RU2331143C1 - Cathode material for sofc on basis of cobalt containing perovskite-like oxides of transition metals - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to the electro-technical field, particularly to the materials for solid oxide fuel cells (SOFC) on the basis of the complex oxides of transition metals. The cathode material is executed on the basis of perovskite-like oxides with the general formula of the transition metals Sr_1-x-yCa_yR_xCo_1-zMn_zO_3-y, where 0<x≤0.75; 0≤y≤1.0; 0≤z<1.0; R is an element from the group containing Sm, Gd and Y. The technical result of the proposed solution is the creation of a cathode material, which possesses simultaneously high conductivity by oxygen ions and electronic conductivity, thus the value of the coefficient of thermal-expansion (CTE) of a cathode material can be successfully applied with electrolytes on the basis of doping by yttrium of zirconium oxide (YSZ) with additional coating or sub-layer on the basis of doped gadolinium of cerium dioxide (GDC), and also direct GDC.

EFFECT: the creation of a cathode material, which possesses simultaneously high conductivity by oxygen ions and electronic conductivity.

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Description

The invention relates to solid oxide fuel cells (SOFC), in particular to cathode materials based on complex transition metal oxides.

Known cathode material for SOFC based on perovskite-like oxides with the general formula (La _1-x A _x ) _1-y MnO ₃ , where A is one of the metals from the group of strontium, calcium, magnesium, barium, yttrium, cerium, ytterbium, and 0 <x≤0.5, 0 <y≤0.2 (EP No. 0633619 A, class H01M 8/12, 1995). The disadvantage of this cathode material is its low ionic conductivity and high coefficient of thermal expansion (CTE).

Of the known cathode materials, the cathode material based on cobalt-containing perovskite-like oxides with the general formula La _1-x Sr _x CoO _3-y , (S. Charojrockul, K.-L. Choy, BCHSteele, Solid State lonics, 121 (1999) 107-113). The disadvantage of this cathode material is the high value of the CTE. The most probable reason for the high CTE values of these known cobaltites is the presence of thermally activated transitions between different spin states of Co ³⁺ cations. One way to reduce the CTE is to partially replace cobalt with cations of other transition metals, for example, iron or manganese.

The objective of the invention is the creation of a cathode material having simultaneously high conductivity by oxygen ions and electronic conductivity, as well as a CTE value comparable to that of an electrolyte.

The specified technical result is achieved by the fact that as the cathode material for SOFC based on cobalt-containing perovskite-like oxides, a compound with the general formula Sr _1-xy Ca _y R _x Co _1-z Mn _z O _3-t , where 0 <x≤0.75;0≤y≤1.0; 0≤z <1.0; R is an element from the group containing Sm, Gd, and Y. The indicated compound has a CTE value not exceeding the CTE of the electrolyte by more than 25%, electrical conductivity at 900 ° C from 60 to 120 S / cm, and at 600 ° C from 45 up to 69 S / cm. These cathode materials exhibit electrocatalytic activity in the oxygen reduction reaction. The specified compound can be successfully used with electrolytes based on yttrium-doped zirconium dioxide (YSZ) with an additional coating (sublayer) based on gadolinium-doped cerium dioxide (GDC), as well as directly GDC.

The analysis of the prior art showed that the claimed combination of essential features set forth in the claims is unknown. This allows us to conclude that it meets the criterion of "novelty."

To verify the conformity of the claimed invention with the criterion of "inventive step", an additional search was carried out for known technical solutions in order to identify features that match the distinctive features of the claimed technical solution from the prototype. It is established that the claimed technical solution does not follow explicitly from the prior art. Therefore, the claimed invention meets the criterion of "inventive step".

The invention is illustrated by drawings and an example of practical implementation.

Figure 1 presents the current-voltage characteristics of model fuel cells for temperatures of 700 ° C, 800 ° C and 900 ° C. Short circuit current reaches 240 mA / cm ² at 900 ° C. Measurements of the dependence of the current-voltage characteristics of SOFC on the partial pressure of oxygen in the pressure range 0.06-0.5 bar. The linearity of the current-voltage characteristics is maintained up to the partial oxygen pressures P (O ₂ ) ~ 0.07 bar, which indicates a rather high catalytic activity of the cathode and the possibility of using it when the air mixture is fed into the oxidation chamber (P (O ₂ ) ~ 0.2 bar).

Figure 2 presents the current-voltage characteristics of the model SOFC with the cathode Sr _0.75 Y _0.25 Co _0.5 Mn _0.5 O _3-y at T = 800 ° C and various oxygen partial pressures.

Figure 3 shows the comparative current-voltage characteristics under the same conditions for SOFC with standard cathode material (LSM) and Sr _0.75 Y _0.25 Co _0.5 Mn _0.5 O _3-y . The characteristics of SOFC with the cathode of the material under study are comparable to the characteristics of another known LSM cathode.

Examples of practical implementation.

Example 1

The sol-gel method using Sr (NO ₃ ) ₂ , Co (NO ₃ ) ₂ 6 Н ₂ O, Y (NO) ₃ ) ₃ 8Н ₂ O and Mn (СН ₃ СОО) ₂ 4Н ₂ O was used to synthesize the cathode material Sr _0.75 Y _0.25 Co _0.5 Mn _0.5 O _3-y . The material was a cubic perovskite a = 3.8205 (3) Å, CTE which was 13.33 ppm K ^-1 (200-600 ° C), 19.6 ppm K ^-1 (600-800 ° C) 300K conductivity - 0.069 S / cm, 873K - 59 S / cm, 1173K - 110.2 S / cm. The density of the sample was 68% of theoretical. The final annealing of the obtained material was carried out at 1300 ° C for 12 hours. As an electrolyte in model SOFCs, YSZ disks with a GDC sublayer deposited on it were used. A cermet composite (~ 65% NiO + ~ 35% YSZ) is used as the anode.

Example 2

The sol-gel method using Ca (NO _{3) 2,} Co (NO _{3) 2} 6 H ₂ O, Y (NO _{3) 3} 8H ₂ O, and Mn (CH ₃ COO) ₂ .4H ₂ O was synthesized cathode material is Ca _0.75 Y _0.25 Co _0.15 Mn _0.85 O _3-y . The material was rhombic perovskite a = 5.3397 (8) Å, b = 7.470 (1) Å, c = 5.2810 (6) Å, KTP of 13.8 ppm K ^-1 , electrical conductivity 300K - 19 S / cm, 1173K - 133 S /cm. The final annealing of the obtained material was carried out at 800 ° C for 12 hours in air. As an electrolyte in model SOFCs, YSZ disks with a GDC sublayer deposited on it were used. A cermet composite (~ 65% NiO + ~ 35% YSZ) is used as the anode.

Claims (1)

A cathode material for a solid oxide fuel cell (SOFC) based on cobalt-containing perovskite-like oxides, characterized in that a compound with the general formula Sr _1-xy Ca _y R _x Co _1-z Mn _z O _3-y , where 0 <x≤0.75;0≤y≤1.0; 0≤z <1.0; R is an element from the group containing Sm, Gd, and Y.

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