Electrode material, method for the production thereof, and use of same

Abstract

A material for an electrode, the material for as well as a method of making the material for an electrode comprising or consisting of a compound of formula (1)

M2Ni1−xCoxO4+δ

and/or of formula (2)

La1−yMyNi1−xCoxO4+δ

where M represents Pr and/or Nd, 0.0≤x≤0.2, 0.25≤δ≤0.3 and 0<y≤10 0.5.

Claims

1. Material for an electrode, the material comprising of a compound of formula (1)
M2Ni1−xCoxO4+δ  (1)
and/or of formula (2)
La1−yMyNi1−xCoxO4+δ  (2) where M represents Pr and/or Nd, 0.0≤x≤0.2, 0.25≤δ≤0.3 and 0<y≤0.5.

2. Material according to claim 1, wherein x has the values 0.0, 0.1 or 0.2.

3. Material according to claim 1, wherein δ has the values 0.25, 0.28 or 0.3.

4. Material according to claim 1, wherein it is selected from Pr2NiO4+δ, Pr2Ni0.9Co0.1O4+δ, Pr2Ni0.8Co0.2O4+δ, Nd2NiO4+δ, Nd2Ni0.9Co0.1O4+δ Nd2Ni0.8Co0.2O4+δ and La1.5Pr0.5Ni1−xCoxO4+δ.

5. Material according to claim 1, wherein the material has a perovskite structure.

6. Material according to claim 5, wherein the material has a layered perovskite structure.

7. Material according to claim 1, wherein it has an average particle size of 0.5 μm to 1 μm, for example 0.8 μm to 0.9 μm, or 0.5 μm to 0.6 μm.

8. Material according to claim 1, further comprising a compound of formula (3) LaNi0.6Fe0.4O3−δ (3) where 0<δ≤0.05.

9. Method for producing a material for an electrode, according to claim 1, comprising the steps of (a) mixing the oxides of the elements Pr, Nd, Ni, Co, La according to the desired compound of formula (1) or (2), (b) drying the mixture from step (a), (c) annealing the mixture at a temperature of 1000° C. to 1400° C. for 4 hours to 20 hours in air.

10. Method according to claim 9, wherein the mixing of the oxides in step (a) is carried out using a ball mill in the presence of a liquid for 2 to 6 hours.

11. Method according to claim 9, wherein the drying in step (b) is carried out at 18° C. to 100° C., for 8 hours to 24 hours.

12. Method according to claim 9, wherein the annealing in step (c) is carried out at a temperature of approximately 1300° C. for approximately 12 hours.

13. Method according to claim 9, wherein, after step (c), the average particle size is adjusted to 0.5 μm to 1 μm.

14. Use of the material according to claim 1 as an electrode material.

15. Use according to claim 14, wherein the electrode is an air electrode or oxygen electrode for a fuel cell or electrolysis, in particular for high temperature electrolysis.

16. Method according to claim 10, wherein the mixing of the oxides in step (a) is carried out using a ball mill in the presence of a liquid for 3 to 5 hours.

17. Method according to claim 11, wherein the mixing of the oxides in step (a) is carried out using a ball mill in the presence of a liquid for 4 hours.

18. Method according to claim 9, wherein the drying in step (b) is carried out at 18° C. to 100° C. for 12 hours.

19. Material according to claim 2, wherein δ has the values 0.25, 0.28 or 0.3.

20. Material for an electrode, the material consisting of a compound of formula (1)
M2Ni1−xCoxO4+δ  (1)
and/or of formula (2)
La1−yMyNi1−xCoxO4+δ  (2) where M represents Pr and/or Nd, 0.0≤x≤0.2, 0.25≤δ≤0.3 and 0<y≤0.5.

Description

[0030] The invention will be explained in more detail below on the basis of the description without restricting the general concept of the invention. In the drawings:

[0031] FIG. 1 shows a voltage/voltage density curves for the single cells with PNO, PNCO10 and PNCO20 electrodes at 800 and 900° C.

[0032] FIG. 2 shows the resistance of the single cells PNO, PNCO10 and PNCO20 at 800° C. and a current density of −1 A.Math.cm.sup.−2 with a 50% H.sub.2+50% H.sub.2O gas mixture.

EXAMPLE: PRODUCTION AND ELECTROCHEMICAL PROPERTIES OF ELECTRODE MATERIALS

Preparation of Materials and Characterizations:

[0033] Three compositions of each series, namely Pr.sub.2Ni.sub.1−xCo.sub.xO.sub.4+δ (PNCO), Nd.sub.2Ni.sub.1−xCo.sub.xO.sub.4+δ (NNCO) and La.sub.1.5Pr.sub.0.5Ni.sub.1−xCo.sub.xO.sub.4+δ (LPNCO), (x=0.0, 0.1 and 0.2) were produced according to a solid-state synthesis method. Higher cobalt contents were not taken into account due to the instability of the layer structure. The corresponding precursors were Pr.sub.6O.sub.11 (Aldrich chem, 99.9%), La.sub.2O.sub.3 (Aldrich chem, 99.9%), Nd.sub.2O.sub.3 (Alfa Aesar, 99%), NiO (Alfa Aesar, 99%) and Co.sub.3O.sub.4 (Alfa Aesar, 99%). In a first step, the powders Pr.sub.6O.sub.11, Nd.sub.2O.sub.3 and La.sub.2O.sub.3 were pre-fired overnight at T=900° C. in order to remove the water content due to their high hygroscopic character. The precursors were weighed according to the composition of the nickelates and then ball-ground with zirconia balls and isopropanol (VWR, 99.8%) for 4 hours at 250 rpm. After drying overnight at 80° C., annealing was carried out at 1300° C. for 12 hours in air to obtain a pure phase. At a lower sintering temperature, some impurities were detected by the XRD. The sintering conditions of 1300° C./12 h result in well crystallized pure phases. The powders obtained were comminuted and ground again with zirconium dioxide balls and isopropanol for 8 h with the aim of obtaining an average particle size of approx. 1 μm (checked by means of particle size distribution and SEM).

[0034] The δ value at room temperature in air was determined by iodometric titration and TGA experiments. The powders were first balanced in air up to 1000° C., then cooled to room temperature at a slow rate (2° C. min.sup.−1), with this cycle being repeated twice to ensure a stable state of the material, i.e. a reproducible oxygen content. A second cycle was then carried out under Ar-5% H.sub.2 flow with a very slow heating rate of (0.5° C..Math.min.sup.−1), with decomposition of the material leading to the determination of the oxygen stoichiometry after cycling the sample to room temperature (La.sub.2O.sub.3, Nd.sub.2O.sub.3, Pr.sub.2O.sub.3, Pr.sub.2O.sub.3, metallic Ni and Co depending on the composition). For all series, an increase in the 6 value was observed upon cobalt substitution. For example, the 6 values obtained are 0.25, 0.28 and 0.30 for Pr.sup.2NiO.sup.4+δ (PNO), Pr.sub.2Ni.sub.0.9Co.sub.0.1O.sub.4+δ (PNCO10) and Pr.sub.2Ni.sub.0.8Co.sub.0.2O.sub.4+δ (PNCO20), respectively.

Electrochemical Performance and Durability as an Oxygen Electrode:

[0035] Electrochemical characterization was carried out with NiO—YSZ-supported cells (NiO YSZ///YSZ//GDC///electrode, CeramTec®, ASC-10C type). The oxygen electrode, i.e. the anode layers (nickelates) were deposited using the screen printing method and sintered in air at 1150° C. for 1 h. The sintering temperature (1150° C.) was optimized for the PNCO series to obtain a controlled homogeneous porous electrode microstructure. For the measurement, gold and nickel grids (1,024 cm.sup.−2 mesh) were used as current collectors for the oxygen and fuel electrodes. The i-V characteristic curve was measured in the electrolysis mode from OCV to 1.5 V with a 50% H.sub.2O and 50% H.sub.2 gas mixture in the temperature range of 700-900° C. The impedance plots were recorded at OCV and from 1.0 to 1.5 V with an increase of 0.1 V, potentiostatically controlled with 50 mV AC amplitude, from 106 Hz to 10-1 Hz, with an IVIUM VERTEX potentiostat/galvanostat with an integrated frequency response analysis module.

[0036] An increase in cell performance was observed with cobalt substitution. The cell current densities obtained under the applied voltage of 1.5 V at 900° C. are 2.11, 2.41 and 3.0 A.Math.cm.sup.−2 for PNO, PNCO10 and PNCO20 single cells and at 800° C. the current densities are 1.6, 1.8 and 1.9 A.Math.cm.sup.−2 for PNO, PNCO10 and PNCO20 single cells (FIG. 1).

[0037] The durability experiments were carried out with the nickelate electrodes containing single cells under SOEC conditions at 800° C. with high current density, i.e. −1.0 A.Math.cm.sup.−2, for up to 250 h with 50% H.sub.2O and 50% H.sub.2 (FIG. 2). All three cells behave differently during the durability test and initially show a rapid increase. The PNO cell shows a continuous increase up to 250 h, but the rate of increase is lower after 70-80 h. The electrolysis voltage increased from 1.38 to 1.43 V for PNO after 250 h, showing the highest total degradation among all. The degradation rate was estimated (in mV.Math.kh.sup.−1) by carrying out a linear adjustment in the voltage vs. A time curve was implemented and ˜88 mV.Math.kh.sup.−1 was found for the PNO cell. However, the other two cells show lower degradation rates, i.e. ˜40 mV.Math.kh.sup.−1 and ˜22 mV.Math.kh.sup.−1 for PNCO10 and PNCO20 single cells, respectively. It is noteworthy that the PNCO20 single cell shows the least degradation after 250 hours under electrolysis conditions.

[0038] Of course, the invention is not limited to the embodiments shown in the figures. The above description is therefore to be considered as illustrative rather than limiting. The following claims are to be understood such that a mentioned feature is present in at least one embodiment of the invention. This does not preclude the presence of other features.