Correlation between Cell Performance and Membrane Electrolyte Characters in Alkaline Direct Methanol Fuel Cells ( II ) ( III )

Searching for alternative power and energy sources has gained much attention due to the high cost and dwindling crude petroleum oil supply. Among the alternative sources, fuel cells are a popular topic because of environmentally friendly advantages. Among several types of fuel cells, proton exchange membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC) use proton conducting polymer membranes. The DMFC is ideal for portable devices due to many advantages over the PEMFC, including higher energy density, simpler system, compact design, and possibility of ambient temperature start-up. The proton exchange membrane based on perfluorosulfonic acid (PFSA) polymer, Nafion for example, is widely used for PEMFC applications. Nafion has high proton conductivity, good thermal, chemical, and mechanical properties. However, the high methanol (MeOH) permeability through Nafion from anode to cathode is too high to use in DMFC devices. This MeOH cross-over causes MeOH poisoning at the cathode and low efficiency of fuel consumption due to reactant (MeOH) losses. Therefore, research works aimed at the development of new electrolyte membranes with suppressed MeOH permeability are actively underway. This proposal is a continued research from previous NSC project. In the previous year, we have prepared poly(vinyl alcohol) (PVA)-fumed silica composites for the DMFC applications and obtained high cell performance, as outlined in Form C012-1. The fuel cell voltage and power density using this electrolyte outperformed the pristine PVA membrane and other literature data. The objectives of this proposal for the next two years are to prepare more PVA nanocomposite membranes, correlate the cell performance with the electrolyte characters, and develop a mathematical model predicting the cell performance for alkaline DMFC applications. Potential PVA composites include the ones containing carbon nano-tubes, nano-particles, polyelectrolyte blending, or nano-metal incorporation. The physical, chemical, electrical properties of the resulting membranes will be characterized. The sorption, diffusion and permeation of MeOH, water and hydroxide ion through the membranes will be determined. The resulting films will be assembled into a single cell and tested for performance to verify the established models. The models will serve a good estimate and save fuel cell experimental costs. Furthermore, optimal electrolyte characters can be explored and be used as guidelines for future material development. The modification methods can be applied to other membranes to suppress MeOH crossover while maintaining sufficient conductivity.

Project ID:PB10007-7239
External Project ID:NSC100-2221-E182-041