In Situ Determination of MEA Resistance and Electrode Diffusivity of a Fuel Cell

Abstract

This paper describes a novel method to determine the membrane electrode assembly ͑MEA͒ resistance and electrode diffusion ͑MRED͒ coefficient for a fuel cell ͑the MRED method͒ under in situ conditions. It is shown that the MRED method allows the determination of ͑i͒ the ohmic resistance of an MEA and ͑ii͒ the mass-transport coefficient of the electrodes. The method is based on the galvanostatic discharge of a fuel cell with interrupted reactant supply. Application of the method to the cathode of a polymer electrolyte membrane fuel cell is demonstrated, and the experimental results are analyzed using a theoretical model based on a simple one-dimensional diffusion process using Fick's law. Comparison of the experimental O 2 mass-transport coefficient with theoretical values indicates that diffusion in the active layer is mass-transport limiting.To meet the power density, reliability, and cost requirements that enable a widespread use of fuel cells, cost reduction and increased power output remain key challenges. To reduce development time and cost, a rapid and convenient means for the optimization of fuel cell designs is needed. This requires foremost a sufficient understanding of the structure-property-performance relationships for the fuel cell and its components. In particular, the dependence of cell voltage and cell voltage degradation on the physicochemical and structural properties of the components of the fuel cell must be better understood. Due to the complexity of the heat-and masstransport processes occurring in fuel cells, there is typically a multitude of parameters to be determined. Therefore, the challenge is the identification of those critical parameters that which have the highest impact on fuel cell performance. This can be done through either theoretical or empirical models, which can then be used as design tools to optimize fuel cell designs more quickly. For the development of these design tools, accurate measurement tools are needed to provide reliable data to establish empirical correlations, to provide model inputs, or to validate model predictions.In this study, we present a novel method for determination of the cell resistance and the effective diffusion coefficient for a fuel cell cathode, which can be used as a measurement tool to provide valuable experimental data for the investigation of the structureperformance relationships for fuel cell electrodes. The membrane electrode assembly ͑MEA͒ resistance and electrode diffusion ͑MRED͒ method allows the investigation of the effect of operating conditions as well as structural properties of the electrodes on performance and can thus support the development of improved design tools for fuel cells.Generally, the cell voltage losses can be kinetic, ohmic, and mass-transport related; 1 therefore, one of the design challenges is to optimize electrode structures so that these cell voltage losses are minimized. Especially on the oxidant side mass-transport losses associated with transport of reactants and products to and from the active catalyst site...

On the Efficiency of an Advanced Automotive Fuel Cell System

“…The three main sources of loss in the system are the slow electrocatalysis at the cathode, the ohmic loss in the membrane and the parasitic power loss in the balance of plant. Additional losses, which could be reduced to improve efficiency, include transport losses of the electroactive species in the porous media of the membrane electrode assembly [1,2].…”

Non-isothermal transient modeling of water transport in PEM fuel cells

“…Berg et al [13] presented a transient discharge model for the cathode, and used it for parameter tuning and determination of liquid water in the membrane electrode assembly (MEA). Stumper et al [14] used a similar approach to determine the MEA resistance and electrode diffusion coefficient. Natarajan and Nguyen [15] presented a two-dimensional twophase transient model for the cathode.…”

Analysis of a cathode catalyst layer model for a polymer electrolyte fuel cell

“…However, these results depend sensitively on the oxygen diffusion coefficient D o and variations are more pronounced as D o decreases. Therefore, it is critical to obtain an accurate estimate for this parameter which is estimated to be D o = 5.0 × 10 −8 m 2 /s, following literature values (Eikerling, 2006;Stumper et al, 2005). This is a factor of 40 smaller than diffusion in the GDL, D g o ≈ 2.0×10 −6 m 2 /s, due to the small pore size in the CL.…”