Improved fuel and electrolyser cell assemblies

Abstract

Described herein is an assembly for a solid oxide fuel or electrolyser cell, comprising a fuel electrode, an air electrode, and a solid-state electrolyte sandwiched therebetween, wherein the assembly further comprises a fuel side interlayer between the fuel electrode and the solid-state electrolyte, as well as methods for producing same and uses thereof.

Description

[0001] IMPROVED FUEL AND ELECTROLYSER CELL ASSEMBLIES

[0002]

[0001] The present application claims priority to Australian provisional patent application no. 2024903568, filed on 1 November2024, the entire contents of which are incorporated herein by crossreference.

[0003] Technical Field

[0004]

[0002] The disclosure herein relates to improved fuel and electrolyser cell assemblies. More particularly, the disclosure herein relates to improved solid oxide fuel and electrolyser cell assemblies comprising one or more interlayers, which find utility in the energy generation and storage sector, amongst other applications.

[0005] Background of Invention

[0006]

[0003] Solid oxide fuel cells (SOFCs) and solid oxide electrolyser cells (SOECs) comprise a cathode, an anode, and an electrolyte. Depending on the configuration, one of the cathode or anode functions as the fuel electrode, being the electrode that comes into contact with the hydrogen or hydrocarbon fuel that is oxidised to form water and optionally oxides of carbon (SOFC mode), or with water / steam fuel that is reduced to form hydrogen gas and oxygen ions (SOEC mode). The other electrode functions as the air electrode, being the electrode that comes into contact with oxygen molecules and that is reduced to form oxygen ions that travel to the fuel electrode (SOFC mode), or with oxygen ions that are oxidised to form oxygen gas (SOEC mode). In electrolysis mode (SOECs), electrical energy is converted to chemical energy (in the form of hydrogen and other hydrogen carriers like methane, methanol, etc.), and in fuel cell mode (SOFCs), chemical energy is converted directly to electrical power.

[0007]

[0004] In cells that operate with a solid electrolyte, such as SOFCs and SOECs, certain challenges are present. The most common solid electrolyte in current usage is yttria-stabilised zirconia (YSZ), which is a dense ionic conductor consisting of ZrO2 doped with Y2O3. This electrolyte has good thermal stability and the ability operate at high temperatures (>1000 °C) in current generation SOFCs / SOECs. Common electrode materials paired with YSZ in SOFC / SOEC applications include nickel-doped YSZ (Ni-YSZ), lanthanum strontium manganate (LSM), and strontium and cobalt codoped lanthanum ferrite (LSCF). However, air side electrode materials can react with the YSZ electrolyte to form insulating zirconate phases or oxidised metal phases at the electrode-electrolyte boundaries in use that affect performance of the cells. Further, electrode delamination is widely reported, especially for perovskite air electrodes, as a result of chemical and / or thermal instability of the electrode-electrolyte interface.

[0008]

[0005] Chemical instability occurs when the electrode has cations with much different mobility, leading to component separation, commonly known as “kinetic demixing”. Perovskites like lanthanum strontium ferrites, manganites, cobaltites, and the like experience strontium segregation under anodic / cathodic currents. This strontium then diffuses to the electrode-electrolyte interface, reacts with the electrolyte and forms a non-conducting oxide phase. Sometimes, cobalt also evaporates from the lattice, diffuses to the electrode-electrolyte interface, and forms cobalt oxide. In the case of air electrodes, formation of these low porosity oxide layers hinders diffusivity of the oxide ions transported across the electrolyte, leading to oxygen build-up at the air electrode / electrolyte interface. Such accumulated oxygen gradually weakens the bonding between the oxide layer and the electrolyte, resulting in complete delamination.

[0009]

[0006] Thermal instability occurs due to thermal expansion coefficient (TEC) mismatch between the electrode and the electrolyte and / or by lattice strain generated from oxygen non-stoichiometry in the electrode. Electrode materials such as perovskites (lanthanum strontium ferrites, manganites, cobaltites, etc.) have naturally different TECs to fluorite solid electrolytes like YSZ, gadolinium oxidedoped ceria (GDC) and scandium stabilised zirconia (ScSZ). However, the formation of oxygen vacancies in electrode lattices can also contribute to TCE mismatch, as neighbouring cations are reduced and their ionic radius increases, causing lattice expansion. If the overall TCE mismatch becomes too large, the applied thermal stress during the operation of the SOFC / SOEC can result in electrode delamination (see Fig. 1 (a)).

[0010]

[0007] SOECs guarantee green hydrogen production at a lower cost compared to other state-of-the- art electrolysers and at a higher efficiency (~90%), and operate at temperatures between 600 to 1000 °C. These high temperatures allow the integration of industrial waste heat into the system that helps reduce the electrical energy requirements, and thus the levelised cost of fuel production, but one of the major bottlenecks of SOEC technology is the cell lifetime. As described above, electrode delamination is a phenomenon that directly and adversely affects cell lifetime.

[0011]

[0008] Previous attempts in the art to solve the problems associated with chemical and / or thermal instability have utilised an interlayer between the solid electrolyte and the air electrode, forming a so- called bi-layer electrolyte. For example, inclusion of a ceramic-based interlayer at the air electrodeelectrolyte interface has been found to reduce chances of delamination in certain cells by 1) restricting the reaction of the electrolyte with any segregated component like strontium, cobalt, etc. from the electrode; and, 2) improving adhesion of the electrode and electrolyte (see Fig. 1 (b)). However, interlayers do require additional processing steps and have compatibility limitations, as well as potentially increasing Ohmic losses of the cell due to increased electrode spacing. Additionally, interlayer effectiveness has been shown for only a limited number of materials under limited operating conditions.

[0012]

[0009] Improved methods of increasing SOFC and SOEC stability and / or performance that address one or more of the above problems, or at least provide a useful alternative, are therefore desirable.

[0013]

[0010] In one aspect, the invention described herein provides assemblies containing an interlayer between an electrode and electrolyte, such as between a fuel side electrode and electrolyte, that can enhance the performance and stability of cells. These assemblies provide protective benefits to SOFCs and SOECs even when thermally sensitive perovskite-based and fluorite-based hybrid electrodes are used, and have demonstrated effectiveness even under high voltage operating conditions.

[0011] A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that the document or matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.

[0014] Summary of the Invention

[0015]

[0012] The present inventors have studied, for the first time, the effect of an interlayer at the fuel electrode to improve cell stability for solid oxide electrochemical cells, which includes solid oxide fuel cell and electrolyser operations. Despite the prejudice in the art against inclusion of an interlayer between the fuel electrode and electrolyte, the present inventors have discovered that inclusion of a fuel side electrode interlayer enhances and improves cell stability, even in the case of non-traditional hybrid electrodes. Surprisingly, where thermal and / or chemical instability of the fuel electrodeelectrolyte interface has never before been identified or studied, and where process simplification and electrode separation has sought to be minimised and therefore taught away from inclusion of a second interlayer, the present inventors have found that in certain embodiments, such as where an air side interlayer is included with a fuel side interlayer in combination, cell performance can actually be enhanced over time.

[0016]

[0013] According to a first aspect of the present invention, there is provided an assembly for a solid oxide fuel or electrolyser cell, comprising: a fuel electrode, an air electrode, and a solid-state electrolyte (SSE) sandwiched therebetween, wherein the assembly further comprises: a fuel side interlayer between the fuel electrode and the SSE. In one embodiment, the assembly further comprises an air side interlayer between the air electrode and the SSE.

[0017]

[0014] In one embodiment, the fuel electrode and / or the air electrode comprises a hybrid material. In one embodiment, the fuel electrode comprises a hybrid material.

[0018]

[0015] The assembly may further comprise an air side interlayer between the air electrode and the SSE. In one embodiment, the air electrode comprises a hybrid material.

[0019]

[0016] In one embodiment, both the fuel electrode and the air electrode comprise a hybrid material, such as the same hybrid material or different hybrid materials.

[0020]

[0017] The hybrid material may be a metal-metal oxide composite. The hybrid material may comprise a fluorite material. The fluorite material may be a metal oxide-doped ceria. The fluorite material may be a metal oxide-doped ceria selected from gadolinium oxide-doped ceria (GDC), samarium oxidedoped ceria (SDC), and yttrium oxide-doped ceria (YDC), or a combination thereof. The hybrid material may comprise a metallic phase transition metal, in one embodiment which can be selected from copper, silver, gold, iron, cobalt, nickel and molybdenum, or may comprise an alloy or combination of any two or more of these. In one embodiment, the hybrid material may comprise a metallic phase transition metal selected from copper, silver, and gold, or may comprise an alloy or combination of any two or more of these. The hybrid material may be selected from Ag-GDC, Cu- GDC, Au / Mo-GDC, Ag / Fe-GDC, Ag / Ni-GDC, Ni / Cu / Co-GDC, Co / Ag-GDC, and Ni / Ag / Fe-GDC.

[0021]

[0018] The hybrid material may comprise a perovskite material. The perovskite material may be an LST material of formula LaxSri.xTiO3, a BSCF material of formula BaxSri.xCoyFei.y03-6, an LSCF material of formula LaxSri.xCoyFei.y03-6 or an LSCM of formula LaxSri.xCryMni.yO3-6, or a combination of any two or more of these. The perovskite material may be Bao.sSro.sCoo.sFeo^Os-a, Lao.6Sro.4Coo.2Feo.803-6, or Lao.ysSro^sCro.sMno.sOs-a, or may be a combination of any two or more of these. The hybrid material may comprise a metallic-phase transition metal, in one embodiment wherein the transition metal can be selected from copper, silver, gold, iron, cobalt, nickel and molybdenum, or an alloy of any two or more of these. The hybrid material may be Ag-LSCF.

[0022]

[0019] The hybrid material may comprise from 10 wt% to 90 wt% of a metallic-phase metal and from 10 wt% to 90 wt% of a metal oxide. In one embodiment, the hybrid material may comprise from 60 wt% to 80 wt% of a metallic phase metal and from 20 wt% to 40 wt% of a metal oxide.

[0023]

[0020] In one embodiment, the fuel electrode and the air electrode may comprise the same hybrid material. In other embodiments, the fuel electrode and the air electrode may each comprise a different hybrid material.

[0024]

[0021] In one embodiment, the fuel electrode and / or the air electrode comprises a perovskite material. Accordingly, the fuel electrode may comprise a perovskite material, or the air electrode may comprise a perovskite material, or both the fuel electrode and the air electrode may comprise a perovskite material, such as the same perovskite material or different perovskite materials. The perovskite material may be an LST material of formula LaxSri.xTiO3, a BSCF material of formula BaxSri.xCOyFei.yC>3-6, an LSCF material of formula LaxSri.xCoyFei.y03-6 or an LSCM of formula LaxSri.xCryMni.yO3-6, or a combination of any two or more of these. The perovskite material may be Bao.sSro.sCoo.sFeo^Os-a, Lao.6Sro.4Coo.2Feo.803-6, or Lao.ysSro^sCro.sMno.sOs-a, or may be a combination of any two or more of these.

[0025]

[0022] In one embodiment, the fuel electrode and / or the air electrode comprises a fluorite material. Accordingly, the fuel electrode may comprise a fluorite material, or the air electrode may comprise a fluorite material, or both the fuel electrode and the air electrode may comprise a fluorite material, such as the same fluorite material or different fluorite materials. The fluorite material may be a metal oxidedoped ceria. The fluorite material may be a metal oxide-doped ceria selected from gadolinium oxidedoped ceria (GDC), samarium oxide-doped ceria (SDC), and yttrium oxide-doped ceria (YDC), or a combination thereof.

[0026]

[0023] In one embodiment, the SSE and the hybrid material may overlap in their composition. In another embodiment, the SSE and the hybrid material may have no overlap in their composition, such as the hybrid material may not comprise the same material as the SSE. In one embodiment, the hybrid material is devoid of yttria stabilised zirconia (YSZ).

[0027]

[0024] The fuel side interlayer may comprise a metal oxide-doped ceria, in one embodiment being selected from: gadolinium oxide-doped ceria (GDC), samarium oxide-doped ceria (SDC), and yttrium oxide-doped ceria (YDC). The fuel side interlayer may have a thickness of from 50 nm to 10 pm, such as of about 100 nm to 5 pm.

[0028]

[0025] The assembly may further comprise an air side interlayer between the air electrode and the SSE, wherein the air electrode comprises a hybrid material. In such embodiments, the air side interlayer may comprise a metal oxide-doped ceria, in one embodiment being selected from: gadolinium oxide-doped ceria (GDC), samarium oxide-doped ceria (SDC), and yttrium oxide-doped ceria (YDC). The air side interlayer may have a thickness of from 50 nm to 10 pm, such as of about 100 nm to 5 pm.

[0029]

[0026] In one embodiment, the fuel side interlayer may improve the performance and / or stability of the solid oxide fuel cell or electrolytic cell relative to an equivalent assembly devoid of a fuel side interlayer. In one embodiment, the fuel side and air side interlayers may improve the performance and / or stability of the solid oxide fuel cell or electrolytic cell relative to an equivalent assembly devoid of a fuel side and an air side interlayer. In one embodiment, the fuel side and air side interlayers may improve the performance and / or stability of the solid oxide fuel cell or electrolytic cell relative to an equivalent assembly devoid of a fuel side interlayer.

[0030]

[0027] In one embodiment, the performance and / or stability is measured as an ability to maintain current density within 5%, or within 10%, of an original current density after an operating period of at least 20 h, or at least 80 h. In one embodiment, the performance and / or stability is measured as an increase in Rohm after 100 h of operation of less than 15%, or less than 5%. In one embodiment, the performance and / or stability is measured as an increase in Rpoiafter 100 h of operation of less than 40%, or less than 20%. In one embodiment, the performance and / or stability is measured as (a) ability to maintain current density within 5%, or within 10%, of an original current density after an operating period of at least 20 h, or at least 80 h; and (b) an increase in Rohm after 100 h of operation of less than 15%, or less than 5%, and (c) an increase in Rpoiafter 100 h of operation of less than 40%, or less than 20%.

[0031]

[0028] The SSE in the assembly may comprise yttria stabilised zirconia (YSZ), doped ceria, or lanthanum gallate.

[0032]

[0029] According to a second aspect of the present invention, there is provided method of producing an assembly for a solid oxide fuel or electrolyser cell, the method comprising: providing a solid-state electrolyte (SSE) having a first surface and a second surface opposing the first surface; forming a first interlayer on the first surface of the SSE; forming a fuel side electrode on the first interlayer; optionally forming a second interlayer on the second surface of the SSE; and forming an air side electrode on either the second surface of the SSE, or if present, on the second interlayer.

[0030] Forming the first interlayer may comprise applying a first interlayer composition to the first surface of the SSE, and sintering the first interlayer composition. In one embodiment, the sintering of the interlayer is at a temperature of 1400 °C or less. Forming the fuel side electrode may comprise applying a fuel side electrode composition to the first interlayer, and sintering the fuel side electrode composition. In one embodiment, the sintering is at a temperature of 900 °C or less. Forming the air side electrode may comprise applying an air side electrode composition to the second surface of the SSE, or if present, to the second interlayer, and sintering the air side electrode composition. In one embodiment, the sintering of the electrode may be at a temperature of 900 °C or less, such as where a hybrid electrode is used. In other embodiments, the sintering of the electrode may be at a temperature of 1400 °C or less.

[0031] The method may comprise forming a second interlayer on the second surface of the SSE, and forming an air side electrode on the second interlayer. Forming the second interlayer may comprise applying a second interlayer composition to the second surface of the SSE, and sintering the second interlayer composition. In one embodiment, the sintering of the interlayer is at a temperature of 1400 °C or less. Forming the second electrode may comprise applying an air side electrode composition to the second interlayer, and sintering the air side electrode composition. In one embodiment, the sintering of the electrode may be at a temperature of 900 °C or less, such as where a hybrid electrode is used. In other embodiments, the sintering of the electrode may be at a temperature of 1400 °C or less.

[0033]

[0032] The first interlayer and the second interlayer, if present, may be formed together in a single step. The fuel side electrode and air side electrodes may be formed together in a single step. The first interlayer, and if present second interlayer, may comprise metal oxide-doped ceria, optionally GDC. The metal oxide-doped ceria may be provided in the form of a slurry comprising particles, wherein the particles have an average particle size of from 10 nm to 1 pm, optionally of from 10 nm to 100 nm.

[0034]

[0033] In one embodiment, the fuel electrode and / or the air electrode comprises a fluorite material and / or a perovskite material. For example, the fuel electrode and the air electrode may each comprise a fluorite material, or a perovskite material, or a mixture of the two. In one embodiment, the fuel electrode and / or the air electrode comprises a hybrid material. For example, as described elsewhere herein, the fuel electrode and the air electrode may both comprise a hybrid material, or just the fuel electrode may comprise a hybrid material, or just the air electrode may comprise a hybrid material. The hybrid material may be a metal-metal oxide composite comprising particles of metal oxide and particles of metal. The metal oxide may be a fluorite material, a perovskite material, or a mixture of the two. The metal may be a transition metal. The hybrid material may comprise from 10 wt% to 90 wt% of a metallic phase transition metal and from 10 wt% to 90 wt% of a metal oxide. In one embodiment, the hybrid material comprises from 60 wt% to 80 wt% of a metallic phase transition metal and from 20 wt% to 40 wt% of a metal oxide.

[0035]

[0034] According to a third aspect of the present invention, there is provided an assembly for a solid oxide fuel or electrolyser cell produced by the method of the second aspect above.

[0036]

[0035] According to a fourth aspect of the present invention, there is provided a solid oxide fuel or electrolyser cell comprising the assembly of the first or third aspects above.

[0037]

[0036] According to a fifth aspect of the present invention, there is provided use of a solid oxide fuel or electrolyser cell comprising the assembly of the first or third aspects above in a device.

[0038] Brief Description of Drawings

[0039]

[0037] Embodiments of the invention will herein be illustrated by way of example only with reference to the accompanying drawings in which:

[0040]

[0038] Figure 1 is a stylised depiction of (a) delamination of a fluorite and perovskite-based hybrid electrode from an electrolyte due to loss of particle contact as a result of thermal expansion coefficient mismatch of electrode and electrolyte, and (b) how incorporation of an interlayer helps mitigate the phenomenon;

[0041]

[0039] Figure 2 shows data for a symmetric SOEC cell, where one cell had no interlayer “without interlayer” (AgGDC cathode, YSZ electrolyte, AgGDC anode) and the other one had an air electrode (anode) side interlayer “with interlayer” (AgGDC cathode, YSZ electrolyte, GDC interlayer, AgGDC anode), (a) corresponding voltage-current characteristics of fresh and tested cells, (b) their chronoamperometric studies over 100 h of continuous operation at 1.6 V and 800 °C for steam electrolysis, and (c) corresponding electrochemical impedance spectra record before and after 100 h testing;

[0042]

[0040] Figure 3 shows data for a schematic of unsymmetric SOEC cell, where one cell had no interlayer “without interlayer” (AgGDC cathode, YSZ electrolyte, AgLSCF anode) and the other one had an air electrode (anode) side interlayer “with interlayer” (AgGDC cathode, YSZ electrolyte, GDC interlayer, AgLSCF anode); (a) corresponding voltage-current characteristics of fresh and tested cells; (b) their chronoamperometric studies over 100 h of continuous operation at 1 .6 V and 800 °C for steam electrolysis; and (c) corresponding electrochemical impedance spectra record before and after 100 h testing. Inset of (b) shows a zoomed-in view of current density over the first 1 h of operation for both the cells;

[0043]

[0041] Figure 4 shows data for symmetric SOEC cell where one cell had only an air electrode (anode) side interlayer “anode side interlayer” (AgGDC cathode, YSZ electrolyte, GDC interlayer, AgGDC anode) and the other had both an air side and fuel side interlayer “both side interlayer” (AgGDC cathode, GDC interlayer, YSZ electrolyte, GDC interlayer, AgGDC anode); (a) corresponding voltagecurrent characteristics of fresh and tested cells; (b) their chronoamperometric studies over 100 h of continuous operation at 1 .6 V and 800 °C for steam electrolysis; and (c) corresponding electrochemical impedance spectra record before and after 100 h testing;

[0044]

[0042] Figure 5 shows data for a unsymmetric SOEC cell where one cell had only an air electrode (anode) side interlayer “anode side interlayer” (AgGDC cathode, YSZ electrolyte, GDC interlayer, AgLSCF anode) and the other had both an air side and fuel side interlayer “both side interlayer” (AgGDC cathode, GDC interlayer, YSZ electrolyte, GDC interlayer, AgLSCF anode); (a) corresponding voltage-current characteristics of fresh and tested cells; (b) their chronoamperometric studies over 100 h of continuous operation at 1.6 V and 800 °C for steam electrolysis; and (c) corresponding electrochemical impedance spectra record before and after 100 h testing;

[0045]

[0043] Figure 6 shows (a) voltage-current characteristics of a fresh and tested SOEC cell with unsymmetric configuration and interlayer at both air and fuel side electrodes; (b) its chronoamperometric studies over 120 h of continuous operation at 1.6 V and 800 °C for steam electrolysis; and (c) corresponding electrochemical impedance spectra recorded before and after 120 h testing;

[0046]

[0044] Figure 7 shows bar graphs demonstrating how the presence / absence of certain interlayers affects (a) % degradation; (b) Rohm; and (c) Rpoiover 100 h of continuous cell operation for both symmetric and non-symmetric cell configurations;

[0045] Figure 8 (a)-(f) shows scanning electron microscopy images of the interface of an Ag-GDC electrode-GDC interlayer-YSZ electrolyte at two different regions under low and high magnification. The GDC interlayer was fired at 1250 °C, YSZ electrolyte at 1400 °C, and Ag-GDC electrode at 825 °C;

[0047]

[0046] Figure 9 (a)-(d) shows electron microscopy images at various degrees of magnification of a sintered GDC interlayer fired at 1250 °C. Grains are elliptical to spherical in shape and vary in size from 0.2 to 0.5 microns. Grain boundaries are distinct, but the overall interlayer microstructure exhibits porosity;

[0048]

[0047] Figure 10 shows (a) current density vs. voltage data; (b) Rohm and Rpoidata; (c) current density; and (d) & (e) electrochemical impedance spectra at 1 .35 V and 1 .6 V respectively, for a symmetric SOEC cell described according to the embodiment in Example 6, where one cell had no interlayer “no interlayer either side” (AgGDC cathode, YSZ electrolyte, AgGDC anode), one had an air electrode (anode) side interlayer “no interlayer cathode”, one had a fuel electrode (cathode) side interlayer “no interlayer anode”, and one cell had no interlayer at all “no interlayer either side”; and

[0049]

[0048] Figure 11 shows (a) and (b) electrochemical impedance spectra at 1.35 V and 1.6 V respectively for a steam flow rate of 50 mL / min for a symmetric SOEC cell described according to the embodiment in Example 7, where one cell had no interlayer “no interlayer either side” (AgGDC cathode, YSZ electrolyte, AgGDC anode), and one cell had an interlayer on both the air and fuel electrode sides “both side in-house interlayer”.

[0050] Detailed Description

[0051]

[0049] Described herein is an assembly for a solid oxide fuel or electrolyser cell, the assembly comprising a fuel electrode, an air electrode, and a solid-state electrolyte (SSE) sandwiched therebetween, wherein the assembly further comprises an interlayer between at least one of the electrodes and the SSE. The electrode adjacent to the interlayer may comprise a hybrid material, in some embodiments, a metal-metal oxide composite. In some embodiments, the term “hybrid electrode” refers to an electrode comprising a hybrid material.

[0052]

[0050] In one embodiment, the present disclosure provides an assembly for a solid oxide fuel or electrolyser cell, the assembly comprising a fuel electrode, an air electrode, and a solid-state electrolyte (SSE) sandwiched therebetween, wherein the assembly further comprises a fuel side interlayer between the fuel electrode and the SSE. In one embodiment, the fuel electrode comprises any suitable electrode material. In another embodiment, the fuel electrode comprises a hybrid material. In one embodiment, the assembly herein contains an interlayer at the fuel side electrode and the fuel side electrode comprises a hybrid material, with the air side electrode comprising any electrode material. In one embodiment, the assembly herein contains an interlayer at the fuel side electrode, and both the fuel side electrode and the air side electrodes comprise any suitable material. In one embodiment, the assembly herein contains an interlayer at the fuel side electrode and at the air side electrode, and both the fuel side electrode and the air side electrodes comprise any suitable material. In one embodiment, the assembly herein contains an interlayer at the fuel side electrode and at the air side electrode, and both the fuel side electrode and the air side electrodes comprise a hybrid material.

[0053]

[0051] In another embodiment, the present disclosure provides an assembly for a solid oxide fuel or electrolyser cell, comprising: a fuel electrode, an air electrode, and a solid-state electrolyte (SSE) sandwiched therebetween, wherein the assembly further comprises a fuel side interlayer between the fuel electrode and the SSE, wherein the fuel electrode comprises a hybrid material; and / or an air side interlayer between the air electrode and the SSE, wherein the air electrode comprises a hybrid material, wherein the hybrid material is a metal-metal oxide composite. In such embodiments, the interlayer can be on the fuel side, the air side, or both, and in such embodiments, wherever the interlayer is present, the electrode adjacent the interlayer comprises a hybrid material that is a metalmetal oxide composite.

[0054]

[0052] In another embodiment, the present disclosure provides an assembly for a solid oxide fuel or electrolyser cell, comprising: a fuel electrode, an air electrode, and a solid-state electrolyte (SSE) sandwiched therebetween, wherein the assembly further comprises a fuel side interlayer between the fuel electrode and the SSE, wherein the fuel electrode comprises a hybrid material; and / or an air side interlayer between the air electrode and the SSE, wherein the air electrode comprises a hybrid material, wherein the hybrid material comprises a fluorite material. In such embodiments, the interlayer can be on the fuel side, the air side, or both, and in such embodiments, wherever the interlayer is present, the electrode adjacent the interlayer comprises a hybrid material that is a metalmetal oxide composite.

[0055]

[0053] The assemblies herein are suitable for use in at least solid oxide fuel cells, solid oxide electrolyser cells, reversible SOFC / SOECs, and the like, including SOECs for applications such as electrochemical oxygen generation, and ceramic oxygen sensors. In one embodiment, the assemblies herein are suitable for use in any high-temperature (800 to 1000 °C) solid oxide electrolyser producing hydrogen, syngas, methane, or any other hydrogen carrier. Similarly, the assemblies herein are suitable for use in any high-temperature solid oxide fuel cell using hydrogen, ammonia, or any other hydrocarbon as fuel. In other embodiments, the assemblies herein are suitable for use in any intermediate temperature (500 to 700 °C) solid oxide electrolyser producing hydrogen, syngas, methane, or any other hydrogen carrier. Similarly, the assemblies herein are suitable for use in any intermediate-temperature solid oxide fuel cell using hydrogen, ammonia, or any other hydrocarbon as fuel.

[0056]

[0054] The present inventors have discovered a surprising performance and stability enhancement of solid oxide cells, particularly SOECs, by incorporating an interlayer on fuel side electrodes, in addition to air side electrodes, that provides benefits to cell operation even under higher voltage and higher current density operations, especially for hybrid electrodes comprising a metal-metal oxide composite. Accordingly, the assemblies herein may dramatically improve the lifetime and stability of solid oxide cells (SOCs), which are a current leading candidate for the global shift towards net-zero energy targets. Whereas previous efforts have concentrated on air side electrode interlayers, fuel side interlayers have not received attention due to their known thermal and chemical stability with solid electrolytes.

[0057]

[0055] As will be discussed further below, the interlayer preferably comprises a fluorite material. In preferred embodiments, the interlayer is a single-phase single-component layer, and in certain embodiments can be incorporated into the assemblies herein via a simple, single-step process.

[0058]

[0056] Advantages of the assemblies described herein in certain embodiments may include one or more of the following:

[0059] • applicable for both single-component electrodes such as lanthanum strontium cobalt ferrite (LSCF) as well as hybrid electrodes and electrodes with a fluorite component;

[0060] • help in extending the cell stability even under higher voltage and higher current density operations;

[0061] • two interlayers can be incorporated simultaneously using a facile single-step process and require no stagewise drying or multi-step impregnations; and / or

[0062] • can be used in both high and intermediate temperature SOFCs or SOECs.

[0063]

[0057] Where the terms “comprise”, “comprises” and “comprising” are used in the specification (including the claims) they are to be interpreted as specifying the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components, or group thereof.

[0064] Assembly

[0065]

[0058] The assemblies herein comprise a fuel electrode and an air electrode. The electrodes herein are envisaged to be comprised of any suitable material, either a single chemical material, or in the form of a hybrid material comprising two or more different chemical materials in combination. Suitable electrode materials are described elsewhere herein, but may include fluorite materials and perovskite materials.

[0066]

[0059] In certain embodiments, at least one of the electrodes in contact with an interlayer comprises a hybrid material. In one embodiment, the assembly comprises a fuel side interlayer between the fuel electrode and the SSE, wherein the fuel electrode comprises a hybrid material.

[0067]

[0060] The term “hybrid material” as used herein refers to a material comprising two or more different chemical materials. In one embodiment, the different chemical materials in the hybrid material comprise at least one material known to be suitable for use in SOFC and / or SOEC electrodes. In one embodiment, the different chemical materials in the hybrid material comprise at least one material known to be suitable for use in SOFC and / or SOEC electrodes, and a metallic phase metal. In one embodiment, the hybrid material herein comprises one or more metallic phase element(s) and one or more metal oxide(s) (a “metal-metal oxide composite”). In one embodiment, the hybrid material herein is a metal-metal oxide composite.

[0068]

[0061] Metal-metal oxide composites may be referred to herein in the format “M-XXX”, where the notation “M-XXX” indicates that metals (M) before the dash (-) are in their metallic phase, and the material initials (XXX) after the dash are metal oxide materials. Alloys or mixtures of metals in the metallic phase (M) in these metal-metal oxide composites may be written as M1 / M2-XXX, where different metallic metals are written separated by a forward slash ( / ). Similarly, mixtures of metal oxides in the XXX phase in these metal-metal oxide composites may be written as M-XXX1 / XXX2, where different metal oxides are written separated by a forward slash ( / ). In such embodiments, M may be one or more metallic phase transition metal(s). In one embodiment, M is selected from copper, silver, gold, iron, cobalt, nickel and molybdenum, or is an alloy of any two or more of these metals. In one embodiment, M is selected from copper, silver, and gold, or is an alloy of any two or more of these metals. In one embodiment, M is selected from silver and gold, or an alloy thereof. In one embodiment, M is silver or an alloy thereof. In one embodiment, M is an alloy of silver with one or more of copper, gold, iron, cobalt, nickel and molybdenum. In one embodiment, the M is selected from copper, silver, and gold, or an alloy comprising one or more of these metals. In one embodiment, the hybrid material comprises M selected from silver and gold or an alloy comprising one or more of these metals. Hybrid electrodes as described herein in particular comprising metals copper, silver and / or gold may have lower thermal stability than commonly used solid electrolyte materials, such as YSZ, and hence be particularly susceptible to thermal mismatch effects. Accordingly, in one embodiment, the interlayer as described herein is particularly useful for hybrid materials comprising these lower melting point metals as M, i.e., metals having a melting point of less than 1100 °C. It will of course be appreciated that in other embodiments, the interlayer as described herein may be useful for other electrode materials, including hybrid materials, that comprise other metals as M, including those having melting points of less than 4000 °C, less than 3000 °C, less than 2000 °C, less than 1900 °C, less than 1800 °C, less than 1700 °C, less than 1600 °C, less than 1500 °C, less than 1400 °C, less than 1300 °C, or less than 1200 °C, or of up to 4000 °C, up to 3000 °C, up to 2000 °C, up to 1900 °C, up to 1800 °C, up to 1700 °C, up to 1600 °C, up to 1500 °C, up to 1400 °C, up to 1300 °C, or up to 1200 °C.

[0069]

[0062] In embodiments where the hybrid material comprises or is a metal-metal oxide composite, the metal-metal oxide composite may comprise any suitable metal(s) and any suitable metal oxide(s). In one embodiment, the hybrid material is a metal-metal oxide composite comprising a metal oxide that is a fluorite material. In other words, in one embodiment, the hybrid material comprises a fluorite material. Fluorite materials are those that adopt a fluorite structure, being generally face centred cubic (FCC) MX2 (where M is a metal and X is a non-metal) after the mineral fluorite, CaF2, which naturally adopts this structure.

[0070]

[0063] In one embodiment, the hybrid material comprises a fluorite material or doped fluorite material. The fluorite material or doped fluorite material may be any suitable fluorite material or doped fluorite material. In one embodiment, the fluorite material or doped fluorite material is one known in the art as useful as an electrode material in SOFCs and / or SOECs in its pure form.

[0071]

[0064] In one embodiment, the hybrid material comprises a metal oxide-doped ceria fluorite material. In one embodiment, the hybrid material is a metal-metal oxide composite comprising a metal oxidedoped ceria fluorite material. Ceria is also known as cerium(IV) oxide, CeC>2, adopts a fluorite type structure, and can be doped by a range of different dopants. In one embodiment, the metal oxidedoped ceria is the metal oxide (“XXX”) of the metal-metal oxide composite (“M-XXX”). In one embodiment, the metal oxide-doped ceria is selected from gadolinium oxide-doped ceria (GDC), samarium oxide-doped ceria (SDC), and yttrium oxide-doped ceria (YDC), or is a combination thereof. In one embodiment, the metal oxide-doped ceria is GDC. In one embodiment, the metal oxide-doped ceria is SDC. In one embodiment, the metal oxide-doped ceria is YDC. Doped ceria materials are commercially available from chemical suppliers such as Sigma Aldrich, the Fuel Cell Store, or may be synthesised according to established literature procedures, such as by calcination or hydrothermal methods, see e.g., Tok et al. (2007) Materials Science and Engineering-. A466: 223. Particle size of the doped ceria materials, applicable also to other particulate solids herein, may be controlled or adjusted by grinding, ball milling, sieving and the like.

[0072]

[0065] Accordingly, in one embodiment, the metal-metal oxide composite is selected from one or more of M-GDC, M-SDC, and M-YDC, where M is one or more metallic phase transition metal(s). In one embodiment, the metallic phase transition metal is selected from copper, silver, gold, iron, cobalt, nickel and molybdenum, or is an alloy of any two or more of these metals. In one embodiment, the metallic phase transition metal is selected from copper, silver, and gold, or is an alloy of any two or more of these metals. In one embodiment, the metallic phase transition metal is selected from silver, and gold, or is an alloy of any two or more of these metals. In one embodiment, the metallic phase transition metal is an alloy of silver with one or more of copper, gold, iron, cobalt, nickel and molybdenum. In one embodiment, the hybrid material comprises a metallic phase transition metal selected from copper, silver, and gold, or an alloy comprising one or more of these metals. In one embodiment, the hybrid material comprises a metallic phase transition metal selected from silver and gold or an alloy comprising one or more of these metals. In one embodiment, the metal-metal oxide composite is selected from one or more of M-GDC, M-SDC, and M-YDC, where M is a metallic phase transition metal selected from copper, silver, gold, iron, cobalt, nickel and molybdenum, or is an alloy of any two or more of these metals. In one embodiment, the metal-metal oxide composite is selected from one or more of M-GDC, M-SDC, and M-YDC, where M is a metallic phase transition metal selected from copper, silver and gold, or an alloy comprising one or more of these metals. In one embodiment, the metal-metal oxide composite comprises M-GDC. In one embodiment, the hybrid material is a metal-metal oxide composite selected from one of Ag-GDC, Cu-GDC, Au / Mo-GDC, Ag / Fe-GDC, Ag / Ni-GDC, Ni / Cu / Co-GDC, Co / Ag-GDC, and Ni / Ag / Fe-GDC. Metal-ceria hybrid materials may be synthesised from powdered doped ceria and powdered metal precursors, such as by combining powdered metal with powdered doped ceria in the desired weight ratio and thoroughly mixing them together, such as using a ball mill or the like. The mixture is then subsequently sintered at a suitable temperature to form the composite.

[0073]

[0066] In another embodiment, the fluorite material is cubic zirconium oxide, ZrO2 (zirconia). In one embodiment, the hybrid material is a metal-metal oxide composite comprising a metal oxide-doped zirconia fluorite material. In one embodiment, the metal oxide-doped zirconia is the metal oxide (“XXX”) of the metal-metal oxide composite (“M-XXX”). In one embodiment, the metal oxide-doped zirconia yttrium oxide-doped zirconia (also known as yttria-stabilised zirconia, YSZ). Doped zirconia materials are commercially available from chemical suppliers such as Sigma Aldrich, or may be synthesised according to established literature procedures, such as using hydrothermal methods, see e.g., Bulletin of Materials Science 2014, 37, 969. In one embodiment, the hybrid material is a metalmetal oxide composite selected from one of Ag-YSZ, Cu-YSZ, Au / Mo-YSZ, Ag / Fe-YSZ, Ag / Ni-YSZ, Ni / Cu / Co-YSZ, Co / Ag-YSZ, Ni / YSZ, and Ni / Ag / Fe-YSZ. In one embodiment, the hybrid material is a metal-metal oxide composite selected from one of Ag-YSZ, Cu-YSZ, Au / Mo-YSZ, Ag / Fe-YSZ, Ag / Ni- YSZ, Ni / Cu / Co-YSZ, Co / Ag-YSZ, and Ni / Ag / Fe-YSZ. Metal-zirconia hybrid materials may be synthesised from doped zirconia and powdered metal precursors, such as by combining powdered metal with powdered doped zirconia in the desired weight ratio and thoroughly mixing them together, such as using a ball mill orthe like. The mixture is then subsequently sintered at a suitable temperature to form the composite.

[0074]

[0067] In one embodiment, the hybrid material comprises a metallic phase transition metal selected from copper, silver, and gold, or an alloy of any two or more of these metals, and a fluorite material. In one embodiment, the hybrid material comprises a metallic phase transition metal selected from silver, and gold, or an alloy of any two or more of these metals, and a fluorite material. In one embodiment, the hybrid material comprises a metallic phase transition metal that is an alloy of silver with one or more of copper, gold, iron, cobalt, nickel and molybdenum, and a fluorite material. In one embodiment, the hybrid material comprises a metallic phase transition metal selected from copper, silver, and gold, or an alloy of any two or more of these metals, and a metal oxide-doped ceria. In one embodiment, the hybrid material comprises a metallic phase transition metal selected from silver, and gold, or an alloy of any two or more of these metals, and a metal oxide-doped ceria. In one embodiment, the hybrid material comprises a metallic phase transition metal that is an alloy of silver with one or more of copper, gold, iron, cobalt, nickel and molybdenum, and a metal oxide-doped ceria. In one embodiment, where the hybrid material is as described in this paragraph, the interlayer is a fluorite material. In one embodiment, where the hybrid material is as described in this paragraph, the interlayer is a doped ceria material. In one embodiment, where the hybrid material is as described in this paragraph, the interlayer is a perovskite material. In one embodiment, where the hybrid material is as described in this paragraph, the interlayer is devoid of a metallic phase.

[0075]

[0068] In one embodiment, the hybrid material comprises a perovskite material. In one embodiment, the hybrid material is a metal-metal oxide composite comprising a perovskite material. Perovskite materials have general formula ABO3, where A and B are different metals (in the form of A2+and B4+ions), and can be doped by a range of different dopants. In one embodiment, the perovskite material is the metal oxide (“XXX”) of the metal-metal oxide composite (“M-XXX”). The perovskite material may be any suitable perovskite material. In one embodiment, the perovskite material is one known in the art as useful as an electrode material in SOFCs and / or SOECs in its pure form. In one embodiment, the perovskite is a doped titanate, cobaltite, nickelate, ferrite, titanate, or manganite. In one embodiment, the perovskite or doped perovskite is not a ferrite perovskite. In one embodiment, the perovskite or doped perovskite is not a ferrite or cobaltite perovskite. In one embodiment, the perovskite material is selected from a BSCF material of formula BaxSri.xCoyFei.y03-6, an LSCF material of formula LaxSri.xCoyFei.y03-6, an LSCM of formula LaxSri.xCryMni.yO3-6, and an LST material of formula LaxSri.xTiO3-6, or a combination of any two or more of these. In one embodiment, the perovskite material is a BSCF material of formula BaxSri.xCoyFei.y03-6. In one embodiment, the perovskite material is an LSCF material of formula LaxSri.xCoyFei.y03-6. In one embodiment, the perovskite material is an LSCM of formula LaxSri.xCryMni.yO3-6. In one embodiment, the perovskite material is an LST material of formula LaxSri.xTiO3-6. In one embodiment, the LSCF material, the BSCF material and / or the LSCM material has: 0 < x < 1 , 0 < y < 1 and 0 < 6 < 1 , or 0 < x < 0.5, 0.05 < x < 0.30, 0.1 < x < 0.65, 0.30 < x < 0.70, 0.25 < x < 0.75, 0.40 < x < 0.80, or x is 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, or 0.95, and 0 < y < 0.5, 0.05 < y < 0.30, 0.1 < y < 0.65, 0.30 < y < 0.70, 0.25 < y < 0.75, 0.40 < y < 0.80, or y is 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, or 0.95. In one embodiment, the LST material has: 0 < x < 1 and 0 < 5 < 1 , or 0 < x < 0.5, 0.05 < x < 0.30, 0.1 < x < 0.65, 0.30 < x < 0.70, 0.25 < x < 0.75, 0.40 < x < 0.80, or x is 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, or 0.95, In one embodiment, the BSCF is Bao.sSro.sCoo.sFeo^Os-a, the LSCF is Lao.6Sro.4Coo.2Feo.803-6, the LSCM is Lao.75Sro.25Cro.5Mno.503-6, and / or the LST is Lao^Sro.sTiOs. It will be understood that the term “perovskite material” herein encompasses doped ABO3 materials. In one embodiment, the perovskite material is the metal oxide (“XXX”) of the metal-metal oxide composite (“M-XXX”). Perovskite materials are commercially available from chemical suppliers such as Sigma Aldrich, or may be synthesised according to established literature procedures, such as using solid state methods, coprecipitation, hydrothermal methods, sol-gel methods, etc., see e.g., Results in Chemistry 2022, 4, 1003219.

[0076]

[0069] Accordingly, in one embodiment, the metal-metal oxide composite is a metallic metalperovskite composite comprising one or more metallic phase transition metal(s) and a doped titanate, cobaltite, nickelate, ferrite, titanate, or manganite. In one embodiment, the metal-metal oxide composite is selected from one or more of M-LSCF, M-BSCF, M-LSCM, and / or M-LST, where M is one or more metallic phase transition metal(s). In one embodiment, the metallic phase transition metal is selected from copper, silver, gold, iron, cobalt, nickel and molybdenum, or is an alloy of any two or more of these metals. In one embodiment, the metallic phase transition metal is an alloy of silver with one or more of copper, gold, iron, cobalt, nickel and molybdenum. In one embodiment, the hybrid material comprises a metallic phase transition metal selected from copper, silver, and gold, or an alloy of one or more of these metals. In one embodiment, the hybrid material comprises a metallic phase transition metal selected from silver, gold, or alloys thereof. In one embodiment, the hybrid material is a metal-metal oxide composite selected from one of Ag-LSCF, Ag-BSCF, Ag-LSCM and Ag-LST. Metal-perovskite hybrid materials may be synthesised from perovskite materials and powdered metal precursors, such as by combining powdered metal with powdered perovskite material in the desired weight ratio and thoroughly mixing them together, such as using a ball mill or the like. The mixture is then subsequently sintered at a suitable temperature to form the composite.

[0077]

[0070] In one embodiment, the hybrid material comprises a fluorite material or doped fluorite material and a perovskite material. The fluorite material or doped fluorite material and the perovskite material may be any suitable materials, such as those described herein. In one embodiment, the fluorite material or doped fluorite material and perovskite material are both known in the art as useful as an electrode material in SOFCs and / or SOECs in their pure form. In one embodiment, the hybrid material comprises a metal oxide-doped ceria fluorite material and / or a metal oxide-doped zirconia fluorite material and a perovskite material. In one embodiment, the hybrid material is a metal-metal oxide composite comprising a metal oxide-doped ceria fluorite material and / or a metal oxide-doped zirconia fluorite material and a perovskite material. In one embodiment, the hybrid material comprises a metal oxide-doped ceria fluorite material and a perovskite material. In one embodiment, the hybrid material is a metal-metal oxide composite comprising a metal oxide-doped ceria fluorite material and a perovskite material.

[0078]

[0071] In one embodiment, the metal-metal oxide composite is selected from one or more of M- GDC / LSCF, M-GDC / BSCF, M-GDC / LSCM, M-GDC / LST, M-SDC / LSCF, M-SDC / BSCF, M- SDC / LSCM, M-SDC / LST, M-YDC / LSCF, M-YDC / BSCF, M-YDC / LSCM, M-YDC / LST, and M- YSZ / LSCF, M-YSZ / BSCF, M-YSZ / LSCM, and M-YSZ / LST, where M is one or more metallic phase transition metal(s). In one embodiment, the metallic phase transition metal is selected from copper, silver, gold, iron, cobalt, nickel and molybdenum, or is an alloy of any two or more of these metals. In one embodiment, the metallic phase transition metal is an alloy of silver with one or more of copper, gold, iron, cobalt, nickel and molybdenum. In one embodiment, the hybrid material is a metal-metal oxide composite selected from one of M-GDC / LSCF, M-GDC / BSCF, M-GDC / LSCM, M-GDC / LST, M- SDC / LSCF, M-SDC / BSCF, M-SDC / LSCM, M-SDC / LST, M-YDC / LSCF, M-YDC / BSCF, M- YDC / LSCM, M-YDC / LST, M-YSZ / LSCF, M-YSZ / BSCF, M-YSZ / LSCM, and M-YSZ / LST, where each M is independently selected from Ag, Cu, Ag and Ni or a combination thereof. Mixed hybrid materials may be synthesised from metal oxide powders and powdered metal precursors, such as by combining powdered metal(s) with powdered metal oxides in the desired weight ratio and thoroughly mixing them together, such as using a ball mill or the like. The mixture is then subsequently sintered at a suitable temperature to form the composite.

[0079]

[0072] The hybrid material may comprise two or more different chemical materials in any suitable proportion by weight. When the hybrid material herein is a metal-metal oxide composite, it may comprise any suitable proportion by weight of metal(s) in the metallic phase and any suitable proportion by weight of metal oxide(s). If more than one metal is present and / or more than one metal oxide is present in the composite, they may be present in any suitable sub-proportion. In one embodiment, the hybrid material herein is a metal-metal oxide composite that comprises from 10 wt% to 90 wt% of metal(s) in the metallic phase and from 90 wt% to 10 wt% of metal oxide(s), or of from 20 wt% to 90 wt% of metal(s) and from 80 wt% to 10 wt% of metal oxide(s), or of from 30 wt% to 85 wt% of metal(s) and from 70 wt% to 15 wt% of metal oxide(s), or of from 50 wt% to 90 wt% of metal(s) and from 10 wt% to 50 wt% of metal oxide(s), or of from 60 wt% to 80 wt% of metal(s) and from 20 wt% to 40 wt% of metal oxide(s), or comprises 10 wt% metallic metal(s) and 90 wt% metal oxide(s), 20 wt% metallic metal(s) and 80 wt% metal oxide(s), 30 wt% metallic metal(s) and 70 wt% metal oxide(s), 40 wt% metallic metal(s) and 60 wt% metal oxide(s), 50 wt% metallic metal(s) and 50 wt% metal oxide(s), 60 wt% metallic metal(s) and 40 wt% metal oxide(s), 70 wt% metallic metal(s) and 30 wt% metal oxide(s), or 80 wt% metallic metal(s) and 20 wt% metal oxide(s).

[0080]

[0073] In one embodiment, the metal-metal oxide composite comprises from 40 wt% to 80 wt% of metal(s) in the metallic phase, such as Ag, Ag / Co, and from 60 wt% to 20 wt% of metal oxide(s), such as GDC, LSCF. In one embodiment, the metal-metal oxide composite comprises from 50 wt% to 80 wt% of metal(s) in the metallic phase, such as Ag, Ag / Co, and from 50 wt% to 20 wt% of metal oxide(s), such as GDC, LSCF. In one embodiment, the metal-metal oxide composite comprises from 60 wt% to 80 wt% of metal(s) in the metallic phase, such as Ag, Ag / Co, and from 40 wt% to 20 wt% of metal oxide(s), such as GDC, LSCF. In another embodiment, the metal-metal oxide composite comprises from 45 wt% to 55 wt% of metal(s) in the metallic phase, such as Ag, Ag / Co, and from 55 wt% to 45 wt% of metal oxide(s), such as GDC, LSCF. In another embodiment, the metal-metal oxide composite comprises about 50 wt% of metal(s) in the metallic phase, such as Ag, Ag / Co, and 50 wt% of metal oxide(s), such as GDC, LSCF. In another embodiment, the metal-metal oxide composite comprises about 70 wt% of metal(s) in the metallic phase, such as Ag, Ag / Co, and 30 wt% of metal oxide(s), such as GDC, LSCF.

[0081]

[0074] In one embodiment, the fuel electrode and / or the air electrode herein are as described in WO 2023 / 193062, the entire contents of which are incorporated herein by cross-reference.

[0082]

[0075] In other embodiments, it will be appreciated that the electrode may comprise a hybrid material other than a metal-metal oxide material, such as including, but not limited to, a mixture of two or more different metal oxides together, a mixture of two or more different fluorite materials together, or a mixture of at least one fluorite material and at least one metal oxide together. The fluorite material(s) may be as described above and may include one or more doped fluorite material(s). The metal oxide(s) may be as described above and may include one or more perovskite and / or doped perovskite(s). In one embodiment, the perovskite or doped perovskite is not a ferrite material. In one embodiment, the perovskite or doped perovskite is not a ferrite or cobaltite perovskite. In one embodiment, the hybrid material comprises a mixture of two or more metal oxide-doped ceria materials selected from: gadolinium oxide-doped ceria (GDC), samarium oxide-doped ceria (SDC), and yttrium oxide-doped ceria (YDC). In one embodiment, the hybrid material comprises a mixture or two or more perovskites selected from: a BSCF material of formula BaxSri.xCoyFei.y03-6, an LSCF material of formula LaxSri.xCoyFei.y03-6, an LSCM of formula LaxSri.xCryMni.yO3-6, and an LST material of formula LaxSri-xTiO3-6. In one embodiment, the hybrid material comprises a mixture of two or more materials selected from: gadolinium oxide-doped ceria (GDC), samarium oxide-doped ceria (SDC), yttrium oxide-doped ceria (YDC), a BSCF material of formula BaxSri.xCoyFei.y03-6, an LSCF material of formula LaxSri.xCoyFei.y03-6, an LSCM of formula LaxSri.xCryMni.yO3-6, and an LST material of formula LaxSri.xTiO3-6.

[0083]

[0076] In one embodiment, the electrode may be a single chemical material. The single phase material may be any suitable material, including but not limited to a perovskite, a doped perovskite, a fluorite, or a doped-fluorite, and differs from the hybrid material in that the entire electrode comprises only one chemical compound. In one embodiment, the electrode is a BSCF material of formula BaxSri.xC0yFei.yO3-6, or an LSCF material of formula LaxSri.xCoyFei.y03-6, or an LSCM of formula LaxSri. xCryMni.yO3-6, or an LST material of formula LaxSri.xTiO3-6, or a gadolinium oxide-doped ceria (GDC), or a samarium oxide-doped ceria (SDC), or a yttrium oxide-doped ceria (YDC). In one embodiment, the electrode is not a ferrite perovskite. In one embodiment, the electrode is not a ferrite or cobaltite perovskite.

[0084]

[0077] The electrode material herein, in some embodiments a hybrid material thus comprises a solid. In one embodiment, the electrode material herein, in some embodiments a hybrid material, comprises a particulate solid. The electrode may comprise one or more chemical materials having any suitable average particle sizes. In one embodiment, the hybrid material may comprise two or more different chemical materials having any suitable average particle sizes. When the hybrid material herein is a metal-metal oxide composite, it may comprise metal(s) in the metallic phase having any suitable average particle sizes, and metal oxide(s) having any suitable average particle sizes. In one embodiment, these average particle sizes are realised during synthesis. In one embodiment, the metal particles have an average particle size of from 50 nm to 10 pm, or of from 50 nm to 500 nm, or of from 250 nm to 750 nm, or of from 500 nm to 2 pm, or of from 1 pm to 5 pm, or of from 2.5 pm to 7.5 pm, or of from 5 pm to 10 pm, or of less than 10 pm, less than 8 pm, less than 5 pm, less than 2 pm, less than 1 pm, less than 500 nm, or less than 100 nm. In one embodiment, the metal oxide particles have an average particle size of from 1 nm to 10 pm, or of from 2 nm to 100 nm, or of from 50 nm to 500 nm, or of from 250 nm to 750 nm, or of from 500 nm to 2 pm, or of from 1 pm to 5 pm, or of from 2.5 pm to 7.5 pm, or of from 5 pm to 10 pm, or of less than 10 pm, less than 8 pm, less than 5 pm, less than 2 pm, less than 1 pm, less than 500 nm, less than 100 nm, less than 50 nm, or less than 10 nm. The average particle size of the metal(s) and the metal oxide(s) may be tuned by selection and / or modification of particular synthesis methods. For example, large particle sizes may be favoured under higher sintering temperatures, whereas smaller particle sizes may be favoured under lower sintering temperature. In embodiments where a single chemical material is used, such as a metal oxide or fluorite material, the particles may have an average particle size of from 1 nm to 10 pm, or of from 2 nm to 100 nm, or of from 50 nm to 500 nm, or of from 250 nm to 750 nm, or of from 500 nm to 2 pm, or of from 1 pm to 5 pm, or of from 2.5 pm to 7.5 pm, or of from 5 pm to 10 pm, or of less than 10 pm, less than 8 pm, less than 5 pm, less than 2 pm, less than 1 pm, less than 500 nm, less than 100 nm, less than 50 nm, or less than 10 nm.

[0085]

[0078] In one embodiment, both the fuel electrode and the air electrode comprise the same material. In one embodiment, both the fuel electrode and the air electrode comprise the same hybrid material. In one embodiment, both the fuel electrode and the air electrode have the same composition. Cells formed from such electrode assemblies are referred to as symmetric. In other embodiments, the fuel electrode and the air electrode each comprise a different material. In one embodiment, the fuel electrode and the air electrode each comprise a different hybrid material. In one embodiment, both the fuel electrode and the air electrode have a different composition. The material, including hybrid material, may be different in either its composition, that is, in the chemical materials it contains, or in the case of a hybrid material, may be different in the proportion of different chemical materials in each electrode. Cells formed from such electrode assemblies are referred to as asymmetric. Symmetric and asymmetric assemblies are both within the scope of the invention described herein.

[0086]

[0079] The SSE in the assemblies herein may be any suitable SSE. The SSE may be any material having recognised utility as an SSE in SOFCs and / or SOECs. In one embodiment, the SSE comprises a doped zirconia, a doped ceria, or a doped lanthanum gallate. In one embodiment, the SSE is selected from a doped zirconia, a doped ceria, and a doped lanthanum gallate. In one embodiment, the doped zirconia is a yttria stabilised zirconia (YSZ), scandium doped zirconia (ScSZ), CaO- stabilised zirconia (CaSZ), or MgO-stabilised zirconia (MgSZ). In one embodiment, the doped ceria is a gadolinia doped ceria (GDC), yttria doped ceria (YDC), samaria doped ceria (SmDC), or neodymium doped ceria (NdDC). In one embodiment, the doped lanthanum gallate is an Lai-xSrxGai-yMgyO3-6 (LSGM) or a transition metal-doped LSGM. In one embodiment, the SSE comprises 3 mol% yttria stabilised zirconia (3YSZ) or 8 mol% yttria stabilised zirconia (8YSZ). In one embodiment, the SSE used herein has a maximum sintering temperature of over about 1400 °C. In one embodiment, the SSE comprises a fluorite material as described elsewhere herein. In one embodiment, the SSE is a fluorite material as described elsewhere herein.

[0087]

[0080] In one embodiment, the SSE does not comprise the same metal oxide as the material, or hybrid material, in at least one electrode. In other words, in one embodiment, the SSE and the material, or hybrid material, in at least one electrode have different chemical compositions. In another embodiment, the SSE does not comprise the same metal oxide as the material, or hybrid material, in both electrodes. In other words, in another embodiment, the SSE and the material, or hybrid material, in both electrodes have different chemical compositions. In one embodiment, the SSE and the material, or hybrid material, in at least one electrode have one or more common phases in their composition. In another embodiment, the SSE and the material, or hybrid material, in both electrodes have one or more common phases in their composition. In one embodiment, the SSE and the material, or hybrid material, in at least one electrode have no common phases in their composition. In one embodiment, the SSE and the material, or hybrid material, in both electrodes have no common phases in their composition.

[0088]

[0081] In one embodiment, the material, or hybrid material, in at least one electrode is devoid of yttria stabilised zirconia (YSZ) when the SSE comprises YSZ. In one embodiment, the material, or hybrid material, in both electrodes is devoid of yttria stabilised zirconia (YSZ) when the SSE comprises YSZ.

[0082] In one embodiment, the SSE is formed from solid particles. In one embodiment, the solid particles have an average particle size of from 1 nm to 10 pm, or of from 2 nm to 100 nm, or of from 50 nm to 500 nm, or of from 250 nm to 750 nm, or of from 500 nm to 2 pm, or of from 1 pm to 5 pm, or of from 2.5 pm to 7.5 pm, or of from 5 pm to 10 pm, or of less than 10 pm, less than 8 pm, less than 5 pm, less than 2 pm, less than 1 pm, less than 500 nm, less than 100 nm, less than 50 nm, or less than 10 nm.

[0089]

[0083] The SSE may have any suitable thickness. In one embodiment, the SSE has a thickness of from 0.1 mm to 2 mm, or of from 0.1 mm to 1 mm, or of from 0.1 mm to 0.5 mm, or of from 0.25 mm to 0.75 mm, or of from 0.45 mm to 0.65 mm, or of from 0.75 mm to 1 mm, or of from 1 mm to 1 .5 mm, or of from 1 mm to 2 mm.

[0090]

[0084] The assemblies herein comprise an interlayer between the SSE and an electrode. The interlayer herein has been found to improve the performance and stability of SOFC and / or SOEC assemblies relative to equivalent assemblies devoid of the interlayer, when used alone on the fuel side or the air side, or when used in combination on the fuel side and the air side. In certain embodiments, such as when used in combination on the fuel side and the air side, the interlayers herein advantageously extend the life of SOFC and / or SOEC assemblies by, e.g., reducing thermal delamination.

[0091]

[0085] The interlayer preferably comprises a single chemical material. The interlayer may be a single layer interlayer. In one embodiment, the single layer interlayer may be formed or sintered in a single step from a single layer of interlayer composition. Such embodiments are preferred for reasons of process simplicity and interlayer integrity.

[0092]

[0086] In other embodiments, the single interlayer may be formed or sintered in a single step from a repeat (stepwise) applications of a single interlayer composition, with e.g., ambient drying in between, prior to sintering. In yet further embodiments, the single interlayer may be formed or sintered in a stepwise program after repeat application and sintering of a single interlayer composition, that is, may be formed by a process of: application of a single interlayer composition, then sintering, then repeat application of composition, then sintering, etc., such as there is 1 repeat, 2 repeats, 3 repeats, 4 repeats, 5 repeats, or up to 10 repeats.

[0093]

[0087] In other embodiments, however, the interlayer may comprise two or more layers of different interlayer compositions. Each interlayer composition may vary in chemical materials present and / or in the proportion of chemical materials. In such embodiments, a gradient interlayer may be constructed having a profile that changes in composition with depth.

[0094]

[0088] References in the following paragraphs to the or an interlayer will be understood as being applicable to either the air side interlayer, the fuel side interlayer, or both.

[0095]

[0089] The interlayer may be formed from any suitable solid material, herein referred to sometimes as an “interlayer material”. However, it has been found that doped ceria materials are particularly suitable interlayer materials. Accordingly, in one embodiment the interlayer comprises doped ceria. Any suitable dopant may be used, but in one embodiment, the ceria is a metal oxide-doped ceria. In one embodiment, the metal oxide-doped ceria is selected from a gadolinium oxide-doped ceria (GDC), yttria doped ceria (YDC), samaria doped ceria (SmDC), and neodymium doped ceria (NdDC). The interlayer herein may comprise a metallic phase in some embodiments, or may be devoid of a metallic phase in others. In one embodiment, where the fuel electrode comprises a hybrid material, the fuel side interlayer is may optionally comprise a metallic phase. In one embodiment, where the air electrode comprises a hybrid material, the air side interlayer may optionally comprise a metallic phase. In one embodiment, where the fuel electrode and air electrode comprise a hybrid material, the fuel and air side interlayers may both optionally comprise a metallic phase. In one embodiment, the interlayer is devoid of a metallic phase. In one embodiment, where the fuel electrode comprises a hybrid material, the fuel side interlayer is devoid of a metallic phase. In one embodiment, where the air electrode comprises a hybrid material, the air side interlayer is devoid of a metallic phase. In one embodiment, where the fuel electrode and air electrode comprise a hybrid material, the fuel and air side interlayers are both devoid of a metallic phase.

[0096]

[0090] In one embodiment, the interlayer comprises doped ceria having a formula MxCei-xO2-6, where M = Gd, Y, Sm or Nd and 0<x<1 , or where x = 0.05, 0.1 , 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 or 0.5, or where 0<x<0.5, or where 0<x<0.4, or where 0<x<0.3. In one embodiment, the interlayer comprises doped ceria having the formula Mo.1Ceo.9O1.9, where M = Gd, Y, Sm or Nd, or having the formula Gdo.1Ceo.9O1 .9. In one embodiment, the interlayer consists of doped ceria having a formula MxCei.xO2-6, where M = Gd, Y, Sm or Nd and 0<x<1 , or where x = 0.05, 0.1 , 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 or 0.5, or where 0<x<0.5, or where 0<x<0.4, or where 0<x<0.3. In one embodiment, the interlayer consists of doped ceria having the formula Mo.1Ceo.9O1.9, where M = Gd, Y, Sm or Nd, or having the formula Gdo.1Ceo.9O1.9. Doped ceria materials may be purchased commercially from suppliers such as Sigma Aldrich, the Fuel Cell Store and Fiaxel, either in the form of powders or in the form of slurries, or may be synthesised according to methods known in the art.

[0097]

[0091] In one embodiment, the interlayer material is particulate. Although any suitable particle size of the interlayer material, such as doped ceria, may be used, in one embodiment, the interlayer material particles have an average particle size of from 10 nm to 1 pm, or of from 10 nm to 50 nm, or of from 10 nm to 100 nm, or of from 100 nm to 400 nm, or of from 25 nm to 250 nm, or of from 50 nm to 500 nm, or of from 100 nm to 1 pm, or of from 250 nm to 1 pm, or of from 500 nm to 1 pm, or of less than 1 pm, less than 750 nm, less than 500 nm, less than 250 nm, less than 100 nm, less than 50 nm, or less than 25 nm.

[0098]

[0092] The interlayer may have any suitable thickness. In one embodiment, this thickness refers to a dried or sintered material thickness. In one embodiment, the interlayer has a dried or sintered thickness of from 50 nm to 10 pm, or of from 50 nm to 1 pm, or of from 50 nm to 500 nm, or of from 250 nm to 750 nm, or of from 500 nm to 2 pm, or of from 1 pm to 5 pm, or of from 1 pm to 2 pm, or of from 2.5 pm to 5 pm, or of from 5 pm to 10 pm, or of from 2.5 pm to 7.5 pm, or of from 7 pm to 10 pm, or of from 5 pm to 10 pm, or of less than 10 pm, less than 7.5 pm, less than 5 pm, less than 2.5 pm, less than 1 pm, less than 500 nm, less than 250 nm, less than 100 nm, or of about 50 nm, 100 nm, 250 nm, 500 nm, 750 nm, 1 pm, 1.25 pm, 1.5 pm, 1.75 pm, 2 pm, 2.5 pm, 3 pm, 3.5 pm, 4 pm, 4.5 pm, 5 pm, 6 pm, 7 pm, 8 pm, 9 pm, or 10 pm. Interlayer thickness, and / or thickness of the SSE and / or electrode layers, may be measured by any suitable technique known in the art, such as by microscopy (scanning electron microscopy or SEM) or X-ray fluorescence (XRF) or the like.

[0099]

[0093] The interlayer may have a porous microstructure. In such embodiments, the porous mi era structure may be desirable to ensure gas flow across the interlayer. The porosity may arise from a granular structure, with spaces between grains of interlayer material forming the porous mi era structure. Accordingly, the interlayer may comprise grains of interlayer material. The grains may have any suitable size. In one embodiment, the grains may vary in size from 0.05 pm to 1 pm, or of from 0.1 pm to 0.75 pm, or of from 0.2 pm to 0.5 pm, or of from 0.1 pm to 0.5 pm, or of from 0.2 pm to 0.75 pm. The grains may have any suitable shape. In one embodiment, the grains are elliptical or spherical in shape.

[0100]

[0094] When both present in the assemblies herein, the fuel side interlayer and the air side interlayer are, in one embodiment, the same. In other words, in one embodiment, the fuel side and air side interlayers, when both present, are chemically identical, being composed of the same material. In other embodiments, when both present in the assemblies herein, the fuel side interlayer and the air side interlayer are different. In other words, in one embodiment, the fuel side and air side interlayers, when both present, are chemically different, being composed of different, non-overlapping materials.

[0095] Assemblies herein may have any suitable structure. In one embodiment, the assembly comprises, in layer order: a fuel side electrode, a fuel side interlayer between the fuel electrode and the SSE, an SSE, and an air electrode. In one embodiment, the assembly comprises, in layer order: a fuel side electrode, a fuel side interlayer between the fuel electrode and the SSE, an SSE, an air side interlayer between the air electrode and the SSE, and an air electrode. In one embodiment, the assembly comprises, in layer order: a fuel side electrode, an SSE, an air side interlayer between the air electrode and the SSE, and an air electrode.

[0101]

[0096] The fuel side interlayer wherein the fuel side interlayer is preferably provided on a surface of the SSE facing the fuel electrode. However, in other embodiments, the fuel side interlayer may be provided on a surface of the fuel electrode, or be provided on both a surface of the fuel electrode and a surface of the SSE facing the fuel electrode.

[0102]

[0097] Similarly, the air side interlayer is preferably provided on a surface of the SSE facing the air electrode. However, in other embodiments, the air side electrode may be provided on a surface of the air electrode, or be provided on both a surface of the air electrode and a surface of the SSE facing the air electrode.

[0103]

[0098] In one embodiment, the assembly herein is connected to an external circuit through current collectors. In some embodiments, a current collector is applied to each electrode. In one embodiment, the current collector is a metallic layer applied to each electrode in the form of a slurry comprising pure metallic powder, such as pure Ag powder, thoroughly dispersed in a solvent, such as terpineol. The slurry may be thoroughly mixed using a ball mill or the like. The slurry may then be applied to the sintered electrode layer. In some embodiments, the current collector may additionally or alternatively comprise metallic wire, optionally tightly coiled for close contact with the electrode layer, or a layer of metallic foil, or the like. Silver is particularly suitable as a current collector metal.

[0104]

[0099] The assembly herein may have any suitable construction. In one embodiment, the SSE is provided in a hollow cylindrical shape, an interlayer is applied either to the outer surface or inner surface of the cylinder, and electrode compositions are applied to the interlayer (where present) or onto the SSE. In another embodiment, the SSE is provided as a sheet, and the interlayer and electrode compositions are applied to the opposing faces of the sheet in a layered manner.

[0105]

[0100] The assemblies herein may be used in an SOFC and / or an SOEC. In one embodiment, disclosed herein is a solid oxide fuel or electrolyser cell comprising an assembly as described herein, or an assembly produced by the methods described herein. In one embodiment, disclosed herein is a solid oxide fuel cell comprising an assembly as described herein, or an assembly produced by the methods described herein. In one embodiment, disclosed herein is an electrolyserfuel cell comprising an assembly as described herein, or an assembly produced by the methods described herein. According to the disclosure herein, the SOFCs or SOECs comprising these assemblies can be high temperature cells operating at temperatures of from 700 to 1000 °C, or intermediate temperature cells operating at temperatures of from 500 to 750 °C.

[0106]

[0101] In one embodiment, the assemblies herein help extend SOFC or SOEC stability under higher voltage and higher current density operations. In some embodiments, the voltage condition for the SOEC operation may be in excess of 1.5 V, such as at least 1.6 V, and the current density at least 300 mA / cm2, such as at least 350 mA / cm2. In some embodiments, assemblies as described herein operating as SOECs at 800 °C at a voltage of 1 .6 V may maintain current density within 3%, or within 5%, or within 7.5%, or within 10%, or within 12.5%, of the original current density at time = 0 after a continuous operating period of at least 20 h, at least 40 h, at least 60 h, at least 80 h, or at least 100 h or at least 500 h, or at least 1000 h, compared to an otherwise equivalent cell lacking a fuel side, or both fuel side and air side, interlayer(s). In one embodiment, assemblies as described herein have ohmic (Rohm) losses after 100 h of operation at 800 °C at a voltage of 1 .6 V measured as an increase in Rohm over time of less than 15%, or less than 10%, or less than 5%, or less than 1%. In some embodiments, Rohm decreases overtime for assemblies as described herein, such as decreases by at least 2%, or at least 3%, or at least 5%, or at least 10%, or at least 25%, or at least 50%, or by from 0.1% to 5% or from 0.1% to 65%. In one embodiment, assemblies as described herein have polarisation (Rpoi) losses after 100 h of operation at 800 °C at a voltage of 1.6 V measured as an increase in Rpoiover time of less than 40%, less than 30%, less than 20%, less than 15%, or less than 10%, or less than 5%, or less than 1%. In some embodiments, Rpoidecreases overtime for assemblies as described herein, such as decreases by at least 5%, or at least 10%, or at least 15%, or at least 20%, or at least 25%, or at least 50%, or by from 10% to 25% or from 5% to 65%.

[0107]

[0102] Also disclosed is use of a solid oxide fuel or electrolyser cell comprising an assembly as described herein, or an assembly produced by the methods described herein, in a device. In one embodiment, a solid oxide fuel cell comprising an assembly as described herein, or an assembly produced by the methods described herein, is used in a device. In another embodiment, a solid oxide electrolytic cell comprising an assembly as described herein, or an assembly produced by the methods described herein, is used in a device. The device may be an auxiliary power unit, a heating device, a portable or stationary electricity generation unit, a fuel generator, or the like.

[0108] Methods of producing the assembly

[0109]

[0103] Described herein is a method of producing an assembly for a solid oxide fuel or electrolyser cell, the method comprising: providing a solid-state electrolyte (SSE) having a first surface and a second surface opposing the first surface; forming a first interlayer on the first surface of the SSE; forming a fuel side electrode on the first interlayer; optionally forming a second interlayer on the second surface of the SSE; and forming an air side electrode on either the second surface of the SSE, or if present, on the second interlayer.

[0104] In one embodiment, the method comprises: providing a solid-state electrolyte (SSE) having a first surface and a second surface opposing the first surface; forming a first interlayer on the first surface of the SSE; forming a fuel side electrode on the first interlayer; optionally forming a second interlayer on the second surface of the SSE; and forming an air side electrode on either the second surface of the SSE, or if present, on the second interlayer, wherein at least the fuel side electrode comprises a hybrid material.

[0110]

[0105] In one embodiment, the method comprises: providing a solid-state electrolyte (SSE) having a first surface and a second surface opposing the first surface; forming a first interlayer on the first surface of the SSE; forming a fuel side electrode on the first interlayer; forming a second interlayer on the second surface of the SSE; and forming an air side electrode on the second interlayer.

[0111]

[0106] In one embodiment, the method comprises: providing a solid-state electrolyte (SSE) having a first surface and a second surface opposing the first surface; forming a first interlayer on the first surface of the SSE; forming a fuel side electrode on the first interlayer; forming a second interlayer on the second surface of the SSE; and forming an air side electrode on the second interlayer, wherein the fuel side electrode and the air side electrode each comprise a hybrid material.

[0112]

[0107] In another embodiment, the method comprises: providing a solid-state electrolyte (SSE) having a first surface and a second surface opposing the first surface; forming a first interlayer on the first surface of the SSE; forming a fuel side electrode on the first interlayer; and forming air side electrode on the second surface of the SSE, wherein the fuel side electrode comprises a hybrid material and the air side electrode is devoid of a hybrid material.

[0113]

[0108] Also described herein is a method of producing an assembly for a solid oxide fuel or electrolysercell, the method comprising: providing a solid-state electrolyte (SSE) having a first surface and a second surface opposing the first surface; forming a first interlayer on the first surface of the SSE; forming a first electrode on the first interlayer; optionally forming a second interlayer on the second surface of the SSE; and forming a second electrode on either the second surface of the SSE, or if present, on the second interlayer, wherein the first electrode and the second electrode are a fuel electrode and an air electrode pair, and at least the first electrode comprises a hybrid material, wherein the hybrid material is a metal-metal oxide composite.

[0114]

[0109] In one embodiment, the method comprises: providing a solid-state electrolyte (SSE) having a first surface and a second surface opposing the first surface; forming a first interlayer on the first surface of the SSE; forming a first electrode on the first interlayer; forming a second interlayer on the second surface of the SSE; and forming a second electrode on the second interlayer, wherein the first electrode and the second electrode are a fuel electrode and an air electrode pair, and both the first electrode and second electrode each comprise a hybrid material, wherein the hybrid material is a metal-metal oxide composite.

[0115]

[0110] In another embodiment, the method comprises: providing a solid-state electrolyte (SSE) having a first surface and a second surface opposing the first surface; forming a first interlayer on the first surface of the SSE; forming a first electrode on the first interlayer; and forming a second electrode on the second surface of the SSE, wherein the first electrode and the second electrode are a fuel electrode and an air electrode pair, wherein the fuel side electrode comprises a hybrid material that is a metal-metal oxide composite and the air side electrode is devoid of a hybrid material.

[0116]

[0111] Also described herein is a method of producing an assembly for a solid oxide fuel or electrolysercell, the method comprising: providing a solid-state electrolyte (SSE) having a first surface and a second surface opposing the first surface; forming a first interlayer on the first surface of the SSE; forming a first electrode on the first interlayer; optionally forming a second interlayer on the second surface of the SSE; and forming a second electrode on either the second surface of the SSE, or if present, on the second interlayer, wherein the first electrode and the second electrode are a fuel electrode and an air electrode pair, and at least the first electrode comprises a hybrid material, wherein the hybrid material comprises a fluorite material.

[0117]

[0112] In one embodiment, the method comprises: providing a solid-state electrolyte (SSE) having a first surface and a second surface opposing the first surface; forming a first interlayer on the first surface of the SSE; forming a first electrode on the first interlayer; forming a second interlayer on the second surface of the SSE; and forming a second electrode on the second interlayer, wherein the first electrode and the second electrode are a fuel electrode and an air electrode pair, and both the first electrode and second electrode each comprise a hybrid material, wherein the hybrid material comprises a fluorite material.

[0118]

[0113] In another embodiment, the method comprises: providing a solid-state electrolyte (SSE) having a first surface and a second surface opposing the first surface; forming a first interlayer on the first surface of the SSE; forming a first electrode on the first interlayer; and forming a second electrode on the second surface of the SSE, wherein the first electrode and the second electrode are a fuel electrode and an air electrode pair, and wherein the fuel side electrode comprises a hybrid material that comprises a fluorite material and the air side electrode is devoid of a hybrid material.

[0119]

[0114] The methods herein comprise providing an SSE having a first surface and a second surface opposing the first surface. The SSE herein may be formed by any suitable method known in the art for forming SSEs. The SSE may be formed by compressing particulate a solid SSE material into the desired shape and sintering it. The SSE having two opposing surfaces may be provided as a cylinder or as a sheet. In one embodiment, the SSE is fabricated into a desired shape, such as a sheet or open ended tube (cylinder) through isostatic pressuring of the solid particles followed by sintering. Although any suitable pressure may be used to compress and shape the SSE, in one embodiment, pressures of from 100 MPa to 250 MPa, such as of from 150 to 200 MPa, such as of 170 MPa, may be used. Although any suitable sintering temperature may be used, and may be selected to be appropriately matched to the thermal stability of the SSE material being used, in one embodiment, the sintering temperature of the SSE is above about 1400 °C, such as above 1450 °C, or above 1500 °C, such as from 1400 to 1550 °C, or of about 1500 °C, for any suitable time, such as from 30 min to 3 h, or from 30 min to 2 h, or from 1 h to 3 h, or from 1.5 h to 2.5 h, or from 1.5 h to 3 h, or about 2 h.

[0120]

[0115] The methods herein comprise forming a first interlayer on the first surface of the SSE. In one embodiment, the first surface of the SSE may be selected, in the case of a cylindrical SSE, to be the inner surface of the cylinder and may be designated as the fuel side. In another embodiment, the first surface of the SSE may be selected, in the case of a cylindrical SSE, to be the outer surface of the cylinder and may be designated as the air side. The first surface of the SSE may be selected, in the case of a sheet of SSE, to be either face of the sheet and may be designated as the fuel side or air side. In some embodiments, the first surface of the SSE is designated as the fuel side, irrespective of the shape of the SSE.

[0121]

[0116] The methods herein optionally additionally comprise forming a second interlayer on the second surface of the SSE. Accordingly, in the following description, process steps applicable to the first interlayer and first interlayer composition are applicable to the second interlayer and second interlayer composition, and may be referred to generically as “the interlayer” with the understanding that the interlayer could be the first or the second interlayer.

[0122]

[0117] The interlayer may be formed by any suitable process. Forming the interlayer may comprise applying an interlayer composition to a surface of the SSE, and sintering the interlayer composition with the SSE. This advantageously allows for higher temperature sintering of the interlayer than may be possible if the interlayer composition is applied to one surface of an electrode instead. This is particularly the case for hybrid electrodes as described herein, which may have lower thermal stability than commonly used solid electrolyte materials, such as YSZ. However, in some embodiments, it may be suitable to apply the interlayer composition to one surface of an electrode.

[0123]

[0118] In one embodiment, forming the first interlayer comprises applying a first interlayer composition to the first surface of the SSE, and sintering the first interlayer composition. In one embodiment, forming the second interlayer comprises applying a second interlayer composition to the second surface of the SSE, and sintering the second interlayer composition. The first and / or second interlayer composition may be co-sintered with the SSE, or may be separately sintered, that is, the SSE may be sintered in a first step and the interlayer composition may be sintered in a second, separate step.

[0124]

[0119] In one embodiment, the interlayer is applied in the form of an interlayer composition, such as slurry, at any suitable thickness. In one embodiment, the interlayer is applied in the form of a slurry comprising a mixture of particles of one or more metal oxide(s) in a liquid dispersant. In one embodiment, the interlayer is applied in the form of a slurry comprising a mixture of particles of one or more metal oxide(s), and optionally particles of one or more metallic phase metal(s), in a liquid dispersant. In one embodiment, the interlayer is applied in the form of a slurry comprising a mixture of particles of one or more metal oxide(s) and particles of one or more metallic phase metal(s) in a liquid dispersant. It will be understood that different interlayer compositions or slurries may shrink on sintering to a different extent, and that a suitable thickness of a given interlayer composition or slurry may be calculated based on a predetermined sintering shrink rate to give a desired final sintered interlayer thickness. In one embodiment, the interlayer composition is applied at a (wet) thickness of from 50 nm to 20 pm, or of from 100 nm to 2 pm, or of from 100 nm to 1000 nm, or of from 500 nm to 1500 nm, or of from 1000 nm to 4 pm, or of from 2 pm to 10 pm, or of from 2 pm to 4 pm, or of from 5 pm to 10 pm, or of from 10 pm to 20 pm, or of from 10 pm to 15 pm, or of from 15 pm to 20 pm, or of less than 20 pm, less than 15 pm, less than 10 pm, less than 5 pm, less than 2 pm, less than 1000 nm, less than 500 nm, less than 200 nm, or of about 100 nm, 200 nm, 500 nm, 1000 nm, 1500 nm, 2 pm, 2.5 pm, 3 pm, 3.5 pm, 4 pm, 5 pm, 6 pm, 7 pm, 8 pm, 9 pm, 10 pm, 12 pm, 14 pm, 16 pm, 18 pm, or 20 pm. In some embodiments, the interlayer composition may shrink on sintering, such as shrink in volume by 40%, or by about 45%, or by about 50%, or by about 55%, or by about 60%.

[0125]

[0120] In one embodiment, the first interlayer is formed in a single sintering step. In other words, repeat layering and sintering of the first interlayer composition / material may not be required to form the first interlayer. Similarly, in one embodiment, the second interlayer, if present, is formed in a single sintering step. In other words, repeat layering and sintering of the second interlayer composition / material may not be required to form the second interlayer. In a further embodiment, the first interlayer is formed at the same time as the second interlayer, if it is present, such that the interlayers on two opposing sides of the SSE are formed simultaneously in a single sintering step. This single-step process advantageously simplifies production of the assemblies herein.

[0126]

[0121] The interlayer composition may comprise the solid interlayer material in a solvent or dispersant. In one embodiment, the interlayer material is suspended in a dispersant to form a slurry, which is then applied to, e.g., at least one surface of the SSE in a layer for sintering and interlayer formation. In one embodiment, the interlayer composition comprises particles of doped ceria in a liquid dispersant in the form of a slurry. The slurry may have any suitable viscosity, adjusted by varying the ratio of solid particles to liquid dispersant to suit the application method and achieve a desired applied thickness of the interlayer material. In one embodiment, the slurry may be adjusted to suit a particular application based on particle size of the solid particles, solid bulk density and / or liquid dispersant viscosity. In one embodiment, the interlayer composition slurry is applied to the desired surface(s) using dip-coating, brushing, doctor blading, spray coating, or the like. The solvent for the slurry may be any suitable solvent, such as may comprise a dispersant, such as an organic compound like terpineol, and optionally one or more polymers, thickeners, and / or plasticisers, or the like to aid in application.

[0127]

[0122] In one embodiment, the interlayer composition is sintered at a maximum temperature of 1400 °C, or is sintered at a temperature of less than 1400 °C, or of less than 1350 °C, of less than 1300 °C, of less than 1250 °C, of less than 1200 °C, of less than 1100 °C, of less than 1000 °C, of less than 900 °C, or of less than 800 °C, or at a temperature of from 800 °C to 1400 °C, or of from 900 °C to 1300 °C, or of from 1000 °C to 1250 °C, or of from 1100 °C to 1400 °C. The sintering temperature may be held for any suitable time period, such as of from 30 min to 3 h, or of 30 min to 2 h, or of from 1 h to 3 h, or of from 1.5 h to 2.5 h, or of from 1.5 h to 3 h, or of about 2 h. Any suitable ramp up rate or ramp down rate may be used to reach the maximum sintering temperature. In one embodiment, the ramp up rate is of from 40 to 80 °C / min, or of from 50 to 70 °C / min, or of from 40 to 65 °C / min, or of from 60 to 80 °C / min, or of from 55 to 65 °C / min, or of about 60 °C / min. In one embodiment, the ramp down rate is of from 70 to 110 °C / min, or of from 80 to 100 °C / min, or of from 85 to 95 °C / min, or of from 70 to 95 °C / min, or of from 85 to 110 °C / min, or of about 90 °C / min. In one embodiment, the interlayer composition is sintered at a temperature of from 1100 °C to 1350 °C for a period of from 1 h to 3 h using a ramp up rate of from 50 to 70 °C / min and a ramp down rate of from 80 to 100 °C / min.

[0123] The methods herein comprise forming a first electrode on the first interlayer. In some embodiments, the first electrode is a fuel side electrode, which means the second electrode is the air side electrode. In other embodiments, the first electrode is the air side electrode and the second electrode is the fuel side electrode. The first electrode, whether fuel or air, is applied to an interlayer on the SSE in the methods herein. The second electrode may be applied directly to the SSE in the event there is no second interlayer, or may be applied to the second interlayer if it is present.

[0128]

[0124] At least one of the electrodes herein may comprise a hybrid material. If present, the hybrid electrode may be used as the first electrode or the electrode in contact with the first interlayer. In some embodiments, both electrodes comprise a hybrid material. The hybrid material may be processed in any suitable way to produce an electrode, such as the first, and optionally second, electrode(s), or the fuel side or air side electrode.

[0129]

[0125] Persons of skill in the art will be familiar with electrode fabrication methods. In one embodiment, the electrode is formed from an electrode composition comprising an electrode material as described elsewhere herein. In one embodiment, the electrode is formed from an electrode composition comprising a hybrid material. In one embodiment, the electrode composition comprises a mixture of particles of a material, or hybrid material, as described herein, such as in the form of a slurry. In one embodiment, where a hybrid electrode is desired, the electrode composition may comprise a mixture of particles of one or more metal oxide(s) and particles of one or more metallic phase metal(s) in a liquid dispersant in the form of a slurry. In one embodiment, the electrode mixture or slurry is thoroughly mixed, in one embodiment using a ball mill or the like for any suitable period, such as at 450 rpm for a period of 2 h. In one embodiment, the slurry may be referred to as an ink base. The slurry may have any suitable viscosity, adjusted by varying the ratio of solid particles to liquid dispersant, to suit the application method and achieve a desired thickness of material or hybrid material. In one embodiment, the material or hybrid material is suspended in a dispersant to form a slurry, which is then applied to a substrate in a layer for sintering and electrode formation. In one embodiment, the slurry is applied using dip-coating, brushing, doctor blading, spray coating, or the like. The solvent for the slurry may comprise a dispersant, such as an organic compound like terpineol, and optionally one or more polymers, thickeners, and / or plasticisers, or the like to aid in application.

[0130]

[0126] In one embodiment, the electrode composition is sintered at a maximum temperature of 1400 °C, or is sintered at a temperature of less than 1400 °C, or of less than 1350 °C, of less than 1300 °C, of less than 1200 °C, of less than 1100 °C, of less than 1000 °C, of less than 900 °C, or of less than 800 °C, or at a temperature of from 800 °C to 1400 °C, or of from 900 °C to 1300 °C, or of from 750 °C to 1000 °C, or of from 800 °C to 900 °C, or of from 900 °C to 1250 °C, or of from 1100 °C to 1400 °C. In one embodiment, the air side electrode composition is sintered at a maximum temperature of about 1250 °C, or of from 800 °C to 1250 °C. In one embodiment, the fuel side electrode composition is sintered at a maximum temperature of about 1450 °C, or of from 800 °C to 1450 °C.

[0131]

[0127] The sintering temperature may be held for any suitable time period, such as of from 30 min to 3 h, or of 30 min to 2 h, or of from 1 h to 3 h, or of from 1 .5 h to 2.5 h, or of from 1 .5 h to 3 h, or of about 2 h. Any suitable ramp up rate or ramp down rate may be used to reach the maximum sintering temperature. In one embodiment, the ramp up rate is of from 100 to 200 °C / h, or of from 100 to 150 °C / h, or of from 125 to 175 °C / h, or of from 140 to 160 °C / h, or of from 150 to 200 °C / h, or of about 150 °C / h. In one embodiment, the ramp down rate is of from 100 to 200 °C / h, or of from 100 to 150 °C / h, or of from 125 to 175 °C / h, or of from 140 to 160 °C / h, or of from 150 to 200 °C / h, or of about 150 °C / h. In one embodiment, the electrode composition is sintered at a temperature of from 800 °C to 1000 °C for a period of from 1 h to 3 h and a ramp down rate of from 125 to 175 °C / min.

[0132]

[0128] In embodiments where one or both electrodes do not comprise a hybrid material, any suitable material that is not a hybrid material (“non-hybrid material”) may be used to produce the electrode. In one embodiment, the non-hybrid material has recognised utility as an SOFC and / or SOEC electrode material. Such materials may include, but are not limited to, pure metal oxides such as perovskite materials, ceria, zirconia, and related doped materials. Persons of skill in the art will appreciate that non-hybrid materials may be used as to fabricate electrodes in the assemblies herein in certain embodiments.

[0133]

[0129] In one embodiment, forming the first electrode comprises applying a first electrode composition to the first interlayer, and sintering the first electrode composition. In one embodiment, forming the second electrode comprises applying a second electrode composition to the second surface of the SSE or the second interlayer, if present, and sintering the second electrode composition. The first and / or second electrode composition may be sintered in a separate, subsequent step to the SSE and the interlayer composition. In one embodiment, the first electrode is formed at the same time as the second electrode, if it is present, such that the electrodes on two opposing sides of the SSE are formed simultaneously in a single sintering step. This single-step process advantageously simplifies production of the assemblies herein.

[0134]

[0130] In one embodiment, the SSE herein is sintered at a temperature of >1400°C, the first and, if being used, second, interlayer is sintered at a temperature of from 1100 °C to 1400 °C, and the electrode composition, comprising a hybrid material, is sintered on the interlayer(s) at a temperature of from 750 °C to 1000 °C. In one embodiment, the SSE herein is sintered at a temperature of from 1400°C to 1500 °C, the first and, if being used, second, interlayer is sintered at a temperature of from 1200 °C to 1300 °C, and the electrode composition, comprising a hybrid material, is sintered on the interlayer(s) at a temperature of from 800 °C to 950 °C.

[0135]

[0131] In one embodiment, there is provided a method of producing an assembly for a solid oxide fuel or electrolyser cell, the method comprising: providing a solid-state electrolyte (SSE) having a first surface and a second surface opposing the first surface; forming a first interlayer on the first surface of the SSE; forming a fuel side electrode on the first interlayer, wherein the fuel side electrode comprises a hybrid material comprising particles of metal oxide, optionally a fluorite material, a perovskite material, or a mixture of the two, and particles of a transition metal, optionally selected from copper, silver and gold, or an alloy thereof; forming a second interlayer on the second surface of the SSE; and forming an air side electrode on the second interlayer, wherein the air side electrode comprises a hybrid material comprising particles of metal oxide, optionally a fluorite material, a perovskite material, or a mixture of the two, and particles of a transition metal, optionally selected from copper, silver and gold, or an alloy thereof.

[0136]

[0132] In another embodiment, there is provided a method of producing an assembly for a solid oxide fuel or electrolyser cell, the method comprising: providing a solid-state electrolyte (SSE) having a first surface and a second surface opposing the first surface; forming a first interlayer on the first surface of the SSE; forming a fuel side electrode on the first interlayer, wherein the fuel side electrode comprises a hybrid material comprising particles of metal oxide, optionally a fluorite material, a perovskite material, or a mixture of the two, and particles of a transition metal, optionally selected from an alloy of silver with one or more of copper, gold, iron, cobalt, nickel and molybdenum; forming a second interlayer on the second surface of the SSE; and forming an air side electrode on the second interlayer, wherein the air side electrode comprises a hybrid material comprising particles of metal oxide, optionally a fluorite material, a perovskite material, or a mixture of the two, and particles of a transition metal, optionally selected from an alloy of silver with one or more of copper, gold, iron, cobalt, nickel and molybdenum.

[0137]

[0133] In one embodiment, there is provided a method of producing an assembly for a solid oxide fuel or electrolyser cell, the method comprising: providing a solid-state electrolyte (SSE) having a first surface and a second surface opposing the first surface; forming a first interlayer on the first surface of the SSE, wherein the first interlayer is optionally devoid of metallic metal; forming a fuel side electrode on the first interlayer, wherein the fuel side electrode comprises a hybrid material comprising particles of metal oxide, optionally a fluorite material, a perovskite material, or a mixture of the two, and particles of a transition metal, optionally selected from copper, silver and gold, or an alloy thereof; forming a second interlayer on the second surface of the SSE, wherein the second interlayer is optionally devoid of metallic metal; and forming an air side electrode on the second interlayer, wherein the air side electrode comprises a hybrid material comprising particles of metal oxide, optionally a fluorite material, a perovskite material, or a mixture of the two, and particles of a transition metal, optionally selected from copper, silver and gold, or an alloy thereof.

[0138]

[0134] In another embodiment, there is provided a method of producing an assembly for a solid oxide fuel or electrolyser cell, the method comprising: providing a solid-state electrolyte (SSE) having a first surface and a second surface opposing the first surface; forming a first interlayer on the first surface of the SSE, wherein the first interlayer is optionally devoid of metallic metal; forming a fuel side electrode on the first interlayer, wherein the fuel side electrode comprises a hybrid material comprising particles of metal oxide, optionally a fluorite material, a perovskite material, or a mixture of the two, and particles of a transition metal, optionally selected from an alloy of silverwith one ormore of copper, gold, iron, cobalt, nickel and molybdenum; forming a second interlayer on the second surface of the SSE, wherein the second interlayer is optionally devoid of metallic metal; and forming an air side electrode on the second interlayer, wherein the air side electrode comprises a hybrid material comprising particles of metal oxide, optionally a fluorite material, a perovskite material, or a mixture of the two, and particles of a transition metal, optionally selected from an alloy of silver with one or more of copper, gold, iron, cobalt, nickel and molybdenum.

[0135] In one embodiment, there is provided a method of producing an assembly for a solid oxide fuel or electrolyser cell, the method comprising: providing a solid-state electrolyte (SSE) having a first surface and a second surface opposing the first surface, wherein the SSE is sintered at a temperature of >1400°C; forming a first interlayer on the first surface of the SSE, wherein the first interlayer is optionally devoid of metallic metal, wherein the interlayer is sintered at a temperature of from 1100 °C to 1400 °C; forming a fuel side electrode on the first interlayer, wherein the fuel side electrode comprises a hybrid material comprising particles of metal oxide, optionally a fluorite material, a perovskite material, or a mixture of the two, and particles of a transition metal, optionally selected from copper, silver and gold, or an alloy thereof, wherein the fuel side electrode composition is sintered on the first interlayer at a temperature of from 750 °C to 1000 °C; forming a second interlayer on the second surface of the SSE, wherein the second interlayer is optionally devoid of metallic metal, wherein the interlayer is sintered at a temperature of from 1100 °C to 1400 °C; and forming an air side electrode on the second interlayer, wherein the air side electrode comprises a hybrid material comprising particles of metal oxide, optionally a fluorite material, a perovskite material, or a mixture of the two, and particles of a transition metal, optionally selected from copper, silver and gold, or an alloy thereof, wherein the air side electrode composition is sintered on the first interlayer at a temperature of from 750 °C to 1000 °C.

[0139]

[0136] In one embodiment, there is provided a method of producing an assembly for a solid oxide fuel or electrolyser cell, the method comprising: providing a solid-state electrolyte (SSE) having a first surface and a second surface opposing the first surface, wherein the SSE is sintered at a temperature of >1400°C; forming a first interlayer on the first surface of the SSE, wherein the first interlayer is optionally devoid of metallic metal, wherein the interlayer is sintered at a temperature of from 1100 °C to 1400 °C; forming a fuel side electrode on the first interlayer, wherein the fuel side electrode comprises a hybrid material comprising particles of metal oxide, optionally a fluorite material, a perovskite material, or a mixture of the two, and particles of a transition metal, optionally selected from an alloy of silver with one or more of copper, gold, iron, cobalt, nickel and molybdenum, wherein the fuel side electrode composition is sintered on the first interlayer at a temperature of from 750 °C to 1000 °C; forming a second interlayer on the second surface of the SSE, wherein the second interlayer is optionally devoid of metallic metal, wherein the interlayer is sintered at a temperature of from 1100 °C to 1400 °C; and forming an air side electrode on the second interlayer, wherein the air side electrode comprises a hybrid material comprising particles of metal oxide, optionally a fluorite material, a perovskite material, or a mixture of the two, and particles of a transition metal, optionally selected from an alloy of silver with one or more of copper, gold, iron, cobalt, nickel and molybdenum, wherein the air side electrode composition is sintered on the first interlayer at a temperature of from 750 °C to 1000 °C.

[0140]

[0137] It should be understood that any numerical range recited herein is intended to include all subranges subsumed therein. For example, a range of "from x to y" or “between x and is intended to include all sub-ranges between x and y and also range end points x and y.

[0138] As used herein, the singular forms “a,” “an,” and “the” may refer to plural articles unless specifically stated otherwise.

[0141] Examples

[0142] 1 . Methods and materials

[0143]

[0139] Open-ended 8YSZ tubes were fabricated using isostatic pressing of yttria stabilized zirconia (8 mol% Yttria) powder at 170 MPa followed by sintering at 1500°C. The thickness of electrolyte produced was 0.35 mm with an inner diameter of 9.37 mm. Gadolinium doped ceria (Gd0.1 Ce0.901.9) paste (Fiaxel) was then brush-coated either outside (for interlayer only on air electrode side) or both inside and outside (for interlayer on both air and fuel electrode sides) the electrolyte tube to form an interlayer having a final sintered thickness of from 5 to 10 pm. This interlayer-coated tube was sintered in static air in a binder burn-off furnace at 1250°C for 2 h using heating rate 60°C / h, dwell at 1250°C for 2h and cooling rate of 90 °C / h.

[0144]

[0140] The mi era structure of the sintered GDC interlayer is shown in Figure 9, in which grains are visible having elliptical to spherical shape and varying in size from 0.2 to 0.5 microns. Grain boundaries are distinct, but the overall interlayer microstructure exhibits porosity.

[0145]

[0141] The cathode (fuel electrode) ink was prepared by mixing Ag powder (Alfa Aesar) and Gd0.1 Ce0.901.9 (Fuel Cell Materials, FCM) along with terpinol (Fuel Cell Materials) based solvent in an appropriate ratio to obtain 70 wt% Ag and 30 wt% GDC (70Ag30GDC). Subsequently, the ink was ball milled at 450 rpm for 2 h in a Planetary Ball Mill. The anode (oxygen electrode) ink was prepared using same method as for the cathode. For 70Ag30GDC anode, the powders used were Ag (Alfa Aesar) and GdO.1CeO.9C1 .9 (Fuel Cell Materials, FCM), whereas for 70Ag30LSCF anode, the powders were La0.60Sr0.40Co0.20Fe0.8003-x (Fuel Cell Materials) and Ag powder (Alfa Aesar).

[0146]

[0142] The cathode ink was brush-coated inside the electrolyte tube and the anode ink was brush- coated outside the tube, followed by sintering in static air at 825 °C for 2 h using heating and cooling ramp rates of 150 °C / h. A thin layer of Ag ink was coated on top of both anode and cathode as a current collection layer. This ink was prepared by ball-milling Ag powder (Alfa Aesar) and terpinol (Fuel Cell Materials) based solvent at 450 rpm for 2 h in a Planetary Ball Mill.

[0147]

[0143] For the current collection, 1) Ag wire (diameter 1 .0 mm) was tightly wound on the outside of the tube across the anode and 2) Ag wire (diameter 1.0 mm) was tightly coiled around an alumina mandrel such that the outer diameter of the helix was in touch with the cathode inside the tube, this was achieved by snugly inserting into the tube covering the entire length of the cathode.

[0148]

[0144] As-prepared tubular SOECs were individually mounted inside a horizontal tubular furnace and heated to 800 °C at a rate of 100 °C / h in industrial-grade bottled N2 (99.0% purity from the British Oxygen Company, BOC) fed to the cathode side at a constant rate of 50 ml / min. The anode was exposed to the ambient inside the furnace. Once at 800 °C, steam was fed to the cathode along with 50 ml / min N2. For all the experiments reported here, a thermocouple was kept very close to the outer electrode (anode) and it read 803±3 °C at all times. Electrochemical impedance spectra were recorded (in the frequency range of 50 KHz to 100 mHz with an amplitude of 20 mV) using a Zahner IM6e Electrochemical station (Zahner Inc., Germany) under open circuit voltage (OCV) and 1.60 V. The voltage-current characteristics were measured using a scan rate of 2.5 mV / s. Constant voltage studies were conducted on the cells at 1 .60 V for more than 100 h.

[0149] 2. Results

[0150] Example 1: effect of interlayer on only one side, i.e., at air electrode, on cell performance and stability under high voltage operation for fluorite-based hybrid air electrode and symmetrical cell configuration

[0151]

[0145] Two solid oxide electrolytic cells were tested for 100 h at 800 °C and a high voltage of 1.6V. Both the cells had a symmetric configuration (Figure 2a), i.e., the same composition for both the fuel electrode (cathode) and the air electrode (anode). The electrodes were composed of 70 wt% silver (Ag) and 30 wt% gadolinia doped ceria (GDC), which is a fluorite material. The electrolyte was 500 microns thick 8 mol% yttria stabilized zirconia (8YSZ). The only difference between the two cells was that one cell had a GDC interlayer (between electrolyte and anode) sintered at 1200 °C, whereas the other one had no such interlayer. The one with interlayer showed only 4.2% drop in current density over 100 h of continuous operation (Figure 2c), whereas the other one showed 14.3% degradation. This observation is consistent with the voltage-current characteristics recorded with fresh and tested cells (Figure 2b). The ohmic (Rohm) and polarisation (Rpoi) losses after 100 h of operation were also quite different for the two cells as calculated from electrochemical impedance spectra (Figure 2d). In the impedance spectra, the first intercept of the arc with the x-axis gives the value of Rohm and the overall length of the intercept gives Rpoi. Rohm encompasses the ohmic resistance of the electrolyte as well as the contact losses coming from electrode-electrolyte interfaces. Rpoiencompasses:

[0152] • Charge transfer losses arising from the kinetics of the reaction between electrons and ionic species at the electrode I electrolyte interface

[0153] • Mass transfer losses arising from gas diffusion, and adsorption / desorption reactions from electrode surface as well as its bulk

[0154]

[0146] For the cell without any interlayer, there was 18.54% increase in Rohm and 42.86% increase in RPoi after 100 h of operation. In contrast, the cell with interlayer showed no increase in Rohm and 14.29% increase in Rpoi(Figure 2d). It has been unanimously agreed upon in the literature that delamination leads to multiple points of detachment between the electrolyte and the electrode. This causes an increase in contact losses at the electrode-electrolyte interface, which is manifested as an increase in Rohm. Such a detachment between the electrolyte and the electrode also attenuates the triple phase boundary (TPB), which is the active region for gas-ion-electron transfer or interaction. This increases the charge transfer and mass transfer losses, manifested as an increase in Rpoi. In the present example, increase in both Rohm and Rpoiafter 100 h of operation for the cell without any air electrode side interlayer can be clearly related to the above explanation. The fact that the cell with only air electrode side interlayer showed no increase in Rohm is promising, but the increase in Rpoistill indicates some degree of delamination at the fuel electrode side. This has been studied and further explained in example 3. Details on how Rohm and Rpoivaried for both cells are provided in Table 1. Example 2: effect of interlayer only on one side, i.e., at the air electrode, on cell performance and stability under high voltage operation for unsymmetrical cell configuration having perovskite-based hybrid air electrode and fluorite-based hybrid fuel electrode

[0155]

[0147] Two solid oxide electrolytic cells with unsymmetrical configuration (fuel electrode, i.e., cathode and air electrode, i.e., anode having different compositions) as shown in Figure 3a were tested for 100 h at 800 °C and 1 .6 V. For both the cells, the cathode comprised a composite of 70 wt% Ag and 30 wt% GDC (AgGDC), the anode comprised a composite of 70 wt% Ag and 30 wt% perovskite material LSCF (70Ag30LSCF) and the electrolyte was 500 microns thick 8YSZ. The only difference between the two cells was that one had GDC interlayer (between electrolyte and anode) sintered at 1200 °C, whereas the other one had no such interlayer. The one with interlayer showed only 2.8% drop in current density over 100 h of continuous operation, whereas the other one showed 15.0% degradation (Figure 3c). This observation is consistent with the voltage-current (V-l) characteristics recorded with fresh and tested cells (Figure 3b). The V-l curves for fresh and tested cells superimposed for the cell with interlayer, whereas that for cell without interlayer did not superimpose. For the cell without any interlayer, there was 19.86% increase in Rohm and 41.86% increase in Rpoiafter 100 h of operation (Figure 3d), clearly indicating delamination at electrode-electrolyte interfaces. In contrast, the cell with interlayer showed no increase in Rohm but still 5.00% increase in Rpoi, possibly due to some degree of delamination at the fuel electrode side. This complies with the findings of example 1 , and has been further studied in example 4. Details on how Rohm and Rpoivaried for both cells are provided in Table 1 . It is further to be noted that above 1 .2 V, current density was higher for the cell with interlayer at any particular voltage (Figure 3b). The current densities started off at similar values for both the cells, however, it sharply dropped by ~ 8% within the first 1 h of operation for the cell without interlayer (inset of Figure 3c). This clearly demonstrates that the presence of interlayer not only enhanced cell stability but also improved cell performance.

[0156] Example 3: effect of interlayer on both air and fuel electrode sides on cell performance and stability under high voltage operation for symmetrical cell configuration having fluorite-based hybrid electrodes

[0157]

[0148] A solid oxide electrolytic cell with symmetric configuration was tested for 100 h at 800 °C and 1 .6 V. Both the air and fuel electrodes comprised a composite of 70 wt% Ag and 30 wt% GDC (AgGDC) with a GDC interlayer on both air electrode and fuel electrode sides (Figure 4a). The electrolyte was 500 pm thick 8YSZ. This cell showed absolutely no degradation over 100 h (Figure 4c). Results have been compared with Example 1 , where one cell had no interlayer and the other one had only air electrode side interlayer. It is to be noted here that the two cells of example 1 , and this cell of Example 3 were identical, the only difference being absence or presence of interlayer. The cell (in example 1) with interlayer only on air electrode side showed 4.2% drop in current density over 100 h of continuous operation (Figure 4c), accompanied by 14.29% increase in Rpoi(Figure 4d). In contrast, the cell with interlayer on both sides showed gradual improvement in current density over first 20 h followed by a very stable performance over next 80 h. The cell with both side interlayer also depicted a significant drop in Rohm and Rpoi(Figure 4d) after 100 h operation, clearly indicating no signs of delamination either on the fuel side or air side electrode-electrolyte interface. The reason for initial higher Rohm and Rpoi (and consequently lower current density) is that the interlayer at the fuel side initially offers additional impedance. However, with onset of steam electrolysis, a partial reducing environment is formed that activates the interlayer and enlarges the triple phase boundary, thus bringing down Rohm and RPoi. This observation is consistent with the voltage-current (V-l) characteristics recorded with fresh and tested cells (Figure 4b). V-l curves for fresh and tested cells almost superimposed for the cell with only anode side interlayer. In contrast, the current densities significantly improved with the cell having both side interlayer post 100 h operation. In fact, current densities were higher than 1) fresh cell having both side interlayer and 2) fresh and tested cells having only anode side interlayer. This again demonstrates that the fuel side interlayer not only enhances cell stability but also improves its performance. Details on how Rohm and Rpoivaried for both cells are provided in Table 1.

[0158] Example 4: effect of interlayer at both air and fuel electrode sides on cell performance and stability under high voltage operation for unsymmetrical cell configuration having perovskite-based hybrid air electrode and fluorite-based hybrid fuel electrode

[0159]

[0149] A solid oxide electrolytic cell with unsymmetric configuration was tested for 100 h at 800 °C and 1 .6 V (Figure 5a). The electrode and electrolyte compositions were identical to the cells tested in example 2, i.e., the fuel electrode was a composite of 70 wt%Ag and 30 wt% GDC (70Ag30GDC), and the air electrode was a composite of 70 wt% Ag and 30 wt% LSCF (70Ag30LSCF). However, this cell had GDC interlayer on both air and fuel electrode sides and showed absolutely no degradation over 100 h of continuous operation at a high voltage of 1 .6 V (Figure 5c). Results have been compared with Example 2 and shown in Figure 5. The cell (in example 2) with interlayer only on air electrode side showed 2.8% drop in current density over 100 h with a commensurate 5% rise in Rpoi. In contrast, the cell with interlayer on both sides showed drop in both Rohm and Rpoi post 100 h of continuous operation (Figure 5d), clearly indicating no signs of delamination either on the fuel side or air side electrodeelectrolyte interface. Such drop in Rohm and Rpoiis in compliance with what had been observed with symmetric cell configuration (Example 3). The V-l curves (Figure 5b) of fresh and tested cell (with both side interlayer) also indicated higher current densities after 100 h of testing. This further corroborates the fact that the fuel side interlayer not only enhances cell stability but also improves its performance. Details on how Rohm and Rpoivaried for both cells are provided in Table 1 .

[0160] Example 5: effect of interlayer at both air and fuel electrode sides on cell performance and stability under high current densities for unsymmetrical cell configuration having fluorite-based hybrid fuel electrode and perovskite-based hybrid air electrode

[0161]

[0150] A solid oxide electrolytic cell with unsymmetric configuration (Figure 6a) was tested for 120 h at 800 °C, 1.6 V and a high current density of 740 mA / cm2. The fuel electrode was a composite of 1 mol%Co, 70 wt% Ag and 30 wt% GDC, the air electrode was a composite of 70 wt% Ag and 30 wt% LSCF. There was GDC interlayer on both sides. The electrolyte was thinned down to 210 pm to achieve higher current densities and examine how stable the cell stayed at such higher currents. This cell was tested for 120 h at 800 °C and 1.6 V with absolutely no degradation under a current density as high as 740 mA / cm2 (Figure 6b). Consistent with previous findings (examples 3 and 4), a decrease in both Rohm and Rpoiwas observed upon 120 h of continuous testing (Figure 6c). As a result, current densities also slightly improved. This indicated 1) excellent stability with no signs of delamination at either air or fuel side electrode-electrolyte interfaces and 2) enhanced cell performance.

[0162] Table 1. R„hm and Rpoivalues before and after lOO h of continuous operation at 800 °C and 1.6V with and without interlayer for different anode / cathode combinations

[0163] 3. Discussion

[0164]

[0151] Findings from the above cited examples have been represented as a bar chart in Figure 7, showing how presence / absence of interlayer affects degradation rate (Figure 7a), Rohm (Figure 7b) and Rpoi (Figure 7c) over 100 h of continuous cell operation. In summary we can conclude that incorporation of an interlayer on only air side electrode (anode in these examples) improves cell performance and stability, but some degradation is still encountered. However, incorporation of interlayer on both air side electrode (anode in these examples) and fuel side electrode (cathode in these examples) mitigates any degradation.

[0165] Example 6: effect of steam flow rate on cell performance for symmetrical cell configuration having fluorite-based hybrid electrodes

[0166]

[0152] A solid oxide electrolytic cell with symmetric configuration was tested for 8 h at 750 °C, and either 1.35 V or 1.6 V. The electrodes were a composite of 50 wt% Ag and 50 wt% GDC. A GDC interlayer (FCM as described above) was applied to either: both fuel and air electrodes, the fuel electrode only, the air electrode only, or neither electrode as a comparative example. Each cell was tested with steam flow rates of 34, 50, 100 and 170 mL / min under both voltages. The results are shown in Fig. 10 and Tables 2a-2b below. For cells with an interlayer on both sides, and to a lesser extent with an interlayer on either the fuel side or the air side, a decrease in both Rohm and Rpoi was observed upon 8 h of continuous testing. As a result, current densities also slightly improved. This indicated excellent stability with no signs of delamination at either air or fuel side electrode-electrolyte interfaces where an interlayer was present on both electrodes and enhanced cell performance.

[0167] Table 2a. Rohm and Rpoivalues under different steam flow rates at 1.35 V and 1.6V for hybrid electrodes in Example 6 with and without interlayers

[0168] Table 2b. Current density values under different steam flow rates at 1.35 V and 1.6V for hybrid electrodes in Example 6 with and without interlayers

[0169] Example 7: effect of alternative interlayer GDC source

[0170]

[0153] Open-ended 8YSZ tubes were fabricated using isostatic pressing of yttria stabilized zirconia (8 mol% Yttria) powder at 170 MPa followed by sintering at 1500°C. The thickness of electrolyte produced was 0.55 mm with an inner diameter of 9.37 mm. Gadolinium doped ceria (Gdo.1Ceo.9O1.9) paste, produced by mixing commercial gadolinia doped ceria powder (GDC-10N) (surface area 10-14 m2 / g; D50 = 0.1 -0.4 pm) purchased from Fuel Cell Materials (9.4 g) with a terpineol ink vehicle binder purchased from Fuel Cell Materials (9.4 g) and ethanol (9 g) in a ball mill at 350 rpm for 6 h, was then brush-coated either outside (for interlayer only on air electrode side) or both inside and outside (for interlayer on both air and fuel electrode sides) the electrolyte tube to form an interlayer having a final sintered thickness of from ~5 to 10 pm. This interlayer-coated tube was sintered in static air in a binder burn-off furnace at 1250 °C for 2 h using heating rate 60 °C / h, dwell at 1250 °C for 2 h and cooling rate of 90 °C / h.

[0171]

[0154] A solid oxide electrolytic cell with symmetric configuration was tested for 24 h at 750 °C, and either 1 .35 V or 1 .6 V. The electrodes were a composite of 50 wt% Ag and 50 wt% GDC. The GDC interlayer was applied to either: both fuel and air electrodes or to neither electrode as a comparative example. Each cell was tested with steam flow rates of 34, 50, 100 and 170 mL / min under both voltages. The results are shown in Fig. 11 and Tables 3a-3b below. For cells with an interlayer on both sides under all four different flow rates, current densities at both 1 .35 V and 1 .6 V doubled upon introducing the interlayer on both electrodes, and both Rohm and Rpol dropped by a factor of two. This indicated excellent stability with no signs of delamination at the air and fuel side electrodeelectrolyte interfaces where an interlayer was present and enhanced cell performance compared to an equivalent cell without any interlayer present.

[0172] Table 3a. Rohm and Rpoivalues under different steam flow rates at 1.35 V and 1.6V for hybrid electrodes in Example 7 with and without interlayers

[0173] Table 3b. Current density values under different steam flow rates at 1.35 V and 1.6V for hybrid electrodes in Example 7 with and without interlayers

[0155] The present invention is described with reference to the above examples. It is to be understood that the examples are illustrative of and not limiting to the invention described herein.

[0174]

[0156] It will be apparent to the person skilled in the art that while the invention has been described in some detail for the purposes of clarity and understanding, various modifications and alterations to the embodiments and methods described herein may be made without departing from the scope of the inventive concept disclosed in this specification.

Claims

1. Claims1 . An assembly for a solid oxide fuel or electrolyser cell, comprising: a fuel electrode, an air electrode, and a solid-state electrolyte (SSE) sandwiched therebetween, wherein the assembly further comprises: a fuel side interlayer between the fuel electrode and the SSE.

2. The assembly of claim 1 , further comprising an air side interlayer between the air electrode and the SSE.

3. The assembly of claim 1 or claim 2, wherein the fuel electrode and / or the air electrode comprises a fluorite material.

4. The assembly of claim 3, wherein the fluorite material is a metal oxide-doped ceria.

5. The assembly of claim 3 or claim 4, wherein the fluorite material is a metal oxide-doped ceria selected from gadolinium oxide-doped ceria (GDC), samarium oxide-doped ceria (SDC), and yttrium oxide-doped ceria (YDC), or a combination thereof.

6. The assembly of any one of the preceding claims, wherein the fuel electrode and / or the air electrode comprises a perovskite material.

7. The assembly of claim 6, wherein the perovskite material is an LST material of formula LaxSri.xTiO3, a BSCF material of formula BaxSri.xCoyFei.y03-6, an LSCF material of formula LaxSri.xC0yFei.yO3-6 or an LSCM of formula LaxSri.xCryMni.yO3-6, or a combination of any two or more of these.

8. The assembly of claim 6 or claim 7, wherein perovskite material is Bao.sSro.sCoo.sFeo^Os-a, Lao.6Sro.4Coo.2Feo.803-6, or Lao.75Sro.25Cro.5M no.5O3-0, or a combination of any two or more of these.

9. The assembly of any one of the preceding claims, wherein the fuel electrode and / or the air electrode comprises a hybrid material.

10. The assembly of claim 9, wherein the fuel electrode comprises a hybrid material.1 1 . The assembly of claim 9 or claim 10, wherein the air electrode and the fuel electrode each comprise a hybrid material.

12. The assembly of any one of claims 9 to 1 1 , wherein the hybrid material is a metal-metal oxide composite.

13. The assembly of any one of claims 9 to 12, wherein the hybrid material comprises a metallic phase transition metal, optionally wherein the transition metal is selected from copper, silver, gold, iron, cobalt, nickel and molybdenum, or an alloy of any two or more of these.

14. The assembly of any one of claims 9 to 13, wherein the hybrid material comprises a metallic phase transition metal selected from copper, silver and gold, or an alloy thereof, optionally wherein the hybrid material is selected from Ag-GDC, Cu-GDC, Au / Mo-GDC, Ag / Fe-GDC, Ag / Ni-GDC, Ni / Cu / Co-GDC, Co / Ag-GDC, Ni / Ag / Fe-GDC, and Ag-LSCF.

15. The assembly of any one of claims 9 to 14, wherein the hybrid material comprises from 10 wt% to 90 wt% of a metallic phase metal and from 10 wt% to 90 wt% of a metal oxide, optionally from 60 wt% to 80 wt% of a metallic phase metal and from 20 wt% to 40 wt% of a metal oxide.

16. The assembly of any one of claims 9 to 15, wherein both the fuel electrode and the air electrode comprise the same hybrid material.

17. The assembly of any one of claims 9 to 15, wherein the fuel electrode and the air electrode comprise each comprise a different hybrid material.

18. The assembly of any one of claims 9 to 17, wherein the hybrid material does not comprise the same material as the SSE.

19. The assembly of any one of the preceding claims, wherein the fuel side interlayer comprises a metal oxide-doped ceria, optionally selected from: gadolinium oxide-doped ceria (GDC), samarium oxide-doped ceria (SDC), and yttrium oxide-doped ceria (YDC).

20. The assembly of any one of the preceding claims, wherein the fuel side interlayer has a thickness of from 50 nm to 10 pm, optionally of about 100 nm to 5 pm.

21. The assembly of any one of the preceding claims, wherein the fuel side interlayer improves the performance and / or stability of the solid oxide fuel cell or electrolytic cell relative to an equivalent assembly devoid of a fuel side interlayer, optionally measured as: (a) ability to maintain current density within 5%, or within 10%, of an original current density after an operating period of at least 20 h, or at least 80 h; (b) an increase in Rohm after 100 h of operation of less than 15%, or less than 5%, or (c) an increase in Rpoiafter 100 h of operation of less than 40%, or less than 20%.

22. The assembly of any one of the preceding claims, further comprising an air side interlayer between the air electrode and the SSE.

23. The assembly of claim 22, wherein the air electrode comprises a hybrid material.

24. The assembly of claim 22 or claim 23, wherein the air side interlayer comprises a metal oxidedoped ceria, optionally selected from: gadolinium oxide-doped ceria (GDC), samarium oxidedoped ceria (SDC), and yttrium oxide-doped ceria (YDC).

25. The assembly of any one of claims 22 to 24, wherein the air side interlayer has a thickness of from 50 nm to 10 pm, optionally of about 100 nm to 5 pm.

26. The assembly of any one of claims 22 to 25, wherein the fuel side and air side interlayers together improve the performance and / or stability of the solid oxide fuel cell or electrolytic cell relative to an equivalent assembly devoid of a fuel side and an air side interlayer, or relative to an equivalent assembly devoid of a fuel side interlayer, optionally measured as: (a) ability to maintain current density within 5%, or within 10%, of an original current density after an operating period of at least 20 h, or at least 80 h; and / or (b) an increase in Rohm after 100 h of operation of less than 15%, or less than 5%, and / or (c) an increase in Rpoiafter 100 h of operation of less than 40%, or less than 20%.

27. The assembly of any one of the preceding claims, wherein the SSE and fuel electrode have a different chemical composition, optionally wherein the SSE comprises yttria stabilised zirconia (YSZ), doped ceria, or lanthanum gallate.

28. An assembly for a solid oxide fuel or electrolyser cell, comprising: a fuel electrode, an air electrode, and a solid-state electrolyte (SSE) sandwiched therebetween, wherein the assembly further comprises: a fuel side interlayer between the fuel electrode and the SSE, wherein the fuel electrode comprises a metal-metal oxide hybrid material, optionally wherein the hybrid material is a metal-metal oxide composite comprising a metallic-phase transition metal selected from copper, silver, and gold, or an alloy thereof.

29. A method of producing an assembly for a solid oxide fuel or electrolyser cell, the method comprising: providing a solid-state electrolyte (SSE) having a first surface and a second surface opposing the first surface; forming a first interlayer on the first surface of the SSE; forming a fuel side electrode on the first interlayer; optionally forming a second interlayer on the second surface of the SSE; and forming an air side electrode on either the second surface of the SSE, or if present, on the second interlayer.

30. The method of claim 29, wherein forming the first interlayer comprises applying a first interlayer composition to the first surface of the SSE, andsintering the first interlayer composition, optionally at a temperature of 1400 °C or less optionally wherein the first interlayer composition is applied in the form of a slurry.31 . The method of claim 29 or claim 30, wherein forming the fuel side electrode comprises applying a fuel side electrode composition to the first interlayer, and sintering the fuel side electrode composition, optionally at a temperature of 900 °C or less.

32. The method of any one of claims 29 to 31 , wherein forming the air side electrode comprises applying an air side electrode composition to the second surface of the SSE, or if present, to the second interlayer, and sintering the air side electrode composition, optionally at a temperature of 900 °C or less.

33. The method of any one of claims 29 to 32, wherein the method comprises: forming a second interlayer on the second surface of the SSE, and forming an air side electrode on the second interlayer.

34. The method of claim 33, wherein forming the second interlayer comprises applying a second interlayer composition to the second surface of the SSE, and sintering the second interlayer composition, optionally at a temperature of 1400 °C or less optionally wherein the second interlayer composition is applied in the form of a slurry.

35. The method of claim 33 or claim 34, wherein forming the second electrode comprises applying an air side electrode composition to the second interlayer, and sintering the air side electrode composition, optionally at a temperature of 900 °C or less.

36. The method of any one of claims 29 to 35, wherein the first interlayer and the second interlayer, if present, are formed together in a single step.

37. The method of any one of claims 29 to 36, wherein the fuel side electrode and air side electrode are formed together in a single step.

38. The method of any one of claims 29 to 37, wherein the first interlayer, and if present second interlayer, comprises metal oxide-doped ceria, optionally GDC.

39. The method of claim 38, wherein the metal oxide-doped ceria is provided in the form of a slurry comprising particles, wherein the particles have an average particle size of from 10 nm to 1 pm, optionally of from 10 nm to 100 nm.

40. The method of any one of claims 29 to 39, wherein the fuel electrode and / or the air electrode comprises a fluorite material and / or a perovskite material.41 . The method of any one of claims 29 to 40, wherein the fuel electrode and / or the air electrode comprises a hybrid material, optionally wherein the metal-metal oxide composite comprises particles of metal oxide, optionally a fluorite material, a perovskite material, or a mixture of the two, and particles of metal, optionally a transition metal.

42. The method of claim 41 , wherein the hybrid material is a metal-metal oxide composite comprising a metallic-phase transition metal selected from copper, silver, and gold, or an alloy thereof.

43. The method of claim 41 or claim 42, wherein the hybrid material comprises from 10 wt% to 90 wt% of a metallic phase transition metal and from 10 wt% to 90 wt% of a metal oxide, optionally from 60 wt% to 80 wt% of a metallic phase transition metal and from 20 wt% to 40 wt% of a metal oxide.

44. An assembly for a solid oxide fuel or electrolyser cell produced by the method of any one of claims 29 to 43.

45. A solid oxide fuel or electrolyser cell comprising the assembly of any one of claims 1 to 28 or claim 44.

46. Use of a solid oxide fuel or electrolyser cell comprising the assembly of any one of claims 1 to 28 or claim 44 in a device.

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