Systems and methods for using cathode exhaust humidity control and monitoring fuel cell stacks

Abstract

This disclosure generally relates to systems and methods for using a relative humidity sensor in the cathode exhaust stream of a fuel cell stack to optimize the performance and efficiency of the fuel cell stack.

Description

[0001] Cross-references to related applications

[0002] Pursuant to Title 35, Section 119(e) of the United States Code and any other applicable laws or regulations, this non-provisional application claims the benefit and priority of U.S. Provisional Patent Application No. 63 / 251403, filed October 1, 2021, the entire disclosure of which is hereby expressly incorporated herein by reference. Technical Field

[0003] This disclosure generally relates to systems and methods for using a relative humidity sensor in the cathode exhaust of a fuel cell stack to optimize the performance and efficiency of the fuel cell stack. Background Technology

[0004] A typical fuel cell engine may include several subsystems that convert chemical potential energy into usable electrical potential energy. At the heart of the fuel cell engine is the fuel cell stack. A fuel cell stack comprises more than one fuel cell assembly that is electrically connected in series, compressed, and combined to provide a simple, compact power source. The stack may be supported by additional subsystems for operation. The main subsystems that enable the electrochemical reactions in a fuel cell engine include a fuel processing subsystem, an air processing subsystem, and / or a coolant subsystem.

[0005] A fuel cell stack comprises a set of structured electrodes, which in some embodiments are separated by a proton exchange membrane (PEM). The PEM facilitates the passage of hydrogen nuclei (e.g., hydrogen atoms minus electrons) between the two electrodes. Each electrode is supplied with a reactant gas (e.g., hydrogen) at the anode and with a reactant gas (e.g., oxygen) at the cathode. A chemical reaction occurs at the membrane, where hydrogen nuclei crossing the membrane combine with oxygen molecules at the cathode to form water (H₂O). This movement of protons / hydrogen nuclei creates a positive charge at the cathode and a negative charge at the anode. The different charges at the anode and cathode allow for a voltage potential that can be utilized as electrical energy and is typically used to charge batteries and / or other electronic devices (e.g., power motors).

[0006] The conflicting requirements of fuel cell stack operation impact the thermodynamic optimization of fuel cell stack operation. For efficient and robust operation of the fuel cell stack, the electrodes must have both sufficient reactant supply and low resistance to core penetration. To prevent fuel shortage, the rate at which reactants (e.g., air and hydrogen) are supplied to the reaction sites must be greater than or equal to the consumption rate. Insufficient reactant supply can lead to accelerated fuel cell aging through carbon corrosion, as the fuel cell may begin to consume catalyst support structures in place of preferred reactants.

[0007] Nuclear permeation resistance is supported by membrane hydration and can be mitigated by retaining some product water within the gas diffusion layer (GDL) and membrane electrode assembly (MEA). Even if oxygen is present at the reaction sites, insufficient water retention can reduce hydrogen nucleus transfer rates, thus degrading fuel cell stack performance. Conversely, even with adequate proton permeation characteristics, excessive water retention can cause oxygen blockage by water molecules. Therefore, the control of parameters managing relative humidity requires careful consideration.

[0008] While many parameters influence fuel cell operation, one objective variable is the relative humidity in the fuel cell exhaust. As cathode air passes through the fuel cell stack, the fuel cell reaction is limited by the cathode air's ability to retain water vapor. The measure of a given volume of air's ability to retain water vapor is called its relative humidity.

[0009] This paper describes systems and methods for using a relative humidity sensor in the exhaust flow of a fuel cell stack to optimize the performance and efficiency of the fuel cell stack. It also describes systems and methods in which information determined by the relative humidity sensor can be used by a controller or control system in a fuel cell engine including the fuel cell stack for closed-loop optimization of the fuel cell stack's operating state. Summary of the Invention

[0010] The embodiments included in this disclosure are intended to meet these and other needs.

[0011] In one aspect of this disclosure, a fuel cell system includes an anode and a cathode, a cathode inlet port, a cathode exhaust port, a cathode inlet airflow, and a cathode exhaust flow. The fuel cell system also includes a sensor in the cathode exhaust flow for determining, measuring, and / or detecting a water content reading in the cathode exhaust flow, and a controller for determining the operation of the fuel cell stack based on the water content reading.

[0012] In some embodiments, the sensor may be a relative humidity sensor, and the water content reading may be a relative humidity reading, including a water vapor content reading in the cathode exhaust stream. In some embodiments, the controller may use closed-loop optimization of the fuel cell stack based on the relative humidity reading when determining the operation of the fuel cell stack.

[0013] In some embodiments, the cathode inlet airflow may be humidified.

[0014] In some embodiments, the relative humidity sensor may be located at the cathode exhaust port. In some embodiments, the system may further include a heat exchanger located downstream of the cathode exhaust port. The relative humidity sensor may be positioned downstream of the heat exchanger at the cathode exhaust port.

[0015] In some embodiments, the system may further include an air compressor. The air compressor may provide conditioned air upstream of the relative humidity sensor and dilute the cathode exhaust stream. The dilution of the cathode exhaust stream may be based on the pressure ratio of the air compressor. The dilution of the cathode exhaust stream may introduce a relative humidity offset proportional to the dilution ratio of the conditioned air to the cathode outlet exhaust. In some embodiments, the conditioned air may be introduced upstream of the relative humidity sensor.

[0016] In some embodiments, the relative humidity sensor may be a dummy relative humidity sensor. In some embodiments, a bypass airflow may be introduced upstream of the relative humidity sensor to dilute the cathode exhaust flow. In some embodiments, the relative humidity sensor may be located on a separate cathode exhaust line including a heater. The heater may increase the air temperature in the separate cathode exhaust line by a set amount.

[0017] In some embodiments, the sensor can determine the water content in the cathode exhaust stream based on measurements of oxygen and nitrogen in the cathode exhaust stream.

[0018] In a second aspect of this disclosure, a fuel cell system includes a fuel cell stack, the fuel cell stack including an anode, a cathode, a cathode inlet port, a cathode exhaust port, a cathode inlet airflow, and a cathode exhaust flow. The fuel cell system further includes a wide-range λ sensor in the cathode exhaust flow for determining or detecting a measured oxygen concentration in the cathode exhaust flow, and a controller for determining the operation of the fuel cell stack based on the measured oxygen concentration and a target oxygen concentration.

[0019] In a third aspect of this disclosure, a method of operating a fuel cell system includes the steps of: determining a target water content or target relative humidity of the cathode exhaust stream based on the current density of the fuel cell stack; using or utilizing a first sensor to determine the water content of the cathode exhaust stream; and adjusting the cathode system by implementing a controller to increase or decrease the determined water content of the cathode exhaust stream based on the target water content or target relative humidity of the cathode exhaust stream.

[0020] In some embodiments, the first sensor may be a relative humidity sensor, and the method may further include detecting a relative humidity reading using the relative humidity sensor. In some embodiments, adjusting the cathode system may further include: determining a target pressure or target temperature of the cathode exhaust flow based on the current density of the fuel cell stack; measuring the current pressure or current temperature in the cathode exhaust flow using a second sensor; changing the current pressure based on the target pressure in the cathode exhaust flow; changing the current temperature in the cathode exhaust flow based on the target temperature; changing the mass flow rate in the cathode system; or changing the temperature of the cathode exhaust flow.

[0021] In some embodiments, the method may further include: agitating the system to cause a change in the water content reading of a first sensor in the cathode exhaust stream, and comparing the change in water content reading with a expected water content reading in the cathode exhaust stream caused by the agitation. If the change in water content reading in the cathode exhaust stream is greater than the expected water content reading in the cathode exhaust stream, it can be determined that the fuel cell stack or system is operating at a relative humidity greater than about 100%. In some embodiments, the difference between the change in water content reading in the cathode exhaust stream and the expected water content reading in the cathode exhaust stream can be used to offset the operation of the fuel cell stack and / or system to ensure that the fuel cell stack and / or system operates at about 100% relative humidity.

[0022] In some embodiments, the method may further include a first sensor determining the water content in the cathode exhaust stream based on oxygen and nitrogen measurements in the cathode exhaust stream. In some embodiments, the system may further include a heat exchanger located downstream of the cathode exhaust port. A relative humidity sensor may be positioned downstream of the heat exchanger at the cathode exhaust port. Attached Figure Description

[0023] Figure 1A This is a schematic diagram of an exemplary fuel cell system, which includes an air delivery system, an electrolyzer, and a fuel cell module comprising a stack of multiple fuel cells.

[0024] Figure 1B It is a cross-sectional view of an exemplary fuel cell system including an air delivery system, an electrolyzer, and multiple fuel cell modules, each including multiple fuel cell stacks;

[0025] Figure 1C yes Figure 1A A perspective view of an exemplary repeating unit of a fuel cell stack in a fuel cell system;

[0026] Figure 1D yes Figure 1C A cross-sectional view of an exemplary repeating unit of a fuel cell stack;

[0027] Figure 2 This is a schematic diagram of one embodiment of a fuel cell stack including a humidity sensor located directly at the cathode exhaust port;

[0028] Figure 3 This is a schematic diagram of one embodiment of a fuel cell stack including a humidity sensor located downstream of a heat exchanger;

[0029] Figure 4 This is a schematic diagram of an embodiment of a fuel cell stack including a humidity sensor and an air compressor, with air bearing exhaust flow.

[0030] Figure 5This is a schematic diagram of an embodiment of a fuel cell stack that includes a humidity sensor and regulated process air in a bypass flow;

[0031] Figure 6 This is a schematic diagram of one embodiment of a fuel cell stack including a wide-range λ sensor; and

[0032] Figure 7 This is a schematic diagram of one embodiment of a fuel cell stack including a humidity sensor, and a heat exchanger reduces the pressure upstream of the relative humidity sensor in a thermal enthalpy manner.

[0033] These and other features, aspects, and advantages of the invention will become more readily understood when the following detailed description is read with reference to the accompanying drawings, which form part of this document and illustrate, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the claims, and it will be understood that other embodiments may be utilized and logical, mechanical, and electrical changes may be made without departing from the spirit and scope of the claims. Therefore, the following detailed description is not intended to be limiting. Detailed Implementation

[0034] This disclosure relates to systems and methods for using a relative humidity sensor 110 in the exhaust flow of a fuel cell stack 12 to optimize the performance and efficiency of the fuel cell stack 12. More specifically, the relative humidity sensor 110, used to measure the water vapor content in the fuel cell stack exhaust, provides information that can be used by a controller or control system in a fuel cell engine including the fuel cell stack 12 for closed-loop optimization of the fuel cell stack operating state.

[0035] like Figure 1A As shown, the fuel cell system 10 typically includes one or more fuel cell stacks 12 or fuel cell modules 14 connected to an auxiliary assembly (BOP) 16 comprising various components to support the electrochemical conversion, generation, and / or distribution of electrical power to help meet modern industrial and commercial needs in an environmentally friendly manner. Figure 1B and 1C As shown, the fuel cell system 10 may include a fuel cell stack 12, which includes multiple individual fuel cells 20. Each fuel cell stack 12 may accommodate multiple fuel cells 20 assembled together in series and / or parallel. Figure 1A and 1B As shown, the fuel cell system 10 may include one or more fuel cell modules 14.

[0036] Each fuel cell module 14 may include multiple fuel cell stacks 12 and / or multiple fuel cells 20. The fuel cell module 14 may also include suitable combinations of associated structural elements, mechanical systems, hardware, firmware, and / or software for supporting the functionality and operation of the fuel cell module 14. Such items include, but are not limited to, piping, sensors, regulators, current collectors, seals, and insulators.

[0037] The fuel cells 20 in the fuel cell stack 12 can be stacked together to multiply and increase the voltage output of a single fuel cell stack 12. The number of fuel cell stacks 12 in the fuel cell system 10 can vary depending on the amount of power required to operate the fuel cell system 10 and meet the power demands of any load. The number of fuel cells 20 in the fuel cell stack 12 can vary depending on the amount of power required to operate the fuel cell system 10, which includes the fuel cell stacks 12.

[0038] The number of fuel cells 20 in each fuel cell stack 12 or fuel cell system 10 can be any number. For example, the number of fuel cells 20 in each fuel cell stack 12 can range from about 100 fuel cells to about 1,000 fuel cells, including any specific number or range of the fuel cells 20 included (e.g., about 200 to about 800). In an embodiment, fuel cell system 10 may include about 20 to about 1,000 fuel cell stacks 12, including any specific number or range of the fuel cell stacks 12 included (e.g., about 200 to about 800). The fuel cells 20 in the fuel cell stacks 12 within fuel cell module 14 can be oriented in any direction to optimize the operating efficiency and functionality of fuel cell system 10.

[0039] The fuel cell 20 in the fuel cell stack 12 can be any type of fuel cell 20. The fuel cell 20 can be a polymer electrolyte membrane or proton exchange membrane (PEM) fuel cell, an anion exchange membrane fuel cell (AEMFC), an alkaline fuel cell (AFC), a molten carbonate fuel cell (MCFC), a direct methanol fuel cell (DMFC), a regenerative fuel cell (RFC), a phosphoric acid fuel cell (PAFC), or a solid oxide fuel cell (SOFC). In an exemplary embodiment, the fuel cell 20 can be a polymer electrolyte membrane or proton exchange membrane (PEM) fuel cell or a solid oxide fuel cell (SOFC).

[0040] exist Figure 1C In the illustrated embodiment, the fuel cell stack 12 includes a plurality of proton exchange membrane (PEM) fuel cells 20. Each fuel cell 20 includes a single membrane electrode assembly (MEA) 22 and gas diffusion layers (GDLs) 24, 26 on either side or both sides of the MEA 22 (see Figure 1C ).like Figure 1C As shown, the fuel cell 20 further includes bipolar plates (BPPs) 28, 30 located on the outer side of each gas diffusion layer (GDL) 24, 26. The aforementioned components (particularly the bipolar plate 30, gas diffusion layer (GDL) 26, membrane electrode assembly (MEA) 22, and gas diffusion layer (GDL) 24) comprise a single repeating unit 50.

[0041] Bipolar plates (BPPs) 28 and 30 are responsible for transporting reactants (such as fuel 32 (e.g., hydrogen) or oxidant 34 (e.g., oxygen, air)) and cooling fluid 36 (e.g., coolant and / or water) within the fuel cell 20. The bipolar plates (BPPs) 28 and 30 can uniformly distribute the reactants 32 and 34 to the active region 40 of each fuel cell 20 via oxidant flow fields 42 and / or fuel flow fields 44 formed on the outer surfaces of the bipolar plates (BPPs) 28 and 30. Within the membrane electrode assembly (MEA) 22, gas diffusion layers (GDLs) 24 and 26, and bipolar plates (BPPs) 28 and 30, the active region 40 where electrochemical reactions occur to generate electrical power produced by the fuel cell 20 is centrally located when the stack 12 is viewed from a top-down perspective.

[0042] like Figure 1D As shown, bipolar plates (BPPs) 28 and 30 may each be configured to have reactant flow fields 42 and 44 formed on opposite outer surfaces of the bipolar plates (BPPs) 28 and 30, and to have a coolant flow field 52 located within the bipolar plates (BPPs) 28 and 30. For example, the bipolar plates (BPPs) 28 and 30 may include a fuel flow field 44 for transferring fuel 32 on one side of the plates 28 and 30 for interaction with the gas diffusion layer (GDL) 26, and an oxidant flow field 42 for transferring oxidant 34 on a second opposite side of the plates 28 and 30 for interaction with the gas diffusion layer (GDL) 24. Figure 1D As shown, the bipolar plates (BPPs) 28, 30 may further include a coolant flow field 52 formed within the plates (BPPs) 28, 30, generally centered between the opposing outer surfaces of the plates (BPPs) 28, 30. The coolant flow field 52 facilitates the flow of cooling fluid 36 through the bipolar plates (BPPs) 28, 30 to regulate the temperature of the plate (BPPs) 28, 30 materials and reactants. The bipolar plates (BPPs) 28, 30 are compressed against adjacent gas diffusion layers (GDLs) 24, 26 to isolate and / or seal one or more reactants 32, 34 within their respective passages 44, 42 to maintain the electrical conductivity required for robust operation of the fuel cell 20 (see [link to relevant documentation]). Figure 1C and 1D ).

[0043] The fuel cell system 10 described herein can be used in stationary and / or immobile power systems, such as industrial applications and power plants. The fuel cell system 10 can also be implemented in conjunction with an air delivery system 18. Additionally, the fuel cell system 10 can also be implemented in conjunction with an electrolyzer 19 and / or other electrolysis systems 19. In one embodiment, the fuel cell system 10 is connected in series or parallel and / or attached to an electrolysis system 19, such as one or more electrolyzers 19 in BOP 16 (see...). Figure 1A In another embodiment, the fuel cell system 10 is not connected in series or parallel and / or attached to the electrolysis system 19, such as one or more electrolyzers 19 in BOP 16.

[0044] This fuel cell system 10 may also be included in mobile applications. In an exemplary embodiment, the fuel cell system 10 is in a vehicle and / or powertrain 100. The vehicle 100 including this fuel cell system 10 may be an automobile, motor vehicle, bus, truck, train, locomotive, aircraft, light vehicle, medium vehicle, or heavy vehicle. The type of vehicle 100 may also include, but is not limited to, commercial vehicles and engines, trains, trolleys, trams, aircraft, buses, boats, ships, and other known vehicles, as well as other machinery and / or manufacturing devices, equipment, gear, etc.

[0045] This fuel cell system 10 may also be included in mobile applications. In an exemplary embodiment, the fuel cell system 10 is in a vehicle and / or powertrain 100. The vehicle 100 including this fuel cell system 10 may be an automobile, motor vehicle, bus, truck, train, locomotive, aircraft, light vehicle, medium vehicle, or heavy vehicle. The type of vehicle 100 may also include, but is not limited to, commercial vehicles and engines, trains, trolleys, trams, aircraft, buses, boats, ships, and other known vehicles, as well as other machinery and / or manufacturing devices, equipment, gear, etc.

[0046] The vehicle and / or power system 100 can be used on roads, highways, railways, aircraft, and / or waterways. The vehicle 100 can be used in applications including but not limited to off-highway transportation, short-tail trucks, and / or mining equipment. For example, an exemplary embodiment of the mining equipment vehicle 100 is a mining truck or a mine transport truck.

[0047] Furthermore, those skilled in the art will recognize that the fuel cell system 10, fuel cell stack 12, and / or fuel cell 20 described in this disclosure can respectively replace any electrochemical system (such as an electrolysis system (e.g., an electrolyzer)), electrolyzer stack, and / or electrolyzer cell (EC). Accordingly, in some embodiments, the features and aspects of the fuel cell system 10, stack 12, or cell 20 described and taught in this disclosure also relate to the electrolyzer, electrolyzer stack, and / or electrolyzer cell (EC). In other embodiments, the features and aspects described or taught in this disclosure do not relate to the features and aspects of the electrolyzer, electrolyzer stack, and / or electrolyzer cell (EC), and are therefore distinguishable from such features and aspects.

[0048] In one embodiment, such as Figure 2 As shown, the fuel cell engine 101 may include a fuel cell stack 12 having a fuel cell 20. The fuel cell stack 12 may include an anode fuel system 92. The anode fuel system 92 may include an anode gas flow 112, and the cathode air system 94 may include a cathode air flow 102. In some embodiments, the pressure and flow rate in the anode fuel system 92 may follow the pressure and flow rate in the cathode air system 94.

[0049] Anode gas flow 112 can enter the anode 114 of fuel cell stack 12. Cathode air flow 102 can enter the cathode 116 at cathode inlet port 104 of fuel cell stack 12 and exit as cathode exhaust 108 at cathode exhaust port 106.

[0050] In one embodiment, the pressure difference between the reactant gases (e.g., the anode gas stream 112 and the cathode air stream 102) may need to be kept to a minimum. Minimum pressure allows for reduced forces experienced by the MEA 22 and GDLs 24, 26 of the fuel cell 20. The ongoing reaction between the fuel 32 (e.g., hydrogen) and the oxidant 34 in the fuel cell stack 12 can generate water vapor in the exhaust stream of the fuel cell stack 12. A relative humidity sensor 110 may be placed directly at the cathode exhaust port 106.

[0051] Total relative humidity (i.e., 100% RH) represents the maximum amount of water vapor that air can contain before thermodynamically favorable conditions for water condensation. Once the relative humidity in the cathode airflow 102 of the fuel cell stack 12 reaches approximately 100%, the reaction at the fuel cell stack 12 becomes increasingly difficult and leads to the formation of liquid water.

[0052] A target relative humidity exists at the outlet of the fuel cell stack 12, and the operation of the fuel cell stack 12 can be optimized for this target relative humidity. The target relative humidity may depend on the operating conditions of the fuel cell stack 12 (e.g., current, pressure, temperature, etc.) and the fuel cell stack design. Different targets may exist for small and large fuel cell stack 12 areas, high and low fuel cell aspect ratios, and / or for different channel lengths. Therefore, the control system 190 in the fuel cell engine 101, which includes the fuel cell stack 12, can determine the target relative humidity based on several factors.

[0053] The ability to target very high humidity levels allows for a direct method of determining the saturation conditions of the fuel cell stack 12. Approximately 100% relative humidity provides mass balance, allowing the maximum amount of product water to be transferred into the exhaust stream without liquid obstruction and with high membrane saturation. This target can be varied slightly from approximately 90% to approximately 110%, as the benefit of either outlier can yield favorable results.

[0054] A slightly drier fuel cell stack 12 outlet produces a very high average fuel cell oxygen supply, and the low current (where proton resistance is not an issue) contributes to longer cell life. A slightly wetter fuel cell stack 12 outlet allows for more active proton conductivity, which promotes high cell power density and is permissible over short durations.

[0055] In some embodiments, the relative humidity sensor 110 may be placed as close as possible to the outlet of the fuel cell stack 12 on the cathode side. In this location, the relative humidity reading determined by the relative humidity sensor 110 may be substantially equal to the relative humidity experienced at the outlet side of the fuel cell stack 12. The reading of the relative humidity sensor 110 can be used to control the air subsystem or cathode air system 94 to achieve a target relative humidity. The outlet relative humidity may be estimated from the operating conditions of the fuel cell stack 12.

[0056] In one embodiment, such as Figure 3 As shown, the fuel cell engine 200 may include a fuel cell stack 12. A relative humidity sensor 110 may be positioned downstream of the heat exchanger 210 at the cathode exhaust port 106. The heat exchanger 210 may be used to increase the temperature of the cathode exhaust 108 by a determined amount using temperature sensors 212, 214 upstream and downstream of the heat exchanger 210.

[0057] The temperature of the cathode exhaust 108 can be increased based on the temperature of the coolant 216 from the coolant supply source 202. Changes in air temperature can reduce the relative humidity of the cathode exhaust 108 by a predictable percentage. In some embodiments, the change in relative humidity can be used to introduce an offset from the actual relative humidity percentage of the cathode exhaust 108 from the regulated heat exchanger exhaust air 208.

[0058] When the relative humidity of the cathode exhaust 108 exceeds 100%, the liquid water formed due to condensation can be disregarded by the relative humidity sensor 110. The cathode exhaust 108 with a relative humidity greater than 100% can still be measured by shifting the relative humidity by changing the air temperature. This can be done by measuring the outlet relative humidity from the heat exchanger 210 and applying the shift value to the measurement. For example, if the measurement is approximately 90% RH and the shift is approximately 20% RH, the water content at the cathode air exhaust 108 could be approximately 110% RH.

[0059] In one embodiment, such as Figure 4 As shown, the fuel cell engine 300 may include a fuel cell stack 12 and a fuel cell 20. An available air bearing exhaust stream 308, utilizing an air compressor 310 in a high-pressure air system, may be used. The air bearing exhaust stream 308 may consist of conditioned air with low relative humidity. The air bearing exhaust stream 308 may be introduced upstream of a relative humidity sensor 110 and may dilute the cathode exhaust stream 108. This dilution may be predicted based on the pressure ratio of the compressor 310 and may introduce a relative humidity offset proportional to the dilution ratio of the air bearing exhaust stream 308 to the cathode exhaust stream 108.

[0060] In one embodiment, such as Figure 5 As shown, the fuel cell engine 400 may include a fuel cell stack 12 and a fuel cell 20. Regulated process air 410 in the bypass airflow 408 of the cathode air system 94 may be used in the fuel cell engine 400, and the bypass airflow 408 may be introduced upstream of the relative humidity sensor 110 to dilute the cathode exhaust flow 108.

[0061] In some embodiments, the virtual relative humidity sensor 111 may be used in conjunction with the relative humidity sensor 110 or as an alternative to the relative humidity sensor 110. The virtual relative humidity sensor 111 may be located on the fuel cell stack 12 or configured to be connected to a computer system or controller of the fuel cell stack 12. The virtual relative humidity sensor 111 may be a sensor that is separate from, not connected to, and / or indirectly connected to the fuel cell stack 12.

[0062] The virtual relative humidity sensor 111 can be controlled manually by a user or operator. The virtual relative humidity sensor 111 can also be controlled automatically, electronically, or in real time. In some embodiments, the virtual relative humidity sensor 111 can be implemented based on mathematical modeling or computer or mathematical algorithms contained in the processor of any such controller or computing device.

[0063] For example, operating pressure, temperature, inlet air mass flow rate of fuel cell stack 12, and / or current generated by fuel cell stack 12 can be measured. The virtual relative humidity sensor 111 can use the measured values ​​as input. Target values ​​for the operation of fuel cell stack 12 can be adjusted to achieve a target relative humidity. In some embodiments, the use of the virtual relative humidity sensor 111 can complement mapping-based methods.

[0064] In one embodiment, the relative humidity sensor 110 may be used in conjunction with a virtual relative humidity sensor for diagnostic purposes. For example, the operating state of the fuel cell stack 12 can be used to estimate the expected relative humidity at the cathode exhaust port 106. This expected value can be compared with the actual relative humidity at the cathode exhaust port 106.

[0065] In one embodiment, such as Figure 6 As shown, the fuel cell engine 500 may include a fuel cell stack 12 and a fuel cell 20. A wide-range λ sensor or an O2 sensor 510 may be used instead of the relative humidity sensor 110, and the wide-range λ sensor 510 can determine the measured value of the oxygen concentration in the cathode exhaust stream 108.

[0066] Since the excess air ratio is predetermined for different operating points of the fuel cell stack 12, the oxygen concentration measurement can be compared with the excess air ratio to determine whether the reaction is occurring at the expected rate. If the oxygen concentration exceeds the expected oxygen concentration, the reaction at the fuel cell stack 12 may be lower than expected. Parameters of the cathode air system 94, such as pressure and / or mass flow rate, can be manipulated based on oxygen sensor readings and target oxygen concentration to maintain the reaction in the fuel cell stack 12 at an optimal rate.

[0067] Internal combustion engines use a λ sensor or oxygen sensor to measure the actual air-fuel ratio during combustion. Although combustion occurs minimally or not at all in the fuel cell stack 12, a wide-range λ sensor 510 can be used to determine the ratio of reactants during the reaction in the fuel cell stack 12 and to control the operation of the fuel cell stack 12. The λ sensor 510 can be used in place of one or more switching sensors or as an alternative.

[0068] If the fuel cell stack 12 has an excess air ratio greater than approximately 1.5 (λ) _AIR For operation, these switch sensors typically provide a nominal excess air ratio (λ) of approximately 1.0. _AIR The digital output is provided below. The control system 190 can measure the relative humidity of the cathode exhaust 108 and control the operation of the fuel cell stack 12 to ensure that the target relative humidity is achieved. The control system 190 can also self-tune each fuel cell motor 500 for optimal operation.

[0069] If a significant difference exists, diagnostic methods can be used to assess the cause of the difference. In some embodiments, diagnostic methods may include pressure sensor 219, temperature sensors 212, 214, mass flow sensor 221, and / or relative humidity sensor 110. In other embodiments, such as Figure 5 As shown, diagnostic methods may include sensor 560 to determine any air leaks in the bypass flow or elsewhere in the fuel cell stack 12.

[0070] In one embodiment, such as Figure 7 As shown, the fuel cell engine 600 may include a separate cathode exhaust line or relative humidity bypass line 608 dedicated to relative humidity sensing. In some embodiments, the separate cathode line or relative humidity bypass line 608 may be configured to be connected in parallel with the normal cathode exhaust 108. In other embodiments, the separate cathode line or relative humidity bypass line 608 may be used to isolate the relative humidity sensor 110. In some embodiments, a heater 210 (e.g., a resistance heater) may be used to change (e.g., increase or decrease) the temperature of the air by a set amount within the separate cathode line or relative humidity bypass line 608.

[0071] A change in temperature can cause a predictable percentage decrease in relative humidity at relative humidity sensor 110. In some embodiments, the temperature change may be calculated based on the constant presence of water and / or a changing air temperature. This change in relative humidity can be used to keep the reading of relative humidity sensor 110 below an upper limit of relative humidity sensor 110, typically around 100%, when the actual cathode relative humidity exceeds 100%. In some embodiments, the measured relative humidity may be shifted into the highest accuracy band of relative humidity sensor 110.

[0072] like Figure 2 As shown, the fuel cell stack 12 may be supported by a fuel handling subsystem or anode fuel system 92, an air handling subsystem or cathode air system 94, and / or a coolant subsystem 96. These components of the fuel cell stack 12 enable electrochemical reactions and / or determine the operation of the fuel cell stack 12. The fuel handling subsystem or anode fuel system 92 may take into account several factors such as excess fuel ratio, fuel pressure, recirculation flow rate, and / or anode-cathode pressure difference to achieve fuel cell stack operation.

[0073] like Figure 2As shown, the anode fuel system 92 may be supplied by a pressurized storage carrier or container 97. Pressure control of the storage container 97 can serve as the primary control mechanism for the anode fuel system 92. In some embodiments, the anode gas flow 112 may form a recirculation loop, wherein anode gas can be continuously contained within the anode fuel system 92. This is the case unless fuel 32 is consumed during the electrochemical reaction or removed by an auxiliary purging event. In other embodiments, a fuel recirculation blower 99 may be employed to facilitate the recirculation of the anode gas flow 112.

[0074] In one embodiment, the cathode air system 94 may operate with an excess air ratio, and the anode fuel system 92 may operate with an excess fuel ratio. The anode fuel system 92 may function to ensure that the pressure of the anode gas flow 122 is such that the pressure difference between the anode 114 and the cathode 116 is in the range of about 30 kPa to about 45 kPa, including any specific pressure difference or range included herein. Additionally or alternatively, the anode fuel system 92 may function to ensure that the flow rate of the anode gas flow 122, or the supply and recirculation of fuel, is sufficient for the reaction rate of the electrochemical reaction and the required excess fuel ratio.

[0075] In some embodiments, water may accumulate in the anode recirculation path during the electrochemical reaction. The accumulated water may be drained during a purging process, during which the anode recirculation loop may be temporarily vented to the atmosphere. The purging duty cycle may include about 0.5% to about 1% of the flow, about 1% to about 3% of the flow, or about 3% to about 5% of the flow, including any specific percentage or range included in any such range. The purging duty cycle has a minimal impact on the operating conditions of the fuel cell stack.

[0076] In one embodiment, active control of one or more subsystems, such as the fuel handling subsystem or anode fuel system 92, the air handling subsystem or cathode air system 94, and / or the coolant subsystem 96, may be required for the efficient and effective operation of the fuel cell engine 101, 200, 300, 400, 500, 600. In some embodiments, the design of the fuel cell stack 12, the specific selection of the MEA 22, and / or the lifetime of the fuel cell stack 12 may be critical to the efficient and effective operation of the fuel cell engine 101, 200, 300, 400, 500, 600. In other embodiments, the operating conditions of the fuel cell stack 12 (such as mass flow rate, pressure, temperature, and electrical load) may be critical to the efficient and effective operation of the fuel cell engine 101, 200, 300, 400, 500, 600.

[0077] The method for determining the optimal operation of the fuel cell stack 12 can use a predetermined mapping and can take into account the amount of water vapor in the exhaust flow of the fuel cell stack 12 or the cathode exhaust 108 without directly considering it.

[0078] Methods for controlling and / or determining optimal operation of fuel cell engines 101, 200, 300, 400, 500, 600, or fuel cell stack 12 may include a control system 190 using a control algorithm to control the fuel cell stack 12. The control algorithm may include the reaction rate of the fuel cell stack 12. The reaction rate may be controlled by controlling the mass flow rate and pressure of the cathode airflow 102, the temperature of the fuel cell stack coolant 36, and / or the electrical output (e.g., current and voltage) of the fuel cell stack 12. In some other embodiments, the integral of the reaction rate of the electrochemical reactions in the fuel cell stack 12 may include the current generated by the fuel cell stack 12 minus any parasitic reactions. Alternatively, parasitic reactions in the fuel cell stack 12 may be minimized.

[0079] Methods for controlling and / or determining optimal operation of fuel cell engines 101, 200, 300, 400, 500, 600 or fuel cell stack 12 may include a control system 190 using a predetermined lookup table or mapping based on variables such as pressure, temperature, and / or airflow. The predetermined lookup table or mapping may be based on experimentally optimized conditions used to establish feedforward objectives. The predetermined lookup table or mapping may be based on experimental tuning. The predetermined lookup table or mapping can be used to predictively respond to changing load conditions to optimize the performance and durability of the fuel cell stack 12. The predetermined lookup table or mapping may be calibrated based on test data obtained by varying pressure, temperature, and / or airflow.

[0080] Methods for controlling and / or determining the optimal operation of fuel cell engines 101, 200, 300, 400, 500, and 600 may be based on tuning the fuel cell stack 12 included in fuel cell engine 101 to maximize the output power of fuel cell stack 12 during testing. Methods for controlling and / or determining the optimal operation of fuel cell engines 101, 200, 300, 400, 500, and 600 may include a control system 190 directly controlling the operating states of one or more fuel cell stacks 12, such as steady-state power output, instantaneous power output, fuel cell stack startup, fuel cell stack shutdown, and / or fuel cell stack recovery. Methods for controlling and / or determining the optimal operation of fuel cell engines 101, 200, 300, 400, 500, and 600 may be implemented to prevent reversible and / or permanent damage to fuel cell stack 12.

[0081] One or more subsystems supporting the fuel cell stack 12 (such as the coolant subsystem 96 and / or any auxiliary subsystems 92, 94) may function in response to the cathode air system 94 and / or the anode fuel system 92. In some embodiments, one or more subsystems supporting the fuel cell stack 12 (such as the coolant subsystem 96 and / or any auxiliary subsystems 92, 94) may typically not have priority in any fuel cell engine control algorithm. The coolant system 96 may control the temperature of the fuel cell stack 12. In some other embodiments, a booster air cooler 98 may be used to regulate the cathode air to a temperature close to the fuel cell stack coolant temperature, and / or may enable the cathode air to operate at temperatures above or below the fuel cell stack coolant temperature.

[0082] Methods for controlling and / or determining optimal operation of the fuel cell engine 101, 200, 300, 400, 500, 600, or fuel cell stack 12 may include a control system 190 implementing an algorithm focused on pressure control. The pressure of the cathode air system 94 may be adjusted to increase or decrease the water content in the cathode exhaust 108. Relative humidity may be used to measure this water content. The water concentration may be measured directly or estimated based on measurements of oxygen or nitrogen in the cathode exhaust 108.

[0083] The target relative humidity, mass flow rate in the cathode exhaust 108, and / or the target temperature of the cathode air system 94 can be determined by the current density of the fuel cell stack 12. In some embodiments, the target relative humidity, mass flow rate in the cathode exhaust 108, and / or the target temperature of the cathode air system 94 can be determined by using a predefined lookup table or mapping.

[0084] Methods for controlling and / or determining optimal operation of the fuel cell engine 101, 200, 300, 400, 500, 600, or fuel cell stack 12 may include the control system 190 implementing an algorithm focused on mass flow control. The mass flow rate of the cathode air system 94 may be adjusted to compensate for current demand, varying excess air ratios, and / or fuel cell stack outlet humidity. In some embodiments, the excess air ratio may be increased or decreased by the control system 190.

[0085] Increasing the excess air ratio can increase the oxygen or oxidant concentration at the reaction site because less overall oxygen or oxidant is consumed during the reaction. Increasing the excess air ratio can increase the reaction at the reaction site and / or reduce the relative humidity in the cathode exhaust 108. In some embodiments, the pressure and temperature of the cathode air system 94 can be determined using a predetermined lookup table or mapping based on the current density of the fuel cell stack 12.

[0086] Methods for controlling and / or determining optimal operation of the fuel cell engine 101, 200, 300, 400, 500, 600, or fuel cell stack 12 may include a control system implementing temperature control. The temperature of the fuel cell stack coolant 36 and / or the intake booster air cooler coolant may be regulated in the coolant subsystem 96. Changing the temperature of the cathode air system 94 alters its ability to retain water vapor, and thus changes the relative humidity in the cathode exhaust 108. In some embodiments, the pressure and mass flow rate of the cathode air system 94 may be determined using a predetermined lookup table or mapping based on the current density of the fuel cell stack 12.

[0087] Methods for controlling and / or determining optimal operation of the fuel cell engine 101, 200, 300, 400, 500, 600 or fuel cell stack 12 can be implemented using sensors. In some embodiments, the sensors can be any type of sensor 212, 214, 210, 219, 221 (e.g., temperature, pressure, current, voltage, flow rate, etc.). In some exemplary embodiments, the sensor is a relative humidity sensor 210. In other embodiments, the sensor can be used to directly measure the water concentration in the cathode exhaust gas, or it can be estimated based on oxygen or nitrogen measurements in the cathode exhaust gas 108.

[0088] In one embodiment, the relative humidity sensor 110 can be used to operate the fuel cell stack 12 when the relative humidity in the cathode exhaust 108 is approximately 100%. In some embodiments, the relative humidity sensor 110 may not detect a situation where the actual water content in the cathode exhaust 108 exceeds approximately 100%. In some embodiments, to verify operation of the fuel cell stack 12 with approximately 100% relative humidity in the cathode exhaust 108, the fuel cell engines 101, 200, 300, 400, 500, and 600 can be perturbed by reducing the cathode pressure by a predetermined amount. Reducing the cathode pressure by a predetermined amount can have a predetermined effect on the relative humidity in the cathode exhaust 108.

[0089] A disturbance can cause a change in the measured relative humidity in the cathode exhaust 108. The actual relative humidity percentage in the cathode exhaust 108 can be compared with the expected relative humidity percentage in the cathode exhaust 108. If the expected and actual relative humidity percentages in the cathode exhaust 108 are equal, the operation of the fuel cell stack 12 can be determined to be at approximately 100% relative humidity prior to the disturbance. If the actual relative humidity percentage in the cathode exhaust 108 is greater than the expected relative humidity percentage, the fuel cell stack 12 can be determined to be operating at a relative humidity greater than approximately 100%.

[0090] Water condensation can occur if the fuel cell stack 12 operates at a relative humidity greater than approximately 100%. However, the water vapor content must not exceed 100% relative humidity before condensation of liquid water is thermodynamically favorable. Therefore, it can be assumed that condensation will generally occur.

[0091] Thermodynamically, water in condensation form is advantageous when the partial pressure of water is greater than the saturation pressure. Kinetics can play a role in determining liquid-vapor-water separation. For example, if the condensation rate is relatively slow, the cathode airflow 102 can be supersaturated (i.e., the relative humidity can be greater than about 100%).

[0092] The difference between the expected and actual relative humidity percentage in the cathode exhaust 108 can be used to offset or alter the operation of the cathode air system 94. This difference can also be used to ensure that the fuel cell stack 12 operates at approximately 100% relative humidity. Disturbed humidity measurements can be performed periodically to ensure accurate metering of the relative humidity in the cathode exhaust.

[0093] The target relative humidity in the cathode exhaust 108 can be determined and / or adjusted by implementing different methods. Methods for determining the target relative humidity in the cathode exhaust 108 may include a controller balancing short-term and long-term demands of the fuel cell stack 12 as input from users (e.g., operators, customers, etc.). Balancing the short-term and long-term demands of the fuel cell stack 12 may include evaluating the immediate performance of the fuel cell stack 12 and its long-term durability.

[0094] A lower relative humidity value in the cathode exhaust 108, ranging from approximately 90% to approximately 120% (including any specific or range of relative humidity described herein), supports long-term operation of the fuel cell stack 12. Under this operating condition, a reduced chance of overflow increases the likelihood of reactants remaining at reaction sites, thereby further reducing the chance of fuel shortage and / or subsequent damage to the fuel cell stack 12. A higher relative humidity value in the cathode exhaust, approximately 110%, increases the likelihood of increased membrane proton conductivity, which can improve the overall performance of the fuel cell stack 12.

[0095] Increased hydration in or near the fuel cell stack 12 can increase localized overflow, particularly towards the cathode. Localized overflow can cause localized fuel shortage and thus localized degradation. Localized degradation may not affect the immediate performance of the fuel cell stack 12, but it can negatively impact its long-term aging.

[0096] In one embodiment, the main variables used for humidity control may include flow rate, pressure, and / or temperature. As the fuel cell stack 12 ages and the effectiveness of the catalyst used in the fuel cell stack 12 decreases, increasing the excess air ratio to achieve the rated current may be advantageous. This modification may also affect the other two variables (i.e., pressure and temperature) because they are inherently related to the determination of the desired relative humidity.

[0097] When the inlet moisture content is variable, implementing methods for monitoring and / or controlling cathode outlet humidity can be important. Monitoring and / or controlling outlet humidity can be crucial in mobile applications when the atmosphere becomes very hot and humid and / or when the fuel cell engine is equipped with a humidification system. Humidification systems are widely used in fuel cell stacks 12 for a variety of reasons, including cell stability and / or achieving high power density. Cost, complexity, and the possibility of failure have led to the development of non-humidified fuel cell architectures at the expense of reduced power density.

[0098] A relative humidity sensor 110, which monitors the relative humidity at the cathode exhaust 108 of the fuel cell stack 12, ensures that the cathode inlet port 104 is not oversaturated and subsequently overflows to the cathode outlet or cathode exhaust port 106. Benefits of a humidification system that includes humidifying the cathode airflow 102 may include increased power density and minimized membrane drying effects. Additional benefits of the humidification system include reduced cathode inlet losses associated with excessively dry air or high cathode stoichiometry.

[0099] A relative humidity sensor 110, which monitors the relative humidity at the cathode exhaust of the fuel cell stack, allows the fuel cell stack 12 to operate in a manner that benefits from the humidification system, while simultaneously monitoring outlet conditions (i.e., preventing overflow and any premature aging effects caused by excessive humidity). Using relative humidity metering at the cathode exhaust of the fuel cell stack allows for closed-loop optimization of the operation of the fuel cell stack 12.

[0100] This method can be used to accurately determine relative humidity readings when the relative humidity at fuel cell stack outlet 108 is greater than approximately 100%. In some embodiments, the method may include reducing the pressure upstream of the relative humidity sensor 110 in an enthalpy manner. In one embodiment, such as Figure 7 As shown, the fuel cell engine 600 may include a fuel cell stack 12, a relative humidity sensor 110, and a heat exchanger 210. This disclosed method allows for a reduction in relative humidity by lowering the total pressure of the exhaust mixture 208 without removing any energy from the flow, as the state will transition to a state closer to the vapor phase.

[0101] The following aspects of the invention are contemplated and non-limiting:

[0102] A first aspect of the present invention relates to a fuel cell system (also referred to as a fuel cell stack system). The fuel cell system includes an anode and a cathode, a cathode inlet port, a cathode exhaust port, a cathode inlet airflow, and a cathode exhaust flow. The fuel cell system also includes a sensor in the cathode exhaust flow for detecting, measuring, and / or determining a water content reading in the cathode exhaust flow, and a controller for determining the operation of the fuel cell stack based on the water content reading.

[0103] A second aspect of the invention relates to a fuel cell system. The fuel cell system includes a fuel cell stack, which includes an anode, a cathode, a cathode inlet port, a cathode exhaust port, a cathode inlet airflow, and a cathode exhaust flow. The fuel cell system further includes a wide-range λ sensor in the cathode exhaust flow for detecting, determining, and / or measuring the oxygen concentration in the cathode exhaust flow, and a controller for determining the operation of the fuel cell stack based on the measured oxygen concentration and a target oxygen concentration.

[0104] In a third aspect of this disclosure, a method of operating a fuel cell system includes the steps of: determining a target water content or target relative humidity of the cathode exhaust stream based on the current density of the fuel cell stack; using or utilizing a first sensor to determine the water content of the cathode exhaust stream; and adjusting the cathode system by implementing a controller to increase or decrease the determined water content of the cathode exhaust stream based on the target water content or target relative humidity of the cathode exhaust stream.

[0105] In some embodiments, the first sensor may be a relative humidity sensor, and the method may further include detecting a relative humidity reading using the relative humidity sensor. In some embodiments, adjusting the cathode system may further include: determining a target pressure or target temperature of the cathode exhaust flow based on the current density of the fuel cell stack; measuring the current pressure or current temperature in the cathode exhaust flow using a second sensor; changing the current pressure based on the target pressure in the cathode exhaust flow; changing the current temperature in the cathode exhaust flow based on the target temperature; changing the mass flow rate in the cathode system; or changing the temperature of the cathode exhaust flow.

[0106] In the first and / or second aspect of the invention, the sensor may be a relative humidity sensor, and the water content reading may be a relative humidity reading, including the water vapor content reading in the cathode exhaust stream. In the first and / or second aspect of the invention, the controller may use closed-loop optimization of the fuel cell stack based on the relative humidity reading when determining the operation of the fuel cell stack.

[0107] In the first and / or second aspects of the invention, the cathode inlet airflow may be humidified.

[0108] In a first and / or second aspect of the invention, the relative humidity sensor may be located at the cathode exhaust port. In a first and / or second aspect of the invention, the system may further include a heat exchanger located downstream of the cathode exhaust port. The relative humidity sensor may be positioned downstream of the heat exchanger at the cathode exhaust port.

[0109] In a first and / or second aspect of the invention, the system may further include an air compressor. The air compressor may provide conditioned air upstream of the relative humidity sensor and dilute the cathode exhaust stream. The dilution of the cathode exhaust stream may be based on the pressure ratio of the air compressor. The dilution of the cathode exhaust stream may introduce a relative humidity offset proportional to the dilution ratio of the conditioned air to the cathode outlet exhaust. In a first and / or second aspect of the invention, the conditioned air may be introduced upstream of the relative humidity sensor.

[0110] In a first and / or second aspect of the invention, the relative humidity sensor may be a dummy relative humidity sensor. In a first and / or second aspect of the invention, a bypass airflow may be introduced upstream of the relative humidity sensor to dilute the cathode exhaust flow. In a first and / or second aspect of the invention, the relative humidity sensor may be located on a separate cathode exhaust line including a heater. The heater may increase the air temperature in the separate cathode exhaust line by a set amount.

[0111] In a first and / or second aspect of the invention, the sensor can determine the water content in the cathode exhaust stream based on measurements of oxygen and nitrogen in the cathode exhaust stream.

[0112] In a third aspect of the invention, the sensor may be a relative humidity sensor, and the method may further include detecting a relative humidity reading using the relative humidity sensor. In a third aspect of the invention, adjusting the cathode system may further include adjusting the pressure in the cathode exhaust stream, the mass flow rate in the cathode system, or the temperature of the cathode exhaust stream.

[0113] In a third aspect of the invention, the method may include a disturbance system to induce a change in the water content reading of a sensor in the cathode exhaust stream, comparing the change in water content reading with a expected water content reading in the cathode exhaust stream caused by the disturbance. If the change in water content reading in the cathode exhaust stream is greater than the expected water content reading in the cathode exhaust stream, it can be determined that the fuel cell stack and / or system is operating at a relative humidity greater than about 100%. In the third aspect of the invention, the difference between the change in water content reading in the cathode exhaust stream and the expected water content reading in the cathode exhaust stream can be used to offset the operation of the fuel cell stack and / or system to ensure that the fuel cell stack and / or system operates at about 100% relative humidity.

[0114] In a third aspect of the invention, the method may further include a sensor for detecting, measuring, and / or determining the water content in the cathode exhaust stream based on oxygen and nitrogen measurements in the cathode exhaust stream. In a third aspect of the invention, the system may further include a heat exchanger located downstream of the cathode exhaust port. A relative humidity sensor may be positioned downstream of the heat exchanger at the cathode exhaust port.

[0115] Features illustrated or described in connection with an exemplary embodiment may be combined with any other features or elements of any other embodiment described herein. Such modifications and variations are intended to be included within the scope of this disclosure. Furthermore, those skilled in the art will recognize that terms well-known to those skilled in the art may be used interchangeably herein.

[0116] The above embodiments have been described in sufficient detail to enable those skilled in the art to practice the claims, and it will be understood that logical, mechanical, and electrical changes may be made without departing from the spirit and scope of the claims. Therefore, the detailed description will not be limited in meaning.

[0117] As used herein, elements or steps described in the singular and beginning with the words “a” or “an” should be understood as not excluding a plurality of the said elements or steps, unless such exclusion is expressly stated. Furthermore, references to “one embodiment” in the subject matter currently described are not intended to be construed as excluding the existence of additional embodiments also incorporated into the described features. Specifying numerical ranges of units, measurements, and / or values ​​includes all numerical values, units, measurements, and / or ranges that include, are substantially composed of, or are comprised of those ranges and / or endpoints, or are within those ranges, whether or not those numerical values, units, measurements, and / or ranges are expressly specified in this disclosure.

[0118] Unless otherwise specified, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. The terms “first,” “second,” “third,” etc., as used herein, do not indicate any order or importance, but are used to distinguish one element from another. The term “or” is intended to be inclusive and refers to any or all of the listed items. Furthermore, the terms “connection” and “linkage” are not limited to physical or mechanical connections or linkages, and may include direct or indirect electrical connections or linkages.

[0119] Furthermore, unless explicitly stated otherwise, embodiments that "comprising," "include," or "have" one or more elements with a particular property may include additional such elements that do not have that property. The terms "comprising" or "comprises" are inclusive and do not exclude additional elements, components, and / or method steps in a composition, compound, formulation, or method of this disclosure. The term "comprising" also refers to embodiments of compositions, compounds, formulations, or methods of this disclosure that are inclusive and do not exclude additional elements, components, or method steps.

[0120] The phrase "consisting of" or "consists of" refers to a compound, composition, formulation, or method that excludes the presence of any additional elements, components, or method steps. The term "consisting of" also refers to the compound, composition, formulation, or method of this disclosure that excludes the presence of any additional elements, components, or method steps.

[0121] The phrase "consisting essentially of" or "consists essentially of" refers to a composition, compound, formulation, or method that includes additional elements, components, or method steps that do not substantially affect the properties of the composition, compound, formulation, or method. The phrase "consisting essentially of" also refers to the compositions, compounds, formulations, or methods of this disclosure that include additional elements, components, or method steps that do not substantially affect the properties of the composition, compound, formulation, or method.

[0122] As used herein and throughout the specification and claims, approximate language may be applied to modify any quantitative expression that may be varied without altering its underlying function. Therefore, a value modified by one or more terms such as “about” and “substantially” is not limited to the specified precise value. In some cases, approximate language may correspond to the precision of the instrument used to measure that value. Scope limitations may be combined and / or interchanged herein and throughout the specification and claims. Unless otherwise indicated by context or language, such scopes are identified and include all subscopes contained herein.

[0123] As used herein, the terms “may” and “may” indicate the possibility of occurring within a set of circumstances; possess a specified quality, characteristic, or function; and / or limit another verb by expressing one or more of the capacity, capacity, or possibility associated with the limiting verb. Therefore, the use of “may” and “may” indicates that the modified term is clearly appropriate, capable, or suitable for the indicated capacity, function, or use, while taking into account that in some cases the modified term may sometimes be inappropriate, incapable, or unsuitable.

[0124] It will be understood that the above description is intended to be illustrative and not restrictive. For example, the above embodiments (and / or aspects thereof) may be used alone, together, or in combination with each other. Furthermore, many modifications may be made to suit particular situations or materials to the teachings of the subject matter set forth herein without departing from its scope. While the dimensions and types of materials described herein are intended to define parameters of the disclosed subject matter, they are by no means limiting and are exemplary embodiments. Many other embodiments will become apparent to those skilled in the art upon review of the above description. Therefore, the scope of the subject matter described herein should be determined by reference to the appended claims together with the full scope of equivalents enjoyed by such claims.

[0125] This written description uses examples to disclose several embodiments (including best modes) of the subject matter set forth herein, and also enables those skilled in the art to practice embodiments of the disclosed subject matter (including making and using apparatus or systems and performing methods). The patentability of the subject matter described herein is defined by the claims, and may include other examples that would occur to those skilled in the art. Such other embodiments are intended to be within the scope of the claims if they have structural elements that are no different from the written language of the claims, or if such other embodiments include equivalent structural elements that are not substantially different from the written language of the claims.

[0126] While only certain features of the invention have been illustrated and described herein, many modifications and alterations will occur to those skilled in the art. Therefore, it will be understood that the appended claims are intended to cover all such modifications and alterations that fall within the true spirit of the invention.

Claims

1. A fuel cell system comprising: a fuel cell stack comprising an anode and a cathode, a cathode inlet port, a cathode exhaust port, a cathode inlet air stream, and a cathode exhaust stream, a heat exchanger downstream of the cathode exhaust port, wherein the heat exchanger is configured to increase a temperature of the cathode exhaust stream and to reduce a water content of the cathode exhaust stream, a sensor positioned downstream of the heat exchanger and in the cathode exhaust stream for detecting a water content reading of the cathode exhaust stream, the sensor being a relative humidity sensor, and a controller for determining an operation of the fuel cell stack based on the water content reading, and wherein a bypass air stream is introduced upstream of the relative humidity sensor to dilute the cathode exhaust stream.

2. The fuel cell system according to claim 1, wherein The water content reading is a relative humidity reading, the relative humidity reading comprising a water vapor content reading in the cathode exhaust stream.

3. The fuel cell system of claim 2, wherein, The controller uses a closed loop optimization of the fuel cell stack based on the relative humidity reading in determining the operation of the fuel cell stack.

4. The fuel cell system of claim 1, wherein, The relative humidity sensor is located at the cathode exhaust port.

5. The fuel cell system of claim 2, further comprising a first temperature sensor positioned upstream of the heat exchanger and a second temperature sensor positioned downstream of the heat exchanger, wherein, The heat exchanger is configured to increase the temperature of the cathode exhaust stream based on the first temperature sensor and the second temperature sensor.

6. The fuel cell system of claim 2, further comprising an air compressor, wherein the air compressor is configured to provide conditioned air upstream of the relative humidity sensor and to dilute the cathode exhaust stream, wherein, The air compressor is configured to dilute the cathode exhaust stream based on a pressure ratio of the air compressor.

7. The fuel cell system of claim 6, wherein, The conditioned air is introduced upstream of the relative humidity sensor.

8. The fuel cell system of claim 2, wherein, The relative humidity sensor is located on a separate cathode exhaust line comprising a heater, and wherein the heater increases an air temperature in the separate cathode exhaust line by a set amount.

9. The fuel cell system of claim 1, wherein, The system further comprises: a wide range lambda sensor in the cathode exhaust stream configured for detecting an oxygen concentration of the cathode exhaust stream.

10. A method of operating a fuel cell stack comprising: determining a target water content or a target relative humidity of a cathode exhaust stream based on a current density of the fuel cell stack, increasing a temperature of the cathode exhaust stream and reducing a water content of the cathode exhaust stream by implementing a heat exchanger downstream of a cathode exhaust port, wherein the heat exchanger reduces a pressure upstream of a relative humidity sensor in an enthalpy manner, wherein a bypass air stream is introduced upstream of the relative humidity sensor to dilute the cathode exhaust stream, and measuring the water content of the cathode exhaust stream with a first sensor, and adjusting a cathode system by implementing a controller to increase or decrease a measured water content of the cathode exhaust stream based on the target water content or the target relative humidity of the cathode exhaust stream.

11. The method of claim 10, wherein, The first sensor is a relative humidity sensor, and the method further comprises detecting a relative humidity reading with the relative humidity sensor.

12. The method of claim 10, wherein, Adjusting the cathode system further includes determining a target pressure or a target temperature of a cathode exhaust stream based on a current density of the fuel cell stack, measuring a current pressure or a current temperature in the cathode exhaust stream with a second sensor, changing the current pressure based on the target pressure in the cathode exhaust stream, changing the current temperature in the cathode exhaust stream based on the target temperature, changing a mass flow rate in the cathode system, or changing a temperature of the cathode exhaust stream.

13. The method of claim 10, further comprising perturbing the system to cause a change in the water content reading of the first sensor in the cathode exhaust stream, comparing the change in the water content reading to an expected water content reading in the cathode exhaust stream due to the perturbation, wherein if the change in the water content reading in the cathode exhaust stream is greater than the expected water content reading in the cathode exhaust stream, determining that the fuel cell stack is operating at about 100% relative humidity.

14. The method of claim 13, further comprising using a difference between the change in the water content reading in the cathode exhaust stream and the expected water content reading in the cathode exhaust stream to offset operation of the fuel cell stack to ensure that the fuel cell stack is operating at about 100% relative humidity.

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