Degradation protection for electrochemical cells and stacks

Abstract

The following disclosure relates to electrochemical cell and stacks and components thereof. More specifically, the following disclosure relates to components or systems configured to protect the degradation of an electrochemical cell or stack having a plurality of electrochemical cells. This may be accomplished by operating the cell or stack in a shielding state, instead of completely shutting down operation of the cell or stack. In the shielding state, the at least one electrochemical cell no longer receives enough voltage to generate gas via electrolysis, but still receives enough voltage to maintain a charged capacitance and protect the at least one electrochemical cell from depolarization or discharge.

Description

DEGRADATION PROTECTION FOR ELECTROCHEMICAL CELLS AND STACKSPRIORITY

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 532,795, filed August 15, 2023, titled DEGRADATION PROTECTION FOR ELECTROCHEMICAL CELLS AND STACKS, which is incorporated herein in its entirety.FIELD

[0002] The following disclosure relates to electrochemical cell and stacks and components thereof. More specifically, the following disclosure relates to components or systems configured to protect the degradation of an electrochemical cell or a stack having a plurality of electrochemical cells.BACKGROUND

[0003] Electrochemical systems use electrical energy to drive a chemical reaction. For example, water (or other liquid) is split to form hydrogen and oxygen (or other gas products). The products may be used as energy sources for later use. Hydrogen has been considered as an ideal energy carrier to store renewable energy. Proton exchange membrane water electrolysis (PEMWE) as a means for hydrogen production offers high product purity, fast load response times, small footprints, high efficiencies, and low maintenance efforts. It is regarded as a promising technology, especially when coupled with renewable energy sources.

[0004] In recent years, improvements in operational efficiency have made electrochemical systems competitive market solutions for energy storage, generation, and / or transport. For example, the cost of generation may be below $10 per kilogram of hydrogen in some cases. Increases in efficiency and / or improvements in operation will continue to drive installation of electrochemical systems.SUMMARY

[0005] In one embodiment, an electrochemical system configured to generate gas via electrolysis of a liquid is provided. The electrochemical system includes at least one electrochemical cell, at least one power supply configured to provide voltage to the at least one electrochemical cell, and a controller in communication with the at least one power supply and the at least one electrochemical cell. The controller is configured to provide instructions to the at least one power supply and the at least one electrochemical cell to:operate in an operating state in which a faradaic voltage is provided to the at least one electrochemical cell and the at least one electrochemical cell is configured to receive the liquid and generate the gas via electrolysis; and ramp down to a shielding state in which a non-faradaic voltage is provided to the at least one electrochemical cell. In the shielding state, the at least one electrochemical cell no longer receives enough voltage to generate hydrogen gas via electrolysis, but still receives enough voltage to maintain a charged capacitance and protect the at least one electrochemical cell from depolarization or discharge.

[0006] In another embodiment, a method for controlling operation of an electrochemical stack having a plurality of electrochemical cells is provided. The method includes providing a faradaic voltage to the electrochemical stack from a power supply to operate the electrochemical stack in an operating state, wherein hydrogen is generated from liquid input to the electrochemical stack via electrolysis. The method further includes receiving, by a controller, instructions from an operator to ramp down operation of the electrochemical stack to a shielding state, wherein, in the shielding state, the plurality of electrochemical cells in the electrochemical stack no longer receives enough voltage to generate hydrogen gas via electrolysis, but still receives enough voltage to maintain a charged capacitance and protect the plurality of electrochemical cells from depolarization or discharge. The method further includes ramping down an amount of voltage provided by the power supply to the electrochemical stack and providing a non-faradaic voltage to the electrochemical stack to operate the electrochemical stack in the shielding state.

[0007] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Exemplary embodiments are described herein with reference to the following drawings.

[0009] Figure 1 depicts an example of an electrochemical or electrolytic cell.

[0010] Figure 2 depicts an example of a system including an electrochemical stack having a plurality of electrochemical cells of Figure 1.

[0011] Figure 3 depicts, in an exploded view, an example of an electrochemical stack including a plurality of substacks.

[0012] Figure 4 depicts an example of a power supply connection to an electrochemical cell or stack.

[0013] Figure 5 depicts an example of a power supply connection to an electrochemical cell or stack having passive balancing circuitry.

[0014] Figure 6 depicts an example of a power supply connection to an electrochemical cell or stack having active balancing circuitry.

[0015] Figure 7 depicts an example communication system between an electrochemical plant or component thereof and a computing device having a controller over a connected network.

[0016] Figure 8 depicts an example of a computing device having a controller.

[0017] Figure 9 shows an example voltage equalization circuit.

[0018] Figure 10 shows an example operating curve for the voltage clamps of Figure 9.

[0019] Figure 11 shows an example method for operation of an electrochemical stack.

[0020] Figure 12 shows an example method of discharge of an electrochemical stack.DETAILED DESCRIPTION

[0021] The following disclosure provides systems, apparatuses, and methods for providing power to an electrochemical cell, substack, or stack to operate the cell, substack, or stack under different operating conditions. Specifically, the amount of current or voltage provided to the cell / substack / stack may vary between an electrolytic condition (i.e., a standard or normal operating condition to generate a gas product (such as hydrogen gas) from a liquid input), a standby condition, or a shielding condition.

[0022] Providing configurations for operating the cell, substack, or stack at varying levels of current or voltage may be advantageous in extending the operating life of the cell, substack, or stack. Additionally, controlling operating of the cell / substack / stack at varying levels of current or voltage may effectively lower the operating / energy costs for the cell / substack / stack.

[0023] In other words, during operation of an electrochemical system having an electrochemical cell, substack, or stack of cells, it may not be desirable to fully operate the system to split water and generate hydrogen. That is, there are certain times for the systemwherein hydrogen generation is not desirable, yet complete shutdown of the system is also not desirable.

[0024] In some cases, a complete shutdown of the electrochemical stack may expedite the degradation of the cells within the stack such that the stack requires maintenance / replacement. Specifically, an electrochemical stack (i.e., in particular for a stack operating at high current density conditions such as at least 3 Amp / cm2) may require replacement after less than 100 cycles, less than 75 cycles, or less than 50 cycles of the stack due to degradation of cells within the stack (wherein each cycle of the stack may refer to a start-up of the stack where voltage increases to greater than 1 V followed by a subsequent shutdown of the stack in which voltage to the stack drops below 1 V).

[0025] In other words, the system may therefore need to be brought into a lower power consumption mode without fully shutting down operation of the electrochemical stack to avoid degradation of the cell / stack and therein extend the operating lifetime of the cell / stack. This may include ramping the operation down into a standby state or standby condition in which the system may remain ready to ramp up to standard operating conditions quickly, safely, and as healthily as possible to produce hydrogen gas. The system alternatively could be ramped down into a shielding state or shielding condition that requires even less power consumption than the standby state / condition while still protecting the cell / substack / stack from uncontrolled discharge and degradation of the cells or from parasitic side reactions occurring within the cells.

[0026] The techniques and architectures herein proceed contrary to the conventional wisdom because they reduce the voltage below nominal operating voltages without necessarily turning off the system. The techniques and architectures herein provide a shielding voltage below a faradaic voltage to prevent depolarization or complete discharge of an electrochemical cell while providing a non-productive state. Counterintuitively, the techniques and architectures herein provide electricity to a system that is not actively performing a yield producing task. Instead, the states provided herein counterintuitively provide voltage input to produce no output at all.

[0027] These operating conditions and arrangements are discussed in greater detail below.Definitions

[0028] As used herein, the term "standby condition," "standby state," or "standby voltage" may refer to a faradaic voltage (or current) that is applied to the electrochemical cell / stack in order generate enough hydrogen electrochemically to maintain a constant pressure in the cathode compartment of the electrolyzer stack to make up for the hydrogen gas lost to leakage across the membrane. The standby voltage may refer to the lowest voltage or current that may safely be held throughout the lifetime of the electrochemical cell without exceeding the 50% lower flammability limit. In certain examples, the standby voltage may be in a range of 1.42-2 V. In certain examples, the temperature of the electrochemical cell / stack is also maintained.

[0029] As used herein, the term "shielding condition," "shielding state," or "shielding voltage" may refer to a non-faradaic voltage (or current) that is applied to the electrochemical cell / stack in order to prevent depolarization or complete discharge of the electrochemical cell. In other words, at the shielding voltage, the electrochemical cell or stack no longer receives enough current or voltage to conduct an electrolysis reaction, but still receives enough current or voltage to maintain a charged capacitance and to shield or protect the anode and cathode of the cell from degradation or parasitic side reactions that may occur in the discharge process. In certain examples, the operating pressure (on the anode and cathode sides of the stack), as well as the temperature for the electrochemical stack are not maintained at the shielding voltage. In certain examples, the shielding voltage may be in a range of 1-1.42 V, 1.2-1.42 V, 1.3-1.42 V, 1-1.2 V, or 1.2-1.3 V.Electrochemical Cells / Stacks

[0030] Figure 1 depicts an example of an electrochemical cell 100 for the production of hydrogen gas and oxygen gas through the splitting of water. The electrochemical cell includes a cathode, an anode, and a membrane positioned between the cathode and anode. Within the water-splitting electrolysis reaction, one interface runs an oxygen evolution reaction (OER) while the other interface runs a hydrogen evolution reaction (HER). For example, the anode reaction is H2O->2H++ / 2C>2+2e and the cathode reaction is 2H++2e->H2. The water electrolysis reaction has recently assumed great importance and renewed attention as a potential foundation for a decarbonized "hydrogen economy." Electrochemical cells for electrolysis of other liquids to generate hydrogen or other gasproducts may be readily implemented using the techniques and architectures discussed herein.

[0031] Figure 2 depicts an example of a system including an electrochemical stack 200 having a plurality of electrochemical cells of Figure 1. In certain examples, the electrochemical stacks may contain 50-1000 cells, 50-100 cells, 500-700 cells, or more than 1000 cells. Any number of cells may make up a stack. The electrochemical cells within the electrochemical stack may be configured to operate with 200 mV or less of pure resistive loss when operating at a high current density (e.g., at least 3 Amps / cm2, at least 4 Amps / cm2, at least 5 Amps / cm2, at least 6 Amps / cm2, at least 7 Amps / cm2, at least 8 Amps / cm2, at least 9 Amps / cm2, or at least 10 Amps / cm2).

[0032] Further, the electrochemical cells within the electrochemical stack may be used in the formation of a large-scale electrochemical plant that may be configured to generate at least 1 megawatt (MW) of power, at least 5 MW, at least 10 MW, at least 25 MW, at least 50 MW, at least 75 MW, at least 100 MW, in a range of 1-100 MW, in a range of 10-100 MW, in a range of 25-100 MW, or in a range of 50-100 MW of power.

[0033] As illustrated in the system of Figure 2, water (H2O) may be supplied to the anodic inlet of an electrolytic cell stack 12. In some embodiments, only the anodic inlet of the cell stack 12 may receive water. In these embodiments, the cathode side of the cell stack 12 may not receive water (e.g., a dry cathode side may be used). In another embodiment, a cathode inlet may also receive water, wherein the water may be supplied to the cathode inlet to cool the cell stack 12 during electrolysis.

[0034] The water supplied to the anodic inlet flows to an anodic inlet manifold that distributes the water to the anode side of the plurality of cells contained with the cell stack 12. In embodiments where water is supplied to the cathode inlet, water supplied to the cathode inlet flows to a cathodic inlet manifold that distributes the water to the cathode side of the plurality of cells in the cell stack 12.

[0035] During electrolysis, oxygen (O2) is produced at the anode side of the electrolytic cells and hydrogen (H2) is produced at the cathode side of the electrolytic cells. Specifically, a water splitting electrolysis reaction is configured to take place within each individual cell in the cell stack 12. Each cell includes one interface (the anode side of the cell) configured to run an oxygen evolution reaction (OER) and another interface (the cathode side of the cell) configured to run a hydrogen evolution reaction (HER), such as depicted in Figure 1.

[0036] During electrolysis, some of the water supplied to the anode side of an electrolytic cell may not be converted into oxygen. Accordingly, a two-phase flow of oxygen and unreacted water is outlet from each of the anode sides of the cells into an anodic outlet manifold 13. The two-phase flow of oxygen and unreacted water flows from out of the cell stack 12 through the anodic outlet manifold 13.

[0037] Additionally, as noted above, in some embodiments, water may be supplied to the cathode side of the cell stack as a coolant. Accordingly, a two-phase flow of hydrogen and water is outlet from each of the cathode sides of the cells to a cathodic outlet manifold 14. The two-phase flow of hydrogen and water flows out of the cell stack 12 through the cathodic outlet manifold 14.Electrochemical Stack Including a Plurality of Substacks

[0038] In certain examples, an electrochemical stack may include a plurality of substacks. Each substack within the plurality of substacks includes a plurality of electrochemical cells. As discussed in greater detail below, this arrangement may be advantageous in providing power to each individual substack of the overall stack.

[0039] Figure 3 depicts such an example of an electrochemical stack 300 including a plurality of substacks. The electrochemical stack 300 also includes a first manifold 302 and a second manifold 304 positioned on opposite ends of the stack 300 such that the plurality of substacks are positioned between the two manifolds. The first manifold 302 and the second manifold 304 are responsible for directing the flow of reactant fluids (water) to the electrochemical cells and collecting the product gases (hydrogen and oxygen) from the cells.

[0040] As depicted in Figure 3, the electrochemical stack 300 includes three substacks: a first substack 320, a second substack 340, and a third substack 360. While three substacks are depicted in this example, the electrochemical stack is not limited to such an arrangement. Instead, the electrochemical stack may include any number of substacks stacked on top of one another (e.g., connecting, abutting, or the like). In other words, the electrochemical stack may include at least 2 substacks, at least 3 substacks, at least 4 substacks, at least 5 substacks, at least 10 substacks, less than or equal to 100 substacks, less than or equal to 50 substacks, less than or equal to 30 substacks, less than or equal to 25 substacks, less than or equal to 20 substacks, in a range of 2-100 substacks, in a range of 3-50 substacks, in a range of 4 to 30 substacks, in a range of 5-25 substacks, or in a range of10-20 substacks. In some examples, the number of substacks within an overall cell stack may be dictated by the desirable total number of cells in the stack. For example, if the total number of cells needed for the overall stack is 200 cells and the substacks include 10 cells per substack, then 20 substacks are needed for the overall stack.

[0041] In Figure 3, each substack depicts its plurality of cells as one layer in terms of simplicity and its two unipolar plates as two separate layers. In other words, substack 320 depicts the plurality of cells as layer 322, which may be positioned between a respective anode unipolar plate 324 and a respective cathode unipolar plate 326. The respective unipolar plates advantageously enclose their respective plurality of cells to form the individual substack.

[0042] Likewise, substack 340 depicts the plurality of cells as layer 342, which is positioned between its respective anode unipolar plate 344 and its respective cathode unipolar plate 346. Similarly, substack 360 depicts the plurality of cells as layer 362, which is positioned between its respective anode unipolar plate 364 and its respective cathode unipolar plate 366.

[0043] The substacks 320, 340, and 360 are stacked on top of one another in between the first manifold 302 and the second manifold 304. For example, the anode unipolar plate 324 of the first substack 320 abuts the internal surface of the first manifold 302. The cathode unipolar plate 326 of the first substack 320 abuts the surface of the anode unipolar plate 344 of the second substack 340. The anode unipolar plate 364 of the third substack 360 abuts the surface of the cathode unipolar plate 346 of the second substack 340. Lastly, the cathode unipolar plate 366 of the third substack 360 abuts the internal surface of the second manifold 304. Thus, the plurality of substacks is positioned between the first manifold 302 and the second manifold 304.Power to the Electrochemical Cells / Substacks / Stacks

[0044] The electrochemical stack, such as depicted in Figures 2 and 3, is configured to be connected to power electronics that provide one or more power supplies to the electrochemical stack.

[0045] Figure 4 depicts an example of a such a power connection. In this figure, an electrolyzer or electrochemical stack is connected on either end (i.e., the positive and negative terminals) of the stack to a power supply. The power supply may be configured toprovide a voltage or current to the stack to operate the stack in one or more operating states (e.g., an operating condition for electrolysis, a standby condition, a shielding condition.)

[0046] While Figure 4 depicts an example 400 in which the entire electrochemical stack is provided power from the power supply, alternative examples are also possible wherein power is provided to individual substacks or individual cells of the overall electrochemical stack. As such, the electrolyzer identified in Figure 4 may refer to a substack or a cell of the electrochemical stack, such that multiple power lines are required from the power supply to provide voltage or current to the plurality of cells or substacks of the overall electrochemical stack. In other words, while not depicted in Figure 3, power lines providing voltage or current may be provided to and connect each unipolar plate within the plurality of substacks of the electrochemical stack to the power supply or plurality of power supplies.

[0047] Returning back to Figure 4, the power supply may receive power from one or more power sources. In certain examples, the power source may be an electrical grid source, e.g., provided from a power utility. Additionally, or alternatively, the power source may include a renewable generation energy source (e.g., solar, wind, hydro). In some cases, the power source may additionally include a battery storage system configured to store power provided from the power source, e.g., generated from the renewable energy source. This may be advantageous in providing power to the electrochemical stack during a power outage, therein retaining the ability to maintain a minimum shielding state and protect the electrochemical cells from discharging or degrading.

[0048] While a single power source and single power supply are depicted in Figure 4, multiple power sources and / or multiple power supplies may be connected to provide power to the stack. In some examples, two or more power sources / power supplies may be present to provide power to the electrochemical stack under different operating conditions of the stack.

[0049] For instance, in certain examples, a power supply may provide a required operating voltage or current to the stack to conduct the electrolysis reaction and generate hydrogen and oxygen gases from a water input. This operating voltage may be equal to or greater than 2 V to effectively conduct the water splitting reaction and generate hydrogen gas. In this example, the same power supply or power source may be configured to providea lower voltage or current to the stack to operate the stack in the standby state or the shielding state as described herein.

[0050] In another, alternative example, multiple power supplies may be provided to operate the electrochemical stack under different operating conditions. For instance, a first power supply or main power supply is configured to provide the operating voltage (e.g., greater than 2 V) to the electrochemical stack to conduct the water splitting reaction and generate hydrogen gas. A separate, second / alternate power supply is present within the system and configured to supply power / voltage to the stack for the standby and / or shielding conditions. This second power supply may be advantageous in controlling the lower power / voltage conditions to the stack and minimizing a voltage ripple applied to each cell of the stack. For example, the first or main power supply may be required to provide enough power to the stack to operate the stack to generate 20 MW of power via the electrolysis reaction. In the standby or shielding state, however, the amount of input power needed to maintain the cell or stack in such a standby or shielding state is on an order of magnitude lower (e.g., at 10 kW).

[0051] As noted above, the standby state or standby voltage may be in a range of 1.42-2 V to generate enough hydrogen electrochemically to maintain a constant pressure in the cathode compartment of the electrolyzer stack to make up for the hydrogen gas lost to leakage across the membrane.

[0052] Further, as noted above, the shielding voltage may be in a range of 1-1.42 V, 1.2- 1.42 V, 1.3-1.42 V, 1-1.2 V, or 1.2-1.3 V. This voltage or current may be applied to the cell in order to maintain the anode and cathode half-cell voltages. This shielding voltage is below the voltage needed for an electrolytic reaction to proceed (i.e., a water splitting, faradaic process), which occurs at approximately 1.42 V. Additionally, the shielding voltage is at or above a minimum voltage needed to prevent depolarization or uncontrolled discharge on either or both of the anode and cathode sides of the cell / substack / stack.

[0053] In other words, the shielding voltage is large enough to provide minimal power requirements, that is, low currents to maintain the charged capacitors of the anode and cathode without splitting water (hence a low current draw). Specifically, the shielding voltage may be advantageous in preventing depolarization, uncontrolled discharge, or complete discharge of the electrochemical cells within the stack without fully shutting down the system or operating the system under electrolytic reaction conditions. Further, thisminimum voltage may advantageously allow the stack to operate at a lowest power input to the stack while effectively protecting or shielding the cells within the stack from uncontrolled discharge and degradation that may occur in such a discharge process. Additionally, this minimum voltage may advantageously be applied to the cell / substack / stack indefinitely without degradation to the cell occurring due to operation at a lower voltage or current (i.e., the cell / substack / stack may still degrade over time, but not any faster under the shielding state). Also, at this low shielding voltage / state, the desired operating temperature of the cell / substack / stack for electrolytic conditions does not need to be maintained, as the temperature does not impact the shielding voltage needed to protect the system. As such, energy costs for maintaining operating temperature conditions may be reduced / saved in this shielding state as well.

[0054] In certain examples, the resistance distribution between cells or between substacks of cells within the overall electrochemical stack may not be uniform, wherein the voltage provided to each cell or each substack of the overall electrochemical stack may vary depending on the resistance distribution. As such, circuitry may be provided within the stack to assist in balancing the voltage to each cell or substack in the overall stack. In one example, passive balancing circuitry may be added to substack / stack to assist in balancing the voltage applied to the cells within the substack / stack. Alternatively, active balancing circuitry may be added to the substack / stack to assist in balancing the voltage applied to the cells within the substack / stack.Figure 11 shows an example method of operating an electrochemical stack 1100. The electrochemical stack is operated by providing a faradaic voltage to the electrochemical stack from a power supply to operate the electrochemical stack in an operating state (1102). In the operating state a gas product (such as hydrogen) is generated from a liquid (such as water) input to the electrochemical stack via electrolysis. At various times the electrochemical stack may be placed into a standby state. Thus, instructions may be received at a controller, from an operator to ramp down operation of the electrochemical stack to a shielding state (1104). In the shielding state, the plurality of electrochemical cells in the electrochemical stack no longer receives enough voltage to generate gas via electrolysis but still receives enough voltage to maintain a charged capacitance (1106). This maintenance of the charged capacitate may protect the plurality of electrochemical cells from depolarization or discharge.

[0055] ramping down an amount of voltage provided by the power supply to the electrochemical stack and providing a non-faradaic voltage to the electrochemical stack to operate the electrochemical stack in the shielding state

[0056] Figure 5 depicts an example of an alternative arrangement 500 between power source / power supply and an electrochemical cell substack or stack having passive balancing circuitry added to the cells of the substack / stack. In this arrangement, one or more power supplies may be provided to a plurality of cells or a plurality of substacks in an electrochemical stack. Figure 5 depicts 4 cells for simplicity. Any number of cells may be present within the substack or stack. Alternatively, cell 1 may refer to substack 1 including a plurality of cells, cell 2 may refer to substack 2 including a second plurality of cells, and so on.

[0057] In this example, the passive balancing circuitry includes four resistors Rl, R2, R3, R4, positioned in circuits with cells (or substacks) 1, 2, 3, 4, respectively. The resistors advantageously limit or regulate the flow of current through the circuits, therein assisting in providing a more uniform voltage across each cell or substack within the electrochemical stack. While the resistors will generate heat in this process, they advantageously provide a cost effective solution to accurately controlling voltage across the cells, therein reducing the risk of dropping below, e.g., 1 V, and degrading a specific cell or substack or rising above 1.42 V within a specific cell or substack and moving into a standby state condition.

[0058] Figure 6 depicts an example of an alternative arrangement 600 between power source / power supply and an electrochemical cell substack or stack having active balancing circuitry added to the cells of the substack / stack. In this arrangement, one or more power supplies may be provided to a plurality of cells or a plurality of substacks in an electrochemical stack. Figure 6 depicts 2 cells for simplicity. Any number of cells may be present within the substack or stack. Alternatively, cell 2 may refer to substack 2 including a plurality of cells, and cell 2 may refer to substack 2 including a second plurality of cells.

[0059] In this example, the active balancing circuitry includes a first switch SW1 and first resistor Rl associated with the first cell / substack 1 and a second switch SW2 and second resistor R2 associated with the second cell / substack 2. Again, the presence of the resistor with a cell or substack is advantageous in limiting or regulating the flow of current through the circuits. The addition of a switch in the balancing circuitry is advantageous in providingactive control of current to the resistor (i.e., an open switch = no flow of current, a closed switch = flow of current to the resistor).

[0060] In certain examples, the current to the resistor may be controlled by a processor or controller providing a signal to the respective switch to open or close the switch. This control may be based on a duty cycle of the pulse width modulation or time. For example, a set value may be input within the system for the voltage of the cell or substack. The processor or controller may receive input (signal) from an ammeter or voltmeter of the cell / substack monitoring the current or voltage across the cell / substack. The processor or controller may, based on the signal received, provide instructions (output a signal) to the cell / substack to turn on / close the switch or increase the duty cycle of the switch.

[0061] S imilar to the passive balancing circuitry example depicted in Figure 5, the active balance circuitry example depicted in Figure 6 is advantageous in controlling voltage or current across the cells, therein reducing the risk of dropping below, e.g., 1 V, and degrading a specific cell or substack or rising above 1.42 V within a specific cell or substack and moving into a standby state condition.

[0062] In some scenarios, when the electrolysis voltage is reduced, e.g., to a shielding voltage, an uneven voltage distribution along all cells may occur. Each cell may behave as having a variable (e.g., transient) capacitance and resistance due the leakage currents and / or other parasitic effects. Thus, in some cases, it may be desirable to equalize the voltage provided to the cells. Figure 9 shows an example voltage equalization circuit 900 for a plurality of electrochemical cells 902 having characterized by a variable internal resistance 904 and a variable internal capacitance 906. In the example voltage equalization circuit 900, voltage clamp 910 is designed to shunt current away from the above-target-voltage cells 902, while being inactive for the below-target-voltage cells 902. The below-target-voltage cells 902 may be pulled up via the voltage supply 908 (while the clamp 910 is inactive for the cells) and then upon reaching the target voltage, the voltage clamp 910 pulls current away from the cells 902 with the amount of current increasing linearly as the voltage of the cell goes above the target. Accordingly, the more above target a cell 902 goes; the harder down the voltage on that cell 902 is pulled. Thus, the cells are pushed toward the target voltage (e.g., either upward by the supply when below target or downward by the voltage clamp 910).

[0063] The example voltage clamp 910 may include a transistor 912 (or other switching device) may selectively shunt current away from the corresponding above-target-voltage cell 902 when active, e.g., when the target voltage (or other reference voltage, Vref) is reached. In some cases, a current limit liimit may be implemented. The current limit may be a maximum current that may be shunted away from a corresponding cell by a voltage clamp 910.

[0064] Figure 10 shows an example operating curve 1000 for the voltage clamps 910. The high voltage cells will have clamps that will shunt current away, creating more leakage current and reducing the cell's impedance. The clamp current may be proportional to the excess voltage on each cell. In some implementations, other operating curves may be used. For example, non-linearly increasing operating curves may be used. For example, a logarithmic response may be used to provide a more aggressive small deviation correction that grows less than proportionally with increasing voltage. Thus, smaller deviations above target may be corrected more quickly. However, in some cases, this may lead to over correction and oscillatory transients in the voltage curve. In various other examples, a quadratic or exponential response may be used to provide a smaller small deviation response with more the proportional response growth with increasing voltage deviation. However, in some cases this may allow for a larger above-target tolerance for the system. Therefore, a response curve may be selected based on various operational parameters and requirements for a particular system.

[0065] In various implementations, the voltage clamp architecture balances cell voltages by inserting a variable impedance across each cell and shunting current, with the end result of having all cell equivalent leakage resistances equal, which may result in the clamp acting as an extra load on when applying shielding voltage. This may result in power dissipation on the clamp circuitry. In some cases, heat management techniques and architectures, such as heatsinks, fluid-based cooling, and / or other heat management techniques may be used. The current limit for a voltage may be selected based on the power dissipation capacity of the clamp system. Accordingly, the current limit may impose a cap on the magnitude of the correction to the voltage a particular clamp may provide.

[0066] In some cases, a balance between the shielding voltage and the reference voltage of the voltage clamp may be selected. For the cells in series, the nominal shielding voltage for the cells may be VSho= (target voltage * number of cells). Using Vref at the targetvoltage may ensure that each cell is prevented from exceeding the target voltage. Supplying a shielding voltage above VSho may ensure that the supplied voltage pushes each cell to Vref, e.g., equal to the target voltage for full balancing (in this example). However, the clamps will on average shunt power leading to heating and power inefficiency. Supplying Vshoor less may result in some cells not fully reaching Vref. Thus, balancing among the cells may be reduced. Accordingly, the relationship between VSho and the selected value for the supplied voltage may be determined based on desired, balancing accuracy, power efficiency, and power dissipation requirements for a system.Discharge of the Electrochemical Stack

[0067] In some cases, such as for system shutdown, maintenance, storage, and / or transport (as discussed further below), the electrochemical stack may be discharged below the shielding state (e.g., because the electrochemical stack in being placed in a state where providing power to the electrochemical stack cannot be done, should not be done, and / or is other undesirable). When an electrolysis system discharges from a shielding state to an off state a number of degradation modes may be induced which result in degradation of individual cell components. In some cases, these degradation modes are acute and incremental and accumulate over time.

[0068] In various scenarios, degradation may be due to the full discharge of the Nernst potential to the grounded state (Voltage cycling). This may degrade the cell voltage and / or compromises the ability of the cell stack to manage crossover. In cases, such degradation may lead to premature end of life of the stack compromising the functionality of the cell stack to meet the product requirements. Additionally or alternatively, the thermal cycling of stack (e.g., due to the change in dissipated heat from the shielded to the off state) may induce mechanical stress. In some cases, thermal cycling on the cell stack components may compromises their ability to manage crossover and to maintain a healthy cell voltage.

[0069] To mitigate the effects of cycling and changing stress, a controlled ramp down of the voltage may be used to prevent the cells from discharging too quickly. However, as recognized herein, the variable resistance / capacitance (e.g., the variable impedance) of the cells may result in different rates of discharge. Thus, specific cells may experience more wear (e.g., due to more extreme cycling) during discharge and / or damage may occur due to the different voltage levels / thermal states of the cells in the same electrochemical stack. Insome scenarios, individual cells may discharge below a ground voltage due to the spread effects. This may provide an additional path of degradation.

[0070] H erein, it is recognized that (contrary to the conventional wisdom) the cells may be discharged at rates with a low spread in discharge rate among the cells. In other words, the ramp down of some cells may be decreased to more slowly discharge the cell and (contrary to the conventional wisdom) the ramp down of some cells may be increased to slightly more quickly discharge the cell. In some cases, the ramp down of cells may be only decreased to more gently discharge cells and bring all cells to a slowest discharge. However, in some cases, exclusively slowing discharge rates may render a mitigation solution insufficient for mitigation of shielding voltage spread as discussed above. Accordingly, some solutions may include slowing discharge rates and speeding discharge rates to allow dual use of the structure for also reducing shielding voltage spread.

[0071] In various implementations, discharge spread may be mitigated using the resistor network of Figure 5. The matched resistors, (e.g., Rl, R2, R3, R4) connected across the individual cells, are selected based on the internal variable impedance of the individual cells. Effectively, for shielding spread mitigation and for discharge spread mitigation, the resistors may be selected to correct for the differences among the individual internal resistances of the resistors. Thus, the resistors selected for mitigation of shielding spread may be effective in mitigating discharge spread.

[0072] In some cases, active mitigation may also correct for higher-order spread effects, which may in various scenarios be of a smaller magnitude than the first-order linear spread. Nevertheless, the correction of higher-order spread effects may reduce voltage spread increasing mitigation performance and militating toward active correction. However, in some cases, passive networks may have relatively lower system cost, lower system complexity, and / or increase robustness. Further, in some cases, performance gains afforded by active correction may be limited. Thus, passive resistor networks may be advantageous in some cases. Accordingly, various implementations may use active correction and various systems may use passive correction.

[0073] In various active correction systems, the active system of Figure 6 may be used to correct for discharge spread. As discussed above, the switches (SW1, SW2) of Figure 6 may be switched (e.g., via variable rate switching, pulse-width modulation, and / or other switching schemes) to adjust the duty cycle of the individual resistor / switch pairs for eachcell (e.g., to provide digital control for spread mitigation). The switches of Figure 6 may include mechanical switches, relays, solid-state switches (such as semiconductor-based switches) or other switch types. The adjustment of duty cycle allows for adjustment of the effective resistance provides be each individual resistor / switch pair. Accordingly, for example, the resistors of Figure 6 may be selected to correct for first order spread effects, while duty cycle adjustment may be used to correct for higher order spread effects. Other architectures may be used.

[0074] To implement the discharge spread mitigation using the system of Figure 9, the system may operate as described above, but the reference voltage (Vref) may be ramped down with the ramp down of the power. Accordingly, the setpoint of the spread correction for the cells may track the discharge progression.

[0075] Figure 12 shows an example method of discharge of an electrochemical stack. To discharge the electrochemical stack the voltage provided by the corresponding power supply may be ramped down (1202) to a non-powered state. During the ramp down, mitigation of spread may be applied (1204). The ramp down may stop when the cells reach the non-powered state (1206).Storage of the Electrochemical Stack

[0076] In various contexts, (as discussed above) the electrochemical stack may be placed out of service and thus discharged. After discharge, the electrochemical stack may be disconnected from power source and / or supplies. Further, the electrochemical stack may be exposed to changing conditions over time during storage. For example, water present within a vat within the cell may undergo chemical and / or settling changes over time. Ion content within the water may change over time. In further or alternative examples, static electricity may build-up and / or dissipate. The electrochemical stack may be exposed to thermal changes (e.g., if stored in non-thermally-controlled conditions), ambient pressure, moisture, and / or other conditions may change over time. As a result of changing conditions, energy may go into or may be removed from the cells of the electrochemical stack. Due to such energy exchange, voltage potentials may, in some cases, build up (or have a risk of building up) across the individual cells. In some scenarios, such voltage build-up across an individual cell may cause damage to the cell and / or a risk thereof.Y1

[0077] The passive resistor network of Figure 5 may be used to mitigate such voltage buildup to protect the individual cells. The resistors (e.g., Rl, R2, R3, R4) connected across the individual cells may prevent voltage buildup by ensuring that current may flow from on terminal of each cell to the other terminal of that cell. Thus, voltages building up across the cells may dissipate (e.g., rather than continuing to build). The active system of Figure 6 may be similarly used to protect the individual cells. The switches (SW1, SW2) may be left in an engaged state such that current may follow across the resistors. With the switches (SW1, SW2) left engaged, the structure of Figure 6 mimics that of Figure 5. Similarly, the voltage equalization circuit of Figure 9 may be used. The transistors within the clamps 910 may be left in a current-passing state. Thus, the resistors of the clamps 910 may be effectively connected across the terminals of the cells 902 coupled to the clamps 910. Thus, the voltage equalization circuit may behave similarly to the resistor network of Figure 5 in this passive current-passing state. Additionally or alternatively, various resistance levels may be effective in mitigating voltage buildup. For example, resistances of milliohms may be used for individual resistance values. In various scenarios, resistances of kilohms may be used. Thus, there may be flexibility in the selection of resistance value used in the protection of the cells from voltage build-up during storage (e.g., after discharge of the electrochemical stack). As a result, a resistor network used during operation of the electrochemical stack for another (e.g., an operational purpose) may be repurposed as a resistor network for protection of the individual cells of the electrochemical stack during storage of the electrochemical stack.Transportation of the Electrochemical Stack

[0078] In various contexts, the electrochemical stack may be transported during the time it is placed out of service and discharged. Similar condition changes such as water condition changes, ambient condition changes (thermal, barometric, humidity), mechanical vibrations, and / or other condition changes may also apply during transport. Indeed, increase likelihood of exposure to mechanical vibrations, occurrence of center of mass shifts, and transportation across different climates (any or all of which may occur during transport) may, in at least some cases, increase the risk and / or intensity of the change in conditions. Accordingly, during transport, risk of energy exchange occurring at the cell-level of the electrochemical stack may increase, in at least some scenarios. Thus, the likelihood ofvoltage build-up may be increased in some stack transportation scenarios. Similarly, the resistor networks discussed above may be used to protect the individual cells during transport of the electrochemical stack.Controlling Operation of the Electrochemical Stack or a Component Thereof

[0079] Figure 7 illustrates an exemplary system 120 for controlling operation of an electrochemical stack or a component / module thereof (e.g., one or more electrochemical substacks or electrochemical cells of a substack / stack). The system 120 includes the electrochemical cell / substack / stack 10 (such as depicted in Figures 2-6), a monitoring system 121, a workstation 128, and a network 127. Additional, different, or fewer components may be provided.

[0080] The monitoring system 121 includes a server 125 and a database 123. The monitoring system 121 may include computer systems and networks of a system operator (e.g., the operator of the electrochemical cell / stack 10). The server database 123 may be configured to store information regarding the operating conditions or setpoints for optimizing the performance of the electrochemical cell / stack 10.

[0081] The monitoring system 121, the workstation 128, and the electrochemical cell / stack 10 are coupled with the network 127. The phrase "coupled with" is defined to mean directly connected to or indirectly connected through one or more intermediate components. Such intermediate components may include hardware and / or software-based components.

[0082] The optional workstation 128 may be a general-purpose computer including programming specialized for providing input to the server 125. For example, the workstation 128 may provide settings for the server 125. The workstation 128 may include at least a memory, a processor, and a communication interface.

[0083] For example, the monitoring system 121 may be configured to monitor and control the voltage or current being applied to the cell / substack / stack by a power source / power supply. In certain examples, an input may be received by the monitoring system 121 from an operator of the system, e.g., via the workstation 128 or any other component over the connected network. The input may include instructions on ramping up or ramping down the electrolytic operation of the cell / substack / stack 10. In other words, an operator may provide input instructions to operate the cell / substack / stack 10 at electrolyticconditions to conduct the water splitting reaction and generate hydrogen gas. Alternatively, the operator may provide input instructions to operate the stack at standby conditions or shielding conditions, as described above. Those input instructions may be relayed to the cell / substack / stack 10 to increase or decrease the voltage or current to the cell / substack / stack 10, and in some cases, control the operating temperature and pressure of the cell / substack / stack 10.

[0084] In certain examples, the control of the cell / substack / stack may include a sequence of instructions or procedures for safely ramping up or ramping down between the various states (i.e., the operating state, the standby state, and the shielding state). For instance, upon receiving instructions to shut down the production of hydrogen for a stack, the controller may provide a sequence of instructions to the power supply to the stack to ramp down the voltage from a voltage above 2 V in the operating state to an intermediate faradaic voltage in a range 1.42-2 V in the standby state, followed subsequently by a further ramp down to a non-faradaic voltage in a range of 1-1.42 V in the shielding state.

[0085] Additional, or alternative sequencing instructions may be generated in order to ramp down (or ramp up) most efficiently and safely the voltage or power to a cell or stack to avoid any inadvertent degradation of the cell or stack.

[0086] Figure 8 illustrates an exemplary server 125 of the system of Figure 7. The server 125 includes a memory 301, a controller or processor 302, and a communication interface 305. The server 125 may be coupled to a database 123 and a workstation 128. The workstation 128 may be used as an input device for the server 125. The communication interface 305 receives data indicative of use inputs made via the workstation 128 or a separate electronic device.

[0087] The controller or processor 302 may include a general processor, digital signal processor, an application specific integrated circuit (ASIC), field programmable gate array (FPGA), analog circuit, digital circuit, combinations thereof, or other now known or later developed processor. The controller or processor 302 may be a single device or combination of devices, such as associated with a network, distributed processing, or cloud computing that is configured to control operation of one or more components of the electrochemical plant or stack.

[0088] The memory 301 may be a volatile memory or a non-volatile memory. The memory 301 may include one or more of a read only memory (ROM), random accessmemory (RAM), a flash memory, an electronic erasable program read only memory (EEPROM), or other type of memory. The memory 301 may be removable from the device 122, such as a secure digital (SD) memory card.

[0089] The communication interface 305 may include any operable connection. An operable connection may be one in which signals, physical communications, and / or logical communications may be sent and / or received. An operable connection may include a physical interface, an electrical interface, and / or a data interface. The communication interface 305 provides for wireless and / or wired communications in any now known or later developed format.

[0090] In the above-described examples, the network 127 may include wired networks, wireless networks, or combinations thereof. The wireless network may be a cellular telephone network, an 802.11, 802.16, 802.20, or WiMax network. Further, the network 127 may be a public network, such as the Internet, a private network, such as an intranet, or combinations thereof, and may utilize a variety of networking protocols now available or later developed including, but not limited to TCP / IP based networking protocols.

[0091] While the non-transitory computer-readable medium is described to be a single medium, the term "computer-readable medium" includes a single medium or multiple media, such as a centralized or distributed database, and / or associated caches and servers that store one or more sets of instructions. The term "computer-readable medium" shall also include any medium that is capable of storing, encoding, or carrying a set of instructions for execution by a processor or that cause a computer system to perform any one or more of the methods or operations disclosed herein.

[0092] In a particular non-limiting example, the computer-readable medium can include a solid-state memory such as a memory card or other package that houses one or more non-volatile read-only memories. Further, the computer-readable medium can be a random-access memory or other volatile re-writable memory. Additionally, the computer- readable medium can include a magneto-optical or optical medium, such as a disk or tapes or other storage device to capture carrier wave signals such as a signal communicated over a transmission medium. A digital file attachment to an e-mail or other self-contained information archive or set of archives may be considered a distribution medium that is a tangible storage medium. Accordingly, the disclosure is considered to include any one ormore of a computer-readable medium or a distribution medium and other equivalents and successor media, in which data or instructions may be stored.

[0093] In an alternative example, dedicated hardware implementations, such as application specific integrated circuits, programmable logic arrays and other hardware devices, can be constructed to implement one or more of the methods described herein. Applications that may include the apparatus and systems of various examples can broadly include a variety of electronic and computer systems. One or more examples described herein may implement functions using two or more specific interconnected hardware modules or devices with related control and data signals that can be communicated between and through the modules, or as portions of an application-specific integrated circuit. Accordingly, the present system encompasses software, firmware, and hardware implementations.

[0094] In accordance with various embodiments of the present disclosure, the methods described herein may be implemented by software programs executable by a computer system. Further, in an exemplary, non-limited embodiment, implementations can include distributed processing, component / object distributed processing, and parallel processing. Alternatively, virtual computer system processing can be constructed to implement one or more of the methods or functionalities as described herein.

[0095] Although the present specification describes components and functions that may be implemented in particular embodiments with reference to particular standards and protocols, the claim scope is not limited to such standards and protocols. For example, standards for Internet and other packet switched network transmission (e.g., TCP / IP, UDP / IP, HTML, HTTP, HTTPS) represent examples of the state of the art. Such standards are periodically superseded by faster or more efficient equivalents having similar functions. Accordingly, replacement standards and protocols having the same or similar functions as those disclosed herein are considered equivalents thereof.

[0096] A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a standalone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data(e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

[0097] The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

[0098] As used in this application, the term "circuitry" or "circuit" refers to all of the following: (a)hardware-only circuit implementations (such as implementations in only analog and / or digital circuitry) and (b) to combinations of circuits and software (and / or firmware), such as (as applicable): (i) to a combination of processor(s) or (ii) to portions of processor(s) / software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and (c) to circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present.

[0099] This definition of "circuitry" applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term "circuitry" would also cover an implementation of merely a processor (or multiple processors) or portion of a processor and its (or their) accompanying software and / or firmware. The term "circuitry" would also cover, for example and if applicable to the particular claim element, a baseband integrated circuit or applications processor integrated circuit for a mobile phone or a similar integrated circuit in server, a cellular network device, or other network device.

[0100] P rocessors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and anyone or more processors of any digital computer. The processor may receive instructions and data from a read only memory or a random-access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices forstoring instructions and data. The computer may also include or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks. However, a computer need not have such devices. Moreover, a computer can be embedded in another device, e.g., a mobile telephone, a personal digital assistant (PDA), a mobile audio player, a Global Positioning System (GPS) receiver, to name just a few. Computer readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media, and memory devices, including by way of example semiconductor memory devices, e.g., E PROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto optical disks; and CD ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

[0101] To provide for interaction with a user, embodiments of the subject matter described in this specification can be implemented on a device having a display, e.g., a CRT (cathode ray tube), LCD (liquid crystal display), or LED (light emitting diode) monitor, for displaying information to the user and a keyboard and a pointing device, e.g., a mouse or a trackball, by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback, e.g., visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input.

[0102] E mbodiments of the subject matter described in this specification can be implemented in a computing system that includes a back end component, e.g., as a data server, or that includes a middleware component, e.g., an application server, or that includes a front end component, e.g., a client computer having a graphical user interface or a Web browser through which a user can interact with an implementation of the subject matter described in this specification, or any combination of one or more such back end, middleware, or front end components. The components of the system can be interconnected by any form or medium of digital data communication, e.g., a communication network. Examples of communication networks include a local area network ("LAN") and a wide area network ("WAN"), e.g., the Internet.

[0103] The computing system can include clients and servers. A client and server may be remote from each other and may interact through a communication network. The relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship with each other.

[0104] One or more embodiments of the disclosure may be referred to herein, individually and / or collectively, by the term "invention" merely for convenience and without intending to voluntarily limit the scope of this application to any particular invention or inventive concept. Moreover, although specific embodiments have been illustrated and described herein, it should be appreciated that any subsequent arrangement designed to achieve the same or similar purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all subsequent adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, are apparent to those of skill in the art upon reviewing the description.

[0105] Table 1 includes various examples.

[0106] As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0107] As used herein, "for example," "for instance," "such as," or "including" are meant to introduce examples that further clarify more general subject matter. Unless otherwiseexpressly indicated, such examples are provided only as an aid for understanding embodiments illustrated in the present disclosure and are not meant to be limiting in any fashion. Nor do these phrases indicate any kind of preference for the disclosed embodiment.

[0108] The Abstract of the Disclosure is provided to comply with 37 C.F.R. §1.72(b) and is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, various features may be grouped together or described in a single embodiment for the purpose of streamlining the disclosure. This disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter may be directed to less than all of the features of any of the disclosed embodiments. Thus, the following claims are incorporated into the Detailed Description, with each claim standing on its own as defining separately claimed subject matter.

[0109] It is intended that the foregoing detailed description be regarded as illustrative rather than limiting and that it is understood that the following claims including all equivalents are intended to define the scope of the disclosure. The claims should not be read as limited to the described order or elements unless stated to that effect. Therefore, all embodiments that come within the scope and spirit of the following claims and equivalents thereto are claimed as the disclosure.

Claims

CLAIMS1. An electrochemical system configured to generate gas via electrolysis of a liquid, the electrochemical system comprising: at least one electrochemical cell; at least one power supply configured to provide voltage to the at least one electrochemical cell; and a controller in communication with the at least one power supply and the at least one electrochemical cell, wherein the controller is configured to provide instructions to the at least one power supply and the at least one electrochemical cell to: operate in an operating state in which a faradaic voltage is provided to the at least one electrochemical cell and the at least one electrochemical cell is configured to receive the liquid and generate the gas via electrolysis; and ramp down to a shielding state in which a non-faradaic voltage is provided to the at least one electrochemical cell, wherein, in the shielding state, the at least one electrochemical cell no longer receives enough voltage to generate the gas via electrolysis, but still receives enough voltage to maintain a charged capacitance and protect the at least one electrochemical cell from depolarization or discharge.

2. The electrochemical system of claim 1, wherein the controller is further configured to provide instructions to the at least one power supply and the at least one electrochemical to ramp down from the operating state to a standby state or ramp up from the shielding state to the standby state, wherein, in the standby state, a faradaic voltage lower than the faradaic voltage at the operating state is provided to the at least one electrochemical cell, wherein the faradaic voltage in the standby state is configured to generate a minimum amount of the gas through electrolysis to maintain a constant pressure and / or temperature on a cathode side of the at least one electrochemical cell.

3. The electrochemical system of claim 2, wherein the faradaic voltage in the standby state is in a range of 1.42 V to 2 V.

4. The electrochemical system of claim 1, wherein the faradaic voltage in the operating state is at least 2 V.

5. The electrochemical system of claim 1, wherein the non-faradaic voltage in the shielding state is in a range of 1 V to 1.42 V.

6. The electrochemical system of claim 1, wherein, in the shielding state, a pressure and / or a temperature of the at least one electrochemical cell is not controlled.

7. The electrochemical system of claim 1, wherein an amount of time spent operating the at least one electrochemical cell in the shielding state does not contribute to or increase a rate of degradation of the at least one electrochemical cell.

8. The electrochemical system of claim 1, wherein the at least one electrochemical cell comprises a plurality of electrochemical cells in an electrochemical stack.

9. The electrochemical system of claim 8, wherein the plurality of electrochemical cells is divided into a plurality of substacks, each substack comprising more than one electrochemical cell.

10. The electrochemical system of claim 9, wherein the at least one power supply is connected to each individual substack and configured to, in conjunction with the controller of the electrochemical system, provide a respective voltage to each individual substack.

11. The electrochemical system of claim 8, wherein the electrochemical stack comprises balancing circuitry configured to control the voltage across the plurality of electrochemical cells.

12. The electrochemical system of claim 11, wherein the balancing circuitry is a passive balancing circuitry in which one or more circuits are provided for one or more electrochemical cells in the plurality of electrochemical cells, wherein each circuit comprises a resistor configured to regulate a flow of current through the circuit.

13. The electrochemical system of claim 11, wherein the balancing circuitry is an active balancing circuitry in which one or more circuits are provided for one or more electrochemical cells in the plurality of electrochemical cells, wherein each circuit comprises a switch configured to move between an open position and a closed position, and a resistor configured to regulate a flow of current through the circuit when the switch is in the closed position.

14. The electrochemical system of claim 1, wherein the at least one power supply comprises a first power supply and a second power supply, wherein the first power supply is configured to provide the faradaic voltage to the at least one electrochemical cell to operate the at least one electrochemical cell in the operating state, and wherein the second power supply is configured to provide the non-faradaic voltage to the at least one electrochemical cell to operate the at least one electrochemical cell in the shielding state.

15. The electrochemical system of claim 1, further comprising: at least one power source configured to provide power to the at least one power supply.

16. The electrochemical system of claim 15, wherein the at least one power source comprises an electrical grid source, a renewable generation energy source, or a combination thereof.

17. The electrochemical system of claim 16, wherein each electrochemical cell of the at least one electrochemical cell is configured to operate with 200 mV or less of pure resistive loss when operating at a current density of at least 3 Amps / cm2.

18. A method for controlling operation of an electrochemical stack having a plurality of electrochemical cells, the method comprising: providing a faradaic voltage to the electrochemical stack from a power supply to operate the electrochemical stack in an operating state, wherein hydrogen is generated from a liquid input to the electrochemical stack via electrolysis; receiving, by a controller, instructions from an operator to ramp down operation of the electrochemical stack to a shielding state, wherein, in the shielding state, the plurality of electrochemical cells in the electrochemical stack no longer receives enough voltage to generate gas via electrolysis, but still receives enough voltage to maintain a charged capacitance and protect the plurality of electrochemical cells from depolarization or discharge; and ramping down an amount of voltage provided by the power supply to the electrochemical stack and providing a non-faradaic voltage to the electrochemical stack to operate the electrochemical stack in the shielding state.

19. The method of claim 18, wherein the ramping down comprises a sequence of instructions from the controller, wherein the sequence of instructions comprises firstly ramping down the amount of voltage provided by the power supply from the operating state to a standby state, and then secondly ramping down the amount of voltage provided by the power supply from the standby state to the shielding state, wherein, in the standby state, a faradaic voltage lower than the faradaic voltage at the operating state is provided to the electrochemical stack, and wherein the faradaic voltage in the standby state is configured to generate a minimum amount of the gas through electrolysis to maintain a constant pressure and / or temperature on a cathode side of the electrochemical stack.

20. A method for controlling operation of an electrochemical stack having a plurality of electrochemical cells, the method comprising: receiving, by a controller, instructions from an operator to place the electrochemical stack to a shielding state, wherein, in the shielding state, the plurality of electrochemicalcells in the electrochemical stack no longer receives enough voltage to generate gas via electrolysis, but still receives enough voltage to maintain a charged capacitance and protect the plurality of electrochemical cells from depolarization or discharge; and providing an amount of voltage by the power supply to the electrochemical stack and providing a non-faradaic voltage to the electrochemical stack to operate the electrochemical stack in the shielding state.

21. A method of protecting an electrochemical stack from cell-to-cell voltage spread during discharge of the electrochemical stack, the method including: receiving at control circuitry a command to discharge the electrochemical stack; in response to the command, ramping down, from a faradaic voltage level and / or a shielding voltage level and to a non-powered voltage, a supplied voltage from a power supply of the electrochemical stack; and during the ramp down, shunting current to narrow the cell-to-cell voltage spread via a matched resistor network, individual resistors of the matched resistor network paired to individual cells of the electrochemical stack to compensate, at least in part, for differences among respective internal impedances of the cells of the electrochemical stack.

22. The method of claim 21, where the resistor network includes a passive resistor network.

23. The method of claim 21, where the individual resistors of the resistor network are coupled the paired individual cells of the electrochemical stack via one or more active electrical components.

24. The method of claim 23, where: the one or more active electrical components include a switch; and the method further includes adjusting a duty cycle via the switch to control an effective resistance across switch and a respective individual resistor of the resistor network.

25. The method of claim 24, where the switch includes a mechanical switch, a relay, and / or a solid-state switch.

26. The method of claim 24, where the switch is configured to stay in an engaged state when the non-powered voltage is reached to support storage and / or transport of the electrochemical stack.

27. The method of claim 24, where adjusting the duty cycle includes adjusting a switching rate and / or a pulse width.

28. The method of claim 23, where the active component includes a transistor controlled in accord with a reference voltage, the transistor configured to control in accord with the reference voltage an effective resistance across switch and a respective individual resistor of the resistor network.

29. The method of claim 28, where the transistor is configured to adjust the effective resistance to pull a respective individual resistor of the resistor network to the reference voltage when a voltage level of the respective individual resistor of the resistor network deviates from the reference voltage.

30. The method of claim 28, where the transistor includes a bipolar junction transistor, and / or a mosfet transistor.

31. The method of claim 28, where the transistor is configured to stay in a currentpassing state when the non-powered voltage is reached to support storage and / or transport of the electrochemical stack.

32. A device including: an electrochemical stack including multiple cells; a power supply for the electrochemical stack; a resistor network configured to protect an electrochemical stack from ce ll-to-ce 11 voltage spread during discharge of the electrochemical stack, individual resistors of thematched resistor network paired to individual cells of the electrochemical stack to compensate, at least in part, for differences among respective internal impedances of the cells of the electrochemical stack; and control circuitry configured to: receive a command to discharge the electrochemical stack; and cause the power supply to ramp down, from a faradaic voltage level and / or a shielding voltage level and to a non-powered voltage, a supplied voltage, wherein: during the ramp down, the resistor network is configured to shunt current to narrow the cel l-to-cell voltage spread via a matched resistor network.

33. The device of claim 32, where the resistor network includes a passive resistor network.

34. The device of claim 32, where the individual resistors of the resistor network are coupled the paired individual cells of the electrochemical stack via one or more active electrical components.

35. The device of claim 34, where: the one or more active electrical components include a switch; and the method further includes adjusting a duty cycle via the switch to control an effective resistance across switch and a respective individual resistor of the resistor network.

36. The device of claim 35, where the switch includes a mechanical switch, a relay, and / or a solid-state switch.

37. The device of claim 35, where the switch is configured to stay in an engaged state when the non-powered voltage is reached to support storage and / or transport of the electrochemical stack.

38. The device of claim 35, where the control circuitry is configured to adjust, via the switch, the duty cycle by adjusting a switching rate and / or a pulse width.

39. The device of claim 34, where the active component includes a transistor controlled in accord with a reference voltage, the transistor configured to control in accord with the reference voltage an effective resistance across switch and a respective individual resistor of the resistor network.

40. The device of claim 39, where the transistor is configured to adjust the effective resistance to pull a respective individual resistor of the resistor network to the reference voltage when a voltage level of the respective individual resistor of the resistor network deviates from the reference voltage.

41. The method of claim 39, where the transistor includes a bipolar junction transistor, and / or a mosfet transistor.

42. The method of claim 39, where the transistor is configured to stay in a currentpassing state when the non-powered voltage is reached to support storage and / or transport of the electrochemical stack.

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