Novel and High Performance Electrodes with Nano-Hybrid Hydrocarbon Ionomers of Pemfc for Broad Temperature Range and Lower Humidity Condition
Ju-Myeung Lee, G.M. Anilkumar, and Takeo Yamaguchi. Department of chemical system engineering, University of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo, Japan
PEMFC (polymer electrolyte membrane fuel cell) especially for automobile is required high performance from the room temperature to 120 oC with low humidification. We succeeded to develop a novel nano-hybrid hydrocarbon MEA (membrane electrode assembly) operating at broad temperature range and make high three-phase boundaries in the catalyst layer. As a key point for the success, we invented a new method that the ionomer was ‘capping' to the nano-sized proton conducting particle. This nano-hybrid proton conductor for the hybrid MEA was prepared from SPES (sulfonated poly (arylene ether sulfone)) ionomer and fully re-dispersible nanozirconia precursor powder in polar aprotic organic solvents. The nano-hybrid catalyst layer was fabricated with catalyst, nanohybrid electrolyte and DMF (N, N'-dimethylformamide) as a solvent. And in situ generation of zirconium hydrogen phosphate (ZrP) in the nano-hybrid matrix was carried out by treating with H3PO4. From the aspect of the structure of the catalyst layer, we controlled the size of nano-hybrid for higher utilization of catalyst and kept the high dispersibility for the proton conduction matrix via capping method which used the physical adsorption between the nano-zirconia precursor and SPES ionomer. The size of the hybrid proton conductor was confirmed by DLS (Dynamic Light Scattering) and the nano-structure change of the catalyst layer was observed by mercury porosimetry. The nano-hybrid MEA was developed by assembling the nano-hybrid electrodes and our original pore-filling membrane with the same nano-hybrid ionomer. The nanohybrid electrodes showed high utilization of catalyst by cyclic voltammetary in accordance with the concept without any leaching out of materials. The nano-hybrid ionomer MEA showed high fuel cell performances without using any perfluorosulfonicacid ionomers. For example, the power density of the MEA showed 285 mW/cm2 with 720mA/ cm2 at 100 oC, 1 atm and around 70 % humidity.