Sputtered Pt3Y Thin Films As Cathode Catalysts with High Activity in PEMFC Measurements

Abstract

Proton exchange membrane fuel cells (PEMFCs) have the potential to become a vital part of sustainable energy systems, provided that cathode catalysts with higher activity and stability are developed. A very promising group of materials for the oxygen reduction reaction (ORR) is the group of alloys with platinum and rare earth elements.[1, 2]. We have recently showed that sputtered thin films of Pt3Y have specific activities for ORR up to seven times higher than polycrystalline Pt in rotating disk measurements, which is similar to that of bulk alloys.[3] In addition, sputtered thin films of Pt3Y with thicknesses about 3 nm show a mass activity more than an order of magnitude higher than state-of-the-art Pt nanoparticles. However, in order to become realistic alternative catalysts these materials need to prove an increased activity also under real fuel cell conditions. By sputtering thin films of Pt3Y on gas diffusion layers (GDLs) we are able to construct full membrane electrode assemblies (MEAs) and evaluate these in single cell measurements.[4] The fuel cell measurements show that Pt3Y has a specific activity up to 2.5 times higher than pure Pt. Detailed characterization reveals important materials properties of the thin films and indicates that the catalyst structure of the films on GDL is not optimal. This suggests that even higher activities should be possible in the fuel cell if the electrode and catalyst structure is improved. References Escudero-Escribano, M., et al., Tuning the activity of Pt alloy electrocatalysts by means of the lanthanide contraction. Science, 2016. 352(6281): p. 73-76.Greeley, J., et al., Alloys of platinum and early transition metals as oxygen reduction electrocatalysts. Nature Chemistry, 2009. 1(7): p. 552-556.Lindahl, N., et al., High Specific and Mass Activity for the Oxygen Reduction Reaction for Thin Film Catalysts of Sputtered Pt3Y. Advanced Materials Interfaces, 2017. 4(13): p. 1700311.Lindahl, N., et al., Fuel cell measurements with cathode catalysts of sputtered Pt3Y thin films. ChemSusChem, 2018. http://dx.doi.org/10.1002/cssc.201800023. Caption. a) Electrochemical single cell characterization of Pt and Pt3Y sputtered catalysts in H2/O2, 80 °C, 1.5 bar absolute pressure, 100% RH, 20 mV s-1. Inset shows a schematic image of the atomic stucture of the Pt3Y. b) Bright-field TEM micrograph of as-sputtered Pt3Y thin film on GDL. The scale-bar is 50 nm. Figure 1