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Neutron Imaging and Modelling of Autonomous Hydration-Dehydration Cycles in PEFCs Operated with Saturated Anode and Dry Cathode Feed

Garcia Sanchez, Daniel and Garcia Salaberri, Pablo Angel and Boillat, Pierre and Vera, Marcos and Friedrich, K. Andreas (2017) Neutron Imaging and Modelling of Autonomous Hydration-Dehydration Cycles in PEFCs Operated with Saturated Anode and Dry Cathode Feed. 7th International Conference on Fundamentals & Development of Fuel Cells, 31 Jan - 2 Febr 2017, Stuttgart, Germany.

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Abstract

In this work, the current fluctuations arising in Polymer Electrolyte Fuel Cells (PEFCs) operated with wet anode and dry cathode feed (RH_a^in≈100%, RH_c^in≈5%) due to the cyclic hydration/dehydration of the membrane are examined. The analysis combines liquid water distributions obtained by neutron imaging experiments and predictions of a 3D two-phase non-isothermal model. The neutron visualizations show that the nonlinear dynamics stem from the periodic shedding of water droplets at the anode inlet chamber. As shown in Figure 1, two well-differentiated processes can be distinguished in analogy to ignition and extinction phenomena in combustion. A fast autocatalytic increase of the current (decrease of HFR) in about 20 s that goes hand-in-hand with the transport of liquid water along the anode channel (ignition), followed by a slower decrease of the current (increase of HFR) in 200 s as the accumulated water is flushed out of the cell (extinction). This challenging scenario is modeled by introducing or not introducing a steady flux of liquid water at the vapor-saturated anode inlet. As can be seen in Figure 2, the low- and high-performance states of the hydration-dehydration cycles are properly captured by the model. The low-performance state is achieved when no liquid water is assumed to enter at the anode inlet, leading to a high ionic resistance and a fairly inhomogeneous current distribution. The membrane dry-out is stronger near the cathode inlet, and decays along the cathode channel due to the membrane humidification by the anode stream. By contrast, the high-performance state is reached when a flux of liquid water is introduced at the anode inlet. The water input humidifies the cell and offsets the membrane dry-out caused by the cathode stream, leading to a low ionic resistance and a homogeneous current distribution. Two important conclusions are obtained from the work: i) liquid water injected into the anode channel is an efficient means for membrane humidification, even in the presence of a dry cathode feed, without incurring in high mass-transport losses; ii) the oscillatory hydration-dehydration regime is a useful operating scenario to study membrane resistance in durability tests.

Item URL in elib:https://elib.dlr.de/118259/
Document Type:Conference or Workshop Item (Speech)
Title:Neutron Imaging and Modelling of Autonomous Hydration-Dehydration Cycles in PEFCs Operated with Saturated Anode and Dry Cathode Feed
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Garcia Sanchez, DanielDaniel.GarciaSanchez (at) dlr.deUNSPECIFIED
Garcia Salaberri, Pablo Angelpagsalab (at) ing.uc3m.esUNSPECIFIED
Boillat, PierrePaul Scherrer Institut (PSI)UNSPECIFIED
Vera, MarcosCIIIUNSPECIFIED
Friedrich, K. Andreasandreas.friedrich (at) dlr.deUNSPECIFIED
Date:2 February 2017
Refereed publication:No
Open Access:No
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
Status:Published
Keywords:PEFC, water management, neutron imaging, modeling, membrane, hydration-dehydration
Event Title:7th International Conference on Fundamentals & Development of Fuel Cells
Event Location:Stuttgart, Germany
Event Type:international Conference
Event Dates:31 Jan - 2 Febr 2017
Organizer:DLR
HGF - Research field:Energy
HGF - Program:Storage and Cross-linked Infrastructures
HGF - Program Themes:Fuel cells
DLR - Research area:Energy
DLR - Program:E SP - Energy Storage
DLR - Research theme (Project):E - Electrochemical Processes (Fuel Cells)
Location: Stuttgart
Institutes and Institutions:Institute of Engineering Thermodynamics > Electrochemical Energy Technology
Deposited By: Garcia Sanchez, Dr Daniel
Deposited On:16 Jan 2018 15:37
Last Modified:16 Jan 2018 15:37

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