Ni–Pt Core–Shell Nanoparticles as Oxygen Reduction Electrocatalysts: Effect of Pt Shell Coverage

Abstract

CoreÀshell nanoparticulate catalysts with a nonprecious metal core and a thin precious metal shell not only save precious metals but also could enhance the catalytic performance of precious metals through properly tuned strain and ligand effects. In this study, we show that, in addition to the nature and composition of core metals, the electrocatalytic properties of the precious metal shell can be tuned by varying its surface coverage. Carbon-supported NiÀPt coreÀshell nanoparticle catalysts (NiÀPt/C) with a series of Pt coverages are synthesized by depositing different amounts of Pt on Ni nanoparticles ca. 5 nm in size. It is found that Pt approximately forms an extended layer on Ni particles as its coverage does not exceed that required for a monolayer formation. The electrocatalytic properties of the NiÀPt/C catalysts, such as the stripping potential for the oxygenated adsorbates, the activity for the oxygen reduction reaction (OPR), and the electrochemical stability under continuous potential cycling, exhibit a volcano type of dependence on Pt coverage, with the apex occurring near the monolayer. This suggests that coreÀshell nanoparticles with a monolayer Pt shell would be active and durable catalysts for the ORR and that extra Pt benefits neither the ORR activity nor the durability of the coreÀshell structured electrocatalysts.

Mo@Pt core–shell nanoparticles as an efficient electrocatalyst for oxygen reduction reaction

“…In the past two decades, various 3d transition metals such as Fe [13][14][15], Co [16][17][18][19], Ni [20][21][22], and Cu [23][24][25] have been shown to significantly promote the ORR activity of Pt due to the strain and ligand effects [26]. However, the reported electrocatalysts have a durability problem for a long-term use owing to most of 3d transition metals suffering from acid leaching [27].…”

Core–Shell-Structured Low-Platinum Electrocatalysts for Fuel Cell Applications

“…Here, optimal performances were achieved by using a monolayer of Pt, whereas shell thicknesses of 2~3 atomic layers lead to behaviors which were almost identical to pure Pt nanoparticles. Chen et al [194] also reported that optimal ORR activity and stability under continuous potential cycling of Ni@Pt core-shell electrocatalysts occurred with a Pt monolayer [194]. All of these reports suggest that a monolayer Pt shell is the optimal thickness for core-shellstructured Ni@Pt ORR electrocatalysts.…”

“…3. The large mismatch between Pt and these 3d metals can result in strong compressive strain, which leads to serious distortions of Pt lattices, resulting in decreased stability of Pt skin structures [147,194].…”

Realization of Both High-Performance and Enhanced Durability of Fuel Cells: Pt-Exoskeleton Structure Electrocatalysts

“…Chen et al have investigated the effect of Pt shell coverage for Ni-Pt core-shell nanoparticles and concluded that increasing the Pt content increased neither the ORR activity nor the durability of the catalyst. 19 However, Choi et al have reported that electrocatalysts with thin Pt shells (Pd:Pt = 1:0.5 and 1:1.0) are less stable than those with thick Pt shells (Pd:Pt = 1:1.5) during harsh potential cycling. 20 Sasaki and Choi independently studied the same materials and obtained different results.…”