Compact high-temperature electrochemical cell stack architecture

Abstract

To provide a fuel cell assembly and a modular fuel cell system.SOLUTION: A fuel cell assembly includes a first housing base. The first housing base includes: a lower gas supply part including a first fuel inlet pipe extending from a first end of the first housing base to a second end of the first housing base and a first used fuel outlet pipe extending from the first end of the first housing base to the second end of the first housing base; an upper mounting plate including a plurality of through holes; and a gas distribution part positioned between the lower gas supply part and the upper mounting plate, the gas distribution part including a plurality of inlet gas distribution channels for fluidically coupling the first fuel inlet pipe to a first subset of the plurality of through holes and a plurality of outlet gas distribution channels for fluidically coupling the first used fuel outlet pipe to a second subset of the plurality of through holes.SELECTED DRAWING: Figure 7A

Description

[Technical Field]

[0001] Cross-reference of related applications This application claims priority and interest to U.S. Provisional Patent Application No. 62 / 501,633, “High Power Density Compact SOFC Stack,” filed on 4 May 2017, the entire disclosure of which is incorporated herein by reference.

[0002] Statement of government rights This invention was created with government support under award number DE-FE0026093, awarded by the DOE. The government reserves certain rights in this invention.

[0003] This disclosure relates to high-temperature fuel cell stacks and electrolytic stacks, and more particularly to solid oxide (SOFC) and solid oxide electrolytic cell (SOEC) stacks, and more specifically to high-power-density compact SOFC stacks. [Background technology]

[0004] Solid oxide fuel cells contain an electrolyte sandwiched between a cathode and an anode. Oxygen reacts with electrons at the cathode to form oxygen ions, which are then conducted to the anode through an ion-conducting ceramic electrolyte. At the anode, the oxygen ions combine with available fuel (e.g., hydrogen and carbon monoxide, methane, some other hydrocarbons, or other suitable fuels) to form products (e.g., water and carbon dioxide), thereby releasing electrons and generating electricity. Such technology can also be operated in reverse to perform electrolysis, forming fuel gas and oxygen when suitable reactants (e.g., water and carbon dioxide) and electricity are supplied. In this implementation form, the technology is called a solid oxide electrolytic cell. Numerous approaches have been seen in the development of SOFCs (anode, cathode, or electrolyte support, monolithic ceramic-to-metal interconnects, planar-to-tubular, and their variations). The biggest challenge to commercializing this technology is achieving a marketable price, reasonable performance, and service life simultaneously. These drivers are closely related. [Overview of the project]

[0005] Embodiments described herein generally relate to electrochemical cells such as fuel cells or electrolytic cells, and more particularly to electrochemical cell stacks including corrugated interconnects interposed between adjacent electrochemical cells and electrically coupled thereto, wherein the corrugations form a plurality of fuel channels on one side and a plurality of oxidizer channels on the opposite side, which are fluidly isolated via a sealing member, and the interconnects are configured to provide compliance to the electrochemical cell stack.

[0006] In some embodiments, the electrochemical cell unit includes a first electrochemical cell comprising a first oxidizer electrode and a first fuel electrode, and a second electrochemical cell comprising a second oxidizer electrode and a second fuel electrode. An interconnect is interposed between the first and second electrochemical cells. The interconnect includes an interconnect main body defining a longitudinal channel along its longitudinal axis. The interconnect main body includes a plurality of corrugations defining a plurality of fuel channels on a first surface of the interconnect main body facing the first electrochemical cell, and a plurality of oxidizer channels on a second surface of the interconnect main body facing the second electrochemical cell. Each of the plurality of fuel channels and plurality of oxidizer channels is positioned around the longitudinal channel.

[0007] In some embodiments, the base of each fuel channel of a plurality of fuel channels is electrically in contact with a second oxidizer electrode, and the base of each oxidizer channel of a plurality of oxidizer channels is electrically in contact with a first fuel electrode. In some embodiments, the electrochemical cell unit further includes an outer sealing member located on the outer circumference of the interconnect on a first surface, and an inner sealing member located on the inner circumference of the interconnect on a second surface around the longitudinal channel. The outer sealing member fluidically seals one of the plurality of fuel channels or the plurality of oxidizer channels from the volume outside the outer circumference, and the inner sealing member fluidically seals the other of the plurality of fuel channels or the plurality of oxidizer channels from the longitudinal channel. In some embodiments, the interconnect main body defines at least one fuel inlet channel and at least one fluid outlet channel fluidly coupled to each of the plurality of fuel channels, and further defines at least one oxidizer inlet channel and at least one oxidizer outlet channel fluidly coupled to each of the plurality of oxidizer channels.

[0008] In some embodiments, an outer sealing member fluidly seals a plurality of fuel channels from the volume outside the outer circumference, and at least one fuel inlet channel and at least one fuel outlet channel are fluidly coupled to the longitudinal channels to receive fuel from a first portion of the longitudinal channels and discharge spent fuel into a second portion of the longitudinal channels. In some embodiments, an inner sealing member may fluidly seal a plurality of oxidizer channels from the longitudinal channels, and at least one oxidizer inlet channel and at least one oxidizer outlet channel are fluidly coupled to the outer circumference of the interconnect to receive oxidizer from a first portion of the volume outside the outer circumference and discharge spent oxidizer from a second portion of the volume outside the outer circumference. In some embodiments, the electrochemical cell unit further includes edge sealing members disposed on at least one of the outer edges of the first and second electrochemical cells adjacent to the outer circumference of the interconnect, or on the inner edges of the first and second electrochemical cells adjacent to the longitudinal channels.

[0009] In some embodiments, the electrochemical cell stack includes a stack of a plurality of electrochemical cell units. Each of the plurality of electrochemical cell units includes a first electrochemical cell including a first oxidizer electrode and a first fuel electrode, a second electrochemical cell including a second oxidizer electrode and a second fuel electrode, and an interconnect interposed between the first and second electrochemical cells. The interconnect includes an interconnect main body defining a longitudinal channel along its longitudinal axis. The longitudinal channel spans the height of the electrochemical cell stack. The interconnect main body includes a plurality of corrugations defining a plurality of fuel channels on a first surface of the interconnect main body facing the first electrochemical cell, and a plurality of oxidizer channels on a second surface of the interconnect main body facing the second electrochemical cell, with each of the plurality of fuel channels and plurality of oxidizer channels positioned around the longitudinal channel.

[0010] In some embodiments, each of a plurality of electrochemical cell units further includes an outer sealing member located on the outer periphery of the interconnect on a first surface, and an inner sealing member located on the inner periphery of the interconnect on a second surface around a longitudinal channel. The outer sealing member fluidically isolates one of the plurality of fuel channels or a plurality of oxidizer channels from the volume outside the outer periphery, and the inner sealing member fluidically isolates the other of the plurality of fuel channels or a plurality of oxidizer channels from the longitudinal channel. In some embodiments, the interconnects included in each of the plurality of electrochemical cell units cooperate to form a bellows-like structure such that the electrochemical cell stack has compliance. In some embodiments, the electrochemical cell stack further includes a post located in the longitudinal channel, the post defining at least one post inlet configured to receive either fuel or oxidizer, and at least one post outlet configured to receive and discharge spent fuel or spent oxidizer from the electrochemical cell stack, the post inlet and post outlet being fluidically isolated from each other.

[0011] In some embodiments, the electrochemical cell stack further includes an upper end plate positioned at the upper end of the electrochemical cell stack around the posts such that a gap is provided between the upper end plate and the posts, and the gap is structured to allow movement of the posts within it to relieve thermal stress. In some embodiments, the electrochemical cell stack further includes a compliant sealing member positioned within the gap, the compliant sealing member providing sufficient compliance to allow movement of the posts. In some embodiments, the electrochemical cell stack further includes an upper end cap positioned on the upper end plate and a secondary sealing member interposed between the upper end plate and the upper end cap. In some embodiments, the upper end plate includes a post interface tube extending axially from the surface of the upper end plate away from the posts, and at least a portion of the post interface tube is positioned around a portion of the posts.

[0012] In some embodiments, the electrochemical cell stack further includes a lower end plate positioned on the lower end of the electrochemical cell stack opposite the upper end. An upper compression plate is positioned on the upper end plate. A bias member is positioned close to the upper end of the electrochemical cell stack and is configured to exert a compressive force on a stack of multiple electrochemical cell units. At least one compression member is coupled to the upper compression plate and is configured to transmit the compressive force from the upper compression plate to the lower end plate. In some embodiments, the electrochemical cell stack further includes a lower compression plate positioned at the lower end of the electrochemical cell stack, and at least one compression member is coupled to the lower compression plate. In some embodiments, the bias member includes a stack of Belleville springs interposed between the upper compression plate and the upper end plate.

[0013] In some embodiments, the electrochemical cell stack further includes a base plate assembly positioned on the lower end of the electrochemical cell stack. The base plate assembly includes a lower end plate defining at least one fuel port and at least one oxidizer port. A high-strength sealing plate is axially aligned with the lower end plate and configured to yield relative to the lower end plate to reduce the transmission of mechanical stress from the high-strength sealing plate to the lower end plate. In some embodiments, the high-strength sealing plate is positioned between a stack of multiple electrochemical cell units and the lower end plate, and the base plate assembly further includes a plurality of short tubes positioned between the high-strength sealing plate and the lower end plate. In some embodiments, the lower end plate is interposed between a stack of multiple electrochemical cell units and the high-strength sealing plate, and the base plate assembly further includes a plurality of short tubes positioned between the high-strength sealing plate and the lower end plate. The short tubes are configured to yield in response to thermal stress so that the high-strength sealing plate is free to move laterally relative to the lower end plate to reduce the transmission of stress to the lower end plate.

[0014] In some embodiments, the electrochemical cell stack includes a manifold positioned around a stack of multiple electrochemical cell units. The manifold defines a volume around its outer circumference. A first portion of the volume provides an inlet for one of the fuels or oxidizers into the electrochemical cell stack, and a second portion of the volume provides an outlet for the spent fuel or oxidizers from the electrochemical cell stack. In some embodiments, the electrochemical cell stack further includes a dielectric sealing member positioned within the volume and configured to fluidly seal the first portion of the volume from the second portion of the volume.

[0015] In some embodiments, the electrochemical cell assembly includes a housing including a housing base. An array of electrochemical cell stacks is arranged on the housing base within the housing. Each of the electrochemical cell stacks included in the array includes a stack of multiple electrochemical cell units. Each of the multiple electrochemical cell units includes a first electrochemical cell including a first oxidizer electrode and a first fuel electrode, a second electrochemical cell including a second oxidizer electrode and a second fuel electrode, and an interconnect interposed between the first and second electrochemical cells. The interconnect includes an interconnect main body defining a longitudinal channel along its longitudinal axis, the longitudinal channel spanning the height of the electrochemical cell stack. The main body of the interconnection includes a plurality of corrugations that define a plurality of fuel channels on the first surface of the main body of the interconnection facing the first electrochemical cell, and a plurality of oxidizer channels on the second surface of the main body of the interconnection facing the second electrochemical cell, with each of the plurality of fuel channels and plurality of oxidizer channels positioned around a longitudinal channel.

[0016] In some embodiments, the electrochemical cell assembly further includes a ring separator positioned around each of the electrochemical cell stacks, and a cross separator positioned between each set of four electrochemical cell stacks contained within the array of electrochemical cell stacks. In some embodiments, the electrochemical cell assembly further includes an oxidizer preheating tube positioned between each set of four electrochemical cell stacks via the corresponding cross separator. In some embodiments, the electrochemical cell assembly further includes a fuel inlet, a fuel outlet, an oxidizer inlet, and an oxidizer outlet, which are fluidically coupled to the array of electrochemical cell stacks through a housing base. The housing base defines at least one heat exchange channel configured to provide heat exchange between fuel entering the housing base through the fuel inlet and spent fuel exiting the housing base through the fuel outlet. In some embodiments, the electrochemical cell assembly further includes a fuel bypass inlet, which is fluidically coupled to the array of electrochemical cell stacks through the housing base, and which bypasses at least one heat exchange channel.

[0017] The above is a summary of the disclosure and therefore inevitably includes simplifications, generalizations, and omissions of details. As a result, those skilled in the art will recognize that the summary is illustrative and not intended to be limiting in any way. Other aspects, features, and advantages of the devices and / or processes described herein, as defined by the claims, will become apparent in the detailed description described herein and to be interpreted in conjunction with the accompanying drawings. [Brief explanation of the drawing]

[0018] The aforementioned and other features of this disclosure will become more fully apparent from the following description and the accompanying claims, which are obtained in conjunction with the accompanying drawings. It should be understood that these drawings only illustrate some of the implementations provided in this disclosure and should therefore not be considered limiting its scope; the disclosure will be described in additional specificities and details through the use of the accompanying drawings.

[0019] [Figure 1A] It is a cross-sectional perspective view of a part of a fuel cell stack having hermetically sealed fuel cell units according to one embodiment.

[0020] [Figure 1B] It is a schematic diagram of a fuel cell unit that can be included in the electrochemical cell stack of Fig. 1A according to one embodiment.

[0021] [Figure 2] It is a front view of a manufactured fuel cell stack according to one embodiment.

[0022] [Figure 3] It is a top schematic diagram of an internal fuel manifold, showing a potential leakage path from the fuel inlet to the fuel outlet.

[0023] [Figure 4A] , [Figure 4B] , [Figure 4C] It is a top schematic diagram of a fuel cell unit according to one embodiment, each showing different possible flow paths for fuel and oxidant gas based on different combinations of internal and external manifold designs. Fig. 4A shows a fuel cell unit including one fuel inlet, one fuel outlet, one oxidant inlet, and one oxidant outlet. Fig. 4B shows a fuel cell unit including two fuel inlets, two fuel outlets, two oxidant inlets, and two oxidant outlets. Fig. 4C shows a fuel cell unit including one fuel inlet, one fuel outlet, two oxidant inlets, and two oxidant outlets.

[0024] [Figure 5] It is a perspective view of an array of fuel cell stacks according to one embodiment.

[0025] [Figure 6] It shows a perspective view of a part of the array shown in Fig. 5, with several fuel cell stacks removed to show the oxidant preheating pipes.

[0026] [Figure 7A] , [Figure 7B] This is a perspective view of an array of fuel cell stacks according to two different embodiments.

[0027] [Figure 7C] Based on the progressive array of fuel cell stacks shown in Figure 7A, deployment scales from 40kW to 350kW are shown.

[0028] [Figure 8A] , [Figure 8B] Figures 7A and 7B are perspective views of the base portion of the array, showing the fuel and oxidizer inlets and outlets of the array.

[0029] [Figure 9A] , [Figure 9B] Figures 7A and 7B are upper views of a portion of the array shown, illustrating the oxidizer preheating tubes and stack mounting points.

[0030] [Figure 10] This is a perspective view of a fuel cell stack with an overlapping seal design, as known in the art.

[0031] [Figure 11] This is a cross-sectional perspective view of an interconnection portion according to one embodiment.

[0032] [Figure 12A] , [Figure 12B] Figure 11 shows the upper and lower views of the interconnection section. Figure 12A shows the fuel side of the upper interconnection section. Figure 12B shows the oxidizer side of the lower interconnection section.

[0033] [Figure 13]This is a schematic cross-sectional view of a fuel cell stack having a bellows-like structure according to one embodiment.

[0034] [Figure 14] This is a photograph showing a cross-section of an electrochemical cell, with the edges sprayed to seal them.

[0035] [Figure 15A] , [Figure 15B] , [Figure 15C] These are upper cross-sectional views of a portion of a fuel cell stack according to three different embodiments, showing posts placed in the longitudinal channels of the stack.

[0036] [Figure 16A] , [Figure 16B] Figures 15A and 15C are cross-sectional perspective views of the upper portion of the fuel cell stack, respectively, showing the central post along with the upper plate and upper cap.

[0037] [Figure 17A] , [Figure 17B] , [Figure 17C] This is a lower perspective view of three different designs of the base plate assembly according to the embodiment.

[0038] [Figure 18] This is an upper perspective view of the main upper plate and post interface tube of an upper compression plate assembly according to one embodiment.

[0039] [Figure 19A] , [Figure 19B] This is a top perspective view of the upper compression plate assembly according to two different embodiments.

[0040] [Figure 20A]This is a graph showing the spring response of a Bellevill spring pack, which may be used in the upper compression plate assembly of Figure 19A according to one embodiment. [Figure 20B] This is a graph showing the creep of a coil spring, which may be used in the upper compression plate assembly of Figure 19B according to another embodiment.

[0041] [Figure 21A] , [Figure 21B] This is a lower perspective view of a fuel cell stack including an outer manifold, according to two different embodiments.

[0042] [Figure 22] The following test data was obtained from tests conducted using a 225-cell (~1kW) stack operating with a gas composition representative of a typical natural gas combustion system application.

[0043] [Figure 23] The following are test data obtained from tests conducted using a 20-cell configuration of the fuel cell stack array shown in Figure 7A, which operates as an electrolytic cell that converts steam into hydrogen.

[0044] [Figure 24] Figure 7A shows the results of implementing a 60-cell fuel cell stack array under various hydrogen fuel cell conditions, with the total test time exceeding one year.

[0045] [Figure 25] Figure 7B shows the results for a 45-cell configuration using the fuel cell stack array, which operates under fuel cell conditions (power generation) of 0.25 A / cm2.

[0046] [Figure 26] The results for a 45-cell configuration using a fuel cell stack array operating under electrolysis (hydrogen production) conditions of -1 A / cm2 are shown.

[0047] Throughout the following detailed description, refer to the accompanying drawings. In the drawings, unless otherwise indicated by the context, similar symbols generally identify similar components. The illustrative implementations described in the detailed description, drawings, and claims are not intended to be limiting. Other implementations may be used and other modifications may be made without departing from the spirit or scope of the subject matter presented herein. The aspects of this disclosure may be arranged, replaced, combined, and designed in a wide variety of different configurations, as generally described herein and shown in the drawings, all of which will be readily understood to be expressly construed and form part of this disclosure. [Modes for carrying out the invention]

[0048] Embodiments described herein generally relate to electrochemical cells such as fuel cells and electrolytic cells, and more particularly to electrochemical cell stacks including corrugated interconnects interposed between adjacent electrochemical cells and electrically coupled thereto, wherein the corrugations form a plurality of fuel channels on one side and a plurality of oxidizer channels on the opposite side, which are fluidly isolated via a sealing member, and the interconnects are configured to provide compliance to the electrochemical cell stack.

[0049] In certain embodiments, a mechanical stack layout is provided that represents a design approach focused on reducing the material content within the stack while maintaining (often improving) the overall design feasibility of current stack technologies. These particular embodiments utilize relatively small, generally annular solid oxide fuel cells and thin interconnects, and their integration results in an order of magnitude increase in power density (W / kg) compared to current baselines. This can be achieved through careful thermal design to ensure maximum thermal communication between the active area (heat-generating location) of the cells and the stack environment.

[0050] Efforts to lower price tend to directly shorten lifespan, as this involves strategies to operate fuel cells more powerfully. Efforts to improve performance (higher power) tend to decrease lifespan and efficiency. Efforts to extend lifespan often involve expensive materials and / or operation at lower power densities, both of which increase price. For example, tubular technology has been proven over long periods (more than 5 years), but is generally considered unacceptable for practical market applications at its price and performance levels. Conversely, planar SOFC technology comes close to achieving price and performance targets, but faces the challenge of achieving practical service life targets. The common focus to bridge this price / performance / service life gap is to develop high-performance cells while increasing size, primarily to reduce manufacturing costs. This is evident in almost all SOFC development activities, whether it's the development of tubular designs with large surface areas or planar designs. An exception to this trend exists in the form of microtubular SOFC cells, primarily advocated by university laboratories for applications requiring rapid thermal transients. Microtubule systems have not progressed as a viable solution for large-scale systems (typically in the range of up to several hundred watts of power).

[0051] In general, mobile applications have an additional set of constraints. Current SOFC technology has shown power densities of around 200 W / L and 100 W / kg in volume and mass indices. Therefore, a 70kW power unit occupies ~350L and weighs about 700kg in stack alone, and increases significantly in the overall power system. Small cars could not accommodate SOFC-based prime power systems due to these weights and volumes. A second constraint for automotive applications is the warm-up time. Current stacks require about an hour to reach an operating temperature of about 750 degrees Celsius from ambient temperature. In actual mobile applications, a start-up time of a few seconds is usually expected, but a start-up time of a few minutes may be acceptable due to changes in expectations and / or secondary power sources such as batteries to cover the first few minutes of operation.

[0052] Finally, one of the key challenges in many fuel cell technologies is managing waste heat and temperature distribution within the stack. As stack size increases, direct heat removal into the environment becomes increasingly impractical. Instead, large stacks rely on endothermic reactions (reforming) and / or convective cooling to the gas flow. Practical experience shows that high flow rates are necessary to achieve convective cooling with a reasonable temperature difference within the stack.

[0053] The embodiments described herein offer different approaches to meeting price, performance, and / or lifespan targets for electrochemical cells (e.g., fuel cells or electrolytic cells) while addressing key challenges. The embodiments described herein also address the weight and volume challenges posed by mobile applications of electrochemical cells, while the heating time is expected to be only a few minutes.

[0054] In short, the embodiments described herein propose to reverse the current trend of gradually increasing cell size and performance, instead proposing to decrease cell size, reduce reliance on cell performance, and focus on tight integration of components optimized for operation in small cells. Through careful integration, certain embodiments described herein can result in a stack with the same or greater output than current stacks, but at 1 / 7 the volume and 1 / 10 the weight.

[0055] The various embodiments described herein may offer advantages including, for example, (1) a reduction in volume per unit power output without requiring improved cell performance (e.g., a reduction of 7 times or more), (2) a reduction in weight per unit power output without requiring improved cell performance (e.g., a reduction of 10 times or more), (3) an expected cost reduction (e.g., a reduction of 10 times or more), (4) a rapid transient response (e.g., 10 times faster than current electrochemical cell stacks, providing heating times of a few minutes instead of several hours), (5) a level of modularity that supports a power range from, for example, 1 kW to many MW in the same stack for both mobile and stationary applications, and (6) an anode. (7) significantly reduces leakage from the to the cathode, thereby increasing efficiency and expanding application possibilities; (8) provides inherent load balancing and redundancy at larger kW ratings (e.g., 10kW and above); (9) enables indirect thermal management within the stack because the conduction distance between the stack core and stack edge is short and heat can be released into the environment; and (10) balances plant requirements by having less airflow, simpler compression requirements, higher voltage / lower current power, and / or shorter transients.

[0056] For example, the embodiments described herein illustrate two specific sizes and implementations of the SOFC stack described herein for which physical hardware and test results are available. These are provided as concrete examples of applications of the embodiments described herein, but smaller, larger, and variations between sizes of these embodiments are also possible. Important size considerations are cell size and cell count. Some embodiments described herein are 21 cm². 2 or 25cm 2 The cell comprises an active area of ​​81 cm² and has been demonstrated with up to 234 cells per stack. Other embodiments described herein include 81 cm². 2 It has cells with an active area of ​​350 or more cells per stack, is designed to operate with a maximum of 45 cells per stack, and has been demonstrated with a maximum of 45 cells per stack.

[0057] In the various embodiments described herein, the electrochemical cell unit and electrochemical cell stack are referred to as the fuel cell unit and fuel cell stack, respectively. However, it should be understood that the various embodiments of the electrochemical cell unit and electrochemical cell stack described herein may operate in reverse, including the electrolytic cell unit and electrochemical cell stack, or any other electrochemical cell unit or stack.

[0058] Figure 1A is a cross-sectional perspective view of a portion of the fuel cell stack 110 shown in Figure 2, according to one embodiment. According to one embodiment, the fuel cell stack 110 includes a plurality of fuel cell units 150, more specifically, a stack of sealed fuel cell units 110. The fuel cell stack 110 includes a plurality of solid oxide fuel cell units 150 alternating with a plurality of interconnection sections 152. For example, Figure 1B shows a schematic diagram of a fuel cell unit 150 that may be included in the fuel cell stack 110. Each fuel cell unit 150 includes a first electrochemical cell 154a including a first fuel electrode 153a (e.g., anode) and a first oxidizer electrode 155a (e.g., cathode), and may include an electrolyte interposed between the first fuel electrode 153a and the first oxidizer electrode 155a. The second electrochemical cell 154b also includes a second fuel electrode 153b and a second oxidizer electrode 155b, and may also include an electrolyte interposed between the second fuel electrode 153a and the second oxidizer electrode 155a. In some embodiments, each of the anodes optionally includes an anode support. In some embodiments, the fuel cell stack 110 can operate in reverse, i.e., as an electrolytic cell stack. In such embodiments, the fuel electrodes 153a / b of the electrochemical cells 154a / b may include cathodes, and the oxidizer electrodes 155a / b of the electrochemical cells 154a / b may include anodes.

[0059] The interconnector 152 is interposed between the first electrochemical cell 154a and the second electrochemical cell 154b. The interconnector 152 includes an interconnector main body 152a that defines a longitudinal channel 120 along its longitudinal axis (e.g., the longitudinal axis of the electrochemical cell stack 110, so that the longitudinal channel 120 can straddle the fuel cell stack 110). The interconnector main body 152a includes a plurality of corrugations that define a plurality of fuel channels 157 on a first surface of the interconnector main body 152a facing the first electrochemical cell 154a, and a plurality of oxidizer channels 159 on a second surface of the interconnector main body facing the second electrochemical cell 154b. Each of the plurality of fuel channels 157 and the plurality of oxidizer channels 159 may be positioned around the longitudinal channel 120, for example, in a symmetrical and / or annular configuration. Each fuel channel base of the plurality of fuel channels 157 may be in electrical contact with the second oxidizer electrode 155b, and each oxidizer channel base of the plurality of oxidizer channels 159 may be in electrical contact with the first fuel electrode 153a.

[0060] For example, the electrochemical cells 154a / b and interconnect 152 are formed such that, once the fuel cell stack 110 is formed, the longitudinal channel 120 extends longitudinally through the fuel cell stack 110. In the embodiment of Figure 1A, the electrochemical cells 154a / b and interconnect 152 have an annular shape, and the longitudinal channel 120 is a central channel located at the axial center of the fuel cell stack 110. Although the fuel cell stack 110 is described as having an annular shape, it may have any other suitable shape, e.g., oval, hexagonal, square, or non-square, or any other shape as long as the longitudinal channel 120 extends longitudinally through the fuel cell stack 110. Furthermore, although the longitudinal channel 120 is described as extending along the geometric center of the fuel cell stack 110, in other embodiments, the longitudinal channel 120 may be offset from the geometric center of the fuel cell stack 110, as long as the longitudinal channel 120 does not partially overlap with the outer edge of the fuel cell stack 110.

[0061] The electrochemical cells 154a / b are sealed alternately at each interconnection 152 on the inner and outer circumferences, as shown in Figures 1A and 1B. This provides a sealed structure that is compliant at the unit cell level, reducing the possibility of thermal stress accumulation.

[0062] Either the fuel or oxidizer gas flows into and is extracted from the fuel cell unit 150 via the longitudinal channel 120, while the other gas flows into and is extracted from the fuel cell unit 150 at the outer periphery of the fuel cell stack 110. In certain embodiments, the fuel flows into and is extracted from the longitudinal channel 120, and the oxidizer is received and extracted at the outer periphery of the fuel cell stack 110. Seals of the sealed cells and interconnects prevent gas mixing. For example, as shown in Figure 1A, an outer seal member 158 may be positioned on the outer periphery of the interconnect 152 on a first surface adjacent to the first electrochemical cell 154a, and an inner seal member 156 may be positioned on the inner periphery of the interconnect 152 on a second surface adjacent to the second electrochemical cell 154b around the longitudinal channel 120. The outer sealing member 158 can fluidly seal one of the multiple fuel channels 157 or the multiple oxidizer channels 159 from the volume outside the outer periphery of the fuel cell stack 110, and the inner sealing member 156 can fluidly seal the other of the multiple fuel channels 157 or the multiple oxidizer channels 159 from the longitudinal channel 120. In particular, as shown in Figure 1A, the outer sealing member 158 fluidly seals the fuel channels 157 from the volume outside the outer periphery, and the inner sealing member 156 fluidly seals the oxidizer channels 159 from the longitudinal channel 120.

[0063] By avoiding leaks that result in the mixing and combustion of fuel and oxidizer, several advantages are obtained, including (i) reduced loss of reactants to the system, (ii) reduced thermal load on the stack (and in particular localized heating that can damage stack components), (iii) reduced vapor generation on the oxidizer side (which reduces volatilization and transport of chromium, which can be a significant degradation mechanism of the oxidizer electrode), and (iv) reduced use of protective cover gas due to reduced cross-leakage during heating and cooling.

[0064] The fuel cell stack 110 can include, for example, 20 to 400 fuel cell units 150, and is limited only by the aspect ratio (height to diameter or width) of the finished stack, if the aspect ratio is too high, it may be difficult to manufacture and package. In various embodiments, the aspect ratio may be in the range of 4:1 to 5:1, although shorter stacks may be useful for specific applications and development purposes. Multiple fuel cell units 150 may be stacked vertically in a tower together with intermediate metal interconnects 152.

[0065] The power output range of each fuel cell stack is approximately 50W to 20kW (for example, 0.5kW to 20kW, 1kW to 15kW, or 5kW to 10kW, including all ranges and values ​​in between) depending on the operating conditions and stack size. In one embodiment, the stack has a power range of approximately 7kW. By reducing the cell count and adjusting the operating conditions, a practical stack of approximately 50W can be manufactured.

[0066] The fuel cell stack 110 or any other electrochemical cell stack described herein provides a cell design that utilizes appropriate geometric arrangements to improve the ability to thermally control the electrochemical cell stack while simultaneously reducing mechanical stresses induced during cell manufacturing and subsequent stack operation. These two advantages make it possible to thin both the interconnect 152 and the cells without compromising their structure.

[0067] The thickness of the interconnect 152 can be in the range of 0.05 to 0.7 mm (e.g., 0.075 to 0.4 mm, or 0.08 mm to 0.15 mm, including all ranges and values ​​in between). The thickness of the electrochemical cell unit may be in the range of 0.2 to 0.4 mm. In certain embodiments, the thickness may be in the range of 0.25 to 0.35 mm. A stack of this design incorporating a 0.12 mm interconnect 152 and 0.3 mm cells has been demonstrated to operate for more than one year. This is approximately 1 / 10 of the thickness of the interconnect material and 1 / 2 of the cell thickness used in typical SOFC stack designs. When end plates, compression systems, and all other components forming the complete stack are included, the stack weight proposed in one embodiment has been found to be about 1 / 10 of the weight of a conventional stack per active area.

[0068] In other words, the material content of the electrochemical cell stack is reduced, and this reduction is significant. This design does not require the use of special materials, and in many areas, the material requirements are simplified compared to conventional electrochemical cell stacks. The compression system may be simplified due to the lower load, as will be explained in more detail below. The manifold is also simplified due to the lower sealing requirements, as will also be explained in more detail below. This reduction in material content reduces the intrinsic cost of the electrochemical cell stack. Although the number of parts per kW increases, the use of smaller parts, the reduction of different parts per layer, and the absence of large tolerances requiring operator intervention also improve the suitability of the parts for automation. Thus, the cost benefits of lower material content may outweigh the overall increase in the number of parts.

[0069] The fuel cell stack 110 shown in Figure 2 contains 234 cells. Each fuel cell unit 150 is annular in shape, with an outer cell diameter of 60 mm, a thickness of 300 microns, and 21 cm². 2It had an active area. Each interconnect 152 was a stamped metal interconnect with a material thickness of 100 microns and a flow channel height of 390 microns. The fuel cell stack 110 also includes a manifold 112 positioned around the stack of a plurality of fuel cell units 150, which can be used to introduce and discharge one of the fuel and oxidizer around the outer periphery of the fuel cell stack 110, and a volume can be defined around the outer periphery of the fuel cell stack 110. For example, a first portion of the volume may provide an inlet for one of the fuel or oxidizer into the fuel cell stack 110, and a second portion of the volume may provide an outlet for the spent fuel or oxidizer from the fuel cell stack 110.

[0070] The embodiments described herein can reduce material content by an order of magnitude while offering many other advantages, such as lowering the cost per kW at the stack and system levels. The improved thermal layout and improved temperature control can simultaneously improve performance and reduce degradation. Furthermore, the embodiments described herein can improve the thermal control of the electrochemical cell stack, thereby allowing for lower cooling airflow and lower inlet temperatures, both of which can improve the balance of plant efficiency.

[0071] Fuel inlet / outlet seals and oxidizer inlet / outlet seals The separation of fuel in from fuel out and oxidizer in from oxidizer out is achieved through a structurally independent manifold (e.g., manifold 112) separate from the stack core, and can be sealed via a compliant seal that is compressible and allows relative motion between the stack core and the manifold. This prevents or reduces thermally induced mechanical stress on the entire structure, thereby protecting the individual components, such as ceramic cells, which are susceptible to brittle fracture when subjected to excessive stress. The compliant seal seals the inlet and outlet of the same gas flow. In other words, the compliant seal separates the fuel inlet from the fuel outlet and the oxidizer inlet from the oxidizer outlet. Preferably, the compliant seal does not seal the fuel and oxidizer gases anywhere. Compliant high-temperature ceramic seals are known to leak because compliance is achieved by them typically involving porosity and being connected filled ceramic structures. In the embodiments described herein, such leaks may be acceptable because they do not result in combustion and have only a slight impact on overall efficiency as long as the leak rate is low (e.g., less than about 5% of the total flow rate). This allows for the advantageous use of external manifold design techniques, which offer cost, weight, and volume advantages. Figure 3 shows a fuel manifold 230, for example, a post (e.g., a central post) placed within the longitudinal channel of an electrochemical cell stack, and a representation of the resulting leak path from fuel in to fuel out.

[0072] Separation of inlet and outlet gases around the stack can be achieved through a sheet metal manifold (e.g., manifold 112) structure that presses compliant seals against the stack core ("stack core" means an assembly of repeated stack components such as cells, interconnects, seals, and end plates). The metal gas separation component may be coated with a dielectric coating to prevent the stack from short-circuiting to the manifold.

[0073] The annular cell design minimizes conduction paths from any part of the cell's heat-generating area to the outer surface of the stack, which helps maintain thermal control of the stack.

[0074] Figures 4A–4C are schematic top views of fuel cell units 250a / b / c according to various embodiments, each showing different possible flow paths for fuel and oxidizer gases based on different combinations of internal and external manifold designs. In other embodiments, fuel cell units 250a / b / c may include an electrochemical cell unit that operates in reverse to function as an electrolytic cell unit. Figure 4A shows fuel cell unit 250a with a single fuel inlet, single fuel outlet, single oxidizer inlet, and single oxidizer outlet. Figure 4B shows fuel cell unit 250b with two fuel inlets, two fuel outlets, two oxidizer inlets, and two oxidizer outlets. Figure 4C shows fuel cell unit 250c with a single fuel inlet, single fuel outlet, two oxidizer inlets, and two oxidizer outlets. These different flow strategies provide different thermal and pressure drop profiles for the stack, allowing for selection of the most suitable one for a particular application.

[0075] For example, the main body of the interconnect (e.g., main body 152a) of the interconnect (e.g., interconnect 152) included in each of the fuel cell units 250a / b / c may define at least one fuel inlet channel and at least one fluid outlet channel, which are fluidically coupled to each of a plurality of fuel channels (e.g., fuel channel 157). The main body of the interconnect may further define at least one oxidizer inlet channel and at least one oxidizer outlet channel, which are fluidically coupled to each of a plurality of oxidizer channels (e.g., oxidizer channel 159). The at least one fuel inlet channel and at least one fuel outlet channel may be fluidically coupled to the longitudinal channel to receive fuel from a first portion of the longitudinal channel and discharge spent fuel to a second portion of the longitudinal channel. An outer sealing member (e.g., outer sealing member 158) may fluidly seal the plurality of fuel channels from the volume outside the outer circumference. Furthermore, at least one oxidizer inlet channel and at least one oxidizer outlet channel may be fluidically coupled to the outer circumference of the interconnection so as to receive the oxidizer from a first portion and discharge the used oxidizer from a second portion of the volume outside the outer circumference. An inner sealing member (e.g., inner sealing member 156) may fluidly seal the multiple oxidizer channels from the longitudinal channels.

[0076] Modular array For large-scale systems, stacks are deployed in modular arrays, for example, in arrays of 20kW to 250kW or more, as shown in Array 100 in Figure 5 or Array 200 in Figure 7A, or in arrays of 40kW to 500kW, as shown in Array 300 in Figure 7B. Large-scale systems may consist of multiple arrays. Stack designs are particularly well-suited to arranged layouts due to their integrated compression systems, direct bolt connections with integrated gas connections, short conduction paths to the environment, and high-voltage-low-current output. By simplifying or eliminating the interface from the stack to the modules, stacks can simplify the design of large-scale systems. Two embodiments of a stack array based on Stack 110 in Figure 2 are described below. Stacks can be arranged in different package sizes depending on the application. Possible size ranges from a single stack (~1.2kW) to a 15x15 array stack (250kW) or more. As an example, a 10x10, 100kW package, including the compression, current collection, and ducting, measures approximately 0.6m x 0.6m x 0.3m (113L), and it is competitive with internal combustion engines.

[0077] Figure 5 is a perspective view of an array 100 of fuel cell stacks 110 according to one embodiment. In this embodiment, fuel is supplied and extracted from the base of the fuel cell stacks 110, while an oxidant gas (e.g., air) is placed in a storage volume above the stack and extracted from the base of the fuel cell stacks 110. Air can generally be used as the primary means of cooling the electrochemical cell stacks 110 due to its high convective heat capacity. The air enters above the fuel cell stacks 110 (or stack array) at a relatively low temperature, cooling the area above the fuel cell stacks 110. Spring compression and current collection can be integrated into this area, where lower temperatures allow for less use of special materials and / or overall materials while maintaining appropriate strength and current capacity.

[0078] In some embodiments, air is heated to an appropriate inlet temperature while flowing from the upper cooler region through the oxidizer preheating tube 116 or inlet tube into the volume surrounding the stack 110, as shown in Figure 6. Sealing between the upper zone and the stack zone may not be complete, which greatly simplifies the overall layout. Figure 6 shows that separation between the upper cooling zone and the lower stack zone is achieved by overlapping separators mounted on the individual fuel cell stacks 110. In the embodiments shown in Figure 6, there are two separator types: ring separators 114 around each stack and cross separators 115 located between each group of four fuel cell stacks 110. For example, the ring separators 114 may be located around each of the fuel cell stacks 110 included in the array 100, and the cross separators 115 may be located between each set of four fuel cell stacks 110 included in the array 100. The oxidizer preheating tube 116 may be located through the corresponding cross separators 115.

[0079] Separators 114 and 115 overlap to provide a barrier that preferentially directs the gas to the oxidizer preheating tube 116. This geometric arrangement of overlapping separators maintains complete freedom for the fuel cell stack 110 to oscillate under thermal load without adding lateral loads to the fuel cell stack 110 or breaking the separation between zones. The oxidizer preheating tube 116 acts as a radiant heat transfer surface, heating the inlet air using radiation from the high-temperature fuel cell stack 110 before bringing the oxidizer (e.g., air) into direct contact with the stack air manifold. The air inlet to the fuel cell stack 110 can be an opening in the air manifold along the entire vertical plane, where air preheated first in the upper zone, second in the oxidizer preheating tube 116, and third by direct contact with the stack manifold can finally enter the fuel cell stack 110 properly. Stack cooling, a major challenge for large SOFC stacks, can be achieved by heating the oxidizer flow. Unlike direct convection cooling, the multi-stage inlet approach allows for a much larger temperature rise than when the oxidizer (e.g., air) is directly introduced into the fuel cell stack 110 core. With appropriate sizing, inlet temperatures of around 200 degrees Celsius (e.g., 150-250 degrees Celsius) can be achieved, compared to 600 degrees Celsius for conventional stacks. This large temperature delta tolerance reduces airflow, lowers preheating load, and simplifies and improves the efficiency of balancing the components of the electrochemical cell assembly (e.g., fuel cell assembly or electrolytic cell assembly) including the array 100.

[0080] Each fuel cell stack 110 may be self-contained except for the air inlet duct and outer insulation. The packaging solution described herein provides efficiency by sharing the air inlet and outer insulation shell among multiple fuel cell stacks 110. In some embodiments, a fuel cell assembly (e.g., fuel cell assembly 20 in Figure 7A) may include the following repeating units: (1) Unit cell (cell + interconnect): ~8W, ~0.8V, (2) Fuel cell stack (hundreds of cells + manifold, compression, etc.): ~1200W, 160V~250V, (3) Array (variable, up to 200 or more stacks, enclosure, insulation, etc.): ~20~250+kW, kV range, and (4) Module (variable, array structure of road transportable size): 1MW+, kV range. In other embodiments, a fuel cell assembly (e.g., fuel cell assembly 40 in Figure 7B) may include the following repeating units: (1) Unit cell (cell + interconnect): ~20W, ~0.8V, (2) Stack (hundreds of cells + manifold, compression, etc.): 7,000W, 160V~350V, (3) 40~350+kW, kV range, (4) Module (variable, road transportable array structure): 1MW+, kV range.

[0081] For high-power implementations (~10kW and above), a modular approach offers additional advantages. Firstly, because stack voltages are high enough, they can be connected in parallel or series-parallel electrical configurations. This provides automatic load limiting; some underperforming stacks automatically pass the current load to electrically parallel stacks. In large multi-stack arrays, the complete loss of a stack has little adverse effect. Secondly, a failed stack can be replaced at a relatively low cost without affecting other stacks. In conventional systems with relatively few stacks, the occurrence of a single vulnerability may necessitate the removal and refurbishment of a large stack that is difficult to manage, whereas in arrays of small stacks, localized weaknesses can be corrected by replacing only the weak stack, smaller devices, and a faster, lower-cost process.

[0082] Figures 7A and 7B are perspective views of electrochemical cell assemblies, including an array of electrochemical cell stacks, according to two different embodiments. The embodiments are similar to those of the embodiments in Figures 5 and 6, except that all gas services, including inlet air, are supplied from the bottom. This reduces the complexity at the top of the stack array, which may provide advantages in initial assembly and service. It also provides advantages in terms of ease of integration into the system and provides the possibility of additional heat transfer between the inlet and outlet airflows. As described herein, the electrochemical cell assemblies in Figures 7A and 7B include a fuel cell assembly having an array of fuel cell stacks. In other embodiments, the electrochemical cell assemblies in Figures 7A and 7B may operate in reverse to operate as an electrolytic cell assembly including an array of electrolytic cell stacks.

[0083] Figure 7A shows a fuel cell assembly 20 according to one embodiment. The fuel cell assembly 20 includes a housing 22 having a housing base 30. An array 200 of fuel cell stacks (e.g., an electrochemical cell stack 110) is positioned on the housing base 30. The array 200 includes a 6x6 array (40+kW array) of fuel cell stacks, with all gas services supplied from below. Figure 7B shows a fuel cell assembly 40 according to another embodiment. The fuel cell assembly 40 includes a housing 42 having a housing base 50 on which an array 300 of fuel cell stacks (e.g., a fuel cell stack 110) is positioned. The array 300 includes an 8x5 array (280+kW array), with all gas services supplied from below. In these layouts, the housing bases 30 and 50 incorporate a heat exchange function to evenly distribute and collect gas to all fuel cell stacks. Figure 8A is a perspective view of the base portion of the fuel cell assembly 20 shown in Figure 7A, showing the fuel and oxidizer inlets and outlets of the array. In the left side of Figure 7A, two stacks are omitted, so two of the oxidizer preheating tubes can be seen. As shown in Figure 8A, the electrochemical cell assembly 20 includes a fuel inlet 22, a fuel outlet 24, an oxidizer inlet 26, and an oxidizer outlet 28, which are fluidically coupled to the array 200 of electrochemical cell stacks through a housing base 30. The housing base 30 also defines at least one heat exchange channel 34 configured to provide heat exchange between fuel entering the housing base 30 through the fuel inlet 22 and spent fuel exiting the housing base 30 through the fuel outlet 24. Multiple stack interfaces 32 (e.g., through-holes) for communicating fuel and oxidizer between the array 200 and the housing base 30, as well as one or more gas distribution channels 36, may also be provided within the housing base 30. Furthermore, a fuel bypass inlet 29 is fluidically coupled to the array 200 of electrochemical cell stacks via the housing base 32 so that the fuel bypass inlet 29 bypasses at least one heat exchange channel.Therefore, the fuel inlet 22 and fuel bypass inlet 29 provide a dual fuel inlet, the fuel bypass inlet 29 going directly to the array 200 of the fuel cell stack, and the fuel inlet 22 going through the heat exchange and reforming section. These dual inlets are selective but provide additional controllability of the stack inlet temperature and in-stack reforming.

[0084] Figure 7C demonstrates the flexibility of array size while maintaining overall module simplicity. Based on the Array 300 fuel cell stack shown in Figure 7B, conceptual arrays from 40kW to 350kW are shown.

[0085] Figure 8B is a perspective view of the base portion of the fuel cell assembly 40 shown in Figure 7B, showing a fuel inlet 42, fuel outlet 44, oxidizer inlet 46, and oxidizer outlet 48, which are fluidly coupled to the array 300. In these embodiments, the upper portion 56 of the housing base 50 takes in fuel and discharges fuel for heat exchange and may also include a fuel reforming section. Multiple stack interfaces 52 are also provided on the housing base 50. The fuel cell assembly 40 shown in Figure 7B does not have a dual inlet.

[0086] In these embodiments, the cold air inlet enters the stack's high-temperature zone from the bottom. Figure 9A is a top view of a portion of the fuel cell stack 200 shown in Figure 7A, showing the oxidizer preheating tube 216 and the stack mounting interface 32. Figure 9B is a top view of a portion of the fuel cell stack 300 shown in Figure 7B, showing the oxidizer preheating tube 316, the fuel preheating tube 318, and the stack mounting interface 52. As seen in Figures 9A and 9B, the arrays 200, 300 in these embodiments also include the oxidizer preheating tube 316, which acts as a radiating surface to absorb heat from the fuel cell stack and use it to preheat the incoming gas. However, in these embodiments, the oxidizer preheating tube 316 leads to the high-temperature zone (not from the top of the array downwards). In these embodiments of the array, the only connection from the top is the top current collection connection. These are relatively simple connections because the current flowing through each stack is small (typically less than 30A in fuel cell operation and typically less than 150A in electrolytic operation).

[0087] Interconnection design When designing for small cells, one of the challenges is sealing. Given a seal with several characteristic leaks that are proportional to the seal area and inversely proportional to the seal thickness in the leak direction, designing to minimize leaks favors larger cells. Firstly, the ratio of the active area to the edge length (sealed length) of the cell is roughly based on the cell size.

number

number

[0088] These constraints mean that narrow seals with low leak rates are desirable to support high-performance, low-leak stacks based around small cells. This type of sealing exists in the form of glass-ceramic seals, brazed joints, or welded joints. One drawback of such seals is that they are not compliant. Compliance may be desirable in SOFC stacks because SOFC stacks operate over a wide temperature range, and during heating or changes in operating conditions, components of the stack move relative to each other to prevent damage from stress accumulation. Some stack designs build compliant functionality into sheet metal interconnects to allow for rigid joints, but the compliant functionality itself is relatively bulky and suffers from the same problems as wide seals. They are space-inefficient in small cell designs.

[0089] Figure 10 is a perspective view of a fuel cell stack with an overlapping seal design known in the art, illustrating a typical compliance challenge in a cross-flow stack configuration. For the sake of discussion, we assume that the fuel flows from the lower left to the upper right and the oxidizer flows from the lower right to the upper left. A manifold separating the fuel from the oxidizer outside the stack is not shown.

[0090] The topmost visible seal is a fuel seal, separating the fuel passing through the cells from the oxidizer on the lower right face of the stack. Directly below the top cells, along the left edge, is an oxidizer seal. This separates the oxygen flowing through the cells from the fuel exposed at the left edge. The pattern is repeated throughout the entire stack and can contain hundreds of cell layers.

[0091] As shown in the foreground of Figure 10, compliance issues arise where seals overlap. The structure in the central foreground is fabricated with repeating layers of seals, cells, seals, and interconnects. Unless one or more of the components yield, there is no ability to absorb the strain (X, Y, or Z) in this region. When the goal is the use of non-compliant or nearly-compliant seals, the cells are often the weakest components of the structure. In this case, in most cases, as stress accumulates, the cells will fail before yielding. This type of structure is not robust against real-world conditions.

[0092] To mitigate unavoidable thermal stress, compliance must be incorporated into the stack design. There are two main approaches to incorporating compliance. In the first approach, seals are fabricated compliantly, often as filled fiber / powder ceramic composites or plate-like materials (e.g., mica) that can move between components to relieve stress. These seals inevitably leak as a result of their structure, limiting the size to which cells can be used before leakage begins to dominate performance. The second approach utilizes special interconnects or additional components that incorporate compliance functionality. This is done, for example, by rigidly sealing a thin metal sheet component to the cell, effectively stretching it around the cell, and then laser-welding this cell-stretched component to the interconnect. In this strategy, there are periphery seals and internal port seals positioned away from both the periphery and the cell junctions. For example, the periphery seal may contain fuel, and the port seal may contain an oxidizer. The additional periphery required for this compliant portion means that small cell sizes are undesirable.

[0093] In contrast, in the embodiments described herein, the interconnects and the overall structure directly provide the desired compliance without compromising sealing properties or adding extra components or space to the design. This design allows for the use of narrow, rigid seals and achieves a compliant bellows-like structure without increasing the size of the structure. This combination of good sealing and a compliant structure in a small area allows for the effective use of small cells.

[0094] Compliant interconnect design can involve many competing design constraints. Firstly, interconnects may be desirable to: (1) provide a controlled flow distribution to both the cell fuel electrode and the cell oxidizer electrode; (2) provide compliance to absorb stress; (3) provide appropriate fuel and oxidizer pressure drops; (4) provide appropriate current conduction paths; and (5) isolate the fuel flow from the oxidizer flow throughout the stack's lifespan.

[0095] Figure 11 is a cross-sectional perspective view of an interconnect 452 according to one embodiment. The interconnect 452 includes an interconnect main body 452a defining a plurality of fuel channels 457 and a plurality of oxidizer channels 459. In Figure 11, the fuel side is facing upward. The fuel channels 457 simultaneously form an electrical contact area with the cell oxidizer electrode. The oxidizer channels 459 simultaneously form an electrical contact area with the cell fuel electrode. The fuel channels 457 are separated by ribs on the upper surface of the interconnect 452, while the oxidizer channels 459 are separated by ribs on the lower side of the interconnect 452. That is, the fuel-side ribs form the oxidizer channels 459, and vice versa. Figures 12A and 12B are upper and lower views, respectively, of the interconnect 452 shown in Figure 11, and depict a longitudinal channel 420 penetrating their geometric centers. Figure 12A shows the upper fuel side of the interconnect, indicating the fuel inlet channel 463 (or fuel outlet channel depending on the flow direction) fluidly coupled to each of the fuel channels 457. Figure 12B shows the lower oxidizer side of the interconnect, indicating the oxidizer inlet channel 465 (or oxidizer outlet channel depending on the flow direction). Figures 12A and 12B show the effective active area supplied by each of the channels 457 on the fuel side (Figure 12A) and the channel 459 on the oxidizer side (Figure 12B) of the interconnect 452. The flat semicircular area superimposed on the interconnect 452 represents the cellular active area exposed to each interconnect channel 457, 459. The active area is a function of both position and size, as well as of each channel 457, 459. The interconnect 452 is designed to provide flow downwards through each of the channels 457, 459, with each channel 457, 459 having an active area proportional to the channel 457, 459 supplied by it. This is achieved with respect to size and spacing constraints that provide adequate current collection from both cell electrodes. Several changes in the geometric arrangement affect the flow and electrical properties on both sides of the interconnect 452. Optionally, a contact intermediate layer may be added between each cell and each interconnect 452 to facilitate electrical contact.

[0096] In the embodiments shown in Figures 12A and 12B, the outer seal member 458 is a fuel seal member located on the outer circumference (Figure 12A). In this embodiment, the inner seal member 456 is an oxidizer seal member located on the inner circumference around the longitudinal channel 420 of the fuel cell stack (Figure 12B). The separation of the fuel seal member from the oxidizer seal member in space and the design of the corrugated interconnect provide the necessary compliance without increasing the perimeter or thickness of the stack. Of course, in embodiments where the oxidizer flows through the longitudinal channel 420, the inner seal member 456 acts as a fuel seal, while the outer seal member 458 acts as an oxidizer seal.

[0097] The base material of the interconnect 452 is approximately 0.1 mm thick (for example, 0.07 to 0.13 mm thick). This allows for proper control of the stack temperature because the active area of ​​the cell is small and the distance from any point on the cell to the edge is relatively small. For large stacks or when the distance is large, the thickness of the interconnect needs to be increased to obtain sufficient thermal conductivity to maintain temperature control of the stack and cells.

[0098] Internal seal design The internal seals located between the interconnects 452 and the cells, and which separate the fuel gas from the oxidizer gas, may be implemented as glass-ceramic seals within the electrochemical cell stacks included in arrays 100, 200, or 300. Their positions may be staggered between the inner and outer diameters in a means of generating a bellows-like structure, as can be seen in the schematic cross-sectional view of Figure 13, which shows a schematic diagram of an electrochemical cell stack including the interconnects 452 and a fuel cell stack 410 compressed between an upper plate 440 and a lower plate 460. In other words, multiple interconnects 452 included in the fuel cell stack 410 cooperate to form a bellows-like structure so that the fuel cell stack 410 has compliance. The interconnects 452 may be about 0.1 mm thick. Thin material coupled with corrugations that generate a flow field creates interconnects 452 that easily relieve stress within their layers. This results in a robust structure that prevents stress accumulation from layer to layer. As shown in Figure 13, it is preferable that no additional separators or metal components are used to provide stress relief. That is, the bellows-like structure of the fuel cell stack 410 is made up of alternating cells 454, outer seals 458, interconnects 452, and inner seals 456.

[0099] In addition to the inner seal 456 and outer seal 458, the edge seal member 461 may be located on at least one of the following: the outer edge of the electrochemical cell 454 (each of the first and second electrochemical cells, e.g., an electrochemical cell unit, e.g., a fuel cell unit or an electrolytic cell unit) adjacent to the outer circumference of the interconnection portion 452; or the inner edge of the electrochemical cell 454 adjacent to the longitudinal channel 420. For example, the edges of the cell anode support are typically porous. In the embodiment shown in Figure 13, the edge seal member 461 is located on the outer edge of the electrochemical cell 454 to provide additional sealing between the fuel gas and the oxidizer gas. Figure 14 is a photograph showing a cross-section of a fuel cell, which may correspond to a sealed electrochemical cell (e.g., electrochemical cell 154a / b shown in Figure 1B).

[0100] Post-design A post can be used as a manifold for a gas (either fuel or oxidizer) passing through a longitudinal channel to an electrochemical cell. The post may be placed in the longitudinal channel and configured to separate the gas inlet from the longitudinal channel into the electrochemical cell from the gas outlet from the electrochemical cell into the longitudinal channel. The post is sealed in place with a ceramic slurry, paste, vat, or a combination thereof to provide a compliant seal between the inlet and outlet flows. The post may be machined metal, a multi-part sheet metal, brazed, or ceramic, with the function of forming a vertical channel into which a compliant sealing material is added.

[0101] Figures 15A to 15C are upper cross-sectional views of portions of a fuel cell stack 510 according to three different embodiments, showing various posts placed in the longitudinal channel 520 of the stack 510. In these embodiments, the longitudinal channel 520 is a central channel extending along the axial center of the stack 510, and therefore the posts in the channel are referred to as “central posts”. However, in other embodiments, the posts may be located in channels offset from the center of the stack 510. In this embodiment, it is also assumed that fuel gas passes through the longitudinal channel 420. Figure 15A shows a circular post 530a according to one embodiment. The post 530 defines a deep groove axially positioned around it to define a post inlet 532a configured to receive fuel and a post outlet 534a configured to receive spent fuel and discharge it into the electrochemical cell stack 510. The post inlet 532a and post outlet 534a are fluidically isolated from each other via a seal recess 536a. Figure 15B shows a post 530b according to another embodiment, positioned in the longitudinal channel 520. The post 530b includes two parallel plates that divide the longitudinal channel 520 into a post inlet 532b, a post outlet 534b, and a seal recess 536 that fluidly isolates the post inlet 532b from the post outlet 534b. In the embodiments of Figures 15A and 15B, the central post 530a / b includes one fuel inlet port and one fuel outlet port.

[0102] Figure 15C shows a post assembly 530c including two fuel inlet plates 531c positioned opposite each other. Two fuel outlet plates 537c are positioned perpendicular to the fuel inlet plate 531c so as to define two post outlets 534c opposite each other. In the embodiment of Figure 15C, the post 534c includes a fuel inlet port separated from two side post channels 532c (e.g., side fuel ports) by a central channel 533c, for example, a fuel inlet plate 531c having a plurality of openings 535c. Fuel flows into the central channel 533c and then into the side post channels 532c through the openings 535c. The central post assembly 530c in this embodiment has two post outlets 534c including a fuel outlet port. A sealing member 539c, such as ceramic caulking material, is inserted into a sealing recess 536c to separate the inlet fuel from the outlet fuel. This seal does not need to be airtight, as the leak path does not result in fuel-air bonding. Rather, the effect of leakage through this seal is to reduce the fuel flow through the stack itself. Moderate leakage (up to a few percent of the total flow) does not significantly affect the stack's performance. Solid oxide fuel cell systems typically operate with excess fuel to sweep reaction products (H2O, CO2, etc.) from the fuel electrodes, so even moderate leakage may not have a significant impact on system characteristics.

[0103] The material of the sealing member 539c used in post 530c may be designed to be somewhat compliant in order to allow thermal stress to dissipate within the structure. As a result of compliance requirements, the sealing member 539c is not firmly bonded to the cell layer and is not airtight. However, it can be designed to be compliant at the same time and to have sufficiently low leakage so that fuel preferentially flows around the interconnect rather than leaking through the seal.

[0104] Figures 16A and 16B are cross-sectional perspective views of the upper portion of the fuel cell stack 510 shown in Figures 15A and 15C, respectively, showing the central posts 530a, 530c along with the upper plates 540a / b and upper caps 542a / b. Direct bonding of the upper and lower plates of the stack could induce unwanted thermal stress. To prevent this, the upper (and optionally lower) joints are structured as compliant fit joints. A sealant (e.g., the same sealant used on the sides of the posts) is provided in the gap between the central posts and the upper and / or lower plates. The allowable movement between the central posts and the upper plates does not need to be large, as long as it is sufficient to relieve thermal stress. The magnitude of the calculation of the desired relative motion is as follows:

number

[0105] More specifically, as shown in Figures 16A and 16B, the upper plate 540a / c is positioned at the upper end of the fuel cell stack 510 around the posts 530a / c, so that a gap 541a / c is provided between the upper plate 540a / c and the posts 530a / c. The gap 541a / c may be structured to allow movement of the posts 530a / c within it to relieve thermal stress. In some embodiments, a compliant sealing member can be positioned within the gap 541a / c. For example, Figure 16B shows a compliant sealing member 543c positioned in the gap 541a / c across the post assembly 530c. The compliant sealing member 543c may be configured to provide sufficient compliance to allow movement of the posts 530c within the gap 541a / c. An upper end cap 542a / c may be positioned on the upper plate 540a / c, for example, to close the stack. The secondary sealing member 544a / c may be interposed between the upper end plate 540a / c and the upper end cap 542a / c.

[0106] A compliant sealing member 543a / c between the central post 530a / c and the upper plate 540a / c and / or lower plate may leak. A secondary sealing member 544a and an upper end cap 542a / c are added above the post 530a / c. Compliance from the secondary sealing member 544a may be undesirable, so it can be made rigid to prevent leakage.

[0107] End plate design The electrochemical cell stacks described herein (e.g., fuel cell stacks or electrolytic cell stacks) may also include a lower end plate in addition to an upper end plate (e.g., upper end plate 540a / c). The lower end plate mechanically supports the stack and provides gas connections for the reactants (fuel and oxidizer gases). The lower end plate provides a sealing surface for other seals of the fuel stack and / or array interface, and further provides a sealing surface for the stack outer manifold (e.g., oxidizer manifold) and posts. The lower end plate provides clearance for mounting and isolates the stack core (cells, interconnects, and seals) from stresses arising at the sealing surfaces and bolt locations. The lower end plate also transmits compressive loads from the compression system to the stack. Furthermore, the lower end plate may function as one of the electrical connection points of the stack.

[0108] Figures 17A to 17C are lower perspective views of three different designs of the base plate assembly 660a / b / c according to embodiments. Each of the base plate assembly 660a / b / c includes a lower end plate 662a / b / c and a high-strength sealing plate 664a / b / c, defining at least one fuel port 666a / b / c and at least one oxidizer port 668a / b / c. The high-strength sealing plate 664a / b / c is axially aligned with the lower end plate 662a / b / c and is configured to yield to the lower end plate 662a / b / c to reduce the transmission of mechanical stress from the high-strength sealing plate 664a / b / c to the lower end plate 662a / b / c. Multiple mounting points 665a / b / c can be provided on the lower end plates 662a / b / c, thereby enabling the connection of an electrochemical cell stack (e.g., a fuel cell or electrolytic cell stack) to the lower end plates 662a / b / c.

[0109] In the embodiments of Figures 17A and 17B, the high-strength sealing plates 664a / b are uppermost plates having a high-strength sealing surface (made of a high-strength superalloy such as Haynes 230, for example). This provides the surface strength required for the interface with the compression sealing member. However, the coefficient of thermal expansion of high-strength superalloys is typically higher than what is permissible in balance with the stack components. Thus, separation is provided between the high-strength sealing surface and the rest of the stack. Figure 17A shows a base plate assembly 660a in which the high-strength sealing plate 664a is separated from the lower end plate 662a by a short tube 663a designed to yield under imposed thermal stress, thereby limiting the transmission of thermal stress within the stack.

[0110] Figure 17B shows a base plate assembly 660b in which the high-strength sealing plate 664b contains a yield point, and as a result, the high-strength sealing plate 660b does not have sufficient strength to transmit stress into the stack through the lower end plate 662b. In the embodiments shown in Figures 17A and 17B, one oxidizer port is delivered through the lower end plate 662a / b, as are the two fuel ports. In embodiments in which the oxidizer, rather than the fuel, is supplied via the post, the lower end plate may instead include one fuel port and two oxidizer ports. A threaded member is introduced to enable the mounting of the lower end plate. The threaded member is isolated in the design to prevent stress from being transmitted to the stack structure. The internal structure of the end plate is designed to carry the load from the compression system to the stack. In this design, it has been demonstrated that the current collection loss at the connection between the lower end plate and the system is less than 0.1%. The upper end plate provides a sealing surface for the oxidizer manifold and the post. Furthermore, it transmits compressive loads from the compression system into the stack and isolates the stack core (cells, interconnects, seals) from stresses induced by the compression system. The upper end plate provides a compliant sliding joint at the top of the post. The upper end plate can also function as one of the electrical connection points of the stack.

[0111] Figure 17C shows a base plate assembly 660c in which the high-strength sealing plate 665c is mechanically separated but contained within the lower end plate 662c, thereby providing the strength necessary to achieve sealing between the stack and the manifold to which it is mounted without imposing thermal stress on the stack structure due to a mismatch in coefficients of thermal expansion (CTE). In other words, the lower end plate 662c is interposed between the stack of multiple fuel cell units and the high-strength sealing plate 664c. Multiple mounting points 665c may be provided on the high-strength sealing plate 664c. The high-strength sealing plate 664c moves freely laterally relative to the lower end plate 662a to reduce stress transfer to it, but when bolted to its mating manifold in the system, it captures a portion of the lower end plate 662c between itself and the mating manifold system. Therefore, the mechanical strength for sealing is provided by the high-strength sealing plate 664c, while the transport of gas from the mating manifold into the stack is carried out by the mechanically isolated and thermally expanded lower end plate 662c. Friction between the high-strength sealing plate 664c and the trapped low-strength, low-CTE lower end plate 662c can be partially mitigated by the ceramic delamination layer, but the trapped portion of the lower end plate 662c is further isolated from the high-strength sealing plate 664c by multiple low-yield tubes (e.g., short low-strength tubes) positioned adjacent to the high-strength sealing plate 664c and the lower end plate 662c, thereby minimizing the possibility of transmitting thermal expansion stress to the stack structure.

[0112] Figure 18 is a top perspective view of an upper end plate 740, including a post interface tube 748 that extends axially from the surface of the upper end plate 740 away from the posts, when the upper end plate is positioned on an electrochemical cell stack (e.g., a fuel cell stack or an electrolytic cell stack). According to some embodiments, the upper end plate 740 may be included in an upper compression plate assembly. At least a portion of the post interface tube 748 may be positioned around a portion of a post (e.g., a central post). The post interface tube 748 can provide a sliding surface to allow slight relative movement between the post and the upper end plate 740.

[0113] In some embodiments, the stack includes an integrated compression system, which allows for easy integration of the stack into the array. One advantage of the small cell area and glass-ceramic seal is that the compression load may be relatively small. For example, the stack shown in Figure 2 used in array 200 in Figure 7A) is designed to operate at 3.5 kgf to 9 kgf (34 N to 88 N), and another stack used in array 300 in Figure 7B is known to operate at 121 cm². 2 and 550cm 2 Compared to 360 kgf and 900 kgf respectively for the stacks, it is designed to operate between 9 kgf and 36 kgf. This simplifies both the design of the compression elements and the compression plates. Firstly, the stiffness requirements of the compression plates at a high level are considered. The maximum deflection of a uniformly loaded 2D beam with pinned end connections is given by:

number

Numerical

[0114] Note that this is only a comparison of order of magnitude, and using the above formula, the stiffness requirement of the pressure plate can be compared with the conventional stiffness requirement of a 550 cm 2 stack. The calculation is for the fuel cell stack 110 in FIG. 2 or the array 200 in FIG. 7A, for example, 25 cm 2 a fuel cell stack having an active area of can be approximately 10,000 times less stiff while providing the same maximum deflection, whereas a fuel cell stack included in the array 300 of FIG. 7B can be approximately 440 times less stiff for the same maximum deflection, for example. This allows the design of the pressure plate to be greatly simplified. It should be noted that the maximum allowable deflection is essentially independent of cell size, since deflection results in the loss of electrical contact.

[0115] Figures 19A and 19B are top perspective views of upper compression plate assemblies 870a / b according to two different embodiments. Each of the upper compression plate assemblies 870a / b may be positioned at the upper end of the electrochemical cell stack and base plate assembly (e.g., base plate assembly 660a / b / c), or a lower end plate (e.g., lower end plate 662a / b / c) may be positioned at the lower end of the electrochemical cell stack opposite to the upper end. The upper compression plate assembly 870a / b includes an upper end plate 840a / b and an upper compression plate 872a / b positioned on the upper end plate 840a / b. A bias member 876a / b is positioned close to the upper end of the electrochemical cell stack and is configured to exert a compressive force on a stack of multiple electrochemical cell units. Furthermore, at least one compression member 879a / b is configured to connect the compression plate 872a / b to a lower compression plate of the base plate assembly, such as a high-strength sealing plate of the base plate assembly, and to transmit compressive force from the upper compression plate 872a / b to the base plate assembly.

[0116] Zooming in further, Figure 19A is a top perspective view of an upper compression plate assembly 870, including an upper compression plate 872a, an upper end plate 840a and post interface tube 848a (e.g., upper end plate 740 in Figure 18), a base member 876a (e.g., a spring pack), and a compression member 879a, according to an embodiment deployed in a fuel cell stack included in the array 200 of Figure 7A. As previously stated herein, the upper end plate 840 is positioned around the post 830a such that a gap exists between them. A compliant sealing member 843a is positioned in the gap above the post 830a. In this embodiment, the bias member 876a is a stack of high-temperature Belleville springs interposed between the upper compression plate 872a and the upper end plate 840a. Other embodiments may use coil springs or various forms of wave washers. The bias member 876a generates a compressive force to compress the stack. Two compression members 879a (e.g., tension rods) carry force from the top to the bottom of the stack, where the compression plate (not shown) transmits the load to the lower end plate. The individual Belleville springs of the bias member 876a are separated by guide shims that align and guide the springs, so as a result the Belleville springs do not drift laterally or become excessively compressed. The Belleville springs are designed to have low stress at operating temperatures. The compression members 879a are made of a superalloy that has high strength at temperatures. They have a higher coefficient of thermal expansion than the stack, and have the effect of slightly releasing the spring pack when heated.

[0117] The upper compression plate assembly 870b in Figure 19B is similar to that in Figure 19A, except that the bias member 876b of the compression plate assembly 870b in Figure 19B includes multiple coil spring sets (eight in this embodiment) rather than a Bellevill spring pack. Furthermore, the post 830b has a compliant sealing member 843b positioned above it, which may be similar to the post assembly 530c described with respect to Figure 15C. The upper compression plate assembly 870b was mounted on a fuel cell stack included in the array 300 in Figure 7B.

[0118] Figure 20A is a graph showing the spring response of a Belleville spring pack, which may be used in the upper compression plate assembly 870a of Figure 19A according to one embodiment. Figure 20B is a graph showing the creep of a coil spring, which may be used in the upper compression plate assembly of Figure 19B according to another embodiment. The difference in stack growth relative to the tension rod has the effect of unloading the stack during heating. This is by design and has the secondary benefit of providing more stack compression during transport at lower temperatures where material creep is not a concern. The geometric arrangement is chosen so that the compression is relieved to the desired compression during operation. The circle represents the point of force application at the peak, which is also where the spring becomes unstable. When pushed to this limit, the spring risks reversing itself on the left side of the force-displacement graph. If this occurs, the spring will no longer provide an effective load to the stack and will not recover without disassembly.

[0119] Therefore, in the design when the stack is cold, the displacement is limited to below the top diamond point (approximately 97 Newtons). When the stack is heated, the difference in thermal expansion allows the spring set to relax to the lower diamond point, where the stack is loaded to 82 Newtons, and the spring stress drops to below 50 MPa, which is within the creep limits of certain superalloys (e.g., Waspaloy, Haynes 282). The "+" point represents the compressive load remaining on the stack after 0.5% creep of the tension rod. After this creep, the load remains at an acceptable 18 Newtons, and at this point, the peak stress of the spring drops to 10 MPa. This unloading of the spring and compressive member slows the net creep rate of the entire system. To make the most of the spring properties, it is permitted to experience higher stresses at room temperature where creep of the material is not a problem. The figures provided illustrate a specific case. Generally, design strategies that consider cold vs. high temperature conditions and system creep during operation apply to all designs, but the details will depend on the goals and requirements of the specific stack.

[0120] Similarly, the coil springs in Figure 19B are designed for lower temperatures and can be relaxed to their high-temperature compression targets during operation. Figure 20B shows a 1.5-year test of a sample coil spring at its operating temperature in pure creep. The desired operating range for this spring is 9 kgf to 36 kgf. This test shows that some creep occurs at 29 kgf, but when the load is reduced to 21 kgf, the spring remains stable against further creep. These results confirm the high-temperature spring design for the target requirements.

[0121] Manifold design The outer manifold connects oxidizer ports from each unit cell to the base plate, where the oxidizer can be delivered to (or from) the oxidizer connection adjacent to the fuel connection. The opposite side of the stack remains open to an environment from which the oxidizer can flow directly from (or to) all cells. For example, Figure 21A (fuel cell stack 110, and fuel cell stack included in array 200) and Figure 21B (electrochemical cell stack of array 300) are lower perspective views of electrochemical cell stacks 910a / b (e.g., fuel cell stack or electrolytic cell stack) including outer manifolds 912a / b.

[0122] Figure 21A shows a configuration with two inlets (front and rear) and two outlets (left and right faces, with paths defined at the base connection point). The lower end plate 962a is positioned at the base of the electrochemical cell stack 910a, and the lower compression plate 982a is positioned below the lower end plate 962a. The compression member 979a transmits a compressive force from the upper compression plate to the lower compression plate 982a, thereby biasing the lower compression plate 982a, which in turn pushes the lower end plate 962a toward the electrochemical cell stack 910a, thereby fixing the electrochemical cell stack 910a in place. Figure 21B shows an alternative implementation of the structure shown in Figure 21A. The same functional parts exist, except for a different configuration in which the mounting bolts 983b descend from the top of the lower compression plate 982b rather than from the bottom, as shown in the embodiment of Figure 21A. Referring to Figures 21A and 21B, the manifolds 912a / b are made of sheet metal and held in place by bolted clips 918a / b. Between the manifolds 912a / b and the end plates and stack core are dielectric seal members 914a / b, which are positioned within the volume defined by the manifolds 912a / b around the electrochemical cell stack and are configured to fluidly seal a first portion of the volume from a second portion of the volume. The dielectric seal members 914a / b separate the oxidizer inlet from the oxidizer outlet. Small leaks across the seal formed by the dielectric seal members 914ab may be tolerated without impairing stack operation.

[0123] In the particular embodiment shown in Figure 21B, the oxidizer outlet (or inlet) port is divided into two, consisting of lower left and upper right openings in a lower end plate (not shown) positioned between the lower compression plate 982b and the electrochemical cell stack 910b. These are routed within the lower end plate to volumes defined by the left and right manifolds 982b of the electrochemical cell stack 910b. In this particular embodiment, two ports are shown that provide a low parasitic pressure drop for the oxidizer flow. The remaining ports (left and right openings) are the fuel input and fuel output ports, and their positions can be swapped as needed.

[0124] Depending on the application, an open or closed manifold may be preferred. The open manifold 912a shown in Figure 21A facilitates thermal coupling to the environment. This is useful, for example, in electrolysis or energy storage systems where operating conditions exist that require the electrochemical cell stack 910a to absorb heat from the environment. In pure electrochemical cell systems where reforming is limited to a level where the stack is operating net-thermally, a complete manifold may be preferred.

[0125] A complete (closed) manifold effectively isolates the operating stack core from its environment. Under exothermic operating conditions, this can potentially lower the ambient temperature by up to 100°C. This can yield significant benefits in terms of reducing the insulation requirements around the stack or stack array, and in allowing the use of lower-quality materials around the stack. This can result in system-level cost savings. It can also mitigate other system-level challenges, such as chromium volatilization, and challenges related to the transport or oxidation of other materials.

[0126] The following sections describe examples of the performance of various electrochemical cell stacks according to the embodiments described herein. These examples are for illustrative purposes only and are not intended to limit the scope of the concepts described herein.

[0127] Examples based on experiments The idea that reducing the size of components can increase overall power density (per kg and per L) contradicts current wisdom. The accepted wisdom is that the process of increasing power density and lowering cost involves increasing the size of each component while reducing the number of components. This assumes that the volume and cost of the stack are heavily influenced by the inactive parts of the stack (seal area, end plates, compression, etc.), and that moving to larger cells reduces the contribution of these inactive areas to the overall stack cost. In planar SOFCs, where cells are thin ceramic components, producing large cells is difficult. Much effort continues to be made to increase the size of SOFC cells.

[0128] In contrast, the embodiments described herein demonstrate that novel designs can lead to higher power density and lower costs as components become smaller. Contrary to current wisdom, moving to smaller cells has been shown to reduce the cost of inactive components by allowing them to be smaller and simpler than their larger counterparts, even when considered in proportion to the total active area or power output.

[0129] Experiments were conducted to compare three different known fuel cell stacks with an exemplary fuel cell stack according to one embodiment. All stacks were manufactured using the same basic materials. Each stack was of a planar solid oxide fuel cell design. Each stack used an anode supported by the same type of nickel-yttria stabilized zirconia cell, but the size and thickness were appropriate for the particular stack. Each stack had metal interconnects made of ferritic stainless steel. Each stack had end plates of appropriate size and strength to support the compressive forces required for stack operation. Stacks manufactured according to the embodiments described herein also included a compression system. 121 cm 2A baseline cell stack of 28 cells with an active area of ​​390 mA / cm² 3 It operated and supplied a total power of 1200W. It measured 190mm x 190mm x 150mm with a total volume of 5.4L and a weight of 17kg, achieving a power-to-weight ratio of 69W / kg and a power-to-volume ratio of 225W / L. 550cm² 2 A 120-cell stack with active area cells produces 290 mA / cm² 2 It operated and supplied a total power of 16,900W. It measured 395mm × 395mm × 618mm with a total volume of 96L and a weight of 238kg (including end plates), achieving a power-to-weight ratio of 71W / kg and a power-to-volume ratio of 176W / L. In contrast, 25cm 2 A stack fabricated according to one embodiment, having 225 cells, each equipped with an active area cell, exhibits a current of 0.39 mA / cm². 2 It operated and supplied a total power of 1760W. Measuring 79mm × 71mm × 254mm with a total volume of 1.4L and a weight of 2.4kg, it is measured to achieve a power-to-weight ratio of 733W / kg and a power-to-volume ratio of 1257W / L. While relatively young compared to other stack designs, this embodiment of the stack has already achieved a tenfold increase in power density by weight and approximately sevenfold increase in power density by volume. This result was unexpected, particularly from the standpoint of the accepted belief that the process of increasing power density and lowering costs involves increasing the size of each component while reducing the number of components.

[0130] The selection of test data is presented in Figures 22 to 24. Figure 22 shows a 225-cell (~1kW) stack contained in array 200, according to an embodiment of fuel cell stack 110, operating with a gas composition representing a typical natural gas combustion system application. Gas conditions include typical levels of gas utilization, typical current density and temperature, and typical levels of in-stack steam reforming for converting inlet natural gas to hydrogen, carbon monoxide, and carbon dioxide. The stack has demonstrated stable operation for over 5000 hours and exhibits a degradation rate consistent with the degradation rate expected from the cell material used. In other words, there are no degradation aspects that could be linked to the stack design. This demonstrates the stack's ability to handle typical flow and thermal conditions, including in-stack reforming, of a natural gas combustion system, while maximizing the potential of the underlying repeatable cell material.

[0131] Figure 23 shows the results for a 20-cell implementation of the same stack, at -2 A / cm². 2 The system is running under extremely aggressive electrolytic conditions. Some test interruptions, caused by plant balance failures (not due to the stack), occurred early in the test and can be seen as spikes in the data at approximately 25,125, and 250 hours of elapsed time. Following the initial degradation that may have been caused by the test interruptions (electrolytic degradation manifests as an increase in voltage), the stack demonstrated operation for more than 1000 hours without degradation despite the aggressive conditions. This demonstrates the stack's flexibility in operating under a wide range of thermal and flow conditions, as well as its relative immunity to degradation.

[0132] Figure 24 shows the results of a 60-cell implementation of a similar stack running under various pure hydrogen fuel cell conditions, where the total test time exceeds one year. While the degradation rate became difficult to determine due to the changes in conditions, the stack exhibited high stability (low degradation) throughout the year of testing, including very high-exothermic test conditions. This can be seen as the relative flatness of the voltage curve, where the step changes correspond to changes in test conditions. This demonstrates the stack's relatively long-term stability and its ability to reject heat when operating in exothermic mode without internal reforming to absorb some of that heat.

[0133] Figures 23 and 24 show the results including thermal cycling, where no change in performance was observed before and after thermal cycling, demonstrating the stack's thermal cycling capability regardless of the use of glass-ceramic seals. This demonstrates the success of an inherently compliant structure, which allows for the use of sealed or nearly sealed glass-ceramic seals while, in other respects, preventing the accumulation of thermal stress that would lead to seal or cell failure.

[0134] Figure 25 shows 0.25 A / cm². 2 The results show a 45-cell implementation configuration of an electrochemical cell stack using Array 300 operating in electrochemical cell mode, demonstrating very low degradation after one thermal cycle. These results are comparable to those of a slightly larger cell stack (81 cm²). 2 This shows cases where the active area does not eliminate thermal stress and does not hinder the ability to extract all the potential from the material set.

[0135] Figure 26 shows -1 A / cm 2 The results show the individual 45-cell implementation configuration of the fuel cell stack with Array 300, operating in electrolysis mode and demonstrating very low degradation and, in fact, a slight improvement in overall performance after 1600 hours of testing. The test also demonstrated its robustness against aggressive transients, having undergone aggressive thermal cycling for a balance of plant failures (non-stack related) that did not adversely affect the stack's performance.

[0136] The aforementioned integrated design addresses many of the major barriers between SOFC technology and the current market, and in part, its stack characteristics offer opportunities for system simplification (high voltage output, low current, compact packaging, low external heat exchange requirements, no external pressure load requirements, etc.) by providing significant cost reduction opportunities at both the stack level (by reducing material content and facilitating part automation) and the system level.

[0137] In all cases, it is understood that the above-described arrangements are merely illustrative examples of many possible specific embodiments representing the applications of the present invention. Without departing from the spirit and scope of the present invention, a number of different other arrangements, including the use of different electrolytes, can be readily devised in accordance with the principles of the concepts described herein.

[0138] Where used herein, the terms “approximately,” “about,” “substantially,” and similar terms are intended to have a broad meaning consistent with the usage generally accepted by those skilled in the art to which the subject matter of this disclosure relates. It should be understood by those skilled in the art considering this disclosure that these terms are intended to enable the description of specific features described and claimed without limiting the scope of those features to the exact numerical range provided. Accordingly, these terms should be construed to indicate that any substantial or insignificant modification or alteration of the subject matter described and claimed is deemed to fall within the scope of the invention as enumerated in the appended claims.

[0139] As used herein, terms such as “joined” and “connected” mean that two members are joined to each other directly or indirectly. Such joining may be fixed (e.g., permanent) or movable (e.g., removable or detachable). Such joining may be achieved by two members or two members and an additional intermediate member being formed integrally with each other as a single, unified body, or by two members or two members and an additional intermediate member being attached to each other.

[0140] References to the position of elements in this specification (e.g., “top,” “bottom,” “upward,” “downward,” etc.) are used solely to describe the orientation of various elements in the figures. It should be noted that the orientation of various elements may differ according to other exemplary embodiments, and such variations are intended to be included in this disclosure.

[0141] It is important to note that the construction and arrangement of various exemplary embodiments are illustrative only. While this disclosure describes in detail only a few embodiments, those skilled in the art who study this disclosure will readily understand that many modifications (e.g., changes in the size, dimensions, structure, shape, and proportions of various elements, parameter values, mounting arrangements, material use, color, orientation, etc.) are possible without substantially departing from the novel teachings and advantages of the subject matter described herein. For example, elements shown as integrally formed may consist of multiple parts or elements, the positions of elements may be reversed or otherwise modified, and the nature or number of individual elements or positions may be changed or altered. The order or sequence of steps of any process or method may be modified or rearranged according to alternative embodiments. Other substitutions, modifications, changes, and omissions can also be made in the design, operating conditions, and arrangements of various exemplary embodiments without departing from the scope of the invention. For example, perforated baffles can be further optimized to achieve the intention of extending dwell time without creating dead zones.

Claims

1. A fuel cell assembly, Including a first housing base, the first housing base is Lower gas supply section, A first fuel inlet pipe extending from the first end of the first housing base to the second end of the first housing base, A lower gas supply section including a first spent fuel outlet pipe extending from a first end of the first housing base to a second end of the first housing base, An upper plate including multiple through holes, A gas distribution section located between the lower gas supply section and the upper plate, the gas distribution section includes a plurality of inlet gas distribution channels that fluidly connect the first fuel inlet pipe to a first subset of the plurality of through holes, and a plurality of outlet gas distribution channels that fluidly connect the first spent fuel outlet pipe to a second subset of the plurality of through holes. Fuel cell assembly.

2. The fuel cell assembly according to claim 1, further comprising a plurality of fuel cell stacks coupled to the upper plate, each fuel cell stack comprising a fuel inlet coupled to one of the first subsets of the plurality of through holes and a spent fuel outlet coupled to one of the second subsets of the plurality of through holes.

3. The fuel cell assembly according to claim 2, wherein the plurality of fuel cell stacks are arranged in an array having at least two rows and at least two columns.

4. The fuel cell assembly according to claim 2, wherein the plurality of fuel cell stacks are configured to receive all of the reaction gas through the first housing base.

5. The fuel cell assembly according to claim 1, wherein the gas distribution unit further includes a fuel reforming unit.

6. The fuel cell assembly according to claim 1, wherein the first gas inlet distribution channel and the first gas outlet distribution channel are configured to perform heat exchange between the spent fuel in the first gas outlet distribution channel and the fuel in the first gas inlet distribution channel.

7. The fuel cell assembly according to claim 6, wherein the lower gas supply section further includes a fuel bypass pipe fluidly coupled to a third subset of the plurality of through holes, the fuel bypass pipe being configured to supply fuel to the third subset of the plurality of through holes without heat exchange from spent fuel in the plurality of outlet gas distribution channels.

8. A second fuel inlet pipe is fluidly coupled to the first fuel inlet pipe, The fuel cell assembly according to claim 1, further comprising a second housing base including a second spent fuel outlet pipe fluidly coupled to the first spent fuel outlet pipe.

9. The fuel cell assembly according to claim 8, wherein the first fuel inlet pipe and the second fuel inlet pipe form a straight combined pipe.

10. The fuel cell assembly according to claim 1, wherein the lower gas supply section further includes a first oxidizer inlet pipe extending from the first end of the first housing base to the second end of the first housing base.

11. The fuel cell assembly according to claim 10, further comprising a plurality of oxidizer preheating tubes coupled to the upper plate and fluidly coupled to the first oxidizer inlet tube.

12. The fuel cell assembly according to claim 11, further comprising a plurality of fuel cell stacks coupled to the upper plate, wherein an oxidizer preheating tube extends upward from the upper plate and is configured to absorb heat emitted from the plurality of fuel cell stacks.

13. A modular fuel cell system comprising multiple fuel cell assemblies, each fuel cell assembly being: Housing base, A fuel inlet pipe extending from the first end of the housing base to the second end of the housing base, A housing base including a spent fuel outlet pipe extending from a first end of the housing base to a second end of the housing base, A plurality of fuel cell stacks coupled to the upper surface of the housing base, each fuel cell stack is: A fuel inlet that is fluidly coupled to the aforementioned fuel inlet pipe, A plurality of fuel cell stacks, each including a spent fuel outlet that is fluidly coupled to the spent fuel outlet pipe, Each fuel inlet pipe is connected to at least one adjacent fuel inlet pipe. A modular fuel cell system in which each spent fuel outlet pipe is connected to at least one adjacent spent fuel outlet pipe.

14. The modular fuel cell system according to claim 13, wherein the fuel inlet pipe forms a linear combination fuel inlet pipe, and the spent fuel outlet pipe forms a linear combination spent fuel outlet pipe.

15. The modular fuel cell system according to claim 13, wherein the plurality of fuel cell stacks of each fuel cell assembly are configured to receive all of the reaction gas through their respective housing bases.

16. A fuel cell assembly, Two or more first rows of first fuel cell stacks, A second row of two or more second fuel cell stacks, Housing base, An upper plate, wherein each of the first fuel cell stacks and each of the second fuel cell stacks are coupled to the first side of the upper plate, A lower gas supply unit that is coupled to the second side of the upper plate, which is opposite to the first side, A fuel inlet pipe extending from a first end of the housing base to a second end of the housing base, the fuel inlet pipe being fluidly coupled to each of the first fuel cell stacks and each of the second fuel cell stacks, A housing base including a lower gas supply section which includes a spent fuel outlet pipe extending from the first end of the housing base to the second end of the housing base, and which is fluidly coupled to each of the first fuel cell stacks and each of the second fuel cell stacks, A fuel cell assembly including a fuel cell.

17. The aforementioned lower gas supply unit An oxidizer inlet pipe extending from the first end of the housing base to the second end of the housing base, wherein the oxidizer inlet pipe is fluidly coupled to each of the first fuel cell stacks and each of the second fuel cell stacks, The fuel cell assembly according to claim 16, further comprising: a spent oxidizer outlet pipe extending from the first end of the housing base to the second end of the housing base, wherein the spent oxidizer outlet pipe is fluidly coupled to each of the first fuel cell stacks and each of the second fuel cell stacks.

18. The fuel cell assembly according to claim 17, further comprising a plurality of oxidizer preheating tubes coupled to the upper plate and fluidly coupled to the oxidizer inlet tube.

19. The fuel cell assembly according to claim 18, wherein the oxidizer preheating tube extends upward from the upper plate and is configured to absorb heat emitted from the first fuel cell stack and the second fuel cell stack.

20. The fuel cell assembly according to claim 17, wherein the fuel inlet pipe is parallel to the spent fuel outlet pipe, the oxidizer inlet pipe, and the spent oxidizer outlet pipe.

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