Understanding and controlling the electrochemical stability or corrosion behavior of nanometer-scale solids is vitally important in a variety of applications such as nanoscale electronics, sensing, and catalysis. For many applications, the increased surface to volume ratio achieved by particle size reduction leads to lower materials cost and higher efficiency, but there are questions as to whether the intrinsic stability of materials also decreases with particle size. An important example of this relates to the stability of Pt catalysts in, for example, proton exchange fuel cells. In this Article, we use electrochemical scanning tunneling microscopy to, for the first time, directly examine the stability of individual Pt nanoparticles as a function of applied potential. We combine this experimental study with ab initio computations to determine the stability, passivation, and dissolution behavior of Pt as a function of particle size and potential. Both approaches clearly show that smaller Pt particles dissolve well below the bulk dissolution potential and through a different mechanism. Pt dissolution from a nanoparticle occurs by direct electro-oxidation of Pt to soluble Pt(2+) cations, unlike bulk Pt, which dissolves from the oxide. These results have important implications for understanding the stability of Pt and Pt alloy catalysts in fuel cell architectures, and for the stability of nanoparticles in general.

Using first-principles density functional theory, we study the effect of particle size and surface structure on the chemisorption energy of OH and O on nanoparticles of Pt. We find that the chemisorption energies of O and OH are strongly affected by the size and structure of the Pt particle varying by up to 1.0 eV at different adsorption sites and particle sizes.