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

中性子小角散乱法による固体高分子形燃料電池のその場観察; 重水素ガスによるコントラスト変調の利用

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

中性子小角散乱で作動中の燃料電池内部の水履歴を定量的に評価するために重水素ガスを燃料とする固体高分子形燃料電池を考案した。中性子小角散乱はプロトン交換膜(ナフィオン)中の重水/軽水混合比を決定するのに対して、IR分光法は流路から排出される水に関して重水/軽水混合比を決定できる。両手法を相補的に活用することで燃料電池内部の水履歴を定量化したのでこれを口頭発表で報告する。

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 t

使用言語	:	English
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発表会議名	:	15th International Small-Angle Scattering Conference (SAS 2012)
開催年月	:	2012/11
開催都市	:	Sydney
開催国	:	Australia
キーワード	:	no keyword

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使用施設	:	JRR-3M(研究炉3)
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受委託・共同研究相手機関	:	新エネルギー・産業技術総合開発機構

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