Mikko Mikkola - Academia.edu (original) (raw)

Papers by Mikko Mikkola

Research paper thumbnail of Studies on Limiting Factors of Polymer Electrolyte Membrane Fuel Cell Cathode Performance

... S. Mikkola, Tommy Rockward, Bryan S. Pivovar and Francisco A. Uribe, ”The Effect of NaCl ... ... more ... S. Mikkola, Tommy Rockward, Bryan S. Pivovar and Francisco A. Uribe, ”The Effect of NaCl ... methodology used for resistance measurement of individual cells in a fuel cell and contributed ... For publication II, the author participated in the development of segmented current collector ...

Research paper thumbnail of Determination of mass diffusion overpotential distribution with flow pulse method from current distribution measurements in a PEMFC

The mass diffusion overpotential distribution in a free-breathing proton exchange membrane fuel c... more The mass diffusion overpotential distribution in a free-breathing proton exchange membrane fuel cell (PEMFC) was determined from current distribution measurements using a flow pulse approach. The current distribution measurements were conducted with a segmented flow-field plate. Flow pulses were fed to the cathode channels to form a uniform oxygen concentration distribution along the channels. Simultaneously, the cell resistance was monitored

Research paper thumbnail of Measurement of ohmic voltage losses in individual cells of a PEMFC stack

Journal of Power Sources, 2002

The ohmic voltage loss in a fuel cell can be determined with the current interruption method. The... more The ohmic voltage loss in a fuel cell can be determined with the current interruption method. The method was utilized to measure the ohmic voltage loss in an individual cell of a fuel cell stack. This was achieved by producing voltage transients and monitoring them with a digital oscilloscope connected in parallel with the individual cell. In this study, the method was applied to a small polymer electrolyte membrane fuel cell (PEMFC) stack in which different air supply levels were employed on the cathode side. In the case of higher air-feed rate, the results revealed an increase of ohmic losses in the middle of the stack by up to 21% at 400 mA cm À2 , compared to the unit cell with the lowest ohmic loss. This probably resulted from the decrease of membrane conductivity because of drying. Comparison to individual cell voltages showed that the decrease of conductivity would not be observed if only the individual cell voltages alone were measured. The total ohmic loss in the stack was measured using the same method to verify the reliability of the measurement system. The results indicate a good agreement between the total ohmic loss and the combined ohmic losses in the individual cells.

Research paper thumbnail of Mass transport in the cathode of a free-breathing polymer electrolyte membrane fuel cell

In small fuel cell applications, it is desirable to take care of the management of reactants, wat... more In small fuel cell applications, it is desirable to take care of the management of reactants, water and heat by passive means in order to minimize parasitic losses. A polymer electrolyte membrane fuel cell, in which air flow on the cathode was driven by free convection, was studied by experimental and modelling methods. The cathode side of the cell had straight vertical channels with their ends open to the ambient air. A two-dimensional, isothermal and steady state model was developed for the cathode side to identify the limiting processes of mass transport. The modelled domain consists of the cathode gas channel and the gas diffusion layer. Experimental data from current distribution measurements were used to provide boundary conditions for oxygen consumption and water production. The model results indicate that at the cell temperature of 40°C the performance of the cell was limited by water removal. At the cell temperature of 60°C, the current distribution was determined by the partial pressure of oxygen.

Research paper thumbnail of Modeling the Effect of Inhomogeneous Compression of GDL on Local Transport Phenomena in a Pem Fuel Cell

Research paper thumbnail of Effect of ambient conditions on performance and current distribution of a polymer electrolyte membrane fuel cell

Journal of Applied Electrochemistry, Feb 28, 2003

The performance and current distribution of a free-breathing polymer electrolyte membrane fuel ce... more The performance and current distribution of a free-breathing polymer electrolyte membrane fuel cell (PEMFC) was studied experimentally in a climate chamber, in which temperature and relative humidity were controlled. The performance was studied by simulating ambient conditions in the temperature range 10 to 40°C. The current distribution was measured with a segmented current collector. The results indicated that the operating conditions have a significant effect on the performance of the fuel cell. It was observed that a temperature gradient between the fuel cell and air is needed to achieve efficient oxygen transport to the electrode. Furthermore, varying the air humidity resulted in major changes in the mass diffusion overpotential at higher temperatures.

Research paper thumbnail of Flooding of Gas Diffusion Backing in PEFCs Physical and Electrochemical Characterization

In polymer electrolyte fuel cells ͑PEFCs͒ gas diffusion backings ͑GDBs͒ have a significant effect... more In polymer electrolyte fuel cells ͑PEFCs͒ gas diffusion backings ͑GDBs͒ have a significant effect on water management and cell performance. In this study, methods for characterizing GDB performance by fuel cell testing and ex situ measurements are presented. The performance of four different commercial GDB materials was tested and significant differences were found between the materials. While the performance and behavior are almost similar in the single-phase region, the flooding behavior of different GDBs in the two-phase region varies widely. The results show that using high clamping pressures increases cell flooding, but the increase varies from material to material. Increased flooding is caused by the combination of decreased porosity and a temperature difference between GDB and current collector. Furthermore, it was observed that the decrease in porosity due to cell compression and corresponding increase in mass-transfer resistance should be studied in the single-phase region, because flooding of the GDB easily becomes the dominating source of mass-transfer resistance. In addition, a literature review on GDB studies and characterization methods was carried out. The review revealed a lack of an established GDB testing regime and the absence of a relation between physical properties of the GDB and fuel cell performance.

Research paper thumbnail of Modeling the Internal Pressure Distribution of a Fuel Cell

Research paper thumbnail of Thermal Conductivity and Contact Resistance of Compressed Gas Diffusion Layer of PEM Fuel Cell

Fuel Cells, 2008

Author s) Title Abstract Keywords (and classification) Place Month -Year Language Number of pages... more Author s) Title Abstract Keywords (and classification) Place Month -Year Language Number of pages ISBN (print) ISBN (electronic) ISSN (print) ISSN (electronic) Serial name Serial number or report code Distribution of the printed publication Internet access (URL) Thermal Conductivity and Contact Resistance of Compressed Gas Diffusion Layer of PEM Fuel Cell

Research paper thumbnail of The Effect of NaCl in the Cathode Air Stream on PEMFC Performance

Fuel Cells, 2007

Real world PEM fuel cell applications most probably will use ambient air as the cathode oxidant. ... more Real world PEM fuel cell applications most probably will use ambient air as the cathode oxidant. Besides the needed oxygen, the immediate atmosphere may contain many impurities, which may have an adverse effect on fuel cell performance. These impurities include vehicle and industry exhausts, fine particles and natural impurities. This is especially true in urban environments and produces concern in applications where air filters are troublesome due to weight or volume considerations. There are few previous studies on oxidant impurities. Pino et al. investigated the effect of CO, NO 2 and SO 2 [1], and Moore et al. included also some common chemical warfare agents [2]. Schmidt et al. have investigated the oxygen reduction reaction on typical carbon supported Pt fuel cell catalyst in the presence of different anions, including chloride [3]

Research paper thumbnail of Measurement of ohmic voltage losses in individual cells of a PEMFC stack

Journal of Power Sources, 2002

The ohmic voltage loss in a fuel cell can be determined with the current interruption method. The... more The ohmic voltage loss in a fuel cell can be determined with the current interruption method. The method was utilized to measure the ohmic voltage loss in an individual cell of a fuel cell stack. This was achieved by producing voltage transients and monitoring them with a digital oscilloscope connected in parallel with the individual cell. In this study, the method was applied to a small polymer electrolyte membrane fuel cell (PEMFC) stack in which different air supply levels were employed on the cathode side. In the case of higher air-feed rate, the results revealed an increase of ohmic losses in the middle of the stack by up to 21% at 400 mA cm À2 , compared to the unit cell with the lowest ohmic loss. This probably resulted from the decrease of membrane conductivity because of drying. Comparison to individual cell voltages showed that the decrease of conductivity would not be observed if only the individual cell voltages alone were measured. The total ohmic loss in the stack was measured using the same method to verify the reliability of the measurement system. The results indicate a good agreement between the total ohmic loss and the combined ohmic losses in the individual cells.

Research paper thumbnail of Measurement of current distribution in a free-breathing PEMFC

Journal of Power Sources, 2002

A measurement system for the mapping of current distribution in a free-breathing polymer electrol... more A measurement system for the mapping of current distribution in a free-breathing polymer electrolyte membrane fuel cell (PEMFC) is introduced. In the measurement system, the ridges of the flow-field are made of gold-plated stainless steel and the rest of the measurement plate is made of a non-conducting material. The gas diffusion layer is not segmented and the error resulting from this is analyzed computationally. The effect of the cell temperature on the current distribution is studied with the measurement system. It appears that the measurement system is useful for PEMFC characterization and even large spatial variations of current density can be measured with it. According to the results, the optimum operating temperature for the studied cell is around 60 8C without external humidification. In addition, it is concluded that the molecular diffusion is dominating mass transport mechanism at low temperatures but the current density profile is more homogeneous at elevated temperatures. #

Research paper thumbnail of Inhomogeneous compression of PEMFC gas diffusion layer

Journal of Power Sources, 2007

The effect of inhomogeneous compression of GDL on the mass and charge transfer in PEMFC is studie... more The effect of inhomogeneous compression of GDL on the mass and charge transfer in PEMFC is studied. The model utilizes experimentally evaluated GDL parameters as a function of thickness. The modeling results are compared with a conventional model that excludes the effects. As a result, it is shown that the inhomogeneous compression has a significant effect on the current density distribution because of the varying contact resistance between GDL and electrode. This also implies that there are possible hot spots occurring inside the electrode, and thus inhomogeneous compression can have significant effects on the lifetime and local performance of the cell. According to the achieved results, the inhomogeneous compression of GDL cannot be neglected.

Research paper thumbnail of Evaluation of planar free-breathing polymer electrolyte membrane fuel cell design

Journal of Power Sources, 2004

A planar cell design for free-breathing fuel cell is studied. The cathode side of the cell was di... more A planar cell design for free-breathing fuel cell is studied. The cathode side of the cell was directly open to ambient air in a way that oxygen needed by the fuel cell reaction was provided by diffusion through the cathode side gas diffusion backing, i.e. the cell had no cathode side flow channels. The aim of the study was to demonstrate the feasibility of the cell concept by experimentally evaluating its performance with polarisation and current transient measurements. The orientation of the cell did not significantly affect the performance of the cell and signs of flooding were not observed. The maximum power density achieved in the polarisation measurements was ∼124 mW cm −2 . The current transient measurements revealed that with a small base load the cell is capable of producing momentarily current densities up to 500 mA cm −2 . The maximum transient power density achieved was ∼194 mW cm −2 at transient current density of 450 mA cm −2 . According to the results it seems that this kind of cell design is feasible for small-scale applications, such as portable computers.

Research paper thumbnail of Modelling compression pressure distribution in fuel cell stacks

Journal of Power Sources, 2009

A general purpose 3D finite element method model has been developed for the estimation of the com... more A general purpose 3D finite element method model has been developed for the estimation of the compression pressure distribution in fuel cell stacks. The model can be used for the optimisation of any type of fuel cell structure at any temperature. The model was validated with pressure sensitive film measurements using PEFC stack components that had low rigidity and were

Research paper thumbnail of Water balance in a free-breathing polymer electrolyte membrane fuel cell

Journal of Applied Electrochemistry, 2000

Water balance in a free-breathing polymer electrolyte membrane fuel cell was studied, focusing on... more Water balance in a free-breathing polymer electrolyte membrane fuel cell was studied, focusing on the effect of anode conditions. The methods used were current distribution measurement, water collection from the anode outlet, and the measurement of cell polarization and resistance. Current density levels were 100 and 200 mA cm )2 , temperature levels were 40 and 60°C, and hydrogen stoichiometry range was from 1.5 to 2.5. The direction of hydrogen flow was varied. The fraction of product water exiting through the anode outlet varied from 0 to 58%, and it was found to increase with increasing temperature and hydrogen flow rate. When the general direction of hydrogen flow was against the direction of air flow, the percentage of water removal through the anode was smaller and the current distributions were more even than in the cases where the direction was the same as that of the air flow. This probably resulted from a more favorable distribution of water over the active area. The results also indicate that the net water transport coefficient varies across the active area. In further measurements, operation with the anode side in dead-end mode was investigated. It was also found that water distribution was more favorable when the general direction of hydrogen flow was against the air flow.

Research paper thumbnail of Characterization of membrane electrode assembly with hydrogen–hydrogen cell and ac-impedance spectroscopy

Electrochimica Acta, 2006

ABSTRACT A measurement system based on a symmetrical hydrogen–hydrogen cell was developed and pre... more ABSTRACT A measurement system based on a symmetrical hydrogen–hydrogen cell was developed and presented. The net water flux through and impedance of Gore™ Primea® Series 58 MEA were measured under different humidity conditions. An equivalent circuit approach was used to analyze impedance measurement data and the dependences of membrane conductivity and reaction kinetics on the humidity were obtained. Modeling work was found necessary to estimate the diffusion coefficient of water in the membrane, because humidity profile inside the cell was uneven and unknown during the net water flux measurements. Gas permeabilities of different cell components and water uptake of the MEA were measured to get parameter values for the modeling work. The actual modeling work was not conducted in this contribution, but is explained in Part II of this paper.

Research paper thumbnail of Contact resistance between gas diffusion layer and catalyst layer of PEM fuel cell

Electrochemistry Communications, 2008

ABSTRACT In this study, the electrical contact resistance between gas diffusion layer (GDL) and c... more ABSTRACT In this study, the electrical contact resistance between gas diffusion layer (GDL) and catalyst layer (CL) on an electrolyte membrane was experimentally evaluated as a function of compression. The contact resistances between the GDL and CL decreased nonlinearly as the GDL thickness decreased due to the compression pressure. The values of the contact resistance between the GDL and CL were found to be more than one order of magnitude larger than the contact resistance between the GDL and graphite, and even comparable to the ionic resistance of the membrane. Because of the large value and variation in contact resistance between the GDL and CL, severe current distribution may be created inside the cell. The results reported here should be highly useful in providing a more accurate picture of the transport phenomena in a fuel cell.

Research paper thumbnail of Mass transport in the cathode of a free-breathing polymer electrolyte membrane fuel cell

In small fuel cell applications, it is desirable to take care of the management of reactants, wat... more In small fuel cell applications, it is desirable to take care of the management of reactants, water and heat by passive means in order to minimize parasitic losses. A polymer electrolyte membrane fuel cell, in which air flow on the cathode was driven by free convection, was studied by experimental and modelling methods. The cathode side of the cell had straight vertical channels with their ends open to the ambient air. A two-dimensional, isothermal and steady state model was developed for the cathode side to identify the limiting processes of mass transport. The modelled domain consists of the cathode gas channel and the gas diffusion layer. Experimental data from current distribution measurements were used to provide boundary conditions for oxygen consumption and water production. The model results indicate that at the cell temperature of 40°C the performance of the cell was limited by water removal. At the cell temperature of 60°C, the current distribution was determined by the partial pressure of oxygen.

Research paper thumbnail of Determination of mass diffusion overpotential distribution with flow pulse method from current distribution measurements in a PEMFC

The mass diffusion overpotential distribution in a free-breathing proton exchange membrane fuel c... more The mass diffusion overpotential distribution in a free-breathing proton exchange membrane fuel cell (PEMFC) was determined from current distribution measurements using a flow pulse approach. The current distribution measurements were conducted with a segmented flow-field plate. Flow pulses were fed to the cathode channels to form a uniform oxygen concentration distribution along the channels. Simultaneously, the cell resistance was monitored

Research paper thumbnail of Studies on Limiting Factors of Polymer Electrolyte Membrane Fuel Cell Cathode Performance

... S. Mikkola, Tommy Rockward, Bryan S. Pivovar and Francisco A. Uribe, ”The Effect of NaCl ... ... more ... S. Mikkola, Tommy Rockward, Bryan S. Pivovar and Francisco A. Uribe, ”The Effect of NaCl ... methodology used for resistance measurement of individual cells in a fuel cell and contributed ... For publication II, the author participated in the development of segmented current collector ...

Research paper thumbnail of Determination of mass diffusion overpotential distribution with flow pulse method from current distribution measurements in a PEMFC

The mass diffusion overpotential distribution in a free-breathing proton exchange membrane fuel c... more The mass diffusion overpotential distribution in a free-breathing proton exchange membrane fuel cell (PEMFC) was determined from current distribution measurements using a flow pulse approach. The current distribution measurements were conducted with a segmented flow-field plate. Flow pulses were fed to the cathode channels to form a uniform oxygen concentration distribution along the channels. Simultaneously, the cell resistance was monitored

Research paper thumbnail of Measurement of ohmic voltage losses in individual cells of a PEMFC stack

Journal of Power Sources, 2002

The ohmic voltage loss in a fuel cell can be determined with the current interruption method. The... more The ohmic voltage loss in a fuel cell can be determined with the current interruption method. The method was utilized to measure the ohmic voltage loss in an individual cell of a fuel cell stack. This was achieved by producing voltage transients and monitoring them with a digital oscilloscope connected in parallel with the individual cell. In this study, the method was applied to a small polymer electrolyte membrane fuel cell (PEMFC) stack in which different air supply levels were employed on the cathode side. In the case of higher air-feed rate, the results revealed an increase of ohmic losses in the middle of the stack by up to 21% at 400 mA cm À2 , compared to the unit cell with the lowest ohmic loss. This probably resulted from the decrease of membrane conductivity because of drying. Comparison to individual cell voltages showed that the decrease of conductivity would not be observed if only the individual cell voltages alone were measured. The total ohmic loss in the stack was measured using the same method to verify the reliability of the measurement system. The results indicate a good agreement between the total ohmic loss and the combined ohmic losses in the individual cells.

Research paper thumbnail of Mass transport in the cathode of a free-breathing polymer electrolyte membrane fuel cell

In small fuel cell applications, it is desirable to take care of the management of reactants, wat... more In small fuel cell applications, it is desirable to take care of the management of reactants, water and heat by passive means in order to minimize parasitic losses. A polymer electrolyte membrane fuel cell, in which air flow on the cathode was driven by free convection, was studied by experimental and modelling methods. The cathode side of the cell had straight vertical channels with their ends open to the ambient air. A two-dimensional, isothermal and steady state model was developed for the cathode side to identify the limiting processes of mass transport. The modelled domain consists of the cathode gas channel and the gas diffusion layer. Experimental data from current distribution measurements were used to provide boundary conditions for oxygen consumption and water production. The model results indicate that at the cell temperature of 40°C the performance of the cell was limited by water removal. At the cell temperature of 60°C, the current distribution was determined by the partial pressure of oxygen.

Research paper thumbnail of Modeling the Effect of Inhomogeneous Compression of GDL on Local Transport Phenomena in a Pem Fuel Cell

Research paper thumbnail of Effect of ambient conditions on performance and current distribution of a polymer electrolyte membrane fuel cell

Journal of Applied Electrochemistry, Feb 28, 2003

The performance and current distribution of a free-breathing polymer electrolyte membrane fuel ce... more The performance and current distribution of a free-breathing polymer electrolyte membrane fuel cell (PEMFC) was studied experimentally in a climate chamber, in which temperature and relative humidity were controlled. The performance was studied by simulating ambient conditions in the temperature range 10 to 40°C. The current distribution was measured with a segmented current collector. The results indicated that the operating conditions have a significant effect on the performance of the fuel cell. It was observed that a temperature gradient between the fuel cell and air is needed to achieve efficient oxygen transport to the electrode. Furthermore, varying the air humidity resulted in major changes in the mass diffusion overpotential at higher temperatures.

Research paper thumbnail of Flooding of Gas Diffusion Backing in PEFCs Physical and Electrochemical Characterization

In polymer electrolyte fuel cells ͑PEFCs͒ gas diffusion backings ͑GDBs͒ have a significant effect... more In polymer electrolyte fuel cells ͑PEFCs͒ gas diffusion backings ͑GDBs͒ have a significant effect on water management and cell performance. In this study, methods for characterizing GDB performance by fuel cell testing and ex situ measurements are presented. The performance of four different commercial GDB materials was tested and significant differences were found between the materials. While the performance and behavior are almost similar in the single-phase region, the flooding behavior of different GDBs in the two-phase region varies widely. The results show that using high clamping pressures increases cell flooding, but the increase varies from material to material. Increased flooding is caused by the combination of decreased porosity and a temperature difference between GDB and current collector. Furthermore, it was observed that the decrease in porosity due to cell compression and corresponding increase in mass-transfer resistance should be studied in the single-phase region, because flooding of the GDB easily becomes the dominating source of mass-transfer resistance. In addition, a literature review on GDB studies and characterization methods was carried out. The review revealed a lack of an established GDB testing regime and the absence of a relation between physical properties of the GDB and fuel cell performance.

Research paper thumbnail of Modeling the Internal Pressure Distribution of a Fuel Cell

Research paper thumbnail of Thermal Conductivity and Contact Resistance of Compressed Gas Diffusion Layer of PEM Fuel Cell

Fuel Cells, 2008

Author s) Title Abstract Keywords (and classification) Place Month -Year Language Number of pages... more Author s) Title Abstract Keywords (and classification) Place Month -Year Language Number of pages ISBN (print) ISBN (electronic) ISSN (print) ISSN (electronic) Serial name Serial number or report code Distribution of the printed publication Internet access (URL) Thermal Conductivity and Contact Resistance of Compressed Gas Diffusion Layer of PEM Fuel Cell

Research paper thumbnail of The Effect of NaCl in the Cathode Air Stream on PEMFC Performance

Fuel Cells, 2007

Real world PEM fuel cell applications most probably will use ambient air as the cathode oxidant. ... more Real world PEM fuel cell applications most probably will use ambient air as the cathode oxidant. Besides the needed oxygen, the immediate atmosphere may contain many impurities, which may have an adverse effect on fuel cell performance. These impurities include vehicle and industry exhausts, fine particles and natural impurities. This is especially true in urban environments and produces concern in applications where air filters are troublesome due to weight or volume considerations. There are few previous studies on oxidant impurities. Pino et al. investigated the effect of CO, NO 2 and SO 2 [1], and Moore et al. included also some common chemical warfare agents [2]. Schmidt et al. have investigated the oxygen reduction reaction on typical carbon supported Pt fuel cell catalyst in the presence of different anions, including chloride [3]

Research paper thumbnail of Measurement of ohmic voltage losses in individual cells of a PEMFC stack

Journal of Power Sources, 2002

The ohmic voltage loss in a fuel cell can be determined with the current interruption method. The... more The ohmic voltage loss in a fuel cell can be determined with the current interruption method. The method was utilized to measure the ohmic voltage loss in an individual cell of a fuel cell stack. This was achieved by producing voltage transients and monitoring them with a digital oscilloscope connected in parallel with the individual cell. In this study, the method was applied to a small polymer electrolyte membrane fuel cell (PEMFC) stack in which different air supply levels were employed on the cathode side. In the case of higher air-feed rate, the results revealed an increase of ohmic losses in the middle of the stack by up to 21% at 400 mA cm À2 , compared to the unit cell with the lowest ohmic loss. This probably resulted from the decrease of membrane conductivity because of drying. Comparison to individual cell voltages showed that the decrease of conductivity would not be observed if only the individual cell voltages alone were measured. The total ohmic loss in the stack was measured using the same method to verify the reliability of the measurement system. The results indicate a good agreement between the total ohmic loss and the combined ohmic losses in the individual cells.

Research paper thumbnail of Measurement of current distribution in a free-breathing PEMFC

Journal of Power Sources, 2002

A measurement system for the mapping of current distribution in a free-breathing polymer electrol... more A measurement system for the mapping of current distribution in a free-breathing polymer electrolyte membrane fuel cell (PEMFC) is introduced. In the measurement system, the ridges of the flow-field are made of gold-plated stainless steel and the rest of the measurement plate is made of a non-conducting material. The gas diffusion layer is not segmented and the error resulting from this is analyzed computationally. The effect of the cell temperature on the current distribution is studied with the measurement system. It appears that the measurement system is useful for PEMFC characterization and even large spatial variations of current density can be measured with it. According to the results, the optimum operating temperature for the studied cell is around 60 8C without external humidification. In addition, it is concluded that the molecular diffusion is dominating mass transport mechanism at low temperatures but the current density profile is more homogeneous at elevated temperatures. #

Research paper thumbnail of Inhomogeneous compression of PEMFC gas diffusion layer

Journal of Power Sources, 2007

The effect of inhomogeneous compression of GDL on the mass and charge transfer in PEMFC is studie... more The effect of inhomogeneous compression of GDL on the mass and charge transfer in PEMFC is studied. The model utilizes experimentally evaluated GDL parameters as a function of thickness. The modeling results are compared with a conventional model that excludes the effects. As a result, it is shown that the inhomogeneous compression has a significant effect on the current density distribution because of the varying contact resistance between GDL and electrode. This also implies that there are possible hot spots occurring inside the electrode, and thus inhomogeneous compression can have significant effects on the lifetime and local performance of the cell. According to the achieved results, the inhomogeneous compression of GDL cannot be neglected.

Research paper thumbnail of Evaluation of planar free-breathing polymer electrolyte membrane fuel cell design

Journal of Power Sources, 2004

A planar cell design for free-breathing fuel cell is studied. The cathode side of the cell was di... more A planar cell design for free-breathing fuel cell is studied. The cathode side of the cell was directly open to ambient air in a way that oxygen needed by the fuel cell reaction was provided by diffusion through the cathode side gas diffusion backing, i.e. the cell had no cathode side flow channels. The aim of the study was to demonstrate the feasibility of the cell concept by experimentally evaluating its performance with polarisation and current transient measurements. The orientation of the cell did not significantly affect the performance of the cell and signs of flooding were not observed. The maximum power density achieved in the polarisation measurements was ∼124 mW cm −2 . The current transient measurements revealed that with a small base load the cell is capable of producing momentarily current densities up to 500 mA cm −2 . The maximum transient power density achieved was ∼194 mW cm −2 at transient current density of 450 mA cm −2 . According to the results it seems that this kind of cell design is feasible for small-scale applications, such as portable computers.

Research paper thumbnail of Modelling compression pressure distribution in fuel cell stacks

Journal of Power Sources, 2009

A general purpose 3D finite element method model has been developed for the estimation of the com... more A general purpose 3D finite element method model has been developed for the estimation of the compression pressure distribution in fuel cell stacks. The model can be used for the optimisation of any type of fuel cell structure at any temperature. The model was validated with pressure sensitive film measurements using PEFC stack components that had low rigidity and were

Research paper thumbnail of Water balance in a free-breathing polymer electrolyte membrane fuel cell

Journal of Applied Electrochemistry, 2000

Water balance in a free-breathing polymer electrolyte membrane fuel cell was studied, focusing on... more Water balance in a free-breathing polymer electrolyte membrane fuel cell was studied, focusing on the effect of anode conditions. The methods used were current distribution measurement, water collection from the anode outlet, and the measurement of cell polarization and resistance. Current density levels were 100 and 200 mA cm )2 , temperature levels were 40 and 60°C, and hydrogen stoichiometry range was from 1.5 to 2.5. The direction of hydrogen flow was varied. The fraction of product water exiting through the anode outlet varied from 0 to 58%, and it was found to increase with increasing temperature and hydrogen flow rate. When the general direction of hydrogen flow was against the direction of air flow, the percentage of water removal through the anode was smaller and the current distributions were more even than in the cases where the direction was the same as that of the air flow. This probably resulted from a more favorable distribution of water over the active area. The results also indicate that the net water transport coefficient varies across the active area. In further measurements, operation with the anode side in dead-end mode was investigated. It was also found that water distribution was more favorable when the general direction of hydrogen flow was against the air flow.

Research paper thumbnail of Characterization of membrane electrode assembly with hydrogen–hydrogen cell and ac-impedance spectroscopy

Electrochimica Acta, 2006

ABSTRACT A measurement system based on a symmetrical hydrogen–hydrogen cell was developed and pre... more ABSTRACT A measurement system based on a symmetrical hydrogen–hydrogen cell was developed and presented. The net water flux through and impedance of Gore™ Primea® Series 58 MEA were measured under different humidity conditions. An equivalent circuit approach was used to analyze impedance measurement data and the dependences of membrane conductivity and reaction kinetics on the humidity were obtained. Modeling work was found necessary to estimate the diffusion coefficient of water in the membrane, because humidity profile inside the cell was uneven and unknown during the net water flux measurements. Gas permeabilities of different cell components and water uptake of the MEA were measured to get parameter values for the modeling work. The actual modeling work was not conducted in this contribution, but is explained in Part II of this paper.

Research paper thumbnail of Contact resistance between gas diffusion layer and catalyst layer of PEM fuel cell

Electrochemistry Communications, 2008

ABSTRACT In this study, the electrical contact resistance between gas diffusion layer (GDL) and c... more ABSTRACT In this study, the electrical contact resistance between gas diffusion layer (GDL) and catalyst layer (CL) on an electrolyte membrane was experimentally evaluated as a function of compression. The contact resistances between the GDL and CL decreased nonlinearly as the GDL thickness decreased due to the compression pressure. The values of the contact resistance between the GDL and CL were found to be more than one order of magnitude larger than the contact resistance between the GDL and graphite, and even comparable to the ionic resistance of the membrane. Because of the large value and variation in contact resistance between the GDL and CL, severe current distribution may be created inside the cell. The results reported here should be highly useful in providing a more accurate picture of the transport phenomena in a fuel cell.

Research paper thumbnail of Mass transport in the cathode of a free-breathing polymer electrolyte membrane fuel cell

In small fuel cell applications, it is desirable to take care of the management of reactants, wat... more In small fuel cell applications, it is desirable to take care of the management of reactants, water and heat by passive means in order to minimize parasitic losses. A polymer electrolyte membrane fuel cell, in which air flow on the cathode was driven by free convection, was studied by experimental and modelling methods. The cathode side of the cell had straight vertical channels with their ends open to the ambient air. A two-dimensional, isothermal and steady state model was developed for the cathode side to identify the limiting processes of mass transport. The modelled domain consists of the cathode gas channel and the gas diffusion layer. Experimental data from current distribution measurements were used to provide boundary conditions for oxygen consumption and water production. The model results indicate that at the cell temperature of 40°C the performance of the cell was limited by water removal. At the cell temperature of 60°C, the current distribution was determined by the partial pressure of oxygen.

Research paper thumbnail of Determination of mass diffusion overpotential distribution with flow pulse method from current distribution measurements in a PEMFC

The mass diffusion overpotential distribution in a free-breathing proton exchange membrane fuel c... more The mass diffusion overpotential distribution in a free-breathing proton exchange membrane fuel cell (PEMFC) was determined from current distribution measurements using a flow pulse approach. The current distribution measurements were conducted with a segmented flow-field plate. Flow pulses were fed to the cathode channels to form a uniform oxygen concentration distribution along the channels. Simultaneously, the cell resistance was monitored