Two-step Reduction Method Research Articles

Impact of H2O exposure on the structure and electrochemical performance of LiVPO4F cathode material

In this work, triclinic structured LiVPO4F is prepared by a simple two-step carbothermal reduction method and subsequently exposed to water under different storage conditions. The impact of exposure on the structure, morphology and electrochemical performance of LiVPO4F is investigated in detail. It is found that the effect of exposure at room temperature (20°C) is slight. In contrast, exposure at 80°C has great effect on the structure and electrochemical properties of LiVPO4F. Li, P and V dissolution into aqueous solution at 80°C results in the formation of a yellowish solution. Electrochemical tests show that LiVPO4F samples aged in water at 80°C for 3 and 5days show poorer electrochemical properties than the pristine sample. LiVPO4F aged in water at 80°C for 15days exhibits higher initial reversible capacity compared with the pristine sample. However, it deteriorates rapidly in the following cycles due to the moisture-sensitive surface, which induces the formation of thick Li2CO3/Li3PO4 film on the surface and leads to a high charge transfer resistance and the degradation of electrochemical performance.

CO2-free power generation on an iron group nanoalloy catalyst via selective oxidation of ethylene glycol to oxalic acid in alkaline media.

An Fe group ternary nanoalloy (NA) catalyst enabled selective electrocatalysis towards CO2-free power generation from highly deliverable ethylene glycol (EG). A solid-solution-type FeCoNi NA catalyst supported on carbon was prepared by a two-step reduction method. High-resolution electron microscopy techniques identified atomic-level mixing of constituent elements in the nanoalloy. We examined the distribution of oxidised species, including CO2, produced on the FeCoNi nanoalloy catalyst in the EG electrooxidation under alkaline conditions. The FeCoNi nanoalloy catalyst exhibited the highest selectivities toward the formation of C2 products and to oxalic acid, i.e., 99 and 60%, respectively, at 0.4 V vs. the reversible hydrogen electrode (RHE), without CO2 generation. We successfully generated power by a direct EG alkaline fuel cell employing the FeCoNi nanoalloy catalyst and a solid-oxide electrolyte with oxygen reduction ability, i.e., a completely precious-metal-free system.

Methanol Electro-Oxidation Using RuRh@Pt/C

A core-shell structure RuRh@Pt/C nanoparticles was prepared by using a two-step reduction method under ultrasonic promotion. The catalytic performance was tested in methanol electrooxidation. X-ray diffraction (XRD), scanning electron microscope (SEM) combined with cyclic voltammetry (CV) were used to characterize the obtained catalyst. The results showed that there was no alloy formed between the core RuRh and the shell Pt. The electrocatalytic activity of RuRh@Pt/C varied with the Ru/Rh ratio in the bimetallic core, among which the catalyst with the Ru/Rh ratio 1:2 and the Pt-shell thickness of 1.5 (Ru1Rh2@Pt1.5/C) showed the highest catalytic activity for methanol. With this catalyst, the current density of the oxidation peak for methanol electro-oxidation reached 2.3 times as that of Pt1.5/C while the corresponding peak potential shifted 60 mV negatively in comparing to that of Pt1.5/C. In addition, the catalyst with the core-shell structure of RuRh@Pt/C possessed much higher CO-tolerance for methanol electro-oxidation, indicating its promising application in low temperature fuel cell.

Spillover enhanced hydrogen uptake of Pt/Pd doped corncob-derived activated carbon with ultra-high surface area at high pressure

Corncob-derived activated carbon (CAC) was prepared by potassium hydroxide activation. The Pt/Pd-doped CAC samples were prepared by two-step reduction method (ethylene glycol reduction plus hydrogen reduction). The as-obtained samples were characterized by N2-sorption, TEM and XRD. The results show the texture of CAC is varied after doping Pt/Pd. The Pd particles are easier to grow up than Pt particles on the surface of activated carbon. For containing Pt samples, the pore size distributions are different from original sample and Pd loaded sample. The hydrogen uptake results show excess hydrogen uptake capacity on the Pt/Pd-doped CAC samples are higher than pure CAC at 298 K, which should be attributed to hydrogen spillover effects. The 2.5%Pt and 2.5%Pd hybrid doped CAC sample shows the highest hydrogen uptake capacity (1.65 wt%) at 298 K and 180 bar, The particle size and distribution of Pt/Pd catalysts could play a crucial role on hydrogen uptake by spillover. The total hydrogen storage capacity analysis show that total H2 storage capacities for all samples are similar, and spillover enhanced H2 uptakes of metal-doped samples could not well support total H2 storage capacity. The total pore volume of porous materials also is a key factor to affect total hydrogen storage capacity.

A Two-Step Model Reduction Method for a Strap-on Launch Vehicle

In this paper, a two-step model reduction method is proposed using a strap-on launch vehicle as research object. In this method, the double-compatible free-interface modal synthesis method is first used for the modeling of the system, and the first step of reduction work is done by preserving the lower-order modes of flexible components of the system in the modeling process for the system. Then the second step of reduction is done for the established dynamic model of the system using the modal cost analysis method. After the two steps of order reduction, a low-order dynamic model of the system can be obtained. Simulation results indicate that this low-order model can reflect the characteristics of the original system effectively and the order is low enough as well.

Synthesis of Core-Shell Co@Pt/C Electrocatalyst and Effects of Stabilizer and pH on Its Performance

Carbon-supported Co@Pt core shell catalysts have been synthesized by the two-step chemical reduction method. The effects of the catalyst preparation conditions including pH value of the initial solution and the stabilizers on the performance of the Co@Pt/C catalyst were investigated. Transmission Electron Microscope (TEM) and X-Ray Diffraction (XRD) techniques were used to characterize the nano-structured catalysts. The electrochemical performance of the as-prepared catalyst was characterized by cyclic voltammograms (CV) and liner sweep voltammogram (LSV) techniques. Additionally, the performance of the catalyst was evaluated by a test in single fuel cell. The results showed that the pH value and stabilizers not only significantly influenced the Co@Pt metal morphology property, but also the electrochemical and single cell performance. The proper pH value for preparation was 12, which might be due to that the pH condition would change the charge of the carbon black surface and higher pH value would be beneficial to the metal particles deposition on the surface of carbon support and form the highly dispersed catalyst. The different hydrophobic reaction, dimensional effect and particle interactions are caused by stabilizers. The evaluation of the fuel cell also proved that the optimization of the preparation was helpful to enhance the catalytic performance.

Efficient finite-element computation of far-fields of phased arrays by order reduction

Purpose – The article aims to present an efficient numerical method for computing the far-fields of phased antenna arrays over broad frequency bands as well as wide ranges of steering and look angles. Design/methodology/approach – The suggested approach combines finite-element analysis, projection-based model-order reduction, and empirical interpolation. Findings – The reduced-order models are highly accurate but significantly smaller than the underlying finite-element models. Thus, they enable a highly efficient numerical far-field computation of phased antenna arrays. The frequency-slicing greedy method proposed in this paper greatly reduces the computational costs for constructing the reduced-order models, compared to state-of-the-art methods. Research limitations/implications – The frequency-slicing greedy method is intended for use with matrix factorization methods. It is not applicable when the underlying finite-element system is solved by iterative methods. Practical implications – In contrast to conventional finite-element models of phased antenna arrays, reduced-order models are very cheap to evaluate. Hence, they provide an enabling technology for computing radiation patterns over broad frequency bands and wide ranges of steering angles. Originality/value – The paper presents a two-step model-order reduction method for efficiently computing the far-field patterns of phased antenna arrays. The suggested frequency-slicing greedy method constructs the reduced-order models in a systematic fashion and improves computing times, compared to existing methods.

Synthesis of Fe0.3Co0.7/rGO nanoparticles as a high performance catalyst for the hydrolytic dehydrogenation of ammonia borane

Well-dispersed Fe0.3Co0.7/rGO nanocatalysts have been synthesized utilizing the two-step reduction method and successfully employed in the hydrolysis of ammonia borane (NH3BH3 AB) at room temperature. The mass percent of the supported Fe0.3Co0.7 nanoparticles (NPs) on graphene (rGO) sheets can reach to the maximum value of 50 wt%. The as-synthesized catalysts exerted satisfying activity and reusability for the hydrolytic dehydrogenation of AB at 298 K, especially for the specimen of 50 wt% Fe0.3Co0.7/rGO NPs. The catalytic hydrolysis reaction was rapidly completed within 1 min.

Pt Decorated Amorphous RuIr Alloys as High Efficiency Electrocatalyst for Methanol Oxidation

This study focuses primarily on improving the utilization and activity of anodic catalysts for methanol electro-oxidation. The Direct Methanol Fuel Cell (DMFC) anodic catalyst, a carbon supported Pt decorated amorphous RuIr nanoparticles catalyst (Pt@RuIr/C) was prepared by a two-step reduction method. The structure of Pt@RuIr/C nanoparticles was confirmed by Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD). The Pt@RuIr electrocatalysts exhibited good uniformity in distribution. Cyclic Voltammetry experiments showed that under the same quality of noble-metal, the Pt@RuIr/C catalyst had higher activity than the PtRuIr/C catalyst for methanol oxidation. It was also shown that the as-prepared structure of the Pt decorated amorphous RuIr alloys could obviously decrease the usage of noble-metal and enhance its catalytic activity at the same time.

Combined method to prepare core–shell structured catalyst for proton exchange membrane fuel cells

This paper reports a modified core–shell structured CuPd@Pt/C catalyst, which was synthesized by combining a two-step reduction method and chemical dealloying step using carbon black Vulcan XC-72R as the supporting material. The physical measurements confirmed that the final catalyst has a complete core–shell structure. The interaction between the core and the shell as well as the particle size, particle size distribution, and morphology of the catalyst particles were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results of inductively coupled plasma atomic emission spectroscopy (ICP-AES) and X-ray photoelectron spectroscopy (XPS) indicated that the Pt and Pd on the surface of the catalyst nanoparticles are mainly in the zero valence oxidation state. Cyclic voltammetry (CV) and rotating disk electrode (RDE) tests were used to measure the electrochemical performance, and the results showed that the modified CuPd@Pt/C catalyst has higher electrochemical catalytic activity in catalyzing the oxygen reduction reaction (ORR) than Pt/C, making it possible to reduce the usage of platinum and leading to a promising low-Pt catalyst for proton exchange membrane fuel cells (PEMFCs).

Synthesis and application of core–shell Co@Pt/C electrocatalysts for proton exchange membrane fuel cells

Co@Pt/C core–shell catalysts are synthesized by a two-step chemical reduction method followed by the heat treatment in H2 and N2 mixture. High Resolution (HR-TEM), EDX (Energy-dispersive X-ray spectroscopy) and in-situ X-ray diffraction (XRD) techniques are used to characterize the nano-structured catalysts. The results show that the core–shell structure of Co@Pt/C is formed and the average particle size is about 3 nm. From the result of the in-situ XRD, it is found that the heat treatment favors for the formation of crystalline structure and the proper particle size of catalyst. The in-situ XRD detection also helps find the optimized heat treatment temperature. The linear sweep voltammetry (LSV) result reveals that the Co@Pt (1:3)/C (reduced) catalyst exhibits the best catalytic activity toward oxygen reduction reaction (ORR). A 130 h life time test for the single cell, in which the membrane electrode assembly (MEA) using Co@Pt (1:3)/C (reduced) as the cathode catalyst, is operated to evaluate the durability. The results of the test show that the formation of the core–shell structure of Co@Pt/C catalyst is favorable to improve the stability and durability.

Nanocomposite of electrochemically reduced graphene oxide and gold nanoparticles enhanced electrochemilunescence of peroxydisulfate and its immunosensing abililty towards human IgG

Direct electrochemiluminescence (ECL) from peroxydisulfate (S2O82-), a common ECL co-reactants, can be efficiently enhanced by nanocomposite of electrochemically reduced graphene oxide (abbreviated ERGO) and gold nanoparticles, which provided a novel sensing strategy for bio-molecules. The nano-Au–ERGO composites were electrochemically prepared by a two-step reduction method, in which graphene oxide (GO) was firstly reduced to graphene at the electrode surface, and then followed by electrochemical reduction of HAuCl4. As 15times enhanced ECL intensity of (S2O82-) was observed with the formation of nanocomposite at glassy carbon electrode (GCE) and immunoreaction occurred at electrode surface can suppress corresponding ECL emissions, a new immunoassay strategy was developed with Human IgG (HIgG) as model molecule. A leaner response from 0.02 to 100ngmL−1 was obtained between the concentration of the target molecular and ECL intensity with a detection limit of 1.3pgmL−1 (S/N=3). The proposed ECL sensor showed high sensitivity, stability and satisfactory reproducibility and opened a new avenue to apply ECL in more biological assays. Besides, this method is economical, efficient, and potentially attractive for clinical immunoassays.

The effect of PVP on the formation and optical properties ZnO/Ag nanocomposites

ZnO/Ag nanocomposites have been prepared by two-step reduction method. Firstly, ZnO core seeds were prepared by the reaction of zinc acetate with KOH under magnetic stirring condition in the presence of poly (N-vinyl-2-pyrrolidone) (PVP). Then, Ag nanoparticles were overgrown on ZnO core seeds with reduction by PVP. ZnO/Ag nanocomposites were characterized by TEM, photoluminescence, UV–visible absorption spectra and XRD. ZnO/Ag nanocomposites exhibit excellent resonance Raman properties. It was found that the metallic Ag in the ZnO/Ag act as electron acceptor to improve the optical properties.

Crystal structures and growth mechanisms of octahedral and decahedral Au@Ag core-shell nanocrystals prepared by a two-step reduction method

Octahedral and decahedral Au@Ag core-shell nanocrystals have been prepared in high yields using a two-step reduction method. In the first step, octahedral or decahedral Au core seeds were prepared by reducing HAuCl4·4H2O in tetraethylene glycol (TEG) under microwave (MW) heating or in diethylene glycol (DEG) under oil-bath heating, respectively, in the presence of polyvinylpyrrolidone (PVP) as a polymer surfactant. In the second step, Ag shells were overgrown on these Au seeds in N,N-dimethylformamide (DMF) in the presence of PVP under oil-bath heating for three hours or MW heating for ten minutes. Crystal structures of products were characterized using TEM, TEM–EDS, and SEM. Under oil-bath heating, octahedral or decahedral Au@Ag nanocrystals covered by uniform Ag shells were prepared. On the other hand, decahedral Au@Ag core-shell particles are formed through stepwise growth of tetrahedral units after covering thin Ag shells over decahedral Au cores under fast MW heating. Since the growth rate of Ag shells on corners having defects is slower than that on flat {111} facets, non-uniform Ag shells were formed under fast MW heating. Optical properties of each nanocrystal were determined by measuring extinction spectra.

Epitaxial growth of Au@Pd core–shell nanocrystals prepared using a PVP-assisted polyol reduction method

Au@Pd core–shell nanocrystals were prepared using a two-step polyol reduction method. First, decahedral Au core seeds with small amounts of octahedral, triangular-platelike, and icosahedral Au particles were prepared by reducing HAuCl4·4H2O in diethylene glycol (DEG) under oil-bath heating in the presence of polyvinylpyrrolidone (PVP) as a polymer surfactant. Then Pd shells were overgrown epitaxially on Au core seeds by reducing Na2PdCl4 in EG with PVP, KBr, and H2O. The resultant crystal shapes were characterized using transmission electron microscopic (TEM), TEM-energy dispersed X-ray spectroscopic (EDS), and selected area electron diffraction (SAED) measurements. Effects of addition of KBr and H2O in the second step and reaction temperature for the yield of core–shell particles and their shape, size, and composition distributions were examined. Results show that both {111} and {100} facets of Pd shells were formed in the presence of KBr, depending on the shapes of Au core seeds, whereas only {111} facets were produced in the absence of KBr. New triangular-platelike, five-twin rod, decahedral, and icosahedral shapes of Au@Pd nanocrystals were prepared using triangular-platelike, decahedral, and icosahedral Au cores. When decahedral Au particles were used as seeds, monodispersed decahedral Au@Pd nanocrystals were prepared in high yield at low temperatures of 20–100 °C in PVP/EG solution. Au acts as a catalyst for Pd2+ reduction in the presence of PVP at low temperatures. This work demonstrates a simple two-step technique for the epitaxial growth of various shapes of Au@Pd nanocrystals.

Synthesis of network reduced graphene oxide in polystyrene matrix by a two-step reduction method for superior conductivity of the composite

Polymer/graphene composites have attracted much attention due to their unique organic–inorganic hybrid structure and exceptional properties. In this paper, we report the synthesis of polystyrene/reduced graphene oxide (PS/r-GO) composites by a two-step in situ reduction technique, which consists of a hydrazine hydrate reduction and a subsequent thermal reduction at 200 °C for 12 h. The structure and micromorphology of PS/r-GO composites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis. The results show that the GO can be efficiently reduced by the two-step in situ reduction method, and the r-GO sheets are well dispersed and ultimately form a continuous network structure in the polymer matrix. PS/r-GO composite films (5 wt% GO) are prepared by the hot press molding method, possessing a conductivity as high as 22.68 S m−1. The superior conductivity arises from the high reduction degree of GO and its high dispersion and the formation of a network structure in the polymer matrix. These polymer/r-GO composites are expected to be applied in multiple electric devices. The techniques for preparing polymer/r-GO composite films could be further extended to other similar systems.

Influence of Carbon Sources on the Electrochemical Performance of LiFePO<sub>4</sub>/C Composite Cathode Material

LiFePO4/C cathode material with different carbon sources was synthesized by using a two-step carbothermal reduction method. The structure and electrochemical properties of the samples were characterized by XRD, SEM and galvano-static charge-discharge method. The effect of different carbon sources on the structure, morphology and its electrochemical properties of the LiFePO4/C composite materials were investigated. The results showed that the properties of the samples depended on carbon sources, significantly. The sample synthesized by citric acid as carbon source had the best electrochemical performance. The reason of performance difference of the LiFePO4/C composite materials caused by carbon source was discussed.

Synthesis and characterization of Cu@Pt/C core-shell structured catalysts for proton exchange membrane fuel cell

A Cu@Pt/C catalyst was synthesized by a two-step reduction method using Vulcan XC-72R as the supporting material. Physical and electrochemical techniques were applied to investigate the structure and performance of the catalyst. X-ray diffraction (XRD) and transmission electron microscopy (TEM) examinations showed that the catalyst has a core-shell structure, the distribution of the catalyst particles is quite uniform, and the particle size ranges from 5 to 6 nm. Cyclic voltammetry (CV) and rotating disk electrode (RDE) tests confirmed the high performance of the Cu@Pt/C catalyst with the atom ratio Cu: Pt of 2.73: 1, making it a promising low-Pt catalyst for proton exchange membrane fuel cell (PEMFC).

Epitaxial Growth of Au@Ni Core−Shell Nanocrystals Prepared Using a Two-Step Reduction Method

Au@Ni core−shell nanocrystals were prepared using a two-step reduction method. First, mixtures of octahedral, triangular and hexagonal platelike, decahedral, and icosahedral Au core seeds were prepared by reducing HAuCl4·4H2O in ethylene glycol (EG) using microwave (MW) heating in the presence of polyvinylpyrrolidone (PVP) as a polymer surfactant. Then, Ni shells were overgrown on Au core seeds by reducing Ni(NO3)2·6H2O in EG with NaOH and PVP using oil bath heating. Resultant crystal structures were characterized using transmission electron microscopic (TEM), high-resolution TEM, TEM−energy dispersed X-ray spectroscopic (EDS), selected area electron diffraction (SAED), and X-ray diffraction (XRD) measurements. Because a very large mismatch (13.6%) exists in lattice constants between Au (0.4079 nm) and Ni (0.3524 nm), the epitaxial growth of Ni shells over Au cores was expected to be difficult. Nevertheless, about 40 monolayers of Ni{111} shells were grown epitaxially on flat planes and sharp corners of Au{111} cores after heating reagent solution at 175 °C for 2 h. The SAED patterns showed Ni layers parallel to Au layers. This result is contrasted with our recent result for Au@Cu with a smaller lattice mismatch between Au and Cu (11.4%). In the case of Au@Cu, although the epitaxial growth of Cu{111} shells over Au core was observed, the growth rate on sharp corners was slower than that on flat {111} facets. Our results and reported data show that the lattice mismatch is not a significant factor for the crystal growth of Au@Ni on sharp corners.

Silver–Polymer Composite Stars: Synthesis and Applications

Colloidal "silver stars" were synthesized upon poly(lactic-co-glycolic) acid nanosphere templates via a facile two-step silver reduction method. Myriad dendrimer-like Ag star morphologies were synthesized by varying the amount of poly(vinyl alcohol) and trisodium citrate used during silver reduction. Scanning electron microscopy studies revealed that star-shaped silver-polymer composites possessing nanoscopic, fractal morphologies with diameters ranging from 500 nm to 7 μm were produced. These composites have broad applications from antibacterial agents to catalysis; two such applications were tested here. Surface-enhanced Raman spectroscopy (SERS) studies showed multiple hot spots of SERS activity within a single star. Electrochemical catalysis experiments demonstrated the feasibility of using the silver stars instead of platinum for the oxygen reduction reaction in alkaline fuel cells.