Anders Lundblad - Academia.edu (original) (raw)

Papers by Anders Lundblad

Journal of Electroanalytical Chemistry, 2006

The electrochemical and mass transport properties of TEABF 4 in a nanoporous (NP) carbon material... more The electrochemical and mass transport properties of TEABF 4 in a nanoporous (NP) carbon material, obtained from silicon carbide, was studied using single particles and a microelectrode technique. The carbon particles of size 100-200 lm were studied by cyclic voltammetry and potential step measurements. The effective diffusion coefficients (D eff ) were calculated starting from the asymptotic solutions of FickÕs second law for short and long time regions. The results show that cycling at low sweep rates was needed in order for the electrolyte to penetrate the inner porosity of the particles. The carbon material showed different electrochemical and mass transport properties depending on the applied potential. At negative polarisation, the results suggest that TEA + was adsorbed on the pore wall, however, being transported very slowly inside the pores. The average D eff after cycling at both positive and negative potentials was 1.1(±0.4) · 10 À8 cm 2 s À1 , using the Cottrell relation and 1.5(±0.6) · 10 À8 cm 2 s À1 , using the radial diffusion solution. The average value of D eff after cycling at negative potentials was 1.7(±0.6) · 10 À8 cm 2 s À1 using both mathematical solutions.

It is well a well-known fact today that a fuel cell or a traction battery probably can not fully ... more It is well a well-known fact today that a fuel cell or a traction battery probably can not fully power an electric vehicle. This is due to the high cost and low power density of both the fuel cell and the candidate batteries.. One way of overcoming this problem could be the introduction of super-capacitors, which can take care of the power demand during acceleration. Moreover, they can store the breaking energy. This concept is under evaluation at several research institutes all over the world.

Introduction A single particle microelectrode technique with a micromanipulator [1] was applied f... more Introduction A single particle microelectrode technique with a micromanipulator [1] was applied for the characterisation of the electrochemical and mass transport properties of a high surface area nanoporous carbon, used as electrode material for double layer capacitor (DLC) [2]. Gas-porosimetry measurements have shown that the pores in the carbon are 8.2 ± 0.2 Å wide and extremely uniform in size [3]. The microelectrode technique, used in this work, has the advantage of reduced IR drop and the resistance due to external mass transport. The carbon material is obtained from silicon carbide, and suffers a thermal treatment, at approx. 1000 o C, with chlorine to produce silicon chloride and a solid skeleton carbon with very narrow pore size distribution according to the reaction: SiC (s) + 2Cl 2 (g) → SiCl 4 (g) + C(s). The solid carbon is, thereafter, purged with argon. Experimental The starting material was silicon carbide powder provided by NORTON AS. A nickel wire was used as a cou...

Journal of The Electrochemical Society

A method for fabricating LiCoO2 electrodes has been developed. LiCoO2 powder was synthesized from... more A method for fabricating LiCoO2 electrodes has been developed. LiCoO2 powder was synthesized from Li2CO3 and CoCO3 powder by calcining in air at 650 C. Electrodes were tape cast in a nonaqueous slurry with and without a graphite poreformer. They were sintered in air at temperatures between 700 and 850 C. Powders and electrodes were characterized by using x-ray diffraction, thermogravimetric analysis, the Brunauer, Emmett, and Teller method, Hg porosimetry, scanning electron microscopy, and a van der Pauw conductivity measurement setup. The electrodes were electrochemically characterized by polarization measurements at different temperatures. Performance of the electrodes, with and without poreformer, respectively, was also determined by measuring polarization curves at different degrees of electrolyte fill.

Journal of Electroanalytical Chemistry

A single particle microelectrode technique with a micromanipulator was applied and adapted for ch... more A single particle microelectrode technique with a micromanipulator was applied and adapted for characterisation of mass transport properties of ionic species in a high surface area nanoporous carbon, with uniform pore size of 8 Å. The effective diffusivity of 6 M KOH in this material was determined by means of potential step experiments on nanoporous carbon particles of different sizes. The results were analysed for short times (Cottrell model) and for long times (spherical diffusion model). The average effective diffusion coefficient for short and long times was 1.5×10−9 and 1.2×10−9 cm2 s−1, respectively. The relatively small diffusivity values are discussed in terms of interaction between the ion hydration shell and water molecules adsorbed on the pore wall.

Fuel Cells, 2004

A two-dimensional, non-isothermal, two-phase model of a polymer electrolyte fuel cell (PEFC) is p... more A two-dimensional, non-isothermal, two-phase model of a polymer electrolyte fuel cell (PEFC) is presented. The model is developed for conditions where variations in the streamwise direction are negligible. In addition, experiments were conducted with a segmented cell comprised of net flow fields. The, experimentally obtained, current distributions were used to validate the PEFC model developed. The PEFC model includes species transport and the phase change of water, coupled with conservation of momentum and mass, in the porous backing of the cathode, and conservation of charge and heat throughout the fuel cell. The current density in the active layer at the cathode is modelled with an agglomerate model, and the contact resistance for heat transfer over the material boundaries is taken into account. Good agreement was obtained between the modelled and experimental polarization curves. A temperature difference of 6 C between the bipolar plate and active layer on the cathode, and a liquid saturation of 6% at the active layer in the cathode were observed at 1 A cm ±2 .

Fuel Cells, 2007

Performance losses due to flooding of gas diffusion layers (GDLs) and flow fields as well as memb... more Performance losses due to flooding of gas diffusion layers (GDLs) and flow fields as well as membrane dehydration are two of the major problems in PEFC. In this investigation, the effect of GDL on the cell water management in PEFC is studied using segmented and single cell experiments. The behaviour of four different commercial GDLs was investigated at both high and low inlet humidity conditions by galvanostatic fuel cell experiments. The influence of varying reactant humidity and gas composition was studied. The results at high inlet humidity show that none of the studied GDLs are significantly flooded on the anode side. On the other hand, when some of the GDLs are used on the cathode side they are flooded, leading to increased mass transfer losses. The results at low inlet humidity conditions show that the characteristics of the GDL influence the membrane hydration. It is also shown that inlet humidity on the anode side has a major effect on flooding at the cathode.

Solid State Ionics, 2007

A novel sulfophenylated polysulfone membrane material has been evaluated in a hydrogen/oxygen fue... more A novel sulfophenylated polysulfone membrane material has been evaluated in a hydrogen/oxygen fuel cell using Nafion-impregnated commercial electrodes. Comparative measurements were performed with Nafion membranes to distinguish between different sources of potential losses. The operational temperatures in the experiments ranged from 60 to 110°C, and the effect of different humidifying conditions was investigated. Membranes that were operated over 300 h under fully humidified conditions showed a slight increase in the cell resistance. At lower humidification levels the cell resistance increased significantly. No difference in the membrane composition between active areas and areas not subjected to ionic currents could be detected by ATR-IR or Raman spectroscopy after fuel cell testing. The best fuel cell performance for these membranes was found at 90°C and 100°C. The current density at a cell voltage of 0.5 V ranged between 100 and 200 mA cm − 2 depending on the operating conditions. The relatively low current densities found when using the new membrane material are explained by high ionic contact resistances between the electrodes and the membrane.

Solid State Ionics, 1997

... Consequently the number of nuclei should be higher when decomposing in air and thus, the resi... more ... Consequently the number of nuclei should be higher when decomposing in air and thus, the residual powder product will have a larger specific surface area. ... Note also that below 350C there should be no CoCO, de composition in CO 2 according to Fig. ...

Journal of Power Sources, 2000

LiCoO -powder was synthesized from carbonate precursors by calcination in air. Greentapes were ta... more LiCoO -powder was synthesized from carbonate precursors by calcination in air. Greentapes were tape-cast using a non-aqueous 2 slurry and 10 mm plastic spheres as pore formers. Sintering was carried out in air at 850-9508C and in argonrair at 500r7508C. The two sintering procedures led to very different sub-micron morphologies, with the primary particles being much smaller in the latter case. The electrochemical performance at 6508C, in terms of overpotential at 160 mArcm 2 , for the air-and argonrair-sintered electrodes was 57 and 81 mV, respectively. The potential drop due to contact resistance between electrode and current collector was estimated to be 100 and Ž . 70 mV, respectively. The electrode materials were characterized by scanning electron microscopy SEM , Hg-porosimetry, the Ž . Ž . Ž . BET-method N -adsorption , X-ray diffractometry XRD , flame atomic absorption spectrometry F-AAS , carbon analysis and a van der 2 Pauw conductivity measurement set-up. q

Journal of Power Sources, 2008

Anatase TiO 2 is evaluated as catalyst support material in authentic Pt-TiO 2 /C composite gas di... more Anatase TiO 2 is evaluated as catalyst support material in authentic Pt-TiO 2 /C composite gas diffusion electrodes (GDEs), as a different approach in the context of improving the proton exchange membrane fuel cell (PEMFC) cathode stability. A thermal stability study shows high carbon stability as Pt nanoparticles are supported on TiO 2 instead of carbon in the Pt-TiO 2 /C composite material, presumably due to a reduced direct contact between Pt and C. The performance of Pt-TiO 2 /C cathodes is investigated electrochemically in assembled membrane-electrode assemblies (MEAs) considering the added carbon fraction and Pt concentration deposited on TiO 2 . The O 2 reduction current for the Pt-TiO 2 alone is expectedly low due to the low electronic conductivity in bulk TiO 2 . However, the Pt-TiO 2 /C composite cathodes show enhanced fuel cell cathode performance with growing carbon fraction and increasing Pt concentration deposited on TiO 2 . The proposed reasons for these observations are improved macroscopic and local electronic conductivity, respectively. Electron micrographs of fuel cell tested Pt-TiO 2 /C composite cathodes illustrate only a minor Pt migration in the Pt-TiO 2 /C structure, in which anatase TiO 2 is used as Pt support. On the whole, the study demonstrates a stable Pt-TiO 2 /C composite material possessing a performance comparable to conventional Pt-C materials when incorporated in a PEMFC cathode.

Journal of The Electrochemical Society, 1997

A method of capillary rise (gravimetrically measured) has been investigated for determination of ... more A method of capillary rise (gravimetrically measured) has been investigated for determination of the electrolyte contact angle in porous electrodes for the molten-carbonate fuel cell. The experiments were conducted on LiCoOâ electrodes in air, at different temperatures (555 to 740 C), to monitor the influence of the temperature on the contact angle. The results indicate that the contact angle decreases

Journal of The Electrochemical Society, 2006

ABSTRACT The electrochemical oxygen reduction reaction on nanostructured supported platinum elect... more ABSTRACT The electrochemical oxygen reduction reaction on nanostructured supported platinum electrodes is measured using a newly developed solid-state polymer electrolyte electrochemical cell. Measurements were made on three types of catalytic surfaces on glassy carbon supports: nanostructured model electrodes prepared by colloidal lithography, a thin thermally evaporated Pt film, and a pure glassy carbon surface. Measurements in nitrogen and oxygen at several different humidities were performed at 60°C in a fuel-cell-like environment. Lowering humidity showed a higher Tafel slope at high potentials for oxygen reduction on the nanostructured catalyst. Good agreement between the electrochemical active area from the hydrogen adsorption peaks and the catalytic area determined from scanning electron microscopy images was found. No significant change of the electrochemically active area with humidity could be found. Double-layer capacitance and oxygen reduction currents increased with increased humidification temperatures.

Journal of The Electrochemical Society, 2006

ABSTRACT The transport properties and morphology of an activated carbon containing macro-, meso-,... more ABSTRACT The transport properties and morphology of an activated carbon containing macro-, meso-, and micropores were studied and compared to a sophisticated fully nanoporous carbon that almost lacks meso- and macropores. The morphology of the activated carbon was studied using nitrogen adsorption methods and the pore size distribution was investigated using Barret, Joyner, and Halenda and density functional theory models. The transport properties were studied using a microelectrode technique that allows for determination of the effective diffusivity, . For the meso/macroporous carbon the effective diffusivity was determined using potential step experiments and analysis for both Cottrell and filling diffusivities were made. The Cottrell diffusivity was smaller than the value of the filling diffusivity, with mean values of and , respectively. This difference in diffusivities is the basis for an agglomerate hypothesis presented for the meso/macroporous carbon. The results for the meso/macroporous carbon are compared with the corresponding results for the sophisticated fully nanoporous carbon. This gave further evidence for the presented agglomerate hypothesis.

Journal of Electroanalytical Chemistry, 2006

The electrochemical and mass transport properties of TEABF 4 in a nanoporous (NP) carbon material... more The electrochemical and mass transport properties of TEABF 4 in a nanoporous (NP) carbon material, obtained from silicon carbide, was studied using single particles and a microelectrode technique. The carbon particles of size 100-200 lm were studied by cyclic voltammetry and potential step measurements. The effective diffusion coefficients (D eff ) were calculated starting from the asymptotic solutions of FickÕs second law for short and long time regions. The results show that cycling at low sweep rates was needed in order for the electrolyte to penetrate the inner porosity of the particles. The carbon material showed different electrochemical and mass transport properties depending on the applied potential. At negative polarisation, the results suggest that TEA + was adsorbed on the pore wall, however, being transported very slowly inside the pores. The average D eff after cycling at both positive and negative potentials was 1.1(±0.4) · 10 À8 cm 2 s À1 , using the Cottrell relation and 1.5(±0.6) · 10 À8 cm 2 s À1 , using the radial diffusion solution. The average value of D eff after cycling at negative potentials was 1.7(±0.6) · 10 À8 cm 2 s À1 using both mathematical solutions.

It is well a well-known fact today that a fuel cell or a traction battery probably can not fully ... more It is well a well-known fact today that a fuel cell or a traction battery probably can not fully power an electric vehicle. This is due to the high cost and low power density of both the fuel cell and the candidate batteries.. One way of overcoming this problem could be the introduction of super-capacitors, which can take care of the power demand during acceleration. Moreover, they can store the breaking energy. This concept is under evaluation at several research institutes all over the world.

Introduction A single particle microelectrode technique with a micromanipulator [1] was applied f... more Introduction A single particle microelectrode technique with a micromanipulator [1] was applied for the characterisation of the electrochemical and mass transport properties of a high surface area nanoporous carbon, used as electrode material for double layer capacitor (DLC) [2]. Gas-porosimetry measurements have shown that the pores in the carbon are 8.2 ± 0.2 Å wide and extremely uniform in size [3]. The microelectrode technique, used in this work, has the advantage of reduced IR drop and the resistance due to external mass transport. The carbon material is obtained from silicon carbide, and suffers a thermal treatment, at approx. 1000 o C, with chlorine to produce silicon chloride and a solid skeleton carbon with very narrow pore size distribution according to the reaction: SiC (s) + 2Cl 2 (g) → SiCl 4 (g) + C(s). The solid carbon is, thereafter, purged with argon. Experimental The starting material was silicon carbide powder provided by NORTON AS. A nickel wire was used as a cou...

Journal of The Electrochemical Society

A method for fabricating LiCoO2 electrodes has been developed. LiCoO2 powder was synthesized from... more A method for fabricating LiCoO2 electrodes has been developed. LiCoO2 powder was synthesized from Li2CO3 and CoCO3 powder by calcining in air at 650 C. Electrodes were tape cast in a nonaqueous slurry with and without a graphite poreformer. They were sintered in air at temperatures between 700 and 850 C. Powders and electrodes were characterized by using x-ray diffraction, thermogravimetric analysis, the Brunauer, Emmett, and Teller method, Hg porosimetry, scanning electron microscopy, and a van der Pauw conductivity measurement setup. The electrodes were electrochemically characterized by polarization measurements at different temperatures. Performance of the electrodes, with and without poreformer, respectively, was also determined by measuring polarization curves at different degrees of electrolyte fill.

Journal of Electroanalytical Chemistry

A single particle microelectrode technique with a micromanipulator was applied and adapted for ch... more A single particle microelectrode technique with a micromanipulator was applied and adapted for characterisation of mass transport properties of ionic species in a high surface area nanoporous carbon, with uniform pore size of 8 Å. The effective diffusivity of 6 M KOH in this material was determined by means of potential step experiments on nanoporous carbon particles of different sizes. The results were analysed for short times (Cottrell model) and for long times (spherical diffusion model). The average effective diffusion coefficient for short and long times was 1.5×10−9 and 1.2×10−9 cm2 s−1, respectively. The relatively small diffusivity values are discussed in terms of interaction between the ion hydration shell and water molecules adsorbed on the pore wall.

Fuel Cells, 2004

A two-dimensional, non-isothermal, two-phase model of a polymer electrolyte fuel cell (PEFC) is p... more A two-dimensional, non-isothermal, two-phase model of a polymer electrolyte fuel cell (PEFC) is presented. The model is developed for conditions where variations in the streamwise direction are negligible. In addition, experiments were conducted with a segmented cell comprised of net flow fields. The, experimentally obtained, current distributions were used to validate the PEFC model developed. The PEFC model includes species transport and the phase change of water, coupled with conservation of momentum and mass, in the porous backing of the cathode, and conservation of charge and heat throughout the fuel cell. The current density in the active layer at the cathode is modelled with an agglomerate model, and the contact resistance for heat transfer over the material boundaries is taken into account. Good agreement was obtained between the modelled and experimental polarization curves. A temperature difference of 6 C between the bipolar plate and active layer on the cathode, and a liquid saturation of 6% at the active layer in the cathode were observed at 1 A cm ±2 .

Fuel Cells, 2007

Performance losses due to flooding of gas diffusion layers (GDLs) and flow fields as well as memb... more Performance losses due to flooding of gas diffusion layers (GDLs) and flow fields as well as membrane dehydration are two of the major problems in PEFC. In this investigation, the effect of GDL on the cell water management in PEFC is studied using segmented and single cell experiments. The behaviour of four different commercial GDLs was investigated at both high and low inlet humidity conditions by galvanostatic fuel cell experiments. The influence of varying reactant humidity and gas composition was studied. The results at high inlet humidity show that none of the studied GDLs are significantly flooded on the anode side. On the other hand, when some of the GDLs are used on the cathode side they are flooded, leading to increased mass transfer losses. The results at low inlet humidity conditions show that the characteristics of the GDL influence the membrane hydration. It is also shown that inlet humidity on the anode side has a major effect on flooding at the cathode.

Solid State Ionics, 2007

A novel sulfophenylated polysulfone membrane material has been evaluated in a hydrogen/oxygen fue... more A novel sulfophenylated polysulfone membrane material has been evaluated in a hydrogen/oxygen fuel cell using Nafion-impregnated commercial electrodes. Comparative measurements were performed with Nafion membranes to distinguish between different sources of potential losses. The operational temperatures in the experiments ranged from 60 to 110°C, and the effect of different humidifying conditions was investigated. Membranes that were operated over 300 h under fully humidified conditions showed a slight increase in the cell resistance. At lower humidification levels the cell resistance increased significantly. No difference in the membrane composition between active areas and areas not subjected to ionic currents could be detected by ATR-IR or Raman spectroscopy after fuel cell testing. The best fuel cell performance for these membranes was found at 90°C and 100°C. The current density at a cell voltage of 0.5 V ranged between 100 and 200 mA cm − 2 depending on the operating conditions. The relatively low current densities found when using the new membrane material are explained by high ionic contact resistances between the electrodes and the membrane.

Solid State Ionics, 1997

... Consequently the number of nuclei should be higher when decomposing in air and thus, the resi... more ... Consequently the number of nuclei should be higher when decomposing in air and thus, the residual powder product will have a larger specific surface area. ... Note also that below 350C there should be no CoCO, de composition in CO 2 according to Fig. ...

Journal of Power Sources, 2000

LiCoO -powder was synthesized from carbonate precursors by calcination in air. Greentapes were ta... more LiCoO -powder was synthesized from carbonate precursors by calcination in air. Greentapes were tape-cast using a non-aqueous 2 slurry and 10 mm plastic spheres as pore formers. Sintering was carried out in air at 850-9508C and in argonrair at 500r7508C. The two sintering procedures led to very different sub-micron morphologies, with the primary particles being much smaller in the latter case. The electrochemical performance at 6508C, in terms of overpotential at 160 mArcm 2 , for the air-and argonrair-sintered electrodes was 57 and 81 mV, respectively. The potential drop due to contact resistance between electrode and current collector was estimated to be 100 and Ž . 70 mV, respectively. The electrode materials were characterized by scanning electron microscopy SEM , Hg-porosimetry, the Ž . Ž . Ž . BET-method N -adsorption , X-ray diffractometry XRD , flame atomic absorption spectrometry F-AAS , carbon analysis and a van der 2 Pauw conductivity measurement set-up. q

Journal of Power Sources, 2008

Anatase TiO 2 is evaluated as catalyst support material in authentic Pt-TiO 2 /C composite gas di... more Anatase TiO 2 is evaluated as catalyst support material in authentic Pt-TiO 2 /C composite gas diffusion electrodes (GDEs), as a different approach in the context of improving the proton exchange membrane fuel cell (PEMFC) cathode stability. A thermal stability study shows high carbon stability as Pt nanoparticles are supported on TiO 2 instead of carbon in the Pt-TiO 2 /C composite material, presumably due to a reduced direct contact between Pt and C. The performance of Pt-TiO 2 /C cathodes is investigated electrochemically in assembled membrane-electrode assemblies (MEAs) considering the added carbon fraction and Pt concentration deposited on TiO 2 . The O 2 reduction current for the Pt-TiO 2 alone is expectedly low due to the low electronic conductivity in bulk TiO 2 . However, the Pt-TiO 2 /C composite cathodes show enhanced fuel cell cathode performance with growing carbon fraction and increasing Pt concentration deposited on TiO 2 . The proposed reasons for these observations are improved macroscopic and local electronic conductivity, respectively. Electron micrographs of fuel cell tested Pt-TiO 2 /C composite cathodes illustrate only a minor Pt migration in the Pt-TiO 2 /C structure, in which anatase TiO 2 is used as Pt support. On the whole, the study demonstrates a stable Pt-TiO 2 /C composite material possessing a performance comparable to conventional Pt-C materials when incorporated in a PEMFC cathode.

Journal of The Electrochemical Society, 1997

A method of capillary rise (gravimetrically measured) has been investigated for determination of ... more A method of capillary rise (gravimetrically measured) has been investigated for determination of the electrolyte contact angle in porous electrodes for the molten-carbonate fuel cell. The experiments were conducted on LiCoOâ electrodes in air, at different temperatures (555 to 740 C), to monitor the influence of the temperature on the contact angle. The results indicate that the contact angle decreases

Journal of The Electrochemical Society, 2006

ABSTRACT The electrochemical oxygen reduction reaction on nanostructured supported platinum elect... more ABSTRACT The electrochemical oxygen reduction reaction on nanostructured supported platinum electrodes is measured using a newly developed solid-state polymer electrolyte electrochemical cell. Measurements were made on three types of catalytic surfaces on glassy carbon supports: nanostructured model electrodes prepared by colloidal lithography, a thin thermally evaporated Pt film, and a pure glassy carbon surface. Measurements in nitrogen and oxygen at several different humidities were performed at 60°C in a fuel-cell-like environment. Lowering humidity showed a higher Tafel slope at high potentials for oxygen reduction on the nanostructured catalyst. Good agreement between the electrochemical active area from the hydrogen adsorption peaks and the catalytic area determined from scanning electron microscopy images was found. No significant change of the electrochemically active area with humidity could be found. Double-layer capacitance and oxygen reduction currents increased with increased humidification temperatures.

Journal of The Electrochemical Society, 2006

ABSTRACT The transport properties and morphology of an activated carbon containing macro-, meso-,... more ABSTRACT The transport properties and morphology of an activated carbon containing macro-, meso-, and micropores were studied and compared to a sophisticated fully nanoporous carbon that almost lacks meso- and macropores. The morphology of the activated carbon was studied using nitrogen adsorption methods and the pore size distribution was investigated using Barret, Joyner, and Halenda and density functional theory models. The transport properties were studied using a microelectrode technique that allows for determination of the effective diffusivity, . For the meso/macroporous carbon the effective diffusivity was determined using potential step experiments and analysis for both Cottrell and filling diffusivities were made. The Cottrell diffusivity was smaller than the value of the filling diffusivity, with mean values of and , respectively. This difference in diffusivities is the basis for an agglomerate hypothesis presented for the meso/macroporous carbon. The results for the meso/macroporous carbon are compared with the corresponding results for the sophisticated fully nanoporous carbon. This gave further evidence for the presented agglomerate hypothesis.