Hollow Metal Nanocrystals with Ultrathin, Porous Walls and Well‐Controlled Surface Structures

Abstract

Recent developments of a novel class of catalytic materials built on hollow nanocrystals having ultrathin, porous walls, and well-controlled surface structures are discussed, with a focus on platinum and the oxygen reduction reaction (ORR). An introduction is given to the critical role of platinum in the proton exchange membrane fuel cells, and the pressing need to develop a strategy for achieving cost-effective and sustainable use of this precious metal. How to maximize the mass activity of ORR catalysts based on platinum by rationally engineering the surface structure while increasing the utilization efficiency of atoms is then discussed. After reporting on the synthetic methods involving galvanic replacement and seed-mediated growth followed by etching, respectively, a number of examples to demonstrate the enhancement in activity and durability for this new class of catalytic materials are showcased. The feasibility to have the methodology extended from platinum to other precious metals such as gold and ruthenium is highlighted. In conclusion, some of the remaining issues and emerging solutions are examined.

One‐Pot Synthesis of Pd@PtnL Core‐Shell Icosahedral Nanocrystals in High Throughput through a Quantitative Analysis of the Reduction Kinetics

“…These low‐coordinated sites have been demonstrated to cause a stronger Pt−O binding and thereby limiting the removal of absorbed O and OH species, which are the typical products of ORR. Consequently, the ORR activity of the Pt icosahedral nanocages in the present study was compromised . Given the rough surface of the Pt shell, we expected that the catalytic stability of both the Pd@Pt 4.5L core‐shell icosahedra and Pt icosahedral nanocages reported in the current work should not surpass those we have reported for the similar ORR catalysts, prepared using seed‐mediated growth .…”

“…A variety of Pd@Pt n L core‐shell nanocrystals have been successfully synthesized, including those with a cubic, octahedral, decahedral, or icosahedral shape . The synthetic method typically involves multiple steps, including synthesis and washing of seeds, as well as conformal deposition of a Pt shell on the core . As a major drawback, each batch of synthesis could only produce about 1 mg of the core‐shell nanocrystals, which is far away from the amount typically required for catalytic evaluation.…”

“…[24][25][26][27][28][29][30] The synthetic method typicallyi nvolves multiple steps, including synthesis and washing of seeds, as well as conformal deposition of aP ts hell on the core. [31,32] As am ajor drawback, each batch of synthesis could only produce about 1mgo ft he core-shell nanocrystals, which is far away from the amount typically required forc atalytic evaluation. Meanwhile, it is challenging to increase the throughput of such as ynthesis because the conformal deposition of Pt shell requires slow injection of ad ilute Pt II precursor into the reactor,i no rder to avoid self-nucleation for the resultant Pt atoms.…”

Fine‐Tuning Intrinsic Strain in Penta‐Twinned Pt–Cu–Mn Nanoframes Boosts Oxygen Reduction Catalysis

“…Based on the aforementioned TEM and ICP‐OES data, it is reasonable to assume that a galvanic replacement reaction occurred between Cu atoms on the surface and Pt 4+ in the solution. After replacement, Pt atoms deposited preferably on the high surface energy regions such as ridges and edges . Meanwhile, Mn precursor was reduced by reducing agent, giving rise to the slight increase of content.…”

Facile Synthesis of Pt Icosahedral Nanocrystals with Controllable Sizes for the Evaluation of Size‐Dependent Activity toward Oxygen Reduction

“…[12] Tremendous efforts have been devoted to the synthesis of Pt nanocrystals enclosed by diverse, but well-defined, surface structures in an effort to tailor and then optimize the catalytic properties. [13][14][15][16][17][18][19] Among Pt polyhedral nanocrystals, those with an icosahedral shape represent a class of attractive materials for catalysis owing to the presence of a high density of twin defects and well-defined {111} facets. [20][21][22][23][24][25] Thus far, there are only a few reports on the synthesis of Pt icosahedral nanocrystals.…”