Ultrathin and Porous 2D PtPdCu Nanoalloys as High-Performance Multifunctional Electrocatalysts for Various Alcohol Oxidation Reactions.

We precisely synthesized two-dimensional (2D) PtPdCu nanostructures with the morphology varying from porous circular nanodisks (CNDs) and triangular nanoplates (TNPs) to triangular nanoboomerangs (TNBs) by tuning the molar ratios of metal precursors. The PtPdCu trimetallic nanoalloys exhibit superior electrocatalytic performances to alcohol oxidation reactions due to their unique structural features and the synergistic effect. Impressively, PtPdCu TNBs exhibit a high mass activity of 3.42 mgPt+Pd-1 and 1.06 A·mgPt-1 for ethanol and methanol oxidation compared to PtPd, PtCu, and pure Pt, which is 3.93 and 4.07 times that of commercial Pt/C catalysts, respectively. Moreover, 2D PtPdCu TNPs and PtPdCu CNDs also show a highly improved electrocatalytic activity. Furthermore, as all-in-one electrocatalysts, PtPdCu nanoalloys display excellent electrocatalytic activity and stability toward the oxidation of other alcohol molecules, such as isopropyl alcohol, glycerol, and ethylene glycol. The enhanced mechanism was well proposed to be the abundant active sites and upshifted d-band center based on density functional theory calculations.

Dodecahedral Au/Pt Nanobowls as Robust Plasmonic Electrocatalysts for Methanol Oxidation under Visible-Light Illumination.

Plasmonic nanostructures with large absorption areas under resonant excitation have been utilized extensively in photon-assisted applications. In this work, dodecahedral Au nanobowls were first prepared by an easy and template-free method only through the introduction of H2 PtCl6 and I- during the growth procedure. The Au nanobowls show electron-field enhancement due to the high curvature of the bowl edge, the open region, and dodecahedral morphology. Au/Pt nanobowls, which couple plasmonic Au and catalytic Pt, were then constructed as plasmonic electrocatalysts for methanol oxidation. The mass activity reached 497.6 mA mg-1 under visible-light illumination, which is 1.9 times that measured in the dark. Simultaneously, the electrocatalytic stability is also greatly improved under light excitation. The enhanced properties of the plasmonic Au/Pt electrocatalysts are ascribed to the synergistic effect of the plasmon-enhanced photothermal and hot-carrier effects on the basis of experimental investigations. This work thus offers an effective methodology to construct efficient plasmonic electrocatalysts for fuel cells.

AuPt Bipyramid Nanoframes as Multifunctional Platforms for In†Situ Monitoring of the Reduction of Nitrobenzene and Enhanced Electrocatalytic Methanol Oxidation.

Multifunctional metal nanostructures with a hollow feature, especially for nanoframes, are highly attractive owing to their high surface-to-volume ratios. However, pre-grown metal nanocrystals are always involved during the preparation procedure, and a synthetic strategy without the use of a pre-grown template is still a challenge. In this article, a template-free strategy is reported for the preparation of novel AuPt alloy nanoframes through simply mixing HAuCl4 and H2 PtCl6 under mild conditions. The alloy nanostructures show a bipyramid-frame hollow architecture with the existence of only the ten ridges and absence of their side faces. This is the first report of bipyramid-like nanoframes and a template-free method under mild conditions. This configuration merges the plasmonic features of Au and highly active catalytic sites of Pt in a single nanostructure, making it an ideal multifunctional platform for catalyzing and monitoring the catalytic reaction in real time. The superior catalytic activity is demonstrated by using the reduction of nitrobenzene to the corresponding aminobenzene as a model reaction. More importantly, the AuPt nanoframes can track the reduction process on the basis of the SERS signals of the reactants, intermediates, and products, which helps to reveal the reaction mechanism. In addition, the AuPt nanoframes show much higher electrocatalytic properties toward the methanol oxidation reaction than commercial Pt/C electrocatalysts.

Ambient Electrosynthesis of Ammonia on a Core-Shell-Structured Au@CeO2 Catalyst: Contribution of Oxygen Vacancies in CeO2.

Electrosynthesis of NH3 through the N2 reduction reaction (NRR) under ambient conditions is regarded as promising technology to replace the industrial energy- and capital-intensive Haber-Bosch process. Herein, a room-temperature spontaneous redox approach to fabricate a core-shell-structured Au@CeO2 composite, with Au nanoparticle sizes below about 10 nm and a loading amount of 3.6 wt %, is reported for the NRR. The results demonstrate that as-synthesized Au@CeO2 possesses a surface area of 40.7 m2 g-1 and a porous structure. As an electrocatalyst, it exhibits high NRR activity, with an NH3 yield rate of 28.2 µg h-1 cm-2 (10.6 µg h-1 mg-1 cat. , 293.8 µg h-1 mg-1 Au ) and a faradaic efficiency of 9.50 % at -0.4 V versus a reversible hydrogen electrode in 0.01 m H2 SO4 electrolyte. The characterization results reveal the presence of rich oxygen vacancies in the CeO2 nanoparticle shell of Au@CeO2 ; these are favorable for N2 adsorption and activation for the NRR. This has been further verified by theoretical calculations. The abundant oxygen vacancies in the CeO2 nanoparticle shell, combined with the Au nanoparticle core of Au@CeO2 , are electrocatalytically active sites for the NRR, and thus, synergistically enhance the conversion of N2 into NH3 .

High-Density Pd Nanorod Arrays on Au Nanocrystals for High-Performance Ethanol Electrooxidation.

In the synthesis of Au/Pd bimetallic nanocrystals, a layer-by-layer growth is favored, owing to the low bonding energy between Pd atoms ( EPd-Pd) in comparison with EAu-Pd, resulting in homogeneous core/shell nanostructures. Herein, we demonstrate designed synthetic tactics to unconventional Au/Pd heterostructures through a deposition-dominant growth pathway of the newly reduced Pd atoms, which break the intrinsically favored layer-by-layer growth. Pd thus grows on Au seeds in a heterogeneous nucleation manner. The resulting anisotropic Pd nanorods array on the two basal facets and three side facets of the Au triangular seeds in a high density to form 2D/1D Au/Pd heterostructures. It is noticed that Pd nanorods align in an extremely high order. They grow almost in a row with the base of the rod located overlapped on the Au surface. This versatile approach has been also applied to other Au nanocrystal seeds, involving hexagonal nanoplates, circular nanodisks, nanorods, and nanobipyramids. Furthermore, the 2D/1D Au/Pd heterostructures exhibit an enhanced electrocatalytic performance toward ethanol oxidation in alkaline condition, owing to their unique structure and the exposure of Au. We believe that our synthetic strategy is highly valuable for the construction of multimetallic nanostructures with desired architectures and thus intriguing properties.

Spontaneous Redox Approach to the Self-Assembly Synthesis of Au/CeO2 Plasmonic Photocatalysts with Rich Oxygen Vacancies for Selective Photocatalytic Conversion of Alcohols.

We present the self-assembly synthesis of core-shell structure Au/CeO2 composites with different Au loadings through a spontaneous chemical redox approach at an ambient temperature utilizing HAuCl4 and Ce(NO3)3 as reaction substrates in an alkaline environment. The results demonstrate that the as-synthesized Au/CeO2 composites exhibit spherical shape morphologies with porous structures, composed of Au nanoparticle (∼10 nm) cores and CeO2 nanoparticle shells with abundant oxygen vacancies. The introduction of Au nanoparticles in CeO2 not only effectively improves the visible light utilization efficiency but also provides rich surface catalytic active sites for highly efficient visible light photocatalysis. As visible light photocatalysts (λ > 400 nm), the as-synthesized Au/CeO2 composites with the Au loading amount ≥4.0 wt % exhibit high conversion and selectivity (∼100%) of benzyl alcohol to benzaldehyde under the given experimental conditions. Moreover, Au/CeO2 also shows a general applicability as a visible light photocatalyst for the selective oxidation of other alcohols to corresponding aldehydes or ketones. The photocatalytic mechanism studies indicate that the photoelectrons/holes produced from the photoexcited Au and the formed superoxide radicals in the oxygen vacancies of CeO2 synergistically contribute to the high performance of the selective photocatalytic oxidation of alcohols to aldehydes or ketones.