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In-Situ S/TEM Probing of the Behavior of Nanoparticles Under Chemical and Electrochemical Reactions in the System Involving Solid, Liquid and Gas

Nanoparticles of either as an active functioning component or as a reaction product is of great importance for a range of science and engineering, such as catalysis, nucleation and growth, metal air-battery, and oxidation and corrosion. A typical example is the deactivation of catalyst particles. Deactivation of supported metal nanoparticle catalysts, especially in relevant gas condition, is a critical challenge for many technological applications, including heterogeneous catalysis, electrocatalysis and fuel cells. It has been commonly realized that deactivation of catalysts stems from surface area loss due to particle coarsening, however, for which the mechanism remains largely unclear. Direct in-situ TEM observation reveals unprecedented details at atomic scale with respect to the behavior of Pt nanoparticles for fuel cell application, especially the coarsening dynamics of Pt nanoparticles on bare CNTs surface and in Nafion covered Pt/CNTs under O2 and H2O gas environment. We found that the coarsening of Pt nanoparticles proceeded through migration and coalescence process. The migration rates of Pt nanoparticles on bare CNT surface is much faster in O2 than that in H2O. The strong oxygen chemisorption on Pt nanoparticles weakens the interaction between Pt and CNT surface, leading to a fast migration in O2. Incorporation of Nafion electrolyte layer put on a mechanically confinement to Pt/CNTs which reduces the Pt migration rate in O2. However, this mechanical confinement is largely relieved by introducing H2O, and a lubricated interface is created, both leading to a faster migration rate of Pt in H2O than that in O2. These results bridge the gap between the previous in situ TEM studies in idealized conditions and the technological relevant conditions of Pt catalyst for PEMFC, thus provide insights to rational design of Pt/carbon catalysts incorporating Nafion electrolyte to achieve a long-lasting PEM fuel cells.