Imaging of Water Profiles in PEM Fuel Cells Using Neutron Radiography: Effect of Operating Conditions and GDL Composition

Abstract

The performance of polymer electrolyte membrane (PEM) fuel cells as a function of cathode inlet relative humidity (RH) and gas diffusion layer (GDL) properties has been characterized. The performance of 50 cm 2 fuel cells at high current densities was a strong function of the polytetrafluoroethylene (PTFE) content in the cathode GDL microporous layer (MPL). The voltage at a current density of 1.4 A cm -2 decreased at all inlet RHs as the PTFE content in the cathode MPL increased from 5 % by weight to 23 % by weight. This was associated with a corresponding increase in the mass transport resistance as measured by AC impedance. The low frequency resistance also increased with increasing cathode inlet RH. These results were validated by high-resolution neutron radiography on specially designed 2.25 cm 2 cells that showed increased water content in the GDLs at high inlet RHs and high microporous layer PTFE content. High-resolution neutron imaging also revealed higher water concentrations at the outlets, cathode GDL, anode flow channel, and MEA/GDL above the land when compared to the inlets, anode GDL, cathode flow channel, and MEA/GDL above the channel respectively.

Anode-Design Strategies for Improved Performance of Polymer-Electrolyte Fuel Cells with Ultra-Thin Electrodes

“…The imaging was performed on 2.5-cm 2 active area MEAs incorporated in specially designed cells. 50 GDL thickness along the neutron path was 1.2 cm, which can be used to convert water thickness into a saturation profile, although the interfaces will not be quantitative due to smoothing and other issues. 22 GDLs were compressed to 80% of their uncompressed thickness.…”

Use of neutron imaging for proton exchange membrane fuel cell (PEMFC) performance analysis and design

“…Manke et al [31] 2007 HMI 100 Tomographic imaging of the three-dimensional water distributions in three-and five-cell stacks. Mukundan et al [32] 2007 NIST 2. 25 Imaging normal to the MEA to observe water gradient from inlet to outlet, and relative water content on anode and cathode.…”

“…Operating conditions: current density = 1.0 A cm −2 , T = 80 • C, P = 100 kPa, and anode/cathode stoichiometric ratios of 1.1/2. [32] channels) is important for understanding the fundamentals of mass transport and its effects on the electrochemical performance of PEMFCs. While the first demonstration of neutron imaging to study fuel cells was for measuring the water gradient across the membrane, [2] there has since been little work on this topic.…”

“…The other study of through-plane water content was focused on the effect of the PTFE content in the bulk substrate and microporous layer (MPL) of three different carbon fiber GDLs on the cathode. [32] The fuel cell had an active area of 2.25 cm 2 , and the depth of the flow channel was chosen to yield a pressure drop near to that of a standard 50-cm 2 cell. Neutron radiography of the through-plane water content revealed that higher PTFE content in the cathode MPL resulted in more flooding, and thus a significant reduction in oxygen mass transport to the cathode.…”

“…The average membrane water content in this case was also dramatically reduced by about 60%, demonstrating that the cathode inlet RH plays a major role in the water retention of the cell. [32]…”