Heterogeneous cell performance of polymer electrolyte fuel cell at high current operation: Respiration mode as non-equilibrium phenomenon

摘要

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 (Dsub2/sub) gas as a fuel. By using Dsub2/sub, we introduce special scattering contrast in a polymer electrolyte film (Nafion?), when the film is originally swollen by Hsub2/subO. After switching from Hsub2/sub to Dsub2/sub gas (humidified with Hsub2/subO), we found that SANS intensity significantly decreases about 40% at the q -position of scattering maximum ( q sub m /sub) 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 Dsub2/subO 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.