Synthesis and Characterization of Pt–Ag Alloy Nanocages with Enhanced Activity and Durability toward Oxygen Reduction

Abstract

Engineering the elemental composition of metal nanocrystals offers an effective strategy for the development of catalysts or electrocatalysts with greatly enhanced activity. Herein, we report the synthesis of Pt-Ag alloy nanocages with an outer edge length of 18 nm and a wall thickness of about 3 nm. Such nanocages with a composition of PtAg could be readily prepared in one step through the galvanic replacement reaction between Ag nanocubes and a Pt(II) precursor. After 10 000 cycles of potential cycling in the range of 0.60-1.0 V as in an accelerated durability test, the composition of the nanocages changed to PtAg, together with a specific activity of 1.23 mA cm toward oxygen reduction, which was 3.3 times that of a state-of-the-art commercial Pt/C catalyst (0.37 mA cm) prior to durability testing. Density functional theory calculations attributed the increased activity to the stabilization of the transition state for breaking the O-O bond in molecular oxygen. Even after 30 000 cycles of potential cycling, the mass activity of the nanocages only dropped from 0.64 to 0.33 A mg, which was still about two times that of the pristine Pt/C catalyst (0.19 A mg).

Defects and Interfaces on PtPb Nanoplates Boost Fuel Cell Electrocatalysis

“…Previous studies reveal that the catalytic behaviors of metallic nanocrystals are heavily influenced by their composition, shape, and structure . This has stimulated the researchers to explore new procedures for making different types of Pt‐based nanocrystals with the optimized parameters for enhancing catalytic activity through adding control agents during the growth, including wires, cages, plates, cubes, spheres, octahedral, and icosahedra . However, these well‐known controls still show the limited ability to maximize the Pt utilization efficiency for achieving more efficient fuel cell catalysis.…”

Controlled Synthesis of Octahedral Platinum‐Based Mesocrystals by Oriented Aggregation

“…In addition, the mass activity of the octahedral Pt-Ag alloy mesocrystals (0.31 Amg Pt À1 )w as also enhanced compared with that of the quasi-spherical Pt-Ag mesocrystals (0.19 Amg Pt À1 )a nd the Pt/C catalyst (0.21 Amg Pt À1 ), again confirming the superiore lectrocatalytic activity of the octahedral Pt-Ag alloy mesocrystals in ORR reactions. [16] Therefore, the octahedral Pt-Ag alloy mesocrystals exhibited am uch enhanced durability in retaining their catalytic activityc ompared with the commercial Pt/C catalyst. Due to the self-supported structure, am ajority of the ECSA of the octahedral Pt-Ag alloy mesocrystals has been retained ( % 70 %) during the cycling process ( Figure S6, Supporting Information).…”

“…To compare quantitatively, the specific andm ass activities werec alculated using the Koutecky-Levich equation, normalized against the ECSA and Pt mass of the catalysts, respectively (Figure 6c and d). The enhancement in the specific activity of the quasi-spherical Pt-Ag mesocrystals may be attributed to stabilized oxygen transitions tates due to the presence of Ag, [16] and to the reduced activation energy due to the presence of possible high-index facets at the junction area between adjacent crystallites. The enhancement in the specific activity of the quasi-spherical Pt-Ag mesocrystals may be attributed to stabilized oxygen transitions tates due to the presence of Ag, [16] and to the reduced activation energy due to the presence of possible high-index facets at the junction area between adjacent crystallites.…”

Solid‐to‐Hollow Conversion of Silver Nanocrystals by Surface‐Protected Etching

“…In a typical synthesis, Ag NSs (≈45 nm) were first prepared by a seeded growth method, as described in our previous report . Then, a very small amount of Pt was deposited on the surface of the Ag NSs for their stabilization by a galvanic replacement reaction in combination with a chemical reduction reaction with a Pt salt . Theoretically, a Pt/Ag ratio of approximately 2.1 mol % is required to form a Pt monolayer on the Ag NSs with a diameter of 45 nm (Supporting Information).…”