(35b) Electrolytes For Low And Intermediate Temperature Fuel Cells: Their Properties And Interplay With Other Components

Polymer electrolytes are the central feature of the eponymous PEM fuel cells. However, a variety of system and other aspects play into what is required of these materials. As systems are developed, specific, application-driven requirements have revealed shortcomings of existing materials. In the face of these shortcomings, at least two possible tacks can be taken: one can develop new and improved materials or one can ?engineer around' the properties of existing materials.

This tutorial will provide an overview of the features of several available electrolyte types together with a critical discussion of their chemistry and physics. These will be put into the context of the requirements of the cell and system to provide additional guidance on electrolyte choices. In particular, we will consider several case studies.

In addition to a critical ?taxonomy' of electrolytes, some topics that will be touched on include an evaluation of the relative importance of electrolyte conductivity to cell performance, limitations due to cross-over of reagents, system start-up, mechanical requirements and material durability in use. Emphasis will be placed on presenting a feeling for the trade-offs inherent in engineering fuel cell systems.

Finally, recently proposed electrolyte types will be critically reviewed in light of all of the above.