(23a) Electrospun Mats Modified by Layer-by-Layer Assembly for Use as Proton Exchange Membranes

Recently, we have developed very promising layer-by-layer (LBL) assembled polymer films for use as the proton exchange membrane (PEM) in direct methanol fuel cells (DMFCs). These materials have the highest ionic conductivity values (35 mS/cm at 25°C and 98% RH) ever obtained from an LBL system.^[1] Additionally, these multilayer systems exhibit low liquid methanol permeability which allow for their incorporation into DMFCs. We have demonstrated that simply coating traditional fuel cell membranes with 3 to 5 bilayers of these LBL films improves the power output of DMFCs by up to 50%.

In an effort to develop PEMs where the LBL materials serve as the only ion conductor, we have utilized electrospun mats as the substrate. We anticipate these composite membranes will be more mechanically robust as compared to the as-assembled LBL films. Because these composite material systems can be greatly modified at the molecular level to alter localized mobility, mechanics, and stability simply by changing the relative compositions of each adsorbed nanolayer of polymer or by altering the nature or composition of the underlying electrospun network, the systems are infinitely tunable and the architectures of the films can be modified across several length scales to achieve highly optimized and readily processable PEMs. Preliminary results indicate these composite PEMs maintain the high ionic conductivity of the original LBL materials.

[1] Argun, A. A.; Ashcraft, J. N.; Hammond, P. T., Highly Conductive, Methanol Resistant Polyelectrolyte Multilayers. Advanced Materials 2008, 20, (8), 1539-1543.