Experimental Validation of an Active Fault Tolerant Control Strategy Applied to a Proton Exchange Membrane Fuel Cell

Round 1

Reviewer 1 Report

The manuscript reported a use tool- Active Fault Tolerant Control (AFTC) strategy, which can not only diagnose these faulty conditions but also modify the fuel cell operations in order to recover a healthy operating point. It is aimed to ensure the reliability of PEMFCs for a large industrialization and commercialization. The manuscript aims at bringing a new contribution to PEMFCs reliability improvement and addressing water management issues, namely the cell flooding and membrane drying out with the developed AFTC tool.

I consider the content of this manuscript will definitely meet the reading interests of the readers of the Electrochem journal. However, there are certain English spelling and grammar issues, and also the discussion and explanation should be further improved.

Therefore, I suggest giving a minor revision and the authors need to clarify some issues or supply some more experimental data to enrich the content. This could be comprehensive and meaningful work after revision.

1. For grammar issues, it is suggested that the author double-check the small grammar errors in the full text, especially the lack and redundant use of definite articles.

2. For the Keywords, ‘reliability’, ‘decision algorithm’, and ‘fuel cell degradation’ should be added in order to attract a broader readership.

3. Line 39, ‘Membrane drying out is defined as an insufficient hydra-tion of the proton exchange membrane, increasing thus its proton resistivity.’ Firstly, proton resistivity is not very commonly used, it should be the ‘drying out may reduce the proton conductivity of the IEMs’. Secondly, why is the hydration so important for IEM? It should be explained. Since the commercial IEM Nafion is composed of hydrophobic backbone and hydrophilic sulfonic acid groups, only when hydrated, the hydrophobic-hydrophilic phase separation leads to the effective proton transfer paths for Nafion. When the membrane is dry, the proton cannot pass through the membrane effectively [Ionics 25.9 (2019): 4219-4229.].

4. Line 84, it should be ‘2.1 Faults related to PEMFC water management’. The same applies to other subtitles, and I suggest the authors to double-check this issue throughout the main text.

5. Line 89, ‘The gas flow rate is also a major factor for flooding occurrence because the lower the gas flow rate is, the lower the amount of water discharged, and the higher the flooding severity is.’ This is only half of what happens. It is true that lower flow rate leads to lower amount of water discharged. But it should also be noticed that lower gas flow rate will also lead to a lower amount of generated water. So it is always a compromise to judge it is more efficient to generate more water and discharge water with higher gas flow rate or it should be better to generate less water in the same time period with lower flow rate to facilitate timely discharge of generated water.

6. There is some error information, for example, ‘Error! No text of specified style in document.-1Error! Reference source not found’. They should be corrected in order to improve readability. I consider it may be due to the software problem during inserting the references.

7. Line 141, ‘Residuals are then compared with two threshold values which’. The sentence seems not completed yet and should be improved.

8. Line 167, ‘This knowledge is very relevant for the AFTC design because it allows the selection of control variables for fault mitigation.’ I consider not ‘this knowledge’, but ‘these above-mentioned parameters’.

9. Line 299, how about the flow rate and backpressure during the fuel cell test? What is the adopted membrane, MEA, and catalyst loading information?

10. On Page 10, the tables are not very easy to read, and I am not sure whether they are shown completely.

11. Some recent literature related to a fault control strategy for PEMFC should be added, for example, IEEE Transactions on Industrial Electronics 67.4 (2019): 2875-2884; Fuel Cells 21.6 (2021): 512-522. Fuel Cells 21.6 (2021): 512-522.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Dear authors,

I have studied the manuscript and found it interesting. The Active Fault Tolerant Control (AFTC) strategy is validated for PEMFCs reliability improvement by addressing water management: cell flooding and membrane drying out.  This paper addresses a topical issue and should be of interest to the research community. Here are some comments and suggestions that you might find of help:

1.       Line 42: Could you please expand on “irreversible degradation”? How is the catalyst affected?

2.       Line 50-51: What “controllers’ setting”? Moreover, my suggestion is to give arguments for choosing the active strategy over the passive one.

3.       Line 84: Replace “1.1” with “2.1”. Renumber accordingly all subsections.

4.       Line 132: Solve the errors in Figure and Table numbers and captions throughout the entire manuscript.

5.       Line 188: Replace “inlet gas flow relative humidity” with “inlet gas relative humidity”

6.       Line 198-199: Is PEMFC temperature the ONLY control variable that can have a direct influence on the membrane water content? What about the inlet gas relative humidity?

7.       The quality of Figure 2 needs to be improved, i.e. increase fonts.

8.       Combine the two tables in lines 377-388. Relative magnitudes imply “%”, check PEMFC temperature. The same comment for similar tables in section 2.3.2.

9.       Check Figure 4. The pressure drop superposition with fuel cell voltage is missing.  The same comment for Figures 5 and 6.

10.   Section 3. Discussion can be merged with section 2. Please reorganize the manuscript, there are too many sections and that makes the content fragmented and harder to follow.

11.   Section “Conclusions” should be more concise.

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

I suggest minor revisions to the manuscript before the publication on Electrochem journal based on the following comments:

1)    English should be revised, many typos are present in the manuscript;

2)    I suggest to expand the bibliography since the percentage of self-citations is a bit high;

3)    Please, have a look to the name of axis in the graph and corresponding units of measure: most of the time they are wrong (not in English or wrong unit of measure);

4)    The manuscript is interesting, but I think that an immediate parameter that can be a measure on how much the control is good or not is missing. Also the conclusions do not contain any reference number to understand whether your control strategies are good. Please, add some parameters and amend conclusions section.

Author Response

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Author Response File: Author Response.pdf