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The anisotropic structure and unique surface properties of one-dimensional (1D) Pt-nanowire (PtNW) make it a promising new type of electrocatalyst for various catalyst applications, especially for fuel cells. However, due to the critical synthesis process, a finely tuning of the synthesis temperature for precisely controlling the morphology and distribution of PtNWs in catalyst electrodes still remains a grand challenge. In this work, we present the temperature-controlled growth of PtNWs with large-area 16 cm 2 carbon paper piece as a direct support. The relationship between the growth temperature and PtNW behavior is studied by physical characterization, and their catalytic activity is measured towards oxygen reduction reaction (ORR) by testing as the cathode in a hydrogen-air fuel cell. The results show that the growth temperature plays a vital role on the behavior of PtNWs thus influencing their properties. The catalyst electrode with PtNWs grown at 40 °C shows the best power performance. A possible mechanism for the influence of temperature on PtNW growth is suggested. The comparison with the state-of-the-art commercial TKK catalyst also shows a better performance and durability. The understanding gained in our work from PtNW catalyst electrode could aid in the design of other novel nanostructures in practical applications. [ABSTRACT FROM AUTHOR] more...

Periodic twins are an intrinsic structural feature of some types of chemically synthesized metallic nanowires but not others. A model that accounts for this well-known observation is presented. The model considers the influence of twin boundary energy and surface energy on nanowire growth kinetics, and it was tested using high-resolution electron microscopy and parallel-nanobeam diffraction data from geometrically identical nanowires of gold and platinum. The effects of twin boundary energy on nanowire growth kinetics can explain the structural difference between the gold and platinum nanowires without the need to speculate about the nature of ligand interactions during growth. [ABSTRACT FROM AUTHOR] more...

A tremendous development of nanotechnology enabled us to prepare precisely structure-controlled nanocrystals (NCs). Recently, such structure controlled NCs have been applied as model catalysts with controlled active sites to evaluate reaction mechanisms. Here, we review our recent works on preparation of shape controlled Pt NCs, such as cube and wire, and on application as model catalysts for olefin hydrogenation to assess active Pt sites. A hydrogen reduction method of Pt(II) ion was adopted in an aqueous phase to prepare Pt cube in the presence of shape forming agent (NaI) and organic protective agent (sodium polyacrylate or sodium succinate). We succeed to prepare Pt cube with high size and shape selectivity, followed by very small Pt cube of less than 3 nm. Such simultaneous control of both size and shape of Pt NCs has been successfully achieved by the sophisticated tuning of multiple conditions for the growth kinetics of Pt nuclei during hydrogen reduction of PtCl in aq. N- , N-dimethylformamide (DMF) solution. The key strategy is to produce small Pt nuclei and to avoid the excessive growth of Pt nuclei, in conjunction with face selective adsorption of anionic protective and shape-forming agents by the control of solvent system. For the preparation of Pt nanowires with high anisotropy, template-assisted methods have been usually used. We have developed facile liquid phase preparation method at room temperature in air without any template. The key factors of the method are: firstly, to use aqueous organic solvent system to control solvent polarity; secondly, to use co-solvent DMF as shape forming agent; thirdly, to use excess NaBH as a stabilizer of Pt nuclei to prevent formation of conventional particles. Single-crystalline Pt nanowires of 2 nm diameter and more than micron length were easily obtained by the reduction of Pt(IV) with excess NaBH in water-DMF-toluene solution (1:8:5 volume ratio) in a short reaction period of 3 h. Then, we have applied shape-controlled Pt NCs protected with PAA prepared by our original methods, such as cube, tetrahedron and wire, as model catalysts for olefin ( cis- and trans-stilbenes) hydrogenation in ethanol to evaluate the active facet of Pt catalysts; e.g., Pt(111) or Pt(100). The estimated TOF values for the hydrogenation of cis- and trans-stilbene decreased in the order: cube > cuboctahedron > tetrahedron ~ nanowire. This tendency indicates that Pt(100) show high activity compared with Pt(111). The result is compatible with measurement of XPS and Raman spectra, suggesting strong adsorption of reactant on Pt(100). Hydrogenation of olefins (1-hexene and cyclohexene) has been carried out over Pt cubes with different sizes (8.2-10.1 nm) as catalysts to get information about active sites of Pt catalysts, e.g., flat facet or edge/corner atoms. The results of similar TOF values among Pt cubes with different sizes imply that the active sites are flat facets. [ABSTRACT FROM AUTHOR] more...

The large-scale practical application of proton exchange membrane fuel cells (PEMFCs) is difficult to achieve if their performance and durability cannot be improved. We successfully synthesized N-doped carbon nanotube (NCNT) supported Pt nanowire catalysts (PtNW/NCNTs) using the soft template method with NCNTs as support. The results of transmission electron microscopy show that the Pt nanowires are uniformly loaded on the support (NCNTs). X-ray photoelectron spectroscopy reveals that the N atom doped on the surface is in the form of graphite N and pyridine N. The electrocatalytic activity of PtNW/NCNTs is studied via the half-cell electrochemistry test. The PtNW/NCNTs show better oxygen reduction reaction activity than commercial Pt/C catalysts. The results of the single-cell polarization experiment reveal that the performance of PEMFCs with PtNW/NCNTs is improved, and the maximum power density is 966 mW cm−2. After 500 h dynamic cycle durability test, the average voltage loss of the single cell is 3.6% for the PtNW/NCNTs catalyst and 7.2% for the Pt/C catalyst. The Pt/C catalyst demonstrates severe Pt nanoparticle growth and aggregation with a broad size distribution, the PtNW along with minimal changes observed. PtNW/NCNTs are a promising replacement to traditional Pt/C catalysts as electrocatalyst in PEMFC applications. [Display omitted] • PtNW/NCNTs were synthesized using the soft template method with NCNTs as support. •The ORR activity of the PtNW/NCNTs catalyst were remarkably improved. •The PtNW has reduced the mass transfer resistance values. •The PtNW/NCNTs catalyst has better performance and life of single cell. [ABSTRACT FROM AUTHOR] more...

• Facile synthesis of Pt nanowires (PtNW) on carbon nanotubes (SWNT) introduced. • 100 times lower Pt content induces comparable activity to state of the art catalyst. • Activity attributed to metallic PtNW – SWNT interactions and morphology. • In an electrolyzer a stable voltage generated for more than 2000 h at a 1 A cm−2. Pertinent existing hydrogen technologies for energy storage require unsustainable amounts of scarce platinum group metals. Here, an electrocatalyst comprising high-aspect-ratio platinum nanowires (PtNWs) on single-walled carbon nanotubes (SWNTs) with ultralow Pt content (340 ng Pt cm−2) is employed for hydrogen evolution reaction (HER). A comparable activity (10 mA cm−2 at −18 mV vs. RHE) to that of state-of-the-art Pt/C (38,000 ng Pt cm−2) is reached in acidic aqueous electrolyte. This is attributed to favorable PtNW interaction with SWNTs and PtNW edge-sites which adsorb hydrogen optimally and aid at alleviating repulsive interactions. Moreover, the metallic nature of Pt, morphological effects and enhanced wetting contribute positively. The PtNW/SWNT relevance is emphasized at a proton-exchange-membrane electrolyzer generating stable voltage for more than 2000 h, successfully competing with the state-of-the-art reference but with one tenth of Pt mass loading. Overall, this work presents an unprecedently efficient HER catalyst and opens up avenues for PtNW/SWNT catalyzing other high-impact reactions. [ABSTRACT FROM AUTHOR] more...