Pt/IrO2–TiO2 cathode catalyst for low temperature polymer electrolyte fuel cell – Application in MEAs, performance and stability issues

Abstract

This work addresses the long-term stability issues of polymer electrolyte fuel cells (PEFC) based on a new oxide supported cathode catalyst generation using commercial Pt/IrO2–TiO2 (Umicore®) as model cathode catalyst. First, the ionomer to oxide supported cathode catalyst ratio has been studied and optimized. The amount of Nafion® ionomer was varied in the electrode composition and an optimum was found for 10wt% ionomer content with respect to the catalyst weight allowing for an optimum triple phase boundary in the gas diffusion electrodes. The initial performance of the MEAs based on the Pt/IrO2–TiO2 catalyst was found to be equivalent to those of Pt/high surface area carbon (HSAC) catalyst. In order to study the stability of the catalytic layers, the manufactured MEAs were exposed to accelerated stress test protocols designed for automotive fuel cell applications. These protocols are simulating the catalyst behaviour during vehicle acceleration and deceleration and during vehicle start-up and shut down triggering respectively platinum dissolution and support corrosion. These experiments were performed in 30cm2 single PEFCs using state-of-the-art catalyst Pt/HSAC (TKK®) for comparison. Specifically in the start–stop related test protocol, the new IrO2–TiO2 catalyst support exhibits remarkable stability with only 25mV cell potential loss at 0.8A/cm2 after 10,000 cycles, whereas the carbon supported Pt catalyst could not reach this current density anymore under these conditions. Moreover a structural catalyst modification is pointed out to occur during the in situ stability tests.