RU2361332C1 - Fuel element - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to fuel elements and can be used for making current sources in different industries. According to the invention, the said fuel element consists of a cathode, anode and electrolyte, each of which contains complex metal oxides. The porous anode is cermet, containing nickel and complex zirconium oxide stabilised by yttrium, ceric oxide subdivided by gadolinium or doped with samarium. The material of electrolyte contains complex oxides of the same type as the anode. The cathode consists of complex oxide Li_xNiO₂, where x=0.1÷0.5, mainly 0.3-0.45. Alkaline and carbon-bearing compounds are added to the electrolyte in amounts of 30-50% of the mass of the electrolyte. Complex oxides of the anode, cathode and electrolyte are obtained from pyrolysis of polymer-salt compositions. The anode has porosity of not less than 30-40%, and specific surface area of oxygen carrying solid oxides, contained in the anode, cathode and electrolyte, is not less than 50 m/g.

EFFECT: simplification of the process of obtaining initial materials for making fuel cells, improvement of their quality, simplification of making each fuel cell, reduced thickness of the electrolyte layer, increased power of the fuel element and stability of its operation under reasonable conditions.

3 dwg

Description

The present invention relates to the field of fuel cells and can be used to create current sources in various industries.

A known fuel cell, the cathode of which is a mixture of nickel powder and lithium oxide (see, for example, US patent No. 4386040, 1983). To form a cathode with a porous structure, this mixture is fired in air. During firing, the composition Li _x Ni _(1-x) O is formed, where x = 0.005 ÷ 0.25, mainly 0.02.

A fuel cell is known whose cathode contains lithiated nickel oxide obtained by reacting nickel powder and nickel carbonate (see, for example, US Pat. No. 5,688,292, 1997).

Known fuel cell, which includes a two-layer cathode (see, for example, US patent No. 6420062, 2002). The first layer contains lithium enriched nickel oxide, and the second contains cerium activated lithium cobaltite.

A fuel cell with a molten carbonate electrolyte is known, the cathode material of which contains lithium oxides, transition metal oxides and an additive (see, for example, RF patent No. 2248649, publication date 2005.03.20). As an additive, rare earth oxide is used in the following proportions by the formula:

Ln _x Li _w T _y O _3-δ ,

where Ln is La or a mixture consisting mainly of La and one or more lanthanides,

T is a transition metal from the following series: Mn, Fe, Co,

x = 0.8-1,

y = 0.5-1,

w = 0.01-0.7,

w + x + y = 2,

δ = 0-1.

A fuel cell is known whose electrolyte located between the cathode and the anode is a bismuth oxide-stabilized yttrium or niobium oxide-conducting ceramic and may contain zirconium oxide (see, for example, RF patent No. 2221315, publication date 01/10/2004, )

A known fuel cell, the electrolyte of which contains an active component in the form of a mixture of carbonates and hydroxides of alkali metals and the forming material is lithium aluminate (see, for example, US patent No. 4115632, 1978).

Known fuel cell, the anode of which is made of a mixture of oxides of Nickel, zirconium and chromium (see, for example, US patent No. 5368951, 1994).

A fuel cell is known whose anode contains particles selected from the group: nickel oxide, cobalt and cerium dioxide, or mixtures thereof, and particles of titanium dioxide inside the main substance — yttrium oxide stabilized zirconia (see, for example, US Pat. No. 6,248,468, 2001 )

A fuel cell is known, the anode of which is a porous nickel alloy, the cathode is porous nickel oxide doped with lithium, and the electrolyte is a eutectic mixture of alkali metal carbonates (see, for example, US patent No. 5354627, 1994).

A known fuel cell comprising a cathode associated with a solid conductive oxidizing ion of an oxidizer electrolyte (see, for example, patent JP 2001256990, publication date - 09/21/2001). As a cathode, cermet made from a mixture containing from 5 to 30% by weight of cerium oxide doped with samarium or gadolinium oxide in an amount of from 10 to 30 mol% was used. The rest of the cermet is nickel oxide.

All the above analogs differ in one way or another with certain shortcomings, the main of which are either high cost, or the complex technology of the formation of the fuel cell, or the instability of the fuel cell, or the unsatisfactory temperature limits of the cell.

Closest to the present invention is a fuel cell according to patent WO 2004/013882 "NANO-COMPOSITE ELECTRODES AND METHOD OF MAKING THE SAME" (publication date 02/12/2004).

This invention relates to methods for producing ceramic electrode materials, which are a mixture of two or more components. At least one of the components must be an ion-conducting ceramic electrolyte material with nanosized particles (for example, yttrium-stabilized zirconium oxide, gadolinium-doped cerium oxide, samarium-doped cerium oxide, etc.) and at least one must be powder of electrode material. The last of these components can be electrically conductive ceramics (for example, lanthanum-strontium manganite, iron-doped praseodymium-strontium manganite, lanthanum-strontium ferrite, cobalt-doped lanthanum-strontium ferrite, etc.) or a precursor of metal electrode material (for example, nickel oxide , copper oxide, etc.).

Such nanocomposite electrodes are applicable in various electrochemical systems such as solid oxide fuel cells, ceramic oxygen generating systems, gas sensors, ceramic membrane reactors, and ceramic gas separation systems.

In the fuel cells, the above materials are used in the following embodiments.

For the manufacture of a ceramic electrolyte membrane, among other materials, yttrium-stabilized zirconium oxide doped with gadolinium cerium oxide, samarium-doped cerium oxide, etc. are used.

For the manufacture of the cathode, lanthanum-strontium manganite, iron-doped praseodymium-strontium manganite, lanthanum-strontium ferrite, cobalt doped with lanthanum-strontium ferrite, etc. are used.

For the manufacture of the anode of the fuel cell, a composite mixture (cermet) of yttrium-stabilized zirconium oxide doped with gadolinium cerium oxide doped with samarium cerium oxide and metal (for example, nickel or copper) is used.

The disadvantage of this invention is the difficulty of obtaining the necessary materials and the difficulty of forming the actual cell of the fuel cell.

An object of the present invention is to provide a new fuel cell.

The technical result consists in simplifying the process of obtaining raw materials for forming a cell of a fuel cell, in improving their quality, in simplifying the formation of an individual cell of a fuel cell, in reducing the thickness of the electrolyte layer, in increasing the power of the fuel cell and its stability under acceptable conditions.

To obtain this technical result, in a fuel cell consisting of a cathode, anode and electrolyte, each of which contains complex metal oxides, the porous anode is a cermet composed of nickel and yttrium-stabilized complex zirconium oxide doped with gadolinium cerium oxide or doped cerium oxide, and the electrolyte material contains complex oxides of the same type as the anode, the cathode consists of a complex oxide Li _x NiO ₂ , where x = 0.1 ÷ 0.5, mainly 0.3 ÷ 0.45, in the composition electrolyte doba alkaline or carbonate compounds in an amount of 30 to 50% by weight of the electrolyte, complex oxides of the anode, cathode and electrolyte are obtained as a result of pyrolysis of polymer-salt compositions, the anode porosity is at least 30-40%, and the specific surface area of the oxygen conducting solid oxides that make up the anode, cathode and electrolyte is at least 50 m ² / g

The essence of the present invention is as follows.

Known methods for producing powders of complex oxides, based on the mechanical grinding of complex oxides after synthesis of the latter (see, for example, patent SU No. 1806046, publication date 03/30/1993). Powders of this type are practically not applicable for the creation of fuel cells.

Known methods for producing complex oxides in which the initial solution is sprayed in a gas stream to obtain a fine powder with a high specific surface area (see, for example, Russian patent No. 2175643, publication date 10.11.2001; US patent No. 7255954, publication date 14.08. 2007). To obtain highly dispersed oxide powders with nanosized particles, atomization of the initial solutions in an ultrasonic field is used (see, for example, patent WO / 2005/037709, publication date April 28, 2005).

A known method of producing powders of complex oxides, based on the pyrolysis of polymer-salt compositions. The application of this method with the simultaneous use of an ultrasonic field makes it possible to stably obtain complex oxide powders with a high yield of nanosized particles. As polymer-salt compositions, solutions of salt compounds with the addition of a polymer, for example polyvinyl alcohol, are usually used (see, for example, SU patent No. 1347511, publication date 23.09.85).

In our work, we studied in more detail the conditions for the preparation of complex oxide powders from polymer-salt compositions by spray pyrolysis in an ultrasonic field: cerium oxide doped with samarium (Ce _0.8 Sm _0.2 O ₂ ), cerium oxide doped with gadolinium (Ce _0.8 Gd _0.2 O ₂ ) stabilized by yttrium zirconium oxide (Zr _0.9 Y _0.1 O ₂ ) and lithiated nickel oxide (Li _x NiO ₂ ), which are the basis for the formation of the fuel cell of the present invention.

The starting materials used were metal oxides and carbonates: NiO “p.p.”, Ce (CO ₃ ) ₂ “p.p.”, Sm ₂ O ₃ “SmO-D”, Li ₂ CO ₃ “p.p. ", Polyvinyl alcohol (PVA) grade 11/2. Oxides and carbonates were dissolved in nitric acid of the corresponding concentration, an aqueous solution of polyvinyl alcohol was added to the resulting solution. Thus prepared, a homogeneous polymer-salt composition was fed into the reactor for carrying out the pyrolysis process under ultrasonic treatment. Pyrolysis products are fine powders of cathode, anode and electrolyte materials.

Among some features of the process, the following can be noted. For example, the formation of the individual phase Ce _0.8 Sm _0.2 O _{2 was} completed in 1-2 minutes at a temperature of about 650 ° C. For comparison, we can say that to obtain a single-phase product by traditional solid-phase synthesis from CeO ₂ and Sm ₂ O ₃ oxides, a temperature of at least 1000 ° C and tens of hours of annealing with intermediate grindings is required.

Pyrolysis of the polymer-salt composition in an ultrasonic field makes it possible to obtain a relatively monosized dispersion powder. The granulometric composition of Ce _0.8 Sm _0.2 O ₂ determined by laser diffraction on an SALD-2201 instrument (Shimadzu) is shown in FIG. 1.

The specific surface is ~ 56 m ² / g. The distribution of fractions is almost monodisperse, the particle diameter of the main fraction varies in the range of 0.2 <D <8 μm. The presence of nanoparticles significantly reduces the sintering temperature of the powder, which facilitates the production of dense (at least 96%) ceramics or the formation of gas-tight coatings on ceramic supports.

One of the options for the fuel cell of the present invention is shown in Fig.2.

Cerium oxide Ce _0.8 Sm _0.2 O ₂ stabilized by samarium was used as the main raw material for the production of the electrolyte and cermet anode. To form a planar cell of a fuel cell, a promising composite electrolyte was selected containing fine powder of Ce _0.8 Sm _0.2 O ₂ with the addition of caustic soda NaOH.

The mechanical mixture of Ce _0.8 Sm _0.2 O ₂ and NaOH was ground and annealed at 300 ° С for 2 hours, after which it was again ground.

As an anode material, Ni-Ce _0.8 Sm _0.2 O ₂ cermet (about 50 wt.% Ni) was chosen, which possesses, at operating temperatures (700-800 ° C), quite good electrical conductivity (mixed electron-ion) of the order of 10 ³ S / cm and resistance to a strong reducing atmosphere.

As the cathode material, lithiated nickel oxide Li _x NiO ₂ (x = 0.4) was used, which practically does not interact with the composite electrolyte and has high electrical conductivity.

The cell of the fuel cell was formed by layer-by-layer “dry” pressing (pressure 200 kgf / cm ² ) of the layers of the Ni-Ce _0.8 Sm _0.2 O ₂ anode, Ce _0.8 Sm _0.2 O ₂ + NaOH composite electrolyte (60% and 40% by weight, respectively) and cathode Li _0.4 NiO ₂ . The thickness of the powder layers (raw, unannealed) did not exceed 0.5 mm. The pressed blank of the electrochemical cell was annealed at the first stage to give it mechanical strength. Then platinum down conductors were attached to the cathode and anode sides. The finished planar element is a durable ceramic tablet (D = 20 mm, l = 0.5 mm) with Pt current collectors. The thickness of the electrolyte layer of the test sample was l _(elec) = 0.10 ± 0.05 mm. The current-voltage characteristic of the obtained SOFC prototype element is presented in Fig. 3. The maximum power of a fuel cell based on Ce _0.8 Sm _0.2 O ₂ + NaOH electrolyte was 105 mW / cm ² at a temperature of 800 ° C, and the open circuit voltage was 0.85 V.

A time-stable voltage value of 0.85 V with an open circuit (tested for 48 hours at 800 ° C) indicates a high degree of gas density of the electrolyte layer. Missing 0.25 V to a theoretical value of 1.1 V for Ce-electrolytes (Ce _1-x Sm _x O ₂ and Ce _1-x Gd _x O ₂ ) are associated with the partial electron transfer characteristic of these electrolytes at the test temperature. The results obtained regarding the values of specific power (105 mW / cm ² at a current strength of 300 mA / cm ² ) show that a similar method of forming a composite cell can reduce the thickness of the electrolyte layer by tens of times, and therefore increase the current and power of the cell.

Thus, the achievement of the technical result, which consists in simplifying the process of obtaining raw materials for forming a cell of a fuel cell and improving their quality, is confirmed. The process of forming an individual cell of a fuel cell is greatly simplified. The thickness of the electrolyte layer is reduced, the power of the fuel cell and the stability of its operation are increased.

Claims (1)

A fuel cell consisting of a cathode, anode, and electrolyte, each of which contains complex metal oxides, the porous anode being a cermet composed of nickel and yttrium-stabilized zirconium oxide doped with gadolinium cerium oxide or doped with samarium cerium oxide, and the electrolyte material contains complex oxides of the same type as the anode, characterized in that the cathode consists of a complex oxide Li _x NiO ₂ , where x = 0.1-0.5, mainly 0.3-0.45, alkaline are added to the electrolyte or carbonate compounds 30-30% of the mass of the electrolyte, complex oxides of the anode, cathode and electrolyte were obtained by pyrolysis of polymer-salt compositions, the anode porosity is not less than 30-40%, and the specific surface of the oxygen-conducting solid oxides that make up the anode , cathode and electrolyte, is not less than 50 m ² / g.

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