Platinum-Based Nanocatalysts for Proton Exchange Membrane Fuel Cells

Licentiate thesis, 2023

Fuel cells have potential to become an integral technology in a future sustainable energy system. For transport applications, the proton exchange membrane fuel cell (PEMFC) is the most promising option, exhibiting light weight and high energy density. However, large-scale commercialization is impeded by expensive catalyst materials and slow oxygen reduction reaction (ORR) kinetics on the cathode side. Several alternatives to the conventional platinum PEMFC catalyst have been proposed and studied during the last decades, one being platinum-rare earth (Pt-RE) metal alloys. With enhanced ORR activities and maintained stability, these materials are highly interesting for deployment in PEMFCs, and could potentially reduce both catalyst material use and overall fuel cell cost. In practical fuel cells, catalysts are required in nanoparticulate form, to facilitate sufficient performance while keeping material utilization high. Unfortunately, scalability remains as a main obstacle for Pt-RE nanoparticle synthesis, as fabrication of these materials has proven challenging, motivated by the high oxygen affinity of the rare-earth metals.

This thesis investigates the use of sputtering onto liquid (SoL) substrates as a potential synthesis method for Pt-RE nanocatalysts. The influence of sputtering parameters, including substrate type and temperature, as well as gas environment, on the size and morphology of platinum-based nanocatalysts are studied. Transmission electron microscopy of platinum sputtered in four different liquids indicates that the size of the nanoparticles is only weakly dependent on temperature. Furthermore, catalyst layers fabricated from the SoL-synthesized nanocatalysts are evaluated in a half cell setup. The electrochemical results shows that high performing catalyst layer fabrication from SoL-synthesized nanoparticles is viable, which opens for further development of the technique.