X ray Tomographic Investigation of Water Distribution in Polymer Electrolyte Membrane Fuel Cells with Different Gas Diffusion Media

In this study, water transport in polymer electrolyte membrane fuel cells PEMFCs is investigated by synchrotron X ray tomography. The measurement technique is used to reveal the relationship between the structure of the gas diffusion media GDM and the water distribution. It is shown how the water distribution and transport is visualized and quantitatively analyzed. We present investigations on three different GDM A GDM with a modified microporous layer MPL , a thick GDM with limited back diffusion and a reference materia

Improved Performance of Polymer Electrolyte Membrane Fuel Cells with Modified Microporous Layer Structures

A possible method to improve membrane humidity conditions in polymer electrolyte membrane fuel cells and, therefore, the cell performance is the optimization of microporous layer MPL structures. In this work, water transport in modified MPL materials in polymer electrolyte membrane fuel cells PEMFCs was investigated by in amp; 8197;operando synchrotron X ray tomography. Three different types of MPLs are compared A reference standard MPL material, an MPL material with a special wavy structure, and an MPL with randomly distributed holes. We found a strong impact of the modified MPL structure on the water distribution at operating temperatures of 40 and 55 amp; 8201; C and an increase of cell performance up to 14 amp; 8201; compared to the reference cell. We assume the water distribution at the membrane to be responsible for the performance increase and provide a detailed discussion

Investigation of water transport dynamics in polymer electrolyte membrane fuel cells based on high porous micro porous layers

In this study, synchrotron X ray imaging is used to investigate the water transport inside newly developed GDM gas diffusion medium in polymer electrolyte membrane fuel cells. Two different measurement techniques, namely in situ radiography and quasi in situ tomography were combined to reveal the relationship between the structure of the MPL microporous layer , the operation temperature and the water flow. The newly developed MPL is equipped with randomly arranged holes. It was found that these holes strongly influence the overall water transport in the whole adjacent GDM. The holes act as nuclei for water transport paths through the GDM. In the future, such tailored GDMs could be used to optimize the efficiency and operating conditions of polymer electrolyte membrane fuel cell

Effects of compression on water distribution in gas diffusion layer materials of PEMFC in a point injection device by means of synchrotron X ray imaging

In this study, ex situ experiments performed with a point injection device are conducted to evaluate water distributions in gas diffusion layer GDL materials which serve as porous transport media in polymer electrolyte membrane fuel cells PEMFCs . In this regard, GDL samples manufactured by SGL Group are placed into the point injection device and visualized by means of synchrotron X ray radiographic and tomographic imaging. The resulting image data undergoes a coordinate transformation that ascertains water agglomerations in GDL pores with regard to their radial displacements from the injection point. In this way, water transport in two different GDL samples possessing the same structural characteristics, but with unique compression rates, are investigated in terms of in plane water distribution. The radial displacement analysis indicated that the pore saturation of the compressed GDL is higher in both the micro porous layer MPL region and the carbon fiber substrate region than that of the uncompressed GDL. The water agglomerations in the uncompressed GDL are predominantly observed in the vicinity of the injection point, indicating a limited in plane transport. Conversely, in the compressed case water accumulations are detected far from the injection point, even at the edge of the GDL, pointing out that compression promotes the in plane transport. Prior to the ex situ experiments, both GDL samples have undergone an ageing procedure to mimic realistic cell operating condition

Neutron radiographic in operando investigation of water transport in polymer electrolyte membrane fuel cells with channel barriers

We present a study on a new type of flow field channel design for polymer electrolyte membrane fuel cells PEMFCs . Small barriers have been implemented into the flow field channels that force the gas flow to move through the gas diffusion layers in order to improve the supply of the catalyst with reactant gases. We investigated the water distribution in the PEMFC with neutron imaging during operation and compared the results with a comparable reference cell without barriers. We found strong hints for an increased mechanical gas flow resistance by the barriers caused by additional liquid water agglomerations. Furthermore water distribution in the barrier flow field is much more homogenous compared to the reference cell. We assume that both effects, namely the gas flow through the GDL and the homogenous water distribution are responsible for the found performance increase of up to 10 . Neutron radiographic in operando investigation of water transport in polymer electrolyte membrane fuel cells with channel barriers PDF Download Available . Available from https www.researchgate.net publication 318055744Neutronradiographicinoperandoinvestigationofwatertransportinpolymerelectrolytemembranefuelcellswithchannelbarriers [accessed Jul 17, 2017

Energy selective neutron imaging by exploiting wavelength gradients of double crystal monochromators simulations and experiments

The potential of wavelength resolved neutron transmission experiments is well known. This paper is focused on the performance of the double crystal monochromator which is widely used at steady state neutron sources and compares simulation results based on neutron ray tracing with experimental results in order to provide a better understanding of the device. The influences of crystal mosacities on the neutron beam is reported for the utilised setup and the resulting wavelength gradients along one direction are determined. For the neutron imaging geometry applied, a wavelength gradient of about 0.005 cm at the sample position was found. Moreover, a new neutron radiography technique for Bragg edge mapping in imaging experiments utilising a neutron wavelength gradient at the sample position was developed and is reported. Experiments and simulations are found to be in good agreemen