Highly Conductive Nanoassemblies for Electrochemical Energy Conversion Devices

The global need for sustainable and carbon-free energy is ever increasing and electrochemical devices such as batteries, fuel cells, and solar cells show great potential. A major component of these devices is an ionic conducting electrolyte which enables fast charge transport between electrodes. Traditionally, liquid or gel electrolytes are used which prohibit widespread use of these devices due to safety concerns. The challenges presented in development of new solid-state ionic conducting polymer materials systems are high conductivity, high mechanical strength and nanometer level control to optimize materials properties. Although the desired properties of solid polymer electrolytes depend on the device application, fast ion conduction is essential to reduce electrical resistance and power losses. Furthermore, it would be desirable to utilize approaches that are cost effective and environmentally friendly.

Alternating charge-based layer-by-layer (LBL) film assembly, combined with the commercial availability of polyelectrolytes used allow for constructing highly conducting solid state ionic conductors targeted towards energy conversion devices such as dye-sensitized solar cells (DSSCs) and proton-exchange membrane fuel cells (PEMFCs). This approach presents strong advantages as it allows the incorporation of many different functional materials within a single thin film at a full range of compositions with exceptional homogeneity. For example, by pairing a sulfonated poly(2,6-dimethyl 1,4-phenylene oxide) (sPPO) with poly(diallyl dimethyl ammonium chloride) (PDAC), we obtain ionic conductivity values of up to 35 mS/cm, the highest ever obtained from an LBL assembled thin film. These multilayer systems also exhibit low liquid methanol permeability, which provides a direct application as proton-exchange membranes in direct-methanol fuel cells (DMFCs). Uniformly coating traditional fuel cell membranes with these LBL films improves the power output of a DMFC by over 50%.