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)
M2Ni1xCoxO4+
and/or of formula (2)
La1yMyNi1xCoxO4+ where M represents Pr and/or Nd, 0.0x0.2, 0.250.3 and 0<y10 0.5.

Claims

1. Material for an electrode, the material comprising of a compound of formula (1)
M.sub.2Ni.sub.1xCo.sub.xO.sub.4+(1)
and/or of formula (2)
La.sub.1-yM.sub.yNi.sub.1xCo.sub.xO.sub.4+(2) where M represents Pr and/or Nd, 0.0x0.2, 0.250.3 and 0<y<0.5, further comprising a compound of formula (3) LaNi.sub.0.6Fe.sub.0.4O.sub.3 (3) where 0<0.05, which is provided as a layer on the compound of formula (1) and/or of formula (2), and wherein the material has a perovskite structure.

2. Material according to claim 1, wherein of formulas (1) and (2) has the values 0.25, 0.28 or 0.3.

3. Material according to claim 1, wherein it is selected from Pr.sub.2NiO.sub.4+, Pr.sub.2Ni.sub.0.9Co.sub.0.1O.sub.4, Pr.sub.2Ni.sub.0.8Co.sub.0.2O.sub.4+, Nd.sub.2NiO.sub.4+, Nd.sub.2Ni.sub.0.9Co.sub.0.1O.sub.4+, Nd.sub.2Ni.sub.0.8Co.sub.0.2O.sub.4+ and La.sub.1.5Pr.sub.0.5Ni.sub.1xCoxO.sub.4+.

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

5. Material according to claim 1, wherein it has an average particle size of 0.5 m to 1 m.

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

7. Material according to claim 6, wherein of formulas (1) and (2) has the values 0.25, 0.28 or 0.3.

Description

(1) 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:

(2) FIG. 1 shows a voltage/voltage density curves for the single cells with PNO, PNCO10 and PNCO20 electrodes at 800 and 900 C.

(3) 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

(4) Preparation of Materials and Characterizations:

(5) Three compositions of each series, namely Pr.sub.2Ni.sub.1xCo.sub.xO.sub.4+ (PNCO), Nd.sub.2Ni.sub.1xCo.sub.xO.sub.4+ (NNCO) and La.sub.1.5Pr.sub.0.5Ni.sub.1xCo.sub.xO.sub.4+ (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 m (checked by means of particle size distribution and SEM).

(6) The 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+ (PNO), Pr.sub.2Ni.sub.0.9Co.sub.0.1O.sub.4+ (PNCO10) and Pr.sub.2Ni.sub.0.8Co.sub.0.2O.sub.4+ (PNCO20), respectively.

(7) Electrochemical Performance and Durability as an Oxygen Electrode:

(8) Electrochemical characterization was carried out with NiOYSZ-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.

(9) 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).

(10) 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.

(11) 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.