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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.

The electrodeposition of tin and tin-nickel on a highly dispersed carbon material is used to obtain composite supports. These composite supports were used in the Pt(0) nanoparticles deposition from Pt(IV) solution by chemical reduction. The composition, structure, and activity of the obtained Pt(SnO2/C) and PtSnNi/C catalysts in the oxygen reduction and alcohol electrooxidation reactions were studied. The composite-support-based platinum catalysts exhibit higher activity in the reactions of alcohols electrooxidation in comparison with the commercial Pt/C analogue. Trimetallic PtSnNi/C catalysts are the most promising materials for the electrooxidation of alcohols.

Catalysts containing bimetallic PtCu-nanoparticles deposited onto carbonaceous and composite SnO2/C supports are prepared by liquid-phase borohydride synthesis. The composition and structure of the synthesized materials, their catalytic activity in the reactions of oxygen electroreduction and methanol electrooxidation, as well as corrosion and morphological stability are investigated. The platinum doping with copper atoms is found to increase the materials’ catalytic activity and stability in comparison with Pt/C, regardless of the type of support used. In addition, the multicomponent PtCu/(SnO2/C) catalyst exhibits the highest tolerance to intermediate products of methanol electrooxidation.

The effect of the SnO2 nanoparticles content on the structure and electrochemical behavior of Pt/(SnO2/C) catalysts containing about 20 wt% Pt was studied. In this case, SnO2/C nanostructured materials were obtained by tin electrodeposition on the carbon particles in suspension. It was found that the optimal combination of stability and activity in the oxygen electroreduction reaction is demonstrated by materials containing 25–30% wt. SnO2. A comparative assessment of the durability and activity of Pt/(SnO2/C) catalysts and a commercial Pt/C catalyst with 20% Pt-loading has been carried out.

Nitrogen-doped carbon materials were prepared by the pyrolysis of carbon black Vulcan XC-72 impregnated with nitrogen-containing Pd (II) and Ni (II) complexes. The composition of materials was studied at different stages of their synthesis. It is shown that nanoparticles of metals and/or their oxides are not the main electroactive component of materials in the oxygen electroreduction reaction (ORR). It is established that the palladium complex provides a much more efficient doping of carbon with nitrogen compared to the nickel complex of a similar composition. This results in the high ORR electrocatalytic activity of the catalyst obtained, palladium complex being used in an alkaline medium. This material is a promising one to be used as an electrocatalyst in fuel cells with an anion-conducting membrane.

The activity of PtCu/C catalysts in methanol electrooxidation is studied in HClO4 solution. The electrochemical behavior of catalysts is compared for samples in the “as obtained” state and after their pretreatment in nitric acid which decreases the copper content in their composition. It is found that the partial selective dissolution of the alloying component renders no negative effect on the behavior of bimetallic catalysts. The prepared materials exhibit the high tolerance toward intermediates of methanol oxidation and their specific activity exceeds by a factor of 5–7 the activity of the commercial Pt/C catalysts. The results of this study open up the possibility of using de-alloyed platinum-copper catalysts in alcohol fuel cells, because this considerably decreases the risk of contamination of the polymeric membrane.

Platinum-containing bimetallic nanoparticles manifest high functional characteristics as electrocatalysts. To use PtCu/C catalysts in low-temperature fuel cells, it is necessary to minimize selective copper dissolution, as copper cations can pollute the polymer membrane and decrease its proton conductivity. The work determines the composition, measures the electrochemically active surface area, and studies the electrochemical behavior of PtCu/C catalysts containing nanoparticles with a “core–shell” structure in the initial state (as-prepared) and after pretreatment in solutions of different acids. The comparative determination of catalyst activity in an electrochemical cell and their testing in a membrane-electrode assembly of fuel cells showed that pretreated PtCu/C materials with a much better stability as compared to Pt/C were also noninferior to the latter as regards their activity in the oxygen electroreduction reaction.

One of important problems associated with the use of Pt/C electrocatalysts in low-temperature fuel cells is their degradation due to oxidation of the carbon support. The use of noncarbon supports resistant to oxidation, for example, oxides of certain metals in the highest degree of oxidation is a promising direction. TiO2 with the high specific surface area (104 m2/g) is synthesized and used in fabrication of supported platinum catalysts. For Pt/TiO2 and carbon-containing composite Pt/TiO2+C, the electrochemically active surface area of platinum and the their activity in oxygen electroreduction reaction are estimated. The assessed stability of synthesized materials far exceeds the stability of commercial Pt/C catalysts.

New nanostructured Pt/(SnO2/C)-electrocatalyst (20 wt % Pt) is synthesized via platinum chemical deposited onto composite SnO2/C-support microparticles (4 wt % Sn). The composite support was prepared beforehand using unique method of the tin electrochemical deposition onto disperse carbon black particles. It was shown by X-ray diffraction and transmission electron microscopy that the platinum and tin oxide nanoparticles distributed over the carbon surface are sized 2.4 and 2.9 nm, respectively. Electrochemical measurements showed the obtained catalyst to approach the commercial Pt/C HiSPEC 3000 catalyst (20 wt % Pt) with respect to its mass-activity in the oxygen electroreduction reaction and to be superior thereto as for the electrochemically active surface area, stability in stress test, and activity in methanol electrooxidation reaction. The peculiarities in electrochemical behavior of the synthesized Pt/(SnO2/C)-electrocatalyst can be explained by the SnO2 nanoparticle effect on the platinum nanoparticle nucleation/growth, as well as presence of Pt–SnO2–C triple junction nanostructure at the surface. The Pt/SnO2 contact provides stable platinum-to-support adhesion and asserts bifunctional catalysis mechanism of the methanol electrooxidation. And the Pt/C junctions provide for electron supplying/retraction to or from the platinum nanoparticles.

Materials containing from 3.1 to 7.7 wt % of cobalt were obtained by electrodeposition of cobalt on Vulcan XC72 carbon powder in suspension. The composition and average diameter of CoO crystallites formed as result of cobalt oxidation in the process of filtering and drying materials, depending on the electrolysis conditions and electrolyte composition, were studied using thermogravimetry and XRD. It is shown that the maximum amount of cobalt can be deposited from electrolytes containing, along with cobalt sulfate, additives of copper and nickel sulfates. Calculations by the Scherrer equation showed that an increase in the CoO content leads to a decrease in the diameter of crystallites, the size of which is in the nano-range. The analysis of X-ray and electrochemical studies indicates the formation, in the course of the borohydride’s synthesis, of combined catalysts containing nanoparticles of the Pt3Co solid solution. The best PtCo/C material demonstrated significant improvement in ORR activity and superior stability compared to commercial Pt/C catalyst of the same platinum loading.

An original method for the preparation of Pt/C materials dispersed by means of platinum electrodeposition on the carbon particles which are in the form of suspension has been proposed. The materials were studied by XRD, cyclic voltammetry, SEM and TEM electron microscopy. The obtained Pt/C materials contain from 9 to 14 wt% Pt. The average size of platinum particles is from 7 to 15 nm; electrochemically active surface area of Pt/C is from 15 to 29 m2 g−1 (Pt). The resulting materials exhibit catalytic activity in the oxygen electroreduction reaction which predominantly flows through the 4-electron mechanism.

PtCu/C electrocatalysts with similar compositions but different distributions of components in bimetallic nanoparticles were obtained by simultaneous and sequential reduction of copper(II) and platinum( IV) in a carbon suspension. The catalyst obtained by multistage synthesis while sequentially increasing the Pt(IV) concentration in the precursor solution added at each stage showed the highest stability and activity in oxygen electroreduction in acidic media. This catalyst was least liable to selective dissolution of copper during its operation. The influence of the architecture of bimetallic PtCu nanoparticles on the electrochemical behavior of the catalysts is due to the peculiarities of the structure rearrangement of nanoparticles during the enrichment of the protective surface layer with platinum.

Stability is one of the most important characteristics of electrocatalysts used in low-temperature fuel cells with a proton exchange membrane. The corrosion-morphological stability of supported electrocatalysts containing platinum and platinum-copper nanoparticles with ~20 wt % Pt was evaluated under the conditions of voltammetry stress testing corresponding to different degradation mechanisms. The effect of the difference in the architecture of Pt–Cu nanoparticles on the stability of catalysts and changes in their composition as a result of stress tests were studied. At close values of the electrochemically active surface area (ECAS), the carbon-supported bimetallic catalysts demonstrated significantly higher stability compared to the commercial Pt/C catalysts. The Pt(Cu)/C catalyst obtained by sequential deposition of copper and platinum showed the highest resistance to the degradation and selective dissolution of copper during the testing.

We investigate the activity of bimetallic PtM/C (M = Ni, Co) catalysts with different microstructures and platinum catalysts supported on a nanostructured composite carrier (SnO2/C) in the electrooxidation reaction of methanol. For bimetallic catalysts, the effect of heat treatment on their structural and functional characteristics is also studied. Among bimetallic catalysts in the as-obtained state, the Pt@Ni/C catalyst prepared by the subsequent reduction of nickel and platinum from solutions of their compounds exhibited the highest activity in the methanol electrooxidation, significantly exceeding that for the commercial Pt/C product. Heat treatment at 350°C increased the activity of the PtCo/C catalyst containing nanoparticles of a solid solution but adversely affected the tolerance of all the studied bimetallic catalysts to the intermediate products of methanol oxidation. All the studied Pt/(SnO2/C) materials demonstrated a higher mass activity in the electrooxidation reaction of methanol compared to commercial Pt/C and bimetallic systems, while the catalyst with a weight fraction of platinum of 12% and a molar ratio of Pt: SnO2 of 1: 1.1 showed the highest mass activity.

Supported PtCu/C electrocatalysts containing core–shell bimetallic PtCu nanoparticles were synthesized by sequential chemical reduction of Cu2+ and Pt(IV) in a carbon suspension, prepared on the basis of ethylene glycol–water solvent, and then treated at different temperatures in the range from 250 to 350 °C. The structural characterization of “as-prepared” PtCu nanoparticles and of those obtained after the thermal treatments was performed by transmission electron microscopy, X-ray diffraction, and Pt L3- and Cu K-edge extended X-ray absorption fine structure spectroscopy. The atomic cluster models of PtCu nanoparticles before and after the thermal treatment, reflecting the character of the components’ distribution, were generated. The electrochemical performance of the obtained PtCu/C electrocatalysts in oxygen reduction reaction was studied by cycling and linear voltammetry.

The structure characteristics and the electrochemical behavior of Pt(Cu)/C electrocatalysts synthesized by consecutive deposition of copper and platinum on carbon-support microparticles is studied. The stability and catalytic activity of Pt(Cu)/C materials in reactions of oxygen electroreduction and methanol electrooxidation are assessed and compared with analogous characteristics of a commercial Pt/C material. It is shown that combining the method of galvanic displacement of Cu by Pt with the additional chemical deposition of Pt favors optimization of the structure and functional characteristics of Pt(Cu)/C electrocatalysts. The effect of thermal treatment on the characteristics and properties of electrocatalysts is studied and the optimal conditions of such pretreatment are revealed.

The architecture of bimetallic nanoparticles has strong influence on durability and activity of PtM/C electrocatalysts in the oxygen electroreduction (ORR) and the methanol electrooxidation reactions (MOR). In the present study the Pt0.8(Cu)/C electrocatalyst was obtained by the methods of successive multistage reduction of platinum and copper from the solutions of their precursors while platinum concentration in the matrix solution was increasing step by step. The composition, structural characteristics and electrochemical behavior of this material were compared with the Pt1.0Cu/C catalyst based on the nanoparticles of a solid solution, which was obtained by the combined single-step chemical reduction of precursors, as well as with a commercial Pt/C sample with the same Pt-loading (20% by weight). The catalyst based on the Pt–Cu gradient nanoparticles demonstrated the highest corrosion-morphological stability in the stress-test, as well as the highest activity in ORR and MOR in the HClO4 solutions. Both of the studied bimetallic catalysts lose a significant amount of copper during the standardizing cycling and the stress-test. In the stabilized composition of the “gradient catalyst” the residual copper content, however, is considerably higher than that of the catalyst with the solid solution nanoparticles. The positive features of the electrochemical behavior of Pt0.8(Cu)/C catalyst arise apparently due to the faster formation of a durable protective layer of platinum on the surface of nanoparticles in the process of functioning, compared to the analogue based on the nanoparticles of the solid solution. High stability and activity of Pt0.8(Cu)/C compared to the Pt/C analogue are associated with the larger size of the nanoparticles and the promoting influence of residual copper on the catalytical activity of platinum.

The influence of the atmosphere composition (CO, Ar, air), in which wet synthesis of Pt/C electrocatalyst was carried out, on the structural and morphological characteristics, and electrochemical behavior of electrocatalysts have been studied. For comparison, commercial Pt/C electrocatalysts with the same platinum loading were also studied. It has been shown that the adsorption of CO molecules on the surface of the growing platinum nuclei leads to the decrease in the average size of the nanoparticles and the narrowing of the size distribution in the Pt/C. Homemade electrocatalysts, with the values of electrochemically active surface area being from 94 to 139 m2 g−1 (Pt), prove to be in no way inferior to their commercial counterparts in oxygen reduction reaction mass activity. Durability of the homemade Pt/C samples in accelerated stress tests exceeds durability of the commercial ones.

The operation-mode stability and the catalytic activity in electrode reactions are the most important properties of electrocatalysts that determine the possibility of using them in fuel cells. The negative linear correlations between stability and catalytic activity of a series of Pt/C and Pt–Cu/C materials in the oxygen electroreduction reaction are revealed and studied. A method of selecting electrocatalysts with the optimal combination of activity and stability is proposed. The Cu@Pt/C catalysts containing bimetallic nanoparticles with the core–shell architecture which demonstrate the anomalously high combination of activity and stability are synthesized.

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.

Carbon supported Pt–Cu and Pt–Co electrocatalysts with increased platinum content on the surface layer of nanoparticles were synthesized by different chemical methods. The compositions, microstructures and electrochemical behaviors of these electrocatalysts were studied using the X-ray diffraction, thermogravimetry, X-ray fluorescence analysis, TEM and cyclic voltammetry. During stability tests (1000 voltammetric cycles in HClO4 solution) the values of electrochemically active surface area (ESA) for Pt–Cu/C catalysts reduced by 34%. Commercial Pt/C catalyst HiSPEC 3000 decreased ESA value by 70% (from 102 to 30 m2g−1 (Pt)) in the similar tests. High stability of the prepared Pt–Cu/C catalysts combined with the high ESA values and ORR activity may be due to the fact that despite a comparatively large size of nanoparticles most of them have a core-shell or hollow (nanoporous) structure. The obtained result demonstrates a great potential for using bimetallic catalyst systems with an uneven surface distribution of metals in nanoparticles as electrocatalysts in low temperature fuel cells and show the way for combining high activity and durability of electrocatalysts.

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.

The sequential chemical reduction of metals (copper or silver) and platinum was used to prepare M@Pt/C electrocatalysts that contain a high content of platinum on the surface of bimetallic nanoparticles. The compositions, microstructures and electrochemical behaviors of these electrocatalysts were studied using X-ray diffraction, thermogravimetry, X-ray fluorescence analysis, TEM and cyclic voltammetry. Depending on the composition and mode of synthesis, the obtained electrocatalysts have electrochemically active surface areas ranging from 35 to 61 m2 g−1 (Pt). The presence of nanoparticles with a core-shell structure was directly confirmed for Cu0.9Pt0.1@Pt/C sample. Copper-containing electrocatalysts exhibited better stability during voltammetric cycling compared to a similar composition of commercial Pt/C electrocatalyst and Ag0.9Pt0.1@Pt/C systems, but one of Ag0.9Pt0.1@Pt/C electrocatalysts has shown the highest specific activity in ORR.

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 article discusses a wide range of issues related to the relationship between the composition and fine structure (architecture) of bimetallic nanoparticles and electrochemical performance of Pt-M/C (M = Cu, Co, Ni) electrocatalysts. Among these questions are: evolution of nanoparticles during thermo-treatment, catalytic activity in the oxygen reduction and methanol electro-oxidation reactions, corrosion-morphological stability of the catalysts, selective dissolution of alloying component.

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.

The microstructures of Pt/C and PtM/C (M = Ni, Cu, or Ag) electrocatalysts were studied using X-ray diffraction and transmission electron microscopy (TEM). The electrochemically active surface areas of the prepared materials were estimated by cyclic voltammetry in 1 M H2SO4. The materials, with metal contents ranging from 30 to 35 wt.%, were synthesized by chemically reducing the metal precursors in water–ethylene glycol solutions. The actual composition of the bimetallic nanoparticles corresponds to a theoretical (1:1) composition for the PtAg/C catalysts, whereas in the PtNi/C and PtCu/C materials, a portion of the alloying component exists in an oxide form. Decreasing the average metallic crystallite sizes from 3.5 to 1.6 nm does not increase the electrochemically active surface area. This apparent contradiction is because a majority of the PtNi and PtCu nanoparticles consist of 2–4 disordered crystallites. In addition, a portion of the PtNi or PtCu nanoparticle surface is covered by nickel or copper oxides, respectively. PtAg nanoparticles, which have a smaller size relative to other bimetallic particles according to the TEM data, are characterized by an intense platinum surface segregation. The agglomeration processes are lowest for the PtAg nanoparticles.

The results of the study of microstructural parameters and the data on the electrochemically active surface area of Pt/C and Pt50M50/C (M = Ni, Cu, Ag) catalysts in 1 M H2SO4 solutions are compared. The metal-carbon nanomaterials were prepared by the method of chemical reduction of metals from the organoaqueous solutions of their compounds. The loading of metal component in them was 30–33 wt %. It is found that actual composition of metal component in the synthesized binary systems fits best the theoretically expected one (1: 1) for the PtAg/C catalyst whereas in the PtNi/C and PtCu/C systems, a considerable fraction of alloying component is present in the form of the corresponding oxides. A decrease in the average size of crystallites of metal component from 3.8 to 1.6 nm in the series of studied materials PtAg/C > Pt/C ≥ PtCu/C s> PtNi/C does not correspond to the character of the variation of electrochemically active surface area of the catalysts: PtNi/C ≈ PtCu/C < Pt/C ≪ PtAg/C increasing from 16–20 to 62–69 m2/g(Pt). The contradiction can be caused by the preferential segregation of platinum on the surface of nanoparticles of PtAg alloy, a higher degree of agglomeration of smaller nanoparticles, and, in the case of PtNi/C and PtCu/C materials, also by the insulation of a fraction of nanoparticle surface area by the corresponding oxides.

Pt/C, Pt 3 Ni/C, and Pt 2 Co/C nanocatalysts for oxygen electrochemical reduction reaction (ORR) were prepared using the borohydride wet synthesis method. The composition and structure of the catalysts were studied using the XRD method and X-ray fluorescence analysis (XRF) methods. It was found that the catalysts are nanostructured metallocomposites. The average diameter of platinum or alloy nanoparticles was 2.5-3.2 nm. The specific metal surface area determined using the carbon monoxide oxidative desorption (CO stripping) method increases in the series of Pt/C < Pt 3 Ni/C < Pt 2 Co/C from 30 to 38 m 2 /g of Pt. The rotating disk electrode (RDE) method was used to investigate the ORR kinetics on the studied electrodes. The limiting kinetic current, overall process rate constant, and reaction order were determined. The character of the obtained dependences allows us to conclude that the process rate of the electrodes with the studied catalytic systems is limited both by diffusion and by kinetic components. The binary catalysts are characterized by the same process mechanism with a slow stage of the first electron transfer as in the case of a pure platinum electrode. Herewith, the specific activity of nanostructured catalysts increases in the series Pt/C < Pt 3 Ni/C < Pt 2 Co/C.

Pt 3 Co/C electrocatalysts produced by the wet synthesis method out of water-ethylene glycol solu- tions of Pt and Co precursors were investigated by X-ray diffraction in conjunction with electrochemical mea- surements. It was shown that varying the binary solvent composition is an effective way to regulate the nano- particle and grain size distribution. It was found that the unit cell parameter of the Pt 3 Co/C electrocatalysts decreases nonlinearly as the particle sizes dwindle. The activity of the made-up Pt 3 Co/C catalysts for the ORR in H 2 SO 4 solution enhances as the particle size, unit cell parameter, and dispersion of the grain size distribution decrease. All the samples studied show higher catalytic activities than the commercial Pt/C materials.

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.

A comparative study of alloy formation processes that occur during the electrochemical intercalation of lithium from lithium chloride solutions in dimethylformamide into intermetallic compounds of magnesium with zinc (MgZn2, Mg2Zn3) and the corresponding individual metals is studied by chronopotentiometric and voltammetric methods. Lithium-containing phases are formed in all samples studied; moreover, for MgZn2 and Mg2Zn3 electrodes, the phases formed are preferentially in the Li-Zn system. The largest number of lithium-containing phases is formed in zinc. It is shown that the electrochemical behavior of intermetallic electrodes is associated with their nature, where a single alloy component plays the key role, namely, zinc for MgZn2 and magnesium for Mg2Zn3. The cathodic intercalation of lithium into MgZn2 is characterized by anomalously low polarizability as compared with the other electrodes. The lithium extraction coefficient K ex Li increases from the first to the tenth cycle for all electrode studied. The highest K ex Li are typical of Zn and the lowest are typical of Mg2Zn3.

Nanosized Pt-Ni//C electrocatalysts are prepared by methods of liquid-phase synthesis. For the factors that have a direct bearing on the composition of the synthesized materials, the pH, temperature, and composition of a water-organic solvent are studied. The weight percentage of metals in the electrocatalyst, the average size of the formed nanoparticles, and the composition of the Pt-Ni alloy are determined by methods of X-ray diffraction and elemental analyses. The electrocatalytic materials that are characterized by a high platinum content of 25–35 wt % and by a small average diameter of their nanoparticles (3.2–4.5 nm) are produced when using water-ethylene glycol mixtures as solvents. The electrocatalytic activity of the obtained Ptx-Ni/C materials in the oxygen electroreduction reaction in a 0.5 M solution of orthophosphoric acid is studied by the potentiodynamic method. The potentiodynamic study makes it possible to single out electrocatalysts whose specific characteristics are superior to those of commercial Pt/C electrocatalyst TEC10V50E.

Electrochemical intercalation of lithium into intermetallic compounds (IMC) MgCd and MgCd3 out of propylene carbonate solutions of LiBF4 is studied. According to chronopotentiometry data, during the intercalation, lithium forms compounds with cadmium: Li3Cd on MgCd or LiCd and Li3Cd on MgCd3. Reactions of solid-phase substitution, which occur on the electrodes, are accompanied by the destruction of initial IMC and generation of magnesium atoms. Chronoamperometry of MgCd–(Li) and MgCd3–(Li) shows the lithium intercalation to be limited by nonstationary diffusion of lithium in the solid phase. The lithium diffusion in MgCd is slower and that in MgCd3is faster than in Cd. The calculated potential dependences of the diffusion coefficient for lithium in MgCd and MgCd3 are linear in semilogarithmic coordinates.

Phase conversions and kinetics of electrochemical intercalation of lithium from dimethylformamide solutions of LiCl into bulk electrodes of bismuth, indium and their intermetallic compounds InBi and In2Bi are studied using chronopotentiometry and chronoamperometry methods. The intercalation is controlled by non-steady-state lithium diffusion in the solid electrode. In the lithium–intermetallic compound systems, both components of alloys take part in the formation of compounds with lithium. Considerable volume changes, which occur during the intercalation, may lead to disintegration of lithium-containing phase constituents with a high lithium content. The “extremum” shape of cathodic chronoamperograms may be due successive and/or parallel reactions in which various lithium-containing compounds form. Some of these reactions are limited by solid-phase diffusion, while others involve the formation and diffusion-controlled growth of three-dimensional nuclei of a new phase.

Kinetics of cathodic intercalation of lithium into aluminum from a 0.5 M LiCl solution in dimethylformamide at the stage of nucleation and growth of intermetallic compound β-LiAl is studied by one- and two-pulse potentiostatic methods. If the length of the first potential pulse is short, the current at the beginning of the second pulse is proportional to the overvoltage squared. The experimental data point to a lamellar-spiral growth of β-LiAl crystals at the initial stage of their development and to a change in the balance between different growth mechanisms as a function of the overvoltage and surface coverage by β-LiAl.

A fast computer model, intended for the calculation of the overall reaction rate (current) of anisotropic or nonhomotetic growth of a new-phase nuclei on the basis of the Voronoi diagram, is designed. The model is used for studying the kinetics of a heterogeneous reaction in the conditions where hemispherical nuclei of the new phase acquire a semiellipsoid shape in the course of an anisotropic growth. The calculation of current transients (potentiostatic i vs. t dependences) is substantially complicated in the initial stage of reaction, where the size of growing nuclei exceeds the critical value by less than an order of magnitude. If semiellipsoid nuclei overlap, the overall reaction rate is not determined by variations in the overall area of the reaction surface, as opposed to the growth of hemispherical nuclei. The kinetics of a nonhomotetic nuclei growth may be described by models designed for an isotropic growth of hemispherical nuclei.

The interfacial surface area and the electrode surface coverage by a product during the nucleation and growth of a new phase are modeled numerically and calculated analytically for electrochemical intercalation of lithium in aluminum in the course of which intermetallic compound Β-LiAl forms. As opposed to the theoretical calculation, the model accounts for mutual influence of the new-phase nuclei on their distribution over the cathode surface under conditions of noninstantaneous nucleation. The ordering of such a distribution varies extremally (passes through a maximum) with increasing size of zones where the nucleation probability is low and which surround the nuclei. This makes the dependence of a maximum specific interfacial area on the zone radius extremal as well. The model may be applied for analyzing potentiostatic current transients during cathodic intercalation of lithium in aluminum from a LiClO4 solution in propylene carbonate.

Comparative study of the regularities of the reaction and specific features of phase formation during electrochemical incorporation of lithium from propylene carbonate solutions in intermetallic aluminum-based compounds (CuAl2, Mg2Al3, and NiAl) and pure metals (Al, Cu, Mg, and Ni) was performed. The initial stage of the process was shown to be dissolution of lithium in the solid phase limited by diffusion for all studied substrates. Trace amounts of lithium-containing by-products, were detected in NiAl, Ni, and Cu samples. The subsequent change in the limiting stage is related to the beginning of formation of a new phase: metallic lithium (on Mg2Al3, NiAl, Mg, Ni, and Cu) or LiAl (on Al and CuAl2 cathodes). In the latter case, the solid-phase substitution occurs, which is formally described by the equation: CuAl2+2Li++2e→2LiAl+Cu. Thus, the specific features of phase formation on the CuAl2 electrode correspond to the highest (among three intermetallides studied) concentration of Al atoms in the crystal lattice of the compound.

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.

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.