(510y) Ion-Exchanged Carbon Supported Platinum Catalysts For Hydrogen Fuel Cells

Supported catalysts provide large specific surface areas for higher reaction rates along with the potential to lower overall cost. Carbon has been employed as the primary support for fuel cell catalysts. However, high cost and limited lifetime performance are two factors that hinder commercialization. Typically, catalysts used in fuel cells are platinum supported on carbon at catalyst contents of ~20-50 wt%, where platinum particles ~2-4 nm are supported on carbon ~20 nm in size. Currently, anode and cathode catalyst layers (electrodes) in fuel cells have platinum loadings ~3-4 times higher than target values required for large-scale automotive applications, which is not acceptable for reasons of both cost and platinum supply limitations. Additionally large voltage losses have been observed in fuel cell lifetime tests, which have been ascribed to platinum coarsening (agglomeration of physically sorbed platinum or reduction in platinum reactive surface area) and dissociation from the carbon support and also oxidative degradation of the carbon support itself. Both cost and lifetime performance are directly linked to platinum surface area (platinum loading and platinum particle size) and platinum/carbon stability.

In this study, carbon supported platinum catalysts were prepared with an ion-exchange method in contrast to the commonly used colloidal method to investigate the ability to control platinum surface area and Pt/C stability. Chemical functionalization of carbon provides a negatively charge surface for ionic adsorption of cation platinum complexes. A variety of carbon blacks were used as supports, including Vulcan^® XC72R, Ketjenblack^® EC300JD and Ketjenblack^® EC600JD. Surface functional groups were quantified by titration and additional characterization was performed using transmission electron microscopy (TEM), Raman and Fourier-transform infrared (FTIR) spectroscopy. Both chemical and thermal reduction methods were investigated to tune particle size and loading of platinum. TEM and thermolysis were used to quantify platinum size distribution and loading, where uniform platinum particles of 1 nm were observed at high loadings. Experimental results indicate that platinum loading and size distribution is related to carbon surface functionalization and reduction procedure. The hydrogen fuel cell performance of the ion-exchanged catalyst was compared to commercial catalyst.