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Degradation Mechanisms of Supported Pt Nanocatalysts in Proton Exchange Membrane Fuel Cells: An Operando Study through Liquid Cell Transmission Electron Microscopy
journal contribution
posted on 2020-03-09, 21:13 authored by Andrea Impagnatiello, Carolina Ferreira Cerqueira, Pierre-Eugène Coulon, Arnaud Morin, Sylvie Escribano, Laure Guetaz, Marie-Claude Clochard, Giancarlo RizzaNanocatalysts’
degradation is a limiting factor for the
development of polymer electrolyte membrane for fuel cells (PEMFCs).
In this work, a dedicated sample holder has been used to mimic the
cathode of a PEMFC at the earliest stages of the aging process, i.e.,
under accelerated stress test after up to 500 cycles. The mechanisms
of surface area loss of supported platinum nanoparticles (Pt NPs)
have been monitored in real-time and operando conditions
by coupling liquid cell transmission electron microscopy (LTEM) to
energy-filtered transmission electron microscopy (EFTEM), while cyclic
voltammograms (CVs) were simultaneously recorded. The study has been
performed using an ink made of a commercial catalyst (Tanaka-TEC10V50E)
containing Pt NPs intended for automotive applications (3.0 ±
0.4 nm). First, a protocol has been set up to mitigate the electron-beam-induced
radiolysis effects to a level that related artifacts are hindered
or at least not appreciably detected during the duration of the experiment.
At the same time, the resolution limit of the microscope has been
pushed below 1 nm. Afterward, several degradation pathways were first
identified and categorized and then correlated to the evolution of
both the electrochemical active surface area (ECSA) and the Pt oxide
reduction peak. We analyze reported evidence that the electrochemical
aging favors the dissolution of the smaller Pt NPs. Dissolved cations
are then observed to redispose onto larger supported Pt particles
(electrochemical Ostwald ripening) or to be transported within the
electrolyte, being either the aqueous acidic solution or the ionomer
where they can precipitate (dissolution/precipitation process).