Electronic Structures of Non-Pt Carbon Alloy Catalysts for Polymer Electrolyte Membrane Fuel Cells Revealed by Synchrotron Radiation Analyses

2011 ◽  
Vol 1318 ◽  
Author(s):  
Masaharu Oshima ◽  
Hideharu Niwa ◽  
Makoto Saito ◽  
Masaki. Kobayashi ◽  
Koji Horiba ◽  
...  
Keyword(s):  
Fuel Cells ◽  
Polymer Electrolyte ◽  
Active Site ◽  
Electronic Structures ◽  
Polymer Electrolyte Membrane ◽  
Pt Catalysts ◽  
X Ray ◽  
Electrolyte Membrane ◽  
X Ray Absorption ◽  
Alloy Catalysts

ABSTRACTThe oxygen reduction reaction (ORR) mechanism of non-Pt catalysts was elucidated by investigating electronic structures of carbon alloy catalysts (CACs) for polymer electrolyte membrane fuel cells (PEMFC). For metal phthalocyanine-based carbon alloy catalysts with 1-2% of nitrogen and less than 0.1% of Co or Fe, photoelectron spectroscopy, X-ray absorption spectroscopy (XAS), and X-ray Absorption Fine Structure (XAFS) have revealed that Co or Fe metal sites are not the ORR active site, whereas the carbon atoms adjacent to graphitic nitrogens at a zigzag edge of graphite may act as the ORR active site, which is in good agreement with first principles calculations. These studies have also revealed that the zigzag edges, detected as a XAS shoulder component, are well evolved for catalysts pyrolyzed at 600°C, which show the maximum ORR activity. Based on these analyses, we have realized significantly improved carbon alloy based ORR performance, up to about 70 % of that with Pt catalysts. Further, to analyze the electronic structure of CACs during operation, we constructed a new in situ soft X-ray emission spectroscopy system with very high energy resolution (ΔE) of 120 meV at 640 eV at the University of Tokyo beamline BL07LSU in SPring-8.

Synchrotron X-ray tomography for investigations of water distribution in polymer electrolyte membrane fuel cells

2011 ◽  
Vol 196 (12) ◽  
pp. 5250-5255 ◽  
Author(s):  
Ph. Krüger ◽  
H. Markötter ◽  
J. Haußmann ◽  
M. Klages ◽  
T. Arlt ◽  
...  
Keyword(s):  
Fuel Cells ◽  
Polymer Electrolyte ◽  
Water Distribution ◽  
Polymer Electrolyte Membrane ◽  
X Ray ◽  
Electrolyte Membrane

Visualization of GDL Deformation by Freezing of Water Using X-Ray Radiography

2010 ◽  
Author(s):  
Jongrok Kim ◽  
Junho Je ◽  
Massoud Kaviany ◽  
Sang Young Son ◽  
Moo Hwan Kim
Keyword(s):  
Fuel Cells ◽  
Polymer Electrolyte ◽  
Chemical Reactions ◽  
Diffusion Layer ◽  
Power Output ◽  
Operating Temperature ◽  
Polymer Electrolyte Membrane ◽  
Gas Diffusion ◽  
X Ray ◽  
Electrolyte Membrane

During operation of Polymer Electrolyte Membrane Fuel Cells (PEMFCs), electro-chemical reactions generate water, which exists as a liquid because of the PEFMC’s low operating temperature. The water remains in the PEFMC after it is turned off. During the winter this water can freeze; associated increase in its volume deforms the gas diffusion layer (GDL). The deformed GDL reduces the cell’s power output and durability. In this investigation, X-ray microscopy was used demonstrate that water freezing changed the geometry of GDL by water freezing.

Calibrating the X-ray attenuation of liquid water and correcting sample movement artefacts duringin operandosynchrotron X-ray radiographic imaging of polymer electrolyte membrane fuel cells

2016 ◽  
Vol 23 (2) ◽  
pp. 590-599 ◽  
Author(s):  
Nan Ge ◽  
Stéphane Chevalier ◽  
James Hinebaugh ◽  
Ronnie Yip ◽  
Jongmin Lee ◽  
...  
Keyword(s):  
Fuel Cells ◽  
Polymer Electrolyte ◽  
Liquid Water ◽  
Polymer Electrolyte Membrane ◽  
Correction Method ◽  
X Ray ◽  
Electrolyte Membrane ◽  
Experimental Apparatus ◽  
Micrometer Scale ◽  
The Impact

Synchrotron X-ray radiography, due to its high temporal and spatial resolutions, provides a valuable means for understanding thein operandowater transport behaviour in polymer electrolyte membrane fuel cells. The purpose of this study is to address the specific artefact of imaging sample movement, which poses a significant challenge to synchrotron-based imaging for fuel cell diagnostics. Specifically, the impact of the micrometer-scale movement of the sample was determined, and a correction methodology was developed. At a photon energy level of 20 keV, a maximum movement of 7.5 µm resulted in a false water thickness of 0.93 cm (9% higher than the maximum amount of water that the experimental apparatus could physically contain). This artefact was corrected by image translations based on the relationship between the false water thickness value and the distance moved by the sample. The implementation of this correction method led to a significant reduction in false water thickness (to ∼0.04 cm). Furthermore, to account for inaccuracies in pixel intensities due to the scattering effect and higher harmonics, a calibration technique was introduced for the liquid water X-ray attenuation coefficient, which was found to be 0.657 ± 0.023 cm−1at 20 keV. The work presented in this paper provides valuable tools for artefact compensation and accuracy improvements for dynamic synchrotron X-ray imaging of fuel cells.

Sign in / Sign up

Export Citation Format

Share Document