Göran Lindbergh

Investigation of Mass-Transport Limitations in the Solid Polymer Fuel Cell Cathode I. Mathematical Model

In this paper, a one-dimensional, steady-state agglomerate model was used to describe the functioning and the mass transport limitations of the cathode in the solid polymer fuel cell (SPFC). This mathematical model is then compared to experimental results obtained on cathodes in an SPFC. The following processes were considered: Tafel kinetics of the oxygen reduction reaction. proton migration, oxygen diffusion in the agglomerates, and diffusion of a ternary gas mixture O 2 /N 2 /water vapor in the pores of the active layer and of the gas backing. The model shows that limitation by proton migration in the active layer or by oxygen diffusion in the agglomerates leads to a doubling of the Tafel slope at higher current densities. For those two types of transport limitations, the dependence of the reaction rate on the active-layer thickness, oxygen partial pressure, and relative humidity of the gas were simulated. When additional limitation due to slow gas phase diffusion appears, the double Tafel slope is distorted. A mathematical expression for the limiting current density due to this process is presented. By using this expression, it is possible to correct the polarization curves for slow gas phase diffusion.

Flooding of Gas Diffusion Backing in PEFCs Physical and Electrochemical Characterization

In polymer electrolyte fuel cells (PEFCs) gas diffusion backings (GDBs) 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.

Transient Techniques for Investigating Mass-Transport Limitations in Gas Diffusion Electrodes I. Modeling the PEFC Cathode

The use of electrochemical impedance spectroscopy and current-interruption techniques with the scope of determining mass-transport limitations in PEFC gas-diffusion electrodes is investigated. The porous electrode is assumed to be composed of spherical agglomerates consisting of a homogeneous mixture of the electrolyte and the electronic phase. The model is applied to the O 2 reduction reaction in the cathode and includes Tafel kinetics for the O 2 reduction, Ohms law for proton migration, Ficks law for O 2 diffusion, and capacitive current due to the contribution of the double layer. A novel impedance is defined, enabling the results to be presented in a simpler manner than with the usual one. It is shown how these transient techniques can be employed to qualitatively separate diffusion from migration effects. The parameter groups that can be quantitatively determined from the processing of experimental data are presented. The effect of O 2 pressure and electrode thickness on the predicted electrode response is also investigated.

Analysis of the Polarization in a Li-Ion Battery Cell by Numerical Simulations

An experimentally validated model was developed to analyze the polarization of a LiNi0.8Co0.15Al0.05O2 vertical bar 1.2 M LiPF6 in ethylene carbonate (EC):ethyl methyl carbonate (EMC) (3:7)vertical ...

A Model for the Porous Direct Methanol Fuel Cells Anode

The influence of the porous structure on the direct methanol fuel cells (DMFC) anode was studied with a model and experimentally. An agglomerate model of the electrode is used and kinetic equations ...

Reduced Two-Phase Model for Analysis of the Anode of a DMFC

An isothermal two-phase ternary mixture model that takes into account conservation of momentum, mass, and species in the anode of a direct methanol fuel cell (DMFC) is presented and analyzed. The slenderness of the anode allows a considerable reduction of the mathematical formulation, without sacrificing the essential physics. The reduced model is then verified and validated against data obtained from an experimental DMFC outfitted with a transparent end plate. Good agreement is achieved. The effect of mass-transfer resistances in the flow field and porous backing are highlighted. The presence of a gas phase is shown to improve the mass transfer of methanol at higher temperatures (>30 degreesC). It is also found that at a temperature of around 30 degreesC, a one-phase model predicts the same current density distribution as a more sophisticated two-phase model. Analysis of the results from the two-phase model, in combination with the experiments, results in a suggestion for an optimal flow field for the liquid-fed DMFC.

Gas Diffusion Electrodes and Membrane Electrode Assemblies Based on a Sulfonated Polysulfone for High-Temperature PEMFC

Membrane electrode assemblies MEAs with a sulfonated polysulfone sPSU as the proton-conducting phase were fuel cellevaluated at varying temperatures in over-humidified conditions. The sPSU was prep ...

In situ micro-Raman on the membrane in a working PEM cell

An electrochemical cell has been designed for in situ micro-Raman measurements on the polymer membrane in an operating polymer electrolyte cell (PEM). The method is applicable to studies of both th ...

Temperature-Dependent Kinetics of the Anode in the DMFC

The methanol oxidation kinetics was studied in a direct methanol fuel cell (DMFC) anode at 303, 323, and 343 K. The experimental result was fitted to a model for the porous anode and the kinetic parameters were extracted. In addition, a simplified kinetic equation for the porous anode was derived which directly gives the current density of the porous anode as a function of the potential, temperature, and methanol concentration. Both the more rigorous kinetic model and the empirical model fit well to the experimental data. The methodology used is shown to be very useful for applied modeling of the DMFC.

Impedance as a Tool for Investigating Aging in Lithium-Ion Porous Electrodes II. Positive Electrode Examination

High-power positive LixNi0.8Co0.15Al0.05O2 composite porous electrodes are known to be the main source of impedance increase in batteries based on GEN2 chemistry. The impedance of positive electrod ...