Akito Masuhara1 3 Keiji Shito1 Yuki Takahashi1 Satoshi Sekine1 Kazuki Koseki1 Keisuke Tabata1 Tomohiro Nohara1 Toshihiko Arita2

1, Yamagata University, Yonezawa, , Japan
3, Roel, Yamagata University, Yonezawa, , Japan
2, IMRAM, Tohoku University, Sendai, , Japan

We designed a novel polymer electrolyte membrane (PEM) for PEFC using inexpensive materials and fabricating precise nanostructures. Hence, we have focused on general inorganic filler filling method, which has advantage on improvement of heat resistance and gas barrier properties of the membrane. Novel model PEM consists of silica nanoparticles (NPs) with proton conductive polymer layer prepared by Reversible Addition-Fragmentation chain Transfer Polymerization with Particles (RAFT PwP)1 on its surface. RAFT PwP can prepare precisely adsorbed hydrophilic polymer layer on particles surface, 2D ion-conductive channel consist of weak acids can be effectively prepared2. RAFT PwP of acrylic acid and styrene with spherical silica NPs successfully synthesized, and coated poly(acrylic acid) and polystyrene block copolymers (PAA-b-PS) on the spherical silica filler particles (silica@PAA-b-PS)3.
Silica@PAA-b-PS was synthesized by the RAFT PwP. Silica@PAA-b-PS measured by 1H NMR, GPC, FT-IR, XPS, TGA, SEM, and TEM. Proton conductivity of the silica@PAA-b-PS was measured under 98% RH with different temperature by impedance analyzer. The dried particles were processed into pellets of 1.3 mm diameter under a pressure of about 7 ton and porous gold paint was coated on quarter-circle onto both side of the pellet for the impedance measurements.
PAA-b-PS were determined to be Mn = 32000, PAA:PS = 61:39 by 1H NMR and GPC. Silica@PAA-b-PS was successfully prepared by RAFT PwP. As the result of PAA-b-PS coating on the silica surface, pelletized silica@PAA-b-PS expressed relatively large proton conductivity of 1.22Χ10-4 S cm-1 (at 60 °C and 98% RH) as PAA based electrolyte with the activation energy of 0.21 eV. This low activation energy suggests proton conductive mechanism is under Grotthuss mechanism. By coating with PS layer, it is possible to maintain proton conduction under low humidity condition. The particle developed can be useful to build novel and further improved filler filling PEM for polymer electrolyte fuel cells (PEFC).

[1] T. Arita, Chem. lett. 42, 801 (2013), WO2014/025045.
[2] Y. Nagao, J. Matsui et. al., Langmuir 29, 6798 (2013)
[3] T. Arita, A. Masuhara, et. al., Japanese Unexamined Patent Application Publication
No. 2017-037762.