posted on 2023-11-21, 16:40authored bySomaye Rasouli, Deborah Myers, Kenji Higashida, Naotoshi Nakashima, Peter Crozier, Paulo Ferreira
The evolution of Pt nanoparticles supported on carbon
nanotubes
is analyzed before and after electrochemical potential cycling, using
identical location aberration-corrected transmission electron microscopy,
for applications in proton exchange membrane fuel cells. The work
is focused on the half-cell accelerated stress test protocol of potential
cycles ranging between 1.0 and 1.5 VRHE to represent the
start-up/shutdown settings of a fuel cell vehicle. The research work
reveals that particle migration and coalescence are key mechanisms
for a reduction in the Pt nanoparticle surface area at the early stages
of potential cycling. The mechanism for particle movement and coalescence
is attributed to carbon corrosion, catalyzed either by Pt or by bulk
corrosion of the carbon nanotubes. Carbon corrosion results in the
appearance of carbon vacancies at the carbon nanotube/Pt nanoparticle
interface during cycling, as well as the formation of edge and surface
defects. During cycling, the concentration of the dissoluble Pt increases.
As soon as a significant amount is reached, subnanometer/atomic clusters
emerge on the carbon nanotube support, which can move and coalesce,
or redeposit on the surface of larger particles through Ostwald ripening.