Stimulation source for hydrogen cell stack health assessment based on EIS

Abstract

The invention relates to a stimulus for hydrogen cell stack health assessment based on EIS. A measurement device for an electrochemical system includes a stimulation circuit configured to simultaneously apply a direct current (DC) stimulation and an alternating current (AC) stimulation to one or more electrochemical cells of the electrochemical system, where the AC stimulation is applied at a plurality of frequencies; an impedance measurement circuit configured to measure an impedance of the one or more electrochemical cells; and a controller configured to synchronize the application of the DC stimulus and the AC stimulus with impedance measurements at a plurality of frequencies and to record the measured impedance of the one or more electrochemical cells.

Description

[0001] Priority Claim

[0002] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 612,896, filed December 20, 2023, the entire content of which is incorporated herein by reference. Technical Field

[0003] This document relates to measurement devices and methods, and particularly to measurement devices and methods for electrochemical systems. Background Art

[0004] An electrolyzer system can include multiple hydrogen production cells connected together as a stack. Hydrogen production cells can be prone to failure. Electrochemical impedance spectroscopy (EIS) is a method for measuring electrochemical impedance. Electrochemical impedance is typically measured by applying an AC (alternating current) signal (such as a sinusoidal test voltage or current) to the electrochemical cell under test and then measuring the current or voltage passing through the electrochemical cell over an appropriate frequency range. This technique can be used to study the electrochemical performance of devices such as hydrogen production cells to evaluate the health of the hydrogen production cells. Brief Description of the Drawings

[0005] In the drawings, which are not necessarily to scale, the same numbers can describe similar components in different views. Similar numbers with different letter suffixes can represent different instances of similar components. The drawings generally illustrate, by way of example and not limitation, the various embodiments discussed in this document.

[0006] Figure 1 is a block diagram of a portion of an example of an electrochemical system.

[0007] Figure 2 is a block diagram of a portion of an example of an electrochemical system with electrochemical impedance spectroscopy (EIS) monitoring capabilities.

[0008] Figure 3 is a flowchart of an example of a method for testing an electrochemical system.

[0009] Figure 4 is a block diagram of another instance of a portion of an electrochemical system.

[0010] Figure 5 is a block diagram of another instance of a portion of an electrochemical system.

[0011] Figure 6 is a block diagram of another example of a portion of an electrochemical system. Detailed Description

[0012] Electrochemical Impedance Spectroscopy (EIS) can be used to quantify the health of electrochemical cells in electrochemical systems such as hydrogen electrolyzer systems, fuel cell systems, or battery cell systems. An example of the EIS process includes applying an electrical stimulus to the electrochemical cell, waiting for a stabilization time, and then measuring the electrochemical impedance of the electrochemical cell. The frequency of the electrical stimulus signal is swept across a frequency range, and the measured electrochemical impedance as a function of frequency is analyzed. EIS monitoring electronic devices attached to one or more electrochemical cells can provide an autonomous recording of signals related to the electrochemical cells, and these signals can provide data on the state of the electrochemical cells.

[0013] Hydrogen electrolyzers are electrochemical systems that have received attention in the clean energy transition and decarbonization efforts of different market sectors. A hydrogen electrolyzer is a device that produces hydrogen through an electrolysis process in which water molecules are decomposed into hydrogen (H2) and oxygen (O2) using electricity. EIS can be used to evaluate the health of electrolyzer cells or stacks and predict the degradation of electrolyzer cells. EIS can also be used to evaluate the health of fuel cell systems and battery systems.

[0014] Figure 1 is a block diagram of a portion that is an example of an electrochemical system of a hydrogen electrolyzer system 100. The system includes an electrochemical cell stack 102 and a power source 104. The electrochemical cell stack 102 includes a plurality of hydrogen production cells connected in series as a stack. The power source 104 applies a DC (direct current) bias voltage to the cell stack 102 to produce hydrogen. Since hydrogen production cells are prone to failure, it is necessary to predict the degradation of hydrogen production cells. Monitoring the cell stack 102 using EIS will predict the degradation of the cells.

[0015] Figure 2 is a block diagram of a partial example of a hydrogen electrolyzer system 200 with EIS monitoring capabilities. The system includes a cell stack 102, a DC power source with a stimulation circuit 204, and an impedance measurement circuit 206. The cell stack 102 can include a plurality of hydrogen production cells as in Figure 1 the example. The stimulation circuit 204 applies a DC stimulus and an AC stimulus to the electrochemical cell stack 102. The DC stimulus is applied to produce hydrogen, and the AC stimulus is applied to measure the electrochemical impedance of each hydrogen production cell of the cell stack 102. The AC stimulus is applied at multiple frequencies, and the impedance measurement circuit 206 measures the impedance of each electrochemical cell.

[0016] The system also includes a controller 208. The controller 208 includes logic circuitry that performs the functions. The logic circuitry can include a microprocessor, an application-specific integrated circuit (ASIC), or other types of processors for interpreting or executing instructions contained in software or firmware. The logic circuitry can also include a precision clock. The controller 208 synchronizes the application of the DC stimulus and the AC stimulus with the impedance measurements at multiple frequencies.

[0017] The impedance measurement circuit 206 may include a precision current sensor 210 for measuring the AC stimulation current. The current sensor 210 may include a shunt resistor, a Hall effect sensor, a current transformer, a magnetic field sensor, or other types of precision current sensors. In a non-limiting example, the measurement of the current sensor 210 may produce a digital current value with a precision of 12 bits or higher. The impedance measurement circuit 206 also includes a voltage sensor 212 for measuring the AC voltage generated by the AC stimulation current.

[0018] The impedance measurement circuit 206 uses the current and voltage values from the sensors to determine the impedance of the electrochemical cell. The controller 208 uses a memory that may be integrated into the controller 208 to record the measured impedance of one or more electrochemical cells. The controller 208 may use the electrochemical impedance determined at multiple frequencies to generate an indication of the condition of one or more hydrogen production cells.

[0019] Figure 3 is a flowchart of an example of a method 300 for testing an electrochemical system including one or more electrochemical cells. At step 305, a DC bias voltage is applied to the electrochemical cell. The electrochemical cell may be Figure 2 the hydrogen production cell of the hydrogen electrolysis cell system 200, and the DC bias voltage may be the DC energy applied to the cell to produce hydrogen. At block 310, an AC stimulation having a DC bias is applied to one or more electrochemical cells. The AC stimulation is applied at multiple frequencies. In a non-limiting example, an AC stimulation having a frequency in the range of 1 hertz (1 Hz) to 10 kilohertz (10 kHz) is applied. The electrochemical system includes an impedance measurement circuit (e.g., Figure 2 the impedance measurement circuit 206 in ). At block 315, the electrochemical impedance of the cell is determined for multiple frequencies.

[0020] The electrochemical system includes a controller (e.g., Figure 2 the controller 208 in ). The controller synchronizes the application of the DC stimulation and the AC stimulation, and synchronizes the application of the AC stimulation with the impedance measurement at multiple frequencies. The AC stimulation may be applied only when the electrochemical impedance of the cell is to be measured. In some examples, the controller waits for a specified stabilization time after applying the AC stimulation before determining the electrochemical impedance.

[0021] The impedance measurement circuit provides an accurate measurement of the AC stimulation current for the controller. In some examples, the controller samples the AC stimulation current at a sampling rate of 5 thousand samples per second (5 ksps) or higher. The impedance measurement circuit provides a measurement of the AC stimulation voltage of the electrochemical cell generated by the AC stimulation current. The controller uses the measurements of the AC current and voltage to determine the electrochemical impedance of the electrochemical cell. The stimulation circuit applies an AC current to the electrochemical cell at multiple frequencies. The controller receives the voltage measurements generated by the AC current and determines the electrochemical impedance at multiple frequencies.

[0022] At block 320, the controller can generate an indication of the condition of one or more electrochemical cells based on the electrochemical impedance determined at multiple frequencies. The controller processes the collected impedance data to detect any anomalies in the electrochemical cells of the battery stack. The controller can compare the curve of the impedance data measured for the electrochemical cell versus frequency with a baseline curve of impedance data versus temperature. If the measured curve is significantly different from the baseline curve, the controller can generate an indication that one or more of the electrochemical cells are abnormal or defective.

[0023] Returning to Figure 2 , the controller 208 can be co-located with, or not co-located with, the impedance measurement circuit 206 and the stimulation circuit 204. The controller 208 can send commands to the stimulation circuit 204 using the isolation interface 214, and the controller 208 can receive one or more impedance data, current data, and voltage data via the isolation interface 214. The data and commands can be sent through the interface 214 using an isolated control area network (ISO-CAN) protocol, an isolated serial port interface (ISO-SPI) protocol, a 10BaseT1S protocol, a 10BaseT1L protocol, or other isolated interface protocols. In some examples, the isolation interface 214 is a wireless interface. For example, the controller 208 sends commands to the stimulation circuit 204 to synchronize the timing of the AC stimulation and the start of the measurement to determine the impedance. The measurement data can be communicated through the isolation interface 214 at a sampling rate or a decimation rate. The impedance measurement circuit 206 can include a synchronous or asynchronous sampling rate converter that provides the measurement data at a rate that is an integer multiple of the AC stimulation frequency.

[0024] The amplitude of the AC stimulation is a fraction of the DC stimulation amplitude. For example, the stimulation circuit 204 can provide power to the AC stimulation that is five percent (0.05x) of the DC stimulation output power. As explained earlier in this document, the stimulation circuit 204 provides the AC stimulation at multiple frequencies (e.g., in the frequency range of 1 Hz - 10 kHz).

[0025] The stimulation circuit 204 can generate DC stimulation from an AC line power supply using a rectifier. Typically, a rectifier circuit is designed to suppress the line frequency (e.g., 50 Hz or 60 Hz) in the generated DC voltage. In some examples, the stimulation circuit 204 includes a rectifier that is designed to emphasize the line frequency as an AC stimulation frequency rather than suppress the line frequency. The stimulation circuit 204 can generate AC signals at the line frequency and multiples of the line frequency for AC stimulation. The stimulation circuit 204 can include a switched-mode converter for regulating the DC output. The stimulation circuit can generate AC signals at the switching frequency and harmonic frequencies of the switching frequency. The AC signal can be or can not be a sinusoidal signal.

[0026] In some examples, the stimulation circuit 204 includes an analog-to-digital converter (ADC) for measuring the frequency of the AC signal, and the frequency measurement value is provided to the controller 208. This provides a more accurate impedance measurement in the EIS monitoring performed by the system, where the impedance is a function of frequency. In certain examples, the electrochemical cell stack 102 can have a natural cell self-resonant frequency that coincides with the harmonics of the line frequency. The impedance measurement can be performed using AC stimulation at the cell resonant frequency and harmonics of the cell resonant frequency.

[0027] The stimulation circuit 204 can include a single power supply circuit, and both DC stimulation and AC stimulation are provided by the same power supply circuit. In some examples, the stimulation circuit 204 includes two power supply circuits; a DC power supply circuit for providing DC stimulation and a separate AC power supply circuit for providing AC stimulation. In some examples, the two power supply circuits of the stimulation circuit 204 include a hybrid power supply circuit that can provide AC and DC stimulation and another AC power supply circuit.

[0028] Figure 4 Another example of a block diagram of a portion of the electrochemical system 400. The stimulation circuit 204 includes a hybrid power supply circuit 416 and an AC power supply circuit 418. To simplify the illustration, the impedance measurement circuit is not shown. The hybrid power supply circuit 416 provides a DC bias and low-frequency AC stimulation. For AC stimulation in a lower frequency range (e.g., <10 Hz), the controller 208 configures the hybrid power supply circuit 416 to deliver DC stimulation and AC stimulation at multiple frequencies up to 10 Hz. The impedance circuit uses the AC stimulation provided by the hybrid power supply circuit 416 to measure the electrochemical impedance for impedance measurements in the lower frequency range. For higher frequencies (e.g., >10 Hz), the controller 208 configures the hybrid power supply to provide a constant DC current without an AC component and configures the AC power supply circuit 418 to provide the AC stimulation at frequencies above 10 Hz. The impedance circuit uses the AC stimulation from the AC power supply circuit 418 to measure the electrochemical impedance in the higher frequency range.

[0029] Figure 5Another example of a block diagram of a portion of an electrochemistry system 500. The stimulation circuit 204 includes a hybrid power supply circuit 516 and an AC power supply circuit 518. The hybrid power supply circuit 416 provides a DC bias and low-frequency (LF) AC stimulation, and the AC power supply circuit 58 provides high-frequency (HF) AC stimulation. Both the hybrid power supply circuit 516 and the AC power supply circuit 518 are switched-mode power supply circuits. The hybrid power supply circuit 516 and the AC power supply circuit 518 are divided based on power switching technology. For example, the hybrid power supply circuit 516 may include a silicon (Si)-based power switch, and the AC power supply circuit 518 may include a silicon carbide (SiC) power switch or a gallium nitride (GaN) power switch to accommodate higher signal frequencies. The controller 208 configures the hybrid power supply circuit 416 to deliver DC stimulation and deliver AC stimulation for impedance measurement in a lower frequency range, configures the hybrid power line 516 to deliver DC stimulation without an AC component, and configures the AC power line 518 to deliver the AC stimulation in a higher frequency range for impedance measurement.

[0030] Figure 6 Another example of a block diagram of a portion of an electrochemistry system 600. The system includes two electrochemical cell stacks 102 and two power supply circuits PS1 and PS2. The power supply circuits provide a DC bias to the electrochemical cell stacks 102A, 102B. An AC stimulation is provided using a bidirectional DC-DC stimulation subsystem 620. The DC-DC stimulation subsystem 620 includes a first isolated bidirectional DC-DC converter 624 and a second isolated bidirectional DC / DC converter 626. The isolated bidirectional DC-DC converter may include a dual active bridge (DAB) topology that uses pulse width modulation (PWM) to generate DC output power.

[0031] Each full-bridge DC-DC converter generates charge from the DC bias generated by its corresponding power supply circuit and stores the charge on an energy storage device. In Figure 6 the example, the energy storage device is an energy storage capacitor (C), but other energy storage devices (such as batteries) may also be used. The charge stored on the energy storage capacitor is used to provide AC stimulation to the electrochemical cell stacks 102A, 102B. The DC-DC converters operate in opposite phases. For example, in the first phase, the first isolated bidirectional DC-DC converter 624 absorbs current from the source PS1 into the energy storage capacitor, and the second isolated bidirectional DC / DC converter 626 supplies current from the energy storage capacitor to the electrochemical cell stack 102B. In the second phase, the first isolated bidirectional DC-DC converter 624 supplies current from the energy storage capacitor to the electrochemical cell stack 102A, and the second isolated bidirectional DC / DC converter 626 absorbs current from the source PS2 into the energy storage capacitor.

[0032] The energy stored in the energy storage capacitor determines the maximum alternating current stimulation and the minimum frequency (f min ) of the alternating current stimulation. In some examples, the power circuits PS1 and PS2 are hybrid power circuits. Below the minimum frequency (f min ) of the bidirectional DC-DC stimulation subsystem 620, the power circuit provides AC stimulation.

[0033] As explained earlier herein, the exemplary electrochemical systems described herein having EIS capabilities can be used with a hydrogen electrolyzer system. The DC bias generated by the stimulation circuit can be the DC operating energy for generating hydrogen in a hydrogen production cell. The electrochemical system having EIS capabilities can also be used with a battery system. The DC bias can be the DC charging energy, and the AC stimulation allows impedance measurements to be made during the charging cycle of the battery cells or battery modules of the battery system.

[0034] The EIS data collected and processed by the electrochemical systems described herein can be used to predict the health of an electrochemical cell or an electrochemical cell stack, predict the degradation of the cell or stack, and identify problem cells to be replaced in the electrochemical cell system.

[0035] Additional description and aspects

[0036] The first aspect (Aspect 1) includes a subject matter (e.g., a measuring device for an electrochemical system), comprising: a stimulation circuit configured to simultaneously apply a direct current (DC) stimulation and an alternating current (AC) stimulation to one or more electrochemical cells of the electrochemical system, wherein the AC stimulation is applied at a plurality of frequencies, an impedance measurement circuit configured to measure the impedance of the one or more electrochemical cells, and a controller configured to synchronize the application of the DC stimulation and the AC stimulation with the impedance measurement at a plurality of frequencies and record the measured impedance of the one or more electrochemical cells.

[0037] In Aspect 2, the subject matter of Aspect 1 optionally includes an impedance measurement circuit comprising: a current sensor for measuring the AC stimulation current applied to the one or more electrochemical cells at a plurality of frequencies; and a voltage sensor configured to measure the voltage of the one or more electrochemical cells when measuring the AC stimulation current. The controller is optionally configured to use the measurements of the AC stimulation current and the voltage of the one or more electrochemical cells to determine the electrochemical impedance at a plurality of frequencies.

[0038] In Aspect 3, the subject matter of one or both of Aspect 1 and Aspect 2 optionally includes a power circuit configured to deliver both the DC stimulation and the AC stimulation to one or more electrochemical cells.

[0039] In aspect 4, the subject matter of one or both of aspects 1 and 2 optionally includes: a hybrid power circuit configured to deliver the DC stimulus and a first frequency range of the AC stimulus; and an AC power circuit configured to deliver a second frequency range of the AC stimulus.

[0040] In aspect 5, the subject matter of one or both of aspects 1 and 2 optionally includes: a DC power circuit configured to apply the DC stimulus; and an AC power circuit configured to apply the AC stimulus.

[0041] In aspect 6, the subject matter of one or any combination of aspects 1-5 optionally includes: a DC-DC converter circuit configured to generate charge from the DC stimulus, store the charge on an energy storage capacitor; and use the energy storage capacitor to provide the AC stimulus.

[0042] In aspect 7, the subject matter of aspect 6 optionally includes an electrochemical cell and a DC-DC converter circuit, the electrochemical cell including a first stack of at least one electrochemical cell and a second stack of at least one electrochemical cell, and the DC-DC converter circuit including a first bidirectional DC-DC converter circuit configured to provide the AC stimulus to the first electrochemical cell stack during a first operation phase and store the charge on the energy storage capacitor during a second operation phase, and a second bidirectional DC-DC converter circuit configured to store the charge on the energy storage capacitor during the first operation phase and provide the AC stimulus to the second electrochemical cell stack during the second operation phase.

[0043] In aspect 8, the subject matter of one or any combination of aspects 1-7 optionally includes a power circuit configured to provide an AC stimulus that includes multiple frequencies derived from one or both of the line frequency and the switching frequency of a switching converter circuit.

[0044] Aspect 9 includes the subject matter (such as a method for testing an electrochemical system), or can optionally be combined with one or any combination of aspects 1-8 to include such subject matter, including: applying a direct current (DC) bias to one or more electrochemical cells of the electrochemical system, applying an alternating current (AC) stimulus having multiple frequencies with the DC bias to the one or more electrochemical cells, determining the electrochemical impedance of the one or more electrochemical cells at the multiple frequencies, and using the electrochemical impedance determined at the multiple frequencies to generate an indication of the condition of the one or more electrochemical cells.

[0045] In aspect 10, the subject matter of aspect 9 optionally includes applying the AC stimulus to the one or more electrochemical cells, waiting for a specified settling time, and measuring the AC stimulus current and AC stimulus voltage at multiple frequencies, and using the measured AC stimulus current and AC stimulus voltage to determine the electrochemical impedance.

[0046] In aspect 11, the subject matter of one or both of aspects 9 and 10 optionally includes providing the DC bias and the AC stimulus using the same power supply circuit.

[0047] In aspect 12, the subject matter of one or both of aspects 9 and 10 optionally includes using a hybrid power supply circuit to provide a first frequency range of the DC bias and the AC stimulus, and using an AC power supply circuit to provide a second frequency range of the AC stimulus.

[0048] In aspect 13, the subject matter of one or both of aspects 9 and 10 optionally includes using a DC power supply circuit to provide the DC bias, and using an AC power supply circuit to provide the AC stimulus.

[0049] In aspect 14, the subject matter of one or any combination of aspects 9 - 13 optionally includes using a DC - DC converter circuit to generate charge from the DC bias, storing the charge generated by the DC - DC converter circuit on an energy storage device, and using the energy storage device to provide the AC stimulus.

[0050] In aspect 15, the subject matter of one or any combination of aspects 9 - 14 optionally includes, during a first phase, using a first bidirectional DC - DC converter circuit to provide the AC stimulus to a first electrochemical cell stack, and storing charge on the energy storage capacitor during a second phase, and during the second phase, using a second bidirectional DC - DC converter circuit to provide the AC stimulus to a second electrochemical cell stack, and storing charge on the energy storage capacitor during the first phase.

[0051] In aspect 16, the subject matter of one or any combination of aspects 9 - 15 optionally includes applying an AC stimulus that has one or both of a line grid frequency and a stimulus switching frequency, and has one or more other frequencies derived from the line grid frequency or the stimulus switching frequency.

[0052] Aspect 17 includes a subject matter (e.g., an electrochemical system), or may optionally be combined with a subject matter of one or any combination of Aspects 1-16 to include such a subject matter, including at least one electrochemical cell stack, a measuring device, and a controller. The at least one electrochemical cell stack includes a plurality of electrochemical cells. The measuring device includes a stimulation circuit configured to simultaneously apply a direct current (DC) stimulation and an alternating current (AC) stimulation to the at least one electrochemical cell stack, wherein the AC stimulation is applied at a plurality of frequencies, and an impedance measurement circuit configured to measure the impedance of the electrochemical cell. The controller is configured to synchronize the application of the DC stimulation and the AC stimulation with the impedance measurement at a plurality of frequencies and record the measured impedance of the electrochemical cell.

[0053] In Aspect 18, the subject matter of Aspect 17 optionally includes an impedance measurement circuit that includes a current sensor for measuring an AC stimulation current of the AC stimulation applied to the electrochemical cell at a plurality of frequencies, and a voltage sensor configured to measure an AC stimulation voltage of the electrochemical cell caused by the AC stimulation current. The controller is optionally configured to scan the frequency of the AC stimulation current to a plurality of frequencies and use the measurements of the AC stimulation current and the AC stimulation voltage to determine the impedance at a plurality of frequencies.

[0054] In Aspect 19, the subject matter of one or both of Aspects 17 and 18 optionally includes at least one electrochemical cell stack that includes a plurality of hydrogen electrolyzer cells connected in series, and the DC stimulation is used to operate the hydrogen electrolyzer.

[0055] In Aspect 20, the subject matter of one or any combination of Aspects 17-19 optionally includes at least one electrochemical cell stack that includes a plurality of battery cells connected in series.

[0056] These non-limiting aspects may be combined in any arrangement or combination. The above detailed description includes references to the drawings that form a part of the detailed description. The drawings illustrate, by way of example, specific embodiments in which the invention may be practiced. These embodiments are also referred to herein as "examples". All publications, patents, and patent documents cited herein are hereby incorporated by reference in their entirety as if individually incorporated by reference. If there is an inconsistency in the usage between this document and the incorporated cited documents, the usage in the incorporated cited documents shall be regarded as a supplement to the usage in this document; for irreconcilable inconsistencies, the usage in this document shall govern.

[0057] In this document, the term "a" or "an" is common in patent documents and is used to include one or more, independent of any other instances or uses of "at least one" or "one or more". In this document, the term "or" is used to refer to non-exclusive, such that "A or B" includes "A but not B", "B but not A", and "A and B", unless otherwise stated. In the appended claims, the terms "comprising" and "wherein" are used as the plain English equivalents of the respective terms "including" and "in which". Further, the terms "comprised of" and "containing" in the following claims are open-ended, meaning that a system, apparatus, article, or process that includes elements other than those listed after such term in the claim is still considered to fall within the scope of that claim. Additionally, in the following claims, the terms "first", "second", and "third", etc. are used only as labels and are not intended to impose a numerical requirement on their objects. The method examples described herein can be implemented, at least in part, by a machine or a computer.

Claims

1. A measuring device for an electrochemical system, the device comprising: a stimulation circuit configured to simultaneously apply a direct current (DC) stimulus and an alternating current (AC) stimulus to one or more electrochemical cells of the electrochemical system, wherein the AC stimulus is applied at a plurality of frequencies; an impedance measurement circuit configured to measure impedance of the one or more electrochemical cells; as well as A controller is configured to synchronize the application of the DC stimulus and the AC stimulus with impedance measurement at a plurality of frequencies and record the measured impedance of the one or more electrochemical cells.

2. The apparatus according to claim 1, wherein the impedance measurement circuit comprises: a current sensor for measuring an AC stimulation current applied to the one or more electrochemical cells at a plurality of frequencies; and a voltage sensor configured to measure a voltage of the one or more electrochemical cells while measuring the AC stimulation current; and Wherein, the controller is configured as: Electrochemical impedance at a plurality of frequencies is determined using measurements of the AC stimulation current and the voltage of the one or more electrochemical cells.

3. The device of claim 1, wherein the stimulation circuit comprises a power circuit configured to deliver both the DC stimulus and the AC stimulus to the one or more electrochemical cells.

4. The device of claim 1, wherein the stimulation circuit comprises: a hybrid power circuit configured to deliver the DC stimulus and a first frequency range of the AC stimulus; and The AC power circuit is configured to deliver a second frequency range of the AC stimulus.

5. The device of claim 1, wherein the stimulation circuit comprises: a DC power supply circuit configured to apply the DC stimulus; and An AC power circuit is configured to apply the AC stimulus.

6. The device of claim 1, wherein the stimulation circuit comprises: The DC-DC converter circuit is configured as: generating an electric charge from the DC stimulation; storing the charge on a storage capacitor; and The AC stimulus is provided using the energy storage capacitor.

7. The device according to claim 6, wherein the one or more electrochemical cells include at least one first stack of electrochemical cells and at least one second stack of electrochemical cells; and Wherein the DC-DC converter circuit comprises: a first bidirectional DC-DC converter circuit configured to provide the AC stimulus to the first electrochemical cell stack in a first operating phase and to store the charge on the energy storage capacitor in a second operating phase; and A second bidirectional DC-DC converter circuit is configured to store the charge on the energy storage capacitor during the first operating phase and provide the AC stimulus to the second electrochemical cell stack during the second operating phase.

8. The device of claim 1, wherein the stimulation circuit comprises: a power circuit configured to provide the AC stimulus; and Wherein the AC stimulus comprises a plurality of frequencies derived from one or both of a line frequency and a switching frequency of the switching converter circuit.

9. A method for testing an electrochemical system, the method comprising: applying a direct current (DC) bias to one or more electrochemical cells of the electrochemical system; applying an alternating current (AC) stimulus having a DC bias to the one or more electrochemical cells, wherein the AC stimulus is applied at a plurality of frequencies; determining an electrochemical impedance of the one or more electrochemical cells at the plurality of frequencies; and The electrochemical impedance determined at a plurality of frequencies is used to generate an indication of a condition of the one or more electrochemical cells.

10. The method of claim 9, wherein determining electrochemical impedance comprises: applying the AC stimulus to the one or more electrochemical cells; Wait for the designated settlement time; and The AC stimulation current and the AC stimulation voltage at a plurality of frequencies are measured, and the electrochemical impedance is determined using the measured AC stimulation current and the AC stimulation voltage.

11. The method of claim 9, wherein applying the DC bias and applying the AC stimulus comprises using the same power supply circuit to provide the DC bias and the AC stimulus.

12. The method of claim 9, wherein applying a DC bias and applying an AC stimulus comprises: Using a hybrid power circuit to provide a first frequency range of DC bias and AC stimulus; and An AC power circuit is used to provide a second frequency range of the AC stimulus.

13. The method of claim 9, wherein applying a DC bias comprises providing the DC bias using a DC power circuit, and applying an AC stimulus comprises providing the AC stimulus using an AC power circuit.

14. The method of claim 9, wherein applying the AC stimulus comprises: generating a charge from the DC bias voltage using a DC-DC converter circuit; storing the charge generated by the DC-DC converter circuit on an energy storage device; and The AC stimulus is provided using the energy storage device.

15. The method of claim 9, wherein applying AC stimulation comprises: providing an AC stimulus to the first electrochemical cell stack using a first bidirectional DC-DC converter circuit during a first phase and storing charge on the energy storage capacitor during a second phase; and During the second phase, an AC stimulus is provided to the second electrochemical cell stack using a second bidirectional DC-DC converter circuit and charge is stored on the energy storage capacitor during the first phase.

16. The method of claim 9, wherein applying an AC stimulus comprises applying an AC stimulus having one or both of a wire grid frequency and a stimulus switching frequency, and having one or more other frequencies derived from the wire grid frequency or the stimulus switching frequency.

17. An electrochemical system, comprising: at least one electrochemical cell stack comprising a plurality of electrochemical cells; Measuring device, comprising: a stimulation circuit configured to simultaneously apply a direct current (DC) stimulus and an alternating current (AC) stimulus to the at least one electrochemical cell stack, wherein the AC stimulus is applied at a plurality of frequencies; and an impedance measurement circuit configured to measure the impedance of the electrochemical cell; and A controller is configured to synchronize application of the DC stimulus and the AC stimulus with impedance measurement at a plurality of frequencies and record the measured impedance of the electrochemical cell.

18. The system of claim 17, wherein the impedance measurement circuit comprises: a current sensor for measuring an AC stimulus current of an AC stimulus applied to the electrochemical cell at a plurality of frequencies; a voltage sensor configured to measure an AC stimulation voltage of the electrochemical cell caused by the AC stimulation current; and Wherein the controller is configured to sweep the frequency of the AC stimulation current to a plurality of frequencies and to determine the impedance at the plurality of frequencies using measurements of the AC stimulation current and the AC stimulation voltage.

19. The system of claim 17, wherein the at least one electrochemical cell stack comprises a plurality of hydrogen electrolyzer cells connected in series, and the DC stimulus is used to operate the hydrogen electrolyzer cells.

20. The system of claim 17, wherein the at least one electrochemical cell stack comprises a plurality of battery cells connected in series.

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