Showing papers on "Platinum published in 2015"
TL;DR: An electrocatalyst for hydrogen generation based on very small amounts of cobalt dispersed as individual atoms on nitrogen-doped graphene is reported, which is robust and highly active in aqueous media with very low overpotentials.
Abstract: Reduction of water to hydrogen through electrocatalysis holds great promise for clean energy, but its large-scale application relies on the development of inexpensive and efficient catalysts to replace precious platinum catalysts. Here we report an electrocatalyst for hydrogen generation based on very small amounts of cobalt dispersed as individual atoms on nitrogen-doped graphene. This catalyst is robust and highly active in aqueous media with very low overpotentials (30 mV). A variety of analytical techniques and electrochemical measurements suggest that the catalytically active sites are associated with the metal centres coordinated to nitrogen. This unusual atomic constitution of supported metals is suggestive of a new approach to preparing extremely efficient single-atom catalysts.
1,262 citations
TL;DR: It may be said that the NiS/Pt/Ti counter electrode is a promising catalytic material to replace the expensive platinum in FDSSCs.
Abstract: A composite film of nickel sulfide/platinum/titanium foil (NiS/Pt/Ti) with low cost and high electrocatalytic activity was synthesized by the use of an in situ electropolymerization route and proposed as a counter electrode (CE) catalyst for flexible dye-sensitized solar cells (FDSSCs). The FDSSC with the NiS/Pt/Ti CE exhibited a comparable power conversion efficiency of 7.20% to the FDSSC with the platinum/titanium (Pt/Ti) CE showing 6.07%. The surface morphology of the NiS/Pt/Ti CE with one-dimensional (1D) structure is characterized by using the scanning electron microscopy (SEM). The NiS/Pt/Ti CE also displayed multiple electrochemical functions of excellent conductivity, great electrocatalytic ability for iodine/triiodine, and low charge transfer resistance of 2.61 ± 0.02 Ω cm2, which were characterized by using the cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel polarization plots. The photocurrent-photovoltage (J-V) character curves were further used to calculate the theoretical optical light performance parameters of the FDSSCs. It may be said that the NiS/Pt/Ti counter electrode is a promising catalytic material to replace the expensive platinum in FDSSCs.
1,036 citations
TL;DR: A robust and highly active catalyst for hydrogen evolution reaction that is constructed by in situ growth of molybdenum disulfide on the surface of cobalt diselenide, which is the best among the non-noble metal hydrogen evolution catalysts and even approaches to the commercial platinum/carbon catalyst.
Abstract: There is substantial research into new catalysts for electroreduction of water. Here, the authors report a robust and active molybdenum disulfide/cobalt diselenide hydrogen evolution catalyst with onset potential of 11 mV and Tafel slope of 36 mV per decade, approaching the activity of platinum.
854 citations
TL;DR: It is demonstrated that infrared spectroscopy can be a fast and convenient characterization method with which to directly distinguish and quantify Pt single atoms from nanoparticles, and directly observe that only Pt nanoparticles show activity for carbon monoxide (CO) oxidation and water-gas shift at low temperatures, whereas Ptsingle atoms behave as spectators.
Abstract: Identification and characterization of catalytic active sites are the prerequisites for an atomic-level understanding of the catalytic mechanism and rational design of high-performance heterogeneous catalysts. Indirect evidence in recent reports suggests that platinum (Pt) single atoms are exceptionally active catalytic sites. We demonstrate that infrared spectroscopy can be a fast and convenient characterization method with which to directly distinguish and quantify Pt single atoms from nanoparticles. In addition, we directly observe that only Pt nanoparticles show activity for carbon monoxide (CO) oxidation and water-gas shift at low temperatures, whereas Pt single atoms behave as spectators. The lack of catalytic activity of Pt single atoms can be partly attributed to the strong binding of CO molecules.
830 citations
TL;DR: A hybrid nanomaterial comprising of one-dimensional ultrathin platinum nanowires grown on two-dimensional single-layered nickel hydroxide, which outperforms currently reported catalysts, and obviously improved catalytic stability is reported.
Abstract: Design and synthesis of effective electrocatalysts for hydrogen evolution reaction in alkaline environments is critical to reduce energy losses in alkaline water electrolysis. Here we report a hybrid nanomaterial comprising of one-dimensional ultrathin platinum nanowires grown on two-dimensional single-layered nickel hydroxide. Judicious surface chemistry to generate the fully exfoliated nickel hydroxide single layers is explored to be the key for controllable growth of ultrathin platinum nanowires with diameters of about 1.8 nm. Impressively, this hybrid nanomaterial exhibits superior electrocatalytic activity for hydrogen evolution reaction in alkaline solution, which outperforms currently reported catalysts, and the obviously improved catalytic stability. We believe that this work may lead towards the development of single-layered metal hydroxide-based hybrid materials for applications in catalysis and energy conversion.
813 citations
TL;DR: Nanocages of platinum are fabricated by depositing a few atomic layers of platinum as conformal shells on palladium nanocrystals with well-defined facets and then etching away the Pd templates.
Abstract: A cost-effective catalyst should have a high dispersion of the active atoms, together with a controllable surface structure for the optimization of activity, selectivity, or both. We fabricated nanocages by depositing a few atomic layers of platinum (Pt) as conformal shells on palladium (Pd) nanocrystals with well-defined facets and then etching away the Pd templates. Density functional theory calculations suggest that the etching is initiated via a mechanism that involves the formation of vacancies through the removal of Pd atoms incorporated into the outermost layer during the deposition of Pt. With the use of Pd nanoscale cubes and octahedra as templates, we obtained Pt cubic and octahedral nanocages enclosed by {100} and {111} facets, respectively, which exhibited distinctive catalytic activities toward oxygen reduction.
793 citations
TL;DR: The correlation between hydrogen oxidation/evolution activity and experimentally measured hydrogen binding energy for polycrystalline platinum examined in several buffer solutions in a wide range of electrolyte pH is reported, strongly supporting the hypothesis that hydrogen binding power is the sole reaction descriptor for the hydrogen oxidation-evolution reaction on monometallic platinum.
Abstract: The hydrogen oxidation/evolution reactions are two of the most fundamental reactions in distributed renewable electrochemical energy conversion and storage systems. The identification of the reaction descriptor is therefore of critical importance for the rational catalyst design and development. Here we report the correlation between hydrogen oxidation/evolution activity and experimentally measured hydrogen binding energy for polycrystalline platinum examined in several buffer solutions in a wide range of electrolyte pH from 0 to 13. The hydrogen oxidation/evolution activity obtained using the rotating disk electrode method is found to decrease with the pH, while the hydrogen binding energy, obtained from cyclic voltammograms, linearly increases with the pH. Correlating the hydrogen oxidation/evolution activity to the hydrogen binding energy renders a monotonic decreasing hydrogen oxidation/evolution activity with the hydrogen binding energy, strongly supporting the hypothesis that hydrogen binding energy is the sole reaction descriptor for the hydrogen oxidation/evolution activity on monometallic platinum.
696 citations
TL;DR: In this article, a 3D hierarchical structure of nickel phosphide (Ni5 P4 ) was used as a bifunctional catalyst for the hydrogen and oxygen evolution reaction in strong acidic and alkaline environment.
Abstract: The investigation of nickel phosphide (Ni5 P4 ) as a catalyst for the hydrogen (HER) and oxygen evolution reaction (OER) in strong acidic and alkaline environment is described. The catalyst can be grown in a 3D hierarchical structure directly on a nickel substrate, thus making it an ideal candidate for practical water splitting devices. The activity of the catalyst towards the HER, together with its high stability especially in acidic solution, makes it one of the best non-noble materials described to date. Furthermore, Ni5 P4 was investigated in the OER and showed activity superior to pristine nickel or platinum. The practical relevance of Ni5 P4 as a bifunctional catalyst for the overall water splitting reaction was demonstrated, with 10 mA cm(-2) achieved below 1.7 V.
612 citations
TL;DR: A non-platinum group metal electrocatalyst with an active site devoid of any direct nitrogen coordination to iron that outperforms the benchmark platinum-based catalyst in alkaline media and is comparable to its best contemporaries in acidic media is reported.
Abstract: Replacement of noble metals in catalysts for cathodic oxygen reduction reaction with transition metals mostly create active sites based on a composite of nitrogen-coordinated transition metal in close concert with non-nitrogen-coordinated carbon-embedded metal atom clusters. Here we report a non-platinum group metal electrocatalyst with an active site devoid of any direct nitrogen coordination to iron that outperforms the benchmark platinum-based catalyst in alkaline media and is comparable to its best contemporaries in acidic media. In situ X-ray absorption spectroscopy in conjunction with ex situ microscopy clearly shows nitrided carbon fibres with embedded iron particles that are not directly involved in the oxygen reduction pathway. Instead, the reaction occurs primarily on the carbon-nitrogen structure in the outer skin of the nitrided carbon fibres. Implications include the potential of creating greater active site density and the potential elimination of any Fenton-type process involving exposed iron ions culminating in peroxide initiated free-radical formation.
563 citations
TL;DR: A novel type of robust cobalt-nitrogen/carbon catalyst for the hydrogen evolution reaction (HER) that is prepared by the pyrolysis of cobalt–N4 macrocycles or cobalt/o-phenylenediamine composites and using silica colloids as a hard template is reported.
Abstract: Replacement of precious platinum with efficient and low-cost catalysts for electrocatalytic hydrogen evolution at low overpotentials holds tremendous promise for clean energy devices. Here we report a novel type of robust cobalt–nitrogen/carbon catalyst for the hydrogen evolution reaction (HER) that is prepared by the pyrolysis of cobalt–N4 macrocycles or cobalt/o-phenylenediamine composites and using silica colloids as a hard template. We identify the well-dispersed molecular CoNx sites on the carbon support as the active sites responsible for the HER. The CoNx/C catalyst exhibits extremely high turnover frequencies per cobalt site in acids, for example, 0.39 and 6.5 s−1 at an overpotential of 100 and 200 mV, respectively, which are higher than those reported for other scalable non-precious metal HER catalysts. Our results suggest the great promise of developing new families of non-precious metal HER catalysts based on the controlled conversion of homogeneous metal complexes into solid-state carbon catalysts via economically scalable protocols. Hydrogen evolution from water promises a future clean energy source, however the cost of noble metal catalysts, which are necessary for high efficiency, are very expensive. Here, the authors fabricate a porous cobalt–nitrogen/carbon catalyst which can deliver high activity and stability but at reduced cost.
552 citations
TL;DR: This work preserves emissive behaviour at both low- and high-concentration regimes for two discrete supramolecular coordination complexes (SCCs) that exhibit variable-wavelength visible- light emission, including rare white-light emission in tetrahydrofuran.
Abstract: Two metallacages containing Pt(II) phosphine centres bridged by organic donors are shown to display dynamic emission behaviour across a range of concentrations. At low concentrations, the individual cages emit. At high concentrations, or on introduction of additional solvents, aggregation occurs that manifests in colour-tunable fluorescence and white-light emission in THF.
TL;DR: γ-Alumina-supported single-atom alloy nanoparticle catalysts with <1 platinum atom per 100 copper atoms are found to exhibit high activity and selectivity for butadiene hydrogenation to butenes under mild conditions, demonstrating transferability from the model study to the catalytic reaction under practical conditions.
Abstract: Platinum is ubiquitous in the production sectors of chemicals and fuels; however, its scarcity in nature and high price will limit future proliferation of platinum-catalysed reactions. One promising approach to conserve platinum involves understanding the smallest number of platinum atoms needed to catalyse a reaction, then designing catalysts with the minimal platinum ensembles. Here we design and test a new generation of platinum-copper nanoparticle catalysts for the selective hydrogenation of 1,3-butadiene,, an industrially important reaction. Isolated platinum atom geometries enable hydrogen activation and spillover but are incapable of C-C bond scission that leads to loss of selectivity and catalyst deactivation. γ-Alumina-supported single-atom alloy nanoparticle catalysts with <1 platinum atom per 100 copper atoms are found to exhibit high activity and selectivity for butadiene hydrogenation to butenes under mild conditions, demonstrating transferability from the model study to the catalytic reaction under practical conditions.
TL;DR: This work reports a system based on palladium icosahedra that demonstrates an effective approach to the development of electrocatalysts with greatly enhanced activity and durability.
Abstract: Core-shell catalysts can enhance activity while reducing the loading of expensive catalyst materials. Here, the authors report a palladium@platinum system in which the platinum shells evolve into a corrugated structure with compressive strains, with subsequent enhancement of oxygen reduction activity.
TL;DR: A review of recent advances in hydrosilylation chemistry mainly published in the last decade can be found in this article, where the utility of catalysts with high selectivity and efficiency is discussed.
Abstract: This review covers the recent advances in hydrosilylation chemistry mainly published in the last decade. Hydrosilylation of olefins is an important reaction for the production of various organosilicon compounds such as industrially important silicone products. Although the utility of platinum catalysts, Speier's and Karstedt's catalysts, has been widely recognized in this field for decades, development of more efficient, selective, and cheaper catalyst systems are still desired for more economical production of organosilicon materials having superior properties. In these contexts, much progress has been made in recent years. In the platinum catalysis systems, continuous progress has been made to further improve selectivity and activity. Several non-precious metal catalysts, such as Fe and Ni catalysts, with good efficiency and selectivity have been developed. Furthermore, unique chemo- and regioselectivity have been achieved not only by precious metal catalysts but also by non-precious metal catalysts. The utility of non-transition metal catalysts including early main group metals, Lewis acidic alane, borane and phosphonium salts as well as N-heterocyclic carbenes has also been disclosed.
TL;DR: It is reported that a hierarchical nanoporous copper-titanium bimetallic electrocatalyst is able to produce hydrogen from water under a mild overpotential at more than twice the rate of state-of-the-art carbon-supported platinum catalyst.
Abstract: A robust and efficient non-precious metal catalyst for hydrogen evolution reaction is one of the key components for carbon dioxide-free hydrogen production. Here we report that a hierarchical nanoporous copper-titanium bimetallic electrocatalyst is able to produce hydrogen from water under a mild overpotential at more than twice the rate of state-of-the-art carbon-supported platinum catalyst. Although both copper and titanium are known to be poor hydrogen evolution catalysts, the combination of these two elements creates unique copper-copper-titanium hollow sites, which have a hydrogen-binding energy very similar to that of platinum, resulting in an exceptional hydrogen evolution activity. In addition, the hierarchical porosity of the nanoporous copper-titanium catalyst also contributes to its high hydrogen evolution activity, because it provides a large-surface area for electrocatalytic hydrogen evolution, and improves the mass transport properties. Moreover, the catalyst is self-supported, eliminating the overpotential associated with the catalyst/support interface.
TL;DR: The one-step synthesis of uniform, ultrafine molybdenum carbide nanoparticles (NPs) within a carbon matrix from inexpensive starting materials makes the catalyst one of the most active acid-stable electrocatalysts ever reported for HER.
Abstract: The replacement of platinum with non-precious-metal electrocatalysts with high efficiency and superior stability for the hydrogen-evolution reaction (HER) remains a great challenge. Herein, we report the one-step synthesis of uniform, ultrafine molybdenum carbide (Mo2C) nanoparticles (NPs) within a carbon matrix from inexpensive starting materials (dicyanamide and ammonium molybdate). The optimized catalyst consisting of Mo2C NPs with sizes lower than 3 nm encapsulated by ultrathin graphene shells (ca. 1-3 layers) showed superior HER activity in acidic media, with a very low onset potential of -6 mV, a small Tafel slope of 41 mV dec(-1), and a large exchange current density of 0.179 mA cm(-2), as well as good stability during operation for 12 h. These excellent properties are similar to those of state-of-the-art 20% Pt/C and make the catalyst one of the most active acid-stable electrocatalysts ever reported for HER.
TL;DR: In this article, α-Mo2C and molybdenum nitride nanoparticles were developed for catalyzing the hydrogen evolution reaction (HER) by simply changing the molar ratio of the urea/metal precursor, and both are crystalline, phase pure and monodisperse in size.
Abstract: Molybdenum carbide and molybdenum nitride nanoparticles have been developed for catalyzing the hydrogen evolution reaction (HER). These nanocatalysts were synthesized by the ‘urea glass’ route. By simply changing the molar ratio of the urea/metal precursor, α-Mo2C and γ-Mo2N nanoparticles, both of which are crystalline, phase pure and monodisperse in size, were obtained. Hydrogen evolution was performed in both 1 M KOH and 0.5 M H2SO4 electrolytes, and characterized by linear sweep voltammetry and electrochemical impedance spectroscopy. The as-synthesized Mo2C showed excellent HER performance especially in KOH. At a catalyst loading of 102 μg cm−2, a low overpotential of 176 mV was needed to produce 10 mA cm−2 of H2. Its measured currents and turnover frequencies for hydrogen evolution at different overpotentials compare favorably against many other recently reported non-precious metal HER catalysts. Online gas chromatography demonstrated that the current efficiency for H2 production is ∼100%. Both Mo2C and Mo2N showed negligible overpotential losses after acceleration degradation tests in acid and alkali. This is noteworthy since very few catalysts are active in these two extreme pHs. An attractive aspect of the α-Mo2C and γ-Mo2N nanoparticles for electrochemical hydrogen evolution is that they are simple and well-characterized in chemical and physical composition. The excellent catalytic activity of the α-Mo2C catalysts can be attributed to their small particle size, which will facilitate a rapid electron transfer for the hydrogen evolution reaction. Our study has placed the as-synthesized α-Mo2C nanoparticles as highly promising alternatives to platinum in the alkaline water electrolyzer.
TL;DR: It is found that the simple reaction-dissociation of O2-supported on metal surfaces can profoundly account for the oxidase-like activities of the metals and pave a way to the rational design of mimetic enzymes based on metal nanomaterials.
Abstract: Metal and alloy nanomaterials have intriguing oxidase- and superoxide dismutation-like (SOD-like) activities. However, origins of these activities remain to be studied. Using density functional theory (DFT) calculations, we investigate mechanisms of oxidase- and SOD-like properties for metals Au, Ag, Pd and Pt and alloys Au4–xMx (x = 1, 2, 3; M = Ag, Pd, Pt). We find that the simple reaction—dissociation of O2—supported on metal surfaces can profoundly account for the oxidase-like activities of the metals. The activation (Eact) and reaction energies (Er) calculated by DFT can be used to effectively predict the activity. As verification, the calculated activity orders for series of metal and alloy nanomaterials are in excellent agreement with those obtained by experiments. Briefly, the activity is critically dependent on two factors, metal compositions and exposed facets. On the basis of these results, an energy-based model is proposed to account for the activation of molecular oxygen. As for SOD-like acti...
TL;DR: It is reported that catalytically similar single-atom-centric Pt sites are formed by binding to sodium ions through -O ligands, the ensemble being equally effective on supports as diverse as TiO2, L-zeolites, and mesoporous silica MCM-41.
Abstract: While it has long been known that different types of support oxides have different capabilities to anchor metals and thus tailor the catalytic behavior, it is not always clear whether the support is a mere carrier of the active metal site, itself not participating directly in the reaction pathway. We report that catalytically similar single-atom-centric Pt sites are formed by binding to sodium ions through −O ligands, the ensemble being equally effective on supports as diverse as TiO2, L-zeolites, and mesoporous silica MCM-41. Loading of 0.5 wt % Pt on all of these supports preserves the Pt in atomic dispersion as Pt(II), and the Pt–O(OH)x– species catalyzes the water-gas shift reaction from ∼120 to 400 °C. Since the effect of the support is “indirect,” these findings pave the way for the use of a variety of earth-abundant supports as carriers of atomically dispersed platinum for applications in catalytic fuel-gas processing.
TL;DR: The mechanisms for both activities and their pH-switchability for metals Au, Ag, Pd and Pt are reported and suggest that both activities are intrinsic properties of metals, regardless of the surfaces and intersections of facets exposed to environments.
TL;DR: In SCEINs the single carbon layer does not prevent desired access of the reactants to the vicinity of the iron nanoparticles but protects the active metallic core from oxidation, which opens new avenues for utilizing active transition metals such as iron in a wide range of applications.
Abstract: Efficient hydrogen evolution reaction (HER) through effective and inexpensive electrocatalysts is a valuable approach for clean and renewable energy systems. Here, single-shell carbon-encapsulated iron nanoparticles (SCEINs) decorated on single-walled carbon nanotubes (SWNTs) are introduced as a novel highly active and durable non-noble-metal catalyst for the HER. This catalyst exhibits catalytic properties superior to previously studied nonprecious materials and comparable to those of platinum. The SCEIN/SWNT is synthesized by a novel fast and low-cost aerosol chemical vapor deposition method in a one-step synthesis. In SCEINs the single carbon layer does not prevent desired access of the reactants to the vicinity of the iron nanoparticles but protects the active metallic core from oxidation. This finding opens new avenues for utilizing active transition metals such as iron in a wide range of applications.
TL;DR: In this paper, a wide range of magnetic iron-doped molybdenum carbide (Mo2-xFexC) nanomaterials were synthesized by a unique amine-metal oxide composite method.
Abstract: Molybdenum-based materials have been widely investigated recently as promising alternatives to platinum for catalyzing the hydrogen evolution reaction (HER). Molybdenum carbide is one of the most studied transition-metal carbides because of its cheap price, high abundance, good conductivity, and catalytic activity. In order to further improve the catalytic activity of molybdenum carbide, some modifications have been applied. In this paper, a wide range of magnetic iron-doped molybdenum carbide (Mo2–xFexC) nanomaterials were synthesized by a unique amine–metal oxide composite method. The amount of iron dopants was controlled by setting different iron/molybdenum ratios in the precursors. Iron-doped molybdenum carbide nanomaterials were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy, Raman microscopy, and X-ray photoelectron spectroscopy. Electrocatalytic HER tests were used to demonstrate the catalytic activity upon addition ...
TL;DR: A critical review of the experimental literature for measurements of the work functions of clean metal surfaces of single-crystals is presented in this article, where the results are used to construct a recommended value for each surface examined, along with an uncertainty estimate for that value.
Abstract: A critical review of the experimental literature for measurements of the work functions of clean metal surfaces of single-crystals is presented. The tables presented include all results found for low-index crystal faces except cases that were known to be contaminated surfaces. These results are used to construct a recommended value of the work function for each surface examined, along with an uncertainty estimate for that value. The uncertainties are based in part on the error distribution for all measured work functions in the literature, which is included here. The metals included in this review are silver (Ag), aluminum (Al), gold (Au), copper (Cu), iron (Fe), iridium (Ir), molybdenum (Mo), niobium (Nb), nickel (Ni), palladium (Pd), platinum (Pt), rhodium (Rh), ruthenium (Ru), tantalum (Ta), and tungsten (W).
TL;DR: Calculations based upon periodic, self-consistent density functional theory suggested that the enhancement in specific activity for the Pd@PtnL octahedra could be attributed to the destabilization of OH on their PtnL*/Pd(111) surface relative to the {111} and {100} facets exposed on the surface of Pt/C.
Abstract: We systematically evaluated two different approaches to the syntheses of Pd@PtnL (n = 2–5) core–shell octahedra. We initially prepared the core–shell octahedra using a polyol-based route by titrating a Pt(IV) precursor into the growth solution containing Pd octahedral seeds at 200 °C through the use of a syringe pump. The number of Pt atomic layers could be precisely controlled from two to five by increasing the volume of the precursor solution while fixing the amount of seeds. We then demonstrated the synthesis of Pd@PtnL octahedra using a water-based route at 95 °C through the one-shot injection of a Pt(II) precursor. Due to the large difference in reaction temperature, the Pd@PtnL octahedra obtained via the water-based route showed sharper corners than their counterparts obtained through the polyol-based route. When compared to a commercial Pt/C catalyst based upon 3.2 nm Pt particles, the Pd@PtnL octahedra prepared using both methods showed similar remarkable enhancement in terms of activity (both spe...
TL;DR: In this article, a series of platinum nanoparticles-deposited carbon nitride nanotubes (Pt/C 3 N 4 NTs) was fabricated by a simple one-step solvothermal treatment strategy.
Abstract: A series of platinum nanoparticles-deposited carbon nitride nanotubes (Pt/C 3 N 4 NTs) was fabricated by a simple one-step solvothermal treatment strategy using graphite carbon nitride (g-C 3 N 4 ) and chloroplatinic acid (H 2 PtCl 6 ·6H 2 O) as precursors. The morphology, porosity, phase and chemical structure, and optical and electronic properties of Pt/C 3 N 4 NTs were well characterized. Compared with bulk g-C 3 N 4 , the as-prepared Pt/C 3 N 4 NTs exhibited efficient photocatalytic activity toward hydrogen evolution from water-splitting and aqueous p -chlorophenol degradation under visible-light irradiation ( λ > 420 nm) as a result of their unique tubular nanostructure and the synergic effect of Pt nanoparticles. Subsequently, the activities of simultaneous hydrogen evolution with organic pollutant degradation were also tested using as-prepared Pt/C 3 N 4 NTs under the representative organic pollutants p -chlorophenol, p -nitrophenol, methylene blue, or rhodamine B as electron donors. Finally, the photocatalytic mechanisms in three different photocatalytic systems were discussed.
TL;DR: In this paper, the performance of a rotating disk electrode (RDE) setup for electrochemical area (ECA) and oxygen reduction reaction (ORR) area specific activity and mass specific activity (MA) was characterized for a statistically significant number of independent samples.
Abstract: Platinum electrocatalysts supported on high surface area and Vulcan carbon blacks (Pt/HSC, Pt/V) were characterized in rotating disk electrode (RDE) setups for electrochemical area (ECA) and oxygen reduction reaction (ORR) area specific activity (SA) and mass specific activity (MA) at 0.9 V. Films fabricated using several ink formulations and film-drying techniques were characterized for a statistically significant number of independent samples. The highest quality Pt/HSC films exhibited MA 870 ± 91 mA/mgPt and SA 864 ± 56 μA/cm2 Pt while Pt/V had MA 706 ± 42 mA/mgPt and SA 1120 ± 70 μA/cm2 Pt when measured in 0.1 M HClO4, 20 mV/s, 100 kPa O2 and 23±2°C. An enhancement factor of 2.8 in themeasured SA was observable on eliminating Nafion ionomer and employing extremely thin, uniform films (~4.5 μg/cm2 Pt) of Pt/HSC. The ECA for Pt/HSC (99 ± 7 m2/gPt) and Pt/V (65 ± 5 m2/gPt) were statistically invariant and insensitive to film uniformity/thickness/fabrication technique; accordingly, enhancements in MA are wholly attributable to increases in SA. Impedance measurements coupled with scanning electron microscopy were used to de-convolute the losses within the catalyst layer and ascribed to the catalyst layer resistance, oxygen diffusion, and sulfonate anion adsorption/blocking. The ramifications of thesemore » results for proton exchange membrane fuel cells have also been examined.« less
TL;DR: The high-yield solution synthesis of gold nanoribbons in the 4H hexagonal polytype, a previously unreported metastable phase of gold, is reported, which may open up new strategies for the crystal phase-controlled synthesis of advanced noble metal nanomaterials.
Abstract: Gold, silver, platinum and palladium typically crystallize with the face-centred cubic structure. Here we report the high-yield solution synthesis of gold nanoribbons in the 4H hexagonal polytype, a previously unreported metastable phase of gold. These gold nanoribbons undergo a phase transition from the original 4H hexagonal to face-centred cubic structure on ligand exchange under ambient conditions. Using monochromated electron energy-loss spectroscopy, the strong infrared plasmon absorption of single 4H gold nanoribbons is observed. Furthermore, the 4H hexagonal phases of silver, palladium and platinum can be readily stabilized through direct epitaxial growth of these metals on the 4H gold nanoribbon surface. Our findings may open up new strategies for the crystal phase-controlled synthesis of advanced noble metal nanomaterials.
TL;DR: This work shows that the nanoscale phase segregation can have directionality and be geometrically controlled to produce a Ni octahedron that is penetrated by Pt atoms along three orthogonal Cartesian axes and is coated by Pt molecules along its edges.
Abstract: Catalytic properties of nanoparticles can be significantly enhanced by controlling nanoscale alloying and its structure. In this work, by using a facet-controlled Pt@Ni core–shell octahedron nanoparticle, we show that the nanoscale phase segregation can have directionality and be geometrically controlled to produce a Ni octahedron that is penetrated by Pt atoms along three orthogonal Cartesian axes and is coated by Pt atoms along its edges. This peculiar anisotropic diffusion of Pt core atoms along the ⟨100⟩ vertex, and then toward the ⟨110⟩ edges, is explained via the minimum strain energy for Ni–Ni pair interactions. The selective removal of the Ni-rich phase by etching then results in structurally fortified Pt-rich skeletal PtNi alloy framework nanostructures. Electrochemical evaluation of this hollow nanoframe suggests that the oxygen reduction reaction (ORR) activity is greatly improved compared to conventional Pt catalysts.
TL;DR: In this paper, a seed growth method was used to produce well-controlled platinum catalysts of different cluster sizes and supported on calcined hydrotalcite for propane dehydrogenation.
Abstract: Platinum cluster size has a significant influence on the activity, selectivity, and stability as well as the reaction mechanism during propane dehydrogenation (PDH). Well-controlled platinum catalysts of different cluster sizes are prepared by a seed growth method and supported on calcined hydrotalcite. The Pt catalysts show strong structure-sensitive behavior both in the C–H bond activation of propane and in the C–C bond activation to yield ethylene, methane, and coke. The Pt clusters of small cluster sizes, with (211) dominating on the surface, have a lower dehydrogenation energy barrier and thus higher activity. However, large Pt clusters with Pt(111) dominating result in a weakened binding strength of propylene and an increased energy barrier for the activation of C–H bonds in propylene, which leads to higher selectivity toward propylene by lowering the possibility of deep dehydrogenation. Kinetic analysis illustrates that the reaction order in hydrogen decreases and activation energy increases with a...
TL;DR: The experimental realization of stable counter-electrode (CE) electrocatalysts by alloying Pt with transition metals for enhanced dissolution resistance to state-of-the-art iodide/triiodide (I(-)/I3(-)) redox electrolyte is presented.
Abstract: The dissolution of platinum (Pt) has been one of the heart issues in developing advanced dye-sensitized solar cells (DSSCs). We present here the experimental realization of stable counter-electrode (CE) electrocatalysts by alloying Pt with transition metals for enhanced dissolution resistance to state-of-the-art iodide/triiodide (I(-)/I3(-)) redox electrolyte. Our focus is placed on the systematic studies of dissolution engineering for PtM0.05 (M=Ni, Co, Fe, Pd, Mo, Cu, Cr, and Au) alloy CE electrocatalysts along with mechanism analysis from thermodynamical aspects, yielding more negative Gibbs free energies for the dissolution reactions of transition metals. The competitive reactions between transition metals with iodide species (I3(-), I2) could protect the Pt atoms from being dissolved by redox electrolyte and therefore remain the high catalytic activity of the Pt electrode.