Thermoelectrochemical converters with dense metal electrodes

Abstract

The present disclosure provides a thermoelectric converter comprising a working fluid and a pair of membrane electrode assemblies (MEAs). Each MEA comprises a pair of electrodes and a thin film electrolyte membrane sandwiched between the electrodes, which electrodes are conductive and permeable to the working fluid. The membrane is conductive to the ions of the working fluid and has a thickness of 0.03 μm to 10 μm. At least one electrode of each MEA comprises a non-porous dense metal. One electrode of each MEA contacts the working fluid at a first and higher pressure, while the other electrode contacts the working fluid at a second and lower pressure. The first MEA is configured to compress the working fluid from a second pressure to a first pressure, and the second MEA is configured to expand the working fluid from the first pressure to the second pressure.

Description

[0001] Cross-references to related patent applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 069,380, filed on August 24, 2020, the entire disclosure of which is incorporated herein by reference. Background Art

[0003] Membrane electrode assemblies (MEAs) have an ion-conducting membrane sandwiched between two electrodes and are used in many electrochemical applications. The most common applications are batteries, fuel cells, and gas separation processes, such as hydrogen or oxygen separation. Generally speaking, when an ionizable working fluid passes through the MEA, it is oxidized on the incoming side, thereby separating electrons from atoms. The resulting ions are conducted through the membrane to the electrode on the opposite side (also known as the outgoing side). On the other hand, electrons are conducted to the electrode on the opposite side through an external circuit. When the ions recombine with electrons in the outgoing electrode, the ions are reduced.

[0004] Generally speaking, it is desirable to pass the ionizable working fluid through the MEA as efficiently as possible. In virtually all applications of interest, the resistance to the passage of the ionizable working fluid through the membrane is problematic. For example, in hydrogen or oxygen separation applications, a greater pressure drop across the membrane as the working fluid passes through the membrane means more energy (and therefore higher costs) is required to supply the source gas at the increased pressure.

[0005] A similar situation exists with fuel cells. The most common type of fuel cell is a proton exchange membrane fuel cell (MEA) with a proton conducting membrane (PCM). This type of fuel cell supplies hydrogen to one electrode and oxygen to the other. Hydrogen ions are conducted through the PCM to the oxygen side of the fuel cell at the potential for the chemical reaction between hydrogen and oxygen. Electrons involved in the chemical reaction are conducted from the hydrogen electrode to the oxygen electrode through an external load. The electrons and hydrogen ions reconstitute hydrogen and complete the reaction with oxygen on the oxygen side of the cell, producing water, which is then discharged from the system. A continuous supply of hydrogen and oxygen to the cell maintains a continuous current flow.

[0006] Alkali Metal Thermo-Electrochemical Conversion (AMTEC) cells have been designed as thermo-electrochemical heat engines. AMTEC heat engines use pressure at high temperatures to force an ionizable working fluid (such as sodium) through an electrochemical cell, generating a voltage potential and an electric current. Electrodes connect the current to an external load. Electrical work is performed when a pressure differential across an electrolyte separator forces molten sodium atoms through the electrolyte. The sodium is ionized upon entering the electrolyte, releasing electrons into the external circuit. On the other side of the electrolyte, the sodium ions recombine with the electrons upon exiting the electrolyte to reform sodium in much the same way as occurs in battery and fuel cell-type electrochemical cells. The recombined sodium leaves the electrochemical cell as an expanding gas at low pressure and high temperature.

[0007] The Johnson Thermoelectrochemical Converter (JTEC) system (disclosed in U.S. Patent No. 7,160,639, filed April 28, 2003) is also a thermoelectrochemical heat engine that uses MEAs to convert heat into electricity. JTEC uses a pair of MEA stacks, specifically hydrogen concentration cells, connected back-to-back, one at a relatively high temperature and one at a relatively low temperature. Hydrogen circulates between the two MEA stacks within the engine via a countercurrent recuperator. The low-temperature MEA stack, connected to the heat sink, serves as the engine's "electrochemical compression" stage, while the high-temperature MEA stack, connected to the heat source, serves as the engine's "electrochemical expansion" stage. As in any heat engine, the expansion process occurring at high temperature generates enough power to drive the compression process occurring at low temperature and provide net output power to an external load.

[0008] However, this conventional engine design is often complicated by the need for a large membrane-to-electrode surface area ratio and the large number of cells connected electrically in series to achieve practical output voltage levels. Specifically, unlike conventional fuel cells, where the open-circuit voltage can exceed 1V, in thermoelectrochemical heat engines, the net output voltage resulting from the Nernst voltage difference between the high- and low-temperature MEAs, derived from the hydrogen pressure ratio, is only in the range of approximately 0.1V under moderately high and low voltage operating conditions. Therefore, several cells must typically be connected in series to achieve useful output voltage levels. Furthermore, the internal impedance of the MEA pair significantly impacts the output power capability.

[0009] The primary efficiency losses associated with MEAs are gas pressure flow losses entering and leaving the porous electrodes, the activation energy required to oxidize and reduce the working fluid at the electrode / membrane interface, and the resistance to ion conduction through the membrane. Pressure losses associated with gas flow are addressed by optimizing electrode thickness, pore size, and pore distribution. Activation losses are generally fixed material properties. Efforts to reduce activation energy losses typically focus on optimizing catalyst loading and distribution, as well as the type of catalyst used.

[0010] The resistance to ion conduction through a membrane is a material property that depends on the intended use. For efficient energy conversion, the membrane ideally possesses a high gas diffusion barrier, as diffusion of the working fluid (e.g., hydrogen) under a pressure differential across the membrane can reduce electrical output and efficiency. The membrane must also exhibit good ion conductivity. However, many known and available membrane materials with good ion conductivity, such as Nafion (a perfluorosulfonic acid-based polymer) manufactured by DuPont, often exhibit very poor molecular diffusion barriers. Low molecular barrier properties necessitate thicker membranes to inhibit diffusion, which in turn results in higher conduction resistance, rendering the material unusable. Conversely, known and available membrane materials with high molecular diffusion barriers often have relatively low ion conductivity, resulting in high system impedance and associated high polarization losses. Therefore, achieving practical power density requires thin membranes, while achieving practical power levels requires large membrane areas while minimizing internal resistive polarization losses.

[0011] Therefore, there is a need for a practical method to utilize existing high-barrier, low-conductivity membrane materials to provide a thermoelectrochemical heat engine that is close to the Carnot equivalent cycle, can operate over a wide range of heat source temperatures, and eliminates the reliability and low efficiency issues associated with mechanical engines. The solid-state heat engine of the present invention meets this need. Summary of the Invention

[0012] In one embodiment, the present invention relates to a thermoelectric converter comprising an ionizable working fluid, and a first membrane electrode assembly and a second membrane electrode assembly electrically coupled to each other. Each membrane electrode assembly comprises a first electrode that is electron-conducting and permeable to the ionizable working fluid; a second electrode that is electron-conducting and permeable to the ionizable working fluid; and a thin film electrolyte membrane sandwiched between the first and second electrodes. The thin film electrolyte membrane is conductive to ions of the ionizable working fluid and has a thickness of 0.03 to 10 microns. At least one of the first and second electrodes of each membrane electrode assembly is composed of a non-porous, dense metal. Due to a working fluid pressure differential applied across each membrane electrode assembly, one of the first and second electrodes of each membrane electrode assembly contacts the working fluid at a first pressure, and the other of the first and second electrodes of each membrane electrode assembly contacts the working fluid at a second pressure lower than the first pressure. The first membrane electrode assembly is configured to expand the working fluid from a first pressure to a second pressure, and the second membrane electrode assembly is configured to compress the working fluid from the second pressure to the first pressure.

[0013] According to the aforementioned embodiment, the first and second MEAs operate at different temperatures. Electrical energy is applied to the second MEA to pump the working fluid through it to a higher pressure to maintain the pressure differential (heat is removed from it), thereby operating the second MEA at a first voltage. The first MEA is also affected by the pressure differential, and the working fluid expands to a lower pressure through the first MEA (supplied with heat to the first MEA), thereby operating at a second voltage different from the first voltage.

[0014] In one embodiment, which can be combined with any of the previously described embodiments, the non-porous dense metal is layered or mounted onto a porous substrate.

[0015] In one embodiment that may be combined with any of the preceding embodiments, at least one of the first electrode and the second electrode of at least one of the first membrane electrode assembly and the second membrane electrode assembly includes a catalyst, and the catalyst is configured to promote oxidation and reduction of the working fluid as the working fluid passes through the corresponding thin film electrolyte membrane.

[0016] In one embodiment which may be combined with any of the preceding embodiments, at least one of the first electrode and the second electrode of at least one of the first and second membrane electrode assemblies comprises palladium or an alloy thereof.

[0017] In one embodiment which may be combined with any of the preceding embodiments, the thermoelectric converter further comprises a recuperator coupling the flow of the working fluid between the first membrane electrode assembly and the second membrane electrode assembly at the first pressure and the second pressure.

[0018] In one embodiment which may be combined with any of the before-addressed embodiments, the converter has a tubular configuration.

[0019] In one embodiment which may be combined with any of the before-mentioned embodiments, each of the first membrane electrode assembly and the second membrane electrode assembly has a tubular structure.

[0020] In one embodiment that may be combined with the aforementioned embodiment, the interior of each of the first membrane electrode assembly and the second membrane electrode assembly forms a first conduit for the working fluid to flow at the first pressure.

[0021] In one embodiment that may be combined with the preceding embodiments, the thermoelectric converter further comprises a housing that at least partially surrounds the first membrane electrode assembly and the second membrane electrode assembly, the space between the first membrane electrode assembly and the second membrane electrode assembly and the housing constituting a second conduit for the working fluid to flow at the second pressure.

[0022] In one embodiment which may be combined with any of the before-addressed embodiments, one of the first electrode and the second electrode is electrically common to both the first membrane electrode assembly and the second membrane electrode assembly.

[0023] In one embodiment which may be combined with any of the before-addressed embodiments, the thermoelectric converter further comprises an external circuit for electrically coupling the first membrane electrode assembly and the second membrane electrode assembly.

[0024] In one embodiment which may be combined with any of the before described embodiments, the invention relates to a thermoelectric converter system comprising a plurality of converters as described above, wherein the plurality of converters are coupled between a first flow of the working fluid at a first temperature and a second flow of the working fluid at a second temperature, the second temperature being lower than the first temperature.

[0025] In one embodiment that may be combined with any of the preceding embodiments, the present invention relates to a method for generating electricity using the above-described thermoelectric converter as a heat pump, the method comprising coupling a first membrane electrode assembly to a heat source at a first temperature, coupling a second membrane electrode assembly to a heat sink at a second temperature, the first temperature being lower than the second temperature, applying power to the second membrane electrode assembly to pump the working fluid from the second pressure to the first pressure, removing heat at the second temperature and a first voltage, and extracting power from the first membrane electrode assembly as the working fluid expands from the first pressure to the second pressure, providing heat to the working fluid at the first temperature and a second voltage, the first voltage being higher than the second voltage.

[0026] In one embodiment which may be combined with any of the preceding embodiments, the method further comprises connecting an external power source in series with the second membrane electrode assembly.

[0027] In one embodiment, which can be combined with any of the above embodiments, the present invention relates to a method for generating electricity using the above-described thermoelectric converter as a heat engine. The method comprises coupling a first membrane electrode assembly to a heat source at a first temperature, coupling a second membrane electrode assembly to a heat sink at a second temperature, the first temperature being higher than the second temperature, applying power to the second membrane electrode assembly to pump the working fluid from the second pressure to the first pressure, removing heat at the second temperature and a first voltage, and extracting power from the first membrane electrode assembly as the working fluid expands from the first pressure to the second pressure, providing heat to the working fluid at the first temperature and a second voltage, the second voltage being higher than the first voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The following detailed description of the preferred embodiments of the present invention will be better understood when read in conjunction with the accompanying drawings. For the purpose of illustrating the invention, there are shown in the drawings presently preferred embodiments. However, it should be understood that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings:

[0029] Figure 1 is a cross-sectional view of a thermoelectrochemical converter including two thin film electrode assemblies according to an embodiment of the present invention;

[0030] Figure 2 is a graphical depiction of hydrogen permeability of several metals suitable for use as electrodes of a membrane electrode assembly of a converter according to an embodiment of the present invention;

[0031] Figure 3 is a table identifying several commercially available hydrogen permeable metal alloys;

[0032] Figure 4 is a cross-sectional view of a thermoelectrochemical converter including two thin film electrode assemblies according to another embodiment of the present invention;

[0033] Figure 5A yes Figure 1 A top plan view of the converter shown in ;

[0034] Figure 5B yes Figure 1 Bottom plan view of the converter shown in ;

[0035] Figure 6 is a plurality of thermoelectric converter conduits operating between a high temperature working fluid stream and a low temperature working fluid stream according to another embodiment of the present invention; and

[0036] Figure 7 is a graphical depiction of several exemplary proton conducting materials suitable for use as electrolyte materials to form ion conducting membranes according to embodiments of the present invention. DETAILED DESCRIPTION

[0037] Certain terms are used in the following description for convenience only and are not limiting. The terms "near", "far", "upward", "downward", "bottom" and "top" refer to the directions mentioned in the figures. According to the present invention, "inward" and "outward" refer to directions toward and away from the geometric center of the device and its designated parts, respectively. Unless otherwise specified herein, the terms "a, an" and "the" are not limited to one element, but should be understood to mean "at least one". The terms include the words mentioned above, their derivatives and words of similar meanings. It should also be understood that terms such as "first", "second", etc. are provided for clarity only. The elements or components identified by these terms and their operations can be easily switched.

[0038] The present invention generally relates to an improved membrane electrode assembly, particularly for use in a thermoelectrochemical converter. More particularly, the present invention relates to a thermoelectrochemical converter having an ionizable working fluid and at least one electrochemical concentration cell, comprising an MEA comprising a thin film electrolyte layer and at least one electrode, more preferably a pair of electrodes, the pair of electrodes sandwiching the thin film electrolyte layer.

[0039] refer to Figure 1 , shows a converter 100 according to one embodiment of the present invention. The converter 100 includes a first electrochemical cell 9 and a second electrochemical cell 11. Each cell 9, 11 includes an ion-conducting MEA, which includes an ion-conducting membrane sandwiched between two electrodes. More specifically, the first electrochemical cell 9 includes a first MEA 40 and the second electrochemical cell 11 includes a second MEA 42. The first MEA and the second MEA 40, 42 both typically have a tubular structure, which means that their electrodes and membranes (which will be described in further detail herein) have a tubular structure. It will be understood by those skilled in the art that each cell may include more than one MEA, and that the MEAs do not need to have a tubular structure. In Figure 1 In the converter 100, the first electrochemical cell 9 and the heat sink Q L Connect the second electrochemical cell 11 to the heat source Q H Connect. Radiator Q L and heat source Q H This will be discussed in detail in this article.

[0040] The first MEA 40 of the first electrochemical cell 9 includes a membrane 6 located between a first electrode 5 and a second electrode 10. The first MEA 42 of the second electrochemical cell 11 includes a membrane 8 located between a first electrode 5 and a second electrode 14. The membranes 6, 8 and the electrodes 5, 10, 14 all have a tubular structure (see FIG. Figure 1 ).

[0041] Each membrane 6, 8 is an ion-conducting membrane. More preferably, each membrane 6, 8 is in the form of a thin film electrolyte layer, most preferably, a dense thin film electrolyte layer. Preferably, the thickness of each thin film electrolyte membrane 6, 8 is less than 10 microns, more preferably 0.03 microns to 10 microns. Preferably, each thin film electrolyte membrane 6, 8 is conductive to the ions of the working fluid. More particularly, the dense thin film electrolyte layer 6, 8 is preferably non-porous and can conduct the ions of the working fluid while being substantially impermeable to the non-ionic components of the working fluid. Thus, the ion-conducting membrane 6, 8 limits the diffusion of unionized working fluid therein. The thin film electrolyte structure of each MEA 40, 42 allows the thermoelectrochemical converter 100 to achieve high power density even when using an electrolyte material with relatively low ionic conductivity.

[0042] refer to Figure 7 , showing various exemplary proton conducting materials suitable for use as electrolyte materials to form the ion conducting membranes of the present invention. Figure 7 The materials shown are particularly suitable for use with hydrogen as the working fluid. Figure 7 The data provided in the can be used to select the best material for a particular application, primarily based on maximizing conductivity for the target operating temperature of the membrane. Figure 7 Several preferred membrane / electrolyte materials are oxides. Figure 7 The preferred membrane / electrolyte material is suitable for application by sputtering or another physical deposition method. Polybenzimidazole (PBI) is the preferred polymer and can therefore be applied by extrusion or another polymer coating technique.

[0043] The first electrode 5 and the second electrode 10, 14 are preferably conductive to electrons and permeable to the ionizable working fluid. The permeability of the electrodes 5, 10, 14 can be atomic or molecular diffusion through a non-porous electrode material, or the electrodes 5, 10, 14 can be permeable due to porosity. In one embodiment, at least one of the electrodes 5, 10, 14 can include one or more additives to promote electronic conductivity and / or one or more catalysts to promote the desired electrochemical reaction.

[0044] Preferably, at least one of the first electrode 5 and the second electrode 10 of MEA 40 and at least one of the first electrode 5 and the second electrode 14 of MEA 42 comprises a non-porous metal, and more preferably a non-porous, dense metal. More preferably, both electrodes 5, 10 and 5, 14 of both MEAs 40 and 42 comprise a non-porous metal, and more preferably a non-porous, dense metal. In a preferred embodiment, at least one electrode 5, 10, 14 (and more preferably all electrodes 5, 10, 14) comprises a solid non-porous metal or a nanoporous material (serving as a support for the thin-film electrolyte layers 6 and 8).

[0045] More specifically, in one embodiment, at least one of electrodes 5, 10, 14 comprises a nanoporous material mounted or coated on a substrate that provides mechanical support for the nanoporous material, thereby forming a nanoporous electrode, with the thin film electrolyte directly supported on the nanoporous material. In one embodiment, the substrate is a porous substrate. Preferably, the nanoporous electrode has a surface smoothness sufficient to serve as a substrate for a thin film electrolyte coating having a thickness of 0.03 to 10 microns. Such an electrode can be composed, for example, of microporous carbon or nanoporous carbon. Examples of such microporous or nanoporous carbon electrodes and how they are formed are disclosed in U.S. Pat. No. 9,046,784 to Wang et al., U.S. Pat. No. 6,632,849 to Yao et al., and an article published by Kondyurin et al., entitled "Nanostructured Carbonized Thin Films Produced by Plasma Immersion Ion Implantation of Block-Polymer Assemblies," pp. 155-160, online record version: Oct. 29, 2007 | DOI: 10.1002 / ppap.200700111. The substrate can be, for example, a silicon wafer, a glass wafer, or a metal wafer.

[0046] In another embodiment, at least one of the electrodes 5, 10, 14 comprises a non-porous material, which is mounted on a substrate that provides mechanical support for the non-porous material, thereby forming a non-porous electrode, and the thin film electrolyte is supported on the non-porous material. In one embodiment, the substrate is a porous substrate. Preferably, at least one of the electrodes 5, 10, 14 comprises a non-porous metal material, which is mounted on a porous electrode substrate, thereby forming a non-porous metal electrode, and the thin film electrolyte is supported on the non-porous metal material. More particularly, at least one of the electrodes 5, 10, 14 may include a thin non-porous metal film that is permeable to the working fluid supported on the porous substrate.

[0047] Alternatively, at least one of the electrodes 5, 10, 14 comprises a dense, self-supporting metal sheet or foil that is permeable to the working fluid.

[0048] In one embodiment, each porous electrode 5, 10, 14 optionally includes a dense metal coating that is permeable to the working fluid and is on the surface of the metal substrate that interfaces with the electrolyte membrane 6, 8. The dense metal coating may include a catalyst to promote oxidation and reduction of the working fluid as it enters and leaves the electrolyte membrane 6, 8. In addition, the metal coating may be formed from a porous substrate that is either electronically conductive or non-electronically conductive, such as porous anodic aluminum oxide (Whatman Anodisc). TM , which can be purchased from SigmaAldrich in the United States)) or supported by conductive materials (such as nickel foam).

[0049] Metal alloys and laminates, particularly metal alloys and laminates that are permeable to the working fluid, are preferably used to form the electrodes 5, 10, 14. Figure 2 , shows several different metals that can be used as electrodes 5, 10, 14 of the present invention. More specifically, Figure 2 The hydrogen permeability of several metals is shown. Particularly in the case where hydrogen is the working fluid, palladium and palladium alloys are preferred. While many metals have higher permeability than palladium, these other materials tend to fail due to embrittlement when placed in a hydrogen environment. Palladium, however, remains stable and has catalytic properties that promote hydrogen reactions. Palladium has also been identified as a suitable catalytic support substrate for thin electrolyte coatings. However, in addition to comprising the anode and catalyzing the ingress of hydrogen molecules, palladium also catalyzes the reduction reaction of the electrolyte at the electrolyte interface. Therefore, it is known that including a less reactive interface layer between the palladium and the electrolyte is beneficial.

[0050] For example, a nickel / palladium foil with a 600 nm thick nickel layer shows a kinetic energy of about 5 × 10 -9 mol s -1 m - 1 pa -0.5 The hydrogen permeability of the material is half that of pure palladium foil. This value is sufficient to enable the external current of the fuel cell to reach at least 2A cm 2See “Thin Film Fuel Cell Based on Nanometer-Thick Membrane of Amorphous Zirconium Phosphate Electrolyte” (Journal of The Electrochemical Society, 158(8)B866-B870(2011)0013-4651 / 2011 / 158(8) / B866 / 5, The Electrochemical Society).

[0051] Compared to the extensive work on developing membranes for hydrogen separation / production, the use of solid metal electrodes for fuel cell applications has been very limited. Figure 3 Several commercially available hydrogen-permeable metal alloys are listed, originally provided by Yin et al., "A Review on the Production and Purification of Biomass-Derived Hydrogen Using Emerging Membrane Technologies," Catalyst, October 6, 2017. Adding silver and / or other alloying metals can improve the mechanical strength and stability of palladium-based membranes. For example, alloying silver into palladium can increase membrane permeability by up to five times compared to pure palladium membranes. A study conducted by Tanaka et al., “Preparation and Characterization of Ceramic Supported Ultra-Thin (approximately 1 μm) Pd-Ag Membranes” (DAPJ Membr. Sci. 2017, 528, 12-23), analyzed ultrathin (approximately 1 μm) Pd-Ag alloy membranes produced by a simultaneous ELP method and found that the membranes had a H2 permeability of 9.0 to 9.4 × 10 -6 mol.m -2 s -1 Pa -1 , H2 / N2 selectivity is between 3300 and 2000.

[0052] Each MEA 40, 42 can be constructed by applying a thin film coating of electrolyte material to an electrode that is permeable to the working fluid. For example, the thin film electrolyte layer or membrane 6, 8 can be applied to the first electrode by sputter deposition, laser ablation, chemical vapor deposition, or any other known thin film deposition technique. The thin film electrolyte layer or membrane 6, 8 can also be applied to the first electrode by spin coating using a nanoparticle slurry of the electrolyte material, by sol-gel coating, or even by atomic layer deposition techniques. For polymer-based electrolyte membranes, inkjet printing, solvent casting, or spin coating are some known application techniques that can be used to form the thin film electrolyte membrane 6, 8. After the thin film electrolyte membrane 6, 8 is formed on one of the electrodes 5, 10, 14, the other electrode 5, 10, 14 is applied on top of the thin film electrolyte membrane 6, 8 to complete the MEA 40, 42. In one embodiment, one or both electrodes 5, 10, 14 of the MEA 40, 42 can include a catalytic material to promote the oxidation and reduction of the working fluid at the electrode-electrolyte interface, or the material of the electrode itself can be catalytic to promote these reactions.

[0053] In one embodiment, after applying the second electrode on top of the thin film electrolyte membranes 6, 8, the assembly structure may be folded or rolled to form the MEA 40, 42 in a tubular configuration.

[0054] In a preferred embodiment, the working fluid is in gaseous form. In a preferred embodiment, the working fluid is hydrogen. Thus, each concentration cell 9, 11 includes an MEA 40, 42 comprised of a proton-conducting electrolyte material sandwiched between two electrodes that are conductive to electrons and permeable to hydrogen. For converters using hydrogen as the working fluid, suitable highly permeable metals for the electrodes of each MEA include, but are not limited to, palladium, niobium, yttrium, tantalum, and alloys thereof, including alloys with silver and / or copper. The proton-conducting electrolyte material of each MEA is in the form of a thin film having a thickness of 0.03 to 10 microns and sandwiched between two hydrogen-permeable electrodes.

[0055] The disclosure provided herein primarily uses hydrogen as an example of a working fluid. However, those skilled in the art will appreciate that the present invention is not intended to be limited to hydrogen as a working fluid. In fact, the principles described herein will also apply to other ionizable working fluids.

[0056] exist Figure 1 In the embodiment of the present invention, the converter 100 has a tubular structure, so that the MEA of the converter 100 also has a generally tubular structure. However, those skilled in the art will understand that the present invention does not require the MEA to be configured in this manner. For example, the MEA may have a flat layered structure and / or be arranged in a stacked manner. However, the description provided herein will focus on converters having a tubular configuration.

[0057] exist Figure 1 In the embodiment of FIG. 5 , the first electrode 5 extends from the MEA 40 of the first electrochemical cell 9 to the MEA 42 of the second electrochemical cell 11 . Figure 1 In the embodiment of FIG. 1 , the first electrode 5 is common, and in particular, electrically common, to the MEAs 40 and 42 of the first electrochemical cell 9 and the second electrochemical cell 11. As described above, the first electrode 5 of the MEAs 40 and 42 has a tubular form, such that a channel or conduit 50 is formed within the interior of the tubular electrode 5 and extends between the first electrochemical cell 9 and the second electrochemical cell 11. The distal end of the conduit 50 is closed by the plug 7. More specifically, the first electrode 5 of the MEAs 40 and 42 and the plug 7 together define a closed conduit 50 that couples the flow of the working fluid between the first electrochemical cell 9 and the second electrochemical cell 11.

[0058] The MEAs 40, 42 are at least partially enclosed in or surrounded by an outer housing, preferably an outer tubular housing 24. A sealing ring 12 may optionally be provided to ensure an airtight or near-airtight seal between the MEAs 40, 42 and the outer housing 24. A conduit 50 is located within the outer housing 24 and extends through the length of the outer housing 24. Thus, the outer housing 24 is divided into distinct chambers, a first or inner chamber within the conduit 50 and a second or outer chamber surrounding the conduit 50. Thus, the outer chamber is essentially the second conduit 52. The first conduit 50 is in direct contact with the first electrode 5, while the second conduit 52 is in direct contact with the second electrode 10 of the MEA 40 of the first cell 9 and the second electrode 14 of the MEA 42 of the second cell 11.

[0059] In one embodiment, the first conduit 50 and the second conduit 52 have a concentric arrangement, with the first conduit 50 contained within the second conduit 52. The second conduit 52 also couples the flow of the working fluid between the first electrochemical cell 9 and the second electrochemical cell 11. Figure 1 and Figure 4 As shown, the first electrochemical cell 9 and the second electrochemical cell 11 and even the entire converter 100 can be configured as a concentric tubular structure, in particular concentric tubular conduits 50, 52. The advantage of the concentric tubular structure is that the stress of the sealing pressure is mainly tensile and compressive, which allows the use of minimal wall thickness.

[0060] The converter 100 is configured to maintain one electrode of each MEA 40, 42 at a relatively low pressure state, and the other electrode of each MEA 40, 42 at a relatively high pressure state. Those skilled in the art will appreciate that, with respect to the working fluid, the terms "high pressure" and "high concentration" are used interchangeably herein. Those skilled in the art will also appreciate that, with respect to the working fluid, the terms "low pressure" and "low concentration" are also used interchangeably. Preferably, the high concentration (i.e., high pressure) sides of the two electrochemical concentration cells 9, 11 are interconnected via a high pressure conduit (i.e., a conduit maintained at a relatively high pressure), while the low concentration (i.e., low pressure) sides of the two electrochemical concentration cells 9, 11 are interconnected via a low pressure conduit (i.e., a conduit maintained at a relatively high pressure).

[0061] More specifically, in Figure 1 In the converter 100 of FIG. 1 , the first electrodes 5 of the MEAs 40 and 42 are maintained at a relatively high voltage, thereby constituting the high-voltage side of the converter 100. Therefore, the first conduit 50 couples the flow of the working fluid between the first electrochemical cell 9 and the second electrochemical cell 11 under a high-voltage state. The second electrodes 10 and 14 of the MEAs 40 and 42 are maintained at a relatively low voltage, thereby constituting the low-voltage side of the converter 100. Therefore, the second conduit 52 couples the flow of the working fluid between the first electrochemical cell 9 and the second electrochemical cell 11 under a low-voltage state.

[0062] Reference Figure 1 The middle section 28 of the converter 100 acts as a recuperator, connecting the working fluid flow between the two electrochemical cells 9 and 11. Figure 1 In the middle section 28 of the converter 100 of the embodiment of FIG. 1 , a barrier layer or coating 26 is provided on the outer length of the electrode 5 across the middle section 28 (i.e., the region between the first cell 9 and the second cell 11). The barrier coating 26 prevents hydrogen from permeating through the hydrogen permeable material of the electrode 5 in the region of the middle section 28.

[0063] Alternatively, as Figure 4 As shown, the batteries 9 , 11 do not need to have an electrically common electrode 5 . Figure 4 The converter 100' and its operation and Figure 1The converter 100 and its operation are identical except for the following. Each MEA 40, 42 includes different electrodes. Thus, the MEA 40 of the first electrochemical cell 9 includes a membrane 6 sandwiched between a first electrode 55 and a second electrode 10, and the MEA 42 of the second electrochemical cell 11 includes a membrane 8 sandwiched between a first electrode 65 and a second electrode 14, the first electrodes 55 and 65 being spaced apart and different from each other. In the middle section 28, a tubular member 27 is provided and extends between the first electrodes 55, 65. The tubular member 27 is preferably made of a material that is impermeable to the working fluid. More particularly, the tubular member 27 is preferably capable of allowing heat transfer while preventing the working fluid from passively diffusing from a high pressure state to a low pressure state without an electrochemical reaction occurring. Thus, in Figure 4 In the embodiment of FIG. 5 , the conduit 50 is formed in a common interior of the tubular member 27 , the first electrode 55 of the MEA 40 of the first cell 9 , and the first electrode 65 of the MEA 42 of the second cell 11 .

[0064] refer to Figure 1 , one of the electrochemical concentration cells 9, 11 receives heat input at an elevated temperature, for example by being connected to a heat source Q H , and operates to convert heat into electrical energy by expanding an ionizable working fluid from a high concentration or high pressure to a low concentration or low pressure, the expansion being carried out at the Nernst potential of the cell. This cell is referred to herein as a "high temperature cell" or "high temperature MEA". Another electrochemical concentration cell 9, 11 is preferably connected to a heat sink Q L The cell is connected to a condenser and operates under electrical input to pump and compress an ionizable working fluid from a low concentration or low pressure to a high concentration or high pressure. The compression is performed at an applied voltage exceeding the Nernst potential of the cell. The compression process consumes electrical energy, and the heat of compression is removed. The cell is referred to herein as a "low-temperature cell" or "low-temperature MEA."

[0065] More particularly, in one embodiment, wherein the MEAs 40, 42 operate as part of a heat engine, the heat source Q to which the MEA 42 of the second cell 11 is coupled is H Preferably, the heat sink Q connected to the MEA 40 of the first cell 9 is Lis at a higher temperature. Therefore, the high-temperature MEA 42 has a higher Nernst voltage than the low-temperature MEA 40. The operation of the engine 100 causes the working fluid to be compressed from the low-voltage electrode 10 of the MEA 40 to the high-voltage electrode 5 in the low-temperature concentration cell 9. The compressed working fluid is then supplied to the high-voltage electrode 5 of the MEA 42 of the high-temperature concentration cell 11 by the high-pressure conduit 50. When the working fluid passes through the thin-film electrolyte membrane 8 from the high-voltage electrode 5 to the low-voltage electrode 14, the working fluid expands through the MEA 42 of the high-temperature cell 11. Subsequently, the working fluid is supplied back to the low-voltage electrode 10 of the low-temperature concentration cell 9 by the low-pressure conduit 52. The voltage generated by the high-temperature MEA 42 is high enough to overcome the Nernst voltage of the low-temperature MEA 40, and there is enough residual voltage to power the external load 34 connected in series.

[0066] More specifically, Figure 1 and Figure 4 The converter 100, 100' operates as a heat engine as described below. Starting from the low temperature, low pressure state 1, electrical energy is provided to the low temperature MEA 40 to pump the working fluid stream 16 through the MEA 40, thereby from the low pressure, low temperature state 1 to the high pressure, low temperature state 2. During the compression process, the temperature of the working fluid is reduced by removing heat Q from the proton conducting membrane 6. L The temperature of the working fluid at the high-pressure, low-temperature state 2 is maintained nearly constant. The thin film 6, which is preferably less than 10 microns thick, is not subject to significant temperature gradients, so the near-isothermal assumption of the process is valid as long as sufficient heat is transferred to the membrane 6 and its substrate. From the high-pressure, low-temperature state 2, the working fluid, as stream 18, passes through a recuperative countercurrent heat exchanger (i.e., middle section 28), where it is heated at approximately constant pressure to the high-pressure, high-temperature state 3, and then flows to the high-temperature MEA 42. The heat 30 required to raise the temperature of the working fluid from the high-pressure, low-temperature state 2 to the high-pressure, high-temperature state 3 is transferred from the working fluid 20 flowing in the opposite direction in the heat exchanger. More specifically, the middle section 28 serves to connect heat 30 from the working fluid stream 20 exiting the high-temperature MEA 42 and flowing in conduit 52 to the working fluid stream 18 flowing in conduit 50 to the high-temperature MEA 42. At the high-temperature MEA 42, electrical energy is generated as the working fluid stream 22 passes through the MEA 42 and expands from the high-pressure, high-temperature state 3 to the low-pressure, high-temperature state 4. Heat Q H is supplied to MEA 42 to maintain a near constant temperature as the working fluid expands. To transition from the low-pressure, high-temperature state 4 to the low-pressure, low-temperature state 1, the working fluid stream 20 passes through a recuperator (i.e., middle section 28), where its temperature is reduced during the constant pressure process by transferring heat to the working fluid 18 as it moves from the high-pressure, low-temperature state 2 to the high-pressure, high-temperature state 3. This cycle continues as the low-temperature MEA 40 pumps the working fluid from low pressure to high pressure.

[0067] During operation of converters 100, 100', the working fluid is compressed in low-temperature electrochemical cell 9 by supplying an electric current at a voltage sufficient to overcome its Nernst potential, thereby pushing the working fluid from the low-pressure side of membrane 6 to the high-pressure side. Meanwhile, the working fluid in high-temperature electrochemical cell 11 is expanded as current (power) is extracted at the Nernst potential. In high-temperature electrochemical cell 11, current flows as the working fluid expands from the high-pressure side of membrane 8 to the low-pressure side. As in any thermodynamic engine employing a working fluid, and consistent with the properties of compressible gases, in converter 100, the amount of work (electricity) extracted during the high-temperature expansion process is greater than the work (electricity) input required for the low-temperature compression process. The difference between the heat energy input to converter 100 to maintain a constant temperature during the high-temperature expansion process and the heat energy removed during the low-temperature compression process to maintain a constant temperature is provided as the difference between the electrical energy output during the high-temperature expansion process and the electrical energy consumed during the low-temperature compression process.

[0068] Consistent with the Nernst equation, the high temperature electrochemical cell 11 will have a higher voltage than the low temperature electrochemical cell 9. Since the current (I) through the two cells is the same, the voltage difference means that the power generated by the expansion of the working fluid in the high temperature electrochemical cell 11 is higher than that in the low temperature electrochemical cell 9. The power output (V HT *I) is sufficient to drive the compression process of the low-temperature electrochemical cell 9 (V LT *I), and provides a net power output ((V HT *I)-(V LT *I)). This voltage difference provides the basis for the operation of the converter 100.

[0069] In another embodiment, where the MEAs 40, 42 are operated as part of a heat pump application, the heat source Q to which the MEA 42 of the second cell 11 is coupled is H The radiator Q connected to the MEA 40 of the first cell 9 L At a lower temperature. Therefore, the working fluid is H The coupled MEA 42 expands at a low temperature because the heat of expansion is from the low temperature heat source Q H is extracted. L In the coupled MEA 40, the working fluid is compressed at high temperature, and the heat of compression is removed at high temperature. Due to its low operating temperature, the Nernst voltage generated by the low-temperature expansion MEA 42 is lower than the Nernst voltage of the high-temperature compression MEA 40. Therefore, an external power source is connected in series with the low-temperature MEA 42 to provide a combined voltage high enough to overcome the Nernst potential of the high-temperature MEA 40, thereby driving the compression process therein.

[0070] Figures 5A to 5BAn end view of a converter 100 configured as a tubular structure is shown. The attractive feature of the converter 100 with a tubular structure is its ability to function as an active heat pipe for heat transfer as a generator or heat pump. Thus, the converter 100 can be configured as a tubular structure having a relatively small diameter, whereby multiple tubes can be arranged to form a structure similar to a set of "heat pipes" used to transfer heat between a heat source and a heat sink, such as Figure 6 shown.

[0071] More specifically, refer to Figure 6 , shows a set of thermoelectric converter tubes coupled between a high-temperature working fluid stream 32 (i.e., a heat source) and a low-temperature working fluid stream 30 (i.e., a heat sink). A high-temperature MEA 42, used for expanding the working fluid, is exposed to and heated by the high-temperature working fluid stream 32, while a low-temperature MEA 40, used for compressing the working fluid, is exposed to and cooled by the low-temperature fluid stream 30. The high-temperature working fluid stream 32 and the low-temperature working fluid stream 30 are isolated from each other by a recuperator section 38, as the working fluid flow within each heat exchanger 28 of each converter tube couples the flow between its respective low-temperature MEA 40 and its respective high-temperature MEA 42 within its concentric tube.

[0072] It will be appreciated by those skilled in the art that changes may be made to the above-described embodiments without departing from the broad inventive concept thereof. It is therefore to be understood that the present invention is not limited to the particular embodiments disclosed, but is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.

Claims

1. A thermoelectric converter comprising: an ionizable working fluid; as well as A first membrane electrode assembly and a second membrane electrode assembly, wherein the first membrane electrode assembly and the second membrane electrode assembly are electrically coupled to each other, each membrane electrode assembly comprising: a first electrode capable of conducting electrons and permeable to the ionizable working fluid, a second electrode that is electron-conducting and permeable to the ionizable working fluid, and a thin film electrolyte membrane sandwiched between the first electrode and the second electrode, the thin film electrolyte membrane being conductive to ions of the ionizable working fluid and having a thickness of 0.03 micrometers to 10 micrometers, wherein at least one of the first electrode and the second electrode of each membrane electrode assembly comprises a non-porous dense metal, wherein, due to a working fluid pressure difference applied across each membrane electrode assembly, one of the first electrode and the second electrode of each membrane electrode assembly contacts the working fluid at a first pressure, and the other of the first electrode and the second electrode of each membrane electrode assembly contacts the working fluid at a second pressure lower than the first pressure, and wherein the first membrane electrode assembly is configured to compress the working fluid from the second pressure to the first pressure, and The second membrane electrode assembly is configured to expand the working fluid from the first pressure to the second pressure.

2. The thermoelectric converter according to claim 1, wherein the non-porous dense metal is layered or mounted on a porous substrate.

3. A thermoelectric converter according to any of the preceding claims, wherein at least one of the first electrode and the second electrode of at least one of the first membrane electrode assembly and the second membrane electrode assembly includes a catalyst, and the catalyst is configured to promote oxidation and reduction of the working fluid when the working fluid passes through the corresponding thin film electrolyte membrane.

4. The thermoelectric converter according to any one of the preceding claims, wherein at least one of the first electrode and the second electrode of at least one of the first and second membrane electrode assemblies comprises palladium or an alloy thereof.

5. The thermoelectric converter according to any of the preceding claims, further comprising a recuperator coupling the flow of the working fluid at the first pressure and the second pressure between the first membrane electrode assembly and the second membrane electrode assembly.

6. A thermoelectric converter according to any preceding claim, wherein the converter has a tubular structure.

7. The thermoelectric converter according to the preceding claim, wherein each of the first membrane electrode assembly and the second membrane electrode assembly has a tubular structure.

8. The thermoelectric converter according to the preceding claim, wherein the interior of each of the first membrane electrode assembly and the second membrane electrode assembly constitutes a first conduit for the flow of the working fluid at the first pressure.

9. The thermoelectric converter according to the preceding claim further comprises a housing at least partially surrounding the first membrane electrode assembly and the second membrane electrode assembly, the space between the first membrane electrode assembly and the second membrane electrode assembly and the housing constituting a second conduit for the working fluid to flow at the second pressure.

10. A thermoelectric converter according to any preceding claim, wherein one of the first electrode and the second electrode is electrically common to both the first membrane electrode assembly and the second membrane electrode assembly.

11. The thermoelectric converter according to any one of the preceding claims, further comprising an external circuit for electrically coupling the first membrane electrode assembly and the second membrane electrode assembly.

12. A thermoelectric converter system comprising a plurality of converters according to claim 6 coupled between a first flow of the working fluid at a first temperature and a second flow of the working fluid at a second temperature, the second temperature being lower than the first temperature.

13. A method for generating electricity using the thermoelectric converter according to claim 1 as a heat pump, the method comprising: connecting the first membrane electrode assembly to a heat sink at a first temperature, and connecting the second membrane electrode assembly to a heat source at a second temperature, wherein the first temperature is higher than the second temperature; applying power to the first membrane electrode assembly to pump the working fluid from the second pressure to the first pressure to remove heat at the first temperature and first voltage; as well as As the working fluid expands from the first pressure to the second pressure, electricity is extracted from the second membrane electrode assembly, providing heat to the working fluid at the second temperature and a second voltage, the first voltage being higher than the second voltage.

14. The method of claim 13, further comprising connecting an external power source in series with the second membrane electrode assembly.

15. A method for generating electricity using the thermoelectric converter according to claim 1 as a heat engine, the method comprising: connecting the first membrane electrode assembly to a heat sink at a first temperature, and connecting the second membrane electrode assembly to a heat source at a second temperature, wherein the first temperature is lower than the second temperature; applying power to the first membrane electrode assembly to pump the working fluid from the second pressure to the first pressure to remove heat at the first temperature and first voltage; as well as As the working fluid expands from the first pressure to the second pressure, electricity is extracted from the second membrane electrode assembly, providing heat to the working fluid at the second temperature and a second voltage, the second voltage being higher than the first voltage.

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