Facile design of Au@Pt core-shell nanostructures: Formation of Pt submonolayers with tunable coverage and their applications in electrocatalysis

A facile design of Pt nanostructures from submonolayer to monolayer has been realized by ion adsorption-in situ electrochemical reduction on Au nanoparticles supported on multiwall carbon nanotubes （CNTs）. The as prepared Au@Pt/CNTs catalysts display coverage-specific electrocatalysis. Au@Pt/CNTs with low Pt coverage is inactive towards methanol oxidation whereas it oxidizes formic acid effectively through a direct pathway with mass specific activity 90 times that of a commercial Pt/C catalyst. Due to its inertness to methanol, it shows high performance in the oxygen reduction reaction （ORR） with high methanol tolerance. In contrast, simply increasing the Pt coverage to above 40% switches the formic acid oxidation process to both direct and indirect catalytic pathways, and also results in high methanol oxidation activity.     

One-step scalable preparation of N-doped nanoporous carbon as a high-performance electrocatalyst for the oxygen reduction reaction

N-doped porous carbon materials have been prepared by a simple one-step pyrolysis of ethylenediaminetetraacetic acid (EDTA) and melamine in the presence of KOH and Co(NO₃)₂·6H₂O. The combination of the high specific area (1485 m²·g^?1), high nitrogen content (10.8%) and suitable graphitic degree results in catalysts exhibiting high activity (with onset and half-wave potentials of 0.88 and 0.79 V vs the reversible hydrogen electrode (RHE), respectively) and four-electron selectivity for the oxygen reduction reaction (ORR) in alkaline medium—comparable to a commercial Pt/C catalyst, but far exceeding Pt/C in stability and durability. Owing to their superb ORR performance, low cost and facile preparation, the catalysts have great potential applications in fuel cells, metal-air batteries, and ORR-related electrochemical industries.      

Enhanced π-π interactions between a C60 fullerene and a buckle bend on a double-walled carbon nanotube

In situ low-voltage aberration corrected transmission electron microscopy (TEM) observations of the dynamic entrapment of a C₆₀ molecule in the saddle of a bent double-walled carbon nanotube is presented. The fullerene interaction is non-covalent, suggesting that enhanced π-π interactions (van der Waals forces) are responsible. Classical molecular dynamics calculations confirm that the increased interaction area associated with a buckle is sufficient to trap a fullerene. Moreover, they show hopping behavior in agreement with our experimental observations. Our findings further our understanding of carbon nanostructure interactions, which are important in the rapidly developing field of low-voltage aberration corrected TEM and nano-carbon device fabrication.      

Dendritic platinum–copper bimetallic nanoassemblies with tunable composition and structure: Arginine-driven self-assembly and enhanced electrocatalytic activity

Novel self-assembled architectures have received a growing amount of attention and have significant potential for application in catalysis/electrocatalysis. Herein, we take advantage of the unique coordination and self-assembly properties of arginine for the preparation of dendritic PtCu bimetallic nanoassemblies with tunable chemical composition and structure. Strong interactions between the arginine molecules are key in driving the self-assembly of primary nanocrystals. In addition, the strong coordination interactions between arginine and metal ions is responsible for the formation of Pt–Cu alloys. We also investigated the electrocatalytic activity of various dendritic PtCu bimetallic nanoassemblies towards the methanol oxidation reaction. Pt₃Cu₁ nanoassemblies exhibited excellent electrocatalytic activity and stability in comparison with other PtCu bimetallic nanoassemblies (Pt₁Cu₃, Pt₁Cu₁) and commercial Pt black, due to their unique dendritic structures and the synergistic effect between the Pt and Cu atoms.

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Light-controlled synthesis of uniform platinum nanodendrites with markedly enhanced electrocatalytic activity

We report a fast in situ seeding approach based on zinc（II） porphyrin （ZnP） under white light irradiation, leading to uniform spherical platinum nanodendrites with tunable sizes. The platinum nanodendrites exhibit significantly improved electrocatalytic activities toward oxygen reduction reaction （ORR） and methanol oxidation reaction （MOR） compared with commercial platinum black.     

Photocatalytic reduction of CO<Subscript>2</Subscript> with H<Subscript>2</Subscript>O over modified TiO<Subscript>2</Subscript> nanofibers: Understanding the reduction pathway

Nanosized metal (Pt or Pd)-decorated TiO₂ nanofibers (NFs) were synthesized by a wet impregnation method. CdSe quantum dots (QDs) were then anchored onto the metal-decorated TiO₂ NFs. The photocatalytic performance of these catalysts was tested for activation and reduction of CO₂ under UV-B light. Gas chromatographic analysis indicated the formation of methanol, formic acid, and methyl formate as the primary products. In the absence of CdSe QDs, Pd-decorated TiO₂ NFs were found to exhibit enhanced performance compared to Pt-decorated TiO₂ NFs for methanol production. However, in the presence of CdSe, Pt-decorated TiO₂ NFs exhibited higher selectivity for methanol, typically producing ～90 ppmg^?1·h^?1 methanol. The CO₂ photoreduction mechanism is proposed to take place via a hydrogenation pathway from first principles calculations, which complement the experimental observations.

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Composition-tuned oxidation levels of Pt–Re bimetallic nanoparticles for the etherification of allylic alcohols

The catalytic performance of metal nanoparticles is often affected by surface oxidation levels. Instead of post-synthesis oxidation/reduction, we propose an efficient method to modulate the oxidation levels by tuning the composition of bimetallic nanoparticles. Here we report a series of Pt–Re bimetallic nanoparticles synthesized via a facile thermal co-reduction process, with a uniform size of approximately 3 nm. The investigation of the growth of the Pt–Re nanoparticles suggests that the Re atoms were enriched on the surface, as confirmed by X-ray photoelectron spectroscopy. Furthermore, X-ray absorption spectroscopy showed that metallic Re was decreased and high-valency ReO_x species were increased in particles with higher Re/Pt ratios. In the etherification of allylic alcohols catalyzed by Pt–Re nanoparticles of different compositions under ambient conditions, particles with higher Re/Pt ratios exhibited significantly better performances. The highest mass activity of Pt–Re bimetallic nanoparticles (127 μmol·g^?1·s^?1) was more than forty times that of the industrial catalyst CH₃ReO₃ (3 μmol·g^?1·s^?1). The catalytically active sites were associated with ReO_x and could be tuned by adjusting the Pt ratio.

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<Emphasis Type="Italic">In-situ</Emphasis> probing of thermal desorption of vapor molecules on a nanowire via work function variance

Nanowire sensors based on variations of their electrical properties show great potential for real-time, in situ monitoring of molecular adsorption and desorption. Although the molecular adsorption-induced change in the electronic work function is very sensitive, it does not have any specificity. However, the temperature dependency of the adsorption-induced work function variation can provide limited selectivity based on the desorption temperature. In this study, we report the in situ probing of molecular desorption by monitoring the work function variations of a single Pt nanowire as a function of temperature. The work function of a clean Pt nanowire shows a significant variation due to vapor adsorption at room temperature. Increasing the temperature of the nanowire results in a variation of the work function due to molecular desorption. Experimentally measured differential work function as a function of temperature shows desorption peaks at 36 and 44 °C for methanol and ethanol molecules respectively. Adsorption-induced variation of the Pt nanowire work function was further confirmed using ultraviolet photoelectron spectroscopy before and after exposure to methanol vapor. These results show that the molecular adsorption/desorption-induced variation of the work function and its temperature dependency can be used for developing nanoscale electro-calorimetric sensors.

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Electrical behaviour of doped-yttria stabilized zirconia ceramic materials

Single-phase sintered ceramic materials (ZrO₂)_1?x {(Y₂O₃) _y (RE₂O₃)_{1-y x} }_x (RE=Nd, Ce, Dy, Er), were synthesized and electrical conductivity and transport number measurements were made as a function of temperature between 500 and 1200° C. The activation energies of conduction were determined, and it was found that the charge carriers in these solid solutions are oxygen ions. The fabricated electrolyte discs were used in cells of the type \(P_{O_2 }\) , Pt/zirconia solid solution/ \(P_{\mathop O\limits^{'} _2 }\) , platinum where \(P_{O_2 }\) =air (0.21 atm) and \(P_{\mathop O\limits^{'} _2 }\) =1 atm or argon-O₂ mixtures. Below 700° C, the e.m.f. deviated from the theoretical values for completely ionic conduction; good agreement was observed above this temperature.     

Superfluorinated copper sulfide nanoprobes for simultaneous <Superscript>19</Superscript>F magnetic resonance imaging and photothermal ablation

Copper sulfide (Cu₇S₄) nanoparticles coated with an ultra-high payload (~5.0 × 10⁷ fluorine atoms per particle) of fluorinated ligands (oleylamine functionalized 3,5-bis(trifluoromethyl)benzaldehyde, ¹⁹F_OAm) exhibited a single intense 19F magnetic resonance (MR) signal and efficient near infrared photothermal performance in water medium. In vivo assessment revealed strong ¹⁹F MR signals at cancerous lesions and effective inhibition of tumor growth after photothermal treatment, indicating the great potential of these fabricated nanoprobes for simultaneous ¹⁹F MR imaging and photothermal therapy.

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Fabrication of patterned boron carbide nanowires and their electrical, field emission, and flexibility properties

Large-area patterned boron carbide nanowires (B₄C NWs) have been synthesized using chemical vapor deposition (CVD). The average diameter of B₄C NWs is about 50 nm, with a mean length of 20 ??m. The B₄C NWs have a single-crystal structure and conductivities around 5.1 × 10^?2 ??^?1·cm^?1. Field emission measurements of patterned B₄C NWs films show that their turn-on electric field is 2.7 V/??m, lower than that of continuous B₄C NWs films. A single nanowire also exhibits excellent flexibility under high-strain bending cycles without deformation or failure. All together, this suggests that B₄C NWs are a promising candidate for flexible cold cathode materials.      

Clean transfer of graphene on Pt foils mediated by a carbon monoxide intercalation process

Noble metals such as Pt are a perfect substrate for the catalytic growth of monolayer graphene. However, the requirements of the subsequent transfer process are not compatible with the traditional etching method. In this work, we find that the interaction of graphene with Pt foil can be weakened through the intercalation of carbon monoxide （CO） under ambient pressure. This intercalation process occurs on both hexagonal-shape graphene islands and irregular graphene patches on changing the CO partial pressure from 0 to 0.6 MPa, as observed by scanning electron microscopy （SEM）, Raman spectroscopy and X-ray photoemission spectroscopy. We demonstrate that, on a practical timescale, the intercalation ratio is proportional to the partial pressure of CO. Furthermore, we develop a clean transfer method of CO-intercalated graphene with water as a peeling agent. We show that this method enables the transfer of tens of micrometer-scale graphene patches onto SiO2/Si, which are free from metal or oxide particle contamination. This transfer method should be a significant step towards the dean transfer of graphene, as well as the recydable use of noble metal substrates.     

Ultraviolet photoconductance of a single hexagonal WO3 nanowire

The ultraviolet (UV) photoconductance properties of a single hexagonal WO₃ nanowire have been studied systematically. The conductance of WO₃ nanowires is very sensitive to ultraviolet B light and a field-effect transistor (FET) nanodevice incorporating a single WO₃ nanowire exhibits excellent sensitivity, reversibility, and wavelength selectivity. A high photoconductivity gain suggests that WO₃ nanowires can be used as the sensing element for UV photodetectors. Measurements under UV light in vacuum show that the adsorption and desorption of oxygen molecules on the surface of the WO₃ nanowire can significantly influence its photoelectrical properties. The WO₃ nanowires have potential applications in biological sensors, optoelectronic devices, optical memory, and other areas.      

Small-sized tungsten nitride anchoring into a 3D CNT-rGO framework as a superior bifunctional catalyst for the methanol oxidation and oxygen reduction reactions

The application of direct methanol fuel cells (DMFC) is hampered by high cost, low activity, and poor CO tolerance by the Pt catalyst. Herein, we designed a fancy 3D hybrid by anchoring tungsten nitride (WN) nanoparticles (NPs), of about 3 nm in size, into a 3D carbon nanotube-reduced graphene oxide framework (CNT-rGO) using an assembly route. After depositing Pt, the contacted and strongly coupled Pt–WN NPs were formed, resulting in electron transfer from Pt to WN. The 3D Pt–WN/CNT-rGO hybrid can be used as a bifunctional electrocatalyst for both methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR). In MOR, the catalysts showed excellent CO tolerance and a high mass activity of 702.4 mA·mg_Pt ^–1, 2.44 and 3.81 times higher than those of Pt/CNT-rGO and Pt/C(JM) catalysts, respectively. The catalyst also exhibited a more positive onset potential (1.03 V), higher mass activity (151.3 mA·mg_Pt ^–1), and better cyclic stability and tolerance in MOR than ORR. The catalyst mainly exhibited a 4e-transfer mechanism with a low peroxide yield. The high activity was closely related to hybrid structure. That is, the 3D framework provided a favorable path for mass-transfer, the CNT-rGO support was favorable for charge transfer, and strongly coupled Pt–WN can enhance the catalytic activity and CO-tolerance of Pt. Pt–WN/CNT-rGO represents a new 3D catalytic platform that is promising as an electrocatalyst for DMFC because it can catalyze both ORR and MOR in an acidic medium with good stability and highly efficient Pt utilization.

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Resistive switching in \hbox {BiFeO}_3-based heterostructures due to ferroelectric modulation on interface Schottky barriers

Ferroelectric \(\hbox {BiFeO}_3\) (BFO) thin films were deposited on (001) \(\hbox {SrTiO}_3\) substrates buffered with \(\hbox {La}_{0.7}\hbox {Sr}_{0.3}\hbox {MnO}_3\) (LSMO) electrodes. Bipolar resistive switching in Pt/BFO/LSMO heterostructures were observed with high stability and long retention. However, transport characteristics of Pt/BFO/LSMO is highly asymmetric and pronounced resistive switching can only be observed by applying negative reading pulses on the Pt top electrodes, i.e. when the Pt/BFO Schottky barrier is reverse-biased. This resistive switching is discussed in terms of a modulation on the Pt/BFO interface Schottky barrier by the polarization switching in ferroelectric BFO. Comparative studies on Pt/BFO/ \(\hbox {SrRuO}_3\) and Pt/BFO/ \(\hbox {LaNiO}_3\) heterostructures reveal that the work function of the electrode materials and the formation of Schottky barriers are significant to the observed resistive switching behaviors.     

Redox-sensitive colorimetric polyaniline nanoprobes synthesized by a solvent-shift process

We have synthesized water-stable polyaniline nanoparticles coated with triarmed polyethylene glycol chains using a solvent-shift method and confirmed their colloidal size and aqueous solubility. Furthermore, we have demonstrated that the polyaniline nanoparticles can be doped with biological dopants to produce distinct color changes allowing the detection of live cancer cells.      

Solution-processable graphene mesh transparent electrodes for organic solar cells

Graphene mesh electrodes (GMEs) with good conductivity and transparency have been fabricated by the standard industrial photolithography and O₂ plasma etching process using graphene solutions. Organic photovoltaic (OPV) cells using GMEs as the transparent electrodes with a blend of poly-(3-hexylthiophene)/phenyl-C₆₁-butyric acid methyl ester (P3HT/PC₆₁BM) as the active layer have been fabricated and exhibit a power conversion efficiency (PCE) of 2.04%, the highest PCE for solution-processed graphene transparent electrode-based solar cells reported to date.      

Architecture of PtFe/C catalyst with high activity and durability for oxygen reduction reaction

A PtFe/C catalyst has been synthesized by impregnation and high-temperature reduction followed by acid-leaching. X-ray diffraction, X-ray photoelectron spectroscopy and X-ray atomic near edge spectroscopy characterization reveal that Pt₃Fe alloy formation occurs during high-temperature reduction and that unstable Fe species are dissolved into acid solution. The difference in Fe concentration from the core region to the surface and strong O-Fe bonding may drive the outward diffusion of Fe to the highly corrugated Pt-skeleton, and the resulting highly dispersed surface FeO _x is stable in acidic medium, leading to the construction of a Pt₃Fe@Pt-FeO _x architecture. The as prepared PtFe/C catalyst demonstrates a higher activity and comparable durability for the oxygen reduction reaction compared with a Pt/C catalyst, which might be due to the synergetic effect of surface and subsurface Fe species in the PtFe/C catalyst.      

Cryptanalysis of a key exchange protocol based on the endomorphisms ring End{(\mathbb{Z}_{p} \times \mathbb{Z}_{p^2})}

Climent et?al. (Appl Algebra Eng Commun Comput 22:91?C108, 2011) identified the elements of the endomorphisms ring End ${(\mathbb{Z}_p \times \mathbb{Z}_{p^2})}$ with elements in a set, E _p , of matrices of size 2?× 2, whose elements in the first row belong to ${\mathbb{Z}_{p}}$ and the elements in the second row belong to ${\mathbb{Z}_{p^2}}$ . By taking advantage of matrix arithmetic, they proposed a key exchange protocol using polynomial functions over E _p defined by polynomials in ${\mathbb{Z}[X]}$ . In this note, we show that this protocol is insecure; it can be broken by solving a set of 10 consistent homogeneous linear equations in 8 unknowns over ${\mathbb{Z}_{p^2}}$ .     

Photocatalytic CO<Subscript>2</Subscript> reduction highly enhanced by oxygen vacancies on Pt-nanoparticle-dispersed gallium oxide

Photocatalytic CO₂ reduction on metal-oxide-based catalysts is promising for solving the energy and environmental crises faced by mankind. The oxygen vacancy (V _o) on metal oxides is expected to be a key factor affecting the efficiency of photocatalytic CO₂ reduction on metal-oxide-based catalysts. Yet, to date, the question of how an V _o influences photocatalytic CO₂ reduction is still unanswered. Herein, we report that, on V _o-rich gallium oxide coated with Pt nanoparticles (V _o-rich Pt/Ga₂O₃), CO₂ is photocatalytically reduced to CO, with a highly enhanced CO evolution rate (21.0 μmol·h^?1) compared to those on V _o-poor Pt/Ga₂O₃ (3.9 μmol·h^?1) and Pt/TiO₂(P25) (6.7 μmol·h^?1). We demonstrate that the V _o leads to improved CO₂ adsorption and separation of the photoinduced charges on Pt/Ga₂O₃, thus enhancing the photocatalytic activity of Pt/Ga₂O₃. Rational fabrication of an V _o is thereby an attractive strategy for developing efficient catalysts for photocatalytic CO₂ reduction.

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