Composition-Tunable PtCu Alloy Nanowires and Electrocatalytic Synergy for Methanol Oxidation Reaction

The ability to impart Pt-based catalysts with high catalytic activity and low cost is essential for advancing fuel cell technologies. This report describes the synthesis of composition-tunable PtCu alloy nanowires (NWs) of ultrathin diameters (ca. 1 nm) to create synergistic catalytic sites along the nanowire surfaces. The bimetallic NWs exhibit composition-tunable fcc-type alloy phase. The electrocatalytic properties of the PtCu alloy NWs for methanol oxidation reaction were shown to display an intriguing composition-dependent catalytic synergy. The maximum mass activity for Pt₃₂Cu₆₈ NWs was about 2 times higher than that of Pt NWs. It also exhibited the highest stability and tolerance to CO poisoning. The enhanced activity and stability were attributed to a bifunctional synergy whereby the alloyed Cu atoms in the Pt lattice provides CO-maneuvering sites for reducing the poisoning effect of CO intermediate species on the active surface sites of the NWs

Synthesis of Ultralong, Monodispersed, and Surfactant-Free Gold Nanowire Catalysts: Growth Mechanism and Electrocatalytic Properties for Methanol Oxidation Reaction

The understanding of factors influencing the growth of nanowires is critical for the precise control of the nanowire morphologies and the design of active nanowire catalysts for fuel cell reactions. While the formation of gold nanoparticles followed by self-assembly into short strings of nanowires is known, little is understood in terms of the control of the morphologies and surface properties toward enhanced electrocatalytic properties. This report describes novel findings of an investigation of the growth mechanism of ultralong, highly monodispersed, and surface surfactant-free gold nanowires (Au NWs) synthesized by a galvanic replacement reaction of Te NWs as an initial template. By manipulating reaction time and Au precursor concentration, an aggregative growth mechanism in terms of 1D and 3D growth pathways for the NW length and diameter, respectively, is revealed to be operative in the template-directed Au NW formation process, shinning some fresh insight into the controllability of the nanowire morphologies. In contrast to the use of various organic surfactants in most previous synthesis of Au NWs and catalysts, the surfactant-free Au NWs synthesized in this work have been demonstrated to exhibit enhanced electrocatalytic activities for methanol oxidation reaction, outperforming those for Au NWs with surface surfactants and Au NP counterparts

Understanding Composition-Dependent Synergy of PtPd Alloy Nanoparticles in Electrocatalytic Oxygen Reduction Reaction

Gaining an insight into the relationship between the bimetallic composition and catalytic activity is essential for the design of nanoalloy catalysts for oxygen reduction reaction. This report describes findings of a study of the composition–activity relationship for PtPd nanoalloy catalysts in oxygen reduction reaction (ORR). Pt_<i>n</i>Pd_{100‑<i>n</i>} nanoalloys with different bimetallic compositions are synthesized by wet chemical method. While the size of the Pt₅₀Pd₅₀ nanoparticles is the largest among the nanoparticles with different compositions, the characterization of the nanoalloys using synchrotron high-energy X-ray diffraction (HE-XRD) coupled to atomic pair distribution function (PDF) analysis reveals that the nanoalloy with an atomic Pt:Pd ratio of 50:50 exhibits an intermediate lattice parameter. Electrochemical characterization of the nanoalloys shows a minimum ORR activity at Pt:Pd ratio close to 50:50, whereas a maximum activity is achieved at Pt:Pd ratio close to 10:90. The composition–activity correlation is assessed by theoretical modeling based on DFT calculation of nanoalloy clusters. In addition to showing an electron transfer from PtPd alloy to oxygen upon its adsorption on the nanoalloy, a relatively large energy difference between HOMO for nanoalloy and LUMO for oxygen is revealed for the nanoalloy with an atomic Pt:Pd ratio of 50:50. By analysis of the adsorption of OH species on PtPd (111) surfaces of different compositions, the strongest adsorption energy is observed for Pt₉₆Pd₁₀₅ (Pt:Pd ≈ 50:50) cluster, which is believed to be likely responsible for the reduced activity. Interestingly, the adsorption energy on Pt₂₄Pd₁₇₇ (Pt:Pd ≈ 10:90) cluster falls in between Pt₉₆Pd₁₀₅ and Pd₂₀₁ clusters, which is believed to be linked to the observation of the highest catalytic activity for the nanoalloy with an atomic Pt:Pd ratio of 10:90. These findings have implications for the design of composition-tunable nanoalloy catalysts for ORR

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

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