Composition Tunability and (111)-Dominant Facets of Ultrathin Platinum–Gold Alloy Nanowires toward Enhanced Electrocatalysis

Abstract

The ability for tuning not only the composition but also the type of surface facets of alloyed nanomaterials is important for the design of catalysts with enhanced activity and stability through optimizing both ensemble and ligand effects. Herein we report the first example of ultrathin platinum-gold alloy nanowires (PtAu NWs) featuring composition-tunable and (111) facet-dominant surface characteristics, and the electrocatalytic enhancement for the oxygen reduction reaction (ORR). PtAu NWs of different bimetallic compositions synthesized by a single-phase and surfactant-free method are shown to display an alloyed, parallel-bundled structure in which the individual nanowires exhibit Boerdijk-Coxeter helix type morphology predominant in (111) facets. Results have revealed intriguing catalytic correlation with the binary composition, exhibiting an activity maximum at a Pt:Au ratio of ∼3:1. As revealed by high-energy synchrotron X-ray diffraction and atomic pair distribution function analysis, NWs of this ratio exhibit a clear shrinkage in interatomic bonding distances. In comparison with PtAu nanoparticles of a similar composition and degree of shrinking of atomic-pair distances, the PtAu NWs display a remarkably higher electrocatalytic activity and stability. The outperformance of NWs over nanoparticles is attributed to the predominant (111)-type facets on the surface balancing the contribution of ensemble and ligand effects, in addition to the composition synergy due to optimal adsorption energies for molecular and atomic oxygen species on the surface as supported by DFT computation of models of the catalysts. The findings open up a new pathway to the design and engineering of alloy nanocatalysts with enhanced activity and durability.

Non‐Noble‐Metal‐Based Electrocatalysts toward the Oxygen Evolution Reaction

“…5)Currently, most of the reported works are based on ex situ techniques, which only give the characterization results of OER catalysts before and after electrochemical measurements but cannot provide the structural evolution information during the OER process. Therefore, in situ techniques are desirable for characterizing the structure–activity relationships of the catalysts 124,125. The combination of in situ techniques, theoretical calculation approaches, and the electrochemical measurements is an effective strategy to unravel the reaction mechanism and hence guide the rational design of efficient OER electrocatalysts. 6)Currently, most of the reported non‐noble‐metal‐based OER electrocatalysts are evaluated in alkaline conditions.…”

Nanoscale Structure Design for High‐Performance Pt‐Based ORR Catalysts

“…Tuning the geometry / dimension of Pt‐based catalysts represents another effective strategy to improve the performance/durability by varying the symmetry and surface area. For example, 1D jagged Pt nanowires (J‐PtNWs) and {111} facet‐dominant PtAu NWs show enhanced ORR electrocatalytic performance over the nanoparticle counterparts. In particular, the unique design of J‐PtNWs (Figure G,H) simultaneously featuring a highly jagged surface topology to ensure ultrahigh SA of 10.95 at 0.9 V versus RHE for ORR; and the 1D geometry is beneficial for retaining the stability of ultrafine (≈2 nm) nanostructures under electrochemical reactions and ensuring more efficient charge transport from the catalytic active sites to external electrodes, leading to better Pt utilization efficiency and unprecedented ECSA up to 120 m 2 g −1 , together delivering a record high MA of 13.6 at 0.9 V versus RHE (Figure ), along with enhanced stability.…”

A Review on Recent Progress in the Aspect of Stability of Oxygen Reduction Electrocatalysts for Proton‐Exchange Membrane Fuel Cell: Quantum Mechanics and Experimental Approaches

“…The ORR activity was enhanced against the surface strain induced by the lattice mismatch between the Pt shell and the PtCo alloy core interface structures . Moreover, with respect to shape controlling, Chang et al reported the first example of ultrathin PdAu alloy nanowires featuring composition‐tunable and (111) facet‐dominant surface characteristics, and the electrocatalytic enhancement for the ORR . According to Beermann et al, the shape‐controlled octahedral PtNi alloy nanoparticles exhibited remarkably high activities for the electroreduction of molecular oxygen (ORR), which makes them fuel‐cell cathode catalysts with an exceptional potential .…”

“…[42] Moreover, with respect to shape controlling, Chang et al reported the first example of ultrathin PdAu alloy nanowires featuring composition-tunable and (111) facet-dominant surface characteristics, and the electrocatalytic enhancement for the ORR. [43] According to Beermann et al, the shape-controlled octahedral PtNi alloy nanoparticles exhibited remarkably high activities for the electroreduction of molecular oxygen (ORR), which makes them fuel-cell cathode catalysts with an exceptional potential. [44] Wang et al proposed that the conformal deposition of Pt as ultrathin shells on facet-controlled Pd nanocrystals offers a great opportunity to enhance the catalytic performance while reducing the loading.…”