Caractérisation du transport de l'eau dans les piles à combustible par Imagerie et Spectroscopie de Résonance Magnétique nucléaire

Abstract : PEMFC use perfluorosulfonic acid membranes (Nafion® for example) as solid electrolyte and their performances are strongly dependent on membrane hydration. Therefore, the accurate knowledge of water distribution in the membrane and in the fuel cell is a fundamental issue. First, self diffusion coefficients have been thoroughly measured by Nuclear Magnetic Resonance (NMR) using B0 gradients and/or B1 gradients. The latter method is more suitable in the case of short relaxation times and for avoiding effects of the so-called internal gradients. Indeed, we were able to observe the decrease of the apparent diffusion coefficient as a function of the diffusion interval whereas this feature is totally absent in the data obtained by B0 gradients. Secondly, electro-osmotic flow effect has been detected in a membrane experiencing an electrical field. The setup consists of two platinum electrodes at each extremity of the membrane. We have observed by Magnetic Resonance Imaging the migration of water when a constant tension between the membranes is imposed. Finally, MRI has been used to study these phenomena into a PEMFC under operation. These experiments, carried out with a whole fuel cell, are more difficult to achieve and they require a PEMFC optimized for the MRI observation. This fuel cell proved to have performances comparable to commercially available fuel cells. Preliminary results indicate a progressive accumulation of water close to the gas outlet while the gas inlet remains dry.
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Jérôme Bedet. Caractérisation du transport de l'eau dans les piles à combustible par Imagerie et Spectroscopie de Résonance Magnétique nucléaire. Autre. Université Henri Poincaré - Nancy 1, 2007. Français. ⟨NNT : 2007NAN10120⟩. ⟨tel-01748284⟩

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