RU2507640C1 - Catalytic electrode for alcohol fuel elements - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: invention relates to a catalytic electrode for membrane-electrode blocks of alcohol (using methanol or ethanol as fuel) fuel elements, where the electric catalytic material is an electroconductive titanium dioxide alloyed with ruthenium oxide with the ruthenium to titanium ratio from 4 to 7 mol %, with platinum nanoparticles with size of 3-5 nm applied on the surface of the spherical particles of titanium oxide alloyed with ruthenium.

EFFECT: development of the method of electrode design with the purpose of most efficient usage of an area of electrode surface and reduced load of platinum or catalytic alloy.

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Description

The present invention relates to the field of chemical current sources, in particular to the composition of the electrocatalyst and the design of the catalytic electrode - an element of the membrane-electrode block of alcohol fuel cells.

The proposed design of the catalytic electrode is a nanostructure layer with a thickness of at least 2 μm and not more than 10 μm, consisting of spherical crystalline particles doped with ruthenium titanium dioxide, with an average diameter of about 20 nm and a narrow particle size distribution on which platinum catalytic metal nanoparticles are chemically deposited groups with an average size of 3 nm. The gaps between the oxide particles are filled with a sulfonated fluoropolymer ionomer (Nafion and similar polymers) with a random distribution of the filled sites. The volume fraction of ionomer is 12%.

The proposed electrode is intended for use in the OIE, for which the prepared dispersion of oxide particles coated with platinum and sulfonated fluoropolymer in the specified ratio is applied to the surface of the ion-exchange polymer membrane by any means: brush, airborne or ultrasonic spraying, screen printing. The OIE with deposited electrodes is designed to work in solid polymer electrochemical devices, primarily in the composition of alcohol fuel cells.

The most effective electrocatalysts for the cathode and anode of low-temperature fuel cells are catalytic systems based on highly dispersed platinum or its alloys. To stabilize the catalyst nanoclusters, electrically conductive carriers with a high surface area are used. Most often, materials based on amorphous or nanostructured carbon (carbon black, nanofibers, nanotubes) are used. However, carbon catalysts are subject to degradation during prolonged operation in the fuel cell, which consists in the oxidation of the carrier material, resulting in agglomeration of platinum particles [1-3]. In addition, in alcohol fuel cells, the platinum metal surface is poisoned by the products of the electrooxidation of alcohols (CO, formaldehyde, etc.), which are “catalytic poisons” [4-6].

To solve both of these problems, scientific and technical solutions based on the use of composite platinum catalysts deposited on oxide supports, which are more resistant to corrosion, are known. In addition to high, compared with carbon materials, corrosion resistance in an oxidizing environment, they can also have a promoting effect in the oxidation of CO and organic poisons, as a result of which the use of oxide carriers of a platinum catalyst leads to an increase in tolerance to catalytic poisons [7-13], [ 14, 15].

A technical solution is also known for using doped titanium dioxide as a carrier for a TE electrocatalyst [previous application]. It is known that titanium dioxide has a high catalytic and photocatalytic activity, since it can activate the electrochemical oxidation of a number of organic fuels by platinum and platinum group metals. In addition, it can catalyze the oxidation of carbon monoxide, providing a high tolerance of the catalyst to poisoning by oxidation products of organic fuels [18].

It is also known to use doped with niobium titanium dioxide to create a catalytic electrode for an alcohol (methanol) fuel cell [19-20]. The authors of [19-22] prepared nanocrystalline doped titanium dioxide with an average crystallite size of 10–20 nm, on the surface of which platinum was deposited with an average particle size of 3 nm. The high dispersion of platinum, as well as the metal-carrier interaction in the resulting material, according to the authors, are factors responsible for a higher catalytic activity compared to platinum on carbon black. A platinum-ruthenium catalyst supported on a nanocrystalline Ti _0.9 Nb _0.1 O ₂ carrier also shows greater catalytic activity compared to commercial PtRu / C from E-TEK [19]. A fuel cell assembled using PtRuTi _0.9 Nb _0.1 O ₂ gives 46% more current than the equivalent E-TEK Pt-Ru / C membrane-electrode block.

Closest to the claimed invention is a technical solution [Patent US 8,187,769, Choi, et al., Supported catalyst for fuel cell, method of preparing the same, electrode for fuel cell including the supported catalyst, membrane electrode assembly including the electrode, and fuel cell including the membrane electrode assembly. May 29, 2012], according to which the electrode design is a layered nanostructure consisting of 3 layers: a carbon substrate, a metal oxide layer (titanium or similar) and a catalytic metal layer (platinum or platinum group metal alloys) deposited on the second layer . In this case, the oxide nanoparticles making up the second layer are randomly distributed over the surface of the carbon substrate.

The disadvantage of this technical solution is that the reaction proceeds in a very thin (X-ray amorphous) layer of oxide particles, and therefore the surface area of the electrode / membrane interface is used extremely inefficiently. The technical solution described is selected for the prototype.

The objective of the invention is to develop a method of organization (design) of the electrode in order to most effectively use the surface area of the electrode and reduce the load of platinum or catalytic alloy.

For more efficient use of the electrode area, it is necessary to organize three-phase boundaries in its volume, however, all known technical solutions for the construction of bulk electrodes for fuel cells using oxide catalyst supports use the same designs as for catalytic electrodes based on carbon nanostructures. However, due to the much lower electronic conductivity of the doped semiconductor oxides, a thinner layer of nanostructured electrocatalytic material is effective. As shown in [23], due to the higher electronic resistances of the oxide support, only a layer 2–15 μm thick adjacent to the current collector (bipolar) plate effectively works.

Therefore, the problem is solved due to the fact that in order to more effectively use the precious catalytic metal in the proposed electrode design, a thinner layer of electrocatalytic material with an average thickness of 5-10 μm and at least 2 μm and not more than 10 μm is used, with filling the gaps between the particles inomer in a volume ratio of 0.12: 0.88. In order to increase the tolerance to catalytic poisons and to reduce electrode degradation due to oxidation, electroconductive titanium dioxide doped with ruthenium oxide in the ratio of ruthenium to titanium from 4 to 10 mol% is used as electrocatalytic material, with titanium oxide spherical particles deposited on the surface 3-5 nm platinum nanoparticles

Example 1

A nanostructured oxide catalytic electrode with a reduced platinum content deposited on an oxide support - titanium dioxide doped with ruthenium (7 mol%). The oxide carrier has a rutile-like structure and has a spherical shape of particles with an average diameter of about 15-25 nm and a narrow particle size distribution. The electronic conductivity of the carrier is 0.08 S / cm. The platinum content on the carrier is about 10% wt., The average particle diameter of platinum is 3 nm.

The thickness of the electrode is 10 μm.

The electrocatalyst was obtained by the standard platinum deposition technique:

500 ml of ethylene glycol was poured onto an oxide support (2 g) and dispersed in ultrasound. Then, NaOH ° cr (to pH ~ 13) was added to the resulting suspension and stirred until sodium hydroxide was completely dissolved. Then a platinum precursor was added with a calculation of 10% wt. platinum in relation to the mass of the carrier. The resulting mixture with constant stirring was kept at a temperature of 130 ° C in an inert atmosphere, then dried in a vacuum oven at a temperature of 100 ° C for 12 hours.

The electrode is obtained by applying an electrocatalytic material from a water-alcohol dispersion with an ionomer, the ionomer content is 12% vol. on the surface of the ion exchange membrane Nafion-112. The electrode is applied by airborne spraying using an airbrush in the form of a dispersion, maintained in a homogeneous state in the field of ultrasound.

The resulting electrode has a high resistance to CO poisoning and high activity in the electrooxidation of methanol, comparable with the properties of electrodes prepared on the basis of commercial Pt, Ru catalysts on carbon supports. The use of this electrode at the anode of an ethanol fuel cell leads to an increase in the power of TE compared with the analog based on traditional PtRu catalysts on carbon carriers (selected as an analog).

Fig. 1. Polarization curves and specific power of a methanol and ethanol fuel cell with the claimed catalyst Pt / Ru-doped TiO ₂ (Ru 7 mol.%) In comparison with cells with a PtRu / C catalyst. Cell temperature: 25 ° C. Anode - Pt loading: 0.5 mg / cm ² . Mugs: Pt / Ru-doped Tyuz (Ru 7 mol.%); squares: PtRu / C. Unshaded characters: voltage TE; encrypted characters: power density. Fuel: 0.5 M methanol solution (gray symbols), 0.5 M ethanol solution (black symbols). Temperature 25 ° C.

Literature

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Claims (2)

1. A catalytic electrode for membrane-electrode blocks of alcohol (using methanol or ethanol as fuel) fuel cells, characterized in that the electroconductive material uses conductive titanium dioxide doped with ruthenium oxide in the ratio of ruthenium to titanium from 4 to 7 mol.% deposited on the surface of spherical particles of ruthenium-doped titanium oxide with platinum nanoparticles 3-5 nm in size. 2. The catalytic electrode for membrane-electrode blocks of alcohol fuel cells according to claim 1, which is a nanostructured layer with a thickness, in order to save platinum, not less than 2 microns and not more than 10 microns, with filling the gaps between the particles of titanium dioxide doped with ruthenium oxide, sulfonated fluoropolymer "Nafion" ionomer in a volume ratio of 0.12: 0.88.

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