Solid oxide fuel cell with internal reformer

Abstract

Solid oxide fuel cell with an integrated reformer, comprising components arranged in a sandwich configuration in the following order: (i) an oxygen electrode (5, 25, 45, 65), (ii) a solid oxide electrolyte (4, 24, 44, 64), (iii) a fuel electrode (3, 23, 43, 53, 63), (iv) a fuel distributor (2, 22, 42, 52, 62) and (v) a reformer (1, 21, 41) having at least one grid layer (51) with a reforming catalyst (14) supported thereon; wherein the at least one grid layer (51) is arranged in at least one of the following configurations: (1) Arrangement on at least one region of the fuel distributor (42) on a side of the fuel distributor (2, 22, 42, 52, 62) facing the fuel electrode (3, 23, 43, 53, 63); and (2) Arrangement as a fifth aspect of the sandwich configuration adjacent to the fuel distributor (2, 22, 42, 52, 62) on a side of the fuel distributor (42) which is opposite a side facing the fuel electrode (43).

Description

GOVERNMENT RIGHTS

[0001] This invention was made with U.S. government support under Contract No. NNX15CC43P, awarded by the National Aeronautics and Space Administration. The U.S. government has certain rights in the invention. CROSS-REFERENCE TO RELATED APPLICATION

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 411,792 (WO 2018 / 080 570 A1), filed on October 24, 2016, which is hereby incorporated by reference in its entirety. FIELD OF THE INVENTION

[0003] In one aspect, the present invention relates to a solid oxide cell ("SOC"), in particular a solid oxide fuel cell ("SOFC") and its inverse embodiment, a solid oxide electrolysis cell ("SOEC"). More specifically, the present invention relates to a solid oxide fuel cell integrating a fuel reformer and its inverse embodiment, a solid oxide electrolysis cell integrating a heater. According to another aspect, the present invention relates to a method for generating electricity in the solid oxide fuel cell having the reformer integrated therein. According to yet another aspect, the present invention relates to a method for electrolyzing water, carbon dioxide, or a mixture thereof in the solid oxide electrolysis cell integrating the heater. BACKGROUND OF THE INVENTION

[0004] As is known in the art, the solid oxide cell ("SOC") is designed as a sandwich assembly comprising components in the following order: a fuel electrode, a solid oxide electrolyte, and an oxygen electrode, the fuel and oxygen electrodes being connected via an external electrical circuit. The solid oxide cell is a device which, in forward operation, provides for the electrochemical reaction of a fuel, such as hydrogen or carbon monoxide, with an oxidant, such as oxygen, to produce a direct electrical current and a chemical product, namely water or carbon dioxide, respectively. The same device, in reverse or regenerative operation, provides for the electrolysis of a fuel, namely water or carbon dioxide, to produce hydrogen and oxygen in the case of water, or alternatively, to produce carbon monoxide and oxygen in the case of carbon dioxide.

[0005] In an SOFC, the fuel is typically fed to the fuel electrode, where it reacts with oxide ions through oxidation to produce the oxidized product and a flow of electrons. The electrons migrate via an embedded current collector and the external circuit to the oxygen electrode, where molecular oxygen is reduced to oxide ions. During the transition, the electrons are available for useful work. The oxide ions produced at the oxygen electrode diffuse through the solid oxide electrolyte to the fuel electrode to complete the chemical reaction.

[0006] The solid oxide electrolyte typically comprises a ceramic material that is a good conductor of oxide ions but a poor conductor or insulator of electrons, ensuring that electrons flow through the external circuit. For example, the solid oxide electrolyte may be constructed of a ceramic material comprising yttria-stabilized zirconia (YSZ) sandwiched between a nickel oxide / YSZ cermet fuel electrode and a doped lanthanum manganite oxygen electrode.

[0007] Because each individual SOFC produces only a small, generally low voltage, a large number of individual fuel cells are typically connected in series to form a stack to achieve higher voltage and current. Each fuel cell stack includes interconnects (or bipolar plates) that separate the individual fuel cells, as well as flow distributors that deliver and distribute the fuel and oxygen flows to their respective electrodes within the stack and remove products from the stack. For the purposes of the present invention, the term "interconnect" is considered equivalent to, and interchangeable with, the term "bipolar plate."Furthermore, the term "fuel interconnect," as used herein, shall refer to an interconnect disposed on the fuel electrode side of the cell; whereas, the term "oxygen interconnect" shall refer to an interconnect disposed on the oxygen electrode side of the cell. The interconnects may be configured to provide dual functionality as flow distributors. Additionally, each fuel cell includes a current collector at each electrode, either as a separate layer or integrated into the associated interconnect. Each individual fuel cell in a stack is often referred to as a "fuel cell repeat unit."

[0008] US 2010 / 0227234 A1 discloses a fuel cell assembly with a fuel reforming unit for reforming a fuel supply for a series of fuel cells forming a fuel cell stack. The reformed fuel supply is first directed to the anode of the fuel cell closest to the reforming unit and then to a distributor outside the stack. The distributor receives the portion of the reformed fuel supply that is not yet completely consumed after passing the first anode and supplies this reformed fuel to the subsequent fuel cells in series. This ensures a gradual fuel supply throughout the stack and optimal fuel utilization in power generation.The reforming unit includes a series of baffles to direct the reformed fuel feed to the first anode and distributor, thus maximizing the utilization of the fuel consumed by the cells in the stack. Furthermore, the cooling generated by the endothermic reaction in the reforming unit is captured and optimally distributed throughout the stack to achieve optimal temperature gradients throughout the stack, enabling optimal operation and extended stack life.

[0009] US 2010 / 0227234 A1 discloses integrated reformer and fuel cell systems for the catalytic partial oxidation of liquid fuels (CPOX). These may comprise a plurality or an array of spaced-apart CPOX reactor units, each reactor unit comprising an elongated tube with a gas-permeable wall having inner and outer surfaces, the wall enclosing an open gas flow channel and having a CPOX catalyst and / or its structure disposed in at least one portion of the wall. The catalyst-containing wall structure and the open gas flow channel enclosed therein define a CPOX reaction zone in the gas phase, the catalyst-containing wall portion being gas-permeable to allow diffusion of the gaseous CPOX reaction mixture therein and of the hydrogen-rich reformate product therefrom.The CPOX liquid fuel reformer may further comprise a vaporizer, one or more igniters, and a source of liquid reformable fuel. The hydrogen-rich reformate may be converted to electricity in a fuel cell unit integrated into the CPOX liquid fuel reactor unit.

[0010] US 2005 / 0202159 A1 discloses a method for manufacturing a ceramic assembly. In one embodiment, the method for manufacturing a ceramic assembly comprises: disposing an electrode precursor on an electrolyte precursor with a sintering shrinkage of the electrolyte, disposing a stabilizer precursor with a sintering shrinkage of the stabilizer on the electrode precursor on a side opposite the electrolyte precursor to form a precursor assembly, and sintering the precursor assembly to form the ceramic assembly comprising a stabilizer layer, an electrode, and an electrolyte. The difference between the sintering shrinkage of the electrolyte and the sintering shrinkage of the stabilizer is at most ±1%, and a surface of the ceramic assembly has a curvature of at most about 5.0 degrees, measured from the horizontal plane.

[0011] US 2006 / 0123705 A1 discloses a fuel reformer comprising a housing having first and second opposing surfaces, a sidewall connecting the first and second opposing surfaces, and an inlet port and an outlet port in the sidewall. Also disposed within the housing are a plate assembly supporting a catalyst and baffles. A main baffle extends into the housing from a point on the sidewall between the inlet and outlet ports. The main baffle cooperates with the housing and the plate assembly to create a path for fuel gas flow through the reformer from the inlet port to the outlet port. At least one first baffle extends within the housing from one of the sidewalls or the main baffle and cooperates with the plate assembly and the housing to alter the gas flow path.For optimized thermal management of high-temperature fuel cells with internal reforming, a desired graded catalyst loading pattern was defined to achieve high cell performance.

[0012] US 2010 / 0227235 A1 discloses a reformer that generates a hydrogen-containing gas from a hydrocarbon-based fuel through a steam reforming reaction. The reformer comprises a reactor vessel and a reforming catalyst bed filled with a granular catalyst having steam reforming activity. The reformer comprises a partition plate that divides the reforming catalyst bed into at least two sections. The partition plate has a higher thermal conductivity than the effective thermal conductivity of the catalyst bed and extends within the reactor vessel from a portion having a higher temperature during nominal operation to a portion having a lower temperature during nominal operation.A high-temperature indirect internal reforming fuel cell has the reformer and a high-temperature fuel cell that generates electrical energy using a hydrogen-containing gas, and the reformer is arranged at a position where it receives heat radiation from the high-temperature fuel cell.

[0013] It is understood that in the aforementioned forward operation, the fuel for the SOFC is supplied as gaseous hydrogen or gaseous carbon monoxide. Since gaseous hydrogen and gaseous carbon monoxide must be pressurized and are not readily available as transportation fuels, these gaseous fuels impose limitations on the size and portability of the fuel cell. To address the problem of gaseous fuel supply, the prior art discloses devices in which a fuel reformer is integrated into the fuel cell or stack to convert, in situ and on demand, a readily available hydrocarbon fuel into a gaseous reformate that provides the hydrogen and carbon monoxide.Certain prior art, for example, US Pat. No. 4,647,516 A, discloses a reforming catalyst in the form of pellets or particles filled into channels or support structures arranged adjacent to the fuel electrode. Particle catalysts are disadvantageously cumbersome, heavy, and prone to abrasion losses. Further prior art, for example, US Pat. No. 6,051,329 A and US Pat. No. 2005 / 0 170 234 A1, disclose a reforming catalyst coated or dispersed on the fuel electrode (referred to as the "anode") or on an interconnect adjacent to the fuel electrode. Coated or dispersed designs, which are disposed directly on the interconnect and fuel electrode, are difficult to manufacture. Furthermore, both prior art designs have problems in that the reforming capability often impairs the expected capabilities of the fuel cell component; for example, the oxidation reaction at the fuel electrode or the current collection at the interconnect is reduced. Furthermore, coating the fuel electrode or interconnect with a reforming catalyst often reduces the reforming capability, leading to coking poisoning of the reforming and fuel cell components.

[0014] It should also be recognized that start-up of prior art solid oxide fuel cells undesirably requires a considerable amount of time. Typically, a supply of preheated oxygen or air is introduced into the cell to slowly heat the cell to its operating temperature of between 800°C and 1000°C. A fuel flow is also initiated at a specific temperature, and SOFC operation begins, approaching steady-state over time. Once the cell reaches its steady-state operating temperature, heat removal is required to ensure safe operation and an acceptable cell lifetime. Prior art solid oxide fuel cells lack fast and efficient heat addition and removal mechanisms.

[0015] In regenerative SOEC operation, a fuel, such as water or carbon dioxide, is fed to the fuel electrode, where the fuel is reduced with electrons supplied by an external power source provided to the cell, producing hydrogen or carbon monoxide and oxide ions. The oxide ions diffuse through the solid oxide electrolyte from the fuel electrode to the oxygen electrode, where electrons are released to produce oxygen gas. In this case, the electrons travel from the oxygen electrode to the fuel electrode through the external circuit.

[0016] Three operating modes for high-temperature electrolysis are generally known: 1) thermoneutral, 2) endothermic, and 3) exothermic. High-temperature electrolysis operates in thermal equilibrium when the electrical energy input equals the total energy demand, with a theoretical electrical conversion efficiency of 100 percent. In thermoneutral mode, the heat demand (Q) required to split water or carbon dioxide, calculated as the product of temperature (T) and entropy change (ΔS), equals the heat released by Joule heating (ohmic losses) in the cell. In exothermic mode, the electrical energy input exceeds the reaction enthalpy, which corresponds to an electrical efficiency below 100 percent. In this mode, heat is generated by the cell and can be reused in the system to preheat the incoming water and / or carbon dioxide.This mode also has the advantage of operating at a higher current density, resulting in a smaller system size; however, it can lead to premature aging of system components. Finally, in endothermic mode, the electrical energy input remains below the reaction enthalpy, resulting in a cell voltage below that in thermoneutral mode. Therefore, heat must be added to the system to maintain temperature.

[0017] The prior art discloses heaters arranged adjacent to one or more fuel cell stacks to provide the required heat input for SOEC operation. See, for example, International Patent Application Publication WO 2014 / 139822 A1. Generally, the arrangement of heaters in prior art devices does not provide for uniform heating of each cell repeat unit in the stack. This can lead to hot or cold spots within the stack, which place greater stress on one part of the stack than on another, ultimately either compromising the stack or rupturing one or more solid oxide cells within the stack.

[0018] The technology would benefit from design improvements in solid oxide cell repeating units and stack assemblies with an integrated reformer / heater unit. Improvements would desirably include faster start-up of the SOFC / SOEC cell and more efficient heat input and heat removal mechanisms compared to known designs. Other improvements include the use of a more compact reformer with higher efficiency and longer lifetime, minimizing coking at the reformer and fuel electrode. Still further improvements would include operation at a lower fuel cell peak temperature and providing greater temperature uniformity within the fuel cell stack, thereby improving fuel cell lifetime.

[0019] It is understood that any SOC system with an integrated reformer should minimize the size of the reformer. More importantly, the reformer should operate with a conversion efficiency of greater than approximately 80 percent in converting the hydrocarbon fuel to hydrogen and carbon monoxide in a single pass, otherwise the resulting reformate will contain a detrimentally high concentration of unreacted hydrocarbon, which may coke at SOFC operating temperatures and critically damage the fuel electrode. BRIEF DESCRIPTION OF THE INVENTION

[0020] According to one aspect, the present invention provides a solid oxide cell (SOC) comprising components arranged in a sandwich configuration in the following order: (i) an oxygen electrode, (ii) a solid oxide electrolyte, (iii) a fuel electrode, (iv) a fuel distributor and (v) at least one grid layer disposed adjacent to the fuel distributor on a side of the fuel distributor opposite a side facing the fuel electrode.

[0021] In certain exemplary embodiments, which are explained in detail below, the solid oxide cell (SOC) of the present invention operates in the forward direction as a solid oxide fuel cell (SOFC) or in the reverse direction as a solid oxide electrolysis cell (SOEC), or it operates in both the forward and reverse directions in a dual manner as a combined SOFC-SOEC.

[0022] In an exemplary embodiment, the present invention provides a solid oxide fuel cell (SOFC) with a reformer integrated therein, comprising components arranged in a sandwich configuration in the following order: (i) an oxygen electrode, (ii) a solid oxide electrolyte, (iii) a fuel electrode, (iv) a fuel distributor and (v) a reformer comprising at least one grid layer having a reforming catalyst supported thereon, wherein the at least one grid layer is arranged in at least one of the following configurations: (1) Arrangement on at least one region of the fuel distributor on a side of the fuel distributor facing the fuel electrode; and (2) Arrangement as a fifth aspect of the sandwich configuration adjacent to the fuel distributor on a side of the fuel distributor opposite a side facing the fuel electrode.

[0023] In a related aspect, the present invention provides a method for generating electricity in the aforementioned solid oxide fuel cell (SOFC) having a reformer integrated therein, comprising the steps of: (a) Providing a solid oxide fuel cell having components arranged in a sandwich configuration in the following order: (i) an oxygen electrode, (ii) a solid oxide electrolyte, (iii) a fuel electrode, (iv) a fuel distributor, (v) a reformer comprising at least one grid layer having a reforming catalyst supported thereon, wherein the at least one grid layer is arranged in at least one of the following configurations: (1) Arrangement on at least one region of the fuel distributor on a side of the fuel distributor facing the fuel electrode; and (2) Arrangement as a fifth aspect of the sandwich configuration adjacent to the fuel distributor on a side of the fuel distributor opposite a side facing the fuel electrode; (b) contacting oxygen with the oxygen electrode under conditions sufficient to generate oxide ions, wherein the oxide ions diffuse from the oxygen electrode through the solid oxide electrolyte to the fuel electrode; (c) contacting, at the reformer, a gaseous hydrocarbon fuel with steam or with an oxidant or with both steam and an oxidant in the presence of the reforming catalyst, wherein the contacting takes place under reaction conditions sufficient to produce a gaseous reformate comprising hydrogen and carbon monoxide; (d) distributing the reformate through the fuel distributor; and (e) contacting the reformate with the oxide ions at the fuel electrode under reaction conditions sufficient to produce water, carbon dioxide or a mixture thereof and an electric current.

[0024] The solid oxide fuel cell according to the present invention offers a combination of advantages not previously found in the prior art. First, the fuel cell according to the present invention eliminates the need for an external reformer and an associated balance of system components, including an external heat exchanger; thereby reducing the weight, size, and complexity that such external components add to the fuel cell stack assembly.Second, while prior art internal reforming designs place the reforming catalyst as a bed of particles adjacent to the fuel electrode, or as a coating bonded to the fuel electrode or fuel interconnect, or as a solid dispersed therein, the inventive solid oxide fuel cell, in contrast, places the reformer as a separate catalytic grid layer on or adjacent to the fuel manifold. In contrast to prior art designs, the invention is advantageously tailored to enable simplified manufacturing and uniform temperature throughout the cell repeat unit and stack assembly. Furthermore, the inventive grid structure, in a metallic and / or otherwise electrically conductive embodiment, provides rapid heat input for start-up and / or shutdown.The grid provides for fuel cell start-up through resistance heating or the exothermic reforming process (CPOX / ATR). Likewise, the grid ensures effective heat dissipation during steady-state operation via the endothermic reforming (SR) process. Active cooling of the fuel electrode via the reforming reaction taking place in the grid adjacent to the fuel electrode also reduces the required heat removal rate (namely, the rate of oxygen or air flow at the oxygen electrode), resulting in increased system efficiency and reduced parasitic losses. These benefits contribute to reducing thermal stress and moderating the SOC temperature, resulting in a longer SOC lifetime.

[0025] More specifically, the reformer used in the present invention, which comprises the grid with a reforming catalyst supported thereon, has demonstrated resistance to carbon formation during steam or partial oxidation reforming of gaseous hydrocarbons. The low thermal mass of the grid provides a substantially uniform temperature profile and the avoidance of carbon-producing cold spots in the reformer. Finally, improved geometric and specific surface areas of the grid support improved conversion of reactants. Compared to the direct supply of pure hydrogen or methane to the fuel cell, the present invention relies on the supply of hydrogen and carbon monoxide generated in the embedded reformer, resulting in increased power density and higher fuel utilization per fuel cell repeat unit.In addition, the reformer can be adapted to endothermic steam reforming (SR), exothermic catalytic partial oxidation (CPOX) or autothermal reforming (ATR) as required.

[0026] If desired, the present invention provides a water-neutral device and process by allowing the water generated during fuel cell operation to be cycled to the reformer and used in the steam reforming process. The present invention also readily allows for the recirculation of fuel off-gas to the fuel electrode, if desired, while minimizing adverse interaction with current collectors and flow distributors and collectors. The design is adaptable to solid oxide stacks from various manufacturers.

[0027] According to another exemplary embodiment, the present invention provides a solid oxide electrolysis cell (SOEC) having a heater integrated therein and components arranged in a sandwich configuration in the following order: (i) an oxygen electrode, (ii) a solid oxide electrolyte, (iii) a fuel electrode, (iv) a fuel distributor, (v) an insulator and (vi) a heater comprising at least one grid layer without a catalyst, the heater being arranged adjacent to the insulator on a side of the insulator opposite a side facing the fuel distributor.

[0028] According to a related aspect, the present invention provides a method for electrolyzing a fuel in the aforementioned solid oxide electrolysis cell (SOEC) having a heater integrated therein, the method comprising the following steps: (a) Providing a solid oxide electrolysis cell having a sandwich configuration in the following order: (i) an oxygen electrode, (ii) a solid oxide electrolyte, (iii) a fuel electrode, (iv) a fuel distributor, (v) an insulator and (vi) a heater comprising at least one grid layer without a catalyst, the heater being arranged adjacent to the insulator on a side of the insulator opposite a side facing the fuel distributor; (b) resistively heating the at least one grid layer and thereby supplying heat to the fuel electrode; (c) supplying a fuel through the fuel distributor and contacting the fuel and an electron supply at the fuel electrode under reaction conditions sufficient to produce a reduced chemical product and oxide ions, wherein the oxide ions migrate from the fuel electrode through the solid oxide electrolyte to the oxygen electrode; and (d) contacting the oxide ions with the oxygen electrode under conditions sufficient to produce molecular oxygen.

[0029] The aforementioned electrolysis cells and electrolysis process ensure rapid heat delivery to each individual solid oxide cell with temperature uniformity to drive endothermic electrolysis. The cell design minimizes adverse interaction with current collectors and flow distributors and can be readily adapted to SOC stacks from various manufacturers. DRAWINGS Fig. 1 shows an embodiment of a solid oxide fuel cell with integrated reformer according to the present invention, in particular of a repeating unit, illustrating a flow path through the SOFC with an internal reforming region. Fig. 2 shows another embodiment of a solid oxide fuel cell with integrated reformer according to the present invention. Fig. 3 shows another embodiment of a solid oxide fuel cell with integrated reformer according to the present invention. Fig. 4 shows another embodiment of a solid oxide fuel cell with integrated reformer according to the present invention. Fig. 5 shows a stack arrangement with a plurality of repeating units constituting the solid oxide fuel cell with integrated reformer according to the Fig. 4 illustrated embodiment. Fig. 6 shows an embodiment of a solid oxide electrolysis cell with integrated heating device according to the present invention. Fig. Figure 7 shows an embodiment of a solid oxide cell according to the invention, in particular of a repeating unit capable of regenerative operation. DETAILED DESCRIPTION OF THE INVENTION

[0030] In its basic concept, the solid oxide cell (SOC) described herein is capable of operating in the forward direction as a solid oxide fuel cell (SOFC) and in the reverse direction as a solid oxide electrolysis cell (SOEC). Each solid oxide cell, which is typically present multiple times in each fuel cell stack, has a sandwich configuration in the following order: (i) an oxygen electrode, (ii) a solid oxide electrolyte, (iii) a fuel electrode, (iv) a fuel distributor; and (v) at least one grid layer disposed adjacent to the fuel distributor on a side of the fuel distributor opposite a side facing the fuel electrode.

[0031] In an exemplary embodiment, the at least one grid layer supports a reforming catalyst capable of either steam reforming (SR), catalytic partial oxidation (CPOX), or autothermal reforming (ATR). In this embodiment, the at least one grid layer with the reforming catalyst supported thereon provides a reformer integrated with each SOC repeating unit in the stack. The resulting repeating unit and fuel cell stack convert a gaseous hydrocarbon, such as methane, into a gaseous reformate comprising hydrogen and carbon monoxide, and subsequently convert the reformate and an oxygen feed into oxidized chemical products, respectively, water and carbon dioxide, and a usable direct electrical current.

[0032] In a further exemplary embodiment, an electrical insulator, designed for example as a seal or frame, is additionally arranged between the fuel distributor and the at least one grid layer. In a further exemplary embodiment, the electrical insulator and the at least one grid layer are combined into a composite piece by applying the insulator to the at least one grid layer as a coating. In these embodiments, the grid does not support a reforming catalyst. The resulting embodiments operate as an electrolytic cell (SOEC) capable of electrolyzing water, carbon dioxide, or a mixture thereof at the fuel electrode to their respective related reduced products, hydrogen, carbon monoxide, or a mixture thereof. Oxygen is produced as a byproduct at the oxygen electrode.

[0033] In yet another exemplary embodiment, the solid oxide cell having the at least one grid layer comprises a reforming catalyst supported thereon and further comprises an electrical insulator, embodied, for example, as a gasket or frame, disposed between the fuel distributor and the at least one grid layer. In this embodiment, the resulting solid oxide cell provides dual or regenerative functionality, namely in the forward direction as a solid oxide fuel cell (SOFC) and in the reverse direction as a solid oxide electrolysis cell (SOEC). In this dual-function embodiment, the solid oxide cell comprises a sandwich configuration with components in the following order: (i) an oxygen electrode, (ii) a solid oxide electrolyte, (iii) a fuel electrode, (iv) a fuel distributor, (v) an insulator; and (vi) a dual reformer heater comprising at least one grid layer having a reforming catalyst supported thereon; wherein the at least one grid layer is disposed adjacent to the insulator on a side of the insulator opposite a side facing the fuel manifold.

[0034] In yet another embodiment, a plurality of any of the above-mentioned solid oxide cells according to the present invention, ie, individual repeating units, are connected in series to form a solid oxide stack. In another embodiment, the solid oxide stack is formed from at least one of the above-mentioned solid oxide cells according to the present invention and at least one of any conventional solid oxide cells. In another embodiment, a plurality of such stacks are combined to form a larger solid oxide cell system.

[0035] As mentioned with reference to Fig. 1, an embodiment according to the present invention (10) is shown consisting of a single solid oxide cell (cell repeating unit) (15) with a reformer integrated therein, which comprises the following components in a sandwich configuration: an oxygen interconnect (6), an oxygen electrode (5), a solid oxide electrolyte (4), a fuel electrode (3), a fuel distributor (2), and a reformer comprising at least one grid layer (1) with a reforming catalyst (14) supported thereon. As shown in Fig. 1, the fuel distributor (2), which also acts as a fuel interconnect or fuel bipolar plate, is formed from a solid material having a flat surface on a side (16) facing the at least one grid layer (1) and further having a series of grooves and channels on an opposite side (18) facing the fuel electrode (3). The grooves and channels serve to direct and distribute a fuel flow to contact the fuel electrode (3). Similarly, the oxygen interconnect (6) also acts as an oxygen distributor due to its design as a solid plate having a series of grooves and channels on a side facing the oxygen electrode (5) to direct and distribute an oxidant flow to contact the oxygen electrode (5) and to discharge it from the cell. In the Fig. In the embodiment illustrated in Figure 1, the grooves and channels of the fuel manifold (2) provide for reformate flow (8, 9) transverse to the oxygen flow (12, 11) provided by the grooves and channels in the oxygen interconnect (6). It is understood that the fuel and oxygen manifolds are not limited to flow structures consisting of grooves and channels; rather, they may provide a variety of other operable flow patterns. Alternative flow configurations include, for example, holes, pores, reticulated grids, and any combination thereof, including the aforementioned grooves and channels.

[0036] With respect to SOFC operation, a flow (7) of steam and a gaseous hydrocarbon fuel, e.g. methane, is fed through the reformer, which comprises at least one layer of a catalytic grid (1) at which the hydrocarbon is reformed under steam to produce a gaseous reformate (8) comprising hydrogen and carbon monoxide. The gaseous reformate (8) exiting the grid reformer (1) is redirected through the fuel distributor (2), which in the embodiment of the Fig. 1 consists of a plurality of flow channels and grooves at which the reformate contacts the fuel electrode (3) so that hydrogen and carbon monoxide are reacted with oxide ions to form water and carbon dioxide, which exit with any unreacted reformate via the fuel outlet stream (9). During the oxidation reaction, electrons are released into an external circuit (not shown) connecting the fuel electrode (3) to the oxygen electrode (5). The electrons migrate through the external circuit to the oxygen electrode (5) and can generate electrical work during the transition. At the oxygen electrode (5), a flow of oxygen or air (12) is introduced into the grooves and channels of the oxygen interconnect (6), where the oxygen is brought into contact with the oxygen electrode (5) and reduced to generate oxide ions.The oxide ions migrate from the oxygen electrode (5) through the solid oxide electrolyte (4) to the fuel electrode (3) to complete the electrochemical reaction. Unreacted oxygen or air exits via a flow (11) on the outlet side of the channels of the oxygen intermediate (6).

[0037] Fig. Figure 2 shows a further embodiment of the present invention (20) comprising the solid oxide fuel cell with integrated reformer from one repeating unit plus an oxygen interconnect from the next repeating unit. This comprises a sandwich construction with components in the following order: an oxygen interconnect (26), an oxygen electrode (25), an oxygen-side seal (27), a solid oxide electrolyte (24), a fuel electrode (23), a fuel-side seal (28), a fuel distributor (which also acts as a fuel interconnect) (22), a reformer having at least one grid layer (21) with a reforming catalyst bonded thereto, and the oxygen interconnect (29) from the adjacent fuel cell unit. As shown in Fig. 2, the grid reformer (21) is arranged on a side of the fuel distributor (22) opposite the side facing the fuel electrode (23). Fig. 2, the reformer (21) is shown as a layer without hatching and catalyst for clarity, but it is understood that the reformer has the previously mentioned catalytic lattice similar to the one shown in Fig. 1 shown embodiment (1). (The same applies to the Fig. 3 to 5). Compared to Fig. 1, where the fuel distributor (2) is constructed with grooves and channels to bring the reformate flow into contact with the fuel electrode (3), in the embodiment of the Fig. 2, the fuel distributor (22) has a series of pores and holes to bring the reformate flow into contact with the fuel electrode (23). Seals (28, 27) create seals that ensure that substantially all suitable gaseous flows come into contact with the fuel or oxygen electrodes (23, 25).

[0038] Fig. Figure 3 illustrates another embodiment of the present invention (40) including a solid oxide fuel cell with an integrated reformer from one repeating unit plus an oxygen interconnect from the next repeating unit. Here, too, a sandwich construction is provided in the following order: an oxygen interconnect (46), an oxygen electrode (45), an oxygen-side seal (47), a solid oxide electrolyte (44), a fuel electrode (43), a fuel-side seal (48), a fuel distributor (also acting as a fuel interconnect) (42), a reformer having at least one grid layer (41) with a reforming catalyst supported thereon, plus an oxygen interconnect (49) from the unit adjacent to the fuel cell unit. As shown in Fig. 3, the grid reformer (41) is arranged on the side of the fuel distributor (42) opposite the side facing the fuel electrode (43). In the present embodiment, the fuel distributor (42) is modified such that the reformer inlet and the fuel electrode outlet (anode outlet) are arranged on the same side / plane, which is a variation of the Fig. 1. The gas distribution is made uniform by modifying the channel configuration within the fuel distributor (42). Seals (48, 47) create seals that ensure that essentially all relevant gas flows come into contact with the fuel or oxygen electrodes (43, 45).

[0039] Fig. Figure 4 illustrates yet another embodiment of the invention (50), in which the reformer, which has the at least one grid layer (51) with the reforming catalyst deposited thereon, is arranged along a front edge of the fuel distributor (52) on a side of the fuel distributor (52) facing the fuel electrode (53). The term "front edge" refers to the edge of the fuel distributor at an inlet to the flow path, as shown in Fig. 4 is represented by an arrow.

[0040] Fig. Figure 5 shows an embodiment of the present invention (30) comprising a stack (33) formed from a plurality of solid oxide cell units with integrated reformer, each unit being as described above in Fig. 4 is described.

[0041] Fig. Figure 6 shows an exemplary embodiment (60) of the present invention of a single solid oxide cell integrating a heater and operating in SOEC mode. The model (60) has the following components in a sandwich configuration: an oxygen interconnect (66), an oxygen electrode (65), a solid oxide electrolyte (64), a fuel electrode (63), a fuel distributor (62) that also functions as a fuel interconnect or fuel bipolar plate, a first electrical insulator seal or frame (68), a heater (61) having at least one mesh layer, preferably a metal mesh, and a second electrical insulator (94) disposed on a side of the mesh (61) opposite a side facing the first electrical insulator (68). In this embodiment, no catalyst is supported on the mesh. As shown in Fig. 6, the fuel distributor (62) is formed from a solid material having a flat surface on a side facing the first insulator (68) and the heater (61), and further having a series of grooves and channels on an opposite side facing the fuel electrode (63), the grooves and channels being provided for directing and distributing a fuel flow (70) across the fuel electrode (63), exiting as flow (90). Similarly, the oxygen interconnect (66) is formed as a solid plate having a series of grooves and channels on a side facing the oxygen electrode (65) for directing and distributing a flow (92) of oxygen and optional purge gas, such as air, through the oxygen interconnect (66), which then exits the cell as flow (91).

[0042] With respect to SOEC operation, the heater (61), which has the at least one grid layer, is resistively heated to supply heat to the cell. The insulator seal (68) provides electrical insulation between the grid (61) and the electrically conductive fuel manifold (62). A fuel flow (70), which is in particular carbon dioxide or water or a mixture thereof, is introduced into the fuel manifold (62), where the fuel comes into contact with the fuel electrode (63) and, via the input of electrons originating from the electrical circuit, leads to the formation of oxide ions (O 2-) and a second chemical product. The second chemical product, which is hydrogen when the fuel is water, or carbon monoxide when the fuel is carbon dioxide, exits the channels of the fuel manifold (62) via the exit flow path (90). The oxide ions migrate from the fuel electrode (63) through the solid oxide electrolyte (64) to the oxygen electrode (65). At the oxygen electrode (65), the oxide ions are converted to oxygen, which is typically swept with a flow (92) of a sweep gas, such as air, oxygen, or steam, through the channels of the oxygen interconnect (66) and exits as flow (91). The electrons collected at the oxygen electrode (65) migrate via the external electrical circuit (not shown) to the fuel electrode (63), where they are consumed to complete the electrolysis reaction.

[0043] Fig. Figure 7 illustrates an embodiment of the SOC according to the present invention capable of regenerative operation, wherein a solid oxide cell (60) of Fig. 6 with components as described above, further comprising a reforming catalyst (14) supported on the grid (61), which in the present case is preferably a metal grid, so that a dual function of heating and reforming is provided. If all or a portion of the at least one grid layer (61) supports a reforming catalyst, the cell can operate in the forward direction as an SOFC and in the reverse direction as an SOEC. In this embodiment in SOFC operation, the fuel flow (72) is directed towards the reforming catalyst, and the reformate exiting as flow (78) is redirected through the fuel distributor (62), as shown in Fig.7. This dual mode of operation is known as “regenerative” mode.

[0044] The aforementioned embodiments of the present invention are illustrated in the accompanying drawings as a sandwich configuration of planar sheets. Other geometries may be suitable, including the planar sheets having a specific curvature. Generally, it is optimal for each layer in the sandwich configuration to have substantially identical external dimensions and an identical surface geometry, so that the layers of the sandwich fit together evenly for thermal and chemical efficiencies.

[0045] In terms of construction materials, the lattice offers a variety of useful functions in thin, compact, and lightweight sheets. In one aspect, the lattice acts as a catalyst substrate. For this function, a steam reforming catalyst (SR), a catalytic partial oxidation catalyst (CPOX), or an autothermal reforming catalyst (ATR) is supported on the lattice such that the resulting catalytic lattice is capable of converting a gaseous hydrocarbon into a gaseous reformate containing hydrogen and carbon monoxide in the presence of steam and / or an oxidizer.In another aspect, the grid, when provided in a metallic or otherwise electrically conductive embodiment, acts as a resistive heating element, rapidly transferring heat across the grid with considerable uniformity to start the reformer for SOFC operation, as well as to provide heat for operation under standby or low-load operating conditions. Accordingly, in one embodiment, an external burner capable of combusting a burner gas such as hydrogen, carbon monoxide, or methane to generate heat to start the SOFC is unnecessary and is eliminated. During steady-state operation of the SOFC, no further resistive heating is required, and the cell generates an exotherm from the electrochemical reaction.In yet another aspect, when the anode / fuel electrode tail gas is recycled to the reformer, the SOFC system of the present invention further minimizes the load on an external combustor to provide the heat required for the recycling process. In SOEC mode, the conductive grid provides continuous heat input through electrical resistance heating for endothermic electrolysis reactions.

[0046] Each grid layer used in the present invention resembles a two-dimensional lattice-like membrane or grid having a plurality of cavities ("cells"), with a third dimension comprising an ultrashort channel length flow path that, in one embodiment, is equal to or not much longer than the diameter of the elements forming the grid. For the purposes of the present invention, the term "ultrashort channel length" refers to channel lengths in a range of about 25 micrometers (µm) (0.001 in.) to about 500 µm (0.02 in.). In one exemplary embodiment, the ultrashort channel length is in the range of about 50 µm (0.002 in.) to about 150 µm (0.006 in.).In contrast, prior art monoliths are three-dimensional structures with long flow paths or channels passing through them, where such long channels refer to a channel length of more than about 1 mm (0.039 inches) and often more than about 5 mm (0.20 inches).

[0047] More specifically, each grid layer in the present invention is typically formed with a plurality of channels or pores having a diameter in the range of about 0.25 millimeters (mm) to about 1.0 mm, with an empty space of greater than about 60 percent, preferably up to about 80 percent or more. A channel length to diameter ratio is generally less than about 2:1, preferably less than about 1:1, and even more preferably less than about 0.5:1. Preferably, the ultrashort channel length grid has a cell density in the range of about 100 to about 1000 cells or flow paths per square centimeter.

[0048] In terms of construction materials, the lattice layers can be individually selected from metals, non-metals, such as ceramic materials, and mixtures of ceramic materials and metals, including cermets. The choice of lattice is tailored to the application. Only for SOFC operation are the lattice layers subject to no restrictions, and any metals, ceramic materials, or mixtures thereof are suitable. Only for SOEC operation are the lattice layers individually constructed from metals or similar electrically conductive materials suitable for resistive heating. For regenerative operation in both SOFC and SOEC modes, the lattice layers are individually constructed from metals or similar electrically conductive materials capable of resistive heating.The lattice is not limited by any manufacturing method; for example, lattices may be formed by weaving or welding fibers, or by an expanded metal technique, as disclosed in US 6,156,444, which is incorporated herein by reference, or by 3D printing or a lost polymer backbone process.

[0049] In more specific exemplary embodiments, the metal mesh is formed from any conductive metal or combination of metals, provided that the resulting structure can withstand the temperatures and chemical environment to which it is exposed. Suitable non-limiting construction materials for the metal mesh include iron-chromium alloys, iron-chromium-aluminum alloys, and iron-chromium-nickel alloys. Such metal meshes are commercially available from, for example, Alpha Aesar and Petro Wire & Steel. In one embodiment, the metal mesh comprises a Microlith® brand metal mesh available from Precision Combustion, Inc., North Haven, Connecticut, USA.As described in U.S. Patents 5,051,241 and 6,156,444, which are incorporated herein by reference, Microlith® grating technology represents a unique design that combines an ultra-short channel length with low thermal mass in a monolith, in contrast to prior art monoliths with much longer channel lengths than those mentioned above.

[0050] The term "ceramic material" refers to inorganic, non-metallic solid materials with a predominant covalent bond, including, but not limited to, metal oxides such as oxides of aluminum, silicon, magnesium, zirconium, titanium, niobium, and chromium, as well as zeolites and titanates. Reference is made to U.S. Patents 6,328,936 and 7,141,092, which detail ultrashort channel length ceramic mesh insulating layers incorporating woven silica, both of which are incorporated herein by reference. The term "cermet" refers to a composite material comprising a ceramic material in combination with a metal, wherein the composite is typically conductive while also exhibiting high temperature, corrosion, and abrasion resistance similar to ceramic materials.

[0051] Compared to prior art monoliths, the ultra-short channel length lattice facilitates the packaging of a larger active surface area in a smaller volume and provides an increased reactive area for a given pressure drop. While conventional honeycomb monoliths with conventional long channels have a fully developed boundary layer over a considerable length of the channels, the ultra-short channel length property of the lattice useful in the present invention avoids boundary layer buildup. Since heat and mass transfer coefficients are dependent on boundary layer thickness, avoiding boundary layer buildup improves transport properties. The advantages of using the ultra-short channel length lattice, and preferably the Microlith® brand, to control and limit the development of a boundary layer of a fluid passing therethrough are described in U.S. Patent No.No. 7,504,047, which is a continuation-in-part of U.S. Patent No. 6,746,657, both of which patents are incorporated herein by reference.

[0052] In another exemplary embodiment, the lattice is formed from an analogous structure of metal, ceramic material, or other fabricated or patterned substrate material with an ultrashort channel length, having an interconnected network of solid struts forming a plurality of pores with an open-cell configuration. The pores may have any shape or diameter; however, typically, a number of pores forming one inch denotes a "pore size," which for most purposes ranges from about 5 to about 80 pores per inch. The relative density of such structures, taken as the density of the structure divided by the density of the solid starting material of the struts, typically ranges from about 2 to about 15 percent.Fabricated or patterned ultrashort channel length substrates are commercially available in a variety of materials that can withstand the operating temperatures of the SOFC and SOEC according to the present invention.

[0053] In the solid oxide cell of the present invention, it is desirable to use 1 to about 10 grid layers per SOC repeat unit. In another embodiment, 1 to about 4 grid layers are used per SOC repeat unit. It is understood that the reforming catalyst, if present, is coated on each grid layer in one embodiment. Alternatively, in another embodiment, the reforming catalyst is coated on at least one, but not all, of the grid layers present. For example, it is possible to use 3 grid layers, with the middle layer coated with a reforming catalyst, while the top and bottom layers are not.

[0054] In another exemplary embodiment, the deposition of the reforming catalyst onto the grid is varied along the length of the grid layer in the direction of fuel flow, thereby providing a catalyst concentration gradient along the direction of fuel flow. In yet another embodiment, the catalyst is deposited onto the grid in a predetermined pattern sufficient to provide a predetermined thermal gradient across the grid under reforming conditions. These two embodiments provide a method for controlling temperature during the reforming process while minimizing thermal stresses on the solid oxide cell. More specifically, in one embodiment, the loading or deposition of the reforming catalyst increases along the length of the grid in the direction of fuel flow.In another embodiment, the reforming catalyst loading increases from an inlet of the fuel flow to a maximum at approximately a midpoint of the length of the grid in the direction of fuel flow and then decreases from the midpoint to the end of the grid at the outlet of the fuel flow.

[0055] The arrangement of the grid in each fuel cell repeat unit is provided in several different embodiments. In one embodiment, the grid is provided on at least a portion of the fuel manifold on a side of the fuel manifold facing the fuel electrode. One way to implement this embodiment involves positioning the grid in at least one layer at the leading edge of the fuel manifold. The term "leading edge" refers to an inlet edge of the flow manifold, where fuel is introduced into the manifold. In contrast, the term "trailing edge" refers to an exit edge of the fuel manifold, where product gases exit the SOC. Another embodiment involves positioning the grid in and along channels or grooves of the fuel manifold.For example, grid strips may be arranged in at least a portion of the channels and grooves of the fuel distributor, preferably along the length of the channels and grooves from the leading edge to the trailing edge. There are no restrictions on the manner in which the grid layer(s) are arranged on the fuel distributor. In addition to the embodiments described above, many other operational embodiments are conceivable.

[0056] In another embodiment, at least one grid layer is disposed adjacent to the fuel distributor on a side of the fuel distributor opposite a side facing the fuel electrode. In another embodiment, at least one grid layer is disposed adjacent to an electrical insulator, which in turn is disposed adjacent to the fuel distributor. Both the electrical insulator and the grid are disposed on a side of the fuel distributor opposite a side of the fuel distributor facing the fuel electrode.

[0057] Any catalyst capable of converting a hydrocarbon fuel into a gaseous mixture containing hydrogen and carbon monoxide (synthesis gas) by either steam reforming (SR), catalytic partial oxidation (CPOX), or autothermal reforming (ATR) is supported for catalytic purposes on the grid in a suitable manner, in particular by layering the catalyst onto the grid. Such catalysts comprise at least one metal selected from metals of Group VIII of the Periodic Table, including iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium, platinum, and combinations thereof. Preferably, the catalyst is selected from the platinum group metals (PGMs), which include ruthenium, rhodium, palladium, osmium, iridium, platinum, and combinations thereof. In one embodiment, the catalyst is supported on an oxide washcoat, suitable non-limiting species of which include titanium dioxide (TiO 2, e.g., anatase and rutile phases), silica (SiO2), magnesium oxide (MgO), alumina (Al2O3), zirconium oxide (ZrO2), and mixtures thereof. The catalyst is bonded to the lattice, with or without the oxide washcoat, by any conventional coating fabrication method known in the art.

[0058] Materials suitable for the fuel and oxygen electrodes should be stable at operating temperatures; should have a thermal expansion coefficient compatible with that of the solid oxide electrolyte; and should be chemically compatible with the solid oxide electrolyte and other materials during fabrication and operation of the solid oxide cell. Functionally, the role of the fuel electrode in forward flow is to combine the oxide ions diffusing through the electrolyte with the gaseous reformate fuel fed to the fuel electrode to produce water and carbon dioxide, as well as a flow of electrons. Typically, the fuel electrode is constructed from a porous ceramic layer that allows the gaseous reformate to flow evenly from the inlet to the outlet.Because the fuel electrode must be electrically and ionically conductive, the fuel electrode typically comprises a combination of ceramic material and metal (cermet) manufactured using standard ceramic processing techniques. Non-limiting examples of cermets suitable as fuel electrodes include nickel-yttria-stabilized zirconia, i.e., Ni-Y2O3-stabilized ZrO2 (Ni-YSZ), and nickel mixed with gadolina-doped ceria, Ni-[(CeO2). 0,8 (GdO2) 0,7 (ZrO2) 0.202 ], also written as Ni-(Ce,Gd)O2, or Ni-(GDC), nickel mixed with yttria-doped ceria-zirconia Ni-[Y2O3-(CeO2) 0,7 (ZrO2) 0,3 ], also written as Ni-YDCZ, and nickel mixed with yttria-doped zirconia (Ni-Y-stabilized ZrO2), also written as Ni-YSZ. Other suitable fuel electrode materials include strontium vanadium molybdenum oxide (Sr2VMoO 6-δ) and lanthanum strontium manganese chromium oxide (LSCM) [(La 0,75 Sr 0,25 ) Mn 0,3 Cr 0,3 O3).

[0059] The solid oxide electrolyte comprises a dense ceramic layer containing oxide ions (O 2- ). Examples of materials from which the solid oxide electrolyte layer can be made include yttria-stabilized zirconia (YSZ), scandium-stabilized zirconia (ScSZ), and gadolinium-stabilized ceria (GDC), as well as ceria-based electrolytes with a fluorite structure and lanthanum gallate (LSGM) with a perovskite crystal structure. As newer electrolytes are developed, these can lead to reduced resistance issues and improved conductivity of oxide ions, which in turn can lead to more robust and high-performance electrolyte layers, any of which can be used in the present invention.

[0060] The oxygen electrode should also be porous to ensure a uniform flow of oxygen throughout the electrode and should retain oxide ions (O 2 ) to the solid oxide electrolyte. Non-limiting examples of materials from which the oxygen electrode may be formed include manganese-modified yttria-stabilized zirconia (Mn-YSZ), lanthanum strontium manganite (LSM), lanthanum strontium ferrite (LSF), (La,Sr)(Co,Fe)O3, and any of the cobalites.

[0061] It should be understood that the present invention is in no way limited by the thickness of any of the fuel electrode, solid oxide electrolyte, or oxygen electrode layers. The thickness of each layer depends, in part, on whether the solid oxide cell is "electrode-supported" or "electrolyte-supported." The term "supported" refers to the layers that provide structural strength to the cell. Other suitable supports include "metal-supported" cells. The greater the emphasis on structural strength, the thicker the layer typically is. Thus, a solid oxide cell can be constructed with the fuel or oxygen electrode the thickest and the electrolyte layer the thinnest. Alternatively, a solid oxide cell can be constructed with the electrolyte layer the thickest and the fuel and oxygen electrodes thinner.

[0062] Each individual solid oxide cell according to the present invention produces less than approximately 1 V under typical operating conditions in SOFC mode, but most SOFC applications require higher voltages. Accordingly, for most practical applications, a plurality of individual SOC repeat units according to the present invention are electrically connected in series to form a stack, thereby achieving a higher voltage required by the application. The stack is constructed by securing each SOC repeat unit between two interconnects that provide strength to the stack and separate the repeat units from each other.

[0063] Because the interconnects are exposed to both the oxidizing and reducing sides of the fuel cell at high temperatures, the interconnects must be very stable. Accordingly, the interconnects are made of any electrically conductive material that can withstand the thermal and chemical environment to which they are exposed. In one embodiment, the interconnects are made of a metallic plate or foil, for example, high-temperature stainless steels such as SS446, SS430, AL454, E-Brite, Crofer 22, or iron-chromium (FeCr) alloys or nickel-chromium (NiCr) alloys. In another embodiment, the interconnects are constructed of cermets (metal-doped ceramic materials), which provide acceptable thermal stability and electrical conductivity.The present invention is not limited to any particular interconnect thickness and any particular interconnect materials.

[0064] It is understood that the fuel-side interconnect forms an additional layer distinct from the grid layer(s) of the present invention, which support the reforming catalyst and function as a reformer and heater. Accordingly, each solid oxide stack typically includes at least one grid layer of the present invention and at least one layer or construction of conventional interconnects within each SOC, which, depending on the design, may additionally function as a fuel distributor and / or current collector. The current collector may be any electrically conductive material, typically metallic and preferably a silver or copper membrane.

[0065] Because each SOC repeat unit in the stack is sandwiched between two interconnects, gaskets are provided around the edges of each repeat unit to ensure a gas-tight seal. The gaskets are typically made of ceramic material (not doped with metal), glass, or a rubber-like gasket.

[0066] Other parts, such as separators and insulators, can be formed from any suitable material that can withstand the temperature and chemicals to which the parts are exposed. The electrical insulator required in certain embodiments of the present invention is formed from any electrically non-conductive material, including heat-resistant ceramic materials that are not doped with metals.

[0067] In forward SOFC operation, the hydrocarbon fuel fed to the reformer includes any hydrocarbon that is in a gaseous state at about 22°C and a pressure of about 1 atm (101 kPa), or any liquid hydrocarbon that is readily vaporized and fed to the reformer as steam. Non-limiting examples of such gaseous hydrocarbons include methane, natural gas, ethane, propane, butane, biogas, and mixtures thereof. Non-limiting examples of liquid hydrocarbons that are readily vaporized include hexane, octane, gasoline, kerosene, and diesel. If steam reforming (SR) is desired, a flow of liquid water is placed in thermal contact with the stack to utilize the heat of the stack to generate the required steam, which is then fed with the hydrocarbon gas to the reformer.The molar ratio of steam to carbon in the hydrocarbon fuel (S / C ratio) during steady-state operation typically ranges from about 1.5:1 to about 4.0:1. When the reformer operates as an exothermic process, an air- or oxygen-containing oxidant stream is fed to the reformer along with the gaseous hydrocarbon, either with steam (ATR) or without steam (CPOX). The oxidant may additionally contain other oxygen-containing components, such as carbon dioxide.The relative amount of oxygen atoms in the oxidizer to carbon atoms in the gaseous hydrocarbon fuel (O / C ratio) as fed to the reformer typically ranges from about 0.1:1 to about 1.3:1, but should preferably be "fuel-rich," or have an atomic carbon content higher than the atomic oxygen content so that little, if any, conversion of the hydrocarbon fuel to carbon dioxide and water occurs. It is understood that when using an oxidizer, the device will be designed, via an O / C ratio or other means, to minimize contact of the oxidizer with the fuel electrode, thereby avoiding electrode damage.In one embodiment, the SOFC is operated with a mixture of hydrocarbon fuel, such as methane, and oxygen until a steady-state operating temperature is reached, at which point the SOFC transitions to steam reforming with a mixture of hydrocarbon fuel and steam. If desired, recirculation of the fuel electrode off-gas (anode tail gas) can optionally be performed with a small amount of oxygen.

[0068] In general, the SR reformer operates at a temperature close to the fuel electrode temperature, typically between about 500 °C and about 1000 °C. CPOX reformers operate at a slightly higher temperature, between about 700 °C and about 1100 °C. The total pressure of the solid oxide fuel cell typically ranges from about 1 bar (100 kPa) to about 5 bar (500 kPa). In SOFC operation, the weight hourly space velocity of the total gas flow to the reformer typically ranges from about 250 liters per hour per gram of catalyst (L / h / g-cat) to about 6000 L / h / g-cat.

[0069] In SR, CPOX, or ATR operation, the reformer output to the fuel electrode is a gaseous reformate comprising hydrogen and carbon monoxide (synthesis gas), although a large amount of nitrogen may be present when air is used as the oxidant. Other byproducts in acceptably small amounts include one or more of carbon dioxide, water, and methane. The lattice reformer used in the present invention produces minimal amounts of unreacted hydrocarbons, resulting in minimal coke formation, longer catalyst life, and less reformer and SOC degradation. It is understood that the conversion of the hydrocarbon fuel in the reforming stage is governed by equilibrium concentrations at the operating temperature.Nevertheless, the lattice reformer of the present invention is capable of achieving a hydrocarbon conversion efficiency of greater than about 80% and even greater than about 90% relative to a steady-state efficiency of 100% in a single pass through the reformer at operating temperatures of 650°C or higher. Furthermore, the lattice reformer used in the present invention can operate for up to 1000 hours without any observable degradation in the performance of the reforming catalyst. In addition, the reformer of the present invention can be cycled through multiple starts and shutdowns without degradation in performance.

[0070] In SOEC operation, the fuel supplied to the fuel electrode comprises water, carbon dioxide, or a mixture thereof. The fuel may contain unreactive components such as hydrogen. Electrons are supplied via an external DC circuit. A purge gas, such as air or an inert gas including, for example, nitrogen or helium, is typically used to remove the generated oxygen from the cell. The operating temperatures, pressures, and space velocities are similar to those specified above for SOFC operation.

[0071] The invention has been described only in connection with a limited number of embodiments, but it is to be clearly understood that the invention is not limited to such disclosed embodiments. Rather, the invention may be modified to include any number of variations, alterations, substitutions, or equivalent arrangements not heretofore described, but which are within the spirit and scope of the invention. While various embodiments of the invention have been described, it is also to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be considered limited by the foregoing description, but is limited only by the scope of the appended claims.

Claims

[1] Solid oxide fuel cell with an integrated reformer, which has components arranged in a sandwich configuration in the following order: (i) an oxygen electrode (5, 25, 45, 65), (ii) a solid oxide electrolyte (4, 24, 44, 64), (iii) a fuel electrode (3, 23, 43, 53, 63), (iv) a fuel distributor (2, 22, 42, 52, 62) and (v) a reformer (1, 21, 41) having at least one grid layer (51) with a reforming catalyst (14) supported thereon; wherein the at least one grid layer (51) is arranged in at least one of the following configurations: (1) Arrangement on at least one region of the fuel distributor (42) on a side of the fuel distributor (2, 22, 42, 52, 62) facing the fuel electrode (3, 23, 43, 53, 63); and (2) Arrangement as a fifth aspect of the sandwich configuration adjacent to the fuel distributor (2, 22, 42, 52, 62) on a side of the fuel distributor (42) which is opposite a side facing the fuel electrode (43). [2] Solid oxide fuel cell according to claim 1, wherein the at least one grid layer (51) each individually has an ultrashort channel length in the range of more than 25 µm to less than 500 µm and a cell density in the range of 100 to 1000 cells per square centimeter. [3] A solid oxide fuel cell according to claim 1 or 2, wherein 1 to 10 grid layers (51) are used, which are optionally provided in a planar configuration. [4] Solid oxide fuel cell according to one of claims 1 to 3, wherein the grid (61) is formed from a metal grid to which the reforming catalyst (14) is applied as a coating. [5] Solid oxide fuel cell according to one of claims 1 to 3, wherein the grid (61) is formed from a ceramic material or a cermet on which the reforming catalyst (14) is applied as a coating. [6] A solid oxide fuel cell according to any one of claims 1 to 5, wherein the reforming catalyst (14) comprises at least one metal selected from elements of Group VIII of the Periodic Table. [7] Solid oxide fuel cell according to one of claims 1 to 6, wherein the reforming catalyst (14) is applied to the at least one grid layer (51) with a concentration gradient measured along the direction of the fuel flow (70). [8] A solid oxide fuel cell according to claim 7, wherein the reforming catalyst (14) is applied to the at least one grid layer (51) in a concentration that increases from a beginning to a center of the grid (61) and decreases from the center to an end of the grid (61), as measured along the direction of the fuel flow (70). [9] A solid oxide fuel cell according to claim 7, wherein the reforming catalyst (14) is applied to the at least one grid layer (51) in a concentration that increases from a beginning to an end of the grid (61) as measured along the direction of the fuel flow (70). [10] A solid oxide fuel cell according to any one of claims 1 to 9, wherein the fuel distributor (42) is formed with a plurality of grooves and channels or with a plurality of holes and pores or a combination thereof. [11] Solid oxide fuel cell according to one of claims 1 to 10, wherein the at least one grid layer (51) is arranged in a predetermined pattern on the fuel distributor (2, 22, 42, 52, 62). [12] A solid oxide fuel cell according to claim 11, wherein the at least one grid layer (51) is arranged along a front edge of the fuel distributor (2, 22, 42, 52, 62). [13] Solid oxide fuel cell according to claim 11, wherein the at least one grid layer (51) is provided in the form of strips arranged in channels and grooves in the fuel distributor (2, 22, 42, 52, 62). [14] Solid oxide fuel cell according to one of claims 1 to 10, wherein the at least one grid layer (51) as a fifth aspect of the sandwich configuration is arranged adjacent to the fuel distributor (2, 22, 42, 52, 62) on a side of the fuel distributor (2, 22, 42, 52, 62) which is opposite a side facing the fuel electrode (3, 23, 43, 53, 63). [15] A solid oxide fuel cell according to claim 14, comprising a sixth component having an interconnection adjacent to the at least one grid layer (51) on a side of the grid (61) opposite a side facing the fuel distributor (2, 22, 42, 52, 62). [16] A solid oxide fuel cell according to any one of claims 1 to 15, wherein the at least one grid layer (51) comprises a structured material having 5 to 80 pores per inch and a density in the range of 2 to 15 percent relative to a density of a starting material from which the structured material is made. [17] A solid oxide fuel cell according to any one of claims 1 to 16, wherein the fuel electrode (3, 23, 43, 53, 63) is selected from nickel-yttria-stabilized zirconia, gadolinium-doped ceria-mixed nickel, yttria-doped ceria-zirconia-mixed nickel, strontium-vanadium-molybdenum-oxide, and lanthanum-strontium-manganese-chromium-oxide, and mixtures thereof. [18] A solid oxide fuel cell according to any one of claims 1 to 17, wherein the solid oxide electrolyte (4, 24, 44, 64) is selected from yttria-stabilized zirconia, scandium oxide-stabilized zirconia, gadolinium-stabilized ceria, ceria-based electrolytes with a fluorite structure and lanthanum gallate with a perovskite crystal structure and mixtures thereof. [19] Solid oxide fuel cell according to one of claims 1 to 18, wherein the oxygen electrode (5, 25, 45, 65) is selected from manganese-modified yttria-stabilized zirconia, lanthanum strontium manganite, lanthanum strontium ferrite, cobalites and mixtures thereof. [20] A solid oxide fuel cell stack comprising at least one solid oxide fuel cell according to any one of claims 1 to 19. [21] A method for generating electricity in a solid oxide fuel cell with a reformer integrated therein, comprising the following steps: (a) Providing a solid oxide fuel cell having components arranged in a sandwich configuration in the following order: (i) an oxygen electrode (5, 25, 45, 65), (ii) a solid oxide electrolyte (4, 24, 44, 64), (iii) a fuel electrode (3, 23, 43, 53, 63), (iv) a fuel distributor (2, 22, 42, 52, 62), and (v) a reformer (1, 21, 41) having at least one grid layer (51) with a reforming catalyst (14) supported thereon; wherein the at least one grid layer (51) is arranged in at least one of the following configurations: (1) Arrangement on at least one region of the fuel distributor (2, 22, 42, 52, 62) on a side of the fuel distributor (2, 22, 42, 52, 62) facing the fuel electrode (3, 23, 43, 53, 63); and (2) Arrangement as a fifth aspect of the sandwich configuration adjacent to the fuel distributor (2, 22, 42, 52, 62) on a side of the fuel distributor (2, 22, 42, 52, 62) which is opposite a side facing the fuel electrode (3, 23, 43, 53, 63); (b) contacting oxygen with the oxygen electrode (5, 25, 45, 65) under conditions sufficient to generate oxide ions, wherein the oxide ions diffuse from the oxygen electrode (5, 25, 45, 65) through the solid oxide electrolyte (4, 24, 44, 64) to the fuel electrode (3, 23, 43, 53, 63); (c) contacting a gaseous hydrocarbon fuel with steam or with an oxidant or with both steam and an oxidant at the reformer (1, 21, 41) in the presence of the reforming catalyst (14), the contacting taking place under reaction conditions sufficient to produce a gaseous reformate comprising hydrogen and carbon monoxide; (d) distributing the reformate through the fuel distributor (42); and (e) contacting the reformate with the oxide ions at the fuel electrode (3, 23, 43, 53, 63) under reaction conditions sufficient to produce water, carbon dioxide or a mixture thereof and electric current. [22] The process of claim 21, wherein the oxygen is provided as molecular oxygen or air; and wherein the gaseous hydrocarbon fuel is selected from methane, natural gas, ethane, propane, butane, biogas, and mixtures thereof; or wherein the gaseous hydrocarbon fuel is selected from vapors of hexane, octane, gasoline, kerosene, diesel, and mixtures thereof. [23] The method of claim 21 or 22, wherein the at least one grating layer (51) each individually has an ultrashort channel length in the range of more than 25 µm to less than 500 µm and a cell density in the range of 100 to 1000 cells per square centimeter. [24] Method according to one of claims 21 to 23, wherein the grid (61) is formed from a metal grid to which the reforming catalyst (14) is applied as a coating. [25] Method according to one of claims 21 to 23, wherein the grid (61) is formed from a ceramic material or cermet to which the reforming catalyst (14) is applied as a coating. [26] A process according to any one of claims 21 to 25, wherein the total pressure under operating conditions is in the range of 100 kPa to 500 kPa; wherein the weight hourly space velocity of the total gas flow to the reformer (1, 21, 41) is in the range of 250 liters per gram of catalyst per hour (L / hg-cat) to about 6000 L / hg-cat. [27] A process according to any one of claims 21 to 26, wherein under operating conditions the temperature in the reformer (1, 21, 41) is in the range of 500 °C to 1000 °C for steam reforming or 700 °C to 1100 °C for catalytic partial oxidation.

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