Reconstruction and dissolution of shape-controlled Pt nanoparticles in acidic electrolytes

Shape-controlled nanoparticles are of utmost scientific and technological importance because of their facet-dependent physical and chemical properties. Under long-term electrochemical conditions, little is known about the stability and fate of these nanoparticles with selected exposed crystallographic orientations (facets) of high surface energy, while it is generally accepted that the surface area decreases. Therefore, the reconstruction and dissolution of platinum nanocubes (Pt-NCs), platinum cuboctahedral (Pt-CO) and platinum polycrystalline (Pt-PC) nanoparticles are investigated using voltammetry and in situ irreversible adsorption of Bi and Ge; the cleanliness of the Pt nanoparticles and the purity of the electrolyte solution are established with systematic voltammetric analysis in a H2SO4 electrolyte of different concentrations (0.01, 0.05, 0.5 and 1 M). The voltammetric results suggest that the {100} terrace sites undergo reconstruction/dissolution at a much higher rate relative to that of the {111} ordered bi-dimensional terrace sites and the reconstruction leads to the formation of {110}/{100} step sites. Therefore, the stability of the Pt-NCs is lower than that of the Pt-CO nanoparticles. The gradual decrease in the H-upd area on prolonged cycling in the lower potential range (0.06-0.6 and 0.06-0.8 V) is attributed to the accumulation of oxy-anions from the electrolyte on the Pt surface. Moreover, dissolution of highly energetic Pt sites also contributes to the reduction in the H-upd area, unlike that observed with low index Pt single crystal surfaces. On cycling to higher potential limits (1.0 and 1.2 V), the adsorbed anions are replaced with the oxygenated species or oxide; the protective oxide layer helps to stabilize the electrochemical surface area (ESA) of the Pt nanoparticles. With cycling, both Pt-NCs and Pt-CO eventually get converted to Pt-PC. These results are supported with cyclic voltammograms, irreversible adsorption of Bi and Ge, and HR-TEM.