In-situ observation of operating polymer electrolyte fuel cell (PEFC) by grazing incident small-angle neutron scattering; Contrast variation by using deuterium gas

Koizumi, Satoshi; Putra, A.; Yamaguchi, Daisuke; Zhao, Y.

In order to visualize water distribution in an operating fuel cell, we combined two different methods using neutron as a probe, i.e., a combined method of small-angle & ultra-small-angle scattering (SANS) and radiography imaging. SANS observes water distribution in a membrane electrolyte assembly (MEA), whereas radiography observes bulk water appeared in a gas flow channel (so called "flooding"). The polymer electrolyte fuel cell (PEFC) was specially designed suitable for small-angle neutron scattering by replacing materials with aluminum in order to decrease background scattering. We employed hydrogen gas (H $_{2}$ ) and deuterated gas (D $_{2}$ ) as a fuel for operation. With exchange of H $_{2}$ and D $_{2}$ , we aim to perform a contrast variation as for polyelectrolyte film (Nafion). When D $_{2}$ gas is used as a fuel, D $_{2}$ O is produced at the cathode and diffuses back to the film. Then the film, originally swollen by H $_{2}$ O, exhibits change of coherent scattering contrast. By changing a fuel gas from H $_{2}$ to D $_{2}$ , SANS quantitatively detected decrease of scattering intensity at scattering maximum originating from the ion-channel in the electrolyte. After quantitative analyses on scattering intensity, which is related to water ratio (H $_{2}$ O/D $_{2}$ O) in the ion channel, we found that 30% of the total water is replaced by D $_{2}$ O by changing the gas from H $_{2}$ to D $_{2}$ . In a stationary state of fuel cell operation using D $_{2}$ , the scattering intensity rhythmically oscillates (respiration of fuel cell). The rhythmic oscillation found for the peak intensity is a non-equilibrium and non-linear phenomenon, in which "flooding" in a flow field is a feedback mechanism to slow down chemical reaction or water production by affecting mass transportation of air at the cathode. A valance between two diffusions, (1) back diffusion of D $_{2}$ O from the cathode to the electrolyte and (2) diffusion of H $_{2}$ O supplied as humidity, determines a time interval of

Language	:	English
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Meeting title	:	2nd International GISAS Meeting (GISAS 2012)
Held date	:	2012/11
Location (city)	:	Kyoto
Location (country)	:	Japan
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Keywords	:	no keyword
Research Facility	:	JRR-3M(研究炉3)
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Cooperating Institute	:	新エネルギー・産業技術総合開発機構

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Registration No. : BB20122501
JAEA Abstracts No. :
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