Jonathan J. Martin

In Situ Experimental Technique for Measurement of Temperature and Current Distribution in Proton Exchange Membrane Fuel Cells

Current distribution data is vital for improved fuel cell designs and improved performance. However, none of the common current mapping techniques is simple to perform and often compromise the design and operation of the fuel cell. By comparison, local temperature measurements with thermocouples are easier to set up and can be done in an unobtrusive way with minimal impact on the fuel cell. Our results show that current mapping can be indirectly conducted through local temperature measurements and have the potential to provide in situ high-resolution data capable of following load cycling and use in real applications.

Magnetic resonance imaging of water content across the Nafion membrane in an operational PEM fuel cell

Water management is critical to optimize the operation of polymer electrolyte membrane fuel cells. At present, numerical models are employed to guide water management in such fuel cells. Accurate measurements of water content variation in polymer electrolyte membrane fuel cells are required to validate these models and to optimize fuel cell behavior. We report a direct water content measurement across the Nafion membrane in an operational polymer electrolyte membrane fuel cell, employing double half k-space spin echo single point imaging techniques. The MRI measurements with T2 mapping were undertaken with a parallel plate resonator to avoid the effects of RF screening. The parallel plate resonator employs the electrodes inherent to the fuel cell to create a resonant circuit at RF frequencies for MR excitation and detection, while still operating as a conventional fuel cell at DC. Three stages of fuel cell operation were investigated: activation, operation and dehydration. Each profile was acquired in 6 min, with 6 microm nominal resolution and a SNR of better than 15.

Spatial and temporal mapping of water content across Nafion membranes under wetting and drying conditions.

Water transport and water management are fundamental to polymer electrolyte membrane fuel cell operation. Accurate measurements of water content within and across the Nafion layer are required to elucidate water transport behavior and validate existing numerical models. We report here a direct measurement of water content profiles across a Nafion layer under wetting and drying conditions, using a novel magnetic resonance imaging methodology developed for this purpose. This method, multi-echo double half k-space spin echo single point imaging, based on a pure phase encode spin echo, is designed for high resolution 1D depth imaging of thin film samples. The method generates high resolution (<8 microm) depth images with an SNR greater than 20, in an image acquisition time of less than 2 min. The high temporal resolution permits water content measurements in the transient states of wetting and drying, in addition to the steady state.

FUEL CELLS – PROTON-EXCHANGE MEMBRANE FUEL CELLS | Life-Limiting Considerations

This article reviews the published in the literature on performance degradation of and mitigation strategies for proton-exchange membrane fuel cells (PEMFCs). Durability is one of the characteristics most necessary for PEMFCs to be accepted as a viable product. In this chapter, a literature-based analysis has been carried out in an attempt to achieve a unified definition of PEMFC lifetime for cells operated under either steady-state or various accelerated conditions. Additionally, the dependence of PEMFC durability on different operating conditions is analyzed. Durability studies of the individual components of a PEMFC are introduced, and various degradation mechanisms are examined. Following this analysis, the emphasis of this review shifts to applicable strategies for alleviating the degradation rate of each component. The lifetime of a PEMFC as a function of operating conditions, component materials, and degradation mechanisms is then established. Finally, this article summarizes accelerated stress testing (AST) methods and protocols for various components, in an attempt to prevent the prolonged test periods and high costs associated with real lifetime tests. A statistical model correlating accelerated testing and real lifetime is also examined in detail in order to facilitate the establishment of AST protocols for PEMFC durability research.

Species, Temperature, and Current Distribution Mapping in Polymer Electrolyte Membrane Fuel Cells

Widespread commercialization of fuel cells will require significant improvements in power density, reliability, and cost, which can only be accomplished through improved understanding of the thermodynamic, fluid dynamic, and electrochemical processes within a fuel cell. To date, a wide range of experimental diagnostic tools have been developed to not only obtain a fundamental understanding of fuel cell dynamics and degradation but also to provide benchmark-quality data for modeling research. Herein, the latest advances are reviewed for three categories of diagnostics for polymer electrolyte membrane (PEM) fuel cells and stacks: species, temperature, and current distribution mapping. We identify species of interest within a fuel cell, while also reviewing the methodology, results, and design implications for each category of diagnostic tool. Capabilities and weaknesses of the techniques are discussed, while placing them within the broader context of fuel cell development.

Current Mapping of a Diagnostic Modeling Cell

Uniformity of current density across the entire active area of the electrode is crucial to the optimization of the cell performance. A non-uniform current density distribution can cause reduced reactant and catalyst utilization, limited energy efficiency, and decreased lifetime of the cell. Determination of current density distribution is vital for designing PEM fuel cells that achieve higher performance and longer life. The common current mapping techniques, such as sub-cell approach, partial MEA, and segmented current collector and flow field, are simple to perform but often compromise the normal design and operation of the fuel cell. By comparison, local current mapping by microthermocouples are easier to set up and can be done without disturbing the operation of the fuel cell, which opens the possibility for carrying out in situ measurements in real practical applications under various conditions.