C. Anson, J. Gerken, Y. Preger, S. Biswas, T. Root, S. Stahl
University of Wisconsin-Madison,
Keywords: fuel cells, platinum-free, flow cathode
Summary:One of the major obstacles preventing widespread implementation of PEM fuel cells is the current requirement for prohibitive loadings of Pt at the cathode to achieve high activity for the oxygen reduction reaction. The Pt catalyst adds substantially to the cost of the system and is prone to poisoning, either from contaminants in the fuel (i.e. for H2 fuels) or the fuel itself (such as MeOH). To address these concerns, we are developing a novel PEM fuel cell, where the oxygen reduction reaction is spatially separated from the electrode. In our chemically regenerable redox cathode, a soluble organic redox mediator undergoes facile reduction at the cathode and transports these electrons through solution to a non-PGM catalyst, where the aerobic oxidation of the mediator (and therefore, reduction of O2) is catalyzed. The oxidized mediator can then return to the electrode, where it is again reduced. The use of non-PGM catalysts in our system does not have the same drawbacks as in conventional PEM fuel cells (for example, high resistances due to thick electrocatalyst layers), and the high performance possible with this approach could lead to a activity- and cost-competitive design relative to conventional PEMFCs. Besides the replacement of Pt, this approach is forecast to require less balance-of-plant relative to conventional PEMFCs, and the integration of non-PGM catalysts can facilitate the use of non-H2 fuels, such as MeOH. Here we will describe the development of the organic mediators and non-PGM catalysts used to demonstrate our concept, and discuss the continued work required to reach a commercially viable fuel cell design.