Neutron-reflectance measurements under controlled temperature and humidities on newhydrocarbon-type fuel-cell membranes formed on Si，SiO2, Pt, and C substrates
Clean Energy Research Center, University of Yamanashi, 4-3-11 Takeda, Kofu 400-8501, Japan
Junji Inukai
1. Introduction
Perfluorosulfonic acid ionomers, such as Nafion, have been practically used for the proton exchange membranes
and the binders in polymer electrolyte fuel cells, because of their high proton conductivity andchemical/mechanical stability. Although the characteristic 3-dimensional network-structures of the hydrated watermolecules in polymer electrolyte are known to be important for obtaining high ion-conductivity inside membranes
and binders for fuel cells, the structures of the networks are little understood. Neutron reflectivity is reflected by
the nanometer-scale structures of thin films.1) Analyzing the previous data obtained by the neutron-reflectivity
experiments performed under the proposals 2016A0246 and 2016B0036, we modeled the 1-dimensional
distributions of water absorbed in Nafion thin films at different relative humidities on Si(100).2) At thefilm/substrate interface, a water-rich layer was found, which changed at different humidities. In order to reduce
cost and increase environmental friendliness, hydrocarbon-type membranes with no fluorine are activelysynthesized and studied. Under this proposal, the reflectivity was measured at different temperatures andhumidities using H2O and D2O on newly-synthesized hydrocarbon-type membranes with an extremely highchemical stability.3)
2. Experimental
Figure 1 shows the chemical formula of an SPP electrolyte.3) SPP thinfilms 100 nm in thickness were formed on flat Si(100), Pt/Si(100),C/Si(100), and SiO2 substrates. The environment-controlled sample
chamber was made of aluminum. Neutron reflectivity measurements
were carried out at 80 ˚C under N2 gas at 30% and 80% RH
humidified with H2O or D2O. The neutron irradiation area was 40 mm

Fig. 1 Chemical structure of SPP.

x 30 mm. Incident angle was 0.3-3.5 degree.
3. Results
Neutron reflectivity curves are shown in Fig. 2, vertically offset for clarity. The oscillations from the reference
substrates are in black, whereas those from the SPP-coated substrates at 30% and 80% RH in red and blue,
respectively. For an SPP thin film on a Si substrate, the oscillations were hardly observed because of the similar
densities of SPP and Si. On Pt/Si and C/Si substrates, clear oscillations from the interference between the thinlayer of Pt or C and Si substrate were observed. Oscillations smaller in amplitude were considered to be originatedfrom the thin SPP film on the substrate. When H2O was used instead of H2O for the humidification, those smaller
oscillations became more distinct reflecting the absorbed water. However, in the high Q region for SPP/C/Si at
80% RH with H2O (Fig. 3(e)), the oscillations were not clear, probably due to the influence of an extremely large
amount of water absorbed in the membrane.
Detailed analyses of the data are now in progress to understand the differences between Nafion and SPP.
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3. Results

Fig. 2 Neutron reflectivity on SPP under N2+D2O on Si (a), Pt/Si (b) and C/Si, and under N2+H2O on Pt/Si (d) andC/Si (e). All reflectivity curves on the reference substrates of Si, Pt/Si, and C/Si are shown in black. Thereflectivity curves with SPP thin films at 30 and 80% RH are shown in red and blue, respectively.
4. Conclusion
Neutron reflectivity on SPP films with a thickness of 100 nm at different substrates at different relative
humidities was successfully measured under nitrogen humidified with either H2O or D2O. The neutron reflectivity
data are being analyzed by curve fitting to understand the 1-dimensional densities of SPP and water at different
humidities.
Reference
1) Y. Ogata, D. Kawaguchi, N. L. Yamada, and K. Tanaka, ACS Macro Lett., 2, 856-859 (2013).
2) T. Kawamoto, M. Aoki, T. Kimura, T. Mizusawa, N. L. Yamada, J. Inukai, Poster ID s2-010,
22nd Topical Meeting of the International Society of Electrochemistry, Tokyo, Japan, April
15-18.
3) J. Miyake, R. Taki, T. Mochizuki, R. Shimizu, R. Akiyama, M. Uchida, K. Miyatake, Science
Advances, 3(10), DOI: 10.1126/sciadv.aao0476.

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