Hydrogen Absorption and Self-Corrosion of Mg Anode: Influence of Aqueous Electrolyte Species

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors report the experimental results from six of their previous papers and attempt to correlate these findings with more recent studies on “Hydrogen absorption and self-corrosion of Mg anode”. While this correlation is of scientific value, it is unclear whether the submitted paper should be classified as a typical review paper. Nevertheless, Section 1 is structured as a review, offering valuable insights, and it should be expanded to include more relevant works. This expanded section could then constitute a major part of the paper, rather than serving merely as the Introduction.

First, the authors should point out in both the Abstract and the Introduction that the paper aims to critically correlate their earlier work with recent works on “hydrogen absorption and self-corrosion of Mg”.

Second, they should highlight why is this correlation being done? They should explain the significance of this correlation. In other words, the authors should make clear, before proceeding to Section 2, what this review has to offer to the reader and note the objective and motivation of this review.

Sections 2 and 3 are extensive summaries of authors’ earlier works, occupying more than half of the paper (pages 6-18). The titles of Sections 2 and 3 should be modified, in order to make this clear, as the current titles may mislead the reader into considering this as a research paper. Also, each main result reported and discussed in Sections 2 and 3 should be directly linked to a corresponding result of a more recent study and accompanied by a brief discussion/comment. In this way, Sections 2 and 3 will have a more critical perspective.

In the summary section, the authors should add a concluding paragraph where they highlight the points where the results of their studies align with those of recent works.

The authors should also specify how  their reported results are useful to the applications mentioned in the first paragraph of the Summary section  (by highlighting the exact points of beneficial contribution).

Comments on the Quality of English Language

There are several minor English language errors in the manuscript that should be corrected, e.g. wrong uses of articles “a” and “the”, omissions of “is” or “are” from passive constructions, missing articles such as “it”, etc.

Author Response

Dear Mr. Reviewer, thank you very much for your work. The authors completely agree with your comments and advice. The article was revised to structure corresponding to the “Review ”. It contains a correlation of recent and old publications describing the mechanisms of NDE and PDE. The English was edited and corrected. The copyright permissions to publish the Figures from the holder Pleiades Publishing were received.

Thank you, corresponding author

Andrei Nazarov, French Corrosion Institute, retired

14/07/2024

Reviewer 2 Report

Comments and Suggestions for Authors

This review manuscript present a comprehensive and interesting overview of the effect of hydrogen on Mg:

There are some points to be considered to improve the quality of the review:

-       Focus and elaborate on the mechanisms regarding Negative or Positive Difference Effects (NDE or PDE). This is a great addition to state-of-art for the subject, and distinguishes this review from others previously published.

-       Elaborate on the activation energies, as well as the electrochemical kinetics for activation-controlled reactions.

-       Elaborate on the thermodynamics of intermediate species and chemical/electrochemical reactions involved.

-       Elaborate on the hydrogen absorption (bulk process) and adsorption isotherms (surface phenomena, different adlayer models), thus including any diffusion mechanism and models.

-       Elaborate on the hydride formation and their corresponding free energies, i.e., reaction thermodynamics.

-       Elaborate on the stability and competition reactions between oxide, hydroxides and hydrides, and the influence of pH and polarization. Provide free energy values and enthalpies for all reactions.

-       Elaborate a section on the inhibition mechanisms (surface coverage, inhibition efficiency, adsorption mechanisms, physisorption vs chemisorption), and provide an additional  paragraph in the summary section thus showing main conclusions. Provide enthalpy values for adsorption reactions.

-       In summary, provide conclusions and main findings (thermodynamics, reaction, and transport (diffusion) in the literature for hydrogen reaction on Mg surfaces.

-       Update references and include recent papers and reviews published during the last two years (2023,2024)

 

Author Response

Dear Mr. Reviewer, thank you very much for your work. The authors completely agree with your comments and advice. The article was revised to structure corresponding to the “Review ”. It contains a correlation of recent and old publications describing the mechanisms of NDE and PDE. The English was edited and corrected. The copyright permissions to publish the Figures from the holder Pleiades Publishing were received.

Thank you, corresponding author

Andrei Nazarov, French Corrosion Institute, retired

14/07/2024

Reviewer 3 Report

Comments and Suggestions for Authors

Referee report to the manuscript entitled “Hydrogen absorption and self-corrosion of Mg anode: influence of aqueous electrolyte species.” submitted to MDPI Corrosion and Materials Degradation by Andrei Nazarov, Tatiana Yurasova and Andrey Marshakov

 

Manuscript has the structure typical for research papers (Introduction, Materials and Methods, Experimental Results, Summary, References) but has been classified as a review paper. Indeed, all experimental material presented in the manuscript has been already published about 30 years ago. Therefore, the reviewed manuscript is a second appearance of an already published material. According to my opinion such situation is unacceptable. Have the authors the permission of the copyright owner of the original version?

 Authors write” These works were published before the Internet era and the storage of PDF articles online and at present these data can be extremely difficult to access. Thus, early published but unknown experimental data in connection with modern studies can be important to discuss in a particular review.” Many authors could say the same. However the manuscript under review is not written in a way the review papers are written usually. Authors separately discussed the papers published by other scientists (Introduction section), and separately (paragraph Experimental Results) their own papers presenting them as if it was original experimental material.

The presented experimental material has already passed the review procedure when published for the first time and the elapsed time (30 years!) verified the authors’ results. Indeed I have not found any misinterpretations and the presented experimental material, if original, would be suitable for publication after some correction (mainly linguistic and editorial). However due to the objections expressed above I cannot recommend publication of this manuscript in the present form.

In the place of the authors I would rather write a “real” review paper, where the papers of the authors were discussed together with the papers of the other authors. The object of the paper (NDE and problems related) is very important and worth a separate review. At the same time contribution of the authors to the knowledge on magnesium corrosion is significant and worth presentation.

Comments on the Quality of English Language

Referee report to the manuscript entitled “Hydrogen absorption and self-corrosion of Mg anode: influence of aqueous electrolyte species.” submitted to MDPI Corrosion and Materials Degradation by Andrei Nazarov, Tatiana Yurasova and Andrey Marshakov

 

Manuscript has the structure typical for research papers (Introduction, Materials and Methods, Experimental Results, Summary, References) but has been classified as a review paper. Indeed, all experimental material presented in the manuscript has been already published about 30 years ago. Therefore, the reviewed manuscript is a second appearance of an already published material. According to my opinion such situation is unacceptable. Have the authors the permission of the copyright owner of the original version?

 Authors write” These works were published before the Internet era and the storage of PDF articles online and at present these data can be extremely difficult to access. Thus, early published but unknown experimental data in connection with modern studies can be important to discuss in a particular review.” Many authors could say the same. However the manuscript under review is not written in a way the review papers are written usually. Authors separately discussed the papers published by other scientists (Introduction section), and separately (paragraph Experimental Results) their own papers presenting them as if it was original experimental material.

The presented experimental material has already passed the review procedure when published for the first time and the elapsed time (30 years!) verified the authors’ results. Indeed I have not found any misinterpretations and the presented experimental material, if original, would be suitable for publication after some correction (mainly linguistic and editorial). However due to the objections expressed above I cannot recommend publication of this manuscript in the present form.

In the place of the authors I would rather write a “real” review paper, where the papers of the authors were discussed together with the papers of the other authors. The object of the paper (NDE and problems related) is very important and worth a separate review. At the same time contribution of the authors to the knowledge on magnesium corrosion is significant and worth presentation.

Author Response

Dear Mr. Reviewer, thank you very much for your work. The authors completely agree with your comments and advice. The article was revised to structure corresponding to the “Review ”. It contains a correlation of recent and old publications describing the mechanisms of NDE and PDE. The English was edited and corrected. The copyright permissions to publish the Figures from the holder Pleiades Publishing were received.

Thank you, corresponding author

Andrei Nazarov, French Corrosion Institute, retired

14/07/2024

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript has been improved and is now worthy of publication.

Author Response

Dear Mrs. or Mr. Reviewer, thank you very much for your work. The authors completely agree with your comments and advice. The article was revised to structure corresponding to the “Review ”. It contains a correlation of recent and old publications describing the mechanisms of NDE and PDE. The English was edited and corrected. The copyright permissions to publish the Figures from the holder Pleiades Publishing were received.

Thank you, corresponding author

Andrei Nazarov, French Corrosion Institute, retired

27/07/2024

Reviewer 2 Report

Comments and Suggestions for Authors

Authors lacked to address major revisions and changes suggested by reviewers. For the review to be considered, authors need to provide amendments and detailed response to all revision suggested by reviewers.

This review manuscript present a comprehensive and interesting overview of the effect of

-       Focus and elaborate on the mechanisms regarding Negative or Positive Difference Effects (NDE or PDE). This is a great addition to state-of-art for the subject, and distinguishes this review from others previously published.

-       Elaborate on the activation energies, as well as the electrochemical kinetics for activation-controlled reactions.

-       Elaborate on the thermodynamics of intermediate species and chemical/electrochemical reactions involved.

-       Elaborate on the hydrogen absorption and adsorption isotherms (different adlayer models), thus including any diffusion mechanism.

-       Elaborate on the hydride formation and their corresponding free energies, i.e., reaction thermodynamics.

-       Elaborate on the stability and competition reactions between oxide, hydroxides and hydrides, and the influence of pH and polarization.

-       Elaborate a section on the inhibition mechanisms (surface coverage, inhibition efficiency, adsorption mechanisms, physisorption vs chemisorption), and provide an additional  paragraph in the summary section thus showing main conclusions.

-       In summary, provide conclusions and main findings (thermodynamics, reaction, and transport (diffusion) in the literature for hydrogen reaction on Mg surfaces.

-       Update references and include recent papers and reviews published during the last two years (2023, 2024).

 

Author Response

 

Dear Mrs. or Mr. reviewer, thank you very much for your work and valuable comments. The authors agree with them and the article was revised according to your contributions.

We would like to note that this particular article is an analysis of available works already published in the literature on the subject: of self-corrosion of Mg anode under PDE and NDE, hydrogen absorption, hydride formation, and the effects of the aqueous electrolyte nature on these parameters. Only data available in these fields were discussed. The article cannot include all studies of electrochemistry and corrosion of Mg in different conditions, the details of works concerning inhibitors of corrosion Mg alloys, pieces of knowledge in formation, thermodynamics, and kinetics of magnesium hydride in case of hydride synthesis using the gas-phase or plasma conditions.

Unfortunately, the thermodynamics and kinetics of the intermediate reactions on the active surface of the metal in aqueous electrolyte in the literature are investigated a little and knowledge is very qualitative. The absence of solid data on the composition, structure, and stoichiometry of the intermediate compounds also limits the thermodynamic and kinetic description of the processes.  Thus, the elaboration of quantitative data will take a large amount of new studies using well-defined and model systems. However, as a result of a particular review, interested researchers can provide these works. 

 

 

This review manuscript present a comprehensive and interesting overview of the effect of hydrogen on Mg:

There are some points to be considered to improve the quality of the review:

-       Focus and elaborate on the mechanisms regarding Negative or Positive Difference Effects (NDE or PDE). This is a great addition to state-of-art for the subject, and distinguishes this review from others previously published. Thank you. These points were added to keywords. The abstract and conclusions also discuss these points.

-       Elaborate on the activation energies, as well as the electrochemical kinetics for activation-controlled reactions. These parameters can be determined from data on the known real anode surface participating in anodic dissolution, and self-dissolution. These processes are complicated and the composition of the products is not known in detail. Only new experiments using model well-defined systems can answer this question.

 -     Elaborate on the thermodynamics of intermediate species and chemical/electrochemical reactions

involved. On the anode surface proceeds a plenty of electrochemical reactions. Most probable ways

are discussed in the comprehensive review: Atrens, A.D.;  Gentle,I.;  Atrens, A. Possible dissolution

pathways participating in the Mg corrosion reaction, Cor. Sci. 2015 , 92, 173–181.

 At present, we are trying to understand what kind of intermediate species are present on the anode surface. Thermodynamics of them is the second question. However, the standard electrochemical potentials based on handbook data were calculated in the article.

 

-       Elaborate on the hydrogen absorption (bulk process) and adsorption isotherms (surface phenomena, different adlayer models), thus including any diffusion mechanism and models.  

We are using the data which are already published. Without additional experiments, we cannot elaborate adsorption and diffusion process quantitatively. At present, the modeling of metal hydrogenation in electrolytes is difficult due to the presence of many parallel and consecutive reactions on the unknown real working surface of an anode. For researchers and experts in models, it will be an interesting task. 

 

-       Elaborate on the hydride formation and their corresponding free energies, i.e., reaction thermodynamics.

The thermodynamics (standard potentials equivalenting to free energy) of the general electrochemical reactions are given in the article using published databases. To evaluate the enthalpy of these reactions, new works with the application of electrochemical calorimetry are needed.

-       Elaborate on the stability and competition reactions between oxide, hydroxides and hydrides, and the influence of pH and polarization. Provide free energy values and enthalpies for all reactions.

      The competition of the reaction of oxide/hydroxide and active surface formation was discussed in the review. The influence of near-surface pH and anodic polarization current are also qualitatively discussed. We provided standard potentials (correspond to free energy), but for enthalpies determination, more experimental work will be needed.

-       Elaborate a section on the inhibition mechanisms (surface coverage, inhibition efficiency, adsorption mechanisms, physisorption vs chemisorption), and provide an additional paragraph in the summary section thus showing main conclusions. Provide enthalpy values for adsorption reactions.

      In the inhibition mechanism, the effect of chelating reagents inhibiting acidification of the anode surface was discussed. The diffusion of the ligands and complex stability as the criteria for anode passivation were pointed out. Additional articles corresponding to the adsorption of carbonate and carboxylates were reviewed, cited, and added to the main conclusions. However, the review is not devoted to inhibitors of free corrosion of Mg, and the thermodynamic of inhibitors impact was not discussed.

-       In summary, provide conclusions and main findings (thermodynamics, reaction, and transport (diffusion) in the literature for hydrogen reaction on Mg surfaces.

      Thank you for your comment. Unfortunately, this literature is very scarce for Mg. It was done in a corresponding review [12] from the experts in this field. These works were also shortly discussed in particular review in concern to self-corrosion and hydrogen effect.

-       Update references and include recent papers and reviews published during the last two years (2023,2024). Recent articles were reviewed and cited.

 

 

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

After corrections the manuscript is suitable for publication.

Comments on the Quality of English Language

After corrections the manuscript is suitable for publication.

Author Response

Dear Mrs. or Mr. Reviewer, thank you very much for your work. The authors completely agree with your comments and advice. The article was completely revised to structure corresponding to the “Review ”. It contains a correlation of recent and old publications describing the mechanisms of NDE and PDE. The English was edited and corrected. The copyright permissions to publish the Figures from the holder Pleiades Publishing were received.

Thank you, corresponding author

Andrei Nazarov, French Corrosion Institute, retired

27/07/2024

Round 3

Reviewer 2 Report

Comments and Suggestions for Authors

Authors have greatly elaborated on the suggested items by reviewers and substantiated their manuscript, thus improving the quality of the paper. 

There are some minor points to be considered (authors can provide amendments to them during proofs revision stage). Thank you

Please, check the electrochemical potential ("E") equations, in particular the ones that refer to pH when OH- species are involved in the reaction, and also electrochemical potential ("E") equations for reactions with stochiometric values different than one.

Eq. 2 :  2H2O + 2e → 2OH- + H2 g ;  E= 0 - 0.059 pH - 0.0295log pH2 (2) (Note reaction is in alkaline media OH-, while electrochemical potential refers to pH).

Eq. 5 : Mg + 2H2O +2e → MgH2 + 2OH- ; E= 0.186 - 0.059 pH (5)         (Note reaction is in alkaline media OH-, while electrochemical potential refers to pH).

 

Author Response

Dear Mrs. /Mr. Reviewer, thank you very much for your work and significant contribution to the article.  The authors completely agree with your comments relatively equations 2 and 5.  In literature, the pOH is not often used. Following this tradition, in Eq.  2 (line 56) was given only standard electrochemical potential "Eo" for alkali pH 14 electrolyte.

 

Mg   →   Mg²⁺  + 2e                                         E^o= -2.363                                                    (1)

2H₂O  +   2e   →    2OH^- + H₂ ^g                       E^o=  -0.828                                                    (2) 

Eo in equation 5 (line 163) was taken from the reference [38] that corresponds to acidic electrolytes. Thus, the electrochemical equation was changed to acidic conditions also. 

Mg + 2H⁺ +2e → MgH₂                                                                                           (5)                                                                                                            

E= 0.186 - 0.059 pH     

Thank you

Please, check the electrochemical potential ("E") equations, in particular the ones that refer to pH when OH- species are involved in the reaction, and also electrochemical potential ("E") equations for reactions with stochiometric values different than one.

Eq. 2 :  2H2O + 2e → 2OH- + H2 g ;  E= 0 - 0.059 pH - 0.0295log pH2 (2) (Note reaction is in alkaline media OH-, while electrochemical potential refers to pH).

Eq. 5 : Mg + 2H2O +2e → MgH2 + 2OH- ; E= 0.186 - 0.059 pH (5)         (Note reaction is in alkaline media OH-, while electrochemical potential refers to pH).