydrogen and methane to compare cell performance and investigate carbon deposition effects. Impedance responses showed one large high-frequency arc, a typical indication of polarization resistance from the anode support. A carbon deposition test with flowing methane at open-circuit showed an arc increase after deposition. The increased impedance arc recovered to its original magnitude when an electrical load was applied. This reversibility of carbon deposition resulted in no change in cell performance. J.-H. Koh, Y.-S. Yoo, J.-W. Park and H.C. Lim: Solid State Ionics 149(3/4) 157–166 (2 August 2002).
Cu-based catalysts on γ-alumina for methanol reforming This work investigated the influence of catalyst properties on activity and selectivity of hydrogen generation by methanol reforming over copperbased catalysts impregnated on γ-alumina pellets. Three copper-based catalysts were tested: Cu/Zn/Al2O3, Cu/Cr/Al2O3 and Cu/Zr/Al2O3. Copper surface area correlated with catalytic activity. The choice of promoter and catalyst composition greatly influenced activity and selectivity for CO2 formation. The highest conversions were achieved for Cu/Zn/Al2O3 for both steam reforming and combined reforming. Complete methanol conversion was only
January 2003
obtained for zinc-containing catalysts for steam reforming. Combined reforming generally yielded a product stream with lower CO than steam reforming. B. Lindström, L.J. Pettersson and P.G. Menon: Applied Catalysis A 234(1/2) 111–125 (8 August 2002).
Novel modified NiO cathode for MCFCs A novel MCFC cathode was prepared by coating nm-size LiFeO2 grains on the surface of a porous NiO cathode using a simple combustion process. Because of its excellent stability in carbonate melts under MCFC cathode conditions, the LiFeO2 coating significantly retarded dissolution of the inner NiO in eutectic Li–K or Li–Na carbonate melts. Although pure LiFeO2 has a much lower electrical conductivity than NiO(Li), the electrical conductivity of LiFeO2coated NiO was similar to NiO(Li) after immersion and lithiation in Li–K carbonates. In unit cell tests the LiFeO2-coated NiO cathode performed better than the NiO cathode. F. Li, H.-Y. Chen, C.-M. Wang and K.-A. Hua: J. of Electroanalytical Chemistry 531(1) 53–60 (9 August 2002).
Electrocatalysis of methanol oxidation This paper reviews and discusses methanol electro-oxidation on Pt electrodes, including voltage and spectroscopic data. Parallel reaction pathways have been demonstrated, producing CO2 and HCOOH or HCHO as soluble products, which depend on system parameters like methanol concentration, electrode roughness, and electrolysis time. Several issues, such as reaction intermediates and oxidation product yield, remain unclear. T. Iwasita: Electrochimica Acta 47(22/23) 3663–3674 (30 August 2002).
Methanol electro-oxidation on PtRu/C gas diffusion electrodes This work studies methanol electro-oxidation on gas diffusion electrodes with PtRu catalysts supported on carbon. The catalyst activity in a half-cell depends on the methanol concentration (maximum close to 2 mol/l). Atomic Ru contents of 25% and above increase the catalyst tolerance to higher methanol concentrations. Pt75Ru25/C exhibits the greatest activity for methanol oxidation. Gas diffusion electrodes with this catalyst showed potentials 0.14 V higher than with E-Tek Pt/C when tested in a single DMFC.
W.H. Lizcano-Valbuena, V.A. Paganin and E.R. Gonzalez: Electrochimica Acta 47(22/23) 3715–3722 (30 August 2002).
High-temperature methanol electro-oxidation in PtRu The structure, chemistry and morphology of various unsupported PtRu electrocatalysts were investigated by X-ray diffraction (XRD), X-ray energy-dispersive analysis and X-ray photoelectron spectroscopy. The metal surfacearea of identically prepared PtRu catalysts increased significantly with increasing Ru. Electrocatalytic activity towards methanol oxidation in DMFCs was studied at 130°C; the bifunctional mechanism was found to govern methanol electro-oxidation on PtRu in the high temperature range, similar to conventional DMFC operation at 60–90°C. A.S. Aricò, P.L. Antonucci, E. Modica, V. Baglio, H. Kim and V. Antonucci: Electrochimica Acta 47(22/23) 3723–3732 (30 August 2002).
PtRu/C catalyst from carbonyl complexes In this new method for producing highly active, carbon-supported PtRu catalysts for methanol oxidation, the catalyst is produced from carbonyl metal complexes by deposition of precursors on carbon in a high boiling-point solvent. The resulting PtRu catalysts are well distributed with high dispersion and narrow size distribution. This method has promising activity, as well as offering an easier route to ternary and quaternary catalysts. A.J. Dickinson, L.P.L. Carrette, J.A. Collins, K.A. Friedrich and U. Stimming: Electrochimica Acta 47(22/23) 3733–3739 (30 August 2002).
DMFC cell performance and cathode research This work discusses long-term anode stability in DMFCs and methanol crossover, reporting on recent accomplishments in cell performance, fuel utilization, overall conversion efficiency and reduced Pt loading in automotive DMFCs. A cathode performance evaluation method is described based on cathode polarization curves, generated from DMFC data, which allowed study of the effect of temperature variation on DMFC cathode potential. The results show that Pt-rich DMFC cathodes, operating on ambient air at 60°C, can deliver high performance of more than 0.85 V versus RHE at 0.100 A/cm2. S.C. Thomas, X. Ren, S. Gottesfeld and P. Zelenay: Electrochimica Acta 47(22/23) 3741–3748 (30 August 2002).
Fuel Cells Bulletin
13
Research Trends Fracture energy and crack growth in surface-treated YSZ for SOFCs The SOFC electrolyte, yttria-stabilized zirconia (YSZ), was coated and co-sintered with different electrode coatings. Two energy release rates – for crack initiation and arrest – characterized the cracking behavior. A 30–50% improvement in fracture resistance compared with untreated YSZ was due to coating effects. Interdiffusion of Mn and Ni from coatings into the YSZ lattice during sintering appears to introduce residual stresses, for improved fracture energy. Crack bridging appears to contribute to improved fracture toughness in surface-treated YSZ. A.N. Kumar and B.F. Sørensen: Materials Science & Engineering A 333(1/2) 380–389 (August 2002).
Carbon deposition in Ni-YSZ anodesupported SOFC with methane An anode-supported planar SOFC was fabricated with LSM (La0.78Sr0.22MnxO3), 8YSZ and Ni/YSZ. A single cell was tested with hydrogen and methane to compare cell performance and investigate carbon deposition effects. Impedance responses showed one large high-frequency arc, a typical indication of polarization resistance from the anode support. A carbon deposition test with flowing methane at open-circuit showed an arc increase after deposition. The increased impedance arc recovered to its original magnitude when an electrical load was applied. This reversibility of carbon deposition resulted in no change in cell performance. J.-H. Koh, Y.-S. Yoo, J.-W. Park and H.C. Lim: Solid State Ionics 149(3/4) 157–166 (2 August 2002).
Cu-based catalysts on γ-alumina for methanol reforming This work investigated the influence of catalyst properties on activity and selectivity of hydrogen generation by methanol reforming over copperbased catalysts impregnated on γ-alumina pellets. Three copper-based catalysts were tested: Cu/Zn/Al2O3, Cu/Cr/Al2O3 and Cu/Zr/Al2O3. Copper surface area correlated with catalytic activity. The choice of promoter and catalyst composition greatly influenced activity and selectivity for CO2 formation. The highest conversions were achieved for Cu/Zn/Al2O3 for both steam reforming and combined reforming. Complete methanol conversion was only
January 2003
obtained for zinc-containing catalysts for steam reforming. Combined reforming generally yielded a product stream with lower CO than steam reforming. B. Lindström, L.J. Pettersson and P.G. Menon: Applied Catalysis A 234(1/2) 111–125 (8 August 2002).
Novel modified NiO cathode for MCFCs A novel MCFC cathode was prepared by coating nm-size LiFeO2 grains on the surface of a porous NiO cathode using a simple combustion process. Because of its excellent stability in carbonate melts under MCFC cathode conditions, the LiFeO2 coating significantly retarded dissolution of the inner NiO in eutectic Li–K or Li–Na carbonate melts. Although pure LiFeO2 has a much lower electrical conductivity than NiO(Li), the electrical conductivity of LiFeO2coated NiO was similar to NiO(Li) after immersion and lithiation in Li–K carbonates. In unit cell tests the LiFeO2-coated NiO cathode performed better than the NiO cathode. F. Li, H.-Y. Chen, C.-M. Wang and K.-A. Hua: J. of Electroanalytical Chemistry 531(1) 53–60 (9 August 2002).
Electrocatalysis of methanol oxidation This paper reviews and discusses methanol electro-oxidation on Pt electrodes, including voltage and spectroscopic data. Parallel reaction pathways have been demonstrated, producing CO2 and HCOOH or HCHO as soluble products, which depend on system parameters like methanol concentration, electrode roughness, and electrolysis time. Several issues, such as reaction intermediates and oxidation product yield, remain unclear. T. Iwasita: Electrochimica Acta 47(22/23) 3663–3674 (30 August 2002).
Methanol electro-oxidation on PtRu/C gas diffusion electrodes This work studies methanol electro-oxidation on gas diffusion electrodes with PtRu catalysts supported on carbon. The catalyst activity in a half-cell depends on the methanol concentration (maximum close to 2 mol/l). Atomic Ru contents of 25% and above increase the catalyst tolerance to higher methanol concentrations. Pt75Ru25/C exhibits the greatest activity for methanol oxidation. Gas diffusion electrodes with this catalyst showed potentials 0.14 V higher than with E-Tek Pt/C when tested in a single DMFC.
W.H. Lizcano-Valbuena, V.A. Paganin and E.R. Gonzalez: Electrochimica Acta 47(22/23) 3715–3722 (30 August 2002).
High-temperature methanol electro-oxidation in PtRu The structure, chemistry and morphology of various unsupported PtRu electrocatalysts were investigated by X-ray diffraction (XRD), X-ray energy-dispersive analysis and X-ray photoelectron spectroscopy. The metal surfacearea of identically prepared PtRu catalysts increased significantly with increasing Ru. Electrocatalytic activity towards methanol oxidation in DMFCs was studied at 130°C; the bifunctional mechanism was found to govern methanol electro-oxidation on PtRu in the high temperature range, similar to conventional DMFC operation at 60–90°C. A.S. Aricò, P.L. Antonucci, E. Modica, V. Baglio, H. Kim and V. Antonucci: Electrochimica Acta 47(22/23) 3723–3732 (30 August 2002).
PtRu/C catalyst from carbonyl complexes In this new method for producing highly active, carbon-supported PtRu catalysts for methanol oxidation, the catalyst is produced from carbonyl metal complexes by deposition of precursors on carbon in a high boiling-point solvent. The resulting PtRu catalysts are well distributed with high dispersion and narrow size distribution. This method has promising activity, as well as offering an easier route to ternary and quaternary catalysts. A.J. Dickinson, L.P.L. Carrette, J.A. Collins, K.A. Friedrich and U. Stimming: Electrochimica Acta 47(22/23) 3733–3739 (30 August 2002).
DMFC cell performance and cathode research This work discusses long-term anode stability in DMFCs and methanol crossover, reporting on recent accomplishments in cell performance, fuel utilization, overall conversion efficiency and reduced Pt loading in automotive DMFCs. A cathode performance evaluation method is described based on cathode polarization curves, generated from DMFC data, which allowed study of the effect of temperature variation on DMFC cathode potential. The results show that Pt-rich DMFC cathodes, operating on ambient air at 60°C, can deliver high performance of more than 0.85 V versus RHE at 0.100 A/cm2. S.C. Thomas, X. Ren, S. Gottesfeld and P. Zelenay: Electrochimica Acta 47(22/23) 3741–3748 (30 August 2002).
Fuel Cells Bulletin
13