Growth of Concave Polyhedral Pd Nanocrystals with 32 Facets Through In Situ Facet‐Selective Etching

Abstract

The control over crystal-plane exposure of nanoparticles in a variety of shapes and material types (such as metals and metal oxides) has attracted much attention because fascinating properties might be accomplished. [1][2][3] In the case of metallic nanocrystals (NCs), it has been demonstrated that the exposed crystal facets of metallic NCs have a large influence on their catalytic reactivity and selectivity. [4][5][6][7] Recent studies indicate that high-index facets of a face-centered cubic (fcc) metal (e.g., Pd, Pt, and Au) generally exhibit significantly enhanced catalytic activity toward specific reactions compared to low-index facets because of a high density of low-coordinated surface atoms. [8][9][10][11][12][13] However, up to date, studies on the design and synthesis of metallic nanostructures enclosed by high-index facets are still insufficient. High-index facets usually disappear during the growth of NCs due to their high surface energies. [14] However, recent studies have shown that the exposure of high-index facets could be realized by tuning the growth kinetics, [15,16] the selective adsorption of specific chemical species, [17][18][19][20] and their epitaxial growth from seeds terminating in high-index facets. [21,22] Herein, we report a synthetic strategy that allows the highyield fabrication of concave polyhedral Pd NCs with 32 facets that are rich in atomic steps and defects on the surface. This nanostructure was successfully prepared through an in situ facet-selective etching growth route. The vital role that iodide ions (I À ) together with ethanolamine as the surface controller play in the formation of concave polyhedral Pd NCs having catalytic active sites is demonstrated. The concave polyhedral Pd NCs exhibit significantly enhanced specific and mass activities towards the electrooxidation of ethanol in comparison to truncated octahedral Pd NCs and commercial Pd black catalysts with low-index facets.In a typical synthesis of concave polyhedral Pd NCs, poly-(vinyl pyrrolidone) (PVP, M W = 30 000), NaI, and an aqueous Na 2 PdCl 4 solution were mixed together with ethanolamine. The resulting homogeneous solution was transferred to a Teflon-lined stainless-steel autoclave with a capacity of 12 mL. The sealed vessel was then heated at 200 8C for 6 h before it was cooled to room temperature (see the Experimental Section for synthesis details). The resulting products were collected by centrifugation and washed several times with water and ethanol.The representative electron microscopic images of the asobtained Pd NCs are shown in Figure 1. As depicted by transmission electron microscopic (TEM) images in Figure 1 a and Figure S1 c and d in the Supporting Information, the product consists of well-shaped NCs with a yield above 90 % and an average apex-to-apex distance of 50 nm. The nanoparticles display a darker contrast in the center compared to the edges, indicating the possible presence of concave features in the NCs. The scanning electron microscopic (SEM) images shown in Figure 1 b and Figure S1...

Solvothermal synthesis of metal nanocrystals and their applications

“…(F-I) Reproduced with permission from Ref. [88,95,90,89], respectively. (J-K) Reproduced with permission from Ref.…”

“…The reversible hydrogen absorption/desorption on Pd shells of Au-Pd core-shell nanocrystals has been exploited for the development of highly spectrally responsive and reusable hydrogen sensors using gold core as plasmonic antennae [87]. Pd nanocrystals with varying morphologies synthesized by solvothermal synthesis methods are shown in Table 2 [88][89][90][91][92][93][94][95][96]. Monodisperse Pd icosahedra ( Fig.…”

“…Another concave structure, concave polyhedral Pd nanocrystals with 32 facets, was prepared in aqueous solutions containing Na 2 PdCl 4 , ethanolamine, NaI, and PVP with a yield above 90% (Fig. 2G) [95]. Small truncated octahedra are the primary product at early reaction stage.…”

In Search of Excellence: Convex versus Concave Noble Metal Nanostructures for Electrocatalytic Applications

“…For instance, Zhang et al reported the highyield fabrication of concave polyhedral Pd nanocrystals with 32 facets that contained multiple atomic steps and defects on their surfaces. [44] The utilized reaction solution consisted of PVP, NaI, and Na 2 PdCl 4 , while the solvent was a mixture of ethanolamine and deionized water. The iodide (I − ) and ethanolamine components played a critical role in forming concave polyhedra with 32 facets.…”

“…[45] Because the facet energies differ as E {100} > E {111} , I − species preferentially etch the {100} nanocrystal facets, which leads to the ultimate formation of concave polyhedral Pd nanocrystals with an octapodal structure. [44] Chen and co-workers successfully synthesized concave rhodium nanocubes via a one-pot solution method using an etchant. [46] A typical synthesis procedure was performed in a Teflon-lined stainless-steel autoclave containing RhCl 3 , PVP, KBr, HCl, and ultra-pure water.…”