Inflating hollow nanocrystals through a repeated Kirkendall cavitation process

Abstract

The Kirkendall effect has been recently used to produce hollow nanostructures by taking advantage of the different diffusion rates of species involved in the chemical transformations of nanoscale objects. Here we demonstrate a nanoscale Kirkendall cavitation process that can transform solid palladium nanocrystals into hollow palladium nanocrystals through insertion and extraction of phosphorus. The key to success in producing monometallic hollow nanocrystals is the effective extraction of phosphorus through an oxidation reaction, which promotes the outward diffusion of phosphorus from the compound nanocrystals of palladium phosphide and consequently the inward diffusion of vacancies and their coalescence into larger voids. We further demonstrate that this Kirkendall cavitation process can be repeated a number of times to gradually inflate the hollow metal nanocrystals, producing nanoshells of increased diameters and decreased thicknesses. The resulting thin palladium nanoshells exhibit enhanced catalytic activity and high durability toward formic acid oxidation.

Self‐Templating Approaches to Hollow Nanostructures

“…Solid metal nanocrystals of M, which become solid nanocrystals of MX after reacting with species X due to the faster inward diffusion of X than M, can be eventually converted to hollow metal nanocrystals with an increased outer diameter through the Kirkendall effect by extracting the faster diffusing species X, as schematically illustrated in Figure a. As a specific example, we reported this “inverse” Kirkendall voiding process by demonstrating the transformation of solid Pd nanocrystals into hollow Pd nanocrystals through insertion and extraction of P . We first synthesized Pd nanocubes with an average edge length of 18 nm.…”

“…High‐resolution HAADF‐STEM images of the obtained hollow nanocrystals after c) one, d) two, and e) three cavitation cycles. Reproduced with permission . Copyright 2017, Nature Publishing Group.…”

Structure-induced hollow Co3O4 nanoparticles with rich oxygen vacancies for efficient CO oxidation

“…Besides, it has been reported that the surface atomic configuration of Co 3 O 4 was strongly influenced by its morphology [12]. Specially, metal oxides with hollow structures were demonstrated to possess more defect sites on their surfaces than the solid counterparts [13][14][15][16][17][18]. Therefore, we could reasonably speculate that fabrication of Co 3 O 4 with hollow structure may maximize the oxygen vacancies on its surface to achieve high catalytic efficiency in CO oxidation.…”

A Universal Strategy toward Ultrasmall Hollow Nanostructures with Remarkable Electrochemical Performance

“…In this regard, with pure bare metal nanoparticles as precursors, liquid‐phase injection synthesis and solid–gas reaction have been mostly employed to produce hollow metallic compounds nanostructures . For example, hollow CoSe 2 , Fe 2 O 3 , Fe 3 O 4 , Co 9 S 8 , PdP 2 , and Ni 2 P nanoparticles were successfully fabricated. However, these preparation methods usually yield relatively large hollow nanoparticles (>40 nm) with single metal components, which suffer from the inefficient large‐scale preparation of dispersed/discrete metal nanoparticles and uncontrollable Kirkendall diffusion process .…”