Synthesis and Characterization of 9 nm Pt–Ni Octahedra with a Record High Activity of 3.3 A/mg_Pt for the Oxygen Reduction Reaction

Abstract

Nanoscale Pt-Ni bimetallic octahedra with controlled sizes have been actively explored in recent years owning to their outstanding activity for the oxygen reduction reaction (ORR). Here we report the synthesis of uniform 9 nm Pt-Ni octahedra with the use of oleylamine and oleic acid as surfactants and W(CO)6 as a source of CO that can promote the formation of {111} facets in the presence of Ni. Through the introduction of benzyl ether as a solvent, the coverage of both surfactants on the surface of resultant Pt-Ni octahedra was significantly reduced while the octahedral shape was still attained. By further removing the surfactants through acetic acid treatment, we observed a specific activity 51-fold higher than that of the state-of-the-art Pt/C catalyst for the ORR at 0.93 V, together with a record high mass activity of 3.3 A mgPt(-1) at 0.9 V (the highest mass activity reported in the literature was 1.45 A mgPt(-1)). Our analysis suggests that this great enhancement of ORR activity could be attributed to the presence of a clean, well-preserved (111) surface for the Pt-Ni octahedra.

Shape-controlled synthesis of Pt-Ir nanocubes with preferential (100) orientation and their unusual enhanced electrocatalytic activities

“…Previous studies from several groups [28,31,54,55] demonstrate the key role of W(CO) 6 in the shape control formation of Pt-based bimetallic NPs. For example, Choi et al [55] and Zhang et al [56] demonstrated the key role of W(CO) 6 in the formation of Pt-Ni and Pt-Cu octahedra enclosed with (111) facets, while Zhang et al [54] found that the presence of W(CO) 6 favors the formation of Pt-Fe, Pe-Co nanocubes. The present work reveals that an appropriate amount of W(CO) 6 is essential for the formation of Pt-Ir nanocubes.…”

“…It has been reported that the CO released from the decomposition of W(CO) 6 adsorbs preferentially onto specific surfaces, contributing to the shape-control formation of Pt-based NPs [56,57]. For pure Pt, CO binds preferentially onto the Pt (100) surface, which results in the formation of Pt nanocubes [55]. However, it is complicated for the Pt alloy NPs.…”

“…However, it is complicated for the Pt alloy NPs. For instance, Choi et al [55] found that introducing a second metal such as Ni and Cu can change the absorption preference of CO from Pt (100) to Pt (111), leading to the formation of an octahedral shape. In contrast, the addition of Fe, Co or Ir in the present work does not change the CO selectively capping on the Pt (100) surface and thus favors the formation of a cubic shape [54,55].…”

“…For instance, Choi et al [55] found that introducing a second metal such as Ni and Cu can change the absorption preference of CO from Pt (100) to Pt (111), leading to the formation of an octahedral shape. In contrast, the addition of Fe, Co or Ir in the present work does not change the CO selectively capping on the Pt (100) surface and thus favors the formation of a cubic shape [54,55]. Furthermore, Zhang et al [31,54] proposed that W atoms decomposed from W(CO) 6 could reduce Pt(acac) 2 to Pt atoms rapidly in the early stage of the reaction, whereas the resultant W cations may be accumulated that will decelerate the subsequent particle growth in the next stage of the reaction [31,54].…”

Elemental Anisotropic Growth and Atomic-Scale Structure of Shape-Controlled Octahedral Pt–Ni–Co Alloy Nanocatalysts

“…These are the premises that led to establish {111}-Pt 3 Ni surfaces as the ideal electrocatalyst for the ORR 18,19 . Since then, many synthetic routes to obtain PtNi nanooctahedra, which ideally exhibit 8 facets with (111) atomic arrangement, have been developed, in which the co-reduction of the metal precursors takes place in the solution-phase [20][21][22][23][24] . A recent study 25 has shed light onto the growth mechanism of binary PtNi octahedral nanoparticles, revealing an anisotropic growth where a Pt-rich phase first develops into hexapod-like concave NCs in a ligand-controlled kinetic process, followed by a layer-by-layer deposition of a Ni-rich phase at the concave {111} facets.…”