Electrochemical cell with redox-stable fuel electrode support

Abstract

To provide an electrochemical cell having an oxidation-reduction stable fuel electrode support.SOLUTION: The electrochemical cell comprises an electrolyte having a first side and an opposing second side, an oxygen electrode located on the first side of the electrolyte, a fuel electrode support, and an active fuel electrode located between the fuel electrode support and the second side of the electrolyte. The fuel electrode substrate comprises a cermet comprising a nickel-containing phase and a ceramic phase. The ceramic phase may include 4 mole percent (mol%) to 10mol% yttria-stabilized zirconia ((4-10) - YSZ) or zirconia doped with at least one of alumina, ceria, or titania. Alternatively or additionally, the nickel-containing phase may include nickel doped with at least one of magnesium oxide, calcium oxide, or titanium oxide.SELECTED DRAWING: Figure 2A

Description

[Technical Field]

[0001] Aspects of the present disclosure relate generally to electrochemical cells, and more particularly to electrochemical cells that include redox-stable fuel electrode (eg, anode) supports. [Background technology]

[0002] A typical solid oxide fuel cell includes a ceramic electrolyte located between an anode electrode and a cathode electrode. A thin electrolyte is generally desirable to provide low ionic resistance. However, thin electrolytes can be damaged during stack fabrication, redox cycling, and / or thermal cycling. Summary of the Invention

[0003] According to various embodiments, an electrochemical cell includes an electrolyte having a first side and an opposite second side, an oxygen electrode located on the first side of the electrolyte, a fuel electrode support, and an active fuel electrode located between the fuel electrode support and the second side of the electrolyte. The fuel electrode support includes a cermet containing a nickel-containing phase and a ceramic phase. The ceramic phase can include 4 mole percent (mol%) to 10 mol% yttria-stabilized zirconia ((4-10)-YSZ) or zirconia doped with at least one of alumina, ceria, or titania. Alternatively or additionally, the nickel-containing phase can include nickel doped with at least one of magnesium oxide, calcium oxide, or titanium oxide.

[0004] The accompanying drawings, which are included to provide a further understanding of the invention, and which are incorporated into and constitute a part of this specification, illustrate exemplary embodiments of the invention and, together with the description, serve to explain the principles of the invention. [Brief explanation of the drawings]

[0005] [Figure 1A] FIG. 1A is a perspective view of an electrochemical stack according to various embodiments of the present disclosure. [Figure 1B] FIG. 1B is a cross-sectional view of a portion of the stack of FIG. 1A. [Figure 2A] FIG. 2A is a cross-sectional view of a fuel electrode-supported electrochemical cell according to various embodiments of the present disclosure. [Figure 2B] FIG. 2B is a cross-sectional view of a co-supported electrochemical cell according to various embodiments of the present disclosure. [Figure 3A] FIG. 3A is an exploded perspective view of an alternative fuel electrode including support ribs according to various embodiments of the present disclosure. [Figure 3B] FIG. 3B is a cross-sectional view of a portion of the fuel electrode of FIG. 3A. [Figure 4A] FIG. 4A is an exploded perspective view of an alternative fuel electrode according to various embodiments of the present disclosure. [Figure 4B] FIG. 4B is a cross-sectional view of a portion of the fuel electrode of FIG. 4A. DETAILED DESCRIPTION OF THE INVENTION

[0006] The present disclosure will be described more fully hereinafter with reference to the accompanying drawings, which show exemplary embodiments of the present invention. However, the present invention may be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these exemplary embodiments are provided so that this disclosure will be comprehensive and will fully convey the scope of the present invention to those skilled in the art. In the drawings, the sizes and relative sizes of layers and regions may be exaggerated for clarity. Like reference numerals in the drawings indicate like elements.

[0007] When an element or layer is referred to as being "on" or "connected to" another element or layer, it is understood that it can be directly on or connected to the other element or layer, or that intervening elements or layers may be present. On the other hand, when an element is referred to as being "directly on" or "directly connected to" another element or layer, there are no intervening elements or layers present. For purposes of this disclosure, it is understood that "at least one of X, Y, and Z" can be interpreted as X only, Y only, Z only, or any combination of two or more items X, Y, and Z (e.g., XYZ, XYY, YZ, ZZ).

[0008] Electrochemical cell systems include fuel cells and electrolysis cell systems. In high-temperature fuel cell systems, such as solid oxide fuel cell (SOFC) systems, an oxidizing stream is directed to the cathode side of the fuel cell, and a fuel stream is directed to the anode side of the fuel cell. The oxidizing stream is typically air, and the fuel stream can be hydrogen (H2) or a hydrocarbon fuel, such as methane, natural gas, pentane, ethanol, or methanol. When fuel cells operate at typical temperatures between 750°C and 950°C, negatively charged oxygen ions can be transferred from the cathode flow stream to the anode flow stream, where they combine with free hydrogen or hydrogen in hydrocarbon molecules to form water vapor and / or with carbon monoxide to form carbon dioxide. Excess electrons from the negatively charged ions are directed back to the cathode side of the fuel cell through the completed electrical circuit between the anode and cathode, resulting in the flow of electrical current through the circuit. In electrolyzer systems, such as solid oxide electrolyzer systems, water (e.g., steam) is separated into hydrogen and oxygen by applying a voltage to the electrolysis cell.

[0009] FIG. 1A is a perspective view of an electrochemical cell stack 50 according to various embodiments of the present disclosure, and FIG. 1B is a cross-sectional view of a portion of the stack 50 according to various embodiments of the present disclosure. In the following embodiments, the stack 50 is described as operating as a solid oxide fuel cell (SOFC) stack 50. However, it should be noted that the stack 50 can also operate as an electrolyzer (e.g., a solid oxide electrolysis cell (SOEC) stack). With reference to FIGS. 1A and 1B, the stack 50 includes electrochemical cells 30, such as fuel cells (e.g., SOFCs) or electrolysis cells (e.g., SOECs), separated by interconnects 10. In the following embodiments, the electrochemical cells 30 are described as fuel cells. With reference to FIG. 1B, each fuel cell 30 includes a cathode electrode 33, a solid oxide electrolyte 35, and an anode electrode 37. However, it should be noted that the electrochemical cells 30 may alternatively include electrolysis cells in which the solid oxide electrolyte 35 is located between the oxygen electrode 33 and the fuel electrode 37.

[0010] Various materials may be used for the cathode electrode 33, electrolyte 35, and anode electrode 37. For example, the anode electrode 37 may include a cermet containing a nickel-containing phase and a ceramic phase. The nickel-containing phase may consist solely of nickel in a reduced state. This phase may form nickel oxide when oxidized. Thus, the anode electrode 37 is preferably annealed in a reducing atmosphere prior to operation to reduce the nickel oxide to nickel. The nickel-containing phase may include other metals in addition to nickel and / or nickel alloys. The ceramic phase may include stabilized zirconia, such as yttria- and / or scandia-stabilized zirconia, and / or doped ceria, such as ceria doped with gadolinia, yttria, and / or samaria.

[0011] The electrolyte 35 may include stabilized zirconia, such as scandia-stabilized zirconia (SSZ) or yttria-stabilized zirconia (YSZ). Alternatively, the electrolyte 35 may include another ion-conducting material, such as doped ceria.

[0012] The cathode electrode 33 may include a conductive material, such as a conductive perovskite material, such as lanthanum strontium manganite (LSM). Other conductive perovskites, such as LSCo, or metals, such as Pt, may also be used. The cathode electrode 33 may also include a ceramic phase similar to the anode electrode 37. The electrodes and electrolyte may include one or more sublayers, each made of one or more of the materials described above.

[0013] An electrochemical cell stack 50 is often constructed from multiple SOFCs 30, which may take the form of planar elements, tubes, or other geometric shapes. While the fuel cell stack in FIG. 1A is oriented vertically, the fuel cell stack may be oriented horizontally or in other orientations. Fuel and air may be supplied to the electrochemically active surfaces, which may be large in area. For example, fuel may be supplied through fuel holes (e.g., fuel riser openings) 52 formed in each interconnect 10. The fuel holes 52 may be aligned to form fuel conduits extending through the stack 50.

[0014] Each interconnect 10 electrically connects adjacent fuel cells 30 in the stack 50. In particular, an interconnect 10 can electrically connect the anode electrode 37 of one fuel cell 30 to the cathode electrode 33 of an adjacent fuel cell 30. FIG. 1B shows that the lower fuel cell 30 is located between two interconnects 10. An optional Ni mesh may be used to electrically connect the interconnect 10 to the anode electrode 37 of the adjacent fuel cell 30.

[0015] Each interconnect 10 includes fuel ribs 12A that at least partially define fuel channels 8A and air ribs 12B that at least partially define oxidant (e.g., air) channels 8B. The interconnects 10 can operate as gas-fuel separators that separate a fuel, such as a hydrocarbon fuel, flowing to the fuel electrode (i.e., anode electrode 37) of one cell in the stack from an oxidant, such as air, flowing to the oxygen electrode (i.e., cathode 33) of an adjacent cell in the stack.

[0016] Each interconnect 10 can be made of or contain a conductive material, such as a metal alloy (e.g., a chromium-iron alloy or stainless steel, e.g., a ferritic stainless steel) having a thermal expansion coefficient similar to that of the solid oxide electrolyte in the cell (e.g., a difference of 0% to 10%). For example, the interconnects 10 can each include a metal substrate including a high-temperature stable metal alloy, such as a chromium-iron alloy, e.g., an alloy of 4 to 6 weight percent iron, optionally 1 weight percent or less yttrium, and the balance chromium, and can electrically connect the anode or fuel side of one fuel cell 30 to the cathode or air side of an adjacent fuel cell 30. A conductive contact layer, such as a nickel layer or nickel mesh, can be provided between the anode electrode 37 and the fuel side of each interconnect 10. A conductive protective layer 11, such as lanthanum strontium manganate and / or manganese cobalt spinel, can be provided on at least the air side of each interconnect 10.

[0017] Electrochemical cells, such as SOFCs and SOECs, are mechanically supported by one or more of their electrodes or electrolytes to increase ease of handling and reliability. For example, cells include electrode-supported cells, electrolyte-supported cells, and co-supported cells. Electrolyte-supported cells include a relatively thick electrolyte on which a relatively thin electrode is formed. Electrode-supported cells include a relatively thick support electrode (e.g., a fuel cell anode) to provide structural support, while co-supported cells can include a relatively thick support electrode and a relatively thick electrolyte.

[0018] Electrolyte-supported cells offer numerous advantages, including improved sealing due to the high density of the surrounding electrolyte and reduction stability due to the thin anode. However, because the electrolyte typically exhibits lower bulk conductivity than the anode or cathode materials, electrolyte-supported cells often exhibit higher area resistivity (e.g., ohmic resistance) values ​​than electrode-supported cells. For example, in electrolyte-supported solid oxide fuel cells, the ohmic resistance of the electrolyte can be the largest contributor to the total area resistivity of the cell at typical operating temperatures (e.g., about 800°C to 850°C).

[0019] Electrode-supported SOFCs and SOECs are typically fabricated by co-sintering a coating of electrolyte material with a supporting electrode material. Electrode-supported cells include anode-supported fuel cells, which have a relatively thick anode, and cathode-supported fuel cells, which have a relatively thick cathode. The terms anode and cathode are reversed for electrolysis cells.

[0020] Fabrication of anode-supported fuel cells (or cathode-supported electrolysis cells) is relatively straightforward, as dense electrolytes can be achieved using sintering temperatures exceeding 1300°C without consideration of interactions between the electrode material and the electrolyte. However, anode-supported fuel cells and cathode-supported electrolysis cells can suffer from redox instability, which can affect the operational reliability of the cells when the fuel cell anode or electrolysis cell cathode is exposed to changes in oxygen partial pressure. Redox instability arises from the volume expansion of Ni to NiO within the fuel cell anode or electrolysis cell cathode, but the open pore space may not be able to fully accommodate this volume expansion. As a result, cracks may form in the electrode, thereby degrading steady-state performance. Severe cracks may propagate to the electrolyte and reduce the Nernst voltage. Thus, various embodiments provide electrodes and co-supported electrochemical cells with improved electrode redox stability.

[0021] 2A is a cross-sectional view of an electrode-supported electrochemical cell 100A according to various embodiments of the present disclosure, and FIG. 2B is a cross-sectional view of a co-supported electrochemical cell 100B according to various embodiments of the present disclosure. The support electrode may comprise an anode electrode for a fuel cell or a cathode electrode for an electrolysis cell. For simplicity, the anode of the fuel cell and the cathode of the electrolysis cell will be referred to as the "fuel electrode," to which fuel or steam, respectively, is supplied during operation of the electrochemical cell. The opposing electrode (i.e., the cathode of the fuel cell and the anode of the electrolysis cell) will be referred to as the "oxygen electrode," to which air is supplied during operation of the electrochemical cell.

[0022] 2A and 2B, electrochemical cells 100A, 100B may include an electrolyte 200, a fuel electrode 300 located on a first side (e.g., the fuel electrode side) of electrolyte 200, and an oxygen electrode 400 located on a second side (e.g., the oxygen electrode side) of electrolyte 200. Electrolyte 200 may be formed from an ionically conductive ceramic material such as a doped zirconia material or a doped ceria material. For example, electrolyte 200 may include scandia-stabilized zirconia (SSZ), yttria-stabilized zirconia (YSZ), yttria-ceria-stabilized zirconia (YCSZ), ytterbia-ceria-scandia-stabilized zirconia (YbCSSZ), or mixtures thereof.

[0023] As disclosed in U.S. Pat. No. 8,580,456, which is incorporated herein by reference, the electrolyte may comprise YbCSSZ, wherein scandia may be present in an amount equal to 9 mol% to 11 mol%, for example 10 mol%, ceria may be present in an amount greater than 0 mol% to 3 mol%, for example 0.5 mol% to 2.5 mol%, for example 1 mol%, and ytterbia may be present in an amount greater than 0 mol% to 2.5 mol%, for example 0.5 mol% to 2 mol%, for example 1 mol%.

[0024] The electrolyte 200 may optionally include a barrier layer 210 located on the oxygen electrode side. The barrier layer 210 may be configured to reduce or prevent diffusion of oxygen electrode materials into the electrolyte 200. For example, the barrier layer 210 may be formed from a doped ceria material, such as samaria-doped ceria (SDC) or gadolinia-doped ceria (GDC).

[0025] The oxygen electrode 400 can be located on the barrier layer 210. The oxygen electrode 400 can be a single-layer structure or a multi-layer structure. For example, the oxygen electrode 400 can include an oxygen electrode functional layer 410 and an oxygen electrode contact layer 420. The oxygen electrode functional layer 410 can include an oxygen electrocatalyst such as lanthanum strontium manganate, lanthanum strontium cobaltite, lanthanum strontium cobalt ferrite, or lanthanum nickel ferrite. The oxygen electrode contact layer 420 can include a conductive material such as lanthanum strontium manganate configured to reduce electrical resistance between the oxygen electrode 400 and an adjacent component, such as an interconnect.

[0026] The fuel electrode 300 can include an active fuel electrode 310 located on the fuel electrode side of the electrolyte 200 and a fuel electrode support 320 located on the active fuel electrode 310. The active fuel electrode 310 can include a cermet including a nickel-containing phase and an ion-conducting ceramic phase, such as SSZ, YSZ, or YbCSSZ, and / or doped ceria, such as ceria doped with gadolinia, yttria, and / or samaria, such as samaria-doped ceria (SDC). Preferably, the active fuel electrode 310 includes a Ni-SDC cermet or a Ni-YbCSSZ cermet. In some embodiments, the Ni phase can include additional dopants, such as Mg, Ca, and / or Ti, to improve phase stability and / or redox resistance.

[0027] The active fuel electrode 310 can be a single-layer structure or a multi-layer structure. For example, the active fuel electrode 310 can include a first functionally graded electrode (FGE) layer 312 and a second FGE layer 314. The first FGE layer 312 can have a higher ratio of nickel-containing phase to ion-conducting ceramic phase than the second FGE layer 314.

[0028] The first FGE layer 312 can have a thickness T1 ranging from about 7 μm to about 17 μm, e.g., from about 10 μm to about 14 μm, or from about 11 μm to about 13 μm. The second FGE layer 314 can have a thickness T2 ranging from about 2 μm to about 10 μm, e.g., from about 4 μm to about 8 μm, or from about 5 μm to about 6 μm. However, the present disclosure is not limited to any particular FGE layer thickness.

[0029] The fuel electrode support 320 can be formed from a cermet material having a metallic phase and a ceramic phase. For example, the fuel electrode support 320 can include a nickel-containing phase (e.g., a nickel phase) and a ceramic phase. The nickel phase can include nickel and / or a nickel alloy and, optionally, can include other additional metal dopants to improve phase stability and / or redox resistance, as discussed in more detail below. The nickel-containing phase can be formed as a nickel oxide-containing phase, with or without additional metal dopant(s), which is then reduced to the nickel-containing phase prior to operation of the electrochemical cell.

[0030] The ceramic phase can include stabilized zirconia, yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (SSZ), or yttria-scandia-stabilized zirconia (YSSZ), and / or doped ceria materials, such as ceria doped with gadolinia, yttria, and / or samaria. The ceramic phase may optionally be doped with additional phase stabilizers, as discussed in more detail below. In one embodiment, the ceramic phase of the fuel electrode support 320 includes YSZ containing about 4 mol% to about 10 mol% yttria (i.e., (4-10)-YSZ). The tetragonal 3-YSZ phase is metastable and prone to localized phase changes to the monoclinic phase. Increasing the yttria content from 4 mol% to 10 mol% increases the phase stability of YSZ. In various embodiments, as described in more detail below, the zirconia ceramic phase may include an additional dopant (e.g., a phase stabilizer) to improve phase stability. The zirconia ceramic phase including the additional phase stabilizer dopant may include (4-10)-YSZ, or zirconia containing less than 4 mol% yttria, e.g., 0 mol% to 3 mol% yttria, and / or 0 mol% to 6 mol% scandia, e.g., 1 mol% to 6 mol% scandia.

[0031] 2A, in the fuel electrode-supported electrochemical cell 100A, the fuel electrode support 320 can have a thickness T3 ranging from about 50 μm to about 400 μm, e.g., from about 75 μm to about 300 μm, or from about 100 μm to about 200 μm. The electrolyte 200 can have a thickness T4 ranging from about 5 μm to about 15 μm, e.g., from about 8 μm to about 12 μm, or from about 10 μm to about 11 μm. Thus, the relatively thick fuel electrode support 320 can support the relatively thin electrolyte 200.

[0032] As shown in FIG. 2B , the co-supported electrochemical cell 100B can include a thinner fuel electrode support 320 and a thicker electrolyte 200 than those of the fuel electrode-supported electrochemical cell 100A. Specifically, the fuel electrode support 320 can have a thickness T5 ranging from about 20 μm to about 100 μm, e.g., from about 25 μm to about 75 μm, or from about 40 μm to about 60 μm. The electrolyte 200 can have a thickness T6 ranging from about 20 μm to about 80 μm, e.g., from about 30 μm to about 70 μm, from about 40 μm to about 60 μm, or from about 50 μm to about 55 μm. The electrolyte 200 can be thicker than, thinner than, or the same thickness as the fuel electrode support 320. The relatively thick electrolyte 200 can be self-supporting. Therefore, the thickness of the fuel electrode support 320 can be reduced compared to the fuel electrode support 320 of the cell 100A without compromising the strength of the cell.

[0033] Figure 3A is an exploded perspective view of an alternative fuel electrode 300A including support ribs, and Figure 3B is a cross-sectional view of a portion of the fuel electrode 300A of Figure 3A, according to various embodiments of the present disclosure. The fuel electrode 300A can be used in the electrochemical cells 100A, 100B of Figures 2A and 2B.

[0034] 3A and 3B, a fuel electrode 300A can include a continuous active fuel electrode 310 disposed on a fuel electrode support 320. The active fuel electrode 310 can include a nickel-containing phase and an ion-conducting ceramic phase, such as stabilized zirconia and / or doped ceria, as described above. The active fuel electrode 310 can be a single-layer or multi-layer structure disposed on the fuel electrode support 320. For example, the active fuel electrode 310 can include a first functionally graded electrode (FGE) layer 312 and a second FGE layer 314. The first FGE layer 312 can have a higher ratio of nickel-containing phase to ion-conducting phase than the second FGE layer 314.

[0035] The fuel electrode support 320 can include a first support layer 330 and a second support layer 340. The first support layer 330 can include first support ribs 332 located within a first matrix layer 334. The second support layer 340 can include second support ribs 342 located within a second matrix layer 344.

[0036] The support ribs 332, 342 can be formed from ceramic materials such as yttria-stabilized zirconia (YSZ), scandia-stabilized zirconia (SSZ), yttria-scandia-stabilized zirconia (YSSZ), and / or doped ceria materials such as ceria doped with gadolinia, yttria, and / or samaria. The ceramic materials may be optionally doped with other elements to enhance phase stability, as discussed below. In some embodiments, the ceramic support ribs 332, 342 are free of free metal phases, such as free nickel phases, and have a nickel content of less than about 1 mol%, e.g., less than 0.5 mol%, less than 0.25 mol%, less than 0.1 mol%, e.g., between 0 mol% and 0.01 mol%. In some embodiments, the support ribs 332, 342 can be nickel-free or contain only trace amounts of nickel diffused from the matrix layers 334, 344.

[0037] The first support ribs 332 can be oriented parallel to one another in a first horizontal direction. The second support ribs 342 can be oriented parallel to one another in a second horizontal direction. The first horizontal direction is different from the second horizontal direction such that the first support ribs 332 intersect the second support ribs 342. In one embodiment, the first horizontal direction can be perpendicular to the second horizontal direction. For example, the first support ribs 332 and the second support ribs 342 can extend with their lengths perpendicular to one another. The ribs 332, 342 can be stacked to form a lattice structure.

[0038] The matrix layers 334, 344 can be stacked together to form a conductive matrix 350 that surrounds the ribs 332, 342. The matrix 350 (i.e., the matrix layers 334, 344) can be formed from a cermet material having a metallic phase and a ceramic phase. For example, the matrix 350 can include a nickel-containing phase and a ceramic phase. The nickel-containing phase can include nickel and / or a nickel alloy, and optionally, other additional metals. The ceramic phase can include stabilized zirconia, e.g., yttria- and / or scandia-stabilized zirconia, and / or doped ceria, e.g., ceria doped with gadolinia, yttria, and / or samaria. In some embodiments, the matrix 350 can preferably include a Ni-YSZ cermet, e.g., a Ni-(4-10)YSZ cermet.

[0039] In various embodiments, the matrix 350 can have a higher porosity than the active fuel electrode 310 because it is supported by the ribs 332, 342. Therefore, the matrix 350 can have more free space to accommodate the expansion of nickel oxide during the nickel oxide-nickel metal redox reaction. Therefore, the matrix 350 can have a higher nickel content, and therefore higher conductivity, than conventional anodes without compromising redox stability. For example, the matrix 350 can have a nickel content that is at least 10 mol % higher than the active fuel electrode 310. However, the total amount of nickel contained in the fuel electrode 300 can be lower than conventional anodes due to the lower nickel content of the ribs 332, 342.

[0040] The ribs 332, 342 can have a lower coefficient of thermal expansion (CTE) than the matrix 350. The inclusion of the ribs 332, 342 in the fuel electrode 300 can reduce the amount of matrix 350 included in the fuel electrode 300. As a result, the ribs 332, 342 can reduce the shrinkage of the green body fuel electrode. In particular, the high temperature and densification of the ribs 332, 342 can prevent or reduce warping of the adjacent electrolyte due to cooling of the matrix 350, which has a higher CTE.

[0041] Prior art anode-supported fuel cells generally require a fuel electrode thickness of at least 300 μm to prevent cell warping and produce a suitably flat cell, however, the strength provided by ribs 332, 342 allows the fuel electrode thickness to be significantly reduced.

[0042] In various embodiments, the ribs 332, 342 can have a height H1 ranging from about 15 μm to about 250 μm, e.g., from about 20 μm to about 100 μm, from about 25 μm to about 75 μm, or from about 25 μm to about 60 μm. However, the ribs 332, 342 can have any suitable height. The heights of the ribs 332, 342 can be the same or different. The ribs 332, 342 can have a width W ranging from about 0.25 mm to about 2 mm, e.g., from about 0.5 mm to about 1.5 mm, from about 0.75 mm to about 1.25 mm, or about 1 mm. The distance D between the ribs 332, 342 can be from about 5 mm to about 15 mm, e.g., from about 7 mm to about 13 mm, from about 8 mm to about 12 mm, or from about 9 mm to about 11 mm. However, the present disclosure is not limited to specific rib dimensions.

[0043] The first FGE layer 312 can have a thickness T1 ranging from about 7 μm to about 17 μm, e.g., from about 10 μm to about 14 μm, or from about 11 μm to about 13 μm. The second FGE layer 314 can have a thickness T2 ranging from about 2 μm to about 10 μm, e.g., from about 4 μm to about 8 μm, or from about 5 μm to about 6 μm. However, the present disclosure is not limited to any particular FGE layer thickness.

[0044] FIG. 4A is an exploded perspective view of an alternative fuel electrode 300B according to various embodiments of the present disclosure, and FIG. 4B is a cross-sectional view of a portion of the fuel electrode 300B of FIG. 4A. The fuel electrode 300B can be used in the electrochemical cells 100A and 100B of FIGS. 2A and 2B. The fuel electrode 300B can also be similar to the fuel electrode 300A of FIGS. 3A and 3B. Therefore, only the differences from the fuel electrode 300A of FIGS. 3A and 3B will be discussed in detail.

[0045] 4A and 4B, a fuel electrode 300B can include an active fuel electrode 310 positioned on a fuel electrode support 360. The fuel electrode support 360 can include a support grid 362 positioned within a conductive matrix 350. The support grid 362 can include coplanar first and second support ribs 364 and 366 that extend across each other in a longitudinal direction. For example, the first support ribs 364 can extend perpendicular to the second support ribs 366. The conductive matrix 350 can be positioned between, around, above, and / or below the support grid 362. In some embodiments, the fuel electrode 300B can include an additional fuel electrode support layer (not shown) positioned below the support grid 362.

[0046] In various embodiments, the fuel electrode support 360 can be formed by gravure printing the support grid 362 onto a substrate or web. Alternatively, the fuel electrode support 360 can be formed by screen printing, dispensing, or inkjet printing to form the support grid 362 without the need to stack different sheets of material. The conductive matrix 350 can be deposited onto the support grid 362 by tape casting using, for example, a doctor blade.

[0047] Solid oxide fuel cell (SOFC) systems operate at high temperatures ranging from about 750°C to about 950°C. During normal shutdown of an SOFC system, the fuel supply to the SOFC is stopped, which can result in oxygen influx to the anode electrode (i.e., fuel electrode) and the SOFC cooling from operating temperature to ambient temperature. If the steam supply to the SOFC cathode (i.e., fuel electrode) is stopped, the SOFC system can also experience oxygen influx.

[0048] This oxygen influx can cause rapid oxidation of Ni to NiO within the Ni-YSZ cermet fuel electrode, which can lead to a localized volume expansion of approximately 70% or more. Without sufficient porosity in the fuel electrode, this volume expansion can lead to electrode and / or electrolyte damage in the fuel electrode, potentially resulting in reactant crossover and / or catastrophic failure. In fuel electrode-supported cells, the fuel electrode support can account for a large portion of the volume change due to its relatively large thickness and / or its location on the outer surface of the cell.

[0049] According to various embodiments, reducing the rate of nickel oxidation can extend the time required for complete oxidation of Ni beyond the normal shutdown cycle time. In other words, reducing the rate of nickel oxidation can reduce the amount of nickel oxidation that occurs during cell cool-down (e.g., reduce the amount of NiO formed), resulting in a robust, high-power cell where oxidation does not cause damage to the fuel electrode. Furthermore, if the fuel electrode does oxidize completely, the mechanically robust support, fabricated from a high-fracture-toughness ceramic, prevents or reduces crack propagation.

[0050] Regarding ceramic materials suitable for use in the ceramic phase of the fuel electrode support 320 described above, metastable tetragonal 3-molar YSZ (3-YSZ) offers improved toughness compared to cubic 8-YSZ through a transformation strengthening mechanism. In particular, the crack tip, acting as a stress concentration point, initiates a localized phase change of ZrO from tetragonal to monoclinic. This localized phase change creates a high-energy phase boundary that increases the energy barrier to crack propagation. However, the metastability of 3-YSZ also leads to phase instability at high temperatures, in humid environments, and during thermal cycling.

[0051] According to various embodiments, the phase stability of a YSZ fuel electrode support material can be increased by increasing the YO content of the YSZ fuel electrode support material. For example, various embodiments can include a YSZ fuel electrode support material having a YO content in the range of about 4 mol% to about 10 mol%, e.g., about 5 mol% to about 10 mol%, about 6 mol% to about 10 mol%, about 7 mol% to about 10 mol%, or about 8 mol% to about 10 mol%.

[0052] The zirconia fuel electrode support material can be additionally doped with one or more metal oxide phase stabilizers, such as aluminum oxide (Al2O3), cerium oxide (CeO2), and / or titanium oxide (TiO2). The zirconia ceramic phase containing the additional phase stabilizer dopant can include (4-10)-YSZ or zirconia containing less than 4 mol% yttria, e.g., 0 mol% to 3 mol% yttria. The phase stabilizer dopant can reduce or prevent the gradual monoclinic phase transformation of the ceramic phase of the fuel electrode support material.

[0053] For example, a YSZ fuel electrode material can include 0.1 mol % to about 2 mol %, such as about 0.5 mol % to about 1 mol % Al2O3. In other words, the fuel electrode support material can include a material having the formula (ZrO2) (1-(x+y)) (Y2O3) x (Al2O3) ywhere x ranges from 0 to about 0.1, e.g., from about 0.04 to about 0.1, or from 0 to about 0.3, and y ranges from 0.001 to about 0.02. In some embodiments, y ranges from about 0.0025 to about 0.015, or from about 0.005 to about 0.01.

[0054] In some embodiments, the YSZ fuel electrode support material can include about 2 mol % to about 12 mol %, e.g., about 3 mol % to about 10 mol %, about 4 mol % to about 9 mol %, or about 5 mol % to about 8 mol % TiO. In other words, the fuel electrode support material can include a material having the formula (ZrO) (1-(x+y)) (Y2O3) x (TiO2) y where x ranges from 0 to about 0.1, for example, from about 0.04 to about 0.1, or from 0 to about 0.3, and y ranges from 0.02 to about 0.12.

[0055] In some embodiments, the YSZ fuel electrode material can include about 3 mol% to about 55 mol%, about 5 mol% to about 50 mol%, or about 10 mol% to about 45 mol% CeO. In other words, the fuel electrode support material can include a compound represented by the formula (ZrO). (1-(x+y)) (Y2O3) x (CeO2) y where x ranges from 0 to about 0.10, for example, from about 0.04 to about 0.1, or from 0 to about 0.3, and y ranges from 0.03 to about 0.55.

[0056] In some embodiments, the YSZ fuel electrode material can include two or more, such as all three, of alumina, titania, and / or ceria.

[0057] The present inventors have discovered that doping the YSZ fuel electrode support material with ceria can also beneficially retard the oxidation of the Ni phase. Ce is believed to act as an oxygen reservoir that retards the oxidation of Ni. In particular, the CeO2 dopant can form non-stoichiometric oxides in reducing environments, thereby retarding the oxidation of Ni under fuel conditions (e.g., when the fuel electrode comprises a SOFC anode supplied with fuel at steady-state cell operating temperatures). 4+ Ce 3+ and O in the form of H2O or CO2. 2- When airflow enters the cell chamber, O2 in the air reacts with available fuel to form H2O or CO2. As the pO2 in the cell chamber increases, Ce 3+ is re-oxidized to thermochemically produce H2 or CO, which can also react with further incoming air.

[0058] When a ceria dopant is utilized as an oxygen reservoir, the amount of ceria should be controlled to balance the amount of oxygen absorbed with the chemical shrinkage that occurs upon oxidation. For example, in a hot box containing approximately 2000 SOFC cells, the inventors have demonstrated that the SOFC cells are oxidized using yttria-stabilized Ce. 0.5 Zr 0.5 If the anode contains O, the air in the hot box (e.g., about 2 m 3 It has been determined that all oxygen can be removed from the air (air) using a ceria dopant concentration of 1000 ppm or less. However, other ceria dopant levels may be utilized to balance the better mechanical strength provided by lower ceria dopant levels, the higher storage volume provided by higher ceria dopant amounts, and the effects of expansion and contraction of the ceria doped ZrO2 upon redox.

[0059] In various embodiments, the inventors have also discovered that doping the nickel phase of the fuel electrode support with redox-controlling dopants, such as magnesium (Mg), calcium (Ca), and / or titanium (Ti), can reduce both the rate of Ni oxidation and reduction. It is noted that Ni, Ti, and Ca can be converted between oxide and metallic forms during redox (e.g., nickel oxide, titania, and / or calcium oxide in the fuel electrode can be reduced after cell fabrication and then re-oxidized after cell shutdown). However, Mg may remain in oxide form (MgO) in metallic Ni after Ni reduction during redox (e.g., it may remain as MgO inclusions).

[0060] Thus, the amount of redox-controlling dopant can be selected to ensure that the Ni oxidation rate is slow enough to prevent excessive nickel oxidation during shutdown operation, and that the nickel reduction rate is fast enough to reduce the nickel oxide in a reasonable time during system startup or restart. For example, the nickel-containing phase of the fuel electrode support can be doped with about 2 wt. % to about 8 wt. %, about 3 wt. % to about 8 wt. %, or about 4 mol. % to about 8 mol. % MgO, CaO, and / or TiO. In other words, the doped nickel in oxide form can be doped with a compound of the formula Ni 1-x D x O2, where D is a dopant selected from Mg, Ca, and Ti, and x ranges from about 0.02 to about 0.08.

[0061] Ca diffusion has been shown to form an insulating phase at the electrode / electrolyte interface of the fuel electrode. However, the inventors have discovered that a Ca-doped Ni fuel electrode material can be utilized in the fuel electrode support 320 without forming such an insulating phase because the distance between the fuel electrode support 320 and the electrolyte 200 prevents and / or significantly reduces Ca migration to the interface. Thus, in various embodiments, a Ca-doped Ni fuel electrode material can be included in the nickel-containing phase of the fuel electrode support 320. However, Ca can be excluded from the nickel-containing phase of the first FGE layer 312 and / or the second FGE layer 314.

[0062] Thus, the redox-controlling dopants of the present disclosure can slow the rate of nickel oxidation, reduce nickel coarsening, and / or reduce diffusion of nickel mesh into the fuel electrode support. The redox-controlling dopants can also reduce cell voltage loss due to redox cycling of the fuel electrode and / or sulfur poisoning compared to a fuel electrode without the redox-controlling dopant.

[0063] According to various embodiments, fuel electrodes comprising the above materials can be fabricated by any common ceramic processing method, including, but not limited to, tape casting, slot die coating, and / or screen printing.

[0064] The fuel cells and electrolysis cells of the disclosed embodiments are designed to reduce greenhouse gas emissions and have a positive impact on the climate.

[0065] Any one or more features from any one or more of the embodiments may be used in any suitable combination with any one or more features from one or more of the other embodiments. While the foregoing represents particularly preferred embodiments, it will be understood that the present invention is not limited thereto. Those skilled in the art will recognize that various modifications can be made to the disclosed embodiments, and that such modifications are intended to be within the scope of the present invention. All publications, patent applications, and patents cited herein are hereby incorporated by reference in their entirety.

Claims

1. an electrolyte having a first side and an opposite second side; an oxygen electrode located on the first side of the electrolyte; a fuel electrode support; an active fuel electrode positioned between the fuel electrode support and the second side of the electrolyte; Equipped with 1. An electrochemical cell, wherein the fuel electrode support comprises a cermet including a nickel-containing phase and a ceramic phase including 4 mole percent (mol%) to 10 mol% yttria-stabilized zirconia ((4-10)-YSZ) or zirconia doped with at least one of alumina, ceria, or titania.

2. 10. The electrochemical cell of claim 1, wherein the ceramic phase comprises the (4-10)-YSZ doped with about 0.1 mol % to about 1 mol % of the alumina.

3. 10. The electrochemical cell of claim 1, wherein the ceramic phase comprises the (4-10)-YSZ doped with about 3 mol % to about 55 mol % of the ceria.

4. 10. The electrochemical cell of claim 1, wherein the ceramic phase comprises the (4-10)-YSZ doped with about 2 mol % to about 12 mol % of the titania.

5. 10. The electrochemical cell of claim 1, wherein the nickel-containing phase comprises Ni doped with about 2 mol% to about 8 mol% MgO.

6. 10. The electrochemical cell of claim 1, wherein the nickel-containing phase comprises Ni doped with about 2 mol % to about 8 mol % CaO.

7. The nickel-containing phase comprises about 2 mol % to about 8 mol % TiO ２ 10. The electrochemical cell of claim 1, comprising Ni doped with

8. 10. The electrochemical cell of claim 1, wherein the electrochemical cell is a fuel electrode-supported cell or a co-supported cell.

9. the electrolyte comprises scandia-stabilized zirconia (SSZ), yttria-stabilized zirconia (YSZ), yttria-ceria-stabilized zirconia (YCSZ), ytterbia-ceria-scandia-stabilized zirconia (YbCSSZ), or mixtures thereof; 10. The electrochemical cell of claim 1, wherein the active fuel electrode comprises a cermet comprising a nickel-containing phase and a doped ceria or stabilized zirconia ceramic phase.

10. 10. The electrochemical cell of claim 1, wherein the electrochemical cell comprises a solid oxide fuel cell, the oxygen electrode comprises a cathode electrode, the active electrode layer comprises an anode electrode, and the fuel electrode support comprises an anode support.

11. 10. The electrochemical cell of claim 1, wherein the electrochemical cell comprises a solid oxide electrolysis cell, the oxygen electrode comprises an anode electrode, the active electrode layer comprises a cathode electrode, and the fuel electrode support comprises a cathode support.

12. An electrochemical cell stack comprising the electrochemical cells of claim 1 separated by interconnects.

13. an electrolyte having a first side and an opposite second side; an oxygen electrode located on the first side of the electrolyte; a fuel electrode support; an active fuel electrode positioned between the fuel electrode support and the second side of the electrolyte; Equipped with An electrochemical cell wherein the fuel electrode support comprises a cermet including a ceramic phase and a nickel-containing phase including nickel doped with at least one of magnesium oxide, calcium oxide, or titanium oxide.

14. 14. The electrochemical cell of claim 13, wherein the nickel-containing phase comprises about 2 mol % to about 8 mol % Ni doped in the magnesium oxide.

15. 14. The electrochemical cell of claim 13, wherein the nickel-containing phase comprises about 2 mol % to about 8 mol % Ni doped with the calcium oxide.

16. 14. The electrochemical cell of claim 13, wherein the nickel-containing phase comprises about 2 mol % to about 8 mol % Ni doped with the titanium oxide.

17. 14. The electrochemical cell of claim 13, wherein the ceramic phase comprises 4 mole percent (mol%) to 10 mol% yttria-stabilized zirconia ((4-10)-YSZ) or zirconia doped with at least one of alumina, ceria, or titania.

18. The ceramic phase is about 0.1 mol % to about 1 mol % of said alumina; about 3 mol % to about 55 mol % of the ceria; or about 2 mol % to about 12 mol % of said titania; 18. The electrochemical cell of claim 17, comprising (4-10)-YSZ doped with

19. 14. An electrochemical cell stack comprising the electrochemical cells of claim 13 separated by an interconnect, wherein the electrochemical cells comprise solid oxide fuel cells, the oxygen electrode comprises a cathode electrode, the active electrode layer comprises an anode electrode, and the fuel electrode support comprises an anode support.

20. 14. An electrochemical cell stack comprising the electrochemical cells of claim 13 separated by an interconnect, wherein the electrochemical cells comprise solid oxide electrolysis cells, the oxygen electrode comprises an anode electrode, the active electrode layer comprises a cathode electrode, and the fuel electrode support comprises a cathode support.

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