Search

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 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.

The development of energy systems based on high specific power hydrogen–air fuel cells using domestic nanostructured materials and technologies is an urgent task. The technologies used for manufacturing proton-exchange membrane fuel cells (PEM FC) by the Russian company BMPower using Pt/C-electrocatalysts of the PM series produced by another Russian company, Prometheus R&D, are presented. It has been shown that, in terms of their functional characteristics, catalysts of the PM series are superior to imported analogues. The use of the PM40 catalyst, as well as other innovative solutions in the field of nanotechnology (nanostructured coatings of bipolar plates, formation of an ionomer on the catalytic layer) makes it possible to achieve a specific power of more than 1 kW/kg in the PEM FC power module with air cooling.

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.

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.

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.

PtCu/C electrocatalysts with bimetallic PtCu nanoparticles were synthesized by successive chemical reduction of Cu2+ and Pt(IV) in a carbon suspension prepared based on an aqueous ethylene glycol solution. The atomic structure of as-prepared PtCu nanoparticles and nanoparticles subjected to thermal treatment at 350°C was examined using PtL 3 and CuK EXAFS spectra, transmission electron microscopy (TEM), and X-ray powder diffraction (XRD). The results of joint analysis of TEM microphotographs, XRD profiles, and EXAFS spectra suggest that the synthesized electrocatalysts contain PtCu nanoparticles with a Cu core–Pt shell structure and copper oxides Cu2O and CuO. Thermal treatment of electrocatalysts at 350°C results in partial reduction of copper oxides and fusion of bimetallic nanoparticles with the formation of both homogeneous and ordered PtCu solid solutions.

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.

Deposited electrocatalysts with different distributions of components in PtCu bimetallic nanoparticles involved in their composition were synthesized by simultaneous and sequential reduction of Cu(2+) and Pt(IV) in a carbon suspension. The dependence of the atomic structure of PtCu nanoparticles on the synthesis conditions and the degree of influence of post-treatment was established from analysis of the changes in Fourier transforms of the experimental Pt and Cu EXAFS spectra, as well as the structural parameters obtained by their fitting before and after the treatment of the materials in an acid solution. A technique was proposed for visualizing the atomic structure of synthesized bimetallic nanoparticles. This technique made it possible to determine the character of the distribution of the components over the nanoparticle volume in accordance with the component composition and local atomic structure parameters determined from EXAFS spectroscopy and to obtain the visualization of the distribution of the components in PtCu nanoparticles synthesized by the aforementioned methods.

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).

X-ray diffraction in combination with X-ray emission and EXAFS spectroscopy were used to study the electronic and atomic structure of metal nanoparticles stabilized on a carbon support in novel PtxCo/C catalysts of different composition with the molar ratio Pt:Co (x) of 1 to 3. Cobalt atoms in nanoparticles, which average size was 2–4 nm, were shown to form chemical bonds both with platinum atoms and carbon atoms of the support material.

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.

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/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.

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.