Peter D Lund | Aalto University, School of Science (original) (raw)

Papers by Peter D Lund

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.

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.

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

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.

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.

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.

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. #

Energy Policy, 2006

This article presents the findings of a European study on energy efficiency in the public sector,... more This article presents the findings of a European study on energy efficiency in the public sector, entitled ''Public procurement of Energy Saving Technologies in Europe'' (PROST), completed in 2003.

Thin Solid Films, 2011

Three characteristically different carbon nanomaterials were compared and analyzed as platinum-fr... more Three characteristically different carbon nanomaterials were compared and analyzed as platinum-free counter electrodes for dye solar cells: 1) single-walled carbon nanotube (SWCNT) random network films on glass, 2) aligned multi-walled carbon nanotube (MWCNT) forest films on Inconel steel and quartz, and 3) pressed carbon nanoparticle composite films on indium tin oxide-polyethylene terephtalate plastic. Results from electrochemical impedance spectroscopy and electron microscopy were discussed in terms of the catalytic activity, conductivity, thickness, transparency and flexibility of the electrode films. The SWCNT films showed reasonable catalytic performance at similar series resistance compared to platinized fluorine doped tin oxide-coated glass. The MWCNTs had similar catalytic activity, but the electrochemical performance of the films was limited by their high porosity. Carbon nanoparticle films had the lowest charge transfer resistance resulting from a combination of high catalytic activity and dense packing of the material.

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.

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.

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

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.

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.

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.

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. #

Energy Policy, 2006

This article presents the findings of a European study on energy efficiency in the public sector,... more This article presents the findings of a European study on energy efficiency in the public sector, entitled ''Public procurement of Energy Saving Technologies in Europe'' (PROST), completed in 2003.

Thin Solid Films, 2011

Three characteristically different carbon nanomaterials were compared and analyzed as platinum-fr... more Three characteristically different carbon nanomaterials were compared and analyzed as platinum-free counter electrodes for dye solar cells: 1) single-walled carbon nanotube (SWCNT) random network films on glass, 2) aligned multi-walled carbon nanotube (MWCNT) forest films on Inconel steel and quartz, and 3) pressed carbon nanoparticle composite films on indium tin oxide-polyethylene terephtalate plastic. Results from electrochemical impedance spectroscopy and electron microscopy were discussed in terms of the catalytic activity, conductivity, thickness, transparency and flexibility of the electrode films. The SWCNT films showed reasonable catalytic performance at similar series resistance compared to platinized fluorine doped tin oxide-coated glass. The MWCNTs had similar catalytic activity, but the electrochemical performance of the films was limited by their high porosity. Carbon nanoparticle films had the lowest charge transfer resistance resulting from a combination of high catalytic activity and dense packing of the material.