>10 MPa) and temperature (>300 °C). [2] This harsh condition is obviously energy consuming and accompanies a large amount of CO 2 output, bringing a serious global warming problem. Alternatively, multiple encouraging strategies, including photocatalysis, mimicking biological nitrogen, and electrocatalysis were gradually developed to realize artificial N 2 fixation at mild conditions. [3][4][5] Among them, N 2 electroreduction is considered as the most promising and environmentally benign way because the electricity utilized during the catalysis can be produced by some renewable sources, such as solar and wind energy. [6] It has been extensively reported that heterogenous catalysts play vital roles in breaking or lowing the energy barrier required in the rate-determining step in electroreduction from N 2 to NH 3 , [7] which is the key in further improving N 2 reduction reaction (NRR) performances. Up to now, although a number of electrocatalysts were investigated, including the metals, [8][9][10][11] the metal oxide or sulfide, [12][13][14] and metal-free compounds, [15][16][17] there are still many shortcomings. One concern is the low NH 3 generation rate ( NH3 r ) and the faradic efficiency (FE) values. It is therefore highly desirable to find effective strategies to further enhance the catalytic activity toward NRR of the heterogenous electrocatalysts.As a result of the high bonding energy of the NN triple bond (941 kJ mol −1 ), [18] N 2 is quite inert. To catalyze the NRR, it is thus indispensable to lower the energy barrier and activate the stable N 2 in an electrocatalytic reaction. Furthermore, the NH3 r and FE values will be significantly improved if the heterogenous electrocatalysts can offer sufficient active sites on their surface. From these perspectives, oxygen vacancies (OVs), one of the most important defects in semiconductor, are of particular interest to enhance the chemisorption and activation of inert N 2 molecules. [19] Furthermore, the OV formation can expose the coordinately unsaturated metal sites, resulting in further capturing and activating N 2 . In addition, the 2D nanosheets have drawn extensive attentions due to their impressive surface structure. [20,21] Generally, the surface area in 2D nanosheets allows a large number of exposed atoms to act as the active sites, which will undoubtedly improve the catalytic activity. The thin nanosheets can decrease the diffusion path, ensuring a rapid electron transport during electrocatalytic procedure. [22] It is therefore feasible that 2D OV-TiO 2 nanostructures will offer a favorable platform to facilitate the Electrocatalysts play vital roles in the enhancement of the catalytic performances of the reduction reaction from N 2 to NH 3 at ambient conditions. This study reports oxygen vacancy-contained TiO 2 nanosheets, which are explored as efficient electrocatalysts toward the N 2 reduction reaction (NRR). Oxygen vacancies are introduced and tuned by annealing the as-prepared TiO 2 nanostructures under H 2 /Ar atmosphere at different temperature...
In the synthesis of Au/Pd bimetallic nanocrystals, a layer-by-layer growth is favored, owing to the low bonding energy between Pd atoms (E Pd–Pd) in comparison with E Au–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.
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 H2PtCl6 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.
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 H2PtCl6 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.
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