3D Printed Flow Field and Fixture for Visualization of Water Distribution in Fuel Cells by X－ray Computed Tomography

三维打印制作的流场夹具用于燃料电池中液态水分布的可视化测量

Robin T． White

Francesco P． Orfino

Mohamed El Hannach

Oliver Luo

Monica Dutta

Alan P． Young

Erik Kjeang

Abstract

This work demonstrates an original approach to three－dimensional， high－resolution， non－destructive visualization of fuel cells during room temperature operation using a commercial micro－X－ray computed tomography （XCT） system． The novel application of 3D printing technology was used to create a customized housing fixture that allows for non－invasive imaging of an operational fuel cell． The use of 3D print materials also allows for rapid prototyping and intricate design of any experimental fixture with minimal cost． Demonstration of imaging capabilities is shown through in situ visualization of the internal MEA components and liquid water after fuel cell operation． Water imaging in fuel cells is particularly challenging using XCT due to small differences in X－ray absorption characteristics between constituent materials． Image processing operations are discussed which allows for the improved segmentation of solid and water to calculate porosity and saturation throughout the gas diffusion layer， as reported herein． Additionally， a membrane thickness increase of approximately 25％ due to swelling under 100％ relative humidity is shown， which has previously been difficult to determine． Overall， the results shown here illustrate the novel use of 3D printed materials and image processing steps to be further used in understanding of fuel cell devices through non－invasive imaging procedures by use in a commercial micro－XCT system．

三维打印的流场夹具

说明为什么需要使用三维打印的流场来加工流场

样品需要旋转获得像，X射线源和检测器的距离仅25mm。

活化前后燃料电池的XCT影响，明显可以识别液态水滴。

While there was no statistically significant change in the catalyst layer
thicknesses， the membrane thickness was observed to expand by 25％
on average， from 20 to 25 μm， due to ionomer hydration during fuel
cell operation．

CCM出现显著的变形，膜的厚度增加25％。

The CCM was composed of a DuPont Nafion NR211 membrane core
with cathode and anode catalyst layers each with a 50：50 Pt／C ratio at
0．4／0．1 mg cm−2 loadings， respectively

在测试的条件下阳极靠近膜的位置孔隙率为0．4，靠近流道处孔隙率为0．8。阴极孔隙率为0．8。

液态水饱和度阴极为0．1，阳极靠近膜的位置0．8，阳极靠近流道处0．2。

面内液态水饱和度变化幅度比较大，脊下液态水饱和度高于流道内液态水饱和度，分别为0．2和0．1。

液态水滴尺寸为20微米，4pL

Conclusions

Commercial XCT scanners have previously been limited in noninvasive
imaging of fuel cells due to low X－ray intensity compared to
synchrotron sources． In the present work， this gap was bridged using
a custom developed 3D printed flow field fixture for high resolution
in situ XCT visualization． We have shown that by the use of a novel
material selection and design along with simple image processing
techniques， high resolution XCT of a full MEA including water segmentation can be obtained using commercial laboratory scanners． The
obtained reconstructed， segmented 3D images were utilized to calculate the porosity and liquid water saturation distributions throughout
the anode and cathode GDLs after fuel cell operation at 100％ RH and
room temperature． Average porosity and saturation values on the order of 80％ and 20％ respectively were obtained． Liquid water droplets
were also observed on the catalyst layer surface with an approximate
diameter of 20 μm and area coverage of 17％． The high resolution
of the XCT scan also allowed for the determination of through－plane
membrane swelling by 25％ under humidification， by measuring the
thickness change after operation． This level of membrane swelling
was further shown to cause CCM undulations due to confinement
inside the fuel cell． Both findings in terms of in situ membrane expansion and CCM undulation during fuel cell operation are significant and
uniquely enabled by the present XCT technique， and cannot be readily
detected through other means． Overall， the present results demonstrate the ability of commercial XCT scanners to provide useful in situ information about various phenomena that occur during fuel cell operation and the novel use of 3D printed materials to fabricate housing fixtures， with any number of intricate designs， which can be used in a wide range of future experiments at low cost．