HK1093818A - Apparatus and method for addition of electrolyte to fuel cells - Google Patents

Description

Apparatus and method for adding electrolyte to fuel cell

Technical Field

The present invention relates to electrochemical fuel cells and methods of using the same. More particularly, the present invention relates to a method and apparatus for adding an electrolyte, such as a molten carbonate electrolyte, to a fuel cell.

The present application claims the benefit of U.S. provisional application No.60/462,645 entitled "Method and Apparatus for addition of mobile carbon Electrolyte to an Operating mobile carbon Electrolyte cell", filed on 14/4/2003, the entire disclosure of which is hereby incorporated by reference for all purposes.

Background

Fuel cells are electrochemical devices that generate direct current (direct electric current) and thermal energy. A fuel cell stack (stack) includes a plurality of fuel cells stacked in a series relationship to achieve a higher available voltage output capacity.

Fuel cells are generally distinguished by the type of electrolyte used. For example, Molten Carbonate Fuel Cells (MCFCs) may use a mixture of lithium carbonate and potassium carbonate as the electrolyte. Phosphoric Acid Fuel Cells (PAFCs) may use a phosphoric acid solution (solution) as an electrolyte. Polymer Electrolyte Fuel Cells (PEFCs) may use a polymer as the electrolyte, such as Nafion , a product of Dupont de Numers corporation. Solid Oxide Fuel Cells (SOFCs) may use yttria-stabilized zirconia as the electrolyte.

For fuel cells utilizing liquid phase electrolytes, depletion of the electrolyte reserve below the level required to partially saturate the pore volume of the fuel cell electrodes may result in decreased catalytic and electrochemical performance of the fuel cell. There is a need in the art for an apparatus to replenish fuel cell electrolyte, and more particularly, an apparatus to replenish liquid phase fuel cell electrolyte when operating a fuel cell or fuel cell stack.

It is an object of the present invention to provide an apparatus and method for replenishing the electrolyte of a fuel cell and/or the electrolyte of a plurality of fuel cells, such as in a fuel cell stack. It is a particular object of certain examples or embodiments to provide an apparatus and method for replenishing electrolyte of a fuel cell or a plurality of fuel cells in a fuel cell stack during operation of the fuel cell.

Disclosure of Invention

According to a first aspect of the invention, an electrolyte delivery apparatus is disclosed. The electrolyte delivery apparatus is configured to provide electrolyte to a fuel cell, such as an operating fuel cell, or a fuel cell, such as in a fuel cell stack. The electrolyte delivery apparatus includes at least: an electrolyte reservoir (reservoir), a fluid conduit (fluid conduit) receiving electrolyte from the electrolyte reservoir, a heating device, and a pressure generator. The electrolyte reservoir and fluid conduit are configured to provide electrolyte to the fuel cell or fuel cell stack. The heating device is in thermal communication with at least a portion of the electrolyte reservoir and/or the fluid conduit and is operable to increase the mobility of the electrolyte in the electrolyte reservoir and/or the fluid conduit, or to liquefy the electrolyte in the case of a solid electrolyte. The pressure generator is operable to force fluid out of the electrolyte reservoir and into the fluid conduit for delivery to the fuel cell or fuel cell stack. The electrolyte delivery apparatus disclosed herein has the advantage of including a semi-continuous or continuous supply of electrolyte to individual fuel cells or fuel cell stacks, such as non-operating or operating fuel cells. Such semi-continuous or continuous supply of electrolyte may improve the efficiency of the fuel cell or fuel cell stack.

In accordance with another aspect, a fuel cell assembly is disclosed. The fuel cell assembly includes a fuel cell, an electrolyte reservoir, a fluid conduit, and a heating device. The fuel cell of the fuel cell assembly includes a cathode electrode, an anode electrode, and an electrolyte reservoir (matrix) between the cathode electrode and the anode electrode. The electrolyte reservoir is in fluid communication with a fluid conduit providing fluid communication between the electrolyte reservoir and the fuel cell for delivering electrolyte to the fuel cell. The electrolyte reservoir includes one or more electrolytes, such as one or more solid or liquid electrolytes, and preferably the same electrolyte as between the cathode and anode of the fuel cell. A heating device is in thermal communication with the electrolyte reservoir and/or the fluid conduit to heat the electrolyte in the fluid conduit and/or the electrolyte reservoir, and is operable to increase the mobility of the electrolyte or to provide liquid electrolyte for delivery to the fuel cell. The fuel cell assembly may further include a pressure generator configured to force fluid out of the electrolyte reservoir and into the fuel cell through the fluid conduit.

According to yet another aspect, a method of supplying electrolyte to a fuel cell is disclosed. The method comprises the following steps: the electrolyte lost from the fuel cell is replaced by providing an electrolyte reservoir comprising electrolyte, heating the electrolyte reservoir to increase the fluidity of at least a portion of the electrolyte, and delivering fluid from the electrolyte reservoir to the fuel cell. The electrolyte reservoir is in fluid communication with the fuel cell via a fluid conduit connecting the electrolyte reservoir and the fuel cell. Fluid from the electrolyte reservoir can be delivered to the fuel cell, for example, by pressurizing the electrolyte reservoir to force fluid out of the electrolyte reservoir and into the fuel cell through a fluid conduit. Other exemplary suitable methods for delivering electrolyte from the electrolyte reservoir to the fuel cell will be discussed below.

It will be appreciated by those of ordinary skill in the art, given the benefit of this disclosure, that the electrolyte delivery apparatus, fuel cell assembly, and methods of using the same provide a number of advantages, including, but not limited to, maintaining a substantially constant supply of electrolyte in an operating fuel cell or fuel cell stack in order to provide a more efficient fuel cell and fuel cell stack.

Drawings

Certain illustrative aspects and examples are described below in conjunction with the following drawings, wherein:

FIG. 1 is a perspective view of yet another exemplary fuel cell assembly including a fuel cell stack and an electrolyte delivery device including a pressure regulated gas (gas), according to certain examples; and

fig. 2 is a diagram of a porous conduit in physical contact with and in fluid communication with a plurality of fuel cells in a fuel cell stack.

It will be appreciated by those of ordinary skill in the art, given the benefit of this disclosure, that the figures and their components are not necessarily to scale and that certain components shown in the figures may be exaggerated, distorted or enlarged relative to other components to help to better understand the exemplary aspects and examples of the present invention that are discussed in detail below.

Detailed Description

The electrolyte delivery apparatus, fuel cell assemblies including the electrolyte delivery apparatus, and methods of using the electrolyte delivery apparatus represent significant technological advances. The device disclosed herein can be used to maintain the electrolyte level virtually constant even during operation of the fuel cell or fuel cell stack. Such a practically constant electrolyte level provides important benefits including, for example, operation of the fuel cell at high capacity without undesirable efficiency degradation caused by electrolyte loss.

According to certain examples, an electrolyte delivery apparatus including an electrolyte reservoir and a fluid conduit is disclosed. The electrolyte reservoir holds a fluid including an electrolyte for delivery by a fluid conduit to a fuel cell in fluid communication with the electrolyte reservoir. In some examples, the electrolyte to be delivered has substantially the same composition as the electrolyte used by the operating fuel cell.

According to certain examples, the electrolyte delivery apparatus and components thereof can take many shapes, dimensions, etc., depending on the environment in which the fuel cell in fluid communication with the electrolyte delivery apparatus is used. In certain examples, the electrolyte reservoir of the electrolyte delivery apparatus is suitably sized to hold about 1L to about 5L of fluid. According to certain examples, the electrolyte reservoir is positioned such that the level of electrolyte stored in the reservoir is physically below the point at which the fluid conduit terminates within a reactant passage (reactant passage) of the fuel cell stack, thereby creating or imposing a fluid head or sump (sump) within the fluid conduit that prevents flow into the fuel cell when the pressure generator is not activated. One of ordinary skill in the art, with the benefit of this disclosure, will be able to select suitable dimensions and configurations for the electrolyte delivery apparatus and its components.

According to certain examples, one or more fluid conduits providing fluid communication between the electrolyte reservoir and the fuel cell have a suitable shape and cross-sectional diameter to efficiently transport electrolyte from the electrolyte reservoir to the fuel cell. One of ordinary skill in the art, with the benefit of this disclosure, will readily select a suitable cross-sectional shape for the fluid conduit, such as circular. In certain other examples, the fluid conduit is generally a cylinder having a length of about 70cm to about 120cm, and more preferably about 80cm to 110 cm. Typically, the fluid conduit is straight and linear, however, in some instances, the fluid conduit may be curved, arced, or take other forms. In certain examples, the fluid conduit has an inner diameter of about 0.005cm to about 0.10cm, and more preferably about 0.01cm to about 0.075 cm. In certain examples, the fluid conduit has an outer diameter of about 0.01 to about 0.15cm, and more preferably about 0.03cm to about 0.075 cm. In certain examples, the fluid conduit has an outer diameter or shape sufficient to be inserted into a reactant passage of a fuel cell or fuel cell stack. The fluid conduit tube may also include an inner diameter and length sufficient to provide a known flow rate of the liquid electrolyte at a known pressure and temperature. In certain other examples, the fluid conduit passes through an enclosure of the fuel cell or fuel cell stack and/or an insulating layer that encapsulates the fuel cell or fuel cell stack. Suitable materials for the fluid conduit include, but are not limited to, stainless steel, high temperature ceramics, and other materials that can transport electrolyte and withstand high temperatures, e.g., about 650 ℃ or higher. In some examples, the fluid conduit includes a flow detector to indicate whether fluid is flowing through the fluid conduit.

According to certain examples, the electrolyte delivery apparatus further comprises a heating device. The heating device is in thermal communication with at least a portion of the electrolyte delivery apparatus and is operable to increase the mobility of, or maintain the mobility of, the electrolyte in the electrolyte reservoir and/or fluid conduit. In some examples, the heating device is a heater such as a thermoelectric or resistive heater, a burner, a conventional oven (oven), a microwave oven, or the like. In certain examples, a first heater, such as an electrical resistance heater, is provided along an exterior surface of the fluid conduit from a point where the fluid conduit passes through the fuel cell or fuel cell stack package to a point where the fluid conduit is fluidly coupled to the electrolyte reservoir. The fluid conduit and/or electrolyte reservoir may also include a thermocouple and controller for measuring and controlling the temperature of the fluid conduit and/or electrolyte tank (chamber). In some examples, the electrolyte reservoir is provided with a second heater that functions independently of the first heater. The second heater may include a thermocouple and a controller for measuring and controlling the temperature of the electrolyte reservoir. Those of ordinary skill in the art, with the benefit of this disclosure, will be able to select and configure suitable heating devices for use in the electrolyte delivery apparatus disclosed herein.

According to certain other examples, the electrolyte delivery apparatus may be housed within an insulated compartment (component) that optionally has an oven or other heating device to increase the fluidity or maintain the flow of electrolyte in the electrolyte reservoir. In some instances, the entire electrolyte delivery apparatus is disposed within the thermally insulated compartment, while in other instances, only one of the electrolyte reservoir or the fluid conduit is disposed within the thermally insulated compartment. In some examples, the thermally insulated compartment also includes a fuel cell or fuel cell stack, while in other examples, the fuel cell or fuel cell stack is positioned outside of the compartment containing the electrolyte delivery apparatus.

According to certain examples, the electrolyte delivery apparatus further includes a pressure generator operable to force fluid out of (or in certain examples withdraw fluid from) the electrolyte reservoir and into the fuel cell. The pressure generator may be any suitable device that can increase the pressure in the electrolyte reservoir, which causes fluid to move out of the electrolyte reservoir and into the fuel cell through the fluid conduit. In some examples, the pressure generator is a gas, a mechanical piston, or a pressure gradient generator. In at least some examples, the fluid is forced out of the electrolyte reservoir and into the fuel cell by a pressure regulated gas supply. In the example of using a pressure-regulated gas for a molten carbonate fuel cell, a gas such as carbon dioxide may be used to generate a high partial pressure of carbon dioxide (partial pressure) within the reservoir in order to avoid decomposition of the molten carbonate electrolyte.

According to certain examples, a controller may be used to control the amount of time that electrolyte flows from the electrolyte delivery device into the fuel cell and/or to control the flow rate. Typically, the controller includes a microprocessor, and a timer or timing circuit that can control the amount of time that the pressure generator is activated to force fluid out of the electrolyte reservoir. The controller may also include a memory unit, suitable software algorithms, suitable sensors such as temperature sensors, etc. One of ordinary skill in the art will be able to select and design an appropriate controller for use with the electrolyte delivery apparatus disclosed herein.

According to certain examples, the electrolyte delivery apparatus is configured for use with a fuel cell or a plurality of fuel cells in a fuel cell stack. Fuel cells are electrochemical devices that generate direct current electrical and thermal energy from a fuel source, such as gases such as hydrogen and oxygen. A fuel cell stack comprises a plurality of fuel cells, for example planar fuel cells, stacked in a series relationship to achieve a higher available voltage output capacity. The fuel cells in the fuel cell stack include anode and cathode electrodes, or electrolyte containers (matrices), commonly referred to as Membrane Electrode Assemblies (MEAs), respectively, applied to opposite surfaces of an electrolyte membrane (membrane). The MEA may be used as an outer casing for the individual cells of a fuel cell stack in combination with devices known as bipolar plates, also known as separator plates, or interconnects. The fuel cell stack may also be packaged by a manifold (manifold) that directs the reactant gases to the housing containing the bipolar plates of the individual fuel cells. The encapsulated fuel cell stack may also be encapsulated by a thermal insulation layer for containing thermal energy generated by or delivered to the fuel cell stack.

Without wishing to be bound by any particular scientific theory, it is believed that the electrolyte is primarily absorbed by the electrolyte reservoir and secondarily absorbed by the electrodes due to the smaller pore size provided by the electrolyte reservoir. That is, capillary action causes the fine pores of the electrolyte reservoir to have preferential saturation relative to the larger pores of the electrodes. Typically, at the time of assembly, a sufficient electrolyte reserve is provided to the fuel cell in order to achieve the desired saturation of the electrolyte reservoir and electrodes. Further without wishing to be bound by any particular theory, it is believed that over a period of time, the electrolyte reserve is depleted by: evaporative loss of electrolyte, corrosion of cell hardware, lithiation of electrodes (lithiation), general film leakage of electrolyte on the cell hardware surfaces (film threading), and/or voltage driven migration of electrolyte from one pole of a fuel cell stack to the opposite pole of the fuel cell stack. Typically, depletion of the electrolyte occurs slowly relative to thousands of hours of fuel cell stack operation. Depletion of the electrolyte reserve below the level required to partially saturate the pore volume of the electrodes can lead to reduced catalytic and electrochemical performance of the fuel cell. Depletion of the electrolyte below the level required to fully saturate the pore volume of the electrolyte reservoir may also result in physical mixing, or crossover, of the reactant gases. Crossover is destructive to the fuel cell because crossover typically results in hot spots that are subsequently generated by oxidation of the anode electrode, reduction of the cathode electrode, and combustion within the fuel cell. Such damage will typically propagate across the fuel cell and will result in premature failure of the fuel cell. To be commercially viable, fuel cell stacks require thousands of hours of high performance operation and, therefore, it is necessary to continuously maintain the electrolyte reserves of the fuel cells at those levels that cause partial saturation of the electrodes and complete saturation of the electrolyte reservoirs. Excess electrolyte may be provided to the fuel cells during assembly, as described in U.S. patent No. 5,773,161 to Farooque et al, wherein a reservoir is provided to contain excess electrolyte within the void space of the bipolar plates separating adjacent cells of the fuel cell stack. However, this approach results in increased complexity and cost of the bipolar plate, and also results in increased corrosion rates in the void spaces that serve as reservoirs within the bipolar plate. Furthermore, the reservoirs provided in the bipolar plates are limited and may deplete the electrolyte over time. A method of adding electrolyte to a molten carbonate fuel cell stack is described in U.S. patent No. 4,596,748 to Katz et al, in which vaporized electrolyte is "sprayed" into the reactant inlet gas stream entering the fuel cell. This approach is disadvantageous because of the uncertainty in electrolyte deposition. A method of adding electrolyte to a molten carbonate fuel cell is described in U.S. patent No. 4,530,887 to Maru et al, wherein the reactant inlet gas stream is "saturated" with electrolyte. This method is also disadvantageous due to the uncertainty of the electrolyte deposition. It has proven difficult to physically replenish electrolyte into a fuel cell, such as a molten carbonate fuel cell, from sources other than reservoirs within the fuel cell, either at the time of assembly or created by saturating reactant gas streams. One method of physically replenishing the electrolyte to the molten carbonate fuel cell is to temporarily stop the operation of the fuel cell. The fuel cell is then cooled to ambient temperature, the surface of the fuel cell containing the reactant channels is exposed, and a slurry (slurry) of solidified particles of electrolyte is physically injected into the exposed channels. The fuel cell is resealed and reheated above the melting temperature of the fuel cell to melt the added electrolyte and absorb the melted electrolyte into the porous electrode and electrolyte reservoir of the fuel cell. The above process requires that the fuel cell be taken off-line and shut down, which reduces availability for the fuel cell to provide usable electrical and thermal energy. In contrast, examples of the electrolyte delivery apparatus disclosed herein may be used to replenish electrolyte during operation of a fuel cell or fuel cell stack without taking the fuel cell or fuel cell stack offline.

According to certain other examples, the electrolyte may be transported within the reactant channels of the fuel cell and may be absorbed through exposed pores of the electrodes associated with the reactant gas channels. In certain examples, the rate of electrolyte flow through the fluid conduit is matched to the rate of electrolyte depletion such that the level of electrolyte is substantially constant when the fuel cell is in operation. According to other examples, the electrolyte absorbed by the electrodes is distributed throughout the MEA by capillary action within the pores of the components comprising the MEA. In at least some examples where the electrolyte delivery apparatus is used with a fuel cell stack, the electrolyte may also be distributed among adjacent fuel cells of the fuel cell stack by using voltage driven migration through membrane leakage. In certain other embodiments, the electrolyte may also be distributed among adjacent fuel cells of the fuel cell stack by voltage driven migration through dedicated conduits comprising porous elements in contact with each cell of the fuel cell stack. Those of ordinary skill in the art, with the benefit of this disclosure, will be able to select and design suitable devices for delivering electrolyte to the different fuel cells in the fuel cell stack.

According to some examples, the fuel cell may also be represented by the physical state of the electrolyte when the fuel cell is operating. For example, the electrolytes of Polymer Exchange Fuel Cells (PEFCs) and Solid Oxide Fuel Cells (SOFCs) are generally considered to be solid under operating conditions, while the electrolytes of Phosphoric Acid Fuel Cells (PAFCs) and Molten Carbonate Fuel Cells (MCFCs) are generally considered to be liquid under operating conditions. Molten carbonate fuel cells are also distinguished from other types of fuel cells by the phase change of the electrolyte as the electrolyte and fuel cell enter operating conditions. Molten carbonate fuel cells operate at about 650 ℃. The electrolyte of a molten carbonate fuel cell, such as a lithium/potassium electrolyte, is solid at ambient temperature and transitions to a liquid at operating temperature. The lithium/potassium electrolyte is typically provided in the form of a eutectic mixture (eutectoic mixture) having a melting point of about 493 c, such as 62 mol% lithium and 38 mol% potassium. An off-eutectic mixture (off-eutectic mixture) of lithium/potassium electrolyte will have a melting temperature different from 493 ℃. The amount of electrolyte within the molten carbonate fuel cell is designed to fully saturate the pore volume of the porous electrolyte vessel in order to achieve separation of the anode and cathode reactant gases within any given cell of the molten carbonate fuel cell stack. Additional electrolyte may be provided to partially saturate the pore volume of the anode and cathode electrodes to enhance the catalytic action of the electrodes. According to certain examples, and as described above, the electrolyte delivery apparatus may be used with a molten carbonate fuel cell. In some examples of the use of the electrolyte delivery apparatus for molten carbonate fuel cells, the electrolyte is a liquid solution of lithium, sodium and/or potassium carbonate saturated in a container, and the anode and cathode electrodes each include a catalyst such as nickel, copper, platinum, palladium, and the like. The electrolyte delivery apparatus may be used to deliver a liquid solution of lithium, sodium and/or potassium carbonate to a molten carbonate fuel cell to replenish lost electrolyte.

According to some examples, the electrolyte delivery apparatus can deliver electrolyte to the fuel cell while the fuel cell is operating or not operating. In certain examples, the electrolyte is typically delivered through reactant channels of the fuel cell, such as channels for introducing reactant gases into the fuel cell.

According to certain other examples, a fuel cell stack is enclosed within a housing, and the fuel cell stack includes a plurality of fuel cells, each of which has a reactant passage. The reactant passage of at least one fuel cell of the fuel cell stack is in fluid communication with the electrolyte reservoir via a fluid conduit. As described above, the electrolyte reservoir contains a reserve of electrolyte. In some examples, at least a first heating device is suitably positioned and operable to heat the fluid conduit. In certain other examples, at least a second heating device is suitably positioned and operable to heat the electrolyte reservoir. In some instances, the electrolyte in the electrolyte reservoir is forced out, for example, with a pressure generator such as a pressure regulated gas supply. In at least some examples, a flow detector is provided and is operable to detect a flow of a pressure-regulated gas for forcing electrolyte out of the electrolyte reservoir into the fluid conduit and into the reactant passage of the fuel cell stack. According to certain examples, the fluid conduit is fluidly coupled to the electrolyte reservoir below a level of electrolyte contained in the reservoir. In some examples, the fuel cell stack includes a porous element operable to distribute electrolyte to other fuel cells of the fuel cell stack. Such porous elements include, but are not limited to, alumina, zirconia, and the like. One of ordinary skill in the art, with the benefit of this disclosure, will be able to select these and other porous elements for distributing electrolyte to the plurality of fuel cells in a fuel cell stack.

According to certain other examples, the fuel cell may further include an insulating layer enclosing at least the fuel cell stack, at least a portion of the fluid conduit, and the electrolyte reservoir. In certain examples, the fluid conduits and electrolyte reservoirs are dielectrically isolated from the fuel cell stack packaging to prevent or impede current loss.

According to certain examples, an electrolyte delivery device is used to deliver and replenish electrolyte in a fuel cell or fuel cell stack. For example, upon determining that at least one fuel cell of the fuel cell stack has depleted its supply of electrolyte below the point at which optimal catalysis occurs, or below the point at which reactant crossover through the electrolyte reservoir occurs, or at any other depletion point determined to require replenishment, the electrolyte delivery apparatus may be activated to supply electrolyte to the fuel cell or fuel cell stack. In at least some examples, upon start-up, the electrolyte reservoir is vented to ambient pressure and heated to a selected operating temperature prior to delivery of any electrolyte. It will be appreciated by those skilled in the art, given the benefit of this disclosure, that the receptacle may be heated by any one or more of the heating means described above, or other suitable heating means as readily selected by one of ordinary skill in the art. The exact heating temperature will generally depend on the electrolyte to be delivered to the fuel cell. For example, in the case of delivering electrolyte to a molten carbonate fuel cell, the operating temperature is about 650 ℃.

Once the operating temperature of the reservoir is reached, the fluid conduit may be heated with a heating device to a desired operating temperature, which is typically the same operating temperature used by the electrolyte reservoir. After the operating temperature of the fluid conduit is reached, the reservoir may be pressurized with a pressure generator to force fluid out of the reservoir. In some instances, the reservoir is pressurized with gas to a known pressure. The rate and amount of electrolyte flow can be predetermined experimentally from a known pressure, a known fluid conduit internal diameter, and a known system operating temperature. In some instances, the electrolyte will continue to flow through the fluid conduit until the reservoir is empty. Once the electrolyte stops flowing, the reservoir may be depressurized by venting the reservoir to ambient pressure by opening a vent or valve in the reservoir. In at least some examples, a timer, such as a gas pressure timer, may be initiated to maintain the pressure for a selected time prior to venting the reservoir. The electrolyte will continue to flow until the timer stops and the controller actuates the valve that controls the flow of pressurized gas and/or vents the reservoir by opening the valve. In addition, the heating device may be turned off and the remaining electrolyte within the reservoir and fluid conduit may be allowed to cool. In some examples, a single heating device is used to heat both the electrolyte reservoir and the fluid conduit.

Persons of ordinary skill in the art having benefit of this disclosure will recognize that the apparatus and methods disclosed herein represent a significant technical advance. Robust devices can be assembled to intermittently, semi-continuously, or continuously add electrolyte to an operating fuel cell in order to increase the efficiency of the fuel cell. The following examples are merely illustrative of several possible configurations and uses of the electrolyte delivery apparatus disclosed herein and should not be construed to limit the scope of the appended claims.

Example 1

Referring to fig. 1, a schematic diagram of a fuel cell assembly 501 is shown. A fuel cell 502, such as a molten carbonate fuel cell, has a housing 503 and a reactant channel 504, the reactant channel 504 being fluidly coupled to an electrolyte reservoir 505 containing an electrolyte supply 506 by a first fluid conduit 507. The first fluid conduit is fluidly coupled to the reservoir below the electrolyte supply level. Preferably, the first fluid conduit is coupled at a location proximate to or on a bottom surface of the electrolyte reservoir. The first fluid conduit may be any structure or device capable of fluidly coupling, or providing fluid communication between, the reservoir and the reactant passage, and may be, for example, a tube, a cylinder, or a hose. The first fluid conduit preferably has an inner diameter, for example, in the range of from about 0.013cm (.005 inches) to about.05 cm (.020 inches), and an outer diameter in the range of from about 0.038cm (.015 inches) to about 0.076cm (.030 inches). The electrolyte reservoir 505 is equipped with a first heater 508 and a thermocouple 509. The first fluid conduit 507 is equipped with a second heater 510 and a thermocouple 511. The electrolyte reservoir 505, and the portion of the first fluid conduit 507 extending from the outer housing 503 to the electrolyte reservoir 505, are enclosed by insulation 512. As understood herein, the first and second heaters may be externally mounted resistive heaters, or any other heater or heating device deemed suitable for its particular purpose by one of ordinary skill in the art having the benefit of this disclosure. The electrolyte reservoir 505 is also provided with a second fluid conduit 513 fluidly coupled to a pressure regulator 514, a flow detector 515, a valve 516, and a pressurized gas supply 520. Elevation 519 of the electrolyte reservoir 505 relative to the reactant channels 504 creates a reservoir or pressure head in a manner that prevents electrolyte 506 from flowing out of the reservoir 505 to the reactant channels 504 when the motive force provided by the pressurized gas supply 520 is not present. The controller 517 controls the actuation of the valve 516 and the first and second heaters 508, 510. The controller 517 may be programmed to activate the valve 516, the first and second heaters 508, 510, and the timer 518.

During operation of the exemplary apparatus shown in fig. 1, the electrolyte reservoir 505 is vented to ambient pressure by the controller 517 opening valve 516. The electrolyte reservoir 505 is heated by the controller 517 and heater 508 to above the melting point of the electrolyte 506 contained within the electrolyte reservoir, i.e., the operating temperature of the electrolyte reservoir. Once the operating temperature of the electrolyte reservoir is reached, the first fluid conduit 507 is heated by the controller 517 and the second heater 510 to above the melting point of the electrolyte 506 contained within the electrolyte reservoir 505, i.e., the first fluid conduit operating temperature. Once the first fluid conduit operating temperature is reached, the electrolyte reservoir 505 is pressurized by the controller 517 and gas pressure regulator 514 with a gas 520, such as carbon dioxide, to a known pressure. The gas pressure timer 518 is started. Upon pressurizing the electrolyte reservoir 505, the liquid electrolyte 506 will begin to flow from the electrolyte reservoir 505 through the first fluid conduit 507 and into the reactant passage 504 of the fuel cell 502. The liquid electrolyte 506 will continue to flow through the first fluid conduit 507 at a rate determined by the pressure of the gas 520 and the inner diameter of the first fluid conduit 507 until the reservoir 505 is empty or until the controller 518 detects that the timer 518 has timed out, at which point the controller 518 deactivates the gas pressure regulator 514 to stop pressurizing the electrolyte reservoir 505. In the event that the electrolyte 506 flows until the electrolyte reservoir 505 is empty, the gas flow detector 505 will detect an elevated gas flow rate and the controller 518 will deactivate the gas pressure regulator 514 to cease pressurizing the electrolyte reservoir 505. The exposed pores of the electrodes may absorb liquid electrolyte 506 that precipitates within the reactant gas channels 504. The electrolyte flow rate through the first fluid conduit 507 may be matched to the electrolyte depletion rate of the electrodes in order to avoid precipitation of excessive amounts of electrolyte within the reactant channels. Persons of ordinary skill in the art, with the benefit of this disclosure, will be able to determine an appropriate rate for their particular purpose. The electrolyte reservoir 505 may also have a replenishment pipe 521, and when the electrolyte reservoir 505 needs to be replenished with the electrolyte 506, the electrolyte slurry may be injected into the electrolyte reservoir 505 through the replenishment pipe 521. The refill tube may be capped. Upon replenishment, the heater 508 is energized to raise the temperature of the electrolyte reservoir 505 and the replenished electrolyte 506 to drive off the slurry solvent. For example, the slurry solvent may be any solvent known to act as an electrolyte slurry solvent, such as alcohol or glycerol. One of ordinary skill in the art, with the benefit of this disclosure, will readily select a suitable temperature for distilling off the slurry solvent, and, in general, the temperature used will depend on the characteristics and properties of the slurry solvent.

In an exemplary configuration, a fluid conduit having an inner diameter of about 0.025cm (.010 inches) and a length of about 91.4cm (36.0 inches) provides a flow rate of electrolyte of about 2.0 grams per minute to a molten carbonate fuel cell operating at an apparatus temperature of about 650 ℃, an apparatus pressure of about 25.4cm (10.0 inches) water column and about 305cm (120.0 inches) water column above ambient atmospheric pressure.

Example 2

In another example, as shown in FIG. 2, electrolyte may also be distributed in adjacent fuel cells 522a, 522b, and 522c of the fuel cell stack 502 using voltage driven migration through membrane leakage or a dedicated conduit 523 comprising a porous member in contact with each fuel cell 522a, 522b, 522c of the fuel cell stack. The dimensions of the dedicated conduit 523 may be selected to provide a particular flow rate of electrolyte 506 that matches the depletion rate of electrolyte of all cells of the fuel cell stack 502, such that all cells of the fuel cell stack 502 are replenished with electrolyte at a rate equal to the depletion rate of electrolyte. The dedicated conduit 523 may comprise pores formed in particles (particles) or fibers (fibers) comprising non-conductive high purity zirconia, alumina, or other materials known to be non-conductive such as ceramics and inert in the presence of an electrolyte such as a molten carbonate electrolyte. Those skilled in the art, with the benefit of this disclosure, will be able to select an appropriate de porous element for inclusion in a fuel cell stack.

Although a number of illustrative aspects and examples are described above, those of ordinary skill in the art, having the benefit of this disclosure, will appreciate that variations, substitutions, and modifications to the above described exemplary aspects and examples are possible. Persons of ordinary skill in the art will also recognize, given the benefit of this disclosure, that certain elements of one example may be added or interchanged with certain elements of other examples. Such alterations, substitutions, modifications, and additions are intended to fall within the spirit and scope of the appended claims.

Claims (21)

1. An electrolyte delivery apparatus comprising:

an electrolyte reservoir comprising an electrolyte;

a fluid conduit in fluid communication with the electrolyte reservoir, the fluid conduit configured to receive electrolyte from the electrolyte reservoir;

a heating device in thermal communication with the electrolyte reservoir and the fluid conduit, the heating device operable to increase the mobility of at least a portion of the electrolyte in the electrolyte reservoir; and

a pressure generator operable to force electrolyte out of the electrolyte reservoir and into the fluid conduit.

2. The electrolyte delivery apparatus of claim 1, wherein the heating device is a resistive heater.

3. The electrolyte delivery device of claim 1, wherein the pressure generator is a pressure regulated gas.

4. The electrolyte delivery apparatus of claim 1, wherein the fluid conduit comprises a stainless steel tube.

5. The electrolyte delivery apparatus of claim 1, further comprising a vent for venting the electrolyte reservoir.

6. A fuel cell assembly comprising:

a fuel cell including a cathode electrode, an anode electrode, and an electrolyte reservoir between the cathode electrode and the anode electrode;

an electrolyte reservoir comprising an electrolyte;

a fluid conduit configured to provide fluid communication between the fuel cell and the electrolyte reservoir; and

a heating device in thermal communication with the electrolyte reservoir and effective to increase the fluidity of the electrolyte to be delivered to the fuel cell.

7. The fuel cell assembly of claim 6, further comprising a pressure generator configured to force liquid electrolyte out of the electrolyte reservoir and into the fuel cell through the fluid conduit.

8. The fuel cell assembly of claim 6, wherein the fuel cell is a molten carbonate fuel cell.

9. The fuel cell assembly of claim 6, wherein the cathode and the anode each comprise a nickel catalyst.

10. The fuel cell assembly of claim 6, wherein the heating device is in thermal communication with both the electrolyte reservoir and the fluid conduit.

11. The fuel cell assembly of claim 6, wherein the fuel cell is a fuel cell stack.

12. The fuel cell assembly of claim 6, further comprising a second fluid conduit configured to replenish electrolyte in the electrolyte reservoir.

13. A molten carbonate fuel cell assembly comprising:

a molten carbonate fuel cell comprising a cathode electrode, an anode electrode, and a molten carbonate electrolyte reservoir between the cathode electrode and the anode electrode;

an electrolyte reservoir comprising a molten carbonate electrolyte;

a fluid conduit configured to provide fluid communication between the molten carbonate fuel cell and the electrolyte reservoir;

a heating device operable to heat the molten carbonate electrolyte in the electrolyte reservoir; and

a pressure generator comprising a pressurized gas operable to force the heated molten carbonate electrolyte out of the electrolyte reservoir.

14. The molten carbonate fuel cell assembly of claim 13 further comprising a thermocouple in thermal communication with the electrolyte reservoir.

15. The molten carbonate fuel cell assembly of claim 13 further comprising a flow detector operable to detect the flow of pressurized gas.

16. The molten carbonate fuel cell assembly of claim 13 further comprising a replenishment tube for adding additional electrolyte to the electrolyte reservoir.

17. The molten carbonate fuel cell assembly of claim 13 further comprising a controller configured to activate the pressure generator.

18. The molten carbonate fuel cell assembly of claim 13 further comprising a timer configured to deactivate the pressure generator after a period of time.

19. A method of supplying electrolyte to a fuel cell, the method comprising:

providing an electrolyte reservoir comprising an electrolyte, wherein the electrolyte reservoir is in fluid communication with the fuel cell via a fluid conduit;

heating the electrolyte reservoir to increase the mobility of at least a portion of the electrolyte in the electrolyte reservoir; and

the electrolyte is transported from the electrolyte reservoir to the fuel cell via a fluid conduit.

20. The method of claim 19, wherein the electrolyte is delivered to an operating fuel cell.

21. The method of claim 19, wherein the fuel cell is a molten carbonate fuel cell.