Quantitative Analysis of the Reduction Kinetics Responsible for the One-Pot Synthesis of Pd–Pt Bimetallic Nanocrystals with Different Structures

Abstract

We report a quantitative understanding of the reduction kinetics responsible for the formation of Pd-Pt bimetallic nanocrystals with two distinctive structures. The syntheses involve the use of KBr to manipulate the reaction kinetics by influencing the redox potentials of metal precursor ions via ligand exchange. In the absence of KBr, the ratio between the initial reduction rates of PdCl4(2-) and PtCl4(2-) was about 10.0, leading to the formation of Pd@Pt octahedra with a core-shell structure. In the presence of 63 mM KBr, the products became Pd-Pt alloy nanocrystals. In this case, the ratio between the initial reduction rates of the two precursors dropped to 2.4 because of ligand exchange and, thus, the formation of PdBr4(2-) and PtBr4(2-). The alloy nanocrystals took a cubic shape owing to the selective capping effect of Br(-) ions toward the {100} facets. Relative to the alloy nanocubes, the Pd@Pt core-shell octahedra showed substantial enhancement in both catalytic activity and durability toward the oxygen reduction reaction (ORR). Specifically, the specific (1.51 mA cm(-2)) and mass (1.05 A mg(-1) Pt) activities of the core-shell octahedra were enhanced by about four- and three-fold relative to the alloy nanocubes (0.39 mA cm(-2) and 0.34 A mg(-1) Pt, respectively). Even after 20000 cycles of accelerated durability test, the core-shell octahedra still exhibited a mass activity of 0.68 A mg(-1) Pt, twice that of a pristine commercial Pt/C catalyst.

Synthesis of Colloidal Metal Nanocrystals: A Comprehensive Review on the Reductants

“…Controlling the reduction kinetics of a salt precursor is a powerful means to control the shapes and structures of metal nanocrystals and thus optimizing their performance in an array of applications. Despite the incredible progress over the last decade, it remains a grand challenge to rationally design a protocol for synthesizing metal nanocrystals with various shapes and structures due to the lack of a quantitative knob for controlling the syntheses . In this section, we focus on the explicit role of reduction kinetics in the synthesis of nanocrystals, which allows us to precisely tune the nucleation and growth pathways in a predictable way.…”

“…In this section, we focus on the explicit role of reduction kinetics in the synthesis of nanocrystals, which allows us to precisely tune the nucleation and growth pathways in a predictable way. To this end, the reduction kinetics was systematically investigated with respect to a set of experimental parameters, such as reaction temperature, the types of precursor and reductant, as well as their concentrations . In these studies, the reduction kinetics was demonstrated to play a pivotal role in generating metal nanocrystals with desired and predictable shapes, structures, and compositions (for systems involving more than one types of metals) by quantitatively correlating the outcome of a synthesis with a set of experimental parameters.…”

Oxygen Reduction Activity and Durability of Ordered and Disordered Pt3Co Alloy Nanoparticle Catalysts at Practical Temperatures of Polymer Electrolyte Fuel Cells

“…2∼7 times compared to that of pure Pt. The enhancement factor has been found to depend on various properties of alloy nanoparticles, e.g., composition, 4,[14][15][16] shape (or size), [17][18][19][20][21] and crystal structure. [22][23][24][25][26][27][28][29] For example, the values of j k for Pt-Co alloys showed a maximum at the atomic ratio of Pt/Co = 3.…”

Shape Control of Monodispersed Sub‐5 nm Pd Tetrahedrons and Laciniate Pd Nanourchins by Maneuvering the Dispersed State of Additives for Boosting ORR Performance

“…For the synthesis of sub-5 nm Pd tetrahedrons, the solution quickly turned to light brown at 2 min, deep brown at 4 min, and dark at 6 min; meanwhile, the synthetic solution of Pd LUs gradually changed from yellow to light brown, deep brown, and black within 1 h. As such, in a typical measurement, each reaction was sampled over the first 30 min period in 2 min intervals and the next 120 min period. According to the pseudo-first-order reaction rate law, ln[A] t = −kt + ln[A] 0 , where [A] 0 is related to the beginning molar concentrations of the precursor, and [A] t is related to the molar concentrations of the precursor at a time of t. [38,39] The k values of the sub-5 nm Pd tetrahedrons and Pd LUs were calculated to be 1.2 × 10 −3 and 9 × 10 −4 s −1 , respectively ( Figure 7e). As soon as the sample was removed from the reaction solution, it was immediately injected into an excess amount of KBr solution to quench the reduction and shift the absorption peak to 312 or 353 nm, respectively.…”