AN ELECTRODE FOR OXYGEN GENERATION

Abstract

An electrode suitable for carrying out oxygen evolution reaction in the electrolysis of water in alkaline conditions. The electrode includes a ceramic material having a stability factor (SF) between 1.67SF2.8 and which is calculated by formula (II), where r.sub.O is the ionic radius of oxide ion (O.sup.2), r.sub.B,av is the weighted average ionic radius of a transition metal, n.sub.A,Av is the weighted average oxidation state of a rare earth or alkaline earth metal, r.sub.A,av is the weighted average ionic radius of a rare earth or alkaline earth metal. An alkaline electrolysis stack includes the electrode, as well as a method for the electrolysis of water in alkaline conditions using the alkaline electrolysis stack.

Claims

1. An electrode suitable for carrying out oxygen evolution reaction in the electrolysis of water in alkaline conditions, the electrode comprising a ceramic material of formula (I) $\begin{array}{cc}{\left[\left(A_x\right)A_{\left(1-x\right)}^{}\right]}_y{B}_z{B}_{\left(1-z\right)}^{}{O}_{3-}& \left(I\right)\end{array}$ where each of A and A, independently, is a rare earth or alkaline earth metal, x is in the range of 0 to 1, y is A-site occupancy and is in the range of 0.5 to 0.99, each of B and B, independently, is a transition metal, z is in the range of 0 to 1, O is oxygen, and 8 is oxygen non-stoichiometry and is in the range of 1 to 1; and a second material, this second material being metallic Ni, a metallic alloy of Fe and Ni, or a hydroxide of Ni and Fe: where stability factor (SF) of the ceramic material is defined in formula (II), $\begin{array}{cc}\mathrm{SF}=\frac{\text{?}}{r_{B,\mathrm{av}}}-n_{A,\mathrm{Av}}\left[n_{A,\mathrm{Av}}-\frac{r_{A,\mathrm{av}}/r_{B,\mathrm{av}}}{\ln \left(\frac{\text{?}}{r_{B,\mathrm{av}}}\right)}\right]& \left(\mathrm{II}\right)\end{array}$ $\text{?}\text{indicates text missing or illegible when filed}$ where r.sub.o is the Shannon ionic radius of oxide ion (O.sup.2), r.sub.B,av is the weighted average Shannon ionic radius of B and B, defined in formula (III), $\begin{array}{cc}{r}_{B,\mathrm{Av}}=z.Math.r_B+\left(1-z\right).Math.\text{?}& \left(\mathrm{III}\right)\end{array}$ $\text{?}\text{indicates text missing or illegible when filed}$ where r.sub.B is the Shannon ionic radius of B and r.sub.B is the ionic radius of B, N.sub.A,Av is the weighted average oxidation state of A and A, defined in formula (IV), $\begin{array}{cc}{n}_{A,\mathrm{Av}}=\left[x.Math.n_A+\left(1-x\right).Math.n_{A^{}}\right].Math.y,& \left(\mathrm{IV}\right)\end{array}$ where n.sub.A is the oxidation state of A and n.sub.A is the oxidation state of A, r.sub.A,av is the weighted average ionic radius of A and A, defined in formula (V), $\begin{array}{cc}{r}_{A,\mathrm{Av}}=\left[x.Math.r_A+\left(1-x\right).Math.r_{A^{}}\right].Math.y,& \left(V\right)\end{array}$ where r.sub.A is the Shannon ionic radius of A and r.sub.A is the ionic radius of A, wherein the ceramic material includes 1.67SF2.8.

2. (canceled)

3. The electrode according to claim 21, wherein the ceramic material of formula (I) is uniformly dispersed on the surface of the second material.

4. The electrode according to claim 21, wherein the particles of the ceramic material are immobilized and partly encapsulated by the second material.

5. The electrode according to claim 1, wherein A is an element from the following list of elements: La, Ce, Gd, Pr, Ba; and wherein A is an element from the following list of elements: Sr, Ca, Ba, Ce; and wherein B or B, independently, is an element from the following list of elements: Mn, Ni, Fe, Co, Ti, Cr.

6. The electrode according to claim 1, wherein y is in the range of 0.6 to 0.98.

7. The electrode according to claim 1, wherein the average particle size of the ceramic material of formula (I) is between 10 nm and 300 nm.

8. The electrode according to claim 1, wherein the ceramic material of formula (I) has a perovskite crystal structure.

9. The electrode according to claim 1, wherein the electrode overpotential towards oxygen evolution reaction is less than or equal to 400 millivolts at a current density of 1 mA/cm.sup.2, when the oxygen evolution reaction is carried out using a rotating disk electrode at a rotation rate of 1500 rpm in 20-35 weight % KOH and at a temperature of 75-85 degrees Celsius.

10. The electrode according to claim 1, wherein the ceramic material of formula (I) is phase-stable for 100 hours in 6 M KOH at 80 degrees Celsius.

11. The electrode according to claim 1, where 1.9SF2.6.

12. An alkaline electrolysis stack comprising at least one electrode according to claim 1.

13. A method for the electrolysis of water in alkaline conditions using the alkaline electrolysis stack according to claim 12.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0034] FIG. 1 shows stability and activity of ceramic materials as function of the stability factor.

DETAILED DESCRIPTION OF DRAWINGS

[0035] FIG. 1a shows the qualitative relationship (in arbitrary units) between the phase stability on the left vertical axis titled Stability (a.u) and the stability factor (SF) on the horizontal axis. More specifically, at low SF values, the phase stability of ceramic materials of the formula [(A.sub.x) A.sub.(1-x)].sub.yB.sub.zB.sub.(1-z)O.sub.3 increases, i.e., they are less prone to decomposition and phase change when exposed to electrolysis conditions. At higher SF values, the phase stability of such materials decreases, and at SF>2.8, the materials are no longer phase-stable under industrially relevant electrolysis conditions. Therefore, materials with SF>2.8 are not particularly well suited for use as oxygen electrodes in alkaline electrolysis cells.

[0036] Furthermore, FIG. 1a also shows the qualitative relationship (in arbitrary units) between the electrochemical activity on the right vertical axis titled Activity (a.u) and the stability factor (SF) on the horizontal axis. More specifically, at high SF values, the electrochemical activity of ceramic materials of the formula [(A.sub.x)A.sub.(1-x)].sub.yB.sub.zB.sub.(1-z)O.sub.3 increases, i.e., overpotential towards OER decreases when these materials are exposed to electrolysis conditions. At lower SF values, the activity of such materials decreases, and at SF<1.67, the materials are no longer active enough under industrially relevant electrolysis conditions. Therefore, materials with SF<1.67 are not particularly well suited for use as oxygen electrodes in alkaline electrolysis cells.

[0037] FIG. 1b shows the qualitative relationship between a parameter stability multiplied by activity, in arbitrary units, on the vertical axis and the stability factor (SF) on the horizontal axis. Optimal material properties, i.e., the combination of high stability and high activity, are obtained when 1.67SF2.8.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

[0038] The method is illustrated in more detail in the non-limiting examples that follow.

EXAMPLES

Example 1 (Comparative Example)

[0039] In Table 1, a selection of ceramic materials from the barium strontium cobaltite-ferrite family are listed, along with the relevant material properties and SF values. The Shannon ionic radius of Ba.sup.2+ with a coordination number of 12 is 1.61 , while the ionic radius of Sr.sup.2+ with a coordination number of 9 is 1.31 , resulting in r.sub.A,av=1.46 . The Shannon ionic radius of Co.sup.3+ with a coordination number of 6 is 0.545 and that of Fe.sup.3+ with a coordination number of 6 is 0.55 . The resulting r.sub.B,av values are provided in Table 1. The SF value remains almost constant regardless of the Co: Fe ratio for (Ba.sub.0.5Sr.sub.0.5).sub.1.0CO.sub.zFe.sub.1-zO.sub.2.5 materials with y=1. For example, Ba.sub.0.5Sr.sub.0.5Co.sub.0.8Fe.sub.0.2O.sub.2.5 with y=1 has an SF value of 3.50, while the SF value for Ba.sub.0.5Sr.sub.0.5Co.sub.0.2Fe.sub.0.8O.sub.3 is 3.49. In other words, regardless of the chosen Co: Fe ratio in (Ba.sub.0.5Sr.sub.0.5).sub.1.0CO.sub.zFe.sub.1-zO.sub.3, the material is predicted not to be phase-stable under conditions relevant for industrial alkaline electrolysis. In good agreement with predictions, Ba.sub.0.5Sr.sub.0.5CO.sub.0.8Fe.sub.0.2O.sub.3 has shown not to be stable in 0.1 M KOH.

[0040] Materials in Table 1 can be synthesized using methods such as (but not limited to) solid state synthesis, co-precipitation, hydrothermal synthesis, sol-gel synthesis, chemical vapor deposition, spray pyrolysis, atmospheric plasma deposition by mixing the metal precursors in desired ratios and optionally treating the resulting mixture to form the correct crystallographic phase. The same methods can be applied for synthesizing materials described also in the examples that follow.

TABLE-US-00001 TABLE 1 r.sub.0(3- Ceramic material y r.sub.A, av/ r.sub.B, av/ n.sub.A, AV )/3 SF (Ba.sub.0.5Sr.sub.0.5).sub.1.0Co.sub.0.8Fe.sub.0.2O.sub.2.5 1 1.46 0.546 2 0.5 1.13 3.50 (Ba.sub.0.5Sr.sub.0.5).sub.1.0Co.sub.0.6 Fe.sub.0.4O.sub.2.5 1 1.46 0.547 2 0.5 1.13 3.49 (Ba.sub.0.5Sr.sub.0.5).sub.1.0Co.sub.0.4 Fe.sub.0.6O.sub.2.5 1 1.46 0.548 2 0.5 1.13 3.49 (Ba.sub.0.5Sr.sub.0.5).sub.1.0Co.sub.0.2 Fe.sub.0.8O.sub.2.5 1 1.46 0.549 2 0.5 1.13 3.49

Example 2 (Comparative Example)

[0041] In Table 2, a selection of ceramic materials from the barium strontium cobaltite-ferrite family are listed, along with the relevant material properties and SF values. In Table 2, the A-site occupancy of (Ba.sub.0.5Sr.sub.0.5).sub.yCO.sub.0.8Fe.sub.0.2O.sub.3 materials is systematically varied in the range 0.7y1. As the value of y decreases, the value of SF increases, i.e. the material becomes less phase-stable. Regardless of the chosen value of y in (Ba.sub.0.5Sr.sub.0.5).sub.yCo.sub.0.8Fe.sub.0.2O.sub.3, the material is predicted not to be phase-stable under conditions relevant for industrial alkaline electrolysis.

TABLE-US-00002 TABLE 2 r.sub.0(3- Ceramic material y r.sub.A, av/ r.sub.B, av/ n.sub.A, AV )/3 SF (Ba.sub.0.5Sr.sub.0.5).sub.1.0Co.sub.0.8Fe.sub.0.2O.sub.2.5 1 1.46 0.546 2 0.50 1.13 3.50 (Ba.sub.0.5Sr.sub.0.5).sub.0.9Co.sub.0.8Fe.sub.0.2O.sub.2.44 0.9 1.314 0.546 1.8 0.56 1.10 3.71 (Ba.sub.0.5Sr.sub.0.5).sub.0.8Co.sub.0.8Fe.sub.0.2O.sub.2.37 0.8 1.168 0.546 1.6 0.63 1.07 3.90 (Ba.sub.0.5Sr.sub.0.5).sub.0.7Co.sub.0.8 Fe.sub.0.2O.sub.2.29 0.7 1.022 0.546 1.4 0.71 1.03 4.10

Example 3 (Comparative Example)

[0042] In Table 3, a selection of ceramic materials from the barium strontium cobaltite-ferrite family are listed, along with the relevant material properties and SF values. In Table 3, the Ba:Sr ratio, x, of (Ba.sub.xSr.sub.1-x).sub.1.0Co.sub.0.8Fe.sub.0.2O.sub.2.5 materials is systematically varied in the range 0.1<x<0.9. Regardless of the chosen value of x in (Ba.sub.xSr.sub.1-x).sub.1.0Co.sub.0.8Fe.sub.0.2O.sub.2.5, the material is predicted not to be phase-stable under conditions relevant for industrial alkaline electrolysis.

TABLE-US-00003 TABLE 3 r.sub.0(3- Ceramic material y r.sub.A, av/ r.sub.B, av/ n.sub.A, AV )/3 SF (Ba.sub.0..sub.9Sr.sub.0..sub.1).sub.1..sub.0Co.sub.0..sub.8Fe.sub.0..sub.2O.sub.2..sub.5 1 1.58 0.546 2 0.5 1.13 3.51 (Ba.sub.0..sub.8Sr.sub.0..sub.2).sub.1..sub.0Co.sub.0..sub.8Fe.sub.0..sub.2O.sub.2..sub.5 1 1.55 0.546 2 0.5 1.13 3.50 (Ba.sub.0..sub.7Sr.sub.0..sub.3).sub.1..sub.0Co.sub.0..sub.8Fe.sub.0..sub.2O.sub.2..sub.5 1 1.52 0.546 2 0.5 1.13 3.50 (Ba.sub.0..sub.6Sr.sub.0..sub.4).sub.1..sub.0Co.sub.0..sub.8Fe.sub.0..sub.2O.sub.2..sub.5 1 1.49 0.546 2 0.5 1.13 3.50 (Ba.sub.0..sub.5Sr.sub.0..sub.5).sub.1..sub.0Co.sub.0..sub.8Fe.sub.0..sub.2O.sub.2..sub.5 1 1.46 0.546 2 0.5 1.13 3.50 (Ba.sub.0..sub.4Sr.sub.0..sub.6).sub.1..sub.0Co.sub.0..sub.8Fe.sub.0..sub.2O.sub.2..sub.5 1 1.43 0.546 2 0.5 1.13 3.50 (Ba.sub.0..sub.3Sr.sub.0..sub.7).sub.1..sub.0Co.sub.0..sub.8Fe.sub.0..sub.2O.sub.2..sub.5 1 1.4 0.546 2 0.5 1.13 3.51 (Ba.sub.0..sub.2Sr.sub.0..sub.8).sub.1..sub.0Co.sub.0..sub.8Fe.sub.0..sub.2O.sub.2..sub.5 1 1.37 0.546 2 0.5 1.13 3.52 (Ba.sub.0..sub.1Sr.sub.0..sub.9).sub.1..sub.0Co.sub.0..sub.8Fe.sub.0..sub.2O.sub.2..sub.5 1 1.34 0.546 2 0.5 1.13 3.53

Example 4 (Comparative Example)

[0043] In Table 4, a selection of ceramic materials from the family (A.sub.0.5Sr.sub.0.5).sub.1.0Co.sub.0.8Fe.sub.0.2O.sub.3 are listed, along with the relevant material properties and SF values. In Table 4, one of the A-site cations, A in (A.sub.0.5Sr.sub.0.5).sub.1.0Co.sub.0.8Fe.sub.0.2O.sub.3 is systematically varied, with A selected from Ba.sup.2+, Ce.sup.3+, Gd.sup.3+, Pr.sup.3+, and La.sup.3+. The Shannon ionic radius of Ba.sup.2+ with a coordination number of 12 is 1.61 , while the ionic radius of Sr.sup.2+ with a coordination number of 9 is 1.31 , resulting in TA, av=1.46 for (Ba.sub.0.5Sr.sub.0.5).sub.1.0Co.sub.0.8Fe.sub.0.2O.sub.2.5. The Shannon ionic radius for La.sup.3+ with a coordination number of 12 is 1.36 , resulting in r.sub.A,av=1.335 for (La.sub.0.5Sr.sub.0.5).sub.1.0Co.sub.0.8Fe.sub.0.2O.sub.2.75. The Shannon ionic radii for Ce.sup.3+ (12-coordinated), Pr.sup.3+ (9-coordinated), and Gd.sup.3+ (8-coordinated) is 1.34 , 1.18 and 1.05 , respectively. The SF values for (Gd.sub.0.5Sr.sub.0.5).sub.1.0CO.sub.0.8Fe.sub.0.2O.sub.2.75, (Pr.sub.0.5Sr.sub.0.5).sub.1.0Co.sub.0.8Fe.sub.0.2O.sub.2.75, (La.sub.0.5Sr.sub.0.5).sub.1.0Co.sub.0.8Fe.sub.0.2O.sub.2.75, and (Ce.sub.0.5Sr.sub.0.5).sub.1.0Co.sub.0.8Fe.sub.0.2O.sub.2.75, are all below 3.1, SF=3.5 while for (Ba.sub.0.5Sr.sub.0.5).sub.1.0Co.sub.0.8Fe.sub.0.2O.sub.2.5. Accordingly, the materials (A.sub.0.5Sr.sub.0.5).sub.1.0Co.sub.0.8Fe.sub.0.2O.sub.3, where A=Ce, Gd, Pr, and La are expected to be more phase-stable than material where A=Ba, but none of the materials are phase-stable enough for use in industrial alkaline electrolyzers.

TABLE-US-00004 TABLE 4 r.sub.0(3- Ceramic material y r.sub.A, av/ r.sub.B, av/ n.sub.A, AV )/3 SF (Ba.sub.0.5Sr.sub.0.5).sub.1.0Co.sub.0.8Fe.sub.0.2O.sub.2.5 1 1.46 0.546 2 0.5 1.13 3.50 (Gd.sub.0.5Sr.sub.0.5).sub.1.0Co.sub.0.8Fe.sub.0.2O.sub.2.75 1 1.1815 0.546 2.5 0.25 1.24 3.02 (Pr.sub.0.5Sr.sub.0.5).sub.1.0Co.sub.0.8Fe.sub.0.2O.sub.2.75 1 1.2445 0.546 2.5 0.25 1.24 2.93 (La.sub.0.5Sr.sub.0.5).sub.1.0Co.sub.0.8Fe.sub.0.2O.sub.2.75 1 1.335 0.546 2.5 0.25 1.24 2.85 (Ce.sub.0.5Sr.sub.0.5).sub.1.0Co.sub.0.8Fe.sub.0.2O.sub.2.75 1 1.325 0.546 2.5 0.25 1.24 2.86

Example 5

[0044] In Table 5, a selection of ceramic materials from the gadolinium strontium cobaltite-ferrite family are listed, along with the relevant material properties and SF values. In Table 5, the Gd: Sr ratio, x, of (Gd.sub.xSr.sub.1-x).sub.0.97Co.sub.0.8Fe.sub.0.2O.sub.3 materials is systematically varied in the range 0.1<x<0.9. In contrast to the comparative example of Example 3, the two A-site cations carry a different positive charge (Gd.sup.3+, Sr.sup.2+), which results in better phase stability at high Gd contents: materials where x<0.2 have SF values below 2.8 and are thus predicted to be phase-stable under conditions relevant for industrial alkaline electrolysis. Materials in Table 5 with 0.2x1 are not phase-stable.

TABLE-US-00005 TABLE 5 r.sub.0(3- Ceramic material y r.sub.A, av/ r.sub.B, av/ n.sub.A, AV )/3 SF (Gd.sub.0.9Sr.sub.0.1).sub.0.97Co.sub.0.8Fe.sub.0.2O.sub.2.91 0.97 1.046 0.546 2.813 0.0935 1.31 2.77 (Gd.sub.08Sr.sub.0.2).sub.0.97Co.sub.0.8Fe.sub.0.2O.sub.2.86 0.97 1.071 0.546 2.716 0.142 1.29 2.89 (Gd.sub.0.7Sr.sub.0.3).sub.0.97Co.sub.0.8Fe.sub.0.2O.sub.2.81 0.97 1.096 0.546 2.619 0.1905 1.26 3.00 (Gd.sub.0.6Sr.sub.0.4).sub.0.97Co.sub.0.8Fe.sub.0.2O.sub.2.76 0.97 1.121 0.546 2.522 0.239 1.24 3.11 (Gd.sub.0.5Sr.sub.0.5).sub.0.97Co.sub.0.8Fe.sub.0.2O.sub.2.71 0.97 1.146 0.546 2.425 0.2875 1.22 3.22 (Gd.sub.0.4Sr.sub.0.6).sub.0.97Co.sub.0.8Fe.sub.0.2O.sub.2.66 0.97 1.171 0.546 2.328 0.336 1.20 3.32 (Gd.sub.0.3Sr.sub.0.7).sub.0.97Co.sub.0.8Fe.sub.0.2O.sub.2.62 0.97 1.196 0.546 2.231 0.3845 1.18 3.41 (Gd.sub.0.2Sr.sub.0.8 ).sub.0.97Co.sub.0.8Fe.sub.0.2O.sub.2.57 0.97 1.221 0.546 2.134 0.433 1.16 3.49 (Gd.sub.0.1Sr.sub.0.9).sub.0.97Co.sub.0.8Fe.sub.0.2O.sub.2.52 0.97 1.246 0.546 2.037 0.4815 1.13 3.56

Example 6

[0045] In Table 6, a selection of ceramic materials from the family (La.sub.0.6A.sub.0.4).sub.0.99Co.sub.0.8Fe.sub.0.2O.sub.3 are listed, along with the relevant material properties and SF values. The Shannon ionic radius of Ca.sup.2+ with a coordination number of 12 is 1.34 , while the ionic radius of Sr.sup.2+ with a coordination number of 9 is 1.31 . The ionic radius of Ba.sup.2+ with a coordination number of 12 is 1.61 and the ionic radius of Ce.sup.3+ with a coordination number of 12 is 1.34 . In Table 6, one of the A-site cations, A in (La.sub.0.6A.sub.0.4).sub.0.99Co.sub.0.8Fe.sub.0.2O.sub.3 is systematically varied, with A selected from Sr.sup.2+, Ca.sup.2+, Ba.sup.2+ and Ce.sup.3+. The SF values for all materials in Table 6 are within the range 1.67SF2.8, but none of the SF values are within the range 1.9SF2.6.

TABLE-US-00006 TABLE 6 r.sub.0(3- Ceramic material y r.sub.A, av/ r.sub.B, av/ n.sub.A, AV )/3 SF (La0. 6Sr0. 4 )0. 99C00. : Fe0.202. 79 0.99 1.3266 0.546 2.574 0.213 1.25 2.72 (La0. 6Ca0. 4 )0. 99C00. 8 Fe0. 202.79 0.99 1.33848 0.546 2.574 0.213 1.25 2.71 (La0. 6Ba0.4)0. 99C00. 8 Fe0. 202.79 0.99 1.4454 0.546 2.574 0.213 1.25 2.67 (La0. 6Ce0. 4)0.99C00. 8 Fe0. 202.98 0.99 1.33848 0.546 2.97 0.015 1.34 1.76

Example 7

[0046] In Table 7, a selection of ceramic materials from the family (La.sub.0.9Sr.sub.0.1).sub.0.97BO.sub.3 are listed, along with the relevant material properties and SF values. In Table 7, the B-site cation, B in (La.sub.0.9Sr.sub.0.1).sub.0.97BO.sub.3 is systematically varied, with B selected from Mn, Ni, Fe, Co, Ti, and Cr. The average oxidation state of Mn, Ni, Fe, Co, and Cr ions is assumed to be 3.1. An exception here is Ti, which is present as Ti.sup.4+ (6-coordinated) with an ionic radius of 0.605 , resulting in =0.455. The ionic radius of Co.sup.3+, Co.sup.4+, Fe.sup.3+, Fe.sup.4+, Mn.sup.3+, Mn.sup.4+, Ni.sup.3+, Ni.sup.4+, Cr.sup.3+, and Cr.sup.4+ (all with a coordination number of 6) is 0.545 , 0.53 , 0.55 , 0.585 , 0.58 , 0.53 , 0.56 , 0.48 , 0.615 , 0.55 , respectively. For all materials in Table 7, 1.67SF2.8.

TABLE-US-00007 TABLE 7 r.sub.0(3- Ceramic material y r.sub.A, av/ r.sub.B, av/ n.sub.A, AV )/3 SF (La.sub.0..sub.9Sr.sub.0..sub.1).sub.0..sub.97CoO.sub.2..sub.96 0.97 1.31435 0.5435 2.813 0.0435 1.33 2.24 (La.sub.0..sub.91Sr.sub.0..sub.1).sub.0..sub.97FeO.sub.2..sub.96 0.97 1.31435 0.5535 2.813 0.0435 1.33 2.21 (La.sub.0..sub.9Sr.sub.0..sub.1).sub.0..sub.97MnO.sub.2..sub.96 0.97 1.31435 0.575 2.813 0.0435 1.33 2.18 (La.sub.0..sub.9Sr.sub.0..sub.1).sub.0..sub.97TiO.sub.3..sub.41 0.97 1.31435 0.605 2.813 -0.407 1.53 2.50 (La.sub.0..sub.9Sr.sub.0..sub.1).sub.0..sub.97NiO.sub.2..sub.96 0.97 1.31435 0.552 2.813 0.0435 1.33 2.22 (La.sub.0..sub.9Sr.sub.0..sub.1).sub.0..sub.97CrO.sub.2..sub.96 0.97 1.31435 0.6085 2.813 0.0435 1.33 2.16

Example 8

[0047] In Table 8, a selection of ceramic materials from the family (La.sub.0.9Sr.sub.0.1).sub.yBO.sub.3+ are listed, along with the relevant material properties and SF values. In Table 8, the B-site cation, B in (La.sub.0.9Sr.sub.0.1).sub.yBO.sub.3+ is systematically varied, with B selected from Mn, Ni, Fe, Co, Ti, and Cr and 0.65<y<0.95. The average charge of Mn, Ni, Fe, Co, and Cr ions is assumed to be 3.1, while Ti is assumed to be present as Ti.sup.4+. Comparing SF values in Table 8 to SF values in Table 7, it is apparent that decreasing the A-site occupancy of ceramic materials systematically increases the SF values, i.e., by varying y, the activity as well as phase stability of the materials can be tailored. Some materials, such as (La.sub.0.9Sr.sub.0.1).sub.0.90TiO.sub.3.31, (La.sub.0.9Sr.sub.0.1).sub.0.8TiO.sub.3.16, (La.sub.0.9Sr.sub.0.1).sub.0.65TiO.sub.2.94, and (La.sub.0.9Sr.sub.0.1).sub.0.90CrO.sub.2.86 become too unstable (SF>2.8), while others, such remain phase-stable (1.67SF2.8).

TABLE-US-00008 TABLE 8 r.sub.0(3- Ceramic material y r.sub.A, av/ r.sub.B, av/ n.sub.A, AV )/3 SF (La.sub.0.9Sr.sub.0.1).sub.0.95CoO.sub.2.93 0.95 1.28725 0.5435 2.755 0.0725 1.32 2.40 (La.sub.0.9Sr.sub.0..sub.1).sub.0.90CoO.sub.2.86 0.9 1.2195 0.5435 2.61 0.145 1.28 2.80 (La.sub.0.9Sr.sub.0.1).sub.0.95FeO.sub.2.93 0.95 1.28725 0.5535 2.755 0.0725 1.32 2.38 (La.sub.0.9Sr.sub.0.1).sub.0.90FeO.sub.2.86 0.9 1.2195 0.5535 2.61 0.145 1.28 2.79 (La.sub.0.9Sr.sub.0.1).sub.0.95MnO.sub.2 .sub.93 0.95 1.28725 0.575 2.755 0.0725 1.32 2.35 (La.sub.0.9Sr.sub.0.1).sub.0.90MnO.sub.2.86 0.9 1.2195 0.575 2.61 0.145 1.28 2.78 (La.sub.0.9Sr.sub.0.1).sub.0.95TiO.sub.3.38 0.95 1.28725 0.605 2.755 0.378 1.52 2.69 (La.sub.0.9Sr.sub.0.1).sub.0.90TiO.sub.3.31 0.9 1.2195 0.605 2.61 0.305 1.49 3.15 (La.sub.0.9Sr.sub.0.1).sub.0.80TiO.sub.3.16 0.8 1.084 0.605 2.32 0.16 1.42 4.10 (La.sub.0.9Sr.sub.0.1).sub.0.65TiO.sub.2.94 0.65 0.88075 0.605 1.885 0.0575 1.32 5.94 (La.sub.0.9Sr.sub.0.1).sub.0.95NiO.sub.2.93 0.95 1.28725 0.552 2.755 0.0725 1.32 2.38 (La.sub.0.9Sr.sub.0.1).sub.0.90NiO.sub.2.86 0.9 1.2195 0.552 2.61 0.145 1.28 2.79 (La.sub.0.9Sr.sub.0.1).sub.0.95CrO.sub.2.93 0.95 1.28725 0.6085 2.755 0.0725 1.32 2.35 (La.sub.0.9Sr.sub.0.1).sub.0.90CrO.sub.2.86 0.9 1.2195 0.6085 2.61 0.145 1.28 2.82

Example 9

[0048] In Table 9, a selection of ceramic materials from the lanthanum nickelate-ferrite family are listed, along with the relevant material properties and SF values. For example, LaNi.sub.0.6Fe.sub.0.4O.sub.3 with y=1 has an SF value of 1.63, while La.sub.0.95Ni.sub.0.6Fe.sub.0.4O.sub.2.925 with y=0.95 has an SF value of 2.10. The SF value for La.sub.0.90Ni.sub.0.6Fe.sub.0.4O.sub.2.85 is 2.55, and the SF values for materials in Table 9 with y0.85 are above 2.8. LaNi.sub.0.6Fe.sub.0.4O.sub.3 (y=1) is phase-stable when exposed to 6 M KOH at 80 C., whereas materials in Table 9 with y0.85 are not. For the more extreme cases, e.g., La.sub.0.5Ni.sub.0.6Fe.sub.0.4O.sub.2.25, the ceramic material does not form the perovskite structure and a multi-phase and multi-component material is present even before exposure to industrial alkaline electrolysis conditions. In the other extreme, LaNi.sub.0.6Fe.sub.0.4O.sub.3 with y=1 with an SF value of 1.63 is not active enough towards the oxygen evolution reaction based on the very low SF value.

TABLE-US-00009 TABLE 9 r.sub.0(3- Ceramic material y r.sub.A, av/ r.sub.B, av/ n.sub.A, AV )/3 SF LaNi.sub.0..sub.6Fe.sub.0.4O.sub.3 1 1.36 0.556 3 0 1.35 1.63 La.sub.0.95Ni.sub.0.6Fe.sub.0.4O.sub.2.925 0.95 1.292 0.556 2.85 0.075 1.32 2.10 La.sub.0.90Ni.sub.0.6Fe.sub.0.4O.sub.2.85 0.9 1.224 0.556 2.7 0.15 1.28 2.55 La.sub.0.85Ni.sub.0.6Fe.sub.0.4O.sub.2.775 0.85 1.156 0.556 2.55 0.225 1.25 2.99 La.sub.0.80Ni.sub.0.6Fe.sub.0.4O.sub.2.7 0.8 1.088 0.556 2.4 0.3 1.22 3.42 La.sub.0.75Ni.sub.0.6Fe.sub.0.4O.sub.2.625 0.75 1.02 0.556 2.25 0.375 1.18 3.86 La.sub.0.70Ni.sub.0.6Fe.sub.0.4O.sub.2.55 0.7 0.952 0.556 2.1 0.45 1.15 4.34 La.sub.0.65Ni.sub.0.6Fe.sub.0.4O.sub.2.475 0.65 0.884 0.556 1.95 0.525 1.11 4.89 La.sub.0.60Ni.sub.0.6Fe.sub.0.4O.sub.2.4 0.6 0.816 0.556 1.8 0.6 1.08 5.59 La.sub.0.55N.sub.0.6Fe.sub.0.4O.sub.2.325 0.55 0.748 0.556 1.65 0.675 1.05 6.64 La.sub.0.5Ni.sub.0.6Fe.sub.0.4O.sub.2.25 0.5 0.68 0.556 1.5 0.75 1.01 8.68

Example 10

[0049] La.sub.0.95CoO.sub.2.925, Pr.sub.0.95CoO.sub.2.925, Gd.sub.0.95CoO.sub.2.925, (La.sub.0.9Sr.sub.0.1).sub.0.95CoO.sub.2.878, La.sub.0.95NiO.sub.2.925, LaFeO.sub.2.925, La.sub.0.95Ni.sub.0.6Co.sub.0.4O.sub.2.925, and La.sub.0.95Ni.sub.0.6Fe.sub.0.4O.sub.2.925 were synthesized using a modified sol-gel synthesis route. The resulting materials were calcined to 800 C. for 3 hours to obtain oxide catalyst materials with perovskite structure as verified by X-ray diffraction measurements. The material properties and SF values are summarized in Table 10.

TABLE-US-00010 TABLE 10 r.sub.0(3- Ceramic material y r.sub.A, av/ r.sub.B, av/ n.sub.A, AV )/3 SF Gd.sub.0.95CoO.sub.2.925 0.95 1.000 0.545 2.85 0.075 1.32 2.91 La.sub.0.95Ni.sub.0.6Fe.sub.0.4O.sub.2.925 0.95 1.292 0.556 2.85 0.075 1.32 2.10 LaFeO.sub.3 0.95 1.36 0.55 3 0 1.35 1.65

[0050] The calcined materials were characterized electrochemically in a rotating disk electrode (RDE) setup. For these measurements, each perovskite material was mixed with Nafion solution, isopropanol and ultrapure water to obtain a slurry. The slurry was coated onto glassy carbon electrodes at a loading of 0.2 mg/cm.sup.2. The electrodes were tested in a three-electrode setup in 0.1 M KOH saturated with argon. OER kinetics were evaluated by applying a linearly changing potential to the electrode and measuring the resulting current. The potential was swept from 1.3 V to 1.9 V and back to 1.3 V vs RHE. The electrode was rotated at 1500 rpm, and the measurements were carried out at room temperature.

[0051] Furthermore, the materials were subjected to a strong alkali treatment to evaluate phase stability. Each material was treated in 6 M KOH for 100-120 hours at a temperature of 80 degrees C. After the treatment, the material was rinsed thoroughly with distilled water, dried and the crystallographic structure of the materials was studied with x-ray diffraction (XRD).

[0052] Specifically, the calcined Gd.sub.0.95CoO.sub.2.925 material was found to consist primarily of a perovskite material, with the main XRD peaks (in the order of decreasing intensity) at 33.86, 34.36, and 33.20 2-theta. The calcined material was highly active electrochemically: the potential required to reach an OER current of 10 mA/cm.sup.2 was 1.67 V. As expected from the high SF value (SF>2.8), the material proved not to be phase stable after the treatment in 6M KOH. The main XRD peaks had changed to (in the order of decreasing intensity) 28.19, 50.70, 41.25, and 29.52 2-theta, indicating that the original perovskite material had decomposed. The KOH-treated material was found to be significantly less active in RDE measurements (1.73 V to reach OER current of 10 mA/cm.sup.2). Gd.sub.0.95CoO.sub.2.925 is an example of a material that is initially electrochemically very active, but insufficiently phase-stable in industrially relevant alkaline electrolysis conditions.

[0053] The calcined La.sub.0.95Ni.sub.0.6Fe.sub.0.4O.sub.2.925 material was found to consist primarily of a perovskite material, with the main XRD peaks (in the order of decreasing intensity) at 32.56, 32.84, and 46.94 2-theta. The calcined material was active electrochemically: the potential required to reach an OER current of 10 mA/cm.sup.2 was 1.66 V. As expected from the SF value (1.67SF2.8), the material proved to be phase stable after the treatment in 6M KOH. The main XRD peaks did not change: (in the order of decreasing intensity) 32.60, 32.80, and 46.98 2-theta, indicating that the original perovskite material remained stable under treatment conditions. The KOH-treated material was found to be somewhat less active in RDE measurements, but the activity was withing acceptable limits (1.72 V to reach OER current of 10 mA/cm.sup.2). La.sub.0.95Ni.sub.0.6Fe.sub.0.4O.sub.2.925 is an example of a material that offers good compromise between electrochemical activity and sufficient phase-stability in industrially relevant alkaline electrolysis conditions.

[0054] The calcined LaFeO.sub.3 material was found to consist primarily of a perovskite material, with the main XRD peaks (in the order of decreasing intensity) at 33.16, 57.40, and 46.16 2-theta. The calcined material was highly inactive electrochemically: the material did not reach an OER current of 10 mA/cm.sup.2 when the potential was increased to 1.9 V, with the current density at 1.9 V being equal to only 3.5 mA/cm.sup.2. As expected from the low SF value (SF<1.67), the material proved to be phase stable after the treatment in 6M KOH. The main XRD peaks did not change, indicating that the original perovskite material had decomposed. LaFeO.sub.3 is an example of a material that is highly stable, but insufficiently active for OER in industrially relevant alkaline electrolysis conditions.

[0055] An electrode suitable for carrying out oxygen evolution reaction in the electrolysis of water in alkaline conditions can be designed according to the following steps: [0056] 1) Pre-select a ceramic material with a formula [(A.sub.x)A.sub.(1-x)].sub.yB.sub.zB.sub.(1-z)O.sub.3, for example LaNi.sub.0.6Fe.sub.0.4O.sub.3. [0057] 2) Based on the ionic radii, oxidation state values, A-site occupancy (y), oxygen non-stoichiometry (d), and A- and B-site doping levels (x and z, respectively), and using the formula for the calculation of SF, estimate the value of SF. For example, SF for LaNi.sub.0.6Fe.sub.0.4O.sub.3 is 1.63. [0058] 3) If SF is within suitable range (1.67<SF2.8), synthesize the material according to the methods listed (but not limited to) in Example 1 and select the ceramic material for further testing, for example by exposing the material for 100 hours to 6 M KOH at 80 degrees Celsius to verify phase-stability. For example, LaNi.sub.0.6Fe.sub.0.4O.sub.3 would not be selected for further testing due to SF<1.67. [0059] 4) In case SF is outside the suitable range, vary the value for y within the range 0.5 to 0.99, and preferably within the range 0.6 to 0.98 to change the SF value. For example, by altering the value of y from 1.0 to 0.95 (from LaNi.sub.0.6Fe.sub.0.4O.sub.3 to La.sub.0.95Ni.sub.0.6Fe.sub.0.4O.sub.2.925), the SF value can be increased to 2.1, thereby satisfying the condition of 1.67 SF2.8. [0060] 5) Alternatively to step 4, SF value can be altered by varying the value for x and/or z. For example, by altering the value of z from 0.6 to 0.1 (from LaNi.sub.0.6Fe.sub.0.4O.sub.3 to LaNi.sub.0.1Fe.sub.0.9O.sub.3), the SF value can be increased from 1.63 to 1.65. [0061] 6) Alternatively to steps 4 or 5, SF value can be altered by varying the elemental composition of the ceramic material. For example, by replacing Fe with Co, i.e., changing the composition of the material from LaNi.sub.0.6Fe.sub.0.4O.sub.3 to LaNi.sub.0.6Co.sub.0.4O.sub.3, the SF value can be increased from 1.63 to 1.64.

[0062] 7) Steps 4, 5, and 6 can be advantageously combined. For example, the SF value of LaNi.sub.0.6Co.sub.0.4O.sub.3 can be increased from 1.64 to 2.04 by decreasing y from 1 to 0.95, i.e., La.sub.0.95Ni.sub.0.6Co.sub.0.4O.sub.2.85, thereby satisfying the condition of 1.67SF2.8.