KR102746643B1 - Methods and systems for controlling water imbalance in electrochemical cells - Google Patents

Abstract

A system and method for controlling water imbalance in an electrochemical cell are provided. The method can include the step of determining a current water imbalance in the electrochemical cell by summing the values of water _in and water _created minus water _out . water _in represents the amount of water introduced into the electrochemical cell by the oxidizer feed gas; water _created represents the amount of water produced by the electrochemical cell in the electrochemical reaction; and water _out represents the amount of water discharged from the electrochemical cell by the oxidizer exhaust gas. The method includes the step of tracking an accumulated water imbalance during operation of the electrochemical cell by repeatedly determining the current water imbalance and continuously summing the results during operation. The method also includes the step of adjusting a flow rate of oxidizer feed gas into the electrochemical cell based on the accumulated water imbalance.

Description

Methods and systems for controlling water imbalance in electrochemical cells

The present disclosure relates to electrochemical cells, and more particularly to methods and systems for controlling water imbalance in an electrochemical cell or stack of cells.

Electrochemical cells, commonly classified as fuel cells or electrolysis cells, are devices that produce electric current from chemical reactions, or use the flow of electric current to drive chemical reactions. For example, a fuel cell converts the chemical energy of a fuel (e.g., hydrogen, natural gas, methanol, gasoline, etc.) and an oxidizer (air or oxygen) into electricity and heat and water as a waste product. A basic fuel cell consists of a negatively charged anode, a positively charged cathode, and an ion-conducting material called an electrolyte.

Different fuel cell technologies use different electrolyte materials. Proton exchange membrane (PEM) fuel cells, for example, use polymer ion-conducting membranes as the electrolyte. In a hydrogen PEM fuel cell, hydrogen atoms are electrochemically separated at the anode into electrons and protons (hydrogen ions). The electrons then flow through a circuit to the cathode, generating electricity, while the protons diffuse through the electrolyte membrane to the cathode. At the cathode, the hydrogen protons combine with electrons and oxygen (supplied to the cathode) to produce water and heat.

An electrolysis cell is a fuel cell that operates in reverse. A basic electrolysis cell functions as a hydrogen generator by decomposing water into hydrogen and oxygen gases when an external potential is applied.

The basic technology of hydrogen fuel cells or electrolysis cells can be applied to electrochemical hydrogen manipulation, such as electrochemical hydrogen compression, purification or expansion. Electrochemical hydrogen manipulation has emerged as a viable alternative to the mechanical systems traditionally used for hydrogen management. The successful commercialization of hydrogen as an energy carrier and the long-term sustainability of the "hydrogen economy" largely depend on the efficiency and cost-effectiveness of fuel cells, electrolysis cells and other hydrogen manipulation/management systems.

In operation, a single fuel cell can typically produce about 1 volt. To obtain a desired amount of power, individual fuel cells are combined to form a fuel cell stack, with the fuel cells being stacked together sequentially.

As mentioned above, in addition to water being produced at the cathode as a byproduct of converting fuel and oxidizer to electricity, water may also be introduced into the cell as moisture/vapor in the oxidizer and/or fuel gases (collectively, “input gases”). And since electrochemical cells can operate under a variety of environmental conditions, the humidity (and other parameters, such as temperature) of the input gases may vary.

Water is typically removed from electrochemical cells by a depleted flow of reactant gases, such as oxygen. Inefficient removal of water can result in flooding of the electrochemical cell with water. Flooding of the electrochemical cell with water can result in a reduction or complete cessation of the flow of reactant gases. Excessive accumulation of water can result in failure of individual electrochemical cells, which can result in instability and/or failure of the electrochemical cell stack.

Although excess water in an electrochemical cell can adversely affect performance, water is necessary to support the operation of the cell. For example, the water content of a polymer membrane increases the ionic conductivity, which enables electrochemical reactions.

Attempts to maintain water balance or equilibrium (i.e., between flooded and dry conditions) have included, for example, correlating current output with water content and adjusting operation when current changes indicate changes in cell performance. However, these correlations do not take into account the rapidly changing equilibrium dynamics, and thus efforts to correct equilibrium may be too late or insufficient, resulting in degraded or even interrupted electrochemical cell performance.

In view of the need to maintain water content equilibrium in electrochemical cells, the present disclosure is directed to methods and systems designed to overcome one or more problems associated with existing water management technologies in electrochemical cells and electrochemical cell stacks.

In one aspect, the present disclosure relates to a method for controlling water imbalance in an electrochemical cell. In some embodiments, the method can include determining a current water imbalance in the electrochemical cell by summing water _in and water _created minus water _out . In some embodiments, water _in can be an amount of water introduced into the electrochemical cell by an oxidizer feed gas; water _created can be an amount of water produced by the electrochemical cell in the electrochemical reaction; and water _out can be an amount of water discharged from the electrochemical cell by the oxidizer exhaust gas. In some embodiments, the method can also include tracking a cumulative water imbalance during operation of the electrochemical cell by repeatedly determining the current water imbalance and summing the results during operation. And, in some embodiments, the method can also include adjusting a flow rate of oxidizer feed gas into the electrochemical cell based on the cumulative water imbalance.

In another aspect, the present disclosure relates to an electrochemical cell system. In some embodiments, the electrochemical cell system can include an electrochemical cell; a plurality of oxidizer gas inlet sensors, an oxidizer gas exhaust sensor, a coolant inlet sensor, a coolant exhaust sensor, and a current transducer; and a controller. In some embodiments, the controller can be configured to determine a current water imbalance in the electrochemical cell by summing water _in and water _created minus water _out . In some embodiments, water _in can be an amount of water introduced into the electrochemical cell by the oxidizer supply gas; water _created can be an amount of water produced by the electrochemical cell in the electrochemical reaction, and water _out can be an amount of water discharged from the electrochemical cell by the oxidizer exhaust gas. In some embodiments, the controller can also be configured to track a cumulative water imbalance during operation of the electrochemical cell by repeatedly determining the current water imbalance and summing the results during operation. Additionally, in some embodiments, the controller may also be configured to adjust the flow rate of oxidant supply gas into the electrochemical cell based on the accumulated water imbalance.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the claimed disclosure.

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

Figure 1 is a schematic diagram of an electrochemical cell system according to an exemplary embodiment.
FIG. 2 is a flow chart illustrating a method for controlling water imbalance in an electrochemical cell system according to an exemplary embodiment.
FIG. 3 is a flow chart illustrating a method for controlling water imbalance in an electrochemical cell system according to an exemplary embodiment, as a continuation of the flow chart of FIG. 2.

Reference will now be made in detail to exemplary embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, like reference numerals will be used throughout the drawings to refer to like or similar parts. While described with respect to an electrochemical cell, and particularly a fuel cell using hydrogen, oxygen and water, it is to be understood that the devices and methods of the present disclosure may be used in various types of fuel cells and electrochemical cells, including but not limited to electrolysis cells, hydrogen purifiers, hydrogen expanders and hydrogen compressors.

FIG. 1 illustrates a schematic diagram of an electrochemical cell system (100) according to an exemplary embodiment of the present disclosure. The electrochemical cell system (100) may include an electrochemical cell (10), which may be, for example, a PEM fuel cell, wherein the PEM fuel cell may have an anode and a cathode separated by an electrolyte. The system (100) may be configured to receive and expel an oxidizer gas (e.g., oxygen or ambient air), a reactant gas (e.g., hydrogen), and a coolant through the electrochemical cell (10). While FIG. 1 and the following description reference an electrochemical cell (10), it should be understood that the description is equally applicable to an electrochemical cell stack that may include a plurality of electrochemical cells (10).

The oxidizer gas may be delivered to the cathode of the electrochemical cell (10), while the fuel gas may be delivered to the anode of the electrochemical cell (10). A coolant may also be delivered to the coolant path of the electrochemical cell (10). The coolant may be supplied to the electrochemical cell (10) via a coolant inlet line (32A) by a coolant pump (44) and exhausted from the electrochemical cell (10) via a coolant outlet line (32B). The oxidizer gas may be supplied to the electrochemical cell (10) via the oxidizer gas inlet line (34A) and exhausted via the oxidizer gas exhaust line (34B). The oxidizer gas may be supplied to the oxidizer gas inlet line (34A) by a compressor (42) or other suitable device. In some embodiments, the compressor (42) may be supplied with the oxidizer (e.g., air) from the ambient environment or another suitable oxidizer source. Fuel gas may be supplied to the cell (10) through a fuel gas inlet line (36A) and may be exhausted through a fuel gas exhaust line (36B). The cell (10) may also include a current circuit (28) connected to an electrical load (30). In operation, the flow of oxidant and fuel gas through the respective inlet lines into the electrochemical cell (10) causes an electrochemical reaction in the electrolyte membrane separating the anode and cathode, thereby generating an electric current that is supplied to the electrical load (30) through the current circuit (28).

The electrochemical cell system (100) may include one or more coolant inlet sensors disposed along the coolant inlet line (32A) and one or more coolant outlet sensors disposed along the coolant outlet line (32B). For example, as illustrated in FIG. 2, the system (100) may include a coolant inlet sensor (20) configured to measure a coolant inlet temperature of coolant supplied to the electrochemical cell (10) via the coolant inlet line (32A). In some embodiments, the system (100) may include a coolant outlet sensor (22) configured to measure a coolant outlet temperature of coolant discharged from the electrochemical cell (10) via the coolant outlet line (32B). In some embodiments, other coolant inlet sensors and coolant outlet sensors may be used to measure other characteristics of the incoming and outgoing coolant. For example, additional temperature sensors, flow sensors, pressure sensors, or conductivity sensors may be used.

The electrochemical cell system (100) may also include one or more oxidizer gas inlet sensors positioned along the oxidizer gas inlet line (34A). According to an exemplary embodiment, the system (100) may include at least four oxidizer gas inlet sensors (24), namely, a first oxidizer gas inlet sensor (24A) for measuring an ambient pressure of the oxidizer feed gas, a second oxidizer gas inlet sensor (24B) for measuring an ambient temperature of the oxidizer feed gas, a third oxidizer gas inlet sensor (24C) for measuring an ambient humidity of the oxidizer feed gas, and a fourth oxidizer gas inlet sensor (24D) for measuring a mass flow rate of the oxidizer feed gas. In some embodiments, a single oxidizer gas inlet device may be used to measure several of these parameters. For example, in some embodiments, the oxidizer sensor (24) may measure the ambient pressure, the ambient temperature, and the humidity of the oxidizer feed gas as a single device. In some embodiments, the oxidizer gas inlet sensor (24) may measure ambient pressure, ambient temperature, oxidizer mass flow rate, and/or humidity of the oxidizer feed gas as a single device. In some embodiments, additional oxidizer gas inlet sensors (24) may be used to measure other properties of the incoming oxidizer feed gas. For example, in some embodiments, the oxidizer gas inlet sensor may be configured to measure oxidizer gas composition, or levels of contaminant species such as carbon monoxide, ammonia, sulfur, volatile organic compounds, and/or other species that may be detrimental to fuel cell operation and life.

The electrochemical cell system (100) may also include one or more oxidizer gas exhaust sensors (26) positioned along the oxidizer gas exhaust line (34B). For example, as illustrated in FIG. 2, the oxidizer gas exhaust sensors (28) may include at least one first oxidizer gas exhaust sensor (26A) for measuring the pressure of oxidizer gas exhausted from the electrochemical cell (10) via the oxidizer gas exhaust line (34B). In some embodiments, additional oxidizer gas exhaust sensors (24) may be used to measure other properties of the oxidizer gas exhausted from the electrochemical cell (10). For example, the system (100) may include a second oxidizer gas exhaust sensor (26B) for measuring the humidity of the oxidizer gas exhausted from the electrochemical cell (10). In other embodiments, oxidizer gas exhaust sensors may be used by the system (100) to measure the flow rate, temperature, or composition of oxidizer gas exhausted from the electrochemical cell (10).

Although not shown in FIG. 1, in some embodiments of the system (100), the fuel gas inlet line (36A) may include one or more fuel gas inlet sensors. These sensors may be configured to measure, for example, temperature, pressure, relative humidity, flow rate, etc. of the fuel supply gas supplied to the electrochemical cell (10). Similarly, the fuel gas exhaust line (36B) may include one or more fuel gas exhaust outlet sensors (not shown). These sensors may be useful for measuring, for example, temperature, pressure, relative humidity, flow rate, etc. of the fuel gas exhausted from the electrochemical cell (10).

As described above, current is generated by the cell (10) and supplied to the electrical load (30) through the current circuit (28). The current may be measured, for example, by a current transducer (46) connected to the current circuit (28). In some embodiments, the current transducer (46) may be, for example, a Hall-effect sensor or a shunt sensor. In some embodiments, the resistance across the electrochemical cell (10), the electrical circuit (28), and/or the electrochemical cell stack may be determined by measuring the cell or stack voltage in response to small changes in current. For example, the current may be perturbed using a high frequency waveform (sine, triangle, square, or other waveform) typically greater than 1000 Hz, or by rapidly connecting or disconnecting a load to the fuel cell stack in a stepwise manner (such as an electric heater or similar device, a "current interrupt" method). The resulting change in cell or stack voltage divided by the imposed change in current is typically proportional to the resistance according to Ohm's law. Specific voltage-current-resistance relationships for a particular fuel cell design can be determined experimentally. Various models for electrochemical cells are known to those skilled in the art and can be used to convert measured voltage and current changes into resistance values that are meaningful for determining the hydration state of the cell.

The system (100) may include a controller (40) as illustrated in FIG. 1. The controller (40) may be configured to communicate with all of the sensors of the system (100), including, for example, the coolant inlet sensor (20), the coolant exhaust sensor (22), the oxidizer gas inlet sensors (24) (e.g., 24A, 24B, 24C, 24D), and the oxidizer gas exhaust sensor (26A). The controller (40) may be configured to receive signals from each of the sensors indicative of a measurement value of the corresponding sensor. The controller (40) may also be configured to communicate with (e.g., to send and receive signals to) the current transducer (46), the compressor (42), the oxidizer gas inlet sensor (24B), the coolant inlet sensor (20), and/or the coolant pump (44).

During operation of the system (100), the amount of water entering the cell and the amount of water produced by the cell must be precisely balanced with the amount of water leaving the cell to prevent the water stored in the cell from increasing (i.e., moving toward a flooding state) or decreasing (i.e., moving toward a dry state). If the cell is operated where the water stored in the cell increases or decreases for too long, the cell may become flooded or dry to the point where cell performance degrades or the cell can no longer operate. Although it is desirable for the water entering the cell plus the water produced by the cell to be perfectly balanced with the water leaving the cell, environmental and operating conditions, measurement errors inherent in the physical system sensors, and/or physical limitations of the hardware used in the system can disrupt a continuous water balance and result in a non-zero amount of cumulative water stored within the cell. This non-zero amount can be a positive amount indicating that more water is stored than desired (i.e., tending to flood), or a negative amount indicating that less water is stored than desired (i.e., tending to dry).

, 몰/초)으로 지칭될 수 있는 산화제 공급 가스에 의해 도입된 물의 양과, water_created(

, 몰/초)로 지칭될 수 있는 전기화학 반응에 의해 생성될 수 있는 물의 양에서 water_out(

, 몰/초)로 지칭될 수 있는 산화제 배출 가스에 의해 전지(10)로부터 방출되는 물의 양을 뺀 값을 합산함으로써 전기화학 전지(10)의 현재 물 불균형을 결정하는 단계를 포함할 수 있다. 따라서 주어진 움직임에서 실시간 물 균형은 식 1에 의해 반영될 수 있다:To address these issues, the present disclosure provides a system and method that tracks accumulated water imbalance (e.g., value) over time and, when the system is able to do so, adjusts the operating conditions of the battery to bring this accumulated water balance back to zero. The disclosed method comprises water _in (

, the amount of water introduced by the oxidizing agent supply gas, which may be referred to as water _created (

, the amount of water that can be produced by an electrochemical reaction (water _out ) which can be expressed in moles/second

, moles/sec) may be included to determine the current water imbalance of the electrochemical cell (10) by adding up the values minus the amount of water released from the cell (10) by the oxidizer exhaust gas, which may be referred to as the current water imbalance. Thus, the real-time water balance in a given motion can be reflected by Equation 1:

(Formula 1)

Here represents the instantaneous water imbalance (mol/sec), , and is as defined above. When this is 0, the water flow (in moles/sec) at a given instant can be considered balanced. If Equation 1 is not 0, a water imbalance may exist. For example, If this is greater than 0, the amount of water in the electrochemical cell (10) will increase, If this is less than 0, the amount of water in the electrochemical cell (10) will decrease. Therefore, the accumulated water imbalance (N) can be calculated as a function of time.

(Formula 2)

In an exemplary embodiment, the amount of water within the electrochemical cell (10) can be tracked during operation. Tracking the cumulative water imbalance can include repeatedly determining the current water imbalance and continuously summing the results during operation. The cumulative water balance (in moles) over a period of time can be expressed by Equation 3.

(Formula 3)

The above equation can be rewritten as follows:

(Formula 4)

Here Is , represents silver Indicates, Is (all in moles/second).

The amount of water entering the electrochemical cell ( ) can be calculated from measurements of oxidizer mass flow rate, ambient temperature, ambient pressure, and ambient relative humidity, as shown in Equations 5 to 7.

(Formula 5)

(Formula 6)

(Formula 7)

Equations 6 and 7 are integrated into Equation 5 to give the amount of water entering the electrochemical cell ( ) can be calculated by Equation 8.

(Formula 8)

The symbol RH ^S represents the relative humidity of the oxidizer supply gas supplied to the cell (10), which can be measured by the third oxidizer gas inlet sensor (24C). The symbol p ^S represents the pressure of the oxidizer supply gas supplied to the cell (10), which can be measured by the first oxidizer gas inlet sensor (24A). The symbol represents the vapor pressure of water evaluated at temperature T ^S , which is a fixed property of water and a function of temperature. Symbol can represent the mass flow rate (grams/second) of the oxidizing gas supplied to the electrochemical cell (10), is the molecular weight (grams/mole) of the wet oxidizer gas, which can be a function of the temperature, pressure and relative humidity of the oxidizer gas. Accordingly, the system (100) and the controller (40) determine the amount of water introduced into the electrochemical cell based on the measured values provided by the oxidizer gas inlet sensor (24). )(mol/sec) can be configured to calculate.

The amount of water produced ( )(mol/sec) can be calculated using Equation 9.

(Formula 9)

In the above equation, i represents current (e.g., in amperes as measured by the current transducer (46), F is the Faraday constant (96485.3 C/mol), and St _A is the effective anode stoichiometry ratio which represents the amount of hydrogen fuel supplied to the cell divided by the amount of hydrogen fuel required to produce the measured current i. St _A is a parameter determined by the fuel cell system and control design, and accounts for "wasted" hydrogen fuel via anode purging into the cathode stream, hydrogen fuel crossing from the anode to the cathode, and/or other similar transfers of hydrogen fuel to the cathode that may be unique to the system.

The amount of water discharged from the electrochemical cell (10) through the exhaust oxidizer gas can be calculated by Equation 10.

(Formula 10)

Here, RH ^E represents the humidity of the oxidizing gas discharged from the electrochemical cell (10). When N (i.e., the solution of Equation 1) is greater than or equal to 0, RH ^E can be 100%. When N is less than 0, an estimate of RH ^E can be determined using a model described in more detail herein. The symbol p ^E represents the pressure of the oxidizing gas discharged from the electrochemical cell (10) through the oxidizing gas exhaust line, which can be measured by the first oxidizing gas exhaust sensor (26A). The symbol represents the vapor pressure of water, which is a fixed property of water and a function of temperature. The temperature used to determine may be the coolant outlet temperature (T ^E ) measured by the coolant exhaust sensor (22). Symbol represents the total flux of non-water species in the oxidizer exhaust gas, which can be calculated by Equation 11.

(Formula 11)

Here can be calculated by Equation 12.

(Formula 12)

can be calculated by Equation 12.

(Formula 13).

As discussed above, when N (i.e., the solution of Equation 2) is greater than or equal to 0, RH ^E can be 100%. When N is less than 0, an estimate of RH ^E can be determined using a model, for example, RH ^E can be derived from experimental data, whereby RH ^E can be consistent with the best performance of the cell (10). For example, the operating characteristics of the electrochemical cell can be monitored over a range of temperatures and flow rates to determine the correlation between RH ^E and electrochemical cell performance. Using RH ^E , Equation 1 can be can be solved for, which leads to Equation 14, which represents the oxidizer flow rate that will result in the water balance operation of the cell.

(Formula 14)

Here, St _A is the anode stoichiometry and f ^E is the mole fraction of the oxidant exhaust stream, which is water. f ^S is the mole fraction of the incoming stream of the oxidizing agent, which is water. Equation 14 can be used to determine the oxidizer gas flow rate to balance the water flow within the cell.

The controller (40) can be configured to perform one or more calculations described herein based on characteristics measured by one or more sensors (e.g., a coolant inlet sensor (20), a coolant exhaust sensor (22), an oxidizer gas inlet sensor (24), an oxidizer gas exhaust sensor (26), and a current transducer (46)) to enable calculation of a target oxidizer feed gas flow rate that balances water flow within the cell. The controller (40) can be configured to adjust the oxidizer feed gas flow rate or to signal another controller or engine to set the oxidizer feed gas flow rate. In some embodiments, the controller (40) can be configured to utilize a PID controller to adjust the oxidizer feed gas flow rate. The adjustment of the oxidizer feed gas flow rate can be configured such that the cumulative water imbalance is zero or approximately zero. In some embodiments, the controller (40) can be configured such that the adjustment of the oxidizer feed gas flow rate moves away from the water-balanced flow rate when the cumulative water balance deviates from zero by a set threshold. For example, when N is greater than 0 (i.e., excess water stored in the cell), the controller may adjust the oxidizer feed gas flow rate to a value greater than the water-balance flow rate to proactively create pure dry conditions to remove water from the cell and drive N toward 0. Conversely, when N is less than 0 (i.e., insufficient water stored in the cell), the controller may adjust the oxidizer feed gas flow rate to a value less than the water-balance flow rate to proactively create pure flooding conditions to add water to the cell and drive N toward 0.

The determination of the current water imbalance as described herein can be repeated by the controller (40) at a set frequency. For example, the controller (40) can be configured to repeat the determination at a frequency of about 0.01 seconds, about 0.1 seconds, about 0.5 seconds, about 1 second, about 2 seconds, about 3 seconds, about 4 seconds, about 5 seconds, about 10 seconds, about 20 seconds, about 30 seconds, or about 60 seconds.

As illustrated in FIG. 1, a coolant may be circulated through the electrochemical cell (10) to control the temperature of the electrochemical cell (10). In some embodiments, the coolant may be supplied to the electrochemical cell (10) at a generally fixed inlet coolant temperature. Under certain conditions, if the cell is not sufficiently cooled, the water imbalance in the cell may reach a point where the oxidizer feed gas flow rate required to bring the water imbalance back to zero exceeds the limitations of the system (100) (e.g., exceeds the output capacity of the compressor (42)). To avoid this situation, the inlet coolant temperature may be set based on a set of ambient conditions (e.g., air temperature, pressure, and humidity) such that the maximum oxidizer feed gas flow rate required to bring the accumulated water imbalance to zero (the result of Equation 14) is within the operating limitations of the compressor (42) that generates the oxidizer feed gas flow.

In some embodiments, the coolant pump (44) that supplies coolant to the electrochemical cell (10) may be configured to generally operate at a fixed speed. This will allow the coolant outlet temperature to vary with fuel cell power. By setting the coolant inlet temperature and setting a constant speed for the coolant pump (44), the associated pump hardware and control hardware required to control the coolant pump (44) can be simplified.

In some embodiments, the system (100) and controller (40) may be configured to periodically recalibrate the accumulated water imbalance to zero. For example, the controller (40) may be configured to temporarily increase the flow rate of the oxidizer supply gas to dry out the electrochemical cell (10). While doing so, the controller (40) may be configured to measure the resistance across the cell (10). In some embodiments, the resistance may be measured using a current-interrupt method or other methods described herein. The controller (40) may be configured to determine when the measured resistance is approximately equal to a target resistance corresponding to a cumulative water imbalance of zero, and thereafter reset a cumulative water imbalance variable within the controller software to zero. This process allows accumulated errors in the water imbalance calculation (due in part to measurement errors used in the equations described above) to be corrected through direct measurement of the water level (i.e., the resistance of the cell). This recalibration process can be performed periodically when the system load can be controlled, for example, during a system shutdown. In some embodiments, during the recalibration, an oxidizer flow rate greater than the water-balance flow rate can be provided to the cell to intentionally dry out the cell while monitoring the resistance increase, stopping the shutdown when the target value is achieved, and resetting a cumulative water imbalance variable in the controller software to zero, for example. The target value can be an absolute value of the resistance, or a relative increase in the resistance from the start of the shutdown process. The target relative increase can be, for example, from about 0.5% to about 300%, from about 0.5% to about 200%, from about 0.5% to about 100%, from about 1.0% to about 50%, or from about 5% to about 25%. In some embodiments, the absolute value of the target resistance can be determined during initial start-up of the electrochemical cell (10).

In some embodiments, the system (100) and the controller (40) can recalibrate the accumulated water imbalance to zero by measuring the humidity of the oxidizer exhaust gas. For example, the controller (40) can temporarily increase the flow rate of the oxidizer supply gas to dry the electrochemical cell (10). While doing so, the controller (40) can be configured to measure the humidity of the oxidizer exhaust gas (e.g., as measured by the second oxidizer gas exhaust humidity sensor (26B)). The controller (40) can be configured to determine when the humidity of the oxidizer exhaust gas is within a target humidity corresponding to a cumulative water imbalance of zero and reset the cumulative water imbalance to zero. The target humidity can be, for example, about 50% to about 99%, about 60% to about 99%, about 70% to about 99%, about 80% to about 99%, about 90% to about 99%, about 50% to about 90%, about 60% to about 90%, about 70% to about 90%, about 80% to about 90%, about 50% to about 80%, about 60% to about 80%, about 70% to about 80%, or about 75% to about 80%.

In some embodiments, the system (100) can be configured to perform recalibration based on both the measured resistance of the oxidizer gas emitted by the electrochemical cell (10) and the measured humidity. In some embodiments, the system (100) can be configured to perform recalibration at a set frequency. For example, the system (100) can be configured to perform recalibration at least once a day or at least once every other day. In some embodiments, recalibration can occur once a day, once every two days, once every three days, once a week, once every two weeks, once a month, once every two months, once every six months, or once a year. In some embodiments, recalibration can be determined based on the run time of the electrochemical cell. For example, recalibration can be initiated after about 1 hour, about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 10 hours, about 15 hours, about 25 hours, about 50 hours, about 100 hours, about 200 hours, or about 500 hours of run time. In some embodiments, recalibration can be performed during a shutdown sequence for the system (100). In some embodiments, recalibration is performed during every shutdown sequence for the system (100). In some embodiments, recalibration is performed once during every two shutdown sequences for the system (100). In some embodiments, recalibration is performed once every 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, or 30 shutdown sequences.

In some embodiments, the system (100) may include a fixed orifice positioned in the oxidizer exhaust gas line. In some embodiments, this orifice may result in achieving a target cathode exhaust pressure at maximum power while maintaining passive control (i.e., without active moving parts).

FIG. 2 illustrates an exemplary process performed by a controller (40) during operation of a system (100) for controlling water balance in an electrochemical cell (10). As depicted in the flow chart of FIG. 2, activation of the water imbalance control may be initiated by activation of the electrochemical cell (10) (step (202)). The controller (40) may begin to track the current passing through the current circuit and measured properties of the oxidizer gas and coolant circulating through the electrochemical cell (10) by receiving signals from various sensors (e.g., the oxidizer gas inlet sensor (24), the coolant inlet sensor (20), the coolant outlet sensor (22), and the oxidizer gas exhaust sensor(s) (26), and the current transducer (46)) from step (202) (step (204). The controller (40) may be configured to continuously track these properties of the electrochemical cell (10) or to repeat the tracking at a periodic frequency.

From step (204), the controller (40) can begin determining a current water imbalance in the electrochemical cell (10) (step (206)). Step (206) can include adding water _in and water _created minus water _out . As described herein, water _in can represent an amount of water introduced into the electrochemical cell by the oxidizer feed gas, water _created can represent an amount of water produced by the electrochemical cell in the electrochemical reaction, and water _out can represent an amount of water discharged from the electrochemical cell by the oxidizer exhaust gas. Measured attributes, values, and equations that can be used to calculate water _in , water _created , and water _out are described herein. The controller (40) can be configured to continuously determine the current water imbalance, or to repeat the determination at a periodic frequency, for example, after each measurement of the attributes (step (204)).

From step (206), the controller (40) can then track the cumulative water imbalance of the electrochemical cell (10) (step (208)). Step (208) can include repeatedly determining the current water imbalance and summing the results during operation of the electrochemical cell (10). An equation that can be used to sum the current water imbalance to track the cumulative water imbalance is described herein. From step (208), the controller (40) can then determine whether the cumulative water imbalance deviates from zero (step (210)). If the cumulative water imbalance does not deviate from zero (e.g., is approximately equal to zero) or is within a set tolerance threshold of zero (step (210) : No), the controller (40) can return to step (204) and repeat the process. In some embodiments, the accumulated water imbalance can deviate from zero by up to 0.1 g of water/cell, up to 0.2 g of water/cell, up to 0.5 g of water/cell, up to 1.0 g of water/cell, up to 2.0 g of water/cell, or up to 5.0 g of water/cell and still be considered within an acceptable threshold of zero. If the accumulated water imbalance deviates from zero (i.e., is not zero) or is outside the set acceptable threshold of zero (step (210) : Yes), the controller (40) can proceed to step (212). Step (212) can include adjusting the flow rate of the oxidizer feed gas into the electrochemical cell (10) based on the accumulated water imbalance. As part of step (212), the controller (40) can calculate an acceptable flow rate for the oxidizer feed gas to bring the accumulated water imbalance to zero within a predetermined amount of time. In some embodiments, the controller (40) may utilize a PID loop to control the regulation. In some embodiments, from step (212), the controller (40) may return to step (202) and repeat the process until the electrochemical cell is shut down or the water imbalance mode is deactivated.

In some embodiments, as illustrated in FIG. 2, between steps (212) and (204), the controller (40) may determine whether a shutdown of the electrochemical cell has been initiated (step (214)). If no shutdown has been initiated (step (214) : No), the controller (40) may return to step (204). If a shutdown has been initiated (step (214) : Yes), the controller (40) may determine whether a recalibration of the accumulated water imbalance is to be invoked prior to shutdown, as illustrated in FIG. 3 (step (216)). If a recalibration is not invoked (step (216) : No) (e.g., if a recalibration has been recently performed), the controller (40) may proceed with a shutdown of the electrochemical cell (10) (step (218)). In some embodiments, between steps (216) and (218), the controller (40) can increase the flow rate of the oxidizer feed gas to the electrochemical cell for a period of time to perform a baseline purge of the cathode side of the electrochemical cell (10) (optional step (217)). The period of step (217) can be fixed (e.g., from about 1 second to about 30 seconds, preferably less than or equal to 15 seconds), or in some embodiments a variable period of time determined by the controller (40). For example, in some embodiments, the controller (40) can determine the period of step (217) based on one or more measured or calculated parameters (e.g., oxidizer gas inlet mass flow rate, oxidizer gas inlet ambient temperature, oxidizer gas inlet ambient pressure, oxidizer gas inlet ambient relative humidity, coolant inlet temperature, coolant outlet temperature, oxidizer gas exhaust temperature, oxidizer gas exhaust pressure, oxidizer gas exhaust relative humidity, or accumulated water imbalance value).

If recalibration is invoked (Step (216) : Yes), in some embodiments (e.g., Option 1), the controller (40) may initiate a recalibration procedure that begins by temporarily increasing the flow rate of oxidizing feed gas to the electrochemical cell (10) to dry out the electrochemical cell (10) (Step (220)). From Step (220), the controller (40) may begin measuring the resistance of the electrochemical cell (10) (Step (222)). From Step (222), the controller (40) may determine whether the measured resistance is approximately equal to a target resistance corresponding to a zero accumulated water imbalance (Step (224)). If the measured resistance does not reach the target resistance within a predetermined shutdown time (Step (224) : No), the controller (40) may return to Step (220) and continue the flow of oxidizing feed gas to the electrochemical cell (10) at the same flow rate, or may further increase the flow. If the measured resistance reaches the target resistance within the predetermined shutdown time (step (224) : Yes), the controller (40) can reset the accumulated water imbalance variable to zero (step (226)). From step (226), the controller (40) can continue the shutdown of the electrochemical cell (10) (step (218)).

In another embodiment of Option 1 (not shown in FIG. 3), the controller (40) may determine when to reset the accumulated water imbalance value based on an increase in measured resistance rather than a target resistance value. For example, when a shutdown is initiated and a recalibration is invoked, the controller (40) may determine whether the measured resistance has increased relative to the baseline resistance measured at the start of the shutdown. The change in resistance can be determined by calculating the difference between the measured resistance and the reference resistance divided by the reference resistance (i.e., {(measured resistance) - (reference resistance)}/(reference resistance). For example, if the resistance has increased from about 0.5% to about 300%, from about 0.5% to about 200%, from about 0.5% to about 100%, from about 1.0% to about 50%, or from about 5% to about 25% compared to the measured baseline resistance when the shutdown is initiated within the predetermined shutdown time, the controller (40) can reset the accumulated water imbalance variable to zero. If the resistance does not increase by the target amount within the predetermined shutdown time, the controller (40) can revert to the increased flow rate step and continue the flow of oxidant supply gas to the electrochemical cell (10) at the same flow rate, or can further increase the flow rate.

In other embodiments (e.g., Option 2), when a recalibration is invoked (Step (216) : Yes), the controller (40) can initiate a recalibration procedure that begins by temporarily increasing the flow rate of the oxidizer feed gas to the electrochemical cell (10) to dry the electrochemical cell (10) (Step (228)). From Step (228), the controller (40) can initiate a humidity measurement of the oxidizer exhaust gas (Step (230)). From Step (230), the controller (40) can determine whether the measured humidity is approximately equal to a target humidity corresponding to a zero cumulative water imbalance (Step (232)). If the measured humidity does not reach the target humidity within a predetermined shutdown time (Step (232) : No), the controller (40) can return to Step (228) and continue the flow of oxidizer feed gas to the electrochemical cell (10) at the same flow rate, or can further increase the flow rate. If the measured humidity reaches the target humidity within the predetermined shutdown time (step (232) : Yes), the controller (40) can reset the accumulated water imbalance variable to zero (step (226)). From step (226) the controller (40) can continue to shut down the electrochemical cell (10) (step (218)). The predetermined shutdown time can be fixed or variable, in which case it can be determined based on one or more variables (e.g., accumulated water imbalance, maximum oxidizer flow rate, operating time limit for the system (100)). The predetermined shutdown time can range from, for example, less than about 1 second to about 20 minutes. For example, the predetermined shutdown time can be about 1 second, about 2 seconds, about 3 seconds, about 4 seconds, about 5 seconds, about 10 seconds, about 15 seconds, about 20 seconds, about 30 seconds, about 40 seconds, about 50 seconds, about 60 seconds, about 75 seconds, about 90 seconds, about 2 minutes, about 3 minutes, about 4 minutes, about 5 minutes, about 6 minutes, about 7 minutes, about 8 minutes, about 9 minutes, about 10 minutes, about 11 minutes, about 12 minutes, about 13 minutes, about 14 minutes, about 15 minutes, about 16 minutes, about 17 minutes, about 18 minutes, about 19 minutes, or about 20 minutes.

In some embodiments, the controller (40) may be configured such that the initial amount of the increase in the flow rate of the oxidizer feed gas (e.g., in steps (220) and (228)) may be fixed based on a predetermined shutdown time (e.g., an optimized predetermined shutdown time). If the controller (40) is unable to achieve recalibration to zero within the fixed predetermined shutdown time (i.e., step (226)), the controller (40) may return to step (220 or 228) and continue at the same flow rate, or may increase the flow rate of the oxidizer to accelerate the recalibration and shutdown process. The amount of this increase may be determined based on, for example, the speed at which the system (100) attempts to complete shutdown, or the cumulative water imbalance value at the time the shutdown is initiated or the controller (40) returns to step (228 or 220).

In some embodiments, the controller (40) can be configured to invoke an excess increase in flow rate based on the accumulated water imbalance at the start of the shutdown sequence. The controller (40) can be configured to determine the flow rate increase based on a predetermined shutdown time and a maximum oxidizer flow rate. For example, the controller (40) can be configured to attempt and optimize (e.g., minimize) the predetermined shutdown time by increasing the oxidizer flow rate to achieve a recalibration to zero within an optimized predetermined shutdown time (reaching step (226)). The increase in the flow rate of the oxidizer gas into the electrochemical cell (10) can be based on a calculated water balance (e.g., ((predetermined water balance value)-(calculated water balance value))/(calculated water balance value). In some embodiments, the increase in the flow rate of the oxidizer gas can be in the range of from about 5% to about 500%, from about 25% to about 400%, from about 50% to about 300%, or from about 75% to about 200%. In some embodiments, the increase in the flow rate of the oxidizer gas can be at least 5%, at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, at least 75%, at least 100%, at least 125%, at least 150%, at least 175%, at least 200%, at least 225%, at least 250%, at least 275%, at least 300%, at least 325%, at least 350%, at least 375%, at least 400%, at least 425%, at least 450%, at least 475%, or at least 500%. In certain circumstances (e.g., where the cumulative water imbalance is high, indicating that the electrochemical cell is further flooded), the excess increase in flow rate called upon may exceed the maximum oxidizer flow rate (e.g., a limitation of the compressor (42)), in which case a recalibration to zero may not be achieved within the optimized predetermined shutdown time. Thus, the controller (40) may need to allow additional shutdown time (e.g., by returning to step (220 or 228)).

The above description has been provided for illustrative purposes. It is not exhaustive or limited to the precise forms or embodiments disclosed. Modifications, adaptations, and other applications of the embodiments will become apparent from consideration of the specification and practice of the disclosed embodiments. For example, the described embodiments of the fuel cell (10) can be adapted for use with a variety of electrochemical cells. Similarly, the arrangement of cells and electrochemical stacks described herein is merely illustrative and can be applied to a range of other fuel cell configurations.

Moreover, while exemplary embodiments have been described herein, the scope includes any and all embodiments having equivalent elements, modifications, omissions, combinations (e.g., aspects across various embodiments), adaptations, and/or changes based on the present disclosure. The elements of the claims are to be construed broadly based on the language used in the claims and are not limited to the examples described in this specification or during the practice of this specification, which examples are to be construed as non-exclusive. Furthermore, the steps of the disclosed methods may be modified in any manner, including by reordering the steps and/or inserting or deleting the steps.

The features and advantages of the present disclosure are apparent from the detailed specification, and thus it is intended that the appended claims cover all cells and battery stacks falling within the true spirit and scope of the present disclosure. As used herein, the term "a" or "an" means "one or more." Similarly, the use of the plural terms does not necessarily mean a plurality unless the context clearly dictates otherwise. Words such as "and" or "or" mean "and/or" unless the context clearly dictates otherwise. Furthermore, since numerous modifications and variations will readily occur to a student of the present disclosure, it is not desirable to limit the present disclosure to the precise construction and operation illustrated and described, and therefore all suitable modifications and equivalents may be reclassified as falling within the scope of the present disclosure.

The term "about" as used herein is used to modify a numerical value above and below a stated value by a variation of 25%, 20%, 15%, 10%, 5%, or 1%. In some embodiments, the term "about" is used to modify a numerical value above and below a stated value by a variation of 10%. In some embodiments, the term "about" is used to modify a numerical value above and below a stated value by a variation of 15%. In some embodiments, the term "about" is used to modify a numerical value above and below a stated value by a variation of 10%. In some embodiments, the term "about" is used to modify a numerical value above and below a stated value by a variation of 5%. In some embodiments, the term "about" is used to modify a numerical value above and below a stated value by a variation of 1%.

The terms “fuel cell” and “electrochemical fuel cell” and their plural variations, as used herein, are used interchangeably and are understood to have the same meaning.

Computer programs, program modules and codes based on the written description of this specification, such as those used by microcontrollers, are readily within the scope of software developers. The computer programs, program modules or codes may be created using various programming technologies. For example, they may be designed in or by MatLab/Simulink, LabVIEW, Java, C, C++, assembly language or any of these programming languages. One or more of these programs, modules or codes may be incorporated into a device system or existing communications software. The programs, modules or codes may also be implemented or replicated in firmware or circuit logic.

Other embodiments of the present disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the present disclosure. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the present disclosure being indicated by the following claims.

Claims (45)

In a method for controlling water imbalance in an electrochemical cell,
A step for determining the current water imbalance in the electrochemical cell by adding the values obtained by subtracting water _out from water _in and water _created .
The above water _in is the amount of water introduced into the electrochemical cell by the oxidizer supply gas;
The above water _created is the amount of water produced by the electrochemical cell from the electrochemical reaction;
The step of determining the current water imbalance, wherein the water _out is the amount of water discharged from the electrochemical cell by the oxidizer exhaust gas;
A step of tracking the cumulative water imbalance during the operation of the electrochemical cell by repeatedly determining the current water imbalance and continuously summing the results during the operation; and
A step of adjusting the flow rate of the oxidizer supply gas entering the electrochemical cell based on the accumulated water imbalance,
The above method:
Temporarily increasing the flow rate of the oxidizing agent supply gas to the electrochemical cell to dry the electrochemical cell;
Measuring the resistance of the above electrochemical cell;
Determine whether the measured resistance is approximately equal to a target resistance corresponding to the accumulated water imbalance being zero;
By resetting the accumulated water imbalance to zero when the measured resistance is approximately equal to the target resistance,
A method for controlling water imbalance in an electrochemical cell, further comprising the step of re-correcting the accumulated water imbalance to zero. A method for controlling water imbalance in an electrochemical cell, wherein in the first aspect, the flow rate adjustment of the oxidizing agent supply gas is controlled using a proportional-integral-differential (PID) controller. A method for controlling water imbalance in an electrochemical cell, wherein in the first aspect, the flow rate of the oxidizer supply gas is adjusted when the accumulated water imbalance deviates from 0 so as to make the accumulated water imbalance 0. A method for controlling water imbalance in an electrochemical cell, wherein in the first aspect, the flow rate of the oxidizer supply gas entering the electrochemical cell is adjusted when the accumulated water balance deviates from 0 by exceeding a set threshold value. A method for controlling water imbalance in an electrochemical cell, wherein the determination of the current water imbalance is repeated at least every 30 seconds. In the first aspect, the coolant is supplied to the electrochemical cell at a generally fixed inlet coolant temperature,
A method of controlling water imbalance in an electrochemical cell, wherein the inlet coolant temperature is set based on a set of ambient conditions such that the potentially maximum oxidizer gas flow rate required to make the accumulated water imbalance zero is within the operating limits of the compressor supplying the oxidizer feed gas flow. A method for controlling water imbalance in an electrochemical cell, wherein in claim 6, the coolant is supplied to the electrochemical cell from a coolant pump generally operating at a fixed speed. A method for controlling water imbalance in an electrochemical cell, wherein the set of ambient conditions in claim 6 comprises air temperature, pressure and humidity. delete A method for controlling water imbalance in an electrochemical cell, wherein in the first aspect, the resistance is measured using a current-interrupt method. A method for controlling water imbalance in an electrochemical cell, wherein the target resistance is determined during an initial start-up test of the electrochemical cell. A method for controlling water imbalance in an electrochemical cell, wherein the target resistance is 50 to 100 mΩ-cm ² in the first aspect. In paragraph 1,
Measuring the reference resistance of the above electrochemical cell;
Temporarily increasing the flow rate of the oxidizing agent supply gas to the electrochemical cell to dry the electrochemical cell;
Measuring the current resistance of the above electrochemical cell;
Determine whether the measured current resistance has increased compared to the reference resistance;
By resetting the accumulated water imbalance to zero when the measured current resistance increases by 0.5% to 300% compared to the reference resistance,
A method for controlling water imbalance in an electrochemical cell, further comprising the step of re-correcting the accumulated water imbalance to zero. A method for controlling water imbalance in an electrochemical cell, wherein the change in resistance from the reference resistance to the current resistance is 25% in the 13th paragraph. A method for controlling water imbalance in an electrochemical cell, wherein in claim 13, the step of re-correcting the accumulated water imbalance to zero is performed at least once a day during a shutdown sequence for the electrochemical cell. In paragraph 1,
Temporarily increasing the flow rate of the oxidizing agent supply gas to the electrochemical cell to dry the electrochemical cell;
Measuring the humidity of the above oxidizer exhaust gas;
Determine whether the measured humidity of the above oxidizer exhaust gas is approximately equal to a target humidity corresponding to a zero accumulated water imbalance;
By resetting the accumulated water imbalance to 0 when the measured humidity is almost equal to the target humidity,
A method for controlling water imbalance in an electrochemical cell, further comprising the step of re-correcting the accumulated water imbalance to zero. A method for controlling water imbalance in an electrochemical cell, wherein the target humidity is 50% to 99% in the 16th paragraph. A method for controlling water imbalance in an electrochemical cell, further comprising the step of controlling the pressure of the oxidizer exhaust gas at maximum power using a fixed orifice located in the oxidizer exhaust gas line in the first aspect. A method for controlling water imbalance in an electrochemical cell, wherein in the first aspect, the water _in is determined based on the humidity of the oxidizer supply gas, the pressure of the oxidizer supply gas, and the flow rate of the oxidizer supply gas. A method for controlling water imbalance in an electrochemical cell, wherein the water _created in the first aspect is determined based on the current generated by the electrochemical cell and the anode stoichiometric ratio. A method for controlling water imbalance in an electrochemical cell, wherein in the first aspect, the water _out is determined based on the humidity of the oxidizing agent exhaust gas and the pressure of the oxidizing agent exhaust gas. In an electrochemical cell system,
electrochemical cell;
a plurality of oxidizer gas inlet sensors, an oxidizer gas discharge sensor, a coolant inlet sensor, a coolant discharge sensor, and a current transducer; and
As a controller,
The current water imbalance in the electrochemical cell is determined by adding the values of water _in and water _created minus water _out .
The above water _in is the amount of water introduced into the electrochemical cell by the oxidizer supply gas;
The above water _created is the amount of water produced by the electrochemical cell in the electrochemical reaction;
The above water _out determines the current water imbalance in the electrochemical cell, which is the amount of water discharged from the electrochemical cell by the oxidizer exhaust gas;
Tracking the cumulative water imbalance during operation of the electrochemical cell by repeatedly determining the current water imbalance and continuously summing the results during operation;
comprising a controller configured to adjust the flow rate of the oxidizer supply gas entering the electrochemical cell based on the accumulated water imbalance;
The above controller:
Temporarily increasing the flow rate of the oxidizing agent supply gas to the electrochemical cell to dry the electrochemical cell;
Measuring the resistance of the above electrochemical cell;
If the measured resistance is approximately equal to the target resistance corresponding to a zero accumulated water imbalance, stopping the flow of the oxidizer supply gas; and
An electrochemical cell system configured to re-correct said accumulated water imbalance to zero by resetting said accumulated water imbalance to zero. An electrochemical cell system, wherein in claim 22, the controller is configured to use a PID loop to adjust the flow rate of the oxidizer supply gas. An electrochemical cell system, wherein in claim 22, the controller is configured to adjust the flow rate of the oxidizer supply gas when the accumulated water imbalance deviates from zero to make the accumulated water imbalance zero. An electrochemical cell system in claim 22, wherein the controller is configured to adjust the flow rate of the oxidizer gas when the accumulated water balance deviates from zero by a set threshold value. In paragraph 22,
An electrochemical cell system, wherein said controller is configured to repeat the determination of said current water imbalance at least every 30 seconds. In paragraph 22,
An electrochemical cell system, wherein the controller is configured to repeatedly adjust the flow rate of the oxidizer supply gas at a frequency of at least 1 Hz. In paragraph 22,
An electrochemical cell system further comprising a coolant pump configured to supply coolant to said electrochemical cell at a generally fixed inlet coolant temperature, said inlet coolant temperature being set based on a set of ambient conditions in such a way as to ensure that the potential maximum oxidant gas flow rate required to render said accumulated water imbalance zero is within the operating limits of a compressor configured to supply said oxidant supply gas flow. An electrochemical cell system according to claim 28, wherein the coolant pump is generally operated at a fixed speed. An electrochemical cell system in accordance with claim 28, wherein the set of ambient conditions comprises air temperature, pressure, and humidity. delete An electrochemical cell system, wherein the resistance is measured using a current-blocking method in claim 22. An electrochemical cell system, wherein the target resistance is determined during an initial start-up test of the electrochemical cell. An electrochemical cell system in claim 22, wherein the target resistance is 50 to 100 mΩ-cm ² . An electrochemical cell system, wherein in claim 22, the controller is configured to re-correct the accumulated water imbalance at least once per day during a shutdown sequence for the electrochemical cell. In paragraph 22,
The above controller:
Temporarily increasing the flow rate of the oxidizing agent supply gas to the electrochemical cell to dry the electrochemical cell;
Measuring the humidity of the above oxidizer exhaust gas;
If the humidity of the oxidizer exhaust gas is less than the target humidity corresponding to a zero accumulated water imbalance, stopping the flow of the oxidizer supply gas; and
An electrochemical cell system configured to re-correct the accumulated water imbalance to zero by resetting the accumulated water imbalance to zero. An electrochemical cell system according to claim 36, wherein the target humidity is 50% to 99%. In paragraph 22,
An electrochemical cell system further comprising a fixed orifice positioned in the oxidizer exhaust gas line configured to control the pressure of the oxidizer exhaust gas at maximum power. In paragraph 22,
An electrochemical cell system, wherein the controller is configured to determine water _in based on the humidity of the oxidizer supply gas, the pressure of the oxidizer supply gas, and the flow rate of the oxidizer supply gas. In paragraph 22,
An electrochemical cell system, wherein the controller is configured to determine the water _created based on the current generated by the electrochemical cell and the current generated by the anode stoichiometric ratio. In paragraph 22,
An electrochemical cell system wherein the controller is configured to determine water _out based on the humidity of the oxidizer exhaust gas and the pressure of the oxidizer exhaust gas. A method for controlling water imbalance in an electrochemical cell, wherein the increase in the flow rate is determined based on at least one of the accumulated water imbalances at a shutdown time and at a predetermined shutdown time. A method for controlling water imbalance in an electrochemical cell, further comprising a second step of increasing the flow rate of the oxidizer supply gas if the accumulated water imbalance is not reset to zero within a predetermined shutdown time in the first aspect. An electrochemical cell system in accordance with claim 36, wherein the increase in flow rate is determined based on at least one of the accumulated water imbalances at a shutdown time and at a predetermined shutdown time. An electrochemical cell system, further comprising a second increase in the flow rate of the oxidizer supply gas if the accumulated water imbalance is not reset to zero within a predetermined shutdown time in accordance with claim 36.

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