WO2011019796A1

WO2011019796A1 - Advanced solid state electrolytic device

Info

Publication number: WO2011019796A1
Application number: PCT/US2010/045131
Authority: WO
Inventors: Arnold Z. Gordon; Sandeep Chawla; Ravi Dodeja; Lynn Keller; Matthieu Ennis
Original assignee: Igr Enterprises, Inc.
Priority date: 2009-08-12
Filing date: 2010-08-11
Publication date: 2011-02-17

Abstract

A new system of external connections is provided for making electrical and mechanical connections between the interiors and exteriors of multiple cells in a stack of solid state electrochemical cells, which connections largely eliminate the stresses and strains inherent in prior art designs.

Description

ADVANCED SOLID STATE ELECTROLYTIC DEVICE

Cross-Reference to Related Application

[0001] Priority is claimed to U.S. provisional application Serial No. 61/233,284, filed August 12, 2009, the disclosure of which is incorporated herein by reference.

BACKGROUND

[0002] Solid state electrolytic devices in which ceramic layers are built up on one or both sides of a porous metal sheet such as shown in Brandon, Development of Metal Supported Solid Oxide Fuel Cells of Operation at 500-600° C, Journal of Materials Engineering and Performance, Vol. 13(3), June 2004, pp 253-255, © ASM International, often exhibit poor structural integrity. One reason is that such fabricated monolithic ceramics are inherently brittle. Another reason is due to the substantial changes in internal temperature experienced by such devices when switching between operating and non-operating modes. Such devices typically operate at temperatures on the order of 600° C to 750° C. As a result, the internal stresses set up between the metal and ceramic components of such devices as they cycle between operating and non-operating modes are often sufficient enough to cause these ceramic components to crack, break, delaminate or otherwise mechanically degrade.

[0003] Commonly-assigned U.S. 5,332,482 to Gordon describes a solid state electrolytic device for separating oxygen from air which is designed to overcome this problem. Commonly-assigned U.S. 6,132,573 discloses additional details of such a device, while commonly-assigned U.S. 6,074,771 discloses a similar device structured to operate as a fuel cell. The disclosures of each of these patents (referred to hereinafter at the "Gordon Patents") are incorporated herein by reference in their entireties.

[0004] A common feature of these devices is that the basic structural unit of each electrolytic cell is a flexible metal ceramic composite in the form of a flexible metal sheet or foil which defines a system of perforations or openings and a layer of solid sintered ceramic surrounding and embedding these perforations. This is illustrated in Figs. 1-3 in which Figs. 1 and 2 schematically illustrate the flexible perforated metal sheet that can be used to form such a composite, while Fig. 3 illustrates the composite so made after an anode and cathode have been added. [0005] As shown in Figs. 1 and 2, flexible metal sheet 10 includes a periphery 12 and a central portion 14, which defines a system of openings or perforations 16. Projecting off one side of flexible metal sheet 10 is gas supply arm 17 defining a flow conduit (not shown), which is provided to aid ingress and/or egress of system gases. Solid state electrolytic devices set up for use as oxygen generators normally use only a single gas supply arm per cell for recovering product O₂ from the anode of the cell, with the cathode of the cell being open to the atmosphere. In contrast, if the device is set up as a fuel cell, two such gas supply arms will normally be used, one for supplying fuel to the anode and the other for recovering exhaust gases from the anode, the cathode of the cell also being open to the atmosphere.

[0006] As illustrated in Fig. 3, a layer of sintered ceramic material 18 surrounds and embeds perforations 16. In the electrolytic cells of the above-noted Gordon patents, a ceramic solid electrolyte is used to make the metal ceramic composite, with the cathode and anode of the cell being formed on opposite sides of this electrolyte layer. This is illustrated in Fig. 3, which shows anode 20 in contact with one major face of sintered ceramic electrolyte 18 and cathode 22 in contact with its other major face.

[0007] As indicated above, the ceramic elements of solid state electrolytic devices are prone to crack and break due to the internal stresses created when such devices cycle between ambient and operating temperatures. They are also prone to mechanical failure from rough physical handling such as bumping, jarring dropping and the like due to the fragile nature of their ceramic components.

[0008] A particular advantage of the metal ceramic composite approach of the above-noted Gordon patents is that it essentially eliminates this structural integrity problem. This is because the portion of flexible metal sheet 10 extending between central portion 14 and outer periphery 12 (where flexible metal sheet 10 is supported) basically acts as a shock absorber, absorbing the internal and external stresses encountered by the device.

[0009] A convenient way to make flexible metal sheet or foil 10 is by photolithography techniques, and so it is common practice to refer to this element as a "photolithographic sheet" or "photolithographic foil." However, any other manufacturing technique which will produce a metal sheet or foil which is both flexible and defines an appropriate system of perforations or openings can also be used to make this element. For convenience, this element is referred to hereinafter as a "flexible perforated metal sheet." [0010] Figs. 4-7 illustrate how a solid state electrolytic cell 24, which is made with the metal ceramic composite electrolyte of Fig. 3, can be used for separating oxygen from air. As schematically illustrated in Fig. 4, air is fed to the cathode side of the cell where an electrical potential applied across cathode 22 and anode 20 causes O₂ molecules to be reduced to oxygen ions, O^"2, at cathode 22. These O^"2 ions then migrate through ceramic electrolyte layer 18, as well as perforations 16 in flexible metal sheet 10 which carries this ceramic electrolyte layer. Ceramic electrolyte layer 18 is made from a sintered particulate ceramic which, as a whole, is gas impervious and electrically insulating but is ion conducting to allow this transfer. These O^" ions are then oxidized at anode 20 to oxygen atoms, which combine to form O₂ molecules which are discharged from the device as product O₂. Oxygen purities on the order of 93 vol.% and greater can be achieved with this technology.

[0011] Fig. 5 illustrates the physical structure of the electrolytic cell schematically illustrated in Fig. 4. As shown in Fig. 5, the basic structural unit of this cell takes the form of metal ceramic composite electrolyte 60 in the form of perforated metal sheet 10 and a layer 18 of sintered particulate solid electrolyte which surrounds and embeds the perforations in this sheet (not shown). Cathode 22 and anode 20, each of which is also normally made from a gas porous electrically conductive sintered mass of particulate ceramics optionally including particulate metals such as silver, are formed on and carried by opposite sides of metal ceramic composite electrolyte 60.

[0012] In order to capture product O₂, bipolar metal member 50 is arranged on the anode side of metal ceramic composite electrolyte 60, with the outer peripheries of both being welded to one another at 120 to form O₂ plenum 65. Bipolar metal member 50 also carries an associated gas supply arm (not shown) for mating with gas supply arm 17 of flexible metal sheet 10, with either one or both of these two gas supply arms being suitably embossed so that together they define a flow conduit (not shown) for withdrawing O₂ produced in O₂ plenum 65 to outside the device. Normally, this flow conduit is connected to a gas transfer tube (not shown) made from stainless steel or other suitable metal for transferring the O₂ product gas to a suitable O₂ product tank by welding or otherwise bonding the outer peripheries of these gas supply arms to this gas transfer tube.

[0013] Small dimples 64 facing anode 20 are formed in bipolar metal member 50 in order to provide enough space to form O₂ plenum 65 when metal ceramic composite electrolyte 60 and bipolar metal member 50 are assembled together. In this regard, Fig. 5 shows these components being spaced apart from another for illustration purposes only. In actual practice, bipolar metal member 50 is in close contact with anode 20 carried by metal ceramic composite electrolyte 60 to keep the thickness of electrolytic cell 24 as small as possible.

[0014] Figs. 6 and 7 illustrate a solid state electrolytic device which is made by assembling a group of the solid state electrolytic cells of Figs. 4 and 5 together. As shown in Fig. 6, multiple solid state electrolytic cells 24 are stacked one atop the other in a head to tail fashion. That is to say, these cells are stacked in such a way that O₂ plenum 65 in upper electrolytic cell 24 is contiguous with air plenum 67 in lower electrolytic cell 24', with bipolar metal member 50 forming the outer boundary of each. With this structure, upper electrolytic cell 24 and lower electrolytic cell 24' are arranged in electrical series so that the entire device can be driven by a single electrical potential provided between cathode 22 of upper cell 24 and anode 20' of lower electrolytic cell 24'.

[0015] Like Fig. 5, Fig. 6 also shows the components of the device in an expanded condition for illustration purposes only. In actual practice, these components will also be closely spaced, as described above in connection with Fig. 6. In this regard, small dimples 65 are provided in the opposite face of bipolar metal member, i.e., the face of bipolar metal member opposite small dimples 64, to provide enough spacing to form air plenum 67 in the same way that small dimples 64 provide enough spacing to form O₂ plenum 65.

[0016] hi actual practice, solid state electrolytic devices embodying this technology are normally made with at least six, and more commonly 8, 10, 12, 15, 20, 25 or even more, electrolytic cells 24 stacked together in this head to tail fashion. As described in the above- noted '482, '573 and '771 patents, these multiple electrolytic cells 24 can be secured together in any convenient manner such as, for example, by attachment together at their corners or other portions of their peripheries with spacers (to accommodate the thickness of each cell) or other suitable support structure. The result is a solid state electrolytic device which is very sturdy and rugged in construction. This is because the basic structural unit of each cell, the metal ceramic composite electrolyte, is flexible and further because these individual metal ceramic composite electrolyte units are attached to one another at the peripheries of flexible perforated metal sheets 10 from which they are made. [0017] Fig. 7 schematically illustrates the operation of a solid state electrolytic device made from multiple stacked solid state electrolytic cells 24 as shown in Fig. 6. As shown in Fig. 7, air is supplied to air plenums 67 of each cell of the stack, while an electrical potential is applied between the cathode of the uppermost cell 24 and the anode of the lowermost cell. This causes a current of electricity to "flow" through the stack and, as a result, for O₂ to be generated at each anode 20 of the stack. This product O₂ is then recovered from each plenum 65 in the stack, thereby producing product O₂.

[0018] In a modification of the above basic design, the approach of the above-noted Gordon patents, i.e., forming the basic structural unit of the cell from a flexible metal ceramic composite in the form of a flexible metal sheet or foil which defines a system of perforations or openings and a layer of generally gas porous sintered ceramic surrounding and embedding these perforations, is extended to form the anode, or the cathode, or an optional ceramic support carrying the anode or cathode from this flexible metal ceramic composite instead of the solid electrolyte layer of the cell. This modification is embodied in application Serial No. 61/372,491 (attorney docket no. 21980/04024), the entire disclosure of which is incorporated herein by reference.

[0019] As indicated above, normal operating temperatures for electrolytic devices of type illustrated above are typically on the order of 600° C to 750° C, which are too high for plastics. As a result, the external connections of the cell, i.e., the electrical and mechanical connections made between the interiors and exteriors of each cell, both for supplying and/or withdrawing electrical power as well as for supplying and/or withdrawing operating gases, are normally made with ceramic and/or metal components. Because ceramics are inherently fragile, and further because the absolute difference between the coefficients of thermal expansion between metals and ceramics are so large, the structural integrity of these external connections can also be a problem when such devices cycle between operating and non- operating modes and/or are exposed to rough physical handling.

SUMMARY OF THE INVENTION

[0020] In accordance with this invention, a new system of external connections is provided for making electrical and mechanical connections between the interiors and exteriors of multiple cells in a stack of solid state electrochemical cells, which connections largely eliminate the stresses, strains and attendant structural integrity problems inherent in earlier designs. [0021] Thus, this invention in one aspect provides an electrolytic device comprising a solid state electrolytic cell comprising a solid ceramic electrolyte having two major, opposite surfaces, an anode on one major surface and a cathode on the other major surface, the solid state electrolytic cell also containing an optional ceramic support on which the anode or the cathode is supported, wherein either the electrolyte, the anode, the cathode or the optional ceramic support comprises a metal ceramic composite formed from a flexible perforated metal sheet defining a system of perforations and a layer of a sintered ceramic material surrounding and embedding the perforations, and wherein the cell further defines an anode gas plenum which is sealed from the external atmosphere, wherein the device further comprises a manifold outside the cell in fluid communication with the gas plenum of the cell, and a flexible metal conduit section connecting the manifold to the cell for accommodating internal stresses created between the cell and the manifold when the device cycles between room temperature and operating temperatures.

[0022] In addition, this invention in another aspect provides an electrolytic device comprising a solid state electrolytic cell comprising a solid ceramic electrolyte having two major, opposite surfaces, an anode on one major surface and a cathode on the other major surface, the solid state electrolytic cell also containing an optional ceramic support on which the anode or the cathode is supported, wherein either the electrolyte, the anode, the cathode or the optional ceramic support comprises a metal ceramic composite formed from a flexible perforated metal sheet defining a system of perforations and a layer of a sintered ceramic material surrounding and embedding the perforations, and wherein the cell further defines an anode gas plenum which is sealed from the external atmosphere, wherein the device further comprises an electrical heater for raising the temperature of the cell, wherein the electrical heater comprises a heating element in the form of a heat generating electrical wire capable of generating heat when an electrical current is passed through the wire and a thermal diffuser in the form of a metal foil or screen in contact with the electrical wire.

[0023] In still another aspect, this invention provides an electrolytic device comprising a solid state electrolytic cell comprising a solid ceramic electrolyte having two major, opposite surfaces, an anode on one major surface and a cathode on the other major surface, the solid state electrolytic cell also containing an optional ceramic support on which the anode or the cathode is supported, wherein either the electrolyte, the anode, the cathode or the optional ceramic support comprises a metal ceramic composite formed from a flexible perforated metal sheet defining a system of perforations and a layer of a sintered ceramic material surrounding and embedding the perforations, and wherein the cell further defines an anode gas plenum which is sealed from the external atmosphere, the device further comprising a pump downstream of and in fluid communication with the electrolytic cell, a pressure sensor arranged to monitor the pressure of the operating gas passing out of electrolytic cell, and a feedback loop structured to operate the pump to maintain to suitable output pressures of gas produced by the device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] This invention may be more readily understood by reference to the following drawings wherein:

[0025] Figs. 1 and 2 schematically illustrate a porous metal sheet that can be used to make a metal ceramic composite electrolyte of the type shown in the above-mentioned Gordon patents.

[0026] Fig. 3 illustrates a preform containing the basic components of a solid state electrolytic cell, i.e., a solid electrolyte layer, an anode and a cathode, which is made with the metal ceramic composite electrolyte of Figs. 1 and 2.

[0027] Figs. 4 and 5 illustrate a solid state electrolytic cell made with the preform of Fig. 3.

[0028] Figs. 6 and 7 illustrate a solid state electrolytic device which is made by assembling a group of the solid state electrolytic cells of Figs. 4 and 5 together.

[0029] Fig. 8 illustrates a flexible metal ceramic composite forming the basic structural unit of a modified solid state electrolytic cell incorporating some of the features of this invention.

[0030] Fig. 9 illustrates a manifold useful for recovering a product gas produced by, or for supplying a fuel gas supplied to, a modified solid state electrochemical cell made with the flexible metal ceramic composite of Fig. 8.

[0031] Fig. 10 is an exploded view illustrating an electrolytic device formed from multiple modified solid state electrochemical cells made with the flexible metal ceramic composite of

Fig. 8 arranged in a stack, Fig. 10 illustrating how the manifold of Fig. 9 can be connected to the multiple cells in this stack.

[0032] Fig. 11 illustrates an insulating conduit segment that can be used to provide thermal and/or electrical insulation between the manifold of Fig. 9 and the modified solid state electrochemical cell to which it is attached. [0033] Fig. 12 illustrates a heater that can be used to heat a solid state electrochemical cell made in accordance with the principles of the Gordon patents to operating temperatures and, in addition, for trim heat during operation.

[0034] Fig. 13 is an exploded view showing how the heater of Fig. 12 can be incorporated within a modified solid state electrochemical cells of the type illustrated in Fig. 8, Fig. 13 also illustrating a so-called "butterfly" arrangement of cells as further described in the above-noted application Serial No. 61/372,491 (attorney docket no. 21980/04024) in which adjacent electrolytic cells are arranged in a head to head relationship and a bipolar metal member is not used.

[0035] Fig. 14 illustrates a pressure regulating system that can be used to monitor and control the pressure of O₂ or other product gas when the inventive solid state electrolytic device is operated in product generating mode.

DETAILED DESCRIPTION

[0036] As indicated above, this invention relates to solid state electrolytic cells and devices in which a flexible metal ceramic composite forms the basic structural unit of the cell. In this context, "solid state" means that the electrolyte of the cell is in solid rather than liquid form at normal cell operating temperatures. Similarly, "forming the basic structural unit of the cell" means that the basic components of the cell, i.e., the electrolyte, anode and cathode, are supported or "carried" by the flexible metal element forming the metal ceramic composite in the sense that at least a substantial portion if not all of the weight of these components is supported by the this flexible metal element during cell operation.

Manifold with Flexible Connections

[0037] As indicated above, the mechanical connections made between the sealed interiors of individual cells of a solid state electrochemical device and the product or supply lines connected to these interiors are subject to substantial mechanical stress as these devices cycle between start up and shut down due to the large difference between room temperature and the normal operating temperatures of these devices, hi accordance with one aspect of this invention, these substantial mechanical stresses are accommodated by connecting the interiors of these cells to a manifold assembly which is located inside the thermal insulation of the device and which includes flexible metal conduits for attaching the manifold to the individual electrolytic cells of the device.

[0038] As shown in Figs. 8, 9 and 10, a solid state electrolytic cell in accordance with this invention, generally indicated at 100, takes the form of a ceramic metal composite 102 in the form of a perforated metal sheet 104 which carries a solid electrolyte in the form of a layer of a sintered ceramic material surrounding and embedding the perforations of this perforated metal sheet. The layer of solid electrolyte defines two major faces, one of which carries a layer 106 of a sintered ceramic material forming the cathode of the cell, the other of which carries another layer of sintered ceramic (not shown) which forms the anode of the cell. Although Fig. 8 shows that the sintered ceramic forming the solid electrolyte of the cell embeds perforated metal sheet 104, it will be appreciated that the alternative approach described in the above noted application Serial No. 61/372,491 (attorney docket no. 21980/04024) in which the anode or cathode or an optional ceramic carrier embeds perforated metal sheet 104 with the other ceramic layers being carried by this supported ceramic layer, can also be used in the practice of all aspects of technology described in this document.

[0039] When a solid state electrochemical device is made by assembling multiple solid state electrolytic cells into a stack, such as illustrated in Fig. 6 discussed above or as illustrated in Fig. 10 further discussed below, anode and cathode gas plenums are defined between adjacent electrolytic cells. For example, Fig. 6 illustrates a conventional arrangement in which adjacent electrolytic cells are arranged in a head to tail relationship. In this approach, bipolar element 50 is used not only to complete each cell, but also to separate the anode gas plenum (O₂ plenum 65 in Fig. 6) from the cathode gas plenum (air plenum 67 in Fig. 6). In contrast, Fig. 10 illustrates a modified approach described in the above noted application Serial No. 61/372,491 (attorney docket no. 21980/04024) in which adjacent electrolytic cells are arranged in a head to head relationship ("butterfly design"). In this approach, bipolar element 50 is not needed, since like electrodes of adjacent cells face one another across a common gas plenum. In other words, the anodes of adjacent cells face one another across a common anode plenum while the cathodes of adjacent cells face one another across a common cathode plenum.

[0040] In both cases, however, the operating gas plenum associated with the anode of the cell (the "first gas plenum" or "anode gas plenum") needs to be sealed from the surrounding atmosphere. For example, when the electrolytic device illustrated in Fig. 6 is operated as an oxygen generator, the anode gas plenum (O₂ plenum 65 in Fig. 6) needs to sealed from the atmosphere so that product O₂ produced in this plenum can be recovered and transferred to a patient or suitable O₂ product tank without loss. In contrast, if this electrolytic device is operated as a fuel cell, anode gas plenum 65 still needs to be sealed from the atmosphere so that fuel can be supplied to this plenum for electrochemical oxidation without loss or risk of unsafe conditions. This same need to seal the anode gas plenum from the atmosphere also applies to the electrolytic device illustrated in Fig. 10 for the same reasons. In solid state electrolytic devices of both types, i.e., the devices of both Figs. 6 and 10, this sealing function is normally accomplished, partially or wholly, by the perforated metal sheet forming the structural backbone of each electrolytic cell, i.e., flexible perforated metal sheet 10 in Figs. 1-3 or flexible perforated metal sheet 104 in Fig. 8.

[0041] For example, in an electrolytic device such as illustrated in Figs. 1-7 in which adjacent electrolytic cells are arranged in a head to tail relationship with bipolar element 50 being provided to complete each cell, anode or O₂ plenum 65 is sealed by flexible perforated metal sheet 10 being joined to bipolar element 50 at their outside edges, usually by welding the imperforated perimeter of the flexible perforated metal sheet to the bipolar element. In contrast, in an electrolytic device such as illustrated in Fig 10 in which adjacent electrolytic cells are arranged in a head to head relationship with no bipolar element 50 being used, the flexible perforated metal sheets 104 of adjacent pairs of cells defining facing anodes are joined to one another at their imperforated outside edges, usually by welding, to seal the anode plenum.

[0042] As described above in connection with Fig. 1, access to the inside of the sealed anode plenum of a solid state electrolytic cell is normally achieved by means of a flow passageway (not shown) embossed in the periphery (gas supply arm 17 in Fig. 1) of the perforated metal sheets and/or bipolar elements forming the sealed anode plenum. Fluid communication is established by connecting this flow passageway to one end (the proximal end) of a stainless steel gas transfer tube, typically with a ceramic or other high temperature cement. Because the proximal end of the stainless steel gas transfer tube is in contact with the perforated metal sheets and/or bipolar elements forming the backbone of the cell, it is subjected to the high operating temperatures encountered by cell during normal operation, typically on the order of 600° C to 750° C. Therefore, conventional practice is to extend this gas transfer tube through and out beyond the layer of thermal insulation surrounding the device by a significant distance {e.g., 35-50 cm) before connecting the other end (distal end) of the gas transfer tube to a manifold or other structure connected to a product/supply tank. [0043] With this approach, the stainless steel gas transfer tube as a whole cools sufficiently during normal device operation so that its distal end can be connected to materials not requiring high temperature resistance, e.g., plastics and the like. In addition, the extended length of the stainless steel gas transfer tube enables the stresses and strains that inherently arise when multiple electrolytic cells arranged in a stack are connected to a common manifold to be accommodated through slight flexing of the individual tubes. The embossed flow passageways formed in the peripheries of a stack of solid state electrolytic cells {e.g., the flow passageways in gas supply arms 17 of Fig. 1) are not always in complete alignment, and so some stress inherently arises when multiple gas transfer tubes are connected to a common manifold, hi addition, cycling of the device between room and operating temperatures inherently introduces additional stresses from the inherent thermal expansion of the metals forming the device. The extended lengths of the stainless steel gas transfer tubes used to connect individual electrolytic cells to a common manifold accommodate these stresses through slight flexing of these tubes along their lengths.

[0044] While the above design is effective in accommodating the stresses and strains that normally arise during construction and operation of a solid state electrochemical device, it reduces device efficiency because its stainless steel gas transfer tubes represent a significant source of heat loss. Stainless steel is highly thermally conductive, and so the multiple stainless steel tubes represent a significant pathway for heat loss, especially since they are intentionally designed long enough to promote this heat loss. This heat loss directly translates into a reduction in device efficiency, since it means that additional power is needed during start-up and operation to maintain the device at its operating temperature, i.e. to compensate for the continuous heat loss through these several gas tubes. Furthermore the thermal loses of these tubes create an undesirable temperature gradient across the cells with the portion of the cells near the tube connection being continuously cooled by the heat loss through the tube. This results in undesirable thermally induced stresses across the electrolytic cell.

[0045] In accordance with this aspect of the present invention, the modified manifold system illustrated in Figs. 8, 9, 10, 11 and 13 is provided to eliminate this problem while simultaneously providing mechanical connections that fully accommodate the stresses and strains inherent in the construction and operation of multi-cell solid state electrolytic devices. In the particular embodiment illustrated in these figures, one end of metallic gas transfer tube 110 (Figs. 8, 11 and 13) made from stainless steel, Inconel or other heat and chemical resistant alloy is connected to the embossed flow conduit (not shown) defined in gas supply arm 112 located on the peripheries of the perforated metal sheets 104 and 104' (Fig. 13) of adjacent solid state electrolytic cells 105 and 105' which together define anode plenum 114 therebetween. The other end of metallic gas transfer tube 110 is connected to manifold 116 (Figs. 9, 10 and 11) via flexible metal conduit section 118, which in the particular embodiment shown is formed from a metal conduit having side wall which are either corrugated or accordion-shaped and which is made from stainless steel, Inconel or other heat and chemical resistant alloy.

[0046] In the particular embodiment shown, this connection between metallic gas transfer tube 110 and flexible metal conduit section 118 is made by insulating conduit segment 120 (Fig. 11) for providing at least one of thermal insulation and electrical insulation between the elements forming anode gas plenum 114 and flexible metal conduit section 118. Insulating conduit segment 120 is desirably made from a ceramic material such as alumina or mullite or glass and secured metallic gas transfer tube 110 and flexible metal conduit section 118 by means of a suitable cement or glue. In an alternative arrangement (not shown), the juxtaposition of flexible metal conduit 118 and insulating conduit segment 120 can be reversed, with flexible metal conduit 118 being connected to metallic gas transfer tube 110 and insulating conduit segment 120 being connected to manifold 116.

[0047] Additionally or alternatively, a gas tight seal can be made between insulating conduit segment 120, on the one hand, and metallic gas transfer tube 110 and flexible metal conduit section 118, on the other hand, by selecting an insulating conduit segment 120 whose coefficient of thermal expansion is less than the coefficients of thermal expansion of both metallic gas transfer tube 110 and flexible metal conduit section 118 and further whose internal flow passageway at room temperature is only slightly larger than the outside diameters of these metallic gas transfer tube and flexible metal conduit section. With this arrangement, the ends of metallic gas transfer tube 110 and flexible metal conduit section 118 can be snug fit inside the flow passageway of insulating conduit segment 120 when the device is at room temperature. Because the above difference in coefficients of thermal expansion, raising the temperature of the device from room temperature to operating temperature causes this snug fit to transform into a secure gas-tight fit due to the greater expansion of the metals forming metallic gas transfer tube 110 and flexible metal conduit section 118. In the particular embodiment shown, the internal passageway in insulating conduit segment 120 as well as the external surfaces of metallic gas transfer tube 110 and flexible metal conduit section 118 are circular in cross-section. Any other configuration such as elliptical, etc., which will achieve a similar gas-tight seal in response to change in temperature can also be used.

[0048] In accordance with another aspect of this invention, a modified heater is provided for use during start-up for heating the device to the elevated temperatures needed for device operation a well as for trim heat during actual operation of the device, i.e., for providing additional heat to individual cells for selectively controlling the temperature of these cells, for example, for providing uniform temperature in all cells of the device. As illustrated in Figs. 12 and 13, heater 122 takes the form of a heating element 124 in the form one or more heat generating electrical wires made from Inconel alloy or another alloy capable of generating heat when an electrical current is passed through the wire and optional thermal diffuser 126 in the form of a metal foil or screen in thermal contact with the electrical wire. As illustrated in Fig. 13, heater 122 is received in anode gas plenum 114 defined by adjacent solid state electrolytic cells 105 and 105' and is generally co-terminous with the anodes of these cells. With this design, heater 122 can provide essentially uniform heat across essentially the entire surface areas of these anodes, thereby uniformly heating these anodes, in contrast with the design illustrated in Fig. 35 of the previously-mentioned U.S. 6,132,573 in which heat is supplied only to the peripheries of each cell.

[0049] In order to electrically insulate heating element 124 from the other metallic components of the device, heating element 124 is received in a tubular metal sheath and a suitable electrical insulator such as MgO or other suitable ceramic is included inside tubular metal sheath 128 in manner to prevent contact between the walls of the metal sheath and heating element 124.

[0050] In an interesting modification of this aspect of the invention, the heat generating wire forming heating element 124 is connected to conventional electrical supply wire 130 (Fig. 8) outside of, but proximate to, the outer periphery of the electrolytic cell. In this context, a "conventional electrical supply wire" will be understood to mean a wire which generates substantially less heat than the heat generated by heating element 124 on a per unit length basis when an electrical current capable of operating the heating element is carried by both wires. Normally, conventional electrical supply wire 130 will be selected so that the amount of heat it generates is 25 % or less than the heat generated by the heat generating electrical wire forming heating element 124. Conventional electrical supply wires 130 generating 10 % or less than the heat generated by heating element 124 are more interesting. The advantage of this approach is that it significantly reduces the amount of electrical energy needed to operate heater 122 and, in addition, also significantly reduces the generation of waste heat outside the device.

[0051] One approach for selecting a conventional electrical supply wire 130 which generates substantially less heat than heating element 124 is make this electrical supply wire from a different alloy than heating element 124. For example, conventional copper supply wires generate far less Joule heat than the alloys typically used for making heat generating electrical wires. Another approach is to select a conventional electrical supply wire 130 which has a larger diameter than the heat generating electrical wire forming heating element 124. For example, an electrical supply wire made from the same Inconel alloy as heating element 124 but having twice its diameter will generate 1/4 (25%) of the heat generated by this heating element on a per unit length basis.

[0052] Conventional electrical supply wire 130 will normally be attached to heating element 124 by welding or the like, but other conventional methods can be used, hi order to electrically insulate the junction between these two components from the other metal elements forming the electrolytic device, this junction can be housed in insulator section 130 (Figs. 10 and 13), which is desirably made from any suitable electrical and thermal insulator such as ceramic or glass.

[0053] hi accordance with another aspect of this invention, a pressure regulating system is provided to monitor and control the pressure of O₂ or other product gas when the inventive solid state electrolytic device is operated in product generating mode. As shown in Fig. 14, the pressure regulating system of this invention, which is generally illustrated at 140, takes the form of pump 142, pressure sensor 144 and feedback control loop 146 including controller 148. In the particular embodiment shown, optional product gas flow and purity sensor 150, product gas reservoir 150, noise diffuser 154 and particulate filter 156 are also provided.

[0054] The purpose of this system is to pressurize the O₂ or other product gas produced in the anode gas plenums of solid state electrolytic cells such as shown in Figs. 6 and 10 to suitable output pressures, i.e., output pressures high enough to flow into a product tank at successively higher pressures and/or to be charged to a patient through necessary or optional intermediary devices such as ventilators, filters, humidifiers and the like. Another purpose is to normalize the pressure in the output line of the electrochemical cell stack and to insulate the electrolytic cells from the pulsations that can be cause by a conventional output pressure pump.

[0055] In this system, and with the device operating as an oxygen generator, low-pressure oxygen gas from the electrochemical cells flows through product gas flow and purity sensor 150 which provides feedback to controller 148 to maintain flow at the desired flow rate setting via stack control. The product gas then flows through reservoir 152 to pressurizing pump 142 which pressurizes the gas to a desired pressure. Reservoir isolates the electrochemical cell stack from pressure pulsations caused by pump 142. Pressurized product gas exits through optional noise diffuser 154 and particulate filter 156.

[0056] The pressure of the low-pressure product gas from the electrochemical cell stack is monitored via pressure sensor 144. Controller 148 adjusts the speed of pump 142 so that this pressure is maintained close to normal atmospheric pressure irrespective of the back-pressure of faced by the output gas, thereby protecting these cells from over or under-pressurization.

[0057] Although only a few embodiments of this invention have been described above, it should be appreciated that many modifications can be made without departing from the spirit and scope of the invention. All such modifications are intended to be included within the scope of this invention, which is to be limited only by the following claims:

Claims

Claims:

1. An electrolytic device comprising

(a) a solid state electrolytic cell comprising a solid ceramic electrolyte having two major, opposite surfaces, an anode on one major surface and a cathode on the other major surface, the solid state electrolytic cell also containing an optional ceramic support on which the anode or the cathode is supported,

wherein either the electrolyte, the anode, the cathode or the optional ceramic support comprises a metal ceramic composite formed from a flexible perforated metal sheet defining a system of perforations and a layer of a sintered ceramic material surrounding and embedding the perforations, and

wherein the cell further defines a gas plenum which is sealed from the external atmosphere and which is in fluid communication with either the anode or the cathode of the cell,

(b) a manifold outside the cell in fluid communication with the gas plenum of the cell, and

(c) a flexible metal conduit section connecting the manifold to the cell for accommodating internal stresses created between the cell and the manifold when the device cycles between room temperature and operating temperatures.

2. The electrolytic device of claim 1, wherein the flexible metal conduit section is defined by side walls which are corrugated or accordion-shaped.

3. The electrolytic device of claims 1 or 2, wherein the flexible metal conduit section is made from Inconel or stainless steel.

4. The electrolytic device of any one of the preceding claims, wherein the electrolytic device further comprises an insulating conduit segment in fluid communication with the flexible metal conduit section for connecting the manifold to the cell, the insulating conduit segment providing at least one of thermal insulation and electrical insulation between the gas plenum and the manifold.

5. The electrolytic device of claim 4, wherein the electrolytic cell further includes a metallic gas transfer tube extending from the gas plenum of the electrolytic cell, the insulating conduit segment being in fluid communication with the metallic gas transfer tube and the flexible metal conduit section.

6. The electrolytic device of claims 4 or 5, wherein the insulating conduit segment is made from at least one of a ceramic material, borosilicate glass or alumina silicate glass.

7. The electrolytic device of claims 5 or 6, wherein the insulating conduit segment is secured to at least one of the metallic gas transfer tube and the flexible metal conduit section by means of a cement or glue.

8. The electrolytic device of claims 5 or 6, wherein the insulating conduit segment defines a flow passageway therein, at least one of the metallic gas transfer tube and the flexible metal conduit section being received in this flow passageway.

9. The electrolytic device of claim 8, wherein the coefficient of thermal expansion of the metallic gas transfer tube or the flexible metal conduit section is greater than the coefficient of thermal expansion of the insulating conduit segment so that an increase in the temperature of the electrolytic device from room temperature to the normal operating temperature of the device causes greater thermal expansion of the metallic gas transfer tube or the flexible metal conduit section relative to the insulating conduit segment.

10. The electrolytic device of claim 9, wherein the flow passageway of the insulating conduit segment is only slightly larger than the outside diameters of both the metallic gas transfer tube and the flexible metal conduit section so that both the metallic gas transfer tube and the flexible metal conduit section can be snug fit inside the flow passageway of the insulating conduit segment while the device is at room temperature and further so that a gas-tight seal is formed between the insulating conduit segment and both the metallic gas transfer tube and the flexible metal conduit section when the device is at its normal operating temperature.

11. The electrolytic device of any one of the preceding claims, further comprising an electrical heater for raising the temperature of the cell, wherein the electrical heater comprises a heating element in the form a heat generating electrical wire capable of generating heat when an electrical current is passed through the wire and an optional thermal diffuser in the form of a metal foil or screen in thermal contact with the electrical wire, wherein the electrical heater is generally co-terminous with the anode of the cell so that the electrical heater can provide essentially uniform heat across essentially the entire surface area of this anode.

12. The electrolytic device of claim 11, wherein the electrical heater includes the thermal diffuser.

13. The electrolytic device of claims 11 or 12, wherein the electrical heater is electrically insulated from the other metal elements forming the device.

14. The electrolytic device of claim 13, wherein the heat generating electrical wire of heating element of the electrical heater is received in a tubular metal sheath, the heating element further comprising an electrical insulator electrically insulating the heat generating electrical wire from the tubular metal sheath.

15. The electrolytic device of claim 14, wherein the electrical insulator is a ceramic and further wherein the heat generating electrical wire is made from an Inconel alloy.

16. The electrolytic device of claim 14, wherein the electrical insulator is MgO.

17. The electrolytic device of any one of claims 11-16, further comprising an electrical supply wire electrically connected to the heat generating electrical wire outside of, but proximate to, the outer periphery of the electrolytic cell, the electrical supply wire being selected so that amount of heat generated by the electrical supply wire is 25 % or less than the heat generated by the heat generating electrical wire on a per unit length basis when an electrical current capable of operating the heating element is carried by both wires.

18. The electrolytic device of claim 17, wherein the electrical supply wire is welded to the heat generating electrical wire to form a welded junction, and further wherein this welded junction is received in an insulator section for electrically insulating this weld junction, the heat generating electrical wire and the electrical supply wire from the other metal elements forming the device.

19. The electrolytic device of claim 18, wherein the insulator section is made from ceramic or glass.

20. The electrolytic device of any one of the preceding claims, further comprising a pump downstream of in fluid communication with the manifold, a pressure sensor arranged to monitor the pressure of the operating gas in the manifold, and a feedback loop structured to operate the pump to maintain a predetermined pressure of operating gas in the gas plenum of the electrolytic cell.

21. The electrolytic device of claim 20, further comprising a by-pass line extending from upstream of the pump to downstream of the pump and a check- valve in the by-pass line structured to prevent the pressure of the operating gas in the gas plenum from exceeding a predetermined value.

22. The electrolytic device of claims 20 or 21, further comprising an operating gas upstream of the pump for isolating the pressure of the operating gas in the gas plenum from pressure pulsations caused by pump.

23. The electrolytic device of any one of claims 20-22, wherein the electrolytic device includes multiple electrolytic cells stacked one atop the other.

24. The electrolytic device of claim 23, wherein adjacent cells are arranged in a head to tail fashion, wherein adjacent cells are separated from one another by a bipolar element which together with the perforated metal sheets of the adjacent cells defines an anode gas plenum sealed from the atmosphere and a cathode gas plenum, wherein each electrolytic cell further includes a metallic gas transfer tube extending from the anode gas plenum of that electrolytic cell, and further wherein the metallic gas transfer tube is joined to the flexible perforated metal sheet and bipolar element of that cell by welding.

25. The electrolytic device of claim 23, wherein adjacent cells are arranged in a head to head fashion so that the anodes of respective pairs of adjacent cells face one another and thereby form anode gas plenums therebetween, the cathodes of these cells forming cathode gas plenums with the cathodes of adjacent pairs of adjacent cells, the anode gas plenums being sealed from the atmosphere by the perforated metal sheets which carry the anodes forming the anode gas plenums, wherein each electrolytic cell further includes a metallic gas transfer tube extending from its anode gas plenum, and further wherein the metallic gas transfer tube is welded to the flexible perforated metal sheets forming the anode gas plenums.

26. An electrolytic device comprising

wherein either the electrolyte, the anode, the cathode or the optional ceramic support comprises a metal ceramic composite formed from a flexible perforated metal sheet defining a system of perforations and a layer of a sintered ceramic material surrounding and embedding the perforations, and wherein the cell further defines a gas plenum which is sealed from the external atmosphere and which is in fluid communication with either the anode or the cathode of the cell, and

(b) an electrical heater for raising the temperature of the cell, wherein the electrical heater comprises a heating element in the form a heat generating electrical wire capable of generating heat when an electrical current is passed through the wire and an optional thermal diffuser in the form of a metal foil or screen in thermal contact with the electrical wire, wherein the electrical heater is associated with the anode or cathode of the electrolytic cell, the electrical heater being generally co-terminous with its associated anode or cathode so that the electrical heater can provide essentially uniform heat across essentially the entire surface area of its associated anode or cathode..

27. The electrolytic device of claim 26, wherein the electrical heater includes the thermal diffuser.

28. The electrolytic device of claims 26 or 27, wherein the electrical heater is electrically insulated from the other metal elements forming the device.

29. The electrolytic device of claim 28, wherein the heat generating electrical wire of heating element of the electrical heater is received in a tubular metal sheath, the heating element further comprising an electrical insulator electrically insulating the heat generating electrical wire from the tubular metal sheath.

30. The electrolytic device of any one of claims 26-29, further comprising an electrical supply wire electrically connected to the heat generating electrical wire outside of, but proximate to, the outer periphery of the electrolytic cell, the electrical supply wire being selected so that amount of heat generated by the electrical supply wire is 25 % or less than the heat generating electrical wire on a per unit length basis when an electrical current capable of operating the heating element is carried by both wires.

31. The electrolytic device of claim 30, wherein the electrical supply wire is welded to the heat generating electrical wire to form a welded junction, and further wherein this welded junction is received in an insulator section for electrically insulating this weld junction, the heat generating electrical wire and the electrical supply wire from the other metal elements forming the device.

32. The electrolytic device of any one of claims 26-31, wherein the electrolytic device includes multiple electrolytic cells stacked one atop the other.

33. The electrolytic device of claim 32, wherein adjacent cells are arranged in a head to tail fashion, wherein adjacent cells are separated from one another by a bipolar element which together with the perforated metal sheets of the adjacent cells defines an anode gas plenum sealed from the atmosphere and a cathode gas plenum, wherein each electrolytic cell further includes a metallic gas transfer tube extending from the anode gas plenum of that electrolytic cell, and further wherein the metallic gas transfer tube is joined to the flexible perforated metal sheet and bipolar element of that cell by welding.

34. The electrolytic device of claim 32, wherein adjacent cells are arranged in a head to head fashion so that the anodes of respective pairs of adjacent cells face one another and thereby form anode gas plenums therebetween, the cathodes of these cells forming cathode gas plenums with the cathodes of adjacent pairs of adjacent cells, the anode gas plenums being sealed from the atmosphere by the perforated metal sheets which carry the anodes forming the anode gas plenums, wherein each electrolytic cell further includes a metallic gas transfer tube extending from its anode gas plenum, and further wherein the metallic gas transfer tube is welded to the flexible perforated metal sheets forming the anode gas plenums.

35. An electrolytic device comprising

wherein the cell further defines an anode gas plenum which is sealed from the external atmosphere and which is in fluid communication with either the anode or the cathode of the cell, and

(b) a pump downstream of and in fluid communication with the electrolytic cell, a pressure sensor arranged to monitor the pressure of the operating gas passing out of electrolytic cell, and a feedback loop structured to operate the pump to maintain to suitable output pressures of gas produced by the device.

36. The electrolytic device of claim 35, further comprising a by-pass line extending from upstream of the pump to downstream of the pump and a check- valve in the by-pass line structured to prevent the pressure of the operating gas in the gas plenum to exceed a predetermined value.

37. The electrolytic device of claims 35 or 36, wherein the electrolytic device includes multiple electrolytic cells stacked one atop the other.

38. The electrolytic device of claim 37, wherein adjacent cells are arranged in a head to tail fashion, wherein adjacent cells are separated from one another by a bipolar element which together with the perforated metal sheets of the adjacent cells defines an anode gas plenum sealed from the atmosphere and a cathode gas plenum, wherein each electrolytic cell further includes a metallic gas transfer tube extending from the anode gas plenum of that electrolytic cell, and further wherein the metallic gas transfer tube is joined to the flexible perforated metal sheet and bipolar element of that cell by welding.

39. The electrolytic device of claim 37, wherein adjacent cells are arranged in a head to head fashion so that the anodes of respective pairs of adjacent cells face one another and thereby form anode gas plenums therebetween, the cathodes of these cells forming cathode gas plenums with the cathodes of adjacent pairs of adjacent cells, the anode gas plenums being sealed from the atmosphere by the perforated metal sheets which carry the anodes forming the anode gas plenums, wherein each electrolytic cell further includes a metallic gas transfer tube extending from its anode gas plenum, and further wherein the metallic gas transfer tube is welded to the flexible perforated metal sheets forming the anode gas plenums.