Direct Synthesis of Intermetallic Platinum–Alloy Nanoparticles Highly Loaded on Carbon Supports for Efficient Electrocatalysis

Abstract

Compared to nanostructured platinum (Pt) catalysts, ordered Pt-based intermetallic nanoparticles supported on a carbon substrate exhibit much enhanced catalytic performance, especially in fuel cell electrocatalysis. However, direct synthesis of homogeneous intermetallic alloy nanocatalysts on carbonaceous supports with high loading is still challenging. Herein, we report a novel synthetic strategy to directly produce highly dispersed MPt alloy nanoparticles (M = Fe, Co, or Ni) on various carbon supports with high catalyst loading. Importantly, a unique bimetallic compound, composed of [M­(bpy)3]2+ cation (bpy = 2,2′-bipyridine) and [PtCl6]2– anion, evenly decomposes on carbon surface and forms uniformly sized intermetallic nanoparticles with a nitrogen-doped carbon protection layer. The excellent oxygen reduction reaction (ORR) activity and stability of the representative reduced graphene oxide (rGO)-supported L10-FePt catalyst (37 wt %-FePt/rGO), exhibiting 18.8 times higher specific activity than commercial Pt/C catalyst without degradation over 20 000 cycles, well demonstrate the effectiveness of our synthetic approach toward uniformly alloyed nanoparticles with high homogeneity.

Pt‐based Intermetallic Nanocatalysts for Promoting the Oxygen Reduction Reaction

“…The use of Pt–M intermetallic catalysts can drive further promotion in catalytic activity of Pt–M alloys 22–34 . The intermetallic structure maximizes the number of Pt–M bonds and engenders the intensified electronic interaction (strain and ligand effects) between the Pt and M elements, resulting in an additional activity enhancement.…”

“…The intensity of the strain effect is dependent on the crystal structure of the interior atoms underneath the surface Pt atoms on a catalyst. While the Pt–M alloy mostly preserves the crystal structure of the constituent Pt and M element, the disorder‐to‐order transformation often turns the crystal structure of the Pt–M alloy into a new phase in the Pt–M intermetallic structure 22–30,32–34 . Since the crystal structure transformation accompanies the changes in the average bond lengths of Pt–M and Pt–Pt, an intermetallic structure typically induces a higher degree of lattice mismatch than an alloy.…”

“…In terms of synthetic simplicity, coating with a carbon shell is a more efficient approach, as the carbon shell does not need to be removed. The carbon shell not only plays the role of protective layer, but also boosts the electric conductivity of the final catalyst 29,33,62 . Hyeon, Sung, and coworkers reported the synthesis of PtFe L1 0 intermetallic NPs coated with an N‐doped carbon shell using dopamine‐coated PtFe alloy NPs (Figure 4(a)).…”

“…The ordered atomic arrangement, which arises from the strong interaction between the two metal elements, leads to excellent chemical stability. During the last decade, intermetallic catalysts whose ORR stability is higher than their random alloy analogs have been reported 27–34 . Interestingly, these intermetallic catalysts have also demonstrated higher intrinsic activity than their alloy counterparts with the same composition 22–26,31 .…”

Surface/Near‐Surface Structure of Highly Active and Durable Pt‐Based Catalysts for Oxygen Reduction Reaction: A Review

“…Recently, carbon shell‐protected Pt–M intermetallics were synthesized through heat treating bimetallic compound of [M(bpy) 3 ] 2+ [PtCl 6 ] 2− (M = Fe, Co and Ni), which decomposed on carbon surface and formed intermetallic nanoparticles protected by the nitrogen‐doped carbon layer. [ 118 ] The protected PtFe intermetallic nanoparticles endowed robust stability and activity, which showed 18 times higher than Pt/C in specific activity for ORR without degradation over stability tests.…”