372017 Electrolyte Membranes for Pemfcs and Solid Alkaline Fuel Cells Using Self-Assembly and Pore-Filling Technologies
Proton exchange membrane fuel cells (PEMFCs) are promising energy devices for residential and motor vehicle applications, largely because of the advantages as high conversion efficiency at low temperature along with no exhaust of carbon dioxide. One of requirements is to simplify the humidification device of the PEMFC electrolyte membranes that provide high proton conductivity under low relative humidity conditions. Solid-state alkaline fuel cells (SAFCs) with the benefits of using non-noble metal catalysts and liquid fuels can directly solve the problems that PEMFCs have. For both of fuel cells, developments of membrane electrolytes are key to achieve the success.
Pore-filling electrolyte membrane is a unique membrane that can suppress the swelling of filled polymer electrolyte because of its rigid porous substrate. Protons can rapidly conduct through this structure without further swelling although fuels cannot transport through the membrane. Also, we found a distinctive phenomenon for proton conduction by generating packed acid structure by using polymer and inorganic electrolytes, and the membrane showed high proton conduction under extremely low humidity condition. The phenomenon is explained by a “packed acid mechanism”, proposed after applying ab initio molecular simulations. A proton normally shuttles between the proton donors and acceptors, which disrupts proton conduction (pseudo-shuttling). The acid–acid interaction in the packed acids eliminates “pseudo-shuttling” and leads to successive proton conductions. Those results will be discussed.
The anion exchange membranes should be developed to improve the performance of SAFCs and require following properties: high OH- conductivity, low fuel permeability and thermal stability in alkaline circumstances. To achieve all these goals of the membranes, novel anion exchange membranes have been developed using self assembly technologies, and the nano-sized structures and distance between the ion-exchange groups were designed. Several types of anion exchange membranes will be shown and those performances will be discussed.