Dealloyed Pt-Ni Polymer Electrolyte Fuel Cell Cathodes: Effects of Catalyst-Ionomer Ink Composition on Structure and Performance

There have been numerous studies on the effects of catalyst-ionomer ink composition and electrode fabrication on the performance of Pt/C-containing polymer electrolyte fuel cell cathodes.^1-9  There have been relatively few studies, however, on relating the ink composition to its agglomerate structure¹⁰ and in relating the structure to the resulting electrode performance, in particular for the more recently-developed Pt alloy and dealloyed Pt alloy catalysts.¹¹  There have also been few studies on the effects of ink composition and electrode preparation on the composition of the alloy nanoparticles.

In this presentation we report on studies using anomalous small angle X-ray scattering (ASAXS), ultra-small angle X-ray scattering (USAXS),¹⁰ X-ray near-edge absorption spectroscopy (XANES), and X-ray fluorescence spectroscopy (XRF) to characterize catalyst-ionomer inks and the resulting electrodes as a function of ionomer to carbon ratio, solvent concentration and type, and catalyst type (Pt or PtNi alloy). It was found that Ni leaches from the PtNi alloy and the extent of leaching is dependent on both the ionomer to carbon ratio and solvent in the ink. We also correlate the properties determined using the X-ray techniques to the electrode performance in a polymer electrolyte fuel cell.  For example, Ni has been found to negatively impact the transport properties of the cathode catalyst layer.¹²

Acknowledgements

This work is part of a collaborative project with Johnson Matthey Fuel Cells, United Technologies Research Center, the University of Texas-Austin, and Indiana University-Purdue University Indianapolis which is supported by the U.S. Department of Energy’s Fuel Cell Technologies Office.  This research used resources of the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science User Facility operated by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.   The USAXS work was performed at APS Sector 15, ChemMatCARS, which is supported by the National Science Foundation/Department of Energy under grant number NSF/CHE-1346572.  The XANES and ASAXS work were performed at APS Sector 12, BESSRC.

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