Effect of Operation Conditions during Fuel Starvation on Ruthenium Migration from Pt/Ru Anode Catalysts

Membrane electrode assemblies developed for use with reformate and containing Pt/Ru (1:1) anode catalysts, have been submitted to a fuel starvation accelerated stress test (AST) protocol in combination with a range of different operation conditions The fuel-starved MEAs were aged under conditions enabling investigation of the effect of temperature (65, 85 °C), current density (200, 400 mA/cm²), relative humidity (40, 80% RH) and number of starvation/recovery cycles (up to 875 cycles). The MEAs were characterized following the AST using scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS).  This characterization has proven to be particularly useful in understanding the mechanism of degradation leading to performance loss of fuel-starved MEAs, and in correlating the observed extent of MEA modification in terms of migration of catalyst species, to the electrochemical parameters observed in situ.

The results show different trends in the evolution of the Ru/Pt ratio at the anode inlet and outlet regions, which is not unexpected given the greater degree of fuel starvation to the MEA at the anode outlet region, than at the anode inlet. At the anode outlet, the Ru/Pt ratio is <1 in the catalyst layer under all AST conditions, indicating that Ru has been lost due to electrochemical corrosion and leaching. Further, the extent of this depletion appears to be strong, and similar in all cases (0.26-0.39). At the anode inlet, the Ru/Pt ratio in the used MEAs ranged from 1 (i.e. unchanged compared with the pristine MEA) to 0.48, and the exact ratio within this range depended closely on the applied AST conditions. Correlation was also observed between the anode catalyst layer thickness and the extent of Ru loss.   

The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2010-2013) for the Fuel Cells and Hydrogen Joint Undertaking under grant agreement KEEPEMALIVE no. 245113.