Electrode Degradation in Polymer Electrolyte Fuel Cells

Abstract: To mitigate the climate crisis, and reduce carbon emissions from e.g. the transport and energy sectors, hydrogen has been proposed to be used as an environmentally friendly alternative energy carrier. Proton exchange membrane fuel cells (PEMFCs) use hydrogen as a fuel to create electricity with the only byproducts being water and heat, and are well suited as a power source for e.g. vehicles. However, for successful commercialisation of PEMFCs, some hurdles need to be overcome. In particular, lifetime is a limiting factor for PEMFC due to harsh operational conditions. To improve lifetime, the mechanisms by which the materials in PEMFCs degrade must first be better understood. In this thesis, I present a study on the behaviour of Pt, which is currently the sate-of-the-art catalyst for PEMFC, during electrochemical procedures in liquid electrolytes, studied using electrochemical quartz crystal micro-balance (EQCM). Mass response and dissolution rates for Pt thin films were studied in acid and alkaline environments. The Pt dissolution rate was found to be similar in alkaline and acidic electrolyte when normalised to electrochemical surface area. Furthermore, I present identical location (IL) microscopy implemented in a real 5 cm2 single-cell fuel cell, to follow the degradation of Pt catalyst on carbon support under realistic operation conditions. With both IL scanning electron microscopy (IL-SEM) and IL transmission electron microscopy (ILTEM), I show that the degradation processes can be followed during different types of ageing processes. IL-SEM show that the carbon support material is stable during normal fuel cell operation conditions, while the Pt particles grow. IL-TEM show similar result for the normal condition operation as seen with the IL-SEM. However, during start-up/shutdown conditions, IL-TEM show that the carbon support lose volume, and collapse on weak points, which brings Pt particles together, and promotes Pt particle growth. The developed IL techniques presented in this thesis helps distinguish the degradation effects of different operation conditions and opens up for further testing of degradation processes under real fuel cell conditions.