Method of making solid oxide electrochemical reactors with printed molds

Abstract

A method is disclosed for making a solid oxide electrochemical cell stack, including steps of providing a first moldable composition having a first liquid composition and first particles adapted to form an interconnect when sintered, providing a second moldable composition comprising having a second liquid composition and second particles adapted to form an anode when sintered, providing a third moldable composition having a third liquid composition and third particles adapted to form an electrolyte when sintered, and providing a fourth moldable composition having a fourth liquid composition and fourth particles adapted to form a cathode when sintered. An unsintered electrochemical cell stack is produced by sequentially printing a first layer mold and depositing within the first layer mold one of the first, second, third and fourth moldable compositions. Subsequent layer molds and are printed and another of the first, second, third and fourth moldable compositions is deposited within each of the subsequent layer mold.

Description

UNITED STATES PATENT APPLICATION ofNicholas Farandos Christopher Matson Scott WoolstonHuntington Tracy Hall Pawel Plonczak Joseph Varley and David R. Hall forMethod of Making Solid Oxide Electrochemical Reactors with Printed MoldsMETHOD OF MAKING SOLID OXIDE ELECTROCHEMICAL REACTORS WITH PRINTED MOLDSCross-Reference to Related Applications

[0001] This application is a continuation-in-part of United States Provisional Applications No. 63 / 611,765, filed December 18, 2023 and entitled Method of Making Solid Oxide Electrochemical Reactors; No. 63 / 611,766 filed December 18, 2023 and entitled Method of Making Solid Oxide Electrochemical Reactors with Printed Molds; No. 63 / 611,768 filed December 18, 2023 and entitled Method of Making a Solid Oxide Electrochemical Reactor in a Housing; No. 63 / 668,752 filed July 8, 2024 and entitled Solid Oxide Fuel Cell Stacks and Methods of Making; and No. 63 / 668,754 filed July 8, 2024 and entitled Solid Oxide Fuel Cell Stack with Integral Housing. The entire disclosures of these five applications, including the drawings, are incorporated herein by reference.TECHNICAL FIELD

[0002] The present invention relates to the field of solid oxide electrochemical reactors and methods of making them.BACKGROUND

[0003] Solid oxide electrochemical reactors (SOERs), defined as having a metal oxide (ceramic) electrolyte, operate at high temperatures, typically 600 - 1000 C where the ionically- conducting electrolyte material is sufficiently conductive. Consequently, SOERs offer several technical and economic advantages over low temperature alternative electrochemical technologies, such as polymer electrolyte membrane fuel cells (PEM) and alkaline reactors. These advantages include i) higher electrical efficiencies; ii) non-requirement for precious metal catalysts; and iii) ability to operate with a wide variety of fuels including reformed hydrocarbons, gasified coal, and hydrogen.

[0004] There are two primary modes of operating SOERs; i) 'fuel cell mode'; and ii) 'electrolysis mode', respectively the conversion of chemical to electrical potential, and viceversa. Notably, other operating modes exist where the electrical potential is neither supplied nor extracted via an external circuit, but used in-situ. Reactors operating in fuel cell and electrolysis mode are called Solid Oxide Fuel Cells (SOFCs) and Electrolysers (SOEs), respectively.

[0005] Henry Cavendish (1731 - 1810) is generally credited with the first observation of solid-state electrochemistry through his findings on the temperature-dependent conductivity of glass in 1774; the electrolytic nature of this glass was published less than 100 years later. The most significant event in history for SOERs occurred in 1899, when Walther Nernst (1864 - 1941) discovered the so called 'Nernst mass' of a conducting ceramic containing 85 mol% ZrO2 and 15 mol% Y2O3, which is still the most common electrolyte material for SOERs, albeit with a Y2O3 concentration of 8 mol%, which is the minimum amount required to stabilize the cubic lattice structure. The conceptual solid oxide fuel cell (SOFC) was first demonstrated in 1937 using a doped zirconia electrolyte, FesO4 cathode, and C anode. Understandably, these electrode materials were poorly suited to SOFCs due to their instability with the reactant and product gases. Shortly after, German scientist Carl Wagner (1901 - 1977) proved that the conductivity of doped-zirconia electrolytes resulted from the presence of oxygen vacancies that were mobile under an oxygen partial pressure gradient. For this reason he is considered the founder of solid state chemistry. In 1957, Wagner published a subsequent paper that laid out the theoretical foundation for SOFCs. Several additional important discoveries were made in the 20th century that significantly improved the performance of SOERs:• The discovery of rare-earth transition metal perovskites that provided enhanced oxygen oxidation / reduction kinetics, particularly doped-lanthanum manganite.• The use of Ni metal as the electronically conducting phase within composite anodes, that provided favorable electrochemical kinetics in the fuel-electrode, and remains the standard electronically conducting material in SOERs.• The co-sintering of composite anodes with the electrolyte at high temperatures, which improved the gas-tightness of the electrolyte and reaction site density, dramatically increasing electrochemical performance and facilitating lower-temperature operation.The oxygen-electrode could then be applied subsequently, and sintered at a lower temperature, preventing its chemical reaction with the electrolyte.

[0006] SOFCs and SOEs are presently deployed in applications including stationary power generation, combined heat and power systems, and CO2 reduction. Advances in materials science, engineering, and understanding of degradation mechanisms have further paved the way for SOERs to become promising candidates for efficient, environmentally friendly energy conversion in various industrial and residential settings.

[0007] Nevertheless, creating SOERs involves several challenges due to the complex interplay of materials, operating conditions, and performance requirements. Some of the key challenges faced during the development and manufacturing of SOERs are described below:

[0008] High Operating Temperatures: SOERs typically operate between 600-1000°C which poses challenges in terms of the materials' thermal compatibility, thermal management, and corrosion. High temperatures can lead to thermal stress, degradation of materials, and unwanted inter-material chemical reactions.

[0009] Materials Compatibility: SOER materials must be stable in the aggressive chemical and thermal environments typically found within these reactors, while maintaining their electrochemical and mechanical properties. Compatibility between electrolytes, electrodes, and interconnects is essential to prevent degradation and ensure long-term stability.

[0010] Component degradation and lifetime: degradation mechanisms including particle coarsening, reaction site poisoning, and mechanical stresses can result in reduced cell performances over time by mechanisms including decreasing reaction site densities, degradation of interfaces between functional layers, and loss of interfacial electrical conductivities. Developing systems and cell designs that mitigate degradation and thus have longer lifetimes is essential for practical applications.

[0011] Sealing and Gas Management: ensuring gas-tight electrolytes, interconnects, and seals and effective management of reactant gases within the cell stack is essential. Anode to cathode leakage compromises efficiency, performance, and safety.

[0012] Carbon Deposition: when operating with hydrocarbon fuels in SOFC mode, carbon deposition may occur within the anode surfaces and lead to performance loss and even catastrophic reactor failure. Mitigating carbon deposition is essential during operation.

[0013] Cost and Manufacturing: developing cost-effective manufacturing processes for producing high-quality, uniform, and durable ceramic components is challenging. Advanced materials and fabrication techniques often add to production costs.

[0014] Stack Integration: designing and assembling stacks that manage thermal expansion differences, ensure adequate sealing between anode, cathode, and the environment, and maintain the required gas supply / removal necessitates complex engineering.

[0015] Start-Up and Thermal Cycling: rapid temperature changes during start-up and shut-down cycles can cause thermal stresses to form, impacting stack integrity. Managing thermal cycling is essential to mitigate mechanical failures.

[0016] Stack Efficiency and Scaling: operating at high electrical efficiencies while scaling up from single cells to full stacks is a challenging engineering exercise.

[0017] Safety: high operating temperatures, particularly with flammable and oxidant gases, presents a safety challenge. Safe operation and mitigation of safety incidents is paramount.SUMMARY

[0018] In a first aspect, the disclosure provides a method of making a solid oxide electrochemical cell stack, including the step of providing a first moldable composition having a first liquid composition and first particles adapted to form an interconnect when sintered. The method also includes the step of providing a second moldable composition comprising having a second liquid composition and second particles adapted to form an anode when sintered. The method further includes the step of providing a third moldable composition having a third liquid composition and third particles adapted to form an electrolyte when sintered. The method still further includes the step of providing a fourth moldable composition having afourth liquid composition and fourth particles adapted to form a cathode when sintered. An unsintered electrochemical cell stack is produced by sequentially printing a first layer mold and depositing within the first layer mold one of the first, second, third and fourth moldable compositions. Subsequent layer molds and are printed and an other of the first, second, third and fourth moldable compositions is deposited within each of the subsequent layer mold. Optionally, one of the first, second, third or fourth moldable compositions is deposited without a printed layer mold. The printing and depositing process is repeated so as to produce unsintered interconnects, anodes, electrolytes and cathodes, each having a predetermined size and shape. The order of depositing each moldable composition is set so as to produce a stack of unsintered cells, each comprising an unsintered anode, an unsintered electrolyte and an unsintered cathode, and so as to provide an unsintered interconnect between each unsintered cell. The unsintered electrochemical cell stack is sintered with sufficient heat and for a sufficient time, so as to convert the first, second, third, and fourth particles to the desired structure for operation of the electrochemical cell stack. The sintering also forms an operational electrochemical stack wherein the interconnects are non-porous and conduct electrons, but not ions. The anodes are porous and conduct electrons and ions. The electrolytes are non-porous and conduct ions, but not electrons. The cathodes are porous and conduct electrons and ions.

[0019] Further aspects and embodiments are provided in the foregoing drawings, detailed description and claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The following drawings are provided to illustrate certain embodiments described herein. The drawings are merely illustrative and are not intended to limit the scope of claimed inventions and are not intended to show every potential feature or embodiment of the claimed inventions. The drawings are not necessarily drawn to scale; in some instances, certain elements of the drawing may be enlarged with respect to other elements of the drawing for purposes of illustration. Reference numbers are used consistently throughout the drawings to indicate corresponding elements, and descriptions provided in the specification should beunderstood as referring to like elements in the drawings unless otherwise noted. Schematic view and diagrams are intended to illustrate the logical flow or structure of the invention but are not necessarily indicative of physical arrangements or hardware configurations unless specifically stated.

[0021] Figure 1 is schematic view of a single SOER cell.

[0022] Figure 2 is a magnified view, showing the various components of the SOER ofFigure 1.

[0023] Figure 3 is a cross-sectional schematic view of the SOER of Figure 1.

[0024] Figure 4 is a cross-sectional schematic view, perpendicular to the cross-sectional view of Figure 3.

[0025] Figure 4a is a cross-sectional schematic view of an anode layer with zig-zag gas channels.

[0026] Figure 4b is a cross-sectional schematic view of an anode layer with branched gas channels, expanding the number of channels toward the outlets.

[0027] Figure 4c is a cross-sectional schematic view of an anode layer with branched gas channels, reducing the number of channels toward the outlets.

[0028] Figure 4d is a cross-sectional schematic view of an anode layer with gas channels that get larger in diameter toward the outlets.

[0029] Figure 4e is a cross-sectional schematic view of an anode layer with gas channels that get smaller in diameter toward the outlets.

[0030] Figure 5 is a cross-sectional schematic view, of a SOER cell with a functional section and current collection section in both electrodes.

[0031] Figure 6 is a cross-sectional schematic view, perpendicular to the cross-sectional view of Figure 5.

[0032] Figure 7 is a schematic perspective view of housing with an SOFC stack inside.

[0033] Figure 8 is a horizontal cross-sectional view of the housing and SOFC stack of Figure 7.

[0034] Figure 9 is a vertical cross-sectional view of the housing and SOFC stack of Figure 7.

[0035] Figure 10 is a vertical cross-sectional view, perpendicular to that of Figure 9, of the housing and SOFC stack of Figure 7.

[0036] Figure 11 is a schematic view of a housing for a SOFC incorporating a heat exchanger.

[0037] Figure 12 is a view similar to Figure 11, with the top removed and illustrates the flow path of the gas passing through the anode.

[0038] Figure 13 is a bottom view of the housing of Figure 11, with the heat exchanger removed, showing the flow path of the gas passing through the cathode.

[0039] Figure 14 is a perspective view of a horizontal slice of a single stage of the anode heat exchanger.

[0040] Figure 15 is a cross-sectional view of one stage of the heat exchanger.

[0041] Figure 16 is a schematic flow diagram showing an embodiment of the balance of plant for the SOFC stack of the present invention.

[0042] Figure 17 is a schematic flow diagram showing an embodiment of the balance of plant for the SOFC stack, including a subsystem to capture and utilize heat generated by the SOFC stack.

[0043] Figure 18 is a schematic diagram of a system to deposit the multiple layers of moldable compositions to build an unsintered SOER stack.

[0044] Figure 19 is similar to Figure 18, with the tray moved to a different station.

[0045] Figure 20 is a schematic diagram of a turntable method for producing unsinteredSOERs by MoldJet Technology.

[0046] Figure 21 is similar to Figure 20, with additional stations.

[0047] Figure 22 is similar to Figure 21, with additional stations.

[0048] Figure 23 is a Scanning Electron Micrograph (SEM) of an anode, electrolyte and cathode.

[0049] Figure 24 is a chronopotentiometry graph.

[0050] Figure 25 is a current-voltage (IV) curve showing how the current density changes with cell potential difference at 850, 900, and 950 C.

[0051] Figure 26 is a Nyquist plot of a co-sintered cell.DETAILED DESCRIPTION

[0052] The following description recites various aspects and embodiments of the inventions disclosed herein. No particular embodiment is intended to define the scope of the invention. Rather, the embodiments provide non-limiting examples of various compositions, and methods that are included within the scope of the claimed inventions. The description is to be read from the perspective of one of ordinary skill in the art. Therefore, information that is well known to the ordinarily skilled artisan is not necessarily included.Definitions

[0053] The following terms and phrases have the meanings indicated below, unless otherwise provided herein. This disclosure may employ other terms and phrases not expressly defined herein. Such other terms and phrases shall have the meanings that they would possess within the context of this disclosure to those of ordinary skill in the art. In some instances, a term or phrase may be defined in the singular or plural. In such instances, it is understood that any term in the singular may include its plural counterpart and vice versa, unless expressly indicated to the contrary.

[0054] As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. For example, reference to "a substituent" encompasses a single substituent as well as two or more substituents, and the like.

[0055] As used herein, "for example," "for instance," "such as," or "including" are meant to introduce examples that further clarify more general subject matter. Unless otherwise expressly indicated, such examples are provided only as an aid for understanding embodiments illustrated in the present disclosure and are not meant to be limiting in any fashion. Nor do these phrases indicate any kind of preference for the disclosed embodiment.

[0056] As used herein, the term "solid oxide electrochemical cell," (SOEC) is meant to refer to an electrochemical cell that converts fuel and oxygen into electricity and heat through a high-temperature process involving ceramic electrolytes or (b) uses electricity and to generate hydrogen and oxygen from water.

[0057] As used herein, the terms "solid oxide electrochemical reactor" (SOER) and SOEC stack are meant to refer to a stack of SOEC's.

[0058] As used herein, the terms "fuel cell" is meant to refer to an electrochemical device that generates electricity by converting the chemical energy of a fuel, such as hydrogen, directly into electrical energy, with water and heat as byproducts. Unless otherwise indicated, the fuel cells referred to herein are solid oxide fuel cells (SOFCs).

[0059] As used herein, the terms "solid oxide fuel cell," and "SOFC" are meant to refer to electrochemical devices that convert fuel and oxygen into electricity and heat through a high-temperature process involving ceramic electrodes and electrolytes. A SOFC comprises an anode, also referred to as a fuel electrode, and cathode, also referred to as an air electrode, separated by an electrolyte and a current collection section on both ends. Although the interconnect is not technically part of the cell that generates electricity, its function in passing current through the stack and out of the stack is crucial. As such, the interconnect will generally be considered part of the cell in the discussion below. Also, the term "repeat unit" is intended to refer to the anode, electrolyte, and cathode with an interconnect.

[0060] As used herein, the term "stack," as used in the terms "solid oxide electrochemical reactor stack," "SOER stack," "fuel cell stack," "solid oxide fuel cell stack," and"SOFC stack" is meant to refer to a stack of electrochemical cells in electrical series with aninterconnect on both ends. The cells in the stack may be arranged vertically, horizontally, coaxially or otherwise.

[0061] As used herein, the term "component," as in, for example, "SOER Component" or "SOFC Component" refers to a component of the cell or repeat unit, such as the anode (fuel electrode), cathode (air electrode), electrolyte and interconnect.

[0062] As used herein, "anode" is meant to refer to the electrode where an oxidation reaction occurs. The anodes may also be referred to as the fuel electrodes or the negative electrodes. It is also noted that in some embodiments, the anode comprises two sections, namely, the functional anode section and the anode current collection section. For simplicity, unless otherwise indicated, the terms "anode" and "fuel electrode" refer to both of these sections.

[0063] As used herein, "cathode" is meant to refer to the electrode where a reduction reaction occurs. The cathodes may also be referred to as the air electrodes or positive electrodes. It is also noted that the cathode preferably comprises two sections, namely, the functional cathode section and the cathode current collection section. For simplicity, unless otherwise indicated, the terms "cathode" and "air electrode" refer to both of these sections.

[0064] As used herein, "electrolyte" is meant to refer to a solid material that allows the conduction of ions between the anode and cathode, enabling electrochemical reactions to occur.

[0065] As used herein, "interconnect" is meant to refer to a material that connects individual cells in a stack in series and provides electrical connections.

[0066] As used herein, the term "fuel" is meant to refer to the material that undergoes electrochemical oxidation to produce electricity. The preferred fuel is either hydrogen or hydrocarbons, such as methane, which are reformed to produce hydrogen and carbon monoxide.

[0067] As used herein, the term "air" will normally refer to ambient air or dehydrated ambient air, but may also include other gas mixes containing oxygen.

[0068] As used herein, the term "Yttrium stabilized zirconia" or its abbreviation "YSZ" is intended to refer to a zirconium dioxide stabilized with yttrium oxide to achieve high ionic conductivity and structural stability at high temperatures.

[0069] As used herein, the term "scandia stabilized zirconia" or its abbreviation "ScSZ" is intended to refer to a zirconium dioxide stabilized with scandium oxide to achieve high ionic conductivity and structural stability at high temperatures.

[0070] As used herein, the term "Ceria stabilized zirconia" or its abbreviation "CeSZ" is intended to refer to a zirconium dioxide stabilized with cerium oxide to achieve high ionic conductivity and structural stability at high temperatures.

[0071] As used herein, the abbreviation "LSCrF" is intended to refer to lanthanum strontium iron chromium oxide.

[0072] As used herein, the terms "sinter" and "sintering" refer to the high temperature process whereby powders are made to coalesce into a dense or porous mass by heating it without a phase change.

[0073] As used herein, the term "green body" is used interchangeably with "unsintered stack" and the like, to refer to the structure that is put together before sintering.

[0074] Herein, the term "bisque" is used as a verb to refer to the heating process by which the green bodies are heated to a relatively low temperature to harden it and prepare it for sintering. In this process, all or substantially all remaining organics are burned out of the green body.

[0075] As used herein, the term "brown body" is intended to refer to the unsintered stack that has been bisqued, i.e. dried and had the organics, such as pore formers, dispersants, binders, etc., substantially burned or dissolved out of the stack.

[0076] As used herein, the term "Tsinter" is used to refer to the operating temperature at which the green body is sintered to produce the operational SOER.

[0077] As used herein, the term "sinter shrinkage" is used to refer to the amount of shrinkage during the sintering step, as measured in the decrease in the lateral dimension.When referring to the simultaneous sintering of an unsintered stack, it is a measurement of the shrinkage of the stack as a whole. When referring to the shrinkage of an individual unsintered component of the stack, the term "unconstrained sinter shrinkage" is used. In other words, if that individual component is sintered by itself, and not constrained by the adjacent components in the stack; the unconstrained sinter shrinkage would give an indication of the stresses induced by simultaneous sintering.

[0078] As used herein, the term "difference in linear sinter shrinkage percentage," or the like, is meant to refer to the difference in the linear sinter shrinkage percentages of two different unconstrained layers. To be clear, this term refers to the difference in the percentages, not the percentage of the difference. For example, if an anode had a linear sinter shrinkage of 19% and a cathode had a linear shrinkage of 20%, the different in linear sinter shrinkage is 1.

[0079] As used herein, the term "coefficient of thermal expansion" and "thermal expansion coefficient," along with the abbreviation "CTE" and symbol "a", refer to the change in a material's length with a change in temperature. As used here, CTE is expressed as a change in length per unit rise in temperature. For purposes here, CTE is expresses as p m1K-1, which can also be expressed as (p / m) / °K or ppm / °K.

[0080] As used herein, the terms "MoldJet Technology," "MoldJet Process" and "MoldJet Method" refers to the methods and apparatuses developed by Tritone Technologies Ltd., which is described below and in the several published US Patent Applications of Tritone. It is also noted that the term MOLDJET® is a registered trademark of Tritone Technologies Ltd.

[0081] As used herein, the term "current-voltage curve" or "IV curve" is intended to refer to a graphical representation of the relationship between the output voltage and the current density of the SOER cell or stack of SOER cells.

[0082] As used herein, the term "chronopotentiometry graph" or "chronopotentiometry chart" is intended to refer to a graphical representation of the variation of current density over time when a constant potential is applied to the SOER cell or stack of SOER cells.

[0083] As used herein, the terms "Nyquist plot" and "Nyquist graph" are intended to refer to a graphical representation of a SOER cell's or stack of SOER cells' electrochemical impedance with varying frequency of applied potential.Overview

[0084] The invention provides a method of making a SOER stack, such as an SOFC, in a process that produces an integral, monolithic stack that is simultaneously sintered, binding all components to each other without the need for a compressive seal, and that mechanically supports itself, optimizing materials utilization.

[0085] An important aspect of the present invention is the selection of materials and compositions for the four components of the SOER repeat units, so as to produce a structure that can be successfully, simultaneously sintered and that can withstand cycling to the high operating temperatures of the SOER, typically between 600 and 1000 °C. To this end, the materials that go into producing the green body are selected with this in mind.

[0086] As one factor, the moldable compositions, namely the powders and other ingredients, are selected so that the components of the green body, namely the unsintered interconnects, anodes, cathodes, and electrolytes, have an unconstrained sinter shrinkage within 20 % of each other. More preferably, the difference in unconstrained sinter shrinkages is less than 10 %. Most preferably, the difference in unconstrained sinter shrinkages is less than 5 %. Stated another way, it is preferable that the difference in linear sinter shrinkage percentage is equal to or less than 5. More preferably, this difference in percentages is less than 2. Most preferably, this difference in percentages is less than 1.

[0087] As another factor, the particles that will be sintered to form the components of the SOER stack are selected so that that, in the operation of the stack, differences in thermal expansion between the components do not cause undue stress on the stack during the cycling through high temperatures during operation. For this reason, the powders that make up the interconnect, electrolyte, cathode and anode are preferably selected so that these three components have a CTE within 3 p m1K1. More preferably, the three components have a CTE within 2 p m1K1, and most preferably, within 1 p m1K1.

[0088] Upon sintering, the stack with its functional components of the cell are operational. This means that the interconnects are non-porous and conduct electrons, but not ions, the anodes are porous and conduct electrons (during operation) and ions, the electrolytes are non-porous and conduct ions, but not electrons, and the cathodes are porous and conduct electrons and ions. It is noted that the terms "non-porous," "conduct" and "not conduct" are used with their typical relative meaning and not in the absolute. For example, the interconnect conducts electrons substantially better than ions and the electrolyte conducts ions substantially better than electrons. Also, all of these materials have some limited degree of porosity and have some limited degree of both ion and electron conduction. Nevertheless, in order to operate with acceptable losses, the relative rates for one sort of transport must be substantially higher than another.Cell

[0089] Each cell or repeat unit in a solid oxide electrochemical cell stack consists of four functional components, namely, an interconnect, an anode, an electrolyte and a cathode. If the repeat unit is at the end of a cell stack, it will have an interconnect on both ends. Each of these components is discussed in detail below. Each of these components may be made up of one or more different compositions.

[0090] A cell will have one of each of the functional components arranged as follows: Each cell includes an interconnect at both ends. Unless that cell is at one end or the other of the stack, each interconnect will be shared by adjacent cells. Those shared interconnects will be adjacent to a cathode from one cell on one side the interconnect, and adjacent to an anode from the other cell on the other side of the interconnect. An electrolyte is positioned between otherwise adjacent cathodes and anodes in the same cell.

[0091] A basic, single SOER cell, is depicted in Figure 1. It is noted that the thicknesses of the layers are not shown to scale but are drawn for easier reference. In this embodiment, a SOFC cell 100 is shown with one interconnect 101 on the top and another interconnect 102 on the bottom. These interconnects are configured to conduct electrons into the cathode 103 and out of the anode 107. They are also configured to block the passages of gases and ionsbetween cells. A cathode 103 is just beneath the interconnect 101. The cathode in this SOFC is configured to pass air through a cathode gas distribution network, depicted and described in more detail below. Beneath cathode is an electrolyte 105. As described in more detail below, the electrolyte 105 is configured to pass ions, in this case oxide O2' ions, from the cathode to the anode. The electrolyte is also configured to block the passage of gases and the passage of electrons. Beneath the electrolyte is an anode 107. As with the cathode, the anode includes a gas distribution network that, in this case, passes fuel, such as hydrogen or a hydrocarbon through the anode and exhausts water and any unused fuel. As noted above, the interconnect 102 conducts electrons out of the anode.

[0092] In the preferred embodiment, these functional components are generally planar and rectangular in shape, thus producing a cell that can be described as a rectangular prism. Nevertheless, other shapes for the functional components are contemplated, such as concentric tubes and stacked domes, thus resulting in cells of a different shape. In one alternative embodiment, the components are disk shaped with a hole through the middle to allow for either air or the fuel to pass through.Cell Stack

[0093] The SOER is made up of multiple cells in a stack. The cell stack is made of these multiple cells that are adjacent to one another and with an interconnect on both ends. When the cells are the shape of rectangular prisms, the stack consists of a vertical or horizontal placement of several cells adjacent one to the other, with the cathode one side of and adjacent to the interconnect and electrolyte, one on each side. A stack consists of multiple cells which are manufactured and processed together as one single body. Preferably, there are more than 20 cells in each stack, more preferably around 50 cells.

[0094] Figure 2 is a schematic view of a simple stack 110 with four cells. Each cell comprises an interconnect 111, an anode 113, an electrolyte 117 and a cathode 119. Within the anodes are gas channels 115, through which the fuel is passed through the cell and out of which water and unused fuel are exhausted from the cell. Preferably, the fuel is hydrogen gas (H2) and carbon monoxide (CO) which are produced by steam reformation of methane (CH4).Within the cathodes 119 are gas channels 121, through which air is passed into and out of the cathodes. Preferably, the air is ambient air. Alternatively, it may be enhanced with more or less oxygen in order to tune the performance of the stack.

[0095] By arranging the anode gas channels and the cathode gas channels perpendicularly, it is possible to feed fuel into the anodes from one side of the stack and to exhaust water and unused fuel from the opposite side of the stack. It also makes it possible to feed air into the cathodes from an orthogonal side of the stack and to exhaust the air from the side opposite that orthogonal side. As will be seen and explained in connection with Figures 7 and 8, this allows one to design a stack cartridge that keeps these gas streams separate.

[0096] Figures 3 and 4 are vertical cross sections at right angles to each other through the stack of Figure 2. Figure 3 depicts the gas channels 115 in the anodes 113 coming out of the page, while the gas channels 121 in the cathodes 119 are running across the page. Figure 4 depicts the gas channels 121 in the cathodes 119 coming out of the page, while the gas channels 115 in the anodes 113 are running across the page. These cross sections also show the interconnects 111 and the electrolytes 117.

[0097] In its simplest from, the gas distribution network in the anode and, as discussed below, the cathode, are straight channels from one end to the other. These channels may have a rectangular cross section, or may be circular or any other shape in cross section. The channels may have a uniform diameter along their length. Alternatively, the diameter may be varied along the length, in order to fine tune the flow rate, pressure and penetration of the gasses traveling through the anode or cathode. For example, as shown in Figure 4d, the channels in the anode layer 331 are smaller at the inlets 333 and larger at the outlets 335. This can increase the pressure of the fuel gas to increase penetration in the anode layer as it moves toward the outlet. In Figure 4e, the channels in the anode 341 are larger at the inlets 343 and smaller at the outlets 345. This can increase the rate of flow of the fuel gas in the anode as it moves toward the outlets.

[0098] In addition to being straight, the channels may have a sinusoidal, zig=zag or other path, again to fine tune the flow rate, pressure and penetration of the gases. As seen inFigure 4a, the channels 303 in the anode layer 301 are zig-zag in shape. In some embodiments, the channels are branched so as to divide the flow of the gases from one side to the other of the anode or cathode. This is shown in Figure 4b, wherein the channels in the cathode layer 307 are branched at 313, so that there are more outlets 311 than inlets 309. In other embodiments, the channels are branched so as to combine channels into fewer channels from one side to the other of the anode or cathode. This is depicted in Figure 4c, which shows the channels in the anode layer 321 being combined at branches 327 so that there are more inlets 323 than outlets 325. Fortuitously, the MoldJet process described below makes possible the fine tuning of the gas channels in order to achieve the optimum distribution of the gases within the anode and cathode.

[0099] Because a stack puts individual cells in series, a greater number of cells in the stack produces a higher voltage. For example, if the voltage across a single cell in the stack is 0.7 volts, a stack of 50 cells produces a theoretical voltage of 35 volts, while a stack of 200 cells produces a theoretical voltage of 140 volts. The actual voltages may be affected by factors such as ohmic losses, etc.[000100] Preferably, the cross section of the stack is rectangular, and its width and its depth are greater than 15cm. The amount of current produced by each SOFC cell will vary depending on several factors. One such factor is the width and depth of the cells. Typically, current densities range between 100 and 600 mA / cm2. Thus, the current produced by a 15 cm square cell could be between 22.5 A and 112.5 A. The current produced by a 50 cm square cell could be between 250 A and 1250 A.[000101] Naturally, the height of the stack is determined by the thickness of each cell and the number of cells. Preferably, the height of the stack is greater than 50mm.Interconnect[000102] The interconnect serves to electrically connect individual cells in the SOER stack.In particular, the interconnect provides an electrical pathway to conduct electrodes from the anode of one cell to the cathode of the adjacent cell in the SOER stack. The interconnects at both ends of the stack are used to electrically connect the stack to the external circuit.[000103] The interconnect also functions to separate the gases, namely the fuel (preferably hydrogen or a hydrocarbon) in the anode of one cell with the air or other oxygen containing gas in the cathode of the adjacent cell in the SOER stack.[000104] The interconnect must also be formed from materials that are chemically and thermally compatible with the other component in the SOER. For example, the interconnect should be made from materials that resist corrosion and interfacial reactions with the electrode materials and the gases in the anodes and cathodes. The sintering shrinkage of the interconnect should be close to that of the other SOER components, so that all the layers in the stack can be simultaneously sintered to produce the monolithic SOER stack.[000105] An important aspect of the invention is the selection of an interconnect material with thermal properties and sintering shrinkage properties compatible with the materials in the other SOER components. While interconnects have been typically made from metals, such as steel or other alloys, such metallic interconnects are not compatible with simultaneous sintering of the other components in the stack.[000106] The interconnects in the present invention are made from ceramics. Preferably, the interconnect is made from a doped Lanthanum Chromium oxide, also referred to as doped lanthanum chromite. More preferably, this material is a perovskite metal oxide which has Strontium doping on the A site, with some A-site deficiency, and Iron doping on the B-site. Alternatively, the A-site of the perovskite does not need to be deficient, and the Strontium A- site doping can be varied from 0.1 to 0.4 or replaced with Calcium or Magnesium. The Fe:Cr ratio on the B-site can be varied from 2:8 to 8:2 and the B-site dopant could alternatively be Nickel, Manganese, Titanium, or no dopant.[000107] These compounds can be defined as (Lai-xSrx)iz(FeyCri-y)O3 where x is from 0.0 to 0.5, y is from 0.0 to 0.7 and z is from 0.0 to 0.1.[000108] Preferably, the doped lanthanum chromium oxide for the interconnect is selected from the group consisting of (Lao.8$ro.2)o.95(Feo.7Cro.3 )C>3, (La0.8Sr0.2)0.95(Cro.5Feo.5)03 , and (Lao.8Sro.2)o.95Cro.7Feo.3)03, as well as mixtures thereof. All of these compounds are abbreviated LSCrF herein.[000109] Preferably, the interconnect is relatively thin, that is, less than 50um. More preferably, the interconnect will be between 10 and 20um. Preferably, the interconnect will have a constant thickness with no lateral features and will be dense after sintering, so that it is gas impermeable, preferably to > 95% of max density.[000110] Alternatively, the interconnect consists of a dense or porous layer of LaSrTiO3 (LST) in addition to the LSCrF layer, located adjacent on the anode side and of a similar thickness.[000111] As another alternative, the interconnect consists of only a layer of LaSrTiO3 (LST).[000112] Preferably, the unsintered interconnect is formed from particles of compounds selected from the group consisting of doped lanthanum chromium oxide, doped strontium titanate, platinum / platinum group metals, as well as combinations thereof.[000113] The interconnect layer is preferably produced by the MoldJet process described below. In other words, a mold is printed out of wax and then filled with the appropriate paste. Because the interconnect is relatively thin, it may be formed from a single layer of paste.Alternatively, the interconnect is produced by ultrasonic spraying of an ink or paste. This thin layer will be deposited on top of the previous functional layer. Preferably a mold or mask is used to achieve the desired shape of the interconnect. For example, a printed mold, such as that described below may be used. In other embodiments, a reusable mask or stencil is used to define the shape of the interconnect as it is deposited. It is noted that whether sprayed or gelcast, the particles that will make up the interconnect, along with the liquid carrier are considered a moldable composition.[000114] In yet other alternative embodiments, gas channels may be formed in the interconnect. In still other embodiments, air channels may be formed with a part of each channel lying in the interconnect and a part lying in the cathode. Nevertheless, both of these embodiments are less preferred, as it is best to keep the interconnect as thin as possible.[000115] While it is preferable to deposit the moldable compositions to form the interconnect on both ends of the unsintered stack, in other embodiments, the interconnect atone or both ends of the stack may be added through a different process, such as spraying, printing or other means of depositing, before or after sintering.Anode[000116] In a SOFC, the anode serves as the electrode where the fuel reacts with oxygen ions (O2“) that migrate through the electrolyte. One of the functions of the anode is fuel oxidation. The anode facilitates the electrochemical oxidation of the fuel, producing electrons and water or carbon dioxide, depending on the fuel type. For hydrogen, the reaction is[000117] In addition, the anode facilitates electron conduction. The anode conducts the electrons generated in the oxidation reaction to the external circuit, creating an electrical current.[000118] The anode also facilitates gas diffusion. It provides a porous structure for the diffusion of fuel gas to the reaction sites and products away from the reaction sites. As discussed in more detail below, this porous structure can be achieved by mixing pore forming particles that are burned or dissolved out of the anode before or during sintering.[000119] The anode also facilitates the catalysis of the chemical reactions. Preferably, the anode is made of a material, such as a nickel-ceramic composite. In the presence of a reducing fuel in the anode, such as H2, the NiO is reduced to leave metallic nickel, which acts as a catalyst to enhance the reaction rate. The metallic nickel from the reduced NiO also facilitates conduction of electrons through the anode.[000120] The anode must also be chemically and thermally compatible with the other components in the cell. For example, the sintering shrinkage of the anode should be close to that of the other SOER components, so that all the layers in the stack can be simultaneously sintered to produce the monolithic SOER stack.[000121] In some embodiments, the anode layer consists of an active or functional section and a current collection section. The active section will be adjacent to the electrolyte. Figures 5 and 6 depict a cell which uses an active section and a current collection section. In particular,the cell 401 includes an interconnect 403 at the top and bottom of the cell. Below the interconnect is the current collection section 405 of the anode. As seen in Figure 5, running through the anode current collection system is the anode gas channel 407, through which the fuel is run through the current collection section 405 of the anode. Below the current collection section 405 is the active or functional section 409 of the anode. Below that, is the electrolyte 411. Below the electrolyte is the active or functional section 413 of the cathode. Below the active section 413 is the current collection section 415 of the cathode. As seen in Figure 6, running through the cathode current collection section is the cathode gas channel 417, through which air is passed through the cathode current collection section 415 of the cathode.[000122] If used, the functional or active section of the anode preferably measures 30-100 urn in thickness. It is preferably comprised of NiO and ScSZ or YSZ preferably in a ratio of 1:1. Alternatively, LST or LSCrF may be used to replace the NiO.[000123] If used, this active section does not need to be as porous as the current collection section. It is preferable to deposit this layer using a single MoldJet layer.[000124] In this embodiment, an anode current collection section is adjacent to the anode active section. This is comprised of 3YSZ and NiO in a ratio of ~4:1 YSZ:NiO. There may also be some porosity in this layer, obtained through the use of pore former in the initial phase. This layer is preferably 300-600um thick and will also include gas channels. These will be preferably rectangular and of a comparable diameter to the thickness of the layer and spaced 3-5mm apart. The channels will preferably run perpendicular to the channels in the cathode. This layer will be produced using multiple layers of the MoldJet process.[000125] Preferably, the unsintered anode is made from particles of compounds selected from the group consisting of nickel oxide, yttria stabilized zirconia (YSZ), scandia stabilized zirconia (SSZ), scandia ceria stabilized zirconia (ScCeSZ), ceria, gadolinium doped ceria, samaria- doped ceria (SDC), doped strontium titanate, cobalt oxide, and doped lanthanum chromium oxide, as well as combinations thereof.[000126] Most preferably, the anode is made from a paste that includes 40 wt% LSCrF, 40 wt% NiO and 20 wt% ScSZ. Preferably, the majority of the particles have a specific surface area of 3.5-6.5 m2 / g.[000127] Adjacent to the anode is the interconnect, which separates the anode from the cathode of the adjacent cell.Electrolyte[000128] The primary function of the electrolyte in a SOER is to facilitate transport of ions while substantially preventing the passage of electrons. The electrolyte facilitates the migration of specific ions, typically oxygen ions (O2, from the cathode to the anode. This ionic conduction allows the electrochemical reactions to take place in the fuel cell. It also enables the flow of oxygen ions through the electrolyte, creating an ionic current that contributes to the generation of electricity.[000129] While the electrolyte permits the movement of ions, it acts as an insulator for electrons. This is essential to maintain the separation of the electron flow in the external circuit (from the anode to the cathode) and the ionic flow through the electrolyte (from cathode to anode). By preventing electrons from passing through the electrolyte, the efficiency of the electrochemical reactions is maximized.[000130] The electrolyte also needs to prevent the fuel gas in the anode from mixing with the oxygen containing gas in the cathode. This is facilitated by ensuring that the electrolyte layer is fully dense upon sintering.[000131] As with the other components in the SOFC stack, the electrolyte needs to be chemically and thermally compatible with the other components and gases.[000132] The electrolyte functional component is between the cathode and the anode in the same cell. Preferably, it consists of a 5-30um thick layer of ScCeSZ (Scandia stabilized Zirconia) that will be fully dense (>95% max density) after sintering.[000133] ScSCeZ is made with Scandia (SC2O3) and ceria (CeO2) added to zirconia (ZrOz) to stabilize its cubic crystal structure, which is favorable for oxygen ion conduction. The additionof scandia introduces oxygen vacancies in the crystal lattice. These vacancies act as pathways for O2“ ions to migrate under the influence of an electric field. At the operating temperatures of the stack, the O2-ions produced at the cathode move through these vacancies to reach the anode.[000134] Alternative materials for the electrolyte include Yttria-Stabilized Zirconia (YSZ), Gadolinium-Doped Ceria (GDC), Yttrium-Doped Barium Zirconate (BZY), and Samaria-Doped Ceria (SmDCe). Some doped perovskite oxide materials can also serve as electrolytes. These include materials like strontium-doped lanthanum manganite (LSM) or strontium-doped lanthanum cobaltite (LSCo), which can exhibit high oxide-ion conductivity.[000135] Preferably, the unsintered electrolyte is made from particles of compounds selected from the group consisting of yttria stabilized zirconia (YSZ), scandia stabilized zirconia (ScSZ), scandia ceria stabilized zirconia (ScCeSZ), ceria, gadolinium doped ceria, SDC, and BZYb and other Barium Zirconates BaZrO3, as well as combinations thereof.[000136] Preferably, the electrolyte is deposited with the MoldJet technology described below. In other embodiments, the electrolyte is deposited using an ultrasonic nozzle or some other form of spray deposition. A mold or a mask may be used to define the edges of the electrolyte, so deposed. Alternatively, the electrolyte is formed using some other form of deposition, such as ink jet printing.Cathode[000137] The cathode is also known as the air electrode or positive electrode in the cell. The cathode serves as the electrode where oxygen from the air is reduced to form oxygen ions (O2“). These oxygen ions then migrate through the electrolyte to the anode, where they participate in the electrochemical oxidation of the fuel.[000138] One function of the cathode is to facilitate reduction of oxygen, according to the chemical reactionO2+ 4 e -> 2 O2[000139] This reaction generates the oxide ions needed for the fuel oxidation reaction in the anode.[000140] The cathode also conducts electrons from the external circuit back to the reaction site, where they combine with oxygen molecules.[000141] The cathode must also facilitate gas diffusion, with a porous structure allowing the oxygen gas, typically in air, to diffuse to the reaction sites. The porosity is preferably achieved using pore forming particles deposited within the cathode layer prior sintering. These pore-forming particles are typically burned out of the cathode layer before or during sintering. The conduction of air / oxygen through the cathode is also provided by a gas distribution network in the cathode, preferably including gas channels formed in the cathode layer.[000142] The composition of the cathode also preferably acts as a catalyst to enhance the reduction reaction.[000143] The cathode must also be chemically and thermally compatible with the other components in the cell. For example, the sintering shrinkage of the cathode should be close to that of the other SOER components, so that all the layers in the stack can be simultaneously sintered to produce the monolithic SOER stack.[000144] As noted above in the discussion of the anode, in some embodiments, the cathode has two sections, the functional or active section which is adjacent the electrolyte and the current collection section which is adjacent the interconnect.[000145] If used, the functional section of the cathode is preferably made from LSCrF and ScCeZ (Scandia ceria stabilized Zirconia). The functional section will consist of a ~30-100um thick layer comprising ~1:1 volume ratio of LSCrF:ScCeZ. The functional section will also have porosity of preferably 20-30%. The porosity is preferably obtained by including a pore former in the fourth moldable composition. Such pore formers can comprise beads of a polymer, such as cellulose, or other combustible material, such as graphite, that is removed during sintering or a pre-sintering heat process.[000146] This functional section of the cathode will be adjacent to the electrolyte and separated from the interconnect by the thicker current collection section or channel section. The current collection section is comprised of a stabilized zirconia (preferably 3YSZ) and LSCrF, in a ratio preferably 50:50 LCSF:YSZ but could be anywhere from 70:30 to 30:70. The layer is also comprised of a bulk porosity, as in the active section, of 20-30% that preferably covers the entire section. There could be a gradation in the material ratios through the layer, increasing in LSCrF fraction closer to the interconnect. This could increase up to 100% LSCrF.[000147] Preferably, the unsintered cathode is made from particles of compounds selected from the group consisting of doped lanthanum chromium oxide, LSCrF, LSM, YSZ, ScSZ, ScCeSZ, CGO, SDC, lanthanum cobaltites, lanthanum ferrites, and platinum group metals, as well as combinations thereof.[000148] The cathode layer will preferably be ~200-750um thick. Within the layer will be a gas distribution network. Preferably, this is provided by a number of sections of voidage (gas channels) which traverse from one side of the layer to the other. Preferably these will be rectangular in cross section. Alternatively, they may be circular or other shapes in cross section. Preferably, the diameter of the gas channel is comparable to the thickness of the layer and spaced ~3-5mm apart. They will not necessarily have a constant cross section. For example, tapering of the channels may be used to tune the gas flow. Also, although the simplest design is for gas channels that are formed in a straight line, other shapes may be used, such as S curves or zigzags to achieve better penetration of the gases into the electrodes. Preferably, the gas channels will pass all the way across the width of the stack. Alternatively, the channels may be formed with branches, etc. to tune the distribution of the gasses within the electrodes.[000149] In the preferred embodiment, the cathode layer is made from a paste containing powders of a similar composition. In the most preferred embodiment, the cathode is made from the same paste as the anode layer. Not only does this simplify production of the stack, but it also provides both the anodes and cathodes with the exact same sintering profile and complete thermal compatibility during operation. Most preferably, the composition of the cathode is the same 40 LCSF / 40 NiO / 20 ScCeZ described above for the anode.[000150] In some embodiments, the cathode layer is produced using the MoldJet process with 2 distinct formulations within the functional layer (active section and channel / current collection section). The active section could be deposited in one MoldJet layer, while the channel section will be deposited using multiple MoldJet layers, 50-100um per layer.Housing for the SOER Stack[000151] Figure 7 is a simplified illustration of a container or housing 501 to house a SOFC stack. Figure 8 is a horizontal cross section through Figure 7. Preferably, the housing is made from a ceramic material which is thermally and chemically compatible with the reactants and materials in the SOFC stack. Suitable materials include sintered, stabilized zirconia, YSZ, or a similar material. Alternatively, the housing may be made from other ceramic materials, such as alumina. The container includes an inlet 529 for fuel and an inlet 503 for air. These inlets may be simple openings. In some embodiment, they are be formed with threads, so that inlet pipes may be threaded therein.[000152] The housing also includes electrical contacts, such as 506 and 508 (See also Figures 9 and 10), which are electrically coupled to one of the interconnects on opposite ends of the stack. This can be accomplished by having one contact touch the top interconnect and the other contact having a conductor touching the bottom interconnect at one end and touching the contact at the other end. Alternatively, as shown in Figures 9 and 10, one contact 506 can be located on the top of the housing and another contact 508 can be located on the bottom of the housing.[000153] The container 501 also includes an outlet 505 for water and unused fuel and an outlet 507 for air. Again, these outlets may be simple openings, or may be threaded.[000154] Referring to Figure 8, the container includes four sidewalls 519, 520, 522 and 524. As shown, the fuel comes in through an inlet 529 in wall 519 and out through an outlet 505 in the opposite wall 522. The air comes in through an inlet 503 in wall 524 and out through an outlet 507 in the opposite wall 520.[000155] Figures 9 and 10 are vertical cross-sectional views perpendicular to each other.Figure 9 shows the gas channels 533 in the anodes 531 running across the page, while the gasZ1channels 534 in the cathodes are coming out of the page. Figure 10 shows the gas channels538 in the anodes 531 coming out of the page, while the gas channels 536 in the cathodes 535 are running across the page.[000156] Figures 8, 9 and 10 also show that the SOFC stack 601 is spaced from the inside of the side walls of the container 501. This space, together with the corner seals 517, create four gas chambers, all isolated from each other on the four sides of the SOFC stack, namely chambers 521, 523, 525 and 527. The chamber 521 communicates with the gas distribution network, e.g. the gas channels in all of the cathodes in the stack, so that air can be inputted to each of the gas channels in each of the cathodes. The chamber 525 communicates with the other end of the gas channels in all of the cathodes, so that air can be exhausted from each of the gas channels in the cathodes. Likewise, the chamber 527 communicates with gas distribution network in all of the anodes in the stack, so that fuel can be inputted to each of the gas channels in each of the anodes. Finally, the chamber 523 communicates with the other end of the gas channels in all of the anodes, so that unused fuel and water can be exhausted from each of the gas channels in each of the anodes.[000157] Preferably, the container 501 is a sintered ceramic body. Preferably, the container is made in a separate process. The container is made with a lid or a bottom that can be positioned and then sealed once the SOFC stack 601 is placed inside. The corner seals 517 may be formed as part of the container 501. However, these seals are preferably inserted once the stack is placed inside the container. Preferably, the top is sealed and the corner seals are formed by a ceramic-to-ce ramie sealant that hardens and may become hermetic upon thermal curing, such as Ceramabond™ 552 available from Aremco Products Inc. (USA), or Aron-C available from Toagosei Co. Ltd. (Japan).[000158] In an alternative embodiment, the container is built up around the SOER stack, preferably by the same MoldJet methods, and then simultaneously sintered with the stack.[000159] Figure 11 is a schematic representation of a housing 901 for a SOFC stack, which includes integral heat exchangers, namely a heat exchanger 903 for the gases (fuel, such as methane to be reformed or hydrogen) fed into and exhausted from the anode and a secondheat exchanger 905 for the gases (air) fed into and exhausted from the cathode. With these two heat exchangers, the intake gases can be heated up and the exhaust gases can be cooled. This is advantageous as it allows an SOFC stack that operates at a higher temperature, such as the preferred stack of this invention, to be compatible with the balance of plant for conventional, lower temperature SOFC stacks. In other words, the object of incorporating the heat exchangers in the SOFC stack housing is to allow the stack to take in air and fuel at standard SOFC temperatures and exhaust air and fuel at standard SOFC temperatures.[000160] As seen in Figure 11 and Figure 12, which is the same as Figure 11, with the top plate 904 removed, the fuel gas enters fuel gas inlet 907 and exits through the fuel gas outlet 909. As shown by the dashed lines, the route of the fuel gas is to first pass through the heat exchanger 903 where it is heated by the fuel gas exhaust. After it passes through the first heat exchanger it passes through the gas channels in the anode layers described above. Upon leaving the gas channels in the anode layers, the fuel gas passes through the heat exchanger as exhaust and is cooled by the intake fuel gas. The cooled exhaust fuel gas then exits the housing through the fuel gas outlet 909.[000161] As seen in Figures 11 and 13, air enters air inlet 913 and exits through the air outlet 911. As shown by the dashed lines, the route of the air is to first pass through the heat exchanger 905 where it is heated by the air exhaust. After it passes through the heat exchanger 905, it passes through the gas channels in the cathode layers described above. Upon leaving the gas channels in the cathode layers, the air passes through the heat exchanger 905 as exhaust and is cooled by the intake air. The cooled exhaust air then exits the housing through the air outlet 911.[000162] Figure 14 is a perspective view of a horizontal slice 921 of one stage of the heat exchanger. Figure 15 is a vertical cross section of the stage of the heat exchanger plate shown in Figure 14.[000163] As can be seen in Figure 14, the stage includes a large slot 923 through which the inlet fuel passes upward. Viewed together with Figure 13, it is seen that the inlet fuel gas passes over the plate and then down through slot 925. As the inlet fuel gas passes through theplate, it is heated by the exhaust, which is isolated from the inlet fuel, so as not to mix, but the separators are thermally conductive, so that the heat can pass from one to the other. The heated fuel gas then passes down slot 925 and is passed through the anode layers in the stack, after which the exhaust fuel gas, including water, passes up through slot 927 and into the heat exchange channels in the plate 921. After being so cooled by the heat exchanger, the exhaust gasses pass down through slot 929 and out the outlet 909.[000164] Figure 15 is a vertical cross section through the middle of one of the heat exchanger stages. As seen, each stage includes multiple, a heat conductive barrier 943 divides the top half and bottom half of the stage. This separates the inlet gas on the top and the outlet gas on the bottom of the stage. As understood in viewing Figures 14 and 15 together, the inlet gas passes through the channels created by the heat conductive fins 941 and out through the slot 925. The exhausted gas flows through the bottom half of the stage and passes out through slot 927. As can be seen, the intake gases and exhaust gases are run in parallel channels, separated by the horizontal 933 wall that allows heat to pass from the hotter gases to the cooler gases. In this way the exhaust gas heats the intake gas and the intake gas cools the exhaust gas.[000165] As seen in Figure 13, the air that is taken into and exhausted out of the stack follows a similar path through the heat exchanger 905. As such, the inlet air is heated and the exhaust air is cooled. Figure 13 also shows the cavity 931 where the stack is fit and the corner seals 935 that keep the gas streams separate.Balance of Plant[000166] The SOFC made with the present invention is operated at high temperatures, preferably above 800°C, more preferably above 900°C.[000167] Figure 16 illustrates the balance of plant for the SOER system, i.e. the remaining preferred components to make the system work.[000168] The heart of the system is the SOFC stack. Fed into the stack is a supply of fuel, which starts off as natural gas (methane) or propane. The natural gas or propane is fed through a compressor and then a desulfurizer. From there, the gas is fed to a preheater / reformer,where at least a portion is converted to hydrogen and carbon dioxide. That gas mixture is fed into the gas channels of the stack that contact the anodes. To convert more of the hydrocarbon, part of the exhaust gas is fed back through the steam reformer. Some or all of the exhaust gas is fed to a tail gas combustor, to ensure that all of the hydrocarbon is combusted before being exhausted.[000169] Air is fed to the gas channels in the cathodes by means of a blower. A heat exchanger with the combusted exhaust is used to preheat the air before it is fed into the stack. Exhaust air is also fed into the tail gas combustor.[000170] The electrical system functions to control the inputs and outputs from the stack, through valves, blowers and the like. The electrical system preferably includes batteries that are charged during low demand times and discharged during peak demand times.[000171] As shown in Figure 17, the preferred system is a Combined Heat and Power (CHP) system, which utilizes, not only the electricity generated, but the heat as well.[000172] In this CHP system, a heat exchanger with the exhaust gas is used to pull off heat and use in the heating portion of the CHP system. This heat may be put to used in applications such as warming air for a building, heating water for residential or commercial uses, desiccating biowaste, turning biowaste into char, in order to sequester carbon.Fabrication of the SOERsMoldjet Technology[000173] At present, the preferred method of forming the unsintered SOER stack is to modify a system developed by T ritone Technologies Ltd. and referred to as MoldJet® Technology. The Tritone MoldJet Technology is described well on the company's website at https: / / tritoneam.com / moldjet-technology / . The technology is also described in the several U.S. Patent Publications of Tritone, namely, US20200269320A1, entitled "Molding method and apparatus, particularly applicable to metal and / or ceramics"; US20220235194A1, entitled "Formulations for additive manufacturing of three-dimensional objects containing sinterable materials"; US20210178484A1, entitled "Hardening method and apparatus, particularlyapplicable to metal and / or ceramics"; US20220072613A1, entitled "Supports for components during debinding and sintering"; US20220314330A1, entitled "Mold preparation and paste filling"; US20220402042A1, entitled "Machine for additive manufacture incorporating molded layers"; and US20230191698A1, entitled "Wax base for an object in additive manufacturing." The entire disclosures of all of these published applications are incorporated herein by reference.[000174] Tritone's MoldJet Technology includes a process and hardware for manufacturing a molded layered product. The process begins by printing a first mold to define one layer of the product. The vertical thickness of this mold can be varied, but is typically 50- lOOum.[000175] Next, the first mold is filled with a cast material, i.e. paste, to form a first layer. This paste is referred to as a moldable composition herein. Preferably, a doctor blade or roller is used to achieve a flat surface on the cast material. Several microns of the deposited structure, including mold and dried paste may be removed at this point by milling the surface, to obtain a flat top surface.[000176] The process continues by printing a second mold on top of the first layer to define a second layer and then filling the second mold, over the first layer, with a cast material. The cast material is a moldable composition, most preferably in the form of a paste. The alternating mold printing and casting are continued until a molded layered product is formed.[000177] At this point, the mold material, preferably wax-based, is removed, preferably by melting. Alternatively, the mold material is removed by dissolution in a solvent, by vaporization or by combustion.Paste Formulations, [anything to update in this section?][000178] For the preferred embodiment of the present invention, the MoldJet process uses a paste including a powder of a sinterable material, preferably in an amount between 75 to 85 by weight of the total weight of the formulation, preferably between 33 to 42.5% by volume percent, plus a binder, and an aqueous solution which comprises water and a water- miscible organic solvent featuring an evaporation rate in a range of from 0.3 to 0.8 on an n-butyl acetate scale. The sinterable powder in each paste, i.e. moldable composition, is the powder adapted to become one of the SOER components. The aqueous solution with its additives is the liquid composition of the moldable compositions.[000179] Various ingredients are included in the liquid composition to achieve the appropriate properties of the paste. In general, a surfactant is used, along with a dispersant and a defoamer. The dispersant may be an emulsifying agent, such as Sodium dodecylbenzensulofonate, sodium lauryl sulfate, Trisodium citrate, Stearic acid, and Citric acid, and those marketed under the trade names Dispex Ultra PX 4483, Dispex Ultra PX 4484, Dispex Ultra PX 4275, Dsipex Ultra PX 4575, DISPERBYK 180, DISPERBYK 192, and DISPERBYK 2060.[000180] A water-miscible, volatile, organic solvent is preferably added to quicken the drying process. Suitable solvents include propylene glycol and propylene glycol methyl ether.[000181] A binder material is also added to the liquid composition that will harden upon heating, so as to preserve the shape of the unsintered components in the stack before sintering. The binder material should be a curable material, which can be cured (hardened) when exposed to heat or other curing energy or to a curing condition such as, for example, pH change. A binder typically comprises a polymerizable material or a polymeric material which can undergo further polymerization (e.g., chain elongation) and / or cross-linking when exposed to a curing condition (e.g., curing energy such as heat) to thereby provide a hardened material. The binder material may be dissolved in an organic solvent in the liquid composition.Exemplary materials suitable for use as a binder include, but are not limited to, those included is the emulsions marketed under the trade names Joncryl® 8224, Joncryl® 2178-E, Joncryl® 537- E, Joncryl® 8211, Joncryl® 617, Joncryl® 652, Joncryl® 646, Joncryl® 142E, Joncryl® 1685, Alberdingk® AC 2523.[000182] Preferably, the liquid phase of the paste includes the ink vehicle (water + plastic binder system) supplied by Tritone. The liquid phase also include at least one dispersant. A defoaming agent should be included, preferably non-silicon-based. Preferably, a plasticizer, such as polyethylene glycol (PEG) or stearic acid are added to the liquid phase to improve theextrudability and moldability of the paste. Finally, ammonia is preferably added to increase the pH of the liquid phase to 10.[000183] Pastes with a high solids content are preferred to prevent undue shrinkage during drying. Pasts with a solids content between 74.5-82.8 wt% have been successfully printed. Some pastes include pore formers, which lowers the weight percent. In terms of volume %, pastes have been made with 33-44% by volume solids.[000184] One, two or up to three dispersants are used in the preferred paste formulations. Dispersants that work by electrostatic repulsion are preferred. Currently, Darvan® C from Vanderbilt Minerals, LLC is the most preferred dispersant for all of the pastes, except for the interconnect paste. The interconnect paste is preferably made with LFSCr55 powder. A dispersant from Lubrizol named AC5110 Solsperse is preferred for this paste. Dispex AA4040 is the preferred dispersant for the electrolyte.[000185] For those pastes with pore formers, it is preferred to use a dispersant, such as Zephrym for 3300 (Croda, UK), to achieve optimum dispersion of the pore former particles.[000186] It is preferred that the volume % of the dispersant to be as low as possible. From 0.8-2% of total liquid is workable. The dispersant concentration should typically range from 0.5-1.5 mg / m2for printing, although higher or lower amounts can be used.[000187] Particle morphology can play a role in the making of printable pastes. It can also play a role in the sinterability of the layers in the stack. Currently, it is preferred to define the particles in the powders used to make pastes in terms of the surface area. If the particles in the powders are in a single phase, the preferred range is from 2-6 m2 / g, while the most preferred surface area is from 3-4 m2 / g. To date, it has been difficult to paste powders with a surface area greater than 6.5 m2 / g. Powders with a surface area from 1-2 m2 / g powder have been good for combining with other powders, but not as successful on their own.[000188] It is preferred in some embodiments to mix powders with different surface areas, in other words, "bimodal" mixtures. For example, a preferred paste contains YSZ from two powders (bimodal), with the surface area of the first in the range 1-2 m2 / g and the surface area of the second in the range of 6-7 m2 / g. The net surface area is about 4 m2 / g.[000189] Some layers of the SOFC stack, such as the anode and cathode, require porosity, and are thus preferably printed with a pore former in the paste. Such pore formers are typically acrylic particles and can be added from 10-35 vol% of the solids .[000190] In all cases, it is important to avoid agglomeration of the various particles in the paste and to achieve as great of homogeneity as possible. This is preferably accomplished by using a ball milling action by placing the paste in a cylindrical container with 5-7mm diameter balls of zirconia. The container is then rotated on rollers for a sufficient time, preferably at least 4 days, and more preferably at least 14 days.[000191] The following properties are used to assess the paste and determine if it is suitable for printing and sintering: viscosity, crack-fee upon drying, defect (such as bubbles) free, sintering shrinkage.Hardware System to Form the Unsintered SOER Stacks[000192] Figures 18 and 19 are simplified schematic views of a hardware system 1001 for depositing the various layers to form unsintered SOER stacks. Preferably, the whole operation is digitally controlled, so as to achieve the appropriate times and conditions at each station.[000193] The system comprises a table 1003, which supports a conveyer 1005, configured to move laterally along the table. Attached to the conveyor is a platform 1007, which in turn supports a tray 1009, onto which the layers are deposited. At the first station 1011, an interconnect is deposited on the tray. Preferably, this is accomplished by the MoldJet process, which first prints a mold and then fills that mold with the appropriate paste to make the unsintered Interconnect. Alternatively, the interconnect(s) may be formed by other additive manufacturing techniques, such as ink / paste jet printing or spraying. The conveyor 1005 may be used to move the tray under the interconnect applicator to produce the appropriate size and shape of the interconnect(s) on the tray.[000194] After the interconnect is deposited by the first station, the conveyor 1005 moves the platform 1007 with the tray 1009 to the second station, which includes means to dry, harden and inspect the interconnect(s), formed at the first station. The drying may be accomplished with warmed air and / or by radiant heat from UV or IR sources.[000195] The conveyor then moves the platform and tray to the third station 1015, at which an electrode is formed on top of each interconnect deposited at the first station. Again, this is preferably accomplished by a MoldJet method, with a printed mold and paste filling that mold. Alternatively, other techniques can be used, such as those described above. Preferably, the unsintered electrode is deposited with gas channels already formed therein.[000196] The conveyor then moves the platform and try to the fourth station 1017, at which the unsintered electrode(s) are dried, hardened and inspected.[000197] The fifth station 1019 the conveyor moves the platform and tray to is one at which the electrolyte is deposited on top of the electrode just formed. Again, the preferred method is to use the MoldJet technology to form the electrolyte. Nevertheless, because the electrolyte is a relatively thin layer, it may be preferred to us an alternative technique, such as spraying or tape casting to form the electrolyte.[000198] The conveyor then moves the platform and tray to the sixth station 1021, whereat the electrolyte is dried, hardened and inspected.[000199] At this point, the conveyor moves the platform and tray back to the third station 1015 to have another electrode formed on top of the electrolyte. Since it is preferred to use the identical composition for the anode and cathode, this station 1015 can be used to form both anodes and cathodes. However, it is noted that the mold for the second electrode will include gas channels running in a perpendicular direction to those of the first electrode.Alternatively, if different compositions for the anodes and cathodes are to be used, a seventh and eighth stations can be added to deposit a different electrode in the unsintered stack.[000200] Once the second electrode is deposited on the stack, the conveyor moves the platform and tray back to the first station to deposit another interconnect on the stack.[000201] These steps are repeated, until the appropriate number of cells, each with an interconnect, anode, electrolyte and cathode have been deposited. An interconnect is formed on both the bottom and top of the stack. At this point, the unsintered stack is removed from the system, either on or off the tray, and treated to remove the mold, fully dry the stack and remove any other organics.[000202] As taught in the Tritone website (tritoneam.com) and in the published applications cited above, the MoldJet process is preferably carried out on an indexed rotary table (turntable) apparatus, whereby the workpiece is advanced to different stations in order to have the different processes applied thereto.[000203] Figure 20 is a simplified schematic view of such a turntable system 1201. As with the embodiment shown in Figures 18 and 19, Preferably, the whole system is digitally controlled, so as to achieve the appropriate times and conditions at each station.[000204] Upon the table 1203 is placed a tray (not shown) that will be moved between the stations and even moved within each station by rotation of the table. As shown, the first station 1205 on the rotary table 1203 is used to deposit an interconnect. As noted above, the preferred method is to print a mold and then fill that mold with the appropriate paste to form the interconnect. However, because the interconnect is relatively thin, this may also be accomplished by other means, such as spray, ink / paste jet printing, tape casting, or the like. At the second station 1207, the interconnect so formed is dried, hardened and inspected.[000205] At the third station 1209, the system determines whether the unsintered stack is to go around the circuit again, or whether it is complete and ready to go on to be demolded, bisqued and sintered.[000206] At the fourth station 1211, a mold for an electrode is printed, while at the fifth station 1213, that mold is filled with the appropriate paste to form the electrode. At the sixth station 1215, the electrode is dried, hardened and inspected. Alternatively, the table 1203 can be rotated in the reverse direction to move the tray back to the second station for drying, hardening and inspecting.[000207] At the seventh station 1217, an electrolyte is deposited. As with the interconnect, the electrolyte is preferably deposited by printing a mold and filling that mold with the appropriate paste to form the electrolyte. Also as with the interconnect, since the electrolyte is a relatively thin layer, it may also be deposited by the alternative means mentioned for the interconnect. At the eighth station 1219, the electrolyte is dried, hardenedand inspected. Alternatively, the tray can be moved back to the second station for drying, hardening and inspecting.[000208] If the SOFC stack is being formed with identical anodes and cathodes, the turntable can be reversed to move the tray back to station 4, 1211, to have a mold printed and then to station 5, 1213, to have the same electrode paste applied to the mold. It is noted that the mold for the second electrode should be printed with gas channels running perpendicular to those in the first electrode. Alternatively, the tray is moved in the original direction to station 9, 1221, to have a mold printed for the second electrode. Once printed, the mold is filled with the paste for the second electrode. That second electrode is dried, hardened and inspected at the eleventh station 1225. Alternatively, the tray can be moved back to the second station for drying, hardening and inspecting the second electrode.[000209] The tray is then rotated to the first station 1205, whereat a interconnect is deposited on top of the second electrode. That interconnect is dried, hardened and inspected at the second station 1207. As it moves to the third station, 1209, the system determines if the unsintered stack is complete, or if the tray is to be sent around the circuit again to build one or more cells. Once the appropriate numbers of cells has been deposited, and an interconnect deposited on top of that, the tray can be moved off the table for post-print processing.[000210] Figure 21, depicts a system 2101 similar to that shown in Figure 20, with a rotary table 2103. The difference is that the stations 2105, 2107, 2109, 2111, 2113, 2115, 2117, 2119, 2121, 2123, 2125, 2127 and 2129, include a station 2105 for printing a mold for the interconnect and a station 2119 for printing a mold for the electrolyte. In addition, station 2113 is specific for printing an anode mold, while station 2125 is specific for printing a cathode mold. Also, station 2115 is specific for filling with anode paste, while station 2127 is specific for filling with cathode paste.[000211] Figure 22, depicts a system 2201 similar to that shown in Figure 21 with a table 2203. The system includes 20 stations, numbered 2205, 2207, 2209, 2211, 223, 2215, 2217, 2219, 2221, 2223, 2225, 2227, and 2239. The major difference is that the system in Figure 22 is set up to form anodes and cathodes with functional sections as well as current collectionsections. Also, the interconnect is deposited by spraying in the first station, 22005. Also, the electrolyte is deposited by spraying in the ninth station, 2221.[000212] At station 20, if the complete stack has been deposited, then the workpiece is removed and sent for sintering. Optionally, the workpiece may be subject to further processing, such as washing or shaping, before sintering.[000213] In an alternative embodiment, the system includes 6 stations for printing molds and 6 stations for filling those molds. Four of these stations may be used to print the interconnect, anode, electrolyte, and cathode. The other 2 stations can be used for printing the container to house the stack. The housing may be printed in one pass, but preferably is built up layer by layer. In some embodiments, the housing is printed layer by layer around the functional components in the same step that they are printed. To best carryout this embodiment, the mold filling stations are configured to print two different materials at the same time, namely, one material for the functional component and another material for the housing layer.[000214] Preferably, the housing or container is printed so as to include the inlets and outlets from the stack. Also, the housing is printed with electrical contacts to electrically connect the SOFC to the system, in which is designed to provide power. Alternatively, the container may be printed without these and then machined or otherwise processed to add them to the container.[000215] Each time the turntable rotates through every station, a single cell has been added to the stack. Thus, if a 50-cell stack is to be produced, the turntable rotates to every station 50 times.[000216] It is noted that these apparatus and methods have been illustrated and described in a simplified way. In carrying out the method, it may be desirable to deposit at least some of the components in multiple layers, i.e. passes on the machine, to build up the entire cell component. In these cases, the machine may be modified to include more stations to accomplish these multiple layers. Alternatively, the machine may be modified to "back up"the turntable to deposit a second, third or more layers of the same paste. This backing up may be done after each layer is dried and hardened, or before.[000217] Figure 22 illustrates another embodiment of the turntable 2201 to produce the unsintered stack. In this embodiment, the apparatus is set up to print the current collection section and functional sections of the anode and cathode in different stations. Also, in this embodiment, the interconnect and the electrolyte are deposited by spraying.[000218] In an alternative embodiment, the mold filling station may be configured to deposit more than one material at a time. For example, the station depositing paste for the anode functional section may deposit the YSZ and NiO separately. In this way the amount of NiO can be varied in different layers, so as to have the highest concentration at the interface with the interconnect, and a lower concentration in the layers farther from that interface.Post-Print Processing[000219] In some embodiments, the MoldJet apparatus uses both heat and vacuum to aid in drying and curing the green body.[000220] The green part then undergoes a sintering process to form the stack. All organic components remaining in the body (including any pore former) are removed from the body at <600°C. The part is then taken up to a maximum temperature, typically in the range of 1450- 1500°C for 1-5 hours. The sintering may be carried out in air, or an inert or reducing atmosphere. This results in a sinter shrinkage, preferably between 10 and 25 %, most preferably between 15 and 18 %. The sintering also gives the structure the final density desired for each of the components.[000221] It is noted that the sinter shrinkage of the stack is affected by various factors. For one thing, the particle size of the powders can affect the sinter shrinkage. In other words, if the particle size and particle size distribution allow for tighter packing in the paste and the green part, there should be less sinter shrinkage. Also, the type and amount of binder used in the paste can affect sinter shrinkage. If the paste and green part have less binder, the sinter shrinkage should be lower.[000222] To produce sintered stacks with lower stress in the various components, it is optimal that each of the components would have similar linear sinter shrinkage percentages if sintered on their own. In other words, it is optimal for each of the components to have an unconstrained sinter shrinkage percentage similar to that of the other components, preferably a difference of less than 2, more preferably less than 1 and most preferably less than 0.5.Other Fabrication Methods[000223] While much of the discussion has been devoted to depositing the layers to make the components of the SOER stack by modifying the Tritone MoldJet® Technology, it is noted that other methods of depositing the layers may be used. For example, the layers may be deposited by ink jet printing the moldable compositions. The layers may also be deposited by tape casting or other gel casting techniques. The layers may also be deposited with the use of permanent molds with mold release technologies. All such methods are deemed within the scope of the present invention.Examples[000224] The following examples are provided to illustrate the embodiments of the invention and are not intended to limit the scope of the invention.Examplel[000225] In this Example 1, the SOER is comprised of an Interconnect made from LSFCr, an electrolyte - made from ScSZ, a functional anode (made from 6:4 by volume NiO:YSZ), a functional cathode (1:1 volume % LSFCnScSZ) and an identical cathode and anode current collection layers which comprise 40% NiO, 40% LSFCr and 20% 8YSZ and also an additional 10- 20% by volume acryllic pore former.[000226] This example includes a functional anode, i.e. a section of the anode where oxidation takes place. The paste for the functional anode is the same as that described above for the anode, with the exception that the NiO and YSZ powders are mixed in a 50 / 50 weight ratio. NiO-YSZ. Thickness 30um.[000227] The geometry of the above-described stack contains 50-100 cells, and has dimensions 15 x 15 cm area. Each of the interconnect, electrolyte and functional layers is 10- 25um thick and the two current collection layers are each 250um thick after sintering. The channels contained within the current collection layer are square in cross section with a height equal to that of the current collection layer and spaced at intervals of 0.6-lmm. This geometry is manufactured using the MoldJet methods outlined previously. Hardening of the parts after printing is performed at a temperature of 25-30 °C for 24 hours. Thermal and solvent demolding of the parts is then accomplished at 85 °C for 4 hours followed by immersion in Heptane. The stacks are then bisque fired to burn out the acrylic pore former and any other organics such as the binder, dispersant, etc. This is done as slowly as possible, typically by heating to 207 °C at 50 °C / h, dwelling for 3 hours, ramping to 300 °C at 1.8-2.4 °C / h, dwelling for 3 hours, ramping to 550 °C at 30-50 °C / h, dwelling for 2 hours, then ramping to the bisque temperature typically 925-1100 C at 100 °C / h, dwelling there for 2 hours, before cooling to room temperature at 100 °C / h.[000228] The stacks are then placed in the sintering furnace and sintered according the following procedure:!. Ramp from room temperature to 1500 °C at 200 °C / h2. Dwell at 1500 °C for 2 hours. The stacks are ramped back to room temperature at 200 °C / hrExample 2[000229] In Example 2, the layout consists of cells with an electryolyte made from 8YSZ, an anode made from NiO:8YSZ (1:1 by weight), a cathode made from LSCrF:YSZ (1:1 by weight) and an interconnect made from LSCrF. The preferred paste for the cathode is identical to that for the anode, namely the 40 / 40 / 20 LSCrF / NiO / ScCeZ pasted described above in the first example.[000230] These cells and stacks are processed in the same way described in Example 1.[000231] The cells are then placed in the sintering furnace and sintered according to the following procedure:[000232] 1. Ramp from room temperature to 1000 °C at 200 °C / h.[000233] 2. Step temperature to 1375 °C and dwell at 1375 °C for 6 hours.[000234] 3. Ramp to 1450 °C at 200 °C / h.[000235] 4. Dwell at 1450 °C for 2 hours.[000236] 5. Ramp back to room temperature at 200 °C / h.Example 3[000237] In Example 3, a single cell with no interconnect, of 28mm pre sintered diameter circle and 2mm thickness was produced by the same method as that described for Example 2.[000238] The NiO reduction was completed at 850 °C with an anode gas that was 33 vol% hydrogen.[000239] Figure 23 is a SEM of the cell that was made as described in Example 3 and tested for 100 hours . The anode layer 2401, comprises sintered YSZ and NiO. The black spots are pores formed in the anode. A gas channel is visible at 2407. The electrolyte layer, comprising sintered YSZ is seen to have a dense structure. The cathode layer 2405 comprises YSZ and LSCrF. The black spots are pores formed in the cathode.[000240] Figure 24 is a chronopotentiometry graph showing the current density of this cell over 100 hours at a constant cell potential difference and operating tempeature.[000241] The cell produced in this Example 3 was prepared for testing as follows: A current collector consisting of silver paste, silver wool and wires are attached to the anode and cathode respectively. The cell is then attached to a ceramic tube by means of a ceramic sealant, such that different gas atmospheres can be supplied to the cathode side and the anode side respectively, with no mixing of the anode and cathode gas atmospheres.[000242] The cell and ceramic tube are placed into a testing furnace such that hydrogen and argon can be supplied to the anode and the cathode is exposed to air at the same temperature.[000243] The silver wires are connected to a potentiostat, allowing electroanalytical experiments on the cell. The cell is ramped to 850 °C at 100 °C / hr in the testing furnace.Hydrogen and argon gases are supplied to the anode side, resulting in the NiO metal oxide being reduced to a porous Ni metal. The cathode side remains in air. Hydrogen and argon are continuously supplied to the anode.[000244] A chronopotentiometry test is run on the cell, with a constant potential of 0.75 V applied. The resultant current density (amount of current passing per unit area of cell) is measured over time. This test was conducted for 100 hours at 850 C.[000245] Figure 25 is an IV (current-voltage) curve for the cell according to Example 3.This was obtained by ramping the testing furnace to 800 °C, 850 °C and 900 °C and performing electroanalytical experiments using a potentiostat at each respective temperature. The open circuit potential difference is measured and then a varying potential is applied by the potentiostat from -0.5V to +0.1V relative to the open circuit potential, and the resulting current density is recorded in the graph at Figure 25. The line 2501 represents the curve at 800 °C. The line 2503 represents the curve at 850 °C. The line 2505 represents the curve at 900 °C.[000246] Figure 26 is a Nyquist plot for the cell made according to Example 3. This was obtained by ramping the testing furnace to 800° C, 850 °C and 900 °C and performing electroanalytical experiments on the cell using a potentiostat for each respective temperature, recording the electrochemical impedance of the cell over a range of frequencies from 10 kHz to 0.1 Hz.Example 4 Paste Formulation[000247] A composition acquired from Tritone is used in all of the pastes. This composition is water based and includes binders and an additional solvent. All of the pastes also include a non-silicon based antifoamer that is added between 0.5-0.8wt% of the liquid.[000248] The paste for the electrode described in example 1 comprises, 40 wt% LSCrF, 40 wt% NiO and 20 wt% ScCeZ. These wt% numbers are for particles of the ceramic powders. The preferred electrode paste also includes 10-15 vol% pore forming particles, preferably acrylate polymer particles with an average particle size of 0.8um diameter. To these powders are added the tritone binder composition, along with dispersants for each of the ceramic materials at 0.5- 1.3 mg / m2. The LSFCr has a surface area between 3-4 m2 / g. The NiO is bimodal with a surfacearea of particle 1 of 3-4 m2 / g and a small amount of a higher surface area >10m2 / g. The ScCeZ preferably has a surface area 4-7m2 / g. The total paste solid weight % is 78-79%.[000249] An alternative paste for the anode / fuel electrode is made with YSZ and NiO particles and includes the Tritone composition and a Darvan C dispersant at 0.7 mg m2of the YSZ and NiO particles. The anode paste also include an acrylic pore former (80-150 urn diameter, spherical) . The pore former is included at a level to give 20-25 vol%of total solids volume. The NiO powder contains one species, having a surface area from 3-4 m2 / g. The YSZ contains two powders (bimodal), with the surface area of the first in the range 1-2 m2 / g and the surface area of the second in the range of 6-7 m2 / g. The net surface area is about 4 m2 / g. The weight percent NiO, in the Ni / YSZ mixture, is preferably between 35 and 65, with 45% most preferred. Total paste solids in the anode paste is 77 wt%.[000250] An alternative paste for the cathode / air electrode is made with LSFCr55 particles and YSZ particles and includes the Tritone composition and a Lubrizol Solsperse dispersant at 0.8 mg m2of the LSFCr55 and YSZ particles. The cathode paste also includes an acrylic pore former (80-150 urn diameter, spherical). The pore former is added to a level of 30-35 vol% of total solids volume. The LSFCr55 powder contains one species of particle, with a surface area from 3-4 m2 / g. The YSZ powder contains two species of particles (bimodal), the first of which has a surface area in the range 1-2 m2 / g and the second of which has a surface area in the range of 6-7 m2 / g. The net surface area is about 4 m2 / g. The weight ratio of LSFCr55 / YSZ is between about 45 / 55 and about 55 / 45, with 50 / 50 being preferred. Total paste solids in the cathode paste is 75.5wt% or 41-42 volume %.[000251] The paste for the electrolyte is made from Scandia Ceria stabilized Zirconium (ScCeZ) particles. The electrolyte paste includes the Tritone composition along with a Dispex dispersant at 1.0m2 / g of the ScCeZ. The surface area of the ScCeZ is between 3-4m2 / g. The solid weight loading of the electrolyte paste is 77-81%.[000252] The paste for the interconnect is made with LSFCr55 powder. The paste includes the T ritone composition together with a dispersant from Lubrizol sold as "AC5110 Solsperse" atat 1.5m2 / g. The surface area of the LSFCr55 powder is 3-4m2 / g. The solid weight loading of the interconnect paste is 80%.[000253] In all cases of paste formulation, it is important to reach the best homogeneity possible. The preferred method to achieve this is to use a ball mill homogoniser with Zirconia grinding media.Example 5 - Printing the Pastes[000254] In this example, which includes functional layers in the electrodes, the pastes described above are printed on the Tritone machine described above. The interconnect paste is printed in a layer 25 urn thick. The Anode (fuel electrode) current collection section layer is printed on top of the interconnect and includes gas channels running parallel to each other therethrough. This layer, including the gas channels is printed to a thickness of 250-400um.The anode functional layer is printed on top of the anode current collection layer to a thickness of 30 urn.[000255] The electrolyte paste is printed on top of the anode functional layer to a thickness of 20 urn.[000256] The cathode (air electrode) functional layer paste is printed on top of the electrolyte layer to a thickness of 30 urn. The cathode current collection layer is printed on top of that to a total thickness of about 250-400um. The cathode current collection layer is printed with gas channels similar to those in the anode, except that they run perpendicular to the gas channels in the anode.[000257] The printing of these layers is repeated until the desired numbers of cells in the stack is reached.Example 6 - Post Printing and Pre-Sintering Steps[000258] The printed stack of cells is transferred to a chamber wherein the mold wax is removed with a solvent and / or heat.[000259] After removal of a substantial amount of the mold wax, the stack is heated in order to remove any last wax and solvents and to set the binder to bind the particle together in preparation of sintering.Example 7 - Sintering[000260] The stack is sintered in an oven to the temperature and for a time sufficient to co-sinter all of the layers in the stack. The rates of heating during sintering and cooling afterward are set so as to achieve the greatest mechanical stability in the stack.Conclusion[000261] All patents and published patent applications referred to herein are incorporated herein by reference. The invention has been described with reference to various specific and preferred embodiments and techniques. Nevertheless, it is understood that many variations and modifications may be made while remaining within the spirit and scope of the invention.

Claims

WHAT IS CLAIMED IS:

1. A method of making a solid oxide electrochemical cell stack, comprising the steps of: providing a first moldable composition comprising: a first liquid composition; first particles adapted to form an interconnect when sintered; providing a second moldable composition comprising: a second liquid composition; second particles adapted to form an anode when sintered; providing a third moldable composition comprising: a third liquid composition; third particles adapted to form an electrolyte when sintered; providing a fourth moldable composition comprising: a fourth liquid composition; fourth particles adapted to form a cathode when sintered; producing an unsintered electrochemical cell stack by sequentially printing a first layer mold and depositing within the first layer mold one of the first, second, third and fourth moldable compositions, and then printing subsequent layer molds and depositing within each of the subsequent layer molds an other of the first, second, third and fourth moldable compositions, and optionally depositing one of the first, second, third or fourth moldable compositions without a printed layer mold, with the printing and depositing process repeated so as to produce unsintered interconnects, anodes, electrolytes and cathodes, each having a predetermined size and shape, and wherein the order of depositing each moldable composition is set so as to produce a stack of unsintered cells, each comprising an unsintered anode, an unsintered electrolyte and an unsintered cathode, and so as to provide an unsintered interconnect between each unsintered cell; sintering the unsintered electrochemical cell stack with sufficient heat and for a sufficient time, so as to: convert the first, second, third, and fourth particles to the desired structure for operation of the electrochemical cell stack; andform an operational electrochemical stack wherein the interconnects are non-porous and conduct electrons, but not ions, the anodes are porous and conduct electrons and ions, the electrolytes are non-porous and conduct ions, but not electrons, and the cathodes are porous and conduct electrons and ions.

2. The method of claim 1, wherein the solid oxide electrochemical cell stack is a solid oxide fuel cell stack.

3. The method of claim 1, wherein the interconnects are formed by depositing the first moldable composition without a printed layer mold.

4. The method of claim 3, wherein the first moldable composition is deposited by spraying.

5. The method of claim 1, wherein the electrolytes are formed by depositing the third moldable composition without a printed layer mold.

6. The method of claim 5, wherein the third moldable composition is deposited by spraying.

7. The method of claim 1, wherein the printed mold layers to produce cathodes are configured to mold channels through which air is passed through the cathodes, and wherein the printed mold layers to produce anodes are configured to mold channels through which fuel is passed through the anodes.

8. The method of claim 7, wherein the channels in at least one of the cathodes and the anodes are zig-zagged in shape.

9. The method of claim 7, wherein the channels in at least one of the cathodes and the anodes are branched.

10. The method of claim 7, wherein the channels in at least one of the cathodes and the anodes comprise inlets and outlets and wherein the inlets have a larger diameter than the outlets.

11. The method of claim 7, wherein the channels in at least one of the cathodes and the anodes comprise inlets and outlets and wherein the inlets have a smaller diameter than the outlets.

12. The method of claim 1, wherein the second and fourth liquid compositions each comprise a binder to hold the second and fourth particles together, respectively, before sintering.

13. The method of claim 12, wherein the first and third liquid compositions each comprise a binder to hold the first and third particles together, respectively, before sintering.

14. The method of claim 12, wherein the binder hardens upon drying and / or heating.

15. The method of claim 12, wherein prior to sintering, the layer molds are removed without adversely affecting the binder.

16. The method of claim 15, wherein the layer molds are removed by melting, by solvent, by combustion, or by a combination of two or more methods.

17. The method of claim 1, wherein the layer molds comprise a hydrocarbon-based wax.

18. The method of claim 1, wherein the unsintered stack is sintered at a temperature above 1300 °C.

19. The method of claim 1, wherein the operational stack is operated at a temperature above 800 °C.

20. The method of claim 1, wherein the first particles are selected from the group consisting of lanthanum doped chromium oxide, lanthanum doped chromium ferrite, doped strontium titanate, platinum / platinum group metals, as well as combinations thereof.

21. The method of claim 1, wherein the second particles are selected from the group consisting of nickel oxide, yttria stabilized zirconia (YSZ), scandia stabilized zirconia (ScSZ), scandia ceria stabilized zirconia (ScCeSZ), ceria, gadolinium doped ceria, samaria-doped ceria (SmDCe), doped strontium titanate, cobalt oxide, and doped lanthanum chromium oxide, as well as combinations thereof.

22. The method of claim 1, wherein the third particles are selected from the group consisting of yttria stabilized zirconia (YSZ), scandia stabilized zirconia (SSZ), scandia ceria stabilized zirconia (ScCeSZ), ceria, gadolinium doped ceria, SDC, and BZYb and other Barium Zirconates BaZrO3, as well as combinations thereof.

23. The method of claim 1, wherein the fourth particles are selected from the group consisting of doped lanthanum chromate, LSM, YSZ, ScSZ, ScCeSZ, CGO, SDC, lanthanum cobaltites, lanthanum ferrites, and platinum group metals, as well as combinations thereof.

24. The method of claim 19, wherein the first, second, third, and fourth liquid compositions are water based.

25. The method of claim 19, wherein the first, second, third, and fourth liquid compositions further comprise a dispersant.

26. The method of claim 1, further comprising the step of adding pore forming particles to the appropriate moldable composition to achieve desired porosity in the SOER components.

Images