Synthesis,characterization and electrocatalytic activity for ethanol oxidation of carbon supported Pt,Pt–Rh,Pt–SnO2 and Pt–Rh–SnO2 nanoclusters

Nanoclusters of Pt, Pt–Rh, Pt–SnO₂ and Pt–Rh–SnO₂ were successfully synthesized by polyol method and deposited on high-area carbon. HRTEM and XRD analysis revealed two phases in the ternary Pt–Rh–SnO₂/C catalyst: solid solution of Rh in Pt and SnO₂. The activity of Pt–Rh–SnO₂/C for ethanol oxidation was found to be much higher than Pt/C and Pt–Rh/C and also superior to Pt–SnO₂/C. Quasi steady-state measurements at various temperatures (30–60 °C), ethanol concentrations (0.01–1 M) and H₂SO₄ concentrations (0.02–0.5 M) showed that Pt–Rh–SnO₂/C is about 20 times more active than Pt/C in the potential range of interest for the fuel cell application.     

Synthesis, structure and thermogravimetric analysis of Ni–Cd and Cu–Cd heterometallic complexes based on flexible carboxylate ligands

Two 3d–4d heterometallic coordination polymers, namely NiCd(mal)₂(H₂O)₄ (1) and [CuCd(bicH₂)(NO₃)Cl₂(H₂O)]?H₂O (2) [H₂mal = malonic acid, bicH₃ = N,N-bis(2-hydroxyethyl) glycine], have been synthesized under mild conditions and characterized by single-crystal X-ray diffraction, elemental analysis and IR spectrophotometry. Complex 1 is a Ni–Cd heterometallic polymer with 2D extended structure bridged by the mal^2? groups. Complex 2 displays an intriguing 3D Cu–Cd architecture and is the first 3d–4d heterometallic bicinate complex. The TG analyses of both complexes are reported.     

Synthesis and properties of Co–Pt alloy silica core-shell particles

This paper describes a method for fabrication of silica-coated Co–Pt alloy nanoparticles in a liquid phase process. The Co–Pt nanoparticles were prepared from CoCl₂ (4.2 × 10⁻⁵ M), H₂PtCl₆ (1.8 × 10⁻⁵ M), citric acid (4 × 10⁻⁴ M) and NaBH₄ (1.2 × 10⁻² M) with a Co:Pt mole ratio of 7:3. The silica coating was performed in water/ethanol solution with a silane coupling agent, 3-aminopropyltrimethoxysilane (8 × 10⁻⁵ M), and a silica source, tetraethoxyorthosilicate (7.2 × 10⁻⁴ M) in the presence of the Co–Pt nanoparticles. Observations with a transmittance electron microscope and a scanning transmission electron microscope revealed that the Co-rich and Pt-rich nanoparticles were coated with silica. According to X-ray diffraction measurements, core particles were crystallized to metallic Co crystallites and fcc Co–Pt alloy crystallites with annealing in air at 300–500 °C. Magnetic properties of the silica-coated particles were strongly dependent on annealing temperature. Maximum values of 11.4 emu/g-sample for saturation magnetization and 365 Oe for coercive field were obtained for the particles annealed at 300 and 500 °C, respectively. Annealing at a temperature as high as 700 °C destroyed the coating structures because of crystallization of silica shell, resulting in reduction in saturation magnetization and coercive field.     

A sinapic acid–calix[4]arene hybrid selectively binds Pb over Hg and Cd

The binding affinity for Pb²⁺, Cd²⁺ and Hg²⁺ of the sinapic acid–calix[4]arene hybrid 2, having four sinapyl pendants at the upper rim, has been investigated via an UV–Vis study. Compound 2 has better complexing ability than the monomeric p-phenetidine derivative 1. This highlights that the clustering of sinapyl units in a basket-like structure, dictated by the calixarene scaffold, greatly enhances the complexing properties. Ligand 2 forms complexes even with Hg²⁺, which is not complexed by 1 at all; the complexes formed by 2 with Pb²⁺ and Cd²⁺ are much stronger than the analogous complexes formed by 1. The UV–Vis investigation shows that the hybrid 2 markedly favors Pb²⁺ over Cd²⁺ and Hg²⁺. Information on the structural properties of the complex species was obtained by ¹H NMR spectroscopy. NMR data show that all three metal ions are placed into the cavity consisting of the calixarene scaffold and the sinapyl pendants, though their binding affects the coordinating regions to a different extent.     

Underpinning energetics of lithium bonding and stability in the Li–Pt–Sn system

Within the Li–Pt–Sn system, we examine the electronic structures and Li-binding of LiPtSn₂, Li₂PtSn and Li₃Pt₂Sn₃ with fluorite-related crystal structures. The structures with totally de-intercalated lithium keep the characteristics of the pristine ternary compound with a reduction of the volume. In Li₃Pt₂Sn₃ the binding energies of lithium belonging to three crystallographically inequivalent Wyckoff sites are different and point to distinct activities of de-intercalation concomitant with site-selective bonding magnitudes. The derived potentials are within the range of non-oxide binary and ternary lithium based compounds and indicate the possibility of at least partial delithiation.     

Unique CO-tolerance of Pt–WOx materials

Well-defined tungsten-oxide-supported platinum nanoparticles (Pt/WO_x) were elaborated by impregnation-reduction of a platinum salt onto commercial monoclinic WO₃. Field-emission gun scanning electron microscopy (FEG-SEM) and transmission electron microscopy (TEM) revealed that the Pt particles are well-distributed on the oxide support, present a narrow particle size distribution centered on ca. 2–3 nm and a low degree of agglomeration. Carbon black was added to ensure electronic percolation in the electrodes during the electrochemical measurements. CO_ads electrooxidation currents were monitored at potentials as low as 0.1 V vs. RHE on Pt/WO_x, demonstrating high CO-tolerance compared to carbon-supported Pt or PtRu catalysts.     

Microstructure and hydrogen production activity of Pt–TiO2 prepared by precipitation–photodeposition

A series of Pt–TiO₂ photocatalysts were prepared by a facile precipitation–photoreduction method under different pH conditions, using H₂PtCl₆ as platinum precursor. The microstructure and chemical state of Pt loaded on the surface of TiO₂ were analyzed by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). It was revealed that the size and distribution of Pt nanoparticles on TiO₂ surface is closely related to the initial pH of H₂PtCl₆ solution. The optimal pH value for forming highly dispersed Pt nanoparticles is 12. The photocatalytic activities of the prepared samples were investigated in terms of hydrogen production. The results indicated that the Pt–TiO₂ sample prepared by precipitation–photodeposition method shows much higher activity than that prepared by traditional photodeposition method.     

Oxidation of Methanol on Pt,Pt–Ru,and Pt–Ru–Mo Electrocatalysts Dispersed in Polyaniline: An in situ Infrared Reflectance Spectroscopy Study

The electrochemical oxidation of methanol was investigated on a Pt–Ru–Mo catalyst with an in situ infrared reflectance spectroscopy. The electrocatalysts were prepared by an electrochemical deposition and dispersed in a conducting three-dimensional matrix of polyaniline (PAni). We observed that CO₂ is produced from methanol oxidation at 350 mV vs. RHE on PAni/Pt–Ru–Mo, which is 100 mV less negative than on PAni/Pt–Ru and 200 mV less than on PAni/Pt. The results suggest that Pt–Ru–Mo is less sensitive to CO_ADS poisoning than Pt–Ru and much more sensitive than Pt. Large differences are observed concerning the average wavenumber of _ADS between Pt–Ru–Mo, Pt–Ru, and Pt.     

Oxidation of carbon monoxide and formic acid on bulk and nanosized Pt–Co alloys

Bulk Pt₃Co and nanosized Pt₃Co and PtCo alloys supported on high area carbon were investigated as the electrocatalysts for the CO_ads and HCOOH oxidation. Pt₃Co alloy with Co electrochemically leached from the surface (Pt skeleton) was employed to separate electronic from ensemble and bifunctional effects of Co. Cyclic voltammetry in 0.1 M HClO₄ showed reduced amount of adsorbed hydrogen on Pt sites on Pt₃Co alloy compared to pure Pt. However, no significant difference in hydrogen adsorption/desorption and Pt-oxide reduction features between Pt₃Co with Pt skeleton structure and bulk Pt was observed. The oxidation of CO_ads on Pt₃Co alloy commenced earlier than on Pt, but this effect on Pt₃Co with Pt skeleton structure was minor indicating that bifunctional mechanism is stronger than the electronic modification of Pt by Co. The HCOOH oxidation rate on Pt₃Co alloy was about seven times higher than on bulk Pt when the reaction rates were compared at 0.4 V, i.e., in the middle of the potential range for the HCOOH oxidation. Like in the case of CO_ads oxidation, Pt skeleton showed similar activity as bulk Pt indicating that the ensemble effect is responsible for the enhanced activity of Pt₃Co alloy toward HCOOH oxidation. The comparison of CO_ads and HCOOH oxidation on Pt₃Co/C and PtCo/C with the same reaction on Pt/C were qualitatively the same as on bulk materials.     

A ratiometric electrochemical biosensor for sensitive detection of Hg based on thymine–Hg–thymine structure

In this paper, a simple, selective and reusable electrochemical biosensor for the sensitive detection of mercury ions (Hg²⁺) has been developed based on thymine (T)-rich stem–loop (hairpin) DNA probe and a dual-signaling electrochemical ratiometric strategy. The assay strategy includes both “signal-on” and “signal-off” elements. The thiolated methylene blue (MB)-modified T-rich hairpin DNA capture probe (MB-P) firstly self-assembled on the gold electrode surface via Au–S bond. In the presence of Hg²⁺, the ferrocene (Fc)-labeled T-rich DNA probe (Fc-P) hybridized with MB-P via the Hg²⁺-mediated coordination of T–Hg²⁺–T base pairs. As a result, the hairpin MB-P was opened, the MB tags were away from the gold electrode surface and the Fc tags closed to the gold electrode surface. These conformation changes led to the decrease of the oxidation peak current of MB (I_MB), accompanied with the increase of that of Fc (I_Fc). The logarithmic value of I_Fc/I_MB is linear with the logarithm of Hg²⁺ concentration in the range from 0.5 nM to 5000 nM, and the detection limit of 0.08 nM is much lower than 10 nM (the US Environmental Protection Agency (EPA) limit of Hg²⁺ in drinking water). What is more, the developed DNA-based electrochemical biosensor could be regenerated by adding cysteine and Mg²⁺. This strategy provides a simple and rapid approach for the detection of Hg²⁺, and has promising application in the detection of Hg²⁺ in real environmental samples.     

Theoretical Study on the Structures and Thermal Properties of Ag–Pt–Ni Trimetallic Clusters

The structures and thermal properties of Ag–Pt–Ni ternary nanoclusters varying with different compositions and sizes are studied by Monte Carlo and molecular dynamics simulations. It can be found that silver atoms tend to occupy the surface and platinum atoms favor the subsurface occupation, whereas the inner is occupied by nickel atoms due to the different surface energies and lattice parameters. In addition, there is a non-monotonous relationship between the melting points and compositions of Ag–Pt–Ni ternary nanoclusters according to molecular dynamics simulations. In addition, a linear decrease in melting point with \(N^{ - 1/3}\) is found for both monometallic and trimetallic clusters. This behavior is consistent with Pawlow’s law.     

Theoretical Study of Interaction between Hydrogen and Small Pt–Sn Intermetallic Clusters

Small clusters, which simulate the active sites of Pt–Sn intermetallics exhibiting a high level of activity and selectivity in the deoxygenation reaction of esters without the loss of carbon mass to form C₁, C₂, and carbon oxides, are constructed and studied with the density functional theory. Molecular adsorption of hydrogen, dissociation of hydrogen molecules at Pt sites, and transition of adsorbed hydrogen atoms from Pt to Sn are considered. The introduction of Sn significantly decreases the affinity of platinum to hydrogen, so that the transition of H atoms to Sn atoms is facilitated with the increase in the amount of Sn. A comparison of the activation energies for such a transition with those of the possible association of hydrogen atoms on tin and the molecular desorption of H₂ showed that the hydrogen spillover in the Pt–Sn intermetallics should not lead to a significant accumulation of hydrogen on tin. In other words, in contrast to Pt atoms, Sn atoms probably cannot serve as active sites of hydrogen adsorption in the deoxygenation reaction.     

Electrochemical and electrochromic properties of nanoworm-shaped Ta2O5–Pt thin-films

A Ta₂O₅–Pt nanostructure electrode was fabricated by means of cosputtering deposition method. Worm-like Pt nanoparticles were produced in Ta₂O₅ matrix as observed by transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). The electrochemical and electrochromic properties of nanoworm-shaped Ta₂O₅–Pt electrode are compared with those of Ta₂O₅ thin-film electrode without Pt nanoparticles.     

Electrodeposition of Thin Cu–Cd–Se Film Layers

The formation of ternary Cu–Cd–Se thin film layers on a polycrystalline Pt electrode during the voltammetric scanning is examined. A sulfuric acid matrix containing selenious acid and uncomplexed Cu²⁺ and Cd²⁺ ions is used in all the cases. The growth kinetics is monitored by cyclic voltammetric measurements. The composition and structure are analyzed by XRD and ex situ Auger electron spectroscopy techniques. An underlying electrodeposition mechanism is proposed for the ternary system formation. It is shown that the growth process has a multistage character. Cu–Cd–Se film layers up to 2.5 m are obtained on a polycrystalline Pt cathode by potentiostatic electrolysis at E = 0.05 V (SHE). The chemical composition of the obtained layer is 39.1, 10.6, and 50.3 at. % Cu, Cd, and Se, respectively.     

Evaluation of stability of silica-supported Fe–Pd and Fe–Pt nanoparticles in aerobic conditions using thermal analysis

The applications of zerovalent iron nanoparticles (nZVI) exploit their high reactivity which decreases due to oxidation in aerobic conditions during manufacture, application, and storage. In this study, we present the new procedure for estimation of the nZVI stability to oxidation in air. The procedure is suitable for characterization of the novel materials based on the supported nZVI. Nanoscale particles were synthesized inside porous silica supports by incipient wetness impregnation with the metal precursor solutions followed by thermal treatment. The TG–DTA studies revealed the decomposition temperature of the supported precursors, as well as the interaction of Fe and precious metal precursors, which resulted in the formation of alloy nanoparticles. Characterization of the samples by XRD confirmed the formation of the nanoparticles of the metallic Pd, Pt, and Fe phases supported on SiO₂ carriers, as well as the formation of solid solutions based on the structure of precious metals. The new procedure for estimation of the nZVI stability included (1) TPR with hydrogen up to 400–425 °C followed by isothermal reduction at these temperatures; (2) in situ reoxidation with oxygen at room temperature. The samples were reduced “as obtained” and after in situ reoxidation. The results of the TPR studies exhibited that introduction of both Pd and Pt protected the Fe nanoparticles from oxidation with oxygen and air at ambient conditions.     

Thermal and electrochemical study of solid-state reaction of mercury with Pt–20% Rh alloy

Thermogravimetry (TG), energy dispersive X-ray microanalysis (EDX), scanning electron microscopy (SEM), mapping surface and X-ray diffraction (XRD) have been used to study the reaction of mercury with platinum–rhodium (Pt–Rh) alloy. The results suggest that, when heated, the electrodeposited Hg film reacts with Pt–Rh to form intermetallic compounds each having a different stability, indicated by separate third mass-loss steps. In the first step, between room temperature and 170 °C, only the bulk Hg is removed. From this temperature to about 224 °C, the mass loss can be attributed to decomposition of the intermetallic PtHg₄. The third step, from 224 to 305 °C, can be ascribed to thermal decomposition of solid solution composed of intermetallic species RhHg₂ and PtHg₂. Intermetallic compound such as PtHg₄, PtHg₂, and RhHg₂ was characterized by XRD. These intermetallic compounds were the main products formed on the surface of the samples after partial removal of the bulk mercury via thermal desorption.     

Synthesis and characterization of bimetallic Pt–Fe/polypyrrole–carbon catalyst as DMFC anode catalyst

A novel synthesis route, concerning in situ interfacial polymerization of pyrrole on carbon black and following co-deposition of Pt and Fe on polypyrrole–carbon support, is developed to prepare the bimetallic Pt–Fe/polypyrrole–carbon catalyst. In this synthesis process, ferrous precursor simultaneously functions as an oxidant for the polymerization of pyrrole. The Pt–Fe/polypyrrole–carbon catalyst shows improved catalytic activity towards methanol oxidation compared to commercial Pt/C catalyst, which may be of great potential in direct methanol fuel cells.     

Cyclic voltammetric behavior of Pd–Pt–Rh ternary alloys

The electrochemical behavior of Pd–Pt–Rh alloys has been investigated using cyclic voltammetry (CV). The alloys were prepared by electrochemical codeposition as limited volume electrodes (less than 1 m in thickness). The morphology of the alloy surface and bulk compositions were examined by the SEM/EDAX method. Surface oxides generation (oxygen adsorption) and oxides reduction (oxygen desorption) currents together with hydrogen adsorption and hydrogen absorption signals can be distinguished on CV curves. During potential cycling through the full hydrogen–oxygen potential range Rh and Pd are preferentially dissolved, which is reflected in a dramatic transformation in the voltammogram shape. The composition changes involve not only the surface but also some atomic layers beneath the surface.     

Preparation and electrochemical performance of graphene–Pt black nanocomposite for electrochemical methanol oxidation

This work reports the preparation, characterization, and electrocatalytic characteristics of a new metallic nanocatalyst. The catalyst, Pt black–graphene oxide (Pt-GO), was prepared by deposition of Pt black on the surface of graphene oxide nanosheet and characterized by transmission electron microscopy (TEM), energy-dispersive spectroscopy (EDS), and voltammetry. The Pt-graphene (Pt-GR) composite modified glassy carbon electrode (Pt-GR/GCE) was prepared with cyclic voltammetric scanning of Pt-GO/GCE in the potential range from ?1.5 to 0.2 in 0.1 M phosphate buffer solution at 50 mV·s^?1 for 5 cycles. The electrocatalytic properties of the Pt-GR/GCE for methanol (CH₃OH) oxidation have been investigated by cyclic voltammetry (CV); high electrocatalytic activity of the Pt-GR/GCE can be observed. This may be attributed to the high dispersion of Pt catalyst and the particular properties of GR support. The long-term stability of Pt-GR composite was investigated in 0.05 M CH₃OH in 0.1 M H₂SO₄ solution. It can be observed that the peak current decreases gradually with the successive scans. The loss may result from the consumption of methanol during the CV scan. It also may be due to the poisoning organic compounds. The results imply that the Pt-GR composite has good potential applications in fuel cells.     

Electrochemical determination of the surface composition of Pd–Pt core–shell nanoparticles

Different amounts of Pt atoms were deposited onto the surface of Pd nanoparticles supported on carbon black by hydroquinone reduction method in anhydrous ethanol. Here, we surveyed electrochemical probing of surface compositions of Pd–Pt surface alloys. They were calculated from hydrogen desorption, carbon monoxide adlayer oxidation, and reduced carbon dioxide oxidation charges. The surface composition of Pt drastically increased up to Pt[0.3]/Pd/C (23.1 at.% of Pt) and then approached that of pure Pt with the moderate rate of increase.