Satoshi Koizumi, Satoru Ueda, Putra Ananda, Yasuyuki Tsutsumi
The heterogeneous performance of polymer electrolyte fuel cell in space and time was discussed for operation at high current density. The cell voltage, detected by a segmented electrode, varies along a gas flow channel from upper to bottom stream and oscillates in time, which is referred as a respiration mode. At the higher current, the cell voltage at different positions started to be synchronized, as the current density increases. In order to investigate a role of water on the respiration, we employed a new method of contrast variation for small-angle neutron scattering (SANS) using deuterium (D2) gas as a fuel. By using D2, we introduce special scattering contrast in a polymer electrolyte film (Nafion®), when the film is originally swollen by H2O. After switching from H2 to D2 gas (humidified with H2O), we found that SANS intensity significantly decreases about 40% at the q-position of scattering maximum (qm) originating from the water-microdomains in the polymer electrolyte. After quantitative analyses of the scattering intensity, it was elucidated that 20 wt% of the total water is occupied by D2O as a steady state. At around the average intensity, SANS intensity oscillates with a time interval ∼100sec, which corresponds to the respiration mode found for voltage. The respiration behavior is considered as a non-linear & non-equilibrium phenomenon in an open system, where water flooding plays a role of feedback to decelerate fuel transportation and chemical reaction of water generation. © 2019 Author(s).
Laboratory of Living Soft Matter, Institute of Quantum Beam Science, Ibaraki University, 162-1, Shirakata, Ibaraki, 319-1106, Japan; Department of Chemistry, Faculty of Mathematics and Natural Science, Universitas Negeri Padang, 25131, Indonesia; FC Development Co., Ltd., Ibaraki University, 4-12-1 Nakanarusawa, Hitachi, Ibaraki, 316-8511, Japan
