LAUSR

The evolution of Pt nanoparticles in proton-exchanged membrane fuel cells is monitored before and after electrochemical potential cycling, using 2D and 3D identical location aberration-corrected transmission electron microscopy. This work demonstrates that 2D images might be a challenge to interpret due to the 3D nature of the carbon support. Thus, it is critical to combine both 2D and 3D observations to be able to fully understand the mechanisms associated with the durability of Pt catalyst nanoparticles. In particular, this investigation reveals that the mechanism of particle migration followed by coalescence is operative mainly across short distances (<0.5 nm). This work also shows that new Pt particles appear on the carbon support, as the result of Pt dissolution, followed by the formation of clusters, which grow by Ostwald ripening. This mechanism of Ostwald ripening is also responsible for changes in shape and particle growth, which later may result in coalescence.