How Stable Are Spherical Platinum Nanoparticles Applied to Fuel Cells?

We report on the synthesis, characterization, and degradation behavior of spherical platinum nanoparticles (Pt-NPs). The Pt-NPs were synthesized with and without carbon-support using the "water-in-oil" microemulsion method. X-ray diffraction (XRD) was used to examine their average crystallite size, which was ca. 4.0 nm. The shape, size, and size distribution of the Pt-NPs were evaluated using transmission electron microscopy (TEM); the average size was ca. 4.0 nm, thus in agreement with the XRD data. The agreement between the XRD and TEM data indicates that the Pt-NPs were singlecrystallites in nature. Thermogravimetric analysis (TGA) measurements were carried out to evaluate the metal loading, which was close to the target value of 40 wt %. Cyclic voltammetry (CV) experiments were performed in 0.50 M aqueous H2SO4 in the s = 1.00-50.0 mV s(-1) potential scan rate to determine the specific surface area (As) of the catalysts and to assess the cleanliness of the system. The Pt surface oxide growth and reduction were successfully examined using in situ confocal Raman spectroscopy. The results allow monitoring the appearance and disappearance of crystallinity in the surface oxide layer. The stability of the catalyst was evaluated by recording 500 CV profiles in 0.50 M aqueous H2SO4 solution in the 0.0S V <= E <= 1.55 V range at s = 50.0 mV s(-1). The corrosion behavior of Pt-NPs was studied using potentiodynamic polarization (PDP) measurements at s = 0.10 mV s(-1) in the presence of different gaseous environments (N-2(g), O-2(g), or H-2(g)). The nature of the dissolved gas has a profound impact on the stability/corrosion behavior of the Pt -NPs. The Pt nanocatalysts are stable in the electrolyte saturated with H-2(g), undergo slight corrosion in the electrolyte saturated with N-2(g), and undergo significant corrosion in the electrolyte saturated with O-2(g). The carbon support also undergoes corrosion and porosity changes. The corrosive degradation of the Pt-NPs and carbon support is pronounced the most in the case of the anodic PDP. Cyclic voltammetry measurements were employed to determine the loss of the electrochemically active surface area (A(ecsa)) of the Pt-NPs prior to and after PDP measurements; the results correlate with the corrosion rates. The new and original results on the characterization and corrosive degradation of the Pt-NPs represent an important contribution that will benefit fuel cell science and technology.