Synchrotron X-ray radioscopic in situ study of high-temperature polymer electrolyte fuel cells - Effect of operation conditions on structure of membrane

Arlt, Tobias; Maier, Wiebke; Tötzke, Christian; Wannek, C.; Markötter, Henning; Wieder, Frank; Banhart, John; Lehnert, Werner; Manke, Ingo

doi:10.1016/j.jpowsour.2013.07.094

Cited by 49 publications

(27 citation statements)

References 31 publications

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“…In order to further analyze the Si particles, the grayscale slices were segmented into binary images, yielding Figure 3c, in which the bright regions correspond to higher-absorbing material, the Si particles, whereas the black regions are assigned to less-absorbing material such as carbon black and polymer binder. Segmentation is performed via a combined approach of filtering and thresholding 48 and produces Figure 3d after labeling. In order to validate the X-ray tomography results qualitatively and quantitatively we compare scanning electron microscopy images (SEM) (Figure 3e) with grayscale slice images as well as the particle size distribution (PSD) measured using laser diffraction with the PSD obtained from the tomographic data (Figure 3f).…”

Section: Resultsmentioning

confidence: 99%

Three-Dimensional Visualization of Gas Evolution and Channel Formation inside a Lithium-Ion Battery

Sun

Markötter

Manke

et al. 2016

ACS Appl. Mater. Interfaces

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Gas generation within lithium ion batteries (LIBs) gives rise to safety concerns that question their applicability. By employing synchrotron X-ray imaging, the gas and channel evolution occurring in an operating LIB have been directly visualized in their inherent 3D state as a function of discharge and charge. Using the spatial 3D distribution of gas bubbles and channels, the active particles that dictate the performance of a functional LIB were identified and visualized in 3D. Delithiation and lithiation are interpreted as the process of activating particles continuously in a step-bystep way. The present work not only demonstrates the generation and evolution of gas within LIB in 3D, but also reveals the distribution of active particles for the first time. These fundamentally findings presented here shed light on a range of processes that could not previously be characterized in 3D and can provide practical guidance for the

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Section: Resultsmentioning

confidence: 99%

Three-Dimensional Visualization of Gas Evolution and Channel Formation inside a Lithium-Ion Battery

Sun

Markötter

Manke

et al. 2016

ACS Appl. Mater. Interfaces

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“…10,11,[16][17][18][19][20][21] In this work, operando X-ray tomographic microscopy (XTM) is used to image the electrolyte redistribution as a function of membrane material (conventional film casted m-PBI 22 and PPA processed p-PBI membranes 23 ), electrolyte loading and current density.…”

Section: 12mentioning

confidence: 99%

Operando X-ray Tomographic Microscopy Imaging of HT-PEFC: A Comparative Study of Phosphoric Acid Electrolyte Migration

Eberhardt

Marone

Stampanoni

et al. 2016

J. Electrochem. Soc.

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Synchrotron based X-ray tomographic microscopy was used to image the redistribution of phosphoric acid in HT-PEFC due to electrolyte migration from cathode to anode. The acid migration rate, transference number of the hydrogen phosphate ion and flooding of the anode gas diffusion layer (GDL) was analyzed for MEAs with different membrane acid doping levels (24-36 mgcm −2 ) and membrane materials (imbibed m-polybenzimidazole (PBI) and polyphosphoric acid (PPA) processed p-PBI). The most influential factors for the acid migration rate are current density and the amount of free acid in the membrane. High doping level of the membrane and current density above 0.4 A cm −2 significantly increase the migration rate. From the migration rates apparent transference numbers for the hydrogen phosphate anions in the order 10 −5 to 10 −4 are calculated at the high current densities. Besides the membrane properties, also the influence of the microstructure of the porous transport layers was analyzed. Most probably cracks in the catalyst and microporous layers facilitate the migration of acid into the anode GDL. High temperature polymer electrolyte fuel cells (HT-PEFC) are operating at temperatures up to 200• C using phosphoric acid (PA) doped polybenzimidazole (PBI) based membranes. This fuel cell technology has a range of beneficial properties. At the higher operating temperatures, the tolerance to fuel gas impurities increases significantly and operation with CO levels of up to 3% and H 2 S up to 10 ppm can be achieved.1,2 Consequently, a fuel processing unit can more easily be thermally integrated into the fuel cell system and used for reforming hydrocarbon-based fuels in the absence of an additional selective CO oxidation gas clean-up step. Furthermore, phosphoric acid exhibits comparable proton conductivity to typical PFSA-type membranes 3 without the need of additional gas humidification due to a fast proton hopping mechanism.4 At a cell temperature of 160• C the higher value waste heat is more easily used than with standard low temperature PEFC technology, therefore HT-PEFC have a significant potential for stationary combined heat and power applications (CHP).The advantageous characteristics of HT-PEFC are based on the physico-chemical properties of the phosphoric acid electrolyte, such as high conductivity due a fast Grotthus like charge transport 4 and low PA vapor pressure. However, understanding of the degradation mechanisms related to PA volume variations due to concentration changes, 5 and redistribution of phosphoric acid in the membrane electrode assembly (MEA) is still limited. Additionally, the interaction of the PBI polymer backbone with PA, the acid doping level 6-8 as well as the membrane synthesis method have a significant influence on properties such as conductivity, mechanical stability.Since phosphoric acid is not covalently bound to the polymer structure of the membrane, a minor part of the ionic current is also carried by the hydrogen phosphate anions, which have a have a small, but finite transference...

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“…[6][7][8][9][10][11] While electrode related degradation seem to be most significant during idling 12 or shutdown/start-up, 13 membrane degradation or acid redistribution predominate during operation at high current loads. [14][15][16] In the higher end of the operating temperature regime (180-200 °C) the PA loss rate increases considerably, eventually leading to acid depletion and proton conductivity decay. 6,17 High water activities, i.e.…”

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confidence: 99%

Exceptional durability enhancement of PA/PBI based polymer electrolyte membrane fuel cells for high temperature operation at 200 °C

et al. 2016

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Synchrotron X-ray radioscopic in situ study of high-temperature polymer electrolyte fuel cells - Effect of operation conditions on structure of membrane

Cited by 49 publications

References 31 publications

Three-Dimensional Visualization of Gas Evolution and Channel Formation inside a Lithium-Ion Battery

Three-Dimensional Visualization of Gas Evolution and Channel Formation inside a Lithium-Ion Battery

Operando X-ray Tomographic Microscopy Imaging of HT-PEFC: A Comparative Study of Phosphoric Acid Electrolyte Migration

Exceptional durability enhancement of PA/PBI based polymer electrolyte membrane fuel cells for high temperature operation at 200 °C

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