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Behavior of Pt/C catalysts obtained by the platinum deposition on standard and nitrogen-doped carbon supports with different microstructure has been studied in the oxygen electroreduction reaction in an acidic electrolyte. The catalysts based on the modified supports are characterized by a uniform spatial distribution of small-sized (1.5–2 nm) Pt nanoparticles over the surface of the supports, which results in high values of the electrochemically active surface area (110–130 m2 g− 1 (Pt)). The use of various stress testing protocols has shown that the Pt/C material based on the N-doped KetjenBlack EC DJ-600 possesses the highest mass activity and durability, which noticeably exceed the corresponding characteristics of the commercial HiSPEC3000 catalyst.

Platinum-carbon catalysts are widely used in manufacturing proton-exchange membrane fuel cells. Increasing Pt/C activity and stability is an urgent task, optimization of their structure seems to be one of the possible solutions. In the present paper, Pt/C electrocatalysts which contained small (2 - 2.6 nm) nanoparticles of a similar size, uniformly distributed over the surface of a carbon support, were obtained by the original method of liquid-phase synthesis. A comparative study of the structural characteristics, catalytic activity in the oxygen electroreduction reaction and durability of the synthesized catalysts, as well as their commercial analogs has been carried out. It was shown that the ordering of the structural and morphological characteristics of Pt/C catalysts makes it possible to reduce the negative effect of NPs small size on their stability. As a result, the obtained catalysts are significantly superior to their commercial analogs in ORR activity, but not inferior to them in terms of stability.

A number of new platinum-based catalysts with Pt loading from 15.2% to 17.3% was obtained by wet chemical synthesis. Ethylene glycol, formaldehyde, and formic acid were used as reducing agents. The synthesis was performed both at ambient conditions and when the solution was saturated with carbon monoxide. It was shown that the catalysts obtained in the CO environment possess a larger electrochemical active surface area (EСSA), 140–146 m2 g−1 (Pt), compared to the analogues that have been made at ambient conditions, 72–120 m2 g−1(Pt). This could be explained by a smaller platinum NPs average size as well as a very narrow distribution of their size. In contrast to the materials synthesized at ambient conditions, the ECSA values of the catalysts, obtained in the CO-saturated media, in fact, do not depend on the type of reducing agent and the synthesis conditions. Such catalysts demonstrate the best mass-activity in ORR, which is higher than that of the commercial Pt/C catalyst HiSPEC 3000 (20% of Pt loading) and the analogues obtained at ambient conditions. Distinctive features of the nanoparticles nucleation/growth and their structure were determined and studied when formic acid was applied as a reducing agent. Absorption processes of the CO molecules on the surface of platinum nuclei are a plausible explanation for the CO influence on nucleation/growth and, therefore, on the microstructure and EСSA, as well as other functional characteristics of Pt/C-catalysts.

The need to reduce platinum content in PEMFC catalyst layers has sparked a new wave of interest in ways to control the microstructure of Pt/C catalysts, which must combine high platinum surface area and activity. A comparative study of platinum nanoparticle nucleation/growth under a liquid-phase synthesis of Pt/C materials, with formaldehyde and formic acid being used as reducing agents, has been carried out. Analysis of the color change in the reaction medium and the in situ spectral-kinetic studies performed with absorption spectroscopy, were used as methods to study the reactions kinetics. The effect of the synthesis temperature on the features of the Pt(IV) reduction stages, nucleation/growth of Pt(0) nanoparticles, as well as on the size of the resulting Pt nanoparticles were studied. The role of the ethylene glycol and its derivatives, formed in the reaction medium at high pH, in the processes of Pt(IV) reduction and in the Pt(0) nanoparticles formation, is shown. The positive effect of the dispersed carbon support on the morphological characteristics of the resulting Pt/C catalysts is demonstrated, with carbon being introduced into the reaction medium in the initial stage of the synthesis. The roles of homogeneous and heterogeneous phase formation in the synthesis of Pt nanoparticles and Pt/C materials in the liquid phase are estimated.

A comparative study of the nucleation/growth processes of the platinum nanoparticles has been carried out with and without ultraviolet (UV) radiation. Platinum‑carbon catalysts containing 20%wt Pt with the average crystallite size ranges from 1.3 to 3.6 nm obtained by the liquid phase synthesis, using various reducing agents. It is shown, that for materials obtained under UV irradiation action the electrochemically active surface area increases up to 80% in comparison with the analogs. Improvement in the functional characteristics of the catalysts is due to narrowing in the size distribution of Pt nanoparticles and an increase in the uniformity of their spatial distribution. The synthesized catalysts demonstrated mass activity in ORR, which significantly exceeded the commercial analog activity. The approaches to the production of nanomaterials shown in the article are of great applied importance, since they can be used for gram-level syntheses.

Composite metal-carbon electrocatalysts PtCu/C containing core-shell bimetallic PtCu nanoparticles were synthesized by sequential chemical reduction of Cu (II) and Pt (IV) in carbon suspension, prepared on the basis of ethylene glycol–water solvent. The characterization of “as prepared” and obtained after the acid treatment PtCu nanoparticles was performed by TEM, XRD, Pt L 3 - and Cu K -edge extended X-ray absorption fine structures (EXAFS). The technique and computational code were proposed for visualization of components distribution over the volume of cluster, which represents the mean bimetallic nanoparticle, according to the values of structural parameters derived from EXAFS. By this technique, the cluster models of PtCu nanoparticles before and after acid treatment, reflecting the character of components’ distribution, were generated. The study of electrochemical performances of the obtained PtCu/C electrocatalyst revealed the similar oxygen reduction reaction (ORR) activity and increased durability compared to commercial Pt/C electrocatalyst E-TEK 20.

In this paper we report the results obtained by a comparative study of catalytic activity of bimetallic (Ru–Rh, Ni–Cu) catalysts synthesized on a surface of different carbon supports: detonation nanodiamonds (DND), infrared pyrolyzed polyacrylonitrile, carbon black Vulcan-XC-72, in steam reforming of methanol (MSR) for hydrogen production. All obtained catalysts were characterized by N 2 physisorption, SEM, TEM, FTIR spectroscopy, X-ray diffraction. It was shown, that activity of catalysts and products distribution depends on metal type, support material and the specific surface area. Support effect was investigated for Ru–Rh system. DND showed the best properties as a catalyst support. Ru–Rh system is more active than Cu–Ni as it is shown on the example of DND supported catalysts. Comparative study between conventional (CR) and membrane (MR) reactors was carried out. MR represented a flow system with a plane Pd-containing membrane. The effect of different catalysts on the MR performances as well as a general comparison of the experimental results was considered. Obtained results demonstrate the ability of the membrane to increase the reaction conversion. The hydrogen stream produced from the MR is ultra pure: especially, it is CO-free and thus suitable to be directly fed to a polymer electrolyte membrane fuel cell.

Electrooxidation of methanol, ethanol, and formic acid was studied on three platinum-containing electrocatalysts: PtCu/C, Pt/(SnO2/C), and Pt/C, Pt content being about 20 wt%. In all reactions, the integral specific activity of the catalysts, estimated from the results of cyclic voltammetry, grows in the Pt/C &lt, Pt/(SnO2/C) &lt, PtCu/C row. The influence of the reagent nature subjected to electrooxidation is manifested both in the difference of the absolute rate values of the corresponding reactions, decreasing in the order CH3OH &gt, HCOOH &gt, C2H5OH, and in the different ratio of these rates on different catalysts and at different potentials. Pt/(SnO2/C) catalyst containing SnO2 nanoparticles is the most active among the studied catalysts in methanol and formic acid electrooxidation reactions under potentiostatic conditions at the E = 0.60 V. Moreover, in formic acid electrooxidation reaction it is significantly superior to even the PtRu/C commercial catalyst. The reasons for the positive influence of Cu atoms and SnO2 nanoparticles on the catalytic activity of platinum are presumably associated with different effects: Interaction of the d-orbitals of copper and platinum atoms in bimetallic nanoparticles and implementation of the bifunctional catalysis mechanism on the adjacent platinum and tin dioxide nanoparticles.

The behavior of supported alloyed and de-alloyed platinum-copper catalysts, which contained 14&ndash, 27% wt. of Pt, was studied in the reactions of methanol electrooxidation (MOR) and oxygen electroreduction (ORR) in 0.1 M HClO4 solutions. Alloyed PtCux/C catalysts were prepared by a multistage sequential deposition of copper and platinum onto a Vulcan XC72 dispersed carbon support. De-alloyed PtCux&minus, y/C catalysts were prepared by PtCux/C materials pretreatment in acid solutions. The effects of the catalysts initial composition and the acid treatment condition on their composition, structure, and catalytic activity in MOR and ORR were studied. Functional characteristics of platinum-copper catalysts were compared with those of commercial Pt/C catalysts when tested, both in an electrochemical cell and in H2/Air membrane-electrode assembly (MEA). It was shown that the acid pretreatment of platinum-copper catalysts practically does not have negative effect on their catalytic activity, but it reduces the amount of copper passing into the solution during the subsequent electrochemical study. The activity of platinum-copper catalysts in the MOR and the current-voltage characteristics of the H2/Air proton-exchange membrane fuel cell MEAs measured in the process of their life tests were much higher than those of the Pt/C catalysts.

Pt/C catalysts containing 10 to 20 wt % Pt have been prepared by chemical reduction of platinum from Pt(IV) solutions. The use of an intermediate hydroxide support (Fe(OH)2 or SiO2 · nH2O) in Pt/C synthesis has been shown to have a significant effect on the weight percentage, crystallite size, and electrochemically active surface area of Pt. We have established how the composition of the liquid-phase synthesis atmosphere (air, Ar, or CO) influences the structural characteristics of the Pt/C materials. The electrochemically active surface area of Pt in the synthesized catalysts ranges from 32 to 152 m2/g Pt.

Nanostructured Pt/C electrocatalysts containing about 20 wt % Pt have been produced by chemical reduction in Pt(IV) solutions. The nature of the reductant (sodium borohydride, ethylene glycol, formaldehyde, or formic acid) and the associated changes in synthesis conditions have a significant effect on the structural characteristics of the materials obtained. In particular, the average size of Pt nanoparticles (crystallites) ranges from 1.8 to 5.5 nm. The largest electrochemically active surface area of the Pt in the catalysts obtained in this study (128 m2/g Pt) considerably exceeds that of E-TEK, a commercially available Pt/C catalyst similar in composition ( 110 m2/g Pt).

For the purpose of reducing the cost and improving the performance of the proton exchange membrane fuel cell (PEMFC), some low-Pt or non-Pt catalysts have been studied in recent years. PtCo/C electrocatalysts are synthesized by a two-step reduction approach followed by the heat treatment. PtCo metal particles are uniformly dispersed on the surface of XC-72 carbon support, with a uniform particle size distribution. The PtCo/C catalyst after 400 degrees C heat treatment has the best electrochemical performance among the as-prepared catalysts, even superior to the commercial Pt/C catalyst. In the durability test, PtCo/C-400 also shows excellent stability with only 6.9% decline of electrochemical surface area (ECSA) after 1000 cyclic voltammetry (CV) cycles. In-situ X-ray absorption near edge structure (XANES) technique is conducted to explore the nanostructure change of Pt during the PEMFC operation. For PtCo/C catalyst, with the fuel cell operation potential decreasing from open circuit voltage (OCV) to 0.3 V, the Pt L-3 white line intensity decreases continuously, indicating the decline of Pt 5d-vacancy due to the adsorption of oxygenated species. (C) 2015 Elsevier B.V. All rights reserved.

The aim of this work was to investigate the morphology, average size, and the electrochemical behavior of platinum nanoparticles electrodeposited from water and mixed water–ethylene glycol solutions of the electrolyte of H2PtCl6 and H2SO4 at a rotating disk electrode coated with Vulcan XC-72 carbon powder. Cyclic voltammetry and linear sweep voltammetry were used to determine the electrochemically active surface area (ESA) and oxygen reduction reaction (ORR) activity of the prepared Pt/C materials, respectively. XRD and scanning electron microscopy were used to study the influence of the electrodeposition methods applied on the morphology of platinum particles deposited in water and mixed water–ethylene glycol solutions. The average size of Pt crystallites was in the range of ca. 6–10 nm, and the average size of deposited Pt particles was in the range of ca. 30–150 nm. It was found that the presence of ethylene glycol in the electrolyte solution increased the overpotential of electrodeposition and it also strongly affected the morphology of Pt deposits when constant current electrodeposition was employed. Moreover, it was shown that pulse current electrodeposition is a more effective method compared to constant current electrodeposition method for the preparation of the Pt/Vulcan electrode with high ESA of Pt and enhanced catalytic activity toward ORR. The results obtained concerning the morphology and the spatial distribution of platinum particles electrodeposited on the surface of carbon support at different conditions demonstrate new possibilities to improve synthesis of Pt/C by electrodeposition methods.

Nanostructured Pt x Ni / C and Pt x Co / C catalysts ( 1 ≤ x ≤ 3 ) containing from 27 to 40 wt % of metal with the average size of metal (alloy) particles from 2.6 to 4.7 nm are obtained using the methods of liquid- phase synthesis. Addition of a doping component is found to yield a decrease in the average nanoparticle sizes and an improved activity of materials in oxygen electroreduction reactions. The obtained catalysts are charac- terized by high specific activity as compared to commercial Pt/C materials. The stability of electrocatalysts to selective dissolution of the doping component is evaluated.

Pt 3 Co/C electrocatalysts prepared by wet synthesis method from water–ethylene glycol solutions of Pt and Co precursors were investigated by X-ray diffraction in conjunction with electrochemical measurements. It was shown that varying the binary solvent composition is an effective means of control over the average nanoparticle size and the grain size distribution. It was found that unit cell parameter of the Pt 3 Co/C electrocatalysts decreases nonlinearly with decreasing particle size. The activity of the prepared Pt 3 Co/C catalysts for the oxygen reduction reaction (ORR) in H 2 SO 4 solution enhances with decrease in the particle size, the unit cell parameter, and the dispersion of the grain size distribution. All samples studied show higher catalytic activities in comparison with the commercial Pt/C materials.

Nanocatalysts PtCu/C with different distribution of components in bimetallic PtCu nanoparticles (NPs) were synthesized by simultaneous and sequential deposition of Cu and Pt on carbon support. Electrochemical stability of the obtained samples PtCu/C was studied using the cyclic voltammetry. Characterization of atomic structure of as prepared PtCu NPs and obtained after acid treatment was performed by Pt L 3- and Cu K-edge EXAFS using the technique for determining local structure parameters of the absorbing atom under strong correlations among them. EXAFS derived parameters were used for generation of structural models of PtCu NPs by the method of cluster simulations. Within this approach, the models of atomic structure of PtCu NPs obtained by the two methods of synthesis, before and after post treatment and after two months from their preparation were revealed.

We investigate the Pólya problem on the sign conversion between the permanent and the determinant over finite fields. The main attention is given to the sufficient conditions which guarantee non-existence of sing-conversion. In addition we show that F3 is the only field with the property that any matrix with the entries from the field is convertible. As a result we obtain that over finite fields there are no analogs of the upper Gibson barrier for the conversion and establish the lower convertibility barrier., * The work on this project is partially supported by the grants MD-2502.2012.1 and RFBR 12-01-00140., 2010 Mathematics Subject Classification: 15A15, 15A04.

International audience; Pt-Co/C electrocatalysts with Pt loadings near 30 wt. % prepared by the impregnation method in water - ethylene glycol solutions were investigated by X-ray diffraction and correlated with electrochemical measurements. We show that the composition of the binary solvent controls the average particle size and its distribution. The unit cell parameter of the Pt3Co alloy decreases nonlinearly with decreasing particle size. The ORR activity of the prepared Pt-Co/C catalysts in H2SO4 solution enhances with decreasing particle size and unit cell parameter as well as with narrowing of the particle size distribution. Corrosion treatment of the synthesized Pt-Co/C materials causes an increase of ca. 1 nm in average particles size accompanied by broadening of the particle size distribution and decreasing Co content in the Pt-Co alloy. All of the synthesized Pt-Co/C materials show higher ORR activities than do the commercial Pt/C electrocatalysts.

Random time sampling of activities (work sampling) is successfully applied to everyone in a division of 350 employees for the purpose of budget planning and cost control. To insure this success several technical and administrative problems had to be solved, especially those relating to the design and management of the sample. An appropriate model is described together with methods of sampling, estimating, and calculating sampling errors. Bias is reduced by using an employee instruction booklet, anonymous reporting, and by classifying and coding activities. Cost of the plan is reduced by using a stratified cluster sample, a check-type data sheet, a simplified method of estimation, and by calling random times by telephone. * This paper was prepared and the project described herein was carried out under the general supervision of E. J. Engquist, Jr., Director of the Statistics Division.

keep our process in control, we can work to a tolerance of ? .005 and produce less than (say) 1% scrap. But they do not tell us where to put the limits. This is not to be expected, since the range is the difference of two observed values of the thing we are measuring, and would therefore remain unaltered however violently the mean value might fluctuate. The chart for means would have to be consulted to find where the nominal value should lie. The proofs of these inequalities are short. Let I be the length of the shortest interval which contains a fraction p of the distribution. Then any interval whose length is less than 1 contains less than p of the distribution. Suppose X1, X2, * . X, is a sample of n, and suppose X, is the least of these values of X. Then if the range Wn of this sample is less than 1, all the n 1 values other than Xr must lie in the interval (X,, X, + l). The probability of this happening is less than p~n-. The least value X, can be picked in n ways. Hence