US-12626941-B2 - Electrochemical cell degradation monitoring method and system

Abstract

An electrochemical cell degradation monitoring method. The method includes applying first and second bias potentials to an electrode of an electrochemical cell during an operating state thereof. The method further includes measuring impedance spectra of the electrode of the electrochemical cell during the operating state biased to the first and second bias potentials. The method also includes determining a deviation in the impedance spectra at the first and second bias potentials. The method determines a degradation state of the electrode of the electrochemical cell in response to the deviation in the impedance spectra at the first and second bias potentials of the electrode of the electrochemical cell.

Inventors

• Shirin Mehrazi
• Bjoern STUEHMEIER
• Jonathan Braaten
• Lei Cheng
• Nathan Craig
• Christina Johnston

Assignees

• ROBERT BOSCH GMBH

Dates

Publication Date

20260512

Application Date

20230309

Claims (20)

1. 1 . An electrochemical cell degradation monitoring method comprising: applying first and second bias potentials to an electrode of an electrochemical cell during an operating state thereof; measuring impedance spectra of the electrode of the electrochemical cell during the operating state biased to the first and second bias potentials; determining a deviation in the impedance spectra at the first and second bias potentials; and determining a degradation state of the electrode of the electrochemical cell in response to the deviation in the first and second impedance spectra at the first and second bias potentials of the electrode of the electrochemical cell.
2. 2 . The electrochemical cell degradation monitoring method of claim 1 , wherein the first and second bias potentials are different.
3. 3 . The electrochemical cell degradation monitoring method of claim 1 , wherein the first and second bias potentials are the same.
4. 4 . The electrochemical cell degradation monitoring method of claim 1 , wherein the electrochemical cell is a fuel cell.
5. 5 . The electrochemical cell degradation monitoring method of claim 4 , wherein the electrode is a cathode.
6. 6 . The electrochemical cell degradation monitoring method of claim 4 , wherein the degradation state is a depleted catalyst region in the electrode of the fuel cell.
7. 7 . The electrochemical cell degradation monitoring method of claim 1 , wherein the electrode is supported by a support, and the degradation state is corrosion of the support.
8. 8 . The electrochemical cell degradation monitoring method of claim 1 , wherein the electrode includes an ionomer, and the degradation state is degradation of the ionomer.
9. 9 . The electrochemical cell degradation monitoring method of claim 1 , wherein the measuring step is carried out using an electrochemical impedance spectroscopy (EIS) based technique.
10. 10 . The electrochemical cell degradation monitoring method of claim 1 , wherein the applying step is carried out using a direct current/direct current (DC/DC) converter.
11. 11 . The electrochemical cell degradation monitoring method of claim 1 , wherein the applying step includes sending first and second alternating current (AC) signals to the electrochemical cell, the first and second AC signals representing the first and second bias potentials, respectively.
12. 12 . The electrochemical cell degradation monitoring method of claim 1 , wherein a proton resistance of the electrode is a proton sheet resistance indicative of a through-plane proton transport of the electrode.
13. 13 . The electrochemical cell degradation monitoring method of claim 12 , wherein the step of determining a deviation in the impedance spectra includes determining the deviation from a forty-five-degree (45°) section in the impedance spectra according to a transition line model for the electrode.
14. 14 . The electrochemical cell degradation monitoring method of claim 13 , wherein the transition line model includes resistance contributions homogeneously distributed in the through-plane proton transport of the electrode at a beginning-of-life state of the electrode.
15. 15 . The electrochemical cell degradation monitoring method of claim 14 , wherein the deviation is a change from a proton sheet resistance at the beginning-of-life state of the electrode.
16. 16 . The electrochemical cell degradation monitoring method of claim 1 , wherein the first bias potential is 0.3V to 0.65V and the second bias potential is below 0.3V or above 0.65V.
17. 17 . The electrochemical cell degradation monitoring method of claim 1 , wherein the operating state is one or more maintenance cycles and/or one or more normal operating cycles.
18. 18 . An electrochemical cell degradation monitoring method comprising: applying first and second bias potentials to an electrode of an electrochemical cell during an operating state at a first number of cycles; measuring impedance spectra of the electrode of the electrochemical cell during the operating state biased to the first and second bias potentials; determining a first characteristic of the impedance spectra at the first and second bias potentials; applying the first and second bias potentials to the electrode of the electrochemical cell during the operating state at a second number of cycles; measuring the impedance spectra of the electrode of the electrochemical cell during the operating state biased to the first and second bias potentials; determining a second characteristic of the impedance spectra at the first and second bias potentials; and determining a degradation state timing of the electrode of the electrochemical cell in response to the first and second characteristics.
19. 19 . The electrochemical cell degradation monitoring method of claim 18 , wherein the second number of cycles is greater than the first number of cycles.
20. 20 . An electrochemical cell degradation monitoring system comprising: an electrochemical cell including an electrode; a direct current/direct current (DC/DC) converter configured to apply first and second bias potentials to the electrode of the electrochemical cell during an operating state thereof, and an electrochemical impedance spectrometer configured to measure impedance spectra of the electrode of the electrochemical cell during the operating state biased to the first and second bias potentials, wherein a deviation in the impedance spectra at the first and second bias potentials are indicative of a degradation state of the electrode.

Description

TECHNICAL FIELD The present disclosure relates to an electrochemical cell (e.g., a fuel cell) degradation monitoring method and system. The degradation monitoring method and system may determine a degradation state (e.g., a depleted catalyst region in an electrode of a fuel cell) by on-line analysis of an electrochemical impedance response of a fuel cell or stack. BACKGROUND Integrating a proton exchange membrane fuel cell (PEMFC) stack into vehicles (e.g., medium-duty and heavy-duty vehicles) is being explored in the transportation section to electrify operation of the vehicles. One component of a fuel cell is a membrane electrode assembly (MEA). The MEA includes a cathode catalyst layer, an anode catalyst layer, and a proton exchange membrane (PEM) sandwiched therebetween. Achieving durability of the cathode catalyst layer of the MEA has been a challenge and represents a hurdle to widespread commercialization of PEMFCs for transportation applications. The lack of durability also presents a major cost driver. The cathode catalyst layer may include a catalyst material (e.g., platinum and/or platinum-based catalyst) on a support (e.g., carbon support) and a proton conducting ionomer. The cathode catalyst layer may be subject to different forms of degradation (e.g., load cycling during operation, air/air starts after long shutdown periods, local fuel starvation events, and operation under extreme environmental conditions). There remains a need to characterize these forms of degradation to enhance the durability of the cathode catalyst layers and allow for state-of-health determination during operation. SUMMARY According to one embodiment, an electrochemical cell degradation monitoring method is disclosed. The method includes applying first and second bias potentials to an electrode of an electrochemical cell during an operating state thereof. The method further includes measuring impedance spectra of the electrode of the electrochemical cell during the operating state biased to the first and second bias potentials. The method also includes determining a deviation in the impedance spectra at the first and second bias potentials. The method determines a degradation state of the electrode of the electrochemical cell in response to the deviation in the impedance spectra at the first and second bias potentials of the electrode of the electrochemical cell. In another embodiment, an electrochemical cell degradation monitoring method is disclosed. The method includes applying first and second bias potentials to an electrode of an electrochemical cell during an operating state at a first number of cycles, measuring impedance spectra of the electrode of the electrochemical cell during the operating state biased to the first and second bias potentials, and determining a first characteristic of the impedance spectra at the first and second bias potentials. The method further includes applying the first and second bias potentials to the electrode of the electrochemical cell during the operating state at a second number of cycles, measuring the impedance spectra of the electrode of the electrochemical cell during the operating state biased to the first and second bias potentials, and determining a second characteristic of the impedance spectra at the first and second bias potentials. The method also includes determining a degradation state timing of the electrode of the electrochemical cell in response to the first and second characteristics. While proton resistivity at the different bias potentials may be used to identify a deviation (and therefore, the presence of a degradation state), other metrics may also be used (e.g., a change in capacitance from carbon corrosion). In yet another embodiment, an electrochemical cell degradation monitoring system is disclosed. The system includes an electrochemical cell including an electrode, a direct current/direct current (DC/DC) converter, and an electrochemical impedance spectrometer. The DC/DC converter is configured to apply first and second bias potentials to the electrode of the electrochemical cell during an operating state thereof. The electrochemical impedance spectrometer is configured to measure impedance spectra of the electrode of the electrochemical cell during the operating state biased to the first and second bias potentials. A deviation in the impedance spectra at the first and second bias potentials are indicative of a degradation state of the electrode. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 depicts a schematic, side view of a membrane electrode assembly of an electrochemical cell (e.g., a fuel cell, a proton exchange membrane fuel cell (PEMFC), electrolyzer, a carbon dioxide electrochemical conversion device, etc.). FIG. 2 depicts a schematic of a flowchart of a fuel cell stack monitoring method using a direct current/direct current (DC/DC) converter and electrochemical impedance spectroscopy (EIS) based techniques. FIG. 3 is a schematic diagram of a transitio