E. V. Zolotukhina

Synthesis of palladium–polypyrrole nanocomposite and its electrocatalytic properties in the oxidation of formaldehyde

Three alternative methods were developed for the synthesis of modifying palladium–polypyrrole layers on the surface of an inert electrode. Their electrocatalytic activity toward formaldehyde under inert atmosphere was checked. All the suggested methods are one-stage and allow synthesis of a film on the electrode surface from a solution containing a palladium salt and pyrrole in the absence of other active reagents. The electrochemical methods (potentiodynamic and double cathodic and anodic pulses techniques) in an aqueous medium give films with poorly reproducible electrocatalytic properties, while the chemical redox synthesis affords films with reproducibly high electroactivity toward methylene glycolate.

Degradation of Pt/C electrocatalysts having different morphology in low-temperature PEM fuel cells

The electrochemical degradation of platinum–carbon catalysts with different morphology has been studied under model conditions in low-temperature proton exchange membrane fuel cells. It has been found that catalysts with an average size of platinum nanoparticles ranging from 2 to 3 nm uniformly distributed over the carbon support exhibit the best current–voltage characteristics; however, they have also the highest degradation rate. It is shown that the main cause of Pt/C electrocatalyst degradation consists of both the detachment of small platinum particles from the carbon support and the recrystallization of platinum, leading to an increase in the average particle size. On the contrary, the catalysts having the initial average size of platinum particles ranging from 3 to 4 nm show a considerable stability in current–voltage characteristics even after 10000 cycles of accelerated degradation.

Electrocatalytic activity of palladium–polypyrrole nanocomposite in the formaldehyde oxidation reaction

Palladium–polypyrrole nanocomposite materials with high electrocatalytic activity toward formaldehyde in an alkaline solution (methylene glycolate) have been synthesized via a one-step redox route. Key factors that have an effect on the sensor properties of palladium nanoparticles have been determined. It has been demonstrated for the first time that the emergence of not only the forward but also the reverse wave of formaldehyde oxidation on palladium particles is associated with the oxidation of methylene glycolate rather than intermediate species.

One-step and one-pot method for synthesis of hybrid composite palladium-polypyrrole-carbon (Pd/PPy/C) nanomaterials

63 A onestep and onepot method to design compos� ite nanomaterials based on conjugated polymer, poly� pyrrole, and palladium nanoparticles by the redox reaction of the monomer and a palladium salt in non� aqueous and aqueous media was described previously in the works of our team (1-3). These composite materials were successfully tested as heterogeneous catalysts for the most known organic syntheses (Suzuki reaction, direct C-C conjugation, Sonogash� ira reaction, etc.) and showed excellent catalytic activ� ity. This fact made such materials interesting for fur� ther investigation. The main feature of palladium-polypyrrole (Pd/PPy) composite nanomaterials consists is that the formation of palladium nanoparticles within polypyr� role globules requires no additional stabilizers in the system. Therefore, no protective layers appear on the surface of palladium nanoparticles so that it remains catalytically active. At the same time, the polymer resulting from the chemical reaction has a porous structure that favors the diffusion of reactants to cata� lytically active centers.

The method of double cathodic-anodic potential (current) pulses for synthesis of composite coatings Prussian blue–polypyrrole on optically transparent electrodes

An original method of one-step electrochemical deposition of electroactive composite films from a mixed solution of precursors of the organic and inorganic components in the mode of double cathodic–anodic pulses is used for the formation of Prussian blue/polypyrrole films on the surface of optically transparent electrodes. The deposition parameters are chosen (the order of deposition of components, the number and amplitude of polarizing pulses, the pulse length) which allow the deposition of composite films with good adhesion to the electrode surface and the high stability of the redox-transition Prussian blue/Prussian white.

Catalytic activity of silver–ion exchanger nanocomposites in methanal oxidation reaction with molecular oxygen

Silver-containing ion exchangers with the surface distribution of silver nanoparticles—promising catalytic materials for the methanal oxidation reaction—have been synthesized by chemical deposition of the metal onto ion-exchange matrices. The resulting materials are evidently superior to the available analogues in that they allow one to carry out the reaction with the high conversion (80–90%) at low temperature and have a high capacity to OH– ions, which play a key role in the oxidation of an aldehyde to gaseous products (CO and CO2).

Electroactive Composite Pd–Polypyrrole and Its Catalytic Properties in the Reaction of Styryl Bromide Cyanation

A composite material in the form of powder is synthesized by a redox reaction in mixed aqueous solution of Pd(NH3)4Cl2 + pyrrole. The composite consists of polypyrrole globules with palladium nanoparticles uniformly distributed inside the latter. Being applied as a film on the electrode surface, both components of this material exhibit redox activity. Palladium particles inside the composite exhibit catalytic properties in cyanation of styryl bromides, a reaction widely used in fine organic synthesis.

Electrochemical synthesis of polypyrrole in powder form

Novel approach to synthesis of conjugated oligomers/polymers is proposed. This approach combines all advantages of electrochemical methods: variation of the oxidation potential in wide range with high precision, direct control of the process rate and product yield, variation of both the doping anion/cation nature and the composition of polymerization medium, absence of chemical oxidative reagents in reaction mixture. Contrary to the conventional use of this synthetic method, it has been exploited in our study for generation of polymeric products outside the electrode surface. This goal has been implemented via oxidation of the monomer at porous electrode with simultaneous pumping of the polymerization medium (monomer in background electrolyte solution) through porous electrode with a certain rate. It leads to electrochemical generation of active intermediates (cation radicals) at the electrode surface with their recombination and subsequent accumulation of the products not only as film on the electrode surface but also as a colloid in solution outside the porous medium. Since this reaction path toward bulk solution products should evidently be favored by slow steps in the course of the polymer formation, this approach has been tested for pyrrole oxidation (both in its pure monomer solution and in the presence of the bromide redox mediator) since this monomer is known of its high rate of polymer chain formation.

Palladium Nanoparticles–Polypyrrole Composite as Effective Catalyst for Fluoroalkylation of Alkenes

Palladium nanoparticles–polypyrrole composite (Pd/PPy) catalyzes the addition of perfluoroalkyl halides to olefins to produce a variety of products with good yields. An effective fluoroalkylation technique tested with various olefins, fluoroalkyl halides and Pd/PPy was developed. The reaction proceeds highly efficient under mild phosphine-free reaction conditions with different substrates, easy catalyst recycling and provides a general and straightforward access to fluoroalkylated products. Furthermore, we were able to control whether the addition of perfluoroalkyl occurs with various monomer (fluoroalkylated alkene or alkane with RF and OH moieties) or dimer formation (under electrochemical conditions).Graphical Abstract

Low-temperature oxidation of methanal on nanostructured silver–amino anion exchanger catalysts

Nanostructured silver–amino anion exchanger composites have been synthesized as catalysts for the low-temperature oxidation of methanal with molecular oxygen in aqueous solution. The oxidative conversion of methanal reaches 80–100% at 298 K. The methanal oxidation reaction is size-dependent, and its rate increases with a decrease in the silver nanoparticle size. The fixed amino groups of anion-exchange matrix play the role of additional active sites for the adsorption of methanal in the form of methylene glycolate–anions, which facilitates the reaction.