In-situ synchrotron X-ray radiography on high temperature polymer electrolyte fuel cells

Maier, Wiebke; Arlt, Tobias; Wannek, C.; Manke, Ingo; Riesemeier, H.; Krüger, Philipp; Scholta, Joachim; Lehnert, Werner; Banhart, John; Stolten, Detlef

doi:10.1016/j.elecom.2010.08.002

Cited by 83 publications

(58 citation statements)

References 12 publications

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“…By increasing the amount of PWA-meso-SiO2 in the membrane to 15 wt%, the durability was significantly improved as further supported by the stable in-situ conductivity (Fig.3D). Except for the initial reduction of performance, the cell voltage decay during 2700 h was found to be as low as 27 μV h -1 , which is comparable and significantly better than the degradation rate of 25 μV h -1 at 160 o C, 39 44 μV h -1 at 170 o C 6 and 60 μV h -1 at 190 o C. 40 As shown in Fig.3E, the stability performance of the 15wt% PWA-meso-SiO2-PA/PBI membrane cell is exceptional as compared to those reported in the literature so far for PA/PBI membrane based cells at 190 and 200 o C. Oono et at tested a commercial PA/PBI membrane cell with Pt catalysts loading of 0.8 Name., 2012, 00, 1-3 This journal is © The Royal Society of Chemistry 20xx…”

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confidence: 76%

“…operation at high current loads, further promote this mechanism, 6,18 due to suppressed pyrophosphate formation. 19 For example, the PA leaching rate at the cathode at 190 °C has been found to be about an order of magnitude higher than at 160 °C. 6,20 As a result, the durability data reported in the literature at 190-200 °C do not extend to much more than a few hundred hours of operation.…”

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confidence: 99%

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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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confidence: 76%

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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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“…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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“…First real in situ attempts for the understanding of the MEA phosphoric acid distribution and re-distribution have been performed by Maier et al 10,11 using in-situ X-ray radiography. In these studies, the distribution of the acid as function of current density could be imaged in-plane, i.e., in the cross-section of the fuel cell, and membrane expansions and contractions on the micrometer scale was interpreted as a result of adapting phosphoric acid concentration as function of water partial pressure.…”

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confidence: 99%

Evaluation of Neutron Imaging for Measuring Phosphoric Acid Distribution in High Temperature PEFCs

Boillat

Biesdorf

Oberholzer

et al. 2013

J. Electrochem. Soc.

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The possibility of using neutron imaging for non-invasive investigation of the phosphoric acid distribution in high temperature polymer electrolyte fuel cells (HT-PEFC) was explored with a small scale test cell. In particular, the issue of providing a suitable reference -necessary for distinguishing the neutron attenuation due to the acid from the attenuation due to the structural components -was solved by using in situ deuteration/protonation of the phosphoric acid, a fully reversible process. Experiments with a nonoperating cell have shown that this isotope exchange can be performed in less than 20 minutes. The possibility of imaging the acid distribution either over the cell area (through-plane imaging) or across the cell structure (in-plane imaging) was demonstrated. Although some discrepancies between the two modes remain, quantitative analysis resulted in a good agreement with the amount of acid used in the cell. The durability of high temperature polymer electrolyte fuel cells (HT-PEFCs) based on phosphoric acid/polymer composites or gels is limited by several processes, mainly found in the degradation of the membrane electrodes assemblies (MEAs) and their components. Membrane thinning and pinhole formation, evaporation of phosphoric acid (both from membrane and catalyst layers), Pt dissolution and carbon corrosion from the catalyst layer have been identified as the main degradation modes.1 Although durability of several 10,000 hours have been demonstrated in laboratory environments, 2,3 operation under realistic conditions including high operating temperatures of up to 180• C, temperature cycles and start/stop cycling, combined with operation on highly impure reformates produced by fuel processors 4 remains challenging in order to reach the desired >40,000 hours required for stationary combined heat and power (CHP) HT fuel cell systems. One of the most important, but widely underestimated and least understood topics in the development of HT-PEFCs is the behavior of the phosphoric acid electrolyte during operation.5 A detailed picture of the initial acid distribution, its re-distribution and evaporation upon fuel cell operation is missing, although it is one of the key points to be addressed when it comes to the design of highly durable MEAs and cells for HT-PEFCs. Recently, the deleterious effect of acid movement from MEA into the pores of bipolar plates on the durability of HT-PEFC MEAs 6 could be demonstrated. In this study, only cells with completely non-porous plate materials suppressing quick acid distributions during operation showed high durability, whereas cells allowing for acid movement from MEA to plates could not be operated for much longer than 300 h, pointing out the importance of understanding the acid transport within the cell. A possibility to measure distribution of liquid electrolyte in alkaline, phosphoric acid and molten carbonate fuel cells by using an electrochemical impedance sensor located in the bipolar plate material has been described by Kunz. 7 In this work, e.g., the phosp...

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In-situ synchrotron X-ray radiography on high temperature polymer electrolyte fuel cells

Cited by 83 publications

References 12 publications

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

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

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

Evaluation of Neutron Imaging for Measuring Phosphoric Acid Distribution in High Temperature PEFCs

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