The development of dual catalysts with high efficiency toward oxygen reduction and evolution reactions (ORR and OER) in acidic media is a significant challenge. Here an active and durable dual catalyst based upon cubic Pt39Ir10Pd11nanocages with an average edge length of 12.3 nm, porous walls as thin as 1.0 nm, and well‐defined {100} facets is reported. The trimetallic nanocages perform better than all the reported dual catalysts in acidic media, with a low ORR‐OER overpotential gap of only 704 mV at a Pt‐Ir‐Pd loading of 16.8 µgPt+Ir+Pdcm−2geo. For ORR at 0.9 V, when benchmarked against the commercial Pt/C and Pt‐Pd nanocages, the trimetallic nanocages exhibit an enhanced mass activity of 0.52 A mg−1Pt+Ir+Pd(about four and two times as high as those of the Pt/C and Pt‐Pd nanocages) and much improved durability. For OER, the trimetallic nanocages show a remarkable mass activity of 0.20 A mg−1Pt+Irat 1.53 V, which is 16.7 and 4.3 fold relative to those of the Pt/C and Pt‐Pd nanocages, respectively. These improvements can be ascribed to the highly open structure of the nanocages, and the possible electronic coupling between Ir and Pt atoms in the lattice.
This article reports a facile method for the synthesis of Pd‐Ru nanocages by activating the galvanic replacement reaction between Pd nanocrystals and a Ru(III) precursor with I
- Award ID(s):
- 1804970
- NSF-PAR ID:
- 10458620
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Small Methods
- Volume:
- 4
- Issue:
- 5
- ISSN:
- 2366-9608
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
more » « less
Abstract A relatively unexplored aspect of noble‐metal nanomaterials is polymorphism, or their ability to crystallize in different crystal phases. Here, a method is reported for the facile synthesis of Ru@Pd core–shell nanocrystals featuring polymorphism, with the core made of hexagonally close‐packed (
hcp) ‐Ru while the Pd shell takes either anhcp or face‐centered cubic (fcc) phase. The polymorphism shows a dependence on the shell thickness, with shells thinner than ≈1.4 nm taking thehcp phase whereas the thicker ones revert tofcc . The injection rate provides an experimental knob for controlling the phase, with one‐shot and drop‐wise injection of the Pd precursor corresponding tofcc ‐Pd andhcp ‐Pd shells, respectively. When these nanocrystals are tested as catalysts toward formic acid oxidation, the Ru@Pdhcp nanocrystals outperform Ru@Pdfcc in terms of both specific activity and peak potential. Density functional theory calculations are also performed to elucidate the origin of this performance enhancement. -
more » « less
Abstract Noble‐metal nanoboxes offer an attractive form of nanomaterials for catalytic applications owing to their open structure and highly efficient use of atoms. Herein, we report the facile synthesis of Ag−Ru core−shell nanocubes and then Ru nanoboxes with a hexagonal close‐packed
(hcp ) structure, as well as evaluation of their catalytic activity toward a model hydrogenation reaction. By adding a solution of Ru(acac)3in ethylene glycol (EG) dropwise to a suspension of silver nanocubes in EG at 170 °C, Ru atoms are generated and deposited onto the entire surface of a nanocube. As the volume of the RuIIIprecursor is increased, Ru atoms are also produced through a galvanic replacement reaction, generating Ag−Ru nanocubes with a hollow interior. The released Ag+ions are then reduced by EG and deposited back onto the nanocubes. By selectively etching away the remaining Ag with aqueous HNO3, the as‐obtained Ag−Ru nanocubes are transformed into Ru nanoboxes, whose walls are characterized by anhcp structure and an ultrathin thickness of a few nanometers. Finally, we evaluated the catalytic properties of the Ru nanoboxes with two different wall thicknesses by using a model hydrogenation reaction; both samples showed excellent performance. -
more » « less
Abstract Despite the pivotal roles played by halide ions (e. g., Cl−and Br−) in directing the evolution of seeds into metal nanocrystals with diverse shapes, it is still unclear how halides affect the reduction kinetics of a salt precursor and thus the outcome of a synthesis. Here we report a quantitative analysis of the multiple roles played by halides in controlling the growth behaviors of Pd seeds with cubic and octahedral shapes, respectively. Our quantitative measurements clearly indicate the existence of a transition point around 10−3 mM min−1for the reduction rate, which separates the reduction into two distinctive pathways (solution
versus surface) for the formation of completely different products. More significantly, we demonstrate that the speciation, reduction kinetics, and reduction pathway of a Pd(II) precursor can all be manipulated by varying the type and/or amount of halides introduced into a synthesis for the deterministic formation of a specific product. This work represents a critical step forward in achieving a quantitative understanding of the multiple roles of halides involved in the shape‐controlled synthesis of Pd nanocrystals, with the knowledge potentially extendible to other noble metals and their alloys. -
more » « less
Abstract This article describes a systematic study of the oxidative etching and regrowth behaviors of Pd nanocrystals, including single‐crystal cubes bounded by {100} facets, single‐crystal octahedra and tetrahedra enclosed by {111} facets; and multiple‐twinned icosahedra covered by {111} facets and twin boundaries. During etching, Pd atoms are preferentially oxidized and removed from the corners regardless of the type of nanocrystal, and the resultant Pd2+ions are then reduced back to elemental Pd. For cubes and icosahedra, the newly formed Pd atoms are deposited on the {100} facets and twin boundaries, respectively, due to their relatively higher energies. For octahedra and tetrahedra, the Pd atoms self‐nucleate in the solution phase, followed by their growth into small particles. We can control the regrowth rate relative to etching rate by varying the concentration of HCl in the reaction solution. As the concentration of HCl is increased, 18‐nm Pd cubes are transformed into octahedra of 23, 18, and 13 nm, respectively, in edge length. Due to the absence of regrowth, however, Pd octahedra are transformed into truncated octahedra, cuboctahedra, and spheres with decreasing sizes whereas Pd tetrahedra evolve into truncated tetrahedra and spheres. In contrast, Pd icosahedra with twin boundaries on the surface are converted to asymmetric icosahedra, flower‐like icosahedra, and spheres. This work not only advances the understanding of etching and growth behaviors of metal nanocrystals with various shapes and twin structures but also offers an alternative method for controlling their shape and size.
