It is known that the surface-plasmon resonance (SPR) in small spherical Au nanoparticles of about 2 nm is strongly damped. We demonstrate that small Au nanorods of high aspect ratio develop a strong longitudinal SPR, of intensity comparable to that in Ag rods, as soon as the resonance energy drops below the onset of the interband transitions due to the geometry. We present ab initio calculations of time-dependent density-functional theory of rods with lengths of up to 7 nm. Changing length and width, not only the energy but also the character of the resonance in Au rods can be tuned. Moreover, the aspect ratio alone is not sufficient to predict even the character of the spectrum; the absolute size matters.

Achieving stability with highly active Ru nanoparticles for electrocatalysis is a major challenge for the oxygen evolution reaction. As improved stability of Ru catalysts has been shown for bulk surfaces with low-index facets, there is an opportunity to incorporate these stable facets into Ru nanoparticles. Now, a new solution synthesis is presented in which hexagonal close-packed structured Ru is grown on Au to form nanoparticles with 3D branches. Exposing low-index facets on these 3D branches creates stable reaction kinetics to achieve high activity and the highest stability observed for Ru nanoparticle oxygen evolution reaction catalysts. These design principles provide a synthetic strategy to achieve stable and active electrocatalysts.

Nanoparticles are the cornerstone of nanotechnology. Their crystal structure and relation to shape are still open problems despite a lot of advances in the field. The classical theory of nanoparticle stability predicts that for sizes <1.5-2 nm the icosahedral structure should be the most stable, then between around 2-5 nm, the decahedral shape should be the most stable. Beyond that, face-centered-cubic (FCC) structures will be the predominant phase. However, in the experimental side, icosahedral (I(h)) and decahedral (D(h)) particles can be observed much beyond the 5 nm limit. In fact, it is possible to find I(h) and D(h) particles even in the mesoscopic range. Conversely, it is possible to find FCC particles with a size <1.5 nm. In this paper we review a number of the mechanisms proposed in the literature that allow the stabilization of nanoparticles. Some of the mechanisms are very interrelated and it becomes difficult to distinguish between them.

MOF-derived nanocatalysts activated under reaction conditions display remarkable activity when compared to several controls.