Electrode Degradation in Polymer Electrolyte Fuel Cells

Licentiatavhandling, 2023

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.