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Lebedeva M.V.

Candidate of Chemical Sciences (Ph.D.), Associate Professor, MIREA – Russian Technological University

Investigation of chemical power sources on an automated electronic load with controlled parameters

https://doi.org/10.58224/2619-0575-2024-7-4-25-36
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 25-36 p.
Abstract
Hybrid installations for converting fuel energy into electricity are a promising way to provide humanity with affordable energy resources. However, the issue of obtaining reagents (hydrogen and oxygen) with high purity remains one of the most urgent. In this work, the energy characteristics of a hydrogen-oxygen fuel cell in combination with a water electrolyzer were investigated. Membrane-electrode assemblies were formed consisting of a modified membrane based on polytetrafluoroethylene with a platinum-containing component (Pt(30%)/C), as well as an anode and cathode made of carbon fabric and porous nickel doped with technical carbon and graphene. The structural characteristics of the material were studied using the scanning electron microscopy method. For the first time the investigation of hydrogen-oxygen membrane-electrode assemblies energy characteristics was carried out on an automated electronic load AKIP-1375/1E with embedded software. In the developed hydrogen-oxygen fuel cell, a more affordable commercial polytetrafluoroethylene-based membrane was used as a solid polymer elec-trolyte instead of the Nafion membrane, which significantly reduced the cost of developed MEA. As a result of the tests carried out, it was found that the maximum specific power is demonstrated by elements constructed on the basis of an anode and a cathode made of porous nickel modified with graphene.
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Energy-efficient nanocomposite membrane-electrode blocks for chemical current sources

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 19-28 p.
Abstract
Electrode materials based on platinum metal nanoparticles are widely used to create alternative energy sources with high specific characteristics. Industrial carbon-containing carriers and perfluorinated proton exchange membranes of the Nafion type are used as matrices for the fuel cell electrodes formation. In this work, new effective polymer-carbon catalysts modified with platinum nanoparticles have been synthesized. Physicochemical and functional characteristics of nanocomposites have been studied by electron microscopy, X-ray phase analysis, small-angle X-ray scattering and cyclic voltammetry. Increased catalytic activity and stability of the formed electrodes in hydrogen-oxygen fuel cells had been found. The test results of hydrogen-air fuel cells in model operating conditions had been obtained. The current density maximum parameters of the membrane-electrode assemblies had been found for nanocomposites formed on multi-walled carbon nanotubes with a solubilization coefficient of ω equal to 1.5 and a platinum content of 0.35 mg/cm2. The creation of new membrane-electrode assemblies helps to reduce the cost of chemical current sources, as well as increase their energy efficiency.
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DEVELOPMENT OF ELECTRODE MATERIALS BASED ON PLATINUM- RUTHENIUM NANOPARTICLES FOR METHANOL FUEL CELLS

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 7-15 p.
Abstract
The creation of effective materials for the functioning of new chemical power sources is currently an urgent task. Fuel cells can use environmentally friendly and energy resources, such as hydrogen and carbon biofuels (methanol and ethanol), which have a wide range of potential applications from portable devices to power plants. The researcher’s attention is attracted by the development of methanol fuel cells, due to their compact design, liquid fuel, low operating temperature and high specific power. However, commercialization of such energy sources is still a difficult task due to the high platinum content on the electrodes, the high cost of precious metals, low durability and delayed kinetics of both anode and cathode reactions. Increasing the activity and reducing the Pt load are two main tasks in the development of methanol fuel cell technology. In the work, bimetallic Pt-Ru nanoparticles were synthesized by chemical reduction in reversed microemulsions to evaluate the parameters of methanol fuel cells. A porous nickel was used as a carrier matrix, which was formed by template synthesis in a dimensional mask of metallic aluminum. As a result of experimental studies of methanol membrane-electrode assemblies of fuel cells based on porous nickel with Pt and Pt-Ru nanoparticles, it was concluded that the maximum voltage and current density are achieved when using electrodes based on platinum-ruthenium nanoparticles with a particle size of no more than 3 nm, a catalyst content of 0.2 mg/cm2 and a process temperature of 60oC.
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FORMATION AND RESEARCH OF BIMETALLIC ELECTRODE MATERIALS ON POLYMER-CARBON CARRIER MATRICES FOR ENERGY POWER SOURCES

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 74-82 p.
Abstract
Fuel cells are promising devices for direct conversion of chemical energy into electrical energy from the point of view of efficiency and low emission of pollutants. The main component of fuel cells is a solid polymer electrolyte. Membranes made of perfluorinated sulfonated copolymers of the Nafion type with different content of sulfogroups satisfy most of the application conditions, because they have a sufficiently high degree of proton conductivity, stability in electrolyte solutions and high mechanical strength. The principal disadvantage of such membranes is their relatively low ion selectivity and a decrease in mechanical strength at temperatures above 100oC. To improve the characteristics of the membrane, various modification methods are used, including various additives and metal nanoparticles. The main obstacle to the widespread large-scale use of fuel cells is their cost, in which the main part is the cost of electrocatalysts based on platinum metals. Therefore, the development of effective electrode materials with a reduced content of platinum metals is an urgent task. In this work, bimetallic platinum-ruthenium nanoparticles were synthesized on combined carrier matrices consisting of a Nafion polymer membrane and carbon nanotubes. The sizes of Pt-Ru nanoparticles were compared with varying the molar ratio of wa-ter:surfactant from 1.5 to 8. It was found that the minimum size is characteristic of nanoparticles obtained with a maximum platinum content in nanoparticles (7:1) and the degree of solubilization ω = 1.5. It was found that in the methanol oxidation reaction, electrode materials based on bimetallic Pt-Ru nanoparticles (7:1) demonstrate the greatest catalytic activity when the catalyst is loaded 0.2 mg/cm2 on polymer substrates with the addition of multi-walled carbon nanotubes at a temperature of 60oC.
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NANOPERFORATION TECHNOLOGY AND FUNCTIONAL PROPERTIES OF COPPER STRUCTURED MATERIALS IN THE PROCESS OF GLUCOSE ANODIC OXIDATION

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 60-69 p.
Abstract
The paper presents an original technology for the synthesis of nanostructured copper electrodes by the method of replicas from metallic aluminum nanomatrices on a pilot high-voltage galvanic installation. The technological scheme used makes it possible to carry out the process of continuous high-voltage microplasma perforation of a metal tape with the formation of nanopores of a given size in the range from 20 to 500 nm at a variable voltage. To study the received replicas, a series of indicator electrodes with a working surface made of replica material was created. Cold rolled copper foil was used as a reference material for the electrode. The visible area of the working surface of the manufactured electrodes was examined using a scanning electron microscope. By the method of cyclic voltammetry, the coefficient of increase in the specific surface area was determined by increasing the peak area corresponding to the reduction of the surface film of copper oxide formed on the surface of the copper electrode in an alkaline medium at positive potentials. For a smooth copper electrode, the surface area was 0.071 mm2. For a nanostructured electrode of the same size, the total surface area was calculated with respect to the ar-eas of current peaks corresponding to the reduction of the surface film of copper (II) oxide on the surface of a mas-sive copper electrode and a nano-porous copper electrode. It was found that the catalytic activity, estimated by the magnitude of the current associated with the oxidation of the model substrate – glucose, is approximately 10 times higher than the increase in activity due to the total surface of copper. The anomalous catalytic effect is discussed from the point of view of increasing the local electric field strength due to the high curvature of the surface of nan-ofibers and from the point of view of changing the conditions of diffusion of the substrate to the electrode surface due to nanostructuring.
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FORMATION OF NANOCOMPOSITE CARBON MATERIALS WITH BIMETALLIC NANOPARTICLES FOR AUTONOMOUS ENERGY SOURCES

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 5-12 p.
Abstract
The development of highly efficient autonomous energy sources allows for stable and uninterrupted power supply of physical and chemical processes and industries under various operating modes. Modern technological methods and approaches to the production of nanostructured electrode materials, as well as the elucidation of the features of the mechanisms of electrochemical reactions based on platinum metal nanoparticles make it possible to design control sensors, fuel cells and electrolyzers with increased energy characteristics. Carbon nanotubes used to create nanostructured electrodes in chemical energy converters have high functional properties compared to other matrices and, modified with nanoparticles with a reduced metal content, can increase the electrocatalytically active electrode surface area and achieve maximum fuel cell power parameters. In this work, the formation of bimetallic nanostructured composites with a variable composition on carbon carrier matrices for the construction of electrodes of autonomous current sources was carried out. Single- and multi-wall carbon nanotubes were chosen as substrates. To obtain composites, bimetallic platinum-palladium nanoparticles with different metal ratios were synthesized. The materials were studied by electron microscopy and X-ray phase analysis. As a result, an optimal algorithm, a synthesis method and conditions for creating nanocomposites with minimal particle sizes are established. The molar ratio water:surfactant changing, as well as the ratio of precursor metals, it is possible to obtain bimetallic platinum-palladium nanoparticles up to 12 nm. The data on the influence of the formation metal nanoparticles conditions on their size, shape and distribution over the matrix surface had been obtained. A series of prototypes has been formed for practical use in the design of current sources.
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PALLADIUM NANOELECTROCATALYSTS ON COMBINED MATRIX-SUPPORTS FOR CHEMICAL POWER SOURCES

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 29-36 p.
Abstract
Fuel cells with direct oxidation of formic acid are promising converters of chemical reaction energy into electricity due to the high open-circuit potential, safe (non-flammable and non-toxic) fuel and higher energy characteristics compared to chemical current sources with direct oxidation of alcohols. The crossover effect with a low formic acid content allows the thin membrane application, as well as a high concentration of fuel (up to 20 M), which helps to increase the structure specific power parameters as a whole. Catalysts based on Pt or Pd are widely used in the electrooxidation reaction of formic acid. It has been known that catalysts based Pd are more effective than that Pt due to their resistance to carbon monoxide as the main reaction product. In this paper, the volt-ampere and watt-ampere characteristics of formic acid-based fuel cells and air under model operating conditions were studied. The tests were carried out on a certified laboratory stand of a fuel cell, to which a working model of the investigated membrane-electrode unit was connected. The optimal characteristics of the catalyst loading are established to achieve optimal parameters of current density and specific power. The creation of new catalysts and the modification of existing ones will help to increase the electrodes operation time, reduce the production cost, in-crease their efficiency by increasing efficiency, and also use as fuel not only hydrogen, but also other fuels such as formic acid.
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PHYSICO-CHEMICAL FEATURES OF THE PALLADIUM NANOCATALYSTS FORMATION ON COMBINED MATRICES-CARRIER FOR FUEL CELLS

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 58-66 p.
Abstract
The development of modern nanotechnological methods and approaches to the synthesis and formation of nanostructures allows us to create new materials that combine various functional properties and unique physical and chemical characteristics. Such structures include composite materials consisting of a structured matrix modified with various fillers. Currently, composites are of particular interest to researchers, in which nanoscale particles play the role of filler, which makes it possible to obtain catalysts with increased activity and stability. Commercial perfluorinated proton exchange membranes of the Nafion type and carbon-containing carriers (carbon nanotubes, graphene, fullerenes) are promising carrier matrices for chemical energy sources – fuel cells. Nanoparticles based on platinum, palladium, or their alloys are excellent materials for the reactions of electrocatalytic oxidation of hydrogen and oxygen reduction that occur in fuel cells. The elements based on the direct oxidation of formic acid mainly use bimetallic nanoparticles based on palladium, which exhibit higher catalytic properties. In this work, new effective polymer-carbon composites modified with palladium nanoparticles were synthesized. Single- and multi-wall carbon nanotubes were chosen as substrates. Physicochemical studies of the obtained materials were carried out using electron microscopy and small-angle X-ray light scattering. The sizes of nanoparticles in the composition of functional carrier matrices are determined. It was found that the carbon filler contributes to the better stabilization of small nanoparticles in the composition of the composite. The data on the influence of the conditions for the formation of metal nanoparticles on their size, shape and distribution over the matrix surface are obtained. The stability of samples with variable palladium loading on various carrier matrices was studied by chronoamperometry. The prospects of using the formed materials for fuel cell electrodes with direct oxidation of formic acid are proved.
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