Avni A. Argun, J. Nathan Ashcraft, and Paula T. Hammond. Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, 66-525, Cambridge, MA 02139
The global need for clean and sustainable energy is ever increasing and electrochemical devices such as fuel cells, batteries, and solar cells show great potential. A major component of these devices is an ion-conducting electrolyte which enables fast charge transport between electrodes. The alternating adsorption of oppositely charged molecular species, known as the electrostatic layer-by-layer (LBL) technique, is a simple and elegant method of constructing highly tailored polymer electrolytes and organic-inorganic composites. We have utilized this method to develop proton-exchange membranes for direct-methanol fuel cells (DMFCs). This approach presents strong advantages as it allows the incorporation of many different functional materials within a single film at a full range of compositions with exceptional homogeneity. By pairing a sulfonated poly(2,6-dimethyl 1,4-phenylene oxide) (sPPO) with various amine-based polymers, we obtain ionic conductivity values of up to 35 mS/cm at fully humidified conditions.(1) Furthermore, these multilayer systems exhibit low liquid methanol permeability and have high chemical and mechanical stability due to the use of aromatic polymers. Coating a traditional fuel cell membrane with these highly conductive LBL films reduces the methanol crossover and improves the power output of DMFCs by up to 50%. (1) Argun, A.A.; Ashcraft, J.N.; Hammond, P.T., “Highly Conductive, Methanol Resistant Polyelectrolyte Multilayers.” Adv. Mater. 2008, 20, 1539-1543.