The Behavior of Carbon-Coated Nanoparticles in Oxidizing and Reducing Gas Environment in Environment TEM (E-TEM) Mode

Abstract

The idea of a carbon-coated nanoparticles for electrochemical catalysis is not new and was widely used in direct methanol fuel cell (DMFC) [1], since the carbon coating acts as a barrier to prevent severe oxidation, thus protecting the nanoparticles from detrimental and irreversible degradation/corrosion. Recently, this type of catalyst was demonstrated to show excellent durability towards hydrogen oxidation and evolution reactions (HOR and HER), but also oxygen evolution and reduction reactions (OER and ORR), both in acid and (especially) in alkaline environment. For example, in alkaline media, Gao et. al and Doan et. al did show the excellent performance of carbon-coated Ni nanoparticles in both HOR and HER, vs. non-coated Ni; the latter degraded quickly because of severe oxidation/passivation or severe hydride poisoning. [2,3] In this work, we synthesize carbon-coated Pd or Pd-Ni nanoparticles that are supported Vulcan carbon and study their electrochemical response in RDE. Their behavior is compared to non-carbon-coated Pd or Pd-Ni. The two kinds of catalysts materials are also thoroughly evaluated in environmental transmission electron microscopy (E-TEM) mode, using various temperature, either in high vacuum, oxygen, or hydrogen gas; these conditions were applied to mimic the inert or oxidizing/reducing environments witnessed in operating fuel cells and observe the behavior of the nanoparticles in such conditions. The experiments were conducted using a FEI TITAN E-TEM at IRCELYON, and the fast camera in the system provided the video of described experiments. It is shown that the carbon-coated Pd or Pd-Ni nanoparticles have enhanced robustness than their non-coated counterparts.