Fuel cell converts chemical energy of fuel into electrical energy with high efficiency and low emission of pollutants. So they have been developed as a promising alternative for energy conversion devices. Polymer Electrolyte Membrane Fuel Cell (PEMFC) is interesting for the mobile and domestic application due to low operating temperature, no leak problem and fast start-up. Perfluorinated membranes from Dupont, Dow, Gore and Asahi Chemical have been used for electrolyte membrane in PEMFC exclusively. They have outstanding chemical and mechanical stability and show excellent performance in PEMFC and DMFC (Direct methanol Fuel Cell) applications. But these perflurinated membranes have a few shortcomings which including high price, high methanol permeability and difficult production process. These drawbacks provoke a research of alternative membranes based on partially perflorinated ionomer and hydrocarbon polymer.
In this research, we prepared hydrocarbon based proton-conducting composite membranes for Fuel Cell and investigated their properties. The sulfonated poly ether ether ketone was used for polymer matrix and inorganic materials such as heteropolyacid, Laponite and MMT was incorporated in polymer membranes. The properties of prepared membranes are investigated by thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and impedance spectroscopy. And water uptake and methanol permeability are examined. The $H_2$-PEMFC and DMFC single cell test was carried out to confirm real fuel cell applications.
The sPEEK membrane and other composites membranes membrane based on sPEEK exhibited 3~3.5*$10^{-3}$ S/cm proton conductivity at room temperature. They also showed thermal stability in fuel cell application because the Td (decomposition temperature) of sPEEK membranes was over 250$^\circ$C. The study for water uptake of the sPEEK/Lapo10 composite membrane showed 30-40% constant swelling value to 80°C due to cohesion of clay and polymer matrix. Also clay incorporated with polymer matrix prevented methanol diffusion, so the methanol permeability of the composite membrane was reduced to 25% compared to that of Nafion.
In single cell test, the sPEEK/Lapo10 composite membrane showed profitable performance comparable to Nafion membrane and they are insensitive to humidifying condition of reactant gases as compared with intrinsic sPEEK membranes. In DMFC application, the sPEEK membranes yielded only 50% performance compared to Nafion due to interface of membrane and electrode assembly. But the sPEEK/Lapo10 composite membrane showed a little higher performance at 80$^\circ$C compared to sPEEK membrane due to dimensional stability.
Finally the hydrocarbon/clay composite membranes have some advantages including the low cost, constant water uptake and low methanol permeability etc, so the these hydrocarbon composite membranes are considered for use in PEMFC and DMFC as alternatives to perfluorinated membranes.
