High Density Catalytic Hot Spots in Ultrafine Wavy Nanowires

Abstract

Structural defects/grain boundaries in metallic materials can exhibit unusual chemical reactivity and play important roles in catalysis. Bulk polycrystalline materials possess many structural defects, which is, however, usually inaccessible to solution reactants and hardly useful for practical catalytic reactions. Typical metallic nanocrystals usually exhibit well-defined crystalline structure with few defects/grain boundaries. Here, we report the design of ultrafine wavy nanowires (WNWs) with a high density of accessible structural defects/grain boundaries as highly active catalytic hot spots. We show that rhodium WNWs can be readily synthesized with controllable number of structural defects and demonstrate the number of structural defects can fundamentally determine their catalytic activity in selective oxidation of benzyl alcohol by O2, with the catalytic activity increasing with the number of structural defects. X-ray photoelectron spectroscopy (XPS) and cyclic voltammograms (CVs) studies demonstrate that the structural defects can significantly alter the chemical state of the Rh WNWs to modulate their catalytic activity. Lastly, our systematic studies further demonstrate that the concept of defect engineering in WNWs for improved catalytic performance is general and can be readily extended to other similar systems, including palladium and iridium WNWs.

Electrodeposition of Rhodium Nanowires Arrays and Their Morphology-Dependent Hydrogen Evolution Activity

“…Up to now, the most promising solution to increase the surface area has been to prepare Rh structures at the nanoscale, which can expose more atoms to the application environment. Many approaches have been reported to synthesize Rh nanocrystals suspended in liquid solutions [9,10,11,12,13] and other 1D nanowires [14,15] and nanotubes [16,17]. Rh crystals at the nanoscale size theoretically can provide high surface area per mass unit, but surface area is unavoidably lost due to the stacking of nanocrystals when immobilized onto a solid substrate for heterogeneous catalysis applications.…”

Mesoporous metallic rhodium nanoparticles

“…has shown that the convex Rh nanocrystals bound by {830} facets exhibit higher activity for ethanol electro-oxidation than irregular Rh nanoparticles, as well as commercial Rh black41. Huang and co-authors pointed out that wavy Rh nanowires have numerous structural defects/grain boundaries that are responsible for high catalytic activity42. Additionally, two-dimensional (2D) Rh nanosheets with exposed Rh atoms in ultrathin layered nanostructures perform well in hydrogenation reactions43.…”

Synthesis of single-crystal hyperbranched rhodium nanoplates with remarkable catalytic properties

“…Importantly, these catalysts exhibited remarkably different current density in the oxygen adsorption/desorption region (0.10-0.80 V). It is well-known that the low-coordinated atoms such as steps, kinks, or structural defects can greatly enhance the oxygen adsorption, thus resulting in large oxygen adsorption/desorption currents [31,40]. All the hyperbranched Rh triangle nanoplates showed larger oxygen adsorption/desorption currents than the commercial Rh black, with Rh branch-6:2 exhibiting the largest current value.…”

“…In the last decade, great efforts have been made to improve the catalytic properties of this noble metal by tailoring the morphologies and surface structures of Rh NCs [32][33][34][35][36][37][38][39][40]. However, owing to the extraordinarily high surface free energy of Rh, successful approaches leading to Rh NCs with high density of low-coordinated edge/corner sites or large surface-tovolume ratios have been scarcely described in the literature.…”