Exploring Fuel Cell Catalyst Layers at Multiple Scales

Abstract

The catalyst layer used in a fuel cell is an archetype of multi-component composite materials used as electrodes in many electrochemical devices. In this talk, we will describe and link together a number of studies of the fuel cell catalyst layer that we have been carried out over the past 10 to 15 years. A major focus of the talk is work on a MURI project with Andrzej Wieckowski together with other ‘all-stars’ in the field. This project combined experiment and theory to evaluate electrocatalysis. We will discuss this effort and Andrzej’s critical role in some of the accomplishments of the team.We will emphasize our work on describing the geometrically constrained limits on utilization of dispersed catalyst in the layer. To answer our original question, the catalyst components were broken down to constituents (Pt nanoparticles, carbon particles, ionomer) and interactions between components were used to build a hierarchical model of the catalyst layer. The interactions were defined in the context of colloidal interaction theory using descriptions of electronic properties of the constituents derived from experimental measurements of refractive index/dielectric properties across a wide range of frequencies. The model satisfactorily captured some aspects of the structure of the catalyst layer, e.g. the tendency toward segregation of components, and provides a good bound to the utilization of catalysts but failed to provide a quantitatively accurate description of certain transport-related physical properties. Acknowledgement We are humbled and honored to have enjoyed the collaboration and scientific spirit of Andrzej Wieckowski as well as his gracious support of our team effort. We gratefully acknowledge the support of this work by the US Army Research Office and the Naval Research Research Office. The significant contributions of Professor J. Adin Mann of Case Western Reserve university and Dr. Karren More of Oak Ridge National Lab are also appreciated.