skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: High resolution neutron imaging of water in PEM fuel cells

Abstract

Optimal water management in Polymer Electrolyte Membrane (PEM) fuel cells is critical to improving the performance and durability of fuel cell systems especially during transient, start-up and shut-down operations. For example, while a high water content is desirable for improved membrane and catalyst ionomer conductivity, high water content can also block gas access to the triple-phase boundary resulting in lowered performance due to catalyst and gas diffusion layer (GDL) flooding. Visualizing liquid water by neutron imaging has been used over the past decade to study the water distribution inside operating fuel cells. In this paper, the results from our imaging at NIST using their recently installed higher resolution ({approx} 25 mm) Microchannel Plate (MCP) detector with a pixel pitch of 14.7 mm are presented. This detector is capable of quantitatively imaging the water inside the MEA (Membrane Electrode Assembly)/GDL (Gas Diffusion Layer) of working fuel cells and can provide the water profiles within these various components in addition to the channel water. Specially designed fuel cells (active area = 2.25 cm{sup 2}) have been used in order to take advantage of the full detector resolution. The cell design is illustrated in a figure where one of the current collector/end platesmore » is shown. The serpentine pattern was machined into a block of aluminum and plated with nickel and then gold to form the flow field. The measurements were performed using beam no. 1 and aperture no. 2 with a fluence rate of 1.9 x 10{sup 6} neutrons cm{sup -2} sec{sup -1}. The cells were assembled with Gore{sup TM} Primea{sup R} MEAs and SGL Sigracet {sup R} 24 series GDLs (PRIMEA, GORE-SELECT and GORE are trademarks of W. L. Gore & Associates, Inc). All the cells were tested at 80 {sup o}C with 1.2 stoichiometry H{sub 2} and 2.0 stoichiometry air flows.« less

Authors:
 [1];  [1];  [1];  [1]
  1. Los Alamos National Laboratory
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
960495
Report Number(s):
LA-UR-08-05051; LA-UR-08-5051
TRN: US201006%%1161
DOE Contract Number:
AC52-06NA25396
Resource Type:
Conference
Resource Relation:
Conference: 2008 Fuel Cell Seminar and Exposition ; October 27, 2008 ; Phoenix
Country of Publication:
United States
Language:
English
Subject:
36; AIR FLOW; ALUMINIUM; CATALYSTS; DIFFUSION; ELECTROLYTES; FUEL CELLS; GOLD; LAYERS; LIQUIDS; MANAGEMENT; MEMBRANES; NEUTRONS; NICKEL; PERFORMANCE; PLATES; POLYMERS; PROTON EXCHANGE MEMBRANE FUEL CELLS; START-UP; STOICHIOMETRY; WATER; WATER SUPPLY

Citation Formats

Mukundan, Rangachary, Borup, Rodney L, Davey, John R, and Spendelow, Jacob S. High resolution neutron imaging of water in PEM fuel cells. United States: N. p., 2008. Web.
Mukundan, Rangachary, Borup, Rodney L, Davey, John R, & Spendelow, Jacob S. High resolution neutron imaging of water in PEM fuel cells. United States.
Mukundan, Rangachary, Borup, Rodney L, Davey, John R, and Spendelow, Jacob S. 2008. "High resolution neutron imaging of water in PEM fuel cells". United States. doi:. https://www.osti.gov/servlets/purl/960495.
@article{osti_960495,
title = {High resolution neutron imaging of water in PEM fuel cells},
author = {Mukundan, Rangachary and Borup, Rodney L and Davey, John R and Spendelow, Jacob S},
abstractNote = {Optimal water management in Polymer Electrolyte Membrane (PEM) fuel cells is critical to improving the performance and durability of fuel cell systems especially during transient, start-up and shut-down operations. For example, while a high water content is desirable for improved membrane and catalyst ionomer conductivity, high water content can also block gas access to the triple-phase boundary resulting in lowered performance due to catalyst and gas diffusion layer (GDL) flooding. Visualizing liquid water by neutron imaging has been used over the past decade to study the water distribution inside operating fuel cells. In this paper, the results from our imaging at NIST using their recently installed higher resolution ({approx} 25 mm) Microchannel Plate (MCP) detector with a pixel pitch of 14.7 mm are presented. This detector is capable of quantitatively imaging the water inside the MEA (Membrane Electrode Assembly)/GDL (Gas Diffusion Layer) of working fuel cells and can provide the water profiles within these various components in addition to the channel water. Specially designed fuel cells (active area = 2.25 cm{sup 2}) have been used in order to take advantage of the full detector resolution. The cell design is illustrated in a figure where one of the current collector/end plates is shown. The serpentine pattern was machined into a block of aluminum and plated with nickel and then gold to form the flow field. The measurements were performed using beam no. 1 and aperture no. 2 with a fluence rate of 1.9 x 10{sup 6} neutrons cm{sup -2} sec{sup -1}. The cells were assembled with Gore{sup TM} Primea{sup R} MEAs and SGL Sigracet {sup R} 24 series GDLs (PRIMEA, GORE-SELECT and GORE are trademarks of W. L. Gore & Associates, Inc). All the cells were tested at 80 {sup o}C with 1.2 stoichiometry H{sub 2} and 2.0 stoichiometry air flows.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2008,
month = 1
}

Conference:
Other availability
Please see Document Availability for additional information on obtaining the full-text document. Library patrons may search WorldCat to identify libraries that hold this conference proceeding.

Save / Share:
  • Water transport in the ionomeric membrane, typically Nafion{reg_sign}, has profound influence on the performance of the polymer electrolyte fuel cell, in terms of internal resistance and overall water balance. In this work, high resolution neutron imaging of the Nafion{reg_sign} membrane is presented in order to measure water content and through-plane gradients in situ under disparate temperature and humidification conditions.
  • Sufficient water content within a polymer electrolyte membrane (PEM) is necessary for adequate ionic conductivity. Membrane hydration is therefore a fundamental requirement for fuel cell operation. The hydration state of the membrane affects the water transport within, as both the diffusion coefficient and electroosmotic drag depend on the water content. Membrane s water uptake is conventionally measured ex situ by weighing freeswelling samples equilibrated at controlled water activity. In the present study, water profiles in Nafion membranes were measured using high-resolution neutron imaging. The state-of-theart, 13 m resolution neutron detector is capable of resolving water distributions across N1120, N1110 andmore » N117 membranes. It provides a means to measure the water uptake and transport properties of fuel cell membranes in situ.« less
  • Sufficient water content within a polymer electrolyte membrane (PEM) is necessary for adequate ionic conductivity. Membrane hydration is therefore a fundamental requirement for fuel cell operation. The hydration state of the membrane affects the water transport within, as both the diffusion coefficient and electro-osmotic drag depend on the water content. Membrane's water uptake is conventionally measured ex situ by weighing free-swelling samples equilibrated at controlled water activity. In the present study, water profiles in Nafion{reg_sign} membranes were measured using the high-resolution neutron imaging. The state-of-the-art, 10 {micro}m resolution neutron detector is capable of resolving water distributions across N1120, N1110 andmore » N117 membranes. It provides a means to measure the water uptake and transport properties of fuel cell membranes in situ.« less
  • To achieve a deeper understanding of water transport and performance issues associated with water management, we have conducted in situ water examinations to help understand the effects of components and operation. High Frequency Resistance (HFR), AC Impedance and neutron radiography were used to measure water content in operating fuel cells under various operating conditions. Variables examined include: sub-freezing conditions, inlet relative humidities, cell temperature, current density and response transients, different flow field orientations and different component materials (membranes, GDLs and MEAs). Quantification of the water within the membrane was made by neutron radiography after equilibration to different humidified gases, duringmore » fuel cell operation and in hydrogen pump mode. The water content was evaluated in bare Nafion{reg_sign} membranes as well as in MEAs operated in both fuel cell and H{sub 2} pump mode. These in situ imaging results allow measurement of the water content and gradients in the PEFC membrane and relate the membrane water transport characteristics to the fuel cell operation and performance under disparate materials and operational combinations. Flow geometry makes a large impact on MEA water content. Higher membrane water with counter flow was measured compared with co-flow for sub-saturated inlet RH's. This correlates to lower HFR and higher performance compared with co-flow. Higher anode stoichiometry helps remove water which accumulates in the anode channels and GDL material. Cell orientation was measured to affect both the water content and cell performance. While membrane water content was measured to be similar regardless of orientation, cells with the cathode on top show flooding and loss of performance compared with similarly operated cells with the anode on top. Transient fuel cell current measurements show a large degree of hysteresis in terms of membrane hydration as measured by HFR. Current step transients from 0.01 A cm{sup -2} to 0.68 A cm{sup -2} consistently show PEM wetting occurring within 5 to 20 sec. Whereas the PEM drying response to the reverse step transient of 0.68 A cm{sup -2} to 0.01 A cm{sup -2}, takes several minutes. The observed faster wetting response is due to reaction water being produced in the cathode and back diffusing into the membrane. The slower PEM drying is due to the water slowly being removed out of the wetted GDLs. This rate of removal of water and hence the PEM hydration level was found to be influenced strongly by the PTFE loadings in the GDL substrate and Microporous layer (MPL). The drying of the membrane is influenced by both the anode and cathode GDL PTFE loadings. Lower PTFE loading in the anode GDL leads to better membrane hydration probably due to the easier incorporation of water from the anode GDL into the membrane. Similarly a lower PTFE loading in the cathode GDL also results in better membrane hydration probably due to the better water retention properties (less hydrophobic) of this GDL. Fuel cells operated isothermal at sub-freezing temperatures show gradual cell performance decay over time and eventually drops to zero. AC impedance analysis indicates that losses are initially due to increasing charge transfer resistance. After time, the rate of decay accelerates rapidly due to mass transport limitations. High frequency resistance also increases over time and is a function of the initial membrane water content. These results indicate that catalyst layer ice formation is influenced strongly by the MEA and is responsible for the long-term degradation of fuel cells operated at sub-freezing temperatures. Water distribution measurements indicate that ice may be fonning mainly in the GDLs at -10 C but are concentrated in the catalyst layer at -20 C.« less
  • No abstract prepared.