Nanoscale structures of radiation-grafted polymer electrolyte membranes investigated via a small-angle neutron scattering technique

Sawada, Shinichi; Yamaguchi, Daisuke; Putra, A.; Koizumi, Satoshi*; Maekawa, Yasunari

Polymer Journal, 45(8), p.797 - 801, 2013/08

https://doi.org/10.1038/pj.2012.218

The nanoscale structures of graft-type polymer electrolyte membranes based on poly(ethylene-co-tetrafluoroethylene) (ETFE) films were investigated using a small-angle neutron scattering (SANS) technique. For comparison, SANS measurements were also performed on two precursor materials, the original ETFE film and polystyrene (PS)-grafted films. The SANS profiles of the grafted films showed shoulder peaks at a d-spacing of approximately 30 nm, which were attributed to the PS grafts introduced into the amorphous phases between the ETFE lamellar crystals. In the ETFE PEMs, the spacing of the polystyrene sulfonic acid (PSSA) grafts and ETFE crystals increased because the graft regions were enlarged by the volume of the attached sulfonic acid groups. Interestingly, the graft / crystal stack spacing in the PEMs did not increase from the dry- to fully-hydrated states. This finding implies restricted water absorption in the PSSA grafts between the ETFE lamellar crystals.

A Combined method of small-angle neutron scattering and neutron radiography to visualize water in operating fuel cell over a wide length scale from nano to millimeter

Koizumi, Satoshi; Yamaguchi, Daisuke; Iwase, Hiroki*; Putra, A.; Maekawa, Yasunari; Matsubayashi, Masahito; Hashimoto, Takeji

no journal, , 

In order to visualize water generated in an operating polymer electrolyte fuel cell (PEFC), a neutron radiography (NR) apparatus, composed of a scintillator, optical mirrors and a CCD camera, was installed at a sample position of the focusing and polarized neutron small-angle scattering (SANS) spectrometer (SANS-J-II) at research reactor JRR-3. By combining SANS and NR, we aim to cover a wide length scale from nanometer to millimeter. The new method succeeded in detecting a spatial distribution of the water generated in individual cell elements; NR detected the water in a gas diffusion layer and a flow-field, whereas SANS quantitatively determines the water content in a membrane electrode assembly (MEA).

In-situ and real time observation of operating polymer electrolyte fuel cell performed by a combined method of small-angle neutron scattering and neutron radiography

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

no journal, , 

In order to visualize water generated in an operating polymer electrolyte fuel cell (PEFC), a neutron radiography (NR) apparatus, composed of a scintillator, optical mirrors and a CCD camera, was installed at a sample position of the focusing and polarized neutron small-angle scattering (SANS) spectrometer (SANS-J-II) at research reactor JRR-3 at Japan Atomic Energy Agency, Tokai, Japan. By combining SANS and NR, we aim to cover a wide length scale from nanometer to millimeter. The new method succeeded in detecting a spatial distribution of the water generated in individual cell elements; NR detected the water in a gas diffusion layer and a flow-field, whereas SANS quantitatively determines the water content in a membrane electrode assembly (MEA).

Microstructures of membrane electrode assembly investigated by polarization analysis neutron small-angle scattering; Water distribution in ion cluster

Koizumi, Satoshi; Putra, A.; Noda, Yohei; Yamaguchi, Daisuke; Tokumasu, Takashi*; Kawakatsu, Toshihiro*

no journal, , 

In order to perform a multi-scale observation on a membrane-electrolyte assembly (MEA) of polymer electrolyte fuel cell (PEFC), small-angle neutron scattering (SANS) was recently reinforced by advanced neutron optics. A focusing ultra-small-angle scattering method was developed by using a neutron lens. By combining a double crystal (Bonse-Hart) method, we are able to reach to 10 micron meter length scale, which corresponds to the size of aggregation by carbon powders in an electrode layer. Polarization analysis enables us to selectively remove incoherent scattering from hydrogen atoms and to detect coherent scattering due to ion-cluster of polymer electrolyte (Nafion) and water distribution in it. In order to output structural information in real space, we examined our SANS results by comparing images in real space obtained by low vacuum SEM and multi-scale computer simulations.

Structural analysis of ETFE-based graft-type polymer electrolyte membranes by small angle X-ray / neutron scattering method

Tran, D. T.; Sawada, Shinichi; Hasegawa, Shin; Putra, A.; Yamaguchi, Daisuke; Oba, Yojiro*; Koizumi, Satoshi; Onuma, Masato*; Maekawa, Yasunari; Katsumura, Yosuke*

no journal, , 

We investigated the structure of the ethylene-co-tetrafluoroethylene (ETFE) based radiation-grafted polymer electrolyte membranes (PEMs) by the small-angle X-ray scattering (SAXS) method. From SAXS profile for the base ETFE film, a lamellar structure with spacing of 23 nm was observed. For the styrene-grafted film and PEM, the lamellar spacing measured by SAXS profiles were 30 and 33 nm, respectively. This can be explained by that the grafted regions were introduced into the amorphous phases in the lamellar structures, thereby extending the lamellar spacing.

Analysis of structure, reaction and mass transfer in the MEA materials

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

no journal, , 

In order to perform a multi-scale observation on a membrane-electrolyte assembly (MEA) of polymer electrolyte fuel cell (PEFC), small-angle neutron scattering (SANS) has been reinforced by advanced neutron optics. A focusing ultra-small-angle scattering method was developed by using a neutron lens, which is made of a single crystal MgF. By combining a double crystal (Bonse-Hart) method, we are able to reach to 10 m length scale, which corresponds to the size of aggregation by carbon powders in an electrode layer. Polarization analysis enables us to selectively remove incoherent scattering from hydrogen atoms and to detect coherent scattering due to ion-cluster of polymer electrolyte (Nafion) and water distribution in it. In order to output structural information in real space, we examined our SANS results by comparing images in real space obtained by low vacuum SEM and multi-scale computer simulations. This year we have achieved the following tree topics: (1) Elucidation of the detailed structure consisting of nano-scale phase separated domains and ion clusters in the block copolymer type model polymer electrolytes by SANS. (2) Advanced observation for the signal originated from ion cluster in Nafion membrane on SANS profile. (3) Determination of the cluster size of water within the catalyst layer of model MEA. To detect the faint signal from the cluster of water residing in the catalyst layer we utilized various experimental techniques.

Neutron is marvelous probe to see operating fuel cell

Putra, A.; Koizumi, Satoshi; Yamaguchi, Daisuke; Zhao, Y.; Noda, Yohei; Iwase, Hiroki*

no journal, , 

Investigation on water history using deuterium fuel cell

Koizumi, Satoshi; Putra, A.; Zhao, Y.; Noda, Yohei; Yamaguchi, Daisuke; Ueda, Satoru*; Gunji, Hiroyuki*; Eguchi, Mika*; Tsutsumi, Yasuyuki*

no journal, , 

In order to investigate water history during fuel cell operation, we employed deuterated gas (D) as a fuel (deuterium fuel cell). With exchange of H and D, we aim to perform a contrast variation as for polyelectrolyte film (Nafion). When D gas is used as a fuel, DO is produced at the cathode and diffuses back to the film. Then the film, originally swollen by HO, exhibits change of coherent scattering contrast. By changing a fuel gas from H to D, 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 (HO/DO) in the ion channel, we could determine the water ration swelling a membrane.

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

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

no journal, , 

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) and deuterated gas (D) as a fuel for operation. With exchange of H and D, we aim to perform a contrast variation as for polyelectrolyte film (Nafion). When D gas is used as a fuel, DO is produced at the cathode and diffuses back to the film. Then the film, originally swollen by HO, exhibits change of coherent scattering contrast. By changing a fuel gas from H to D, 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 (HO/DO) in the ion channel, we found that 30% of the total water is replaced by DO by changing the gas from H to D. In a stationary state of fuel cell operation using D, 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 DO from the cathode to the electrolyte and (2) diffusion of HO supplied as humidity, determines a time interval of t

Analysis of PEFC system with deuterated materials

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

no journal, , 

With using a big advantage of neutron, which can well distinguish the difference between deuteron and neutron, the distribution and transfer of water in an operating PEFC system was observed and analyzed by small-angle neutron scattering method. Concerning the operation of PEFC system by deuterium gas the efficiency increased by 5%. This is consistent with the calculation of free energy. The deuterium gas and deuterium oxide was also used for the labeling and distinction between the water generated by reaction and the water came from humidifier.