Preparation and Characterization of Composite Hydrogen Barrier Coatings with (Graphene–Epoxy Resin)/(Silicon Carbide–Epoxy Resin)/(Graphene–Epoxy Resin) Sandwich Structures

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The study focuses on the problem of choosing effective barriers to prevent hydrogen embrittlement. For this aim, the authors chose a three-layer structure containing the epoxy resin (ER) as the based coatings, and the graphene (GN) and the silicon carbide (SiC) as the additives to prepare the (GN-ER)/(SiC-ER)/(GN-ER) sandwich structures. This barrier variant has shown a high value of PRF and can serve as a starting point for the synthesis and research of such types of coatings. The work has great potential for acceptanc to the Coatings. However, there are now major comments that should be answered.

1. In the abstract, as well as in the conclusion, the authors indicate that the paper provides “... may provide a theoretical basis for improving the hydrogen barrier...”. I believe that the applied aspect is also very important as a result of this research.
2. The keyword ”performance” is hardly sufficient to characterize this study. It should either be supplemented or deleted.
3. Introduction, Line 34. Here it should be noted the important role of hydrogen transporters in the form of LOHC: liquid organic hydrogen carriers (for example, https://doi.org/10.1021/jacs.2c13324] and [https://doi.org/10.1016/j.coelec.2022.101207), which also make it possible to solve the problem of transportation in another way, but at the same time do not detract from the search for a solution to the problem of an effective H₂-barrier in existing pipelines.
4. The supplementary file currently does not contain optional information that complements the content of the manuscript, but contains drawings, highlights, figure captions, and the like, which is probably not the usual SI content.
5. The experimental section. Line 144. The working and auxiliary electrodes are not specified. Concentrations are recommended to be designated as 0.2 mol L^-1, as already indicated elsewhere in the manuscript. Line 150: What is “mete"? Lines 139,141,143161: the name of the device and the manufacturer should be given in parentheses, for example, the ”galvanostat/potentiostat Autolab PGSTAT 302N (Metrohm, Switzerland)”.
6. "Results and discussion" part can be divided into logical sections, for example, 3.1. XRD diffraction analysis (Lines 166-199); 3.2. SEM research;..., and so on.
7. Lines 230, 256 and elsewhere. Correct to ”..cm^-2". Also, the current density is usually denoted as the J.
8. Figures 5,6 and the results in Figure 7. Have the authors tried to change the sequence of protective layers? Perhaps this can lead to better PRF values.
9. What can the authors say about the durability and stability of the resulting coating? Are there any data on repeated use?
10. References to the literature are not currently designed according to the MDPI template. There are also no DOI indexes.

 

Author Response

Point-by-point response to the comments made by the reviewer(s)

REVIEWER REPORT(S):

Reviewer #1:

Comments and Suggestions for Authors

The study focuses on the problem of choosing effective barriers to prevent hydrogen embrittlement. For this aim, the authors chose a three-layer structure containing the epoxy resin (ER) as the based coatings, and the graphene (GN) and the silicon carbide (SiC) as the additives to prepare the (GN-ER)/(SiC-ER)/(GN-ER) sandwich structures. This barrier variant has shown a high value of PRF and can serve as a starting point for the synthesis and research of such types of coatings. The work has great potential for acceptanc to the Coatings. However, there are now major comments that should be answered.

Response to the reviewer #1:

Thanks for your helpful comments on our paper. We have revised our paper according to your comments. We also responded point by point to your comments as listed below, along with clear indications of the locations of the revisions, which are shown in red.

 

Comment 1. In the abstract, as well as in the conclusion, the authors indicate that the paper provides “... may provide a theoretical basis for improving the hydrogen barrier...”. I believe that the applied aspect is also very important as a result of this research.

Response: Thank you for your great suggestion. We agree with this suggestion. According to your suggestion, we have added the application prospects of the study in the abstract, introduction, and conclusions. In the revised manuscript, the changes can be found in the abstract on the page 1 line 26 to 28, in the introduction on the page 3 line 104 to 106, and in the conclusions on the page 10 line 375 to 378, respectively.

 

Comment 2. The keyword “performance” is hardly sufficient to characterize this study. It should either be supplemented or deleted.

Response: Thank you for your great suggestion. We agree with this suggestion. According to your suggestion, we have supplemented the keywords and replaced the permeation reduction factor with the performance. In the revised manuscript, the changes can be found in the abstract on the page 1 line 29 to 30.

 

Comment 3. Introduction, Line 34. Here it should be noted the important role of hydrogen transporters in the form of LOHC: liquid organic hydrogen carriers (for example, https://doi.org/10.1021/jacs.2c13324] and [https://doi.org/10.1016/j.coelec.2022.101207), which also make it possible to solve the problem of transportation in another way, but at the same time do not detract from the search for a solution to the problem of an effective H2-barrier in existing pipelines.

Response: Thank you for your great suggestion. We agree with this suggestion. According to your suggestion, we have supplemented the researches of LOHC, and add the references. In the revised manuscript, the descriptions can be found in the introduction on the page 2 line 44 to 51. The added the references as follow:

“[8] Cho, J.; Kim, B.; Venkateshalu, S.; Chung, D.Y.; Lee, K.; Choi, S.. Electrochemically activatable liquid organic hydrogen carriers and their applications. J. Am. Chem. Soc.. 2023, 145, 16951-16965. https://doi.org/10.1021/jacs.2c13324

[9] Lebedeva, O.; Kultin, D.; Каlenchuk Al.; Кustov L.. Advances and prospects in electrocatalytic hydrogenation of aromatic hydrocarbons for synthesis of “loaded” liquid organic hydrogen carriers. Curr. Opin. Electroche. 2023, 38, 101207. https://doi.org/10.1016/j.coelec.2022.101207

[10] Rullo, F.; Beier, C.K.; Henseler, J; Bösmann A.; Preuster P., Wasserscheid P.; Geißelbrecht M.. Pushing activity and stability of LOHC dehydrogenation catalysts by strict LOHC quality protocols. Int. J. Hydrogen. Energ. 2025, 98, 606-613. https://doi.org/10.1016/j.ijhydene.2024.12.104”

 

Comment 4. The supplementary file currently does not contain optional information that complements the content of the manuscript, but contains drawings, highlights, figure captions, and the like, which is probably not the usual SI content.

Response: Thank you for your kind suggestion. We are very sorry for any inconvenience caused to you. The SI content should be supplementary the information to the manuscript, not existing the drawings, highlights, figure captions and so on, because the drawings, highlights, figure captions are listed separately. Therefore, we have deleted the original SI.

 

Comment 5. The experimental section. Line 144. The working and auxiliary electrodes are not specified. Concentrations are recommended to be designated as 0.2 mol·L^-1, as already indicated elsewhere in the manuscript. Line 150: What is “mete"? Lines 139,141,143161: the name of the device and the manufacturer should be given in parentheses, for example, the ”galvanostat/potentiostat Autolab PGSTAT 302N (Metrohm, Switzerland)”.

Response: Thank you for your great suggestion. According to your suggestion, we have added the working electrodes, auxiliary electrodes and the reference electrodes in the experimental section on the page 4 line 168 to 170. We have corrected the unit of the concentrations as 0.2 mol·L^-1 and 3 g·L^-1 in the experimental section on the page 4 line 170 to 171. In the experimental section, the “mete" is an error. We are very sorry for any inconvenience caused to you. We have corrected the “mete" as “meter". According to your suggestion, the name of the device and the manufacturer are given in parentheses, which are in the experimental section on the page 4 line 161, 163, 165, 166, and on the page 5 line 186.

 

Comment 6. "Results and discussion" part can be divided into logical sections, for example, 3.1. XRD diffraction analysis (Lines 166-199); 3.2. SEM research;..., and so on.

Response: Thank you for your great suggestion. We agree with this suggestion. According to your suggestion, the "Results and discussion" part have been divided into the logical sections, such as “3.1 XRD diffraction analysis of the coatings, 3.2 SEM research on the coatings, 3.3 Hydrogen barrier performances of the coatings”.

 

Comment 7. Lines 230, 256 and elsewhere. Correct to ”..cm^-2". Also, the current density is usually denoted as the J.

Response: Thank you for your great suggestion. We are very sorry for any inconvenience caused to you. According to your suggestion, we have corrected the error as cm^-2 in the results and discussion on the page 7 line 267, 276, 277, 283, and on the page 8 line 293. Moreover, the current density is denoted as the J in the results and discussion on the page 7 line 267, 274, 275, 277, 283, 284, 286, 288, 293.

 

Comment 8. Figures 5,6 and the results in Figure 7. Have the authors tried to change the sequence of protective layers? Perhaps this can lead to better PRF values.

Response: Thank you for your kind suggestion. We agree with this suggestion. We have made the single-layer structure, the double-layers structures, and the three-layers structures hydrogen barrier coatings, changing the orders of the double-layers and the three-layers coatings. For example, we synthesized the S3-S6, like the (SiC-ER)/(GN-ER), (GN-ER)/(SiC-ER), (SiC-ER)/(GN-ER)/(SiC-ER) and (GN-ER)/(SiC-ER)/(GN-ER). We found that changing the sequences of the three-layers structures coatings with sandwich structures can improve the PRF. We did not conduct the performance studies on the three-layer structurs coatings with the same adjacent layers, such as the (GN-ER)/(GN-ER)/(SiC-ER), (SiC-ER)/(GN-ER)/(GN-ER), (SiC-ER)/(SiC-ER)/(GN-ER), and (GN-ER)/(SiC-ER)/(SiC-ER). These structures may lead to the better PRF values, and we will conduct the further researches in the future.

 

Comment 9. What can the authors say about the durability and stability of the resulting coating? Are there any data on repeated use?

Response: Thank you for your constructive suggestion. The durability and stability testing of the hydrogen barrier coatings are the indicators of their long-term stability and resistance to failure in the hydrogen environments. The durability testing of the hydrogen barrier coatings includes the high-pressure cycling testing, mechanical performance change testing, adhesive strength testing and so on. The stability testing of the hydrogen barrier coatings includes the thermal stability testing, cycling stability testing and so on. We have completed the adhesive strength testing at room temperature and atmospheric pressure, and have not conducted any other durability testing and stability testing. From the comparison of adhesive strength with the S-1 to S-6, increasing the number of layers can reduce the adhesive strength and can enhance the PRF. Also, changing the composite method can affect the adhesive strength. The adhesive strength data show the good repeatability. We can choose the coatings that balance the relative high PRF and relative high adhesive strength according to the actual working conditions. Due to the characteristics of the epoxy resin (ER), such as the S-6, the coatings of ER substrate is expected to be applied in the temperature range of -45 ℃ to 250 ℃, maintaining the good corrosion resistance and long-term service stability. In the future, we will conduct in-depth researches on the durability and stability of the composite coatings in our next research.

 

Comment 10. References to the literature are not currently designed according to the MDPI template. There are also no DOI indexes.

Response: Thank you for your great suggestion. According to your suggestion, we have modified the format of the references according to the MDPI template. We have added DOI indexes for all the references. In the revised manuscript, the changes can be found in the abstract on the page 10 line 387 to 389, the page 11 line 390 to 418, the page 12 line 419 to 446, the page 13 line 447 to 475, the page 14 line 476 to 502, the page 15 line 503 to 531, and the page 16 line 532 to 545, which are as follow:

“[1] Li, X.F.; Yin, J., Zhang, J.; Wang, Y.F.; Song, X.L.; Zhang, Y.; Ren, X.C.. Hydrogen embrittlement and failure mechanisms of multi-principal element alloys: A review. J. Mater. Sci. Technol. 2022, 122, 20-32. https://doi.org/10.1016/j.jmst.2022.01.008

[2] Meda, U.S.; Bhat, N.; Pandey, A.; Subramanya, K.N.; Lourdu Antony Raj, M.A.. Challenges associated with hydrogen storage systems due to the hydrogen embrittlement of high strength steels. Int. J. Hydrogen. Energ. 2023, 48, 17894-17913. https://doi.org/10.1016/j.ijhydene.2023.01.292

[3] Kim, T.; Lee, J.; Kim, S.; Hong, E.; Lee, H.. Hydrogen permeation barrier of carbon-doped TiZrN coatings by laser carburization. Corros. Sci. 2021, 19, 109700. https://doi.org/10.1016/j.corsci.2021.109700

[4] Bull, S.K.; Champ, T.A., Raj, S.V.; O’Brien, R.C.; Musgrave, C.B.; Weimer. A.W.. Atomic layer deposited boron nitride nanoscale films act as high temperature hydrogen barriers. Appl. Surf. Sci. 2021, 565, 150428. https://doi.org/10.1016/j.apsusc.2021.150428

[5] Dehghanian, H.A.; Hosseinabadi, N.. The hydrogen storage capacity of Al-Cu alloy with permeable alumina hydrogen permeation barrier (HPB) applied by plasma electrolytic oxidation (PEO). Int. J. Hydrogen. Energ. 2022, 47, 7339-7350. https://doi.org/10.1016/j.ijhydene.2021.12.049

[6] Li, Z.L.; Yan, S.F.; Chen, W.D.; Zhang, Z.H.; Kang, Y.X.; Ma, W.. The effect of current density on the anodic oxidation hydrogen barrier film on ZrH_1.8 surface. Corros. Sci. 2024, 227, 111740. https://doi.org/10.1016/j.corsci.2023.111740

[7] Zhou, C.L.; Huang, Y.L.; Liu, X.H.; Huang, Y.; Wu, H.; Hua, Z.L.; Chu, P.K.; Yin. Y.S.. Functionalized graphite nanosheet/organosilicon composite coatings with soft-hard structures: Excellent wear resistance and hydrogen barrier properties. Surf. Coat. Tech. 2025, 496, 131684. https://doi.org/10.1016/j.surfcoat.2024.131684

[8] Cho, J.; Kim, B.; Venkateshalu, S.; Chung, D.Y.; Lee, K.; Choi, S.. Electrochemically activatable liquid organic hydrogen carriers and their applications. J. Am. Chem. Soc.. 2023, 145, 16951-16965. https://doi.org/10.1021/jacs.2c13324

[9] Lebedeva, O.; Kultin, D.; Каlenchuk Al.; Кustov L.. Advances and prospects in electrocatalytic hydrogenation of aromatic hydrocarbons for synthesis of “loaded” liquid organic hydrogen carriers. Curr. Opin. Electroche. 2023, 38, 101207. https://doi.org/10.1016/j.coelec.2022.101207

[10] Rullo, F.; Beier, C.K.; Henseler, J; Bösmann A.; Preuster P., Wasserscheid P.; Geißelbrecht M.. Pushing activity and stability of LOHC dehydrogenation catalysts by strict LOHC quality protocols. Int. J. Hydrogen. Energ. 2025, 98, 606-613. https://doi.org/10.1016/j.ijhydene.2024.12.104

[11] Wu, M.; Chen, Y.; Peng, J.Q.; Yan, G.Q.; Sun, Y.P.; Zhang, J.D.; Zhang, S.L.; Wang, L.J.. Hydrogen permeation resistance and characterization of Si-Al and Si-Zr composite sol oxide coating on surface of zirconium hydride. Rare Metals, 2017, 36, 55-60. https://doi.org/10.1007/s12598-016-0724-5

[12] Li, P.; Chen, K.; Zhao, L.L.; Zhang, H.Y.; Sun, H.X.; Yang, X.J.; Kim, N.H.; Lee, J.H.; Niu, Q.J.. Preparation of modified graphene oxide/polyethyleneimine film with enhanced hydrogen barrier properties by reactive layer-by-layer self-assembly. Compos. Part. B-eng. 2019, 166, 663-672. https://doi.org/10.1016/j.compositesb.2019.02.058

[13] Huang, J.; Xie, H.; Luo, L.M.; Zan. X.; Liu, D.G.; Wu, Y.C.. Preparation and properties of FeAl/Al₂O₃ composite tritium permeation barrier coating on surface of 316L stainless steel. Surf. Coat. Tech. 2020, 383, 125282. https://doi.org/10.1016/j.surfcoat.2019.125282

[14] Wang F.Y.; Wang, J.; Lu, W.; Li, W.G.; Chu, D.L.; Wang, W.H.. Multi-layer structured AlN/Er₂O₃ coating: Enhanced thermal stability and hydrogen isotope permeation resistance. Ceram. Int. 2024, 50, 40902-40910. https://doi.org/10.1016/j.ceramint.2024.07.403

[15] Liu, J.G.; Bi, H.S.; Zhang, Q.S.; Liu, S.Q.; Li, H.W.; Cui, G.. Design, fabrication, and hydrogen blocking performance of alumina/zirconia functional gradient coatings. Ceram. Int. 2024, 50, 40902-40910. https://doi.org/10.1016/j.ceramint.2024.08.413

[15] Wan, H.X.; Cheng, Z.L.; Song, D.D.; Chen, C.F.. Preparation and performance study of waterborne epoxy resin/non-covalent modified graphene oxide hydrogen barrier coatings. Int. J. Hydrogen. Energ. 2024, 53, 218-228. https://doi.org/10.1016/j.ijhydene.2023.12.051

[17] Yuan, S.C.; Zhang, S.; Wei, J.T.; Gao, Y.; Zhu, Y.J.; Wang, H.Y.. Materials selection, design, and regulation of polymer-based hydrogen barrier composite coatings, membranes and films for effective hydrogen storage and transportation: A comprehensive review. Int. J. Hydrogen. Energ. 2024, 91, 555-573. https://doi.org/10.1016/j.ijhydene.2024.10.066

[18] Seo, O.B.; Saha, S.; Kim, N.H.; Lee, J.H.. Preparation of functionalized mxene-stitched-graphene oxide/poly (ethylene-co-acrylic acid) nanocomposite with enhanced hydrogen gas barrier properties. J. Membrane. Sci. 2021, 640, 119839. https://doi.org/10.1016/j.memsci.2021.119839

[19] Saha, S.; Son. W.S.; Kim, N.H.; Lee. J.H.. Fabrication of impermeable dense architecture containing covalently stitched graphene oxide/boron nitride hybrid nanofiller reinforced semi-interpenetrating network for hydrogen gas barrier applications. J. Mater. Chem. A. 2022, 10, 4376-4391. https://doi.org/10.1039/D1TA09486F

[20] Nam, T.H.; Lee, J.H.; Choi, S.R.; Yoo, J.B.; Kim, J.Gu.. Graphene coating as a protective barrier against hydrogen embrittlement. Int. J. Hydrogen. Energ. 2014, 39, 11810-11817. https://doi.org/10.1016/j.ijhydene.2014.05.132

[21] Fan, Y.J.; Huang, Y.F.; Cui, B.; Zhou, Q.. Graphene coating on nickel as effective barriers against hydrogen embrittlement. Surf. Coat. Tech. 2019, 374, 610-616. https://doi.org/10.1016/j.surfcoat.2019.06.044

[22] Zhao, L.L.; Zhang, H.Y.; Kim, N.H.; Hui, D.; Lee, J.H.; Li, Q., Sun, H.X.; Li, P.. Preparation of graphene oxide/polyethyleneimine layer-by-layer assembled film for enhanced hydrogen barrier property. Compos. Part. B-eng. 2016, 92, 252-258. https://doi.org/10.1016/j.compositesb.2016.02.037

[23] Bandyopadhyay, P.; Park, W.B.; Layek, R.K.; Uddin, M.E.; Kim, N.H.; Kim, H.G.; Lee, J.H.. Hexylamine functionalized reduced graphene oxide/polyurethane nanocomposite-coated nylon for enhanced hydrogen gas barrier film. J. Membrane. Sci. 2016, 500, 106-114. https://doi.org/10.1016/j.memsci.2015.11.029

[24] Liu, H.Y.; Bandyopadhyay, P.; Kshetri, T.; Kim, N.H.; Ku B.C.; Moon, B.; Lee, J.H.. Layer-by-layer assembled polyelectrolyte-decorated graphene multilayer film for hydrogen gas barrier application. Compos. Part. B-eng. 2017, 114, 339-347. https://doi.org/10.1016/j.compositesb.2017.02.007

[25] Alkrunz, M.; Shajahan, S.; Elkaffas, R.; Schiffer, A.; Zheng, L.X.; Liao, K.; Khan, M.Y., Anjum, D.; Zweiri, Y.; Samad, Y.A.. Fabrication and characterization of rippled graphene/LDPE composites with enhanced hydrogen barrier properties. Int. J. Hydrogen. Energ. 2024, 85, 794-803. https://doi.org/10.1016/j.ijhydene.2024.08.346

[26] Liu, M.F.; Lin, K.L.; Zhou, M.Y.; Wallwork, A.; Bissett, M.A.; Young, R.J.; Kinloch, I.A.. Mechanism of gas barrier improvement of graphene/polypropylene nanocomposites for new-generation light-weight hydrogen storage. Compos. Sci. Technol. 2024, 249, 110483. https://doi.org/10.1016/j.compscitech.2024.110483

[27] Wan, H.X.; Song, X.X.; Cheng, Z.L.; Min, W.L.; Song, D.D.; Chen, C.F.. Construction and properties of graphene oxide hydrogen-blocking coatings. Int. J. Hydrogen. Energ. 2024, 84, 410-419. https://doi.org/10.1016/j.ijhydene.2024.08.230

[28] Longhi, M.; Zini, L.P.; Kunst, S.R.; Zattera, A.J.. Influence of the type of epoxy resin and concentration of glycidylisobutyl-poss in the properties of nanocomposites. Polym. Polym. Compos. 2017, 25, 593-602. https://doi.org/10.1177/096739111702500804

[29] Joseph, E.J.; Panneerselvam, K.. Manufacturing and characterization of tungsten particulate-reinforced aw106 epoxy resin composites. Transactions of the Indian Institute of Metals 2021, 74, 817-825. https://doi.org/10.1007/s12666-021-02202-z

[30] Sujith, R.; Chauhan, P.K.; Gangadhar, J.; Maheshwari, A.. Graphene nanoplatelets as nanofillers in mesoporous silicon oxycarbide polymer derived ceramics. Sci. Rep-UK. 2018, 8, 17633. https://doi.org/10.1038/s41598-018-36080-1

[31] Wei, S.N.; Guan, L.; Song, B.Z.; Fan, B.B.; Zhao, B.; Zhang, R.. Seeds-induced synthesis of SiC by microwave heating. Ceram. Int. 2019, 45, 9771-9775. https://doi.org/10.1016/j.ceramint.2019.02.012

[32] Yang, H.Y.; Li, M.Y.; Zhou, X.G.; Wang, H.L.; Yu, J.S.. Flexural modulus of SiC/SiC composites sintered by microwave and conventional heating. Ceram. Int. 2019, 45, 10142-10148. https://doi.org/10.1016/j.ceramint.2019.02.062

[33] Li, B.B.; Mao, B.X.; Wang, X.B.; He, T.. Fabrication and frictional wear property of bamboo-like SiC nanowires reinforced SiC coating. Surf. Coat. Tech. 2019, 45, 10142-10148. https://doi.org/10.1016/j.surfcoat.2020.125647

[34] Lü, X.X.; Li, L.B.; Sun, J.J.; Yang, J.H.; Jiao, J.. Microstructure and tensile behavior of (BN/SiC)_n coated SiC fibers and SiC/SiC minicomposites. J. Eur. Ceram. Soc. 2023, 43, 1828-1842. https://doi.org/10.1016/j.jeurceramsoc.2022.12.032

[35] Stobinski, L.; Lesiak, B.; Malolepszy, A.; Mazurkiewicz, M.; Mierzwa, B.; Zemek, J.; Jiricek, P.; Bieloshapka, I.. Graphene oxide and reduced graphene oxide studied by the XRD, TEM and electron spectroscopy methods. J. Electron. Spectrosc. 2014, 195, 145-154. http://dx.doi.org/10.1016/j.elspec.2014.07.003

[36] Hu, Z.R.; Tong, G.Q.; Lin, D.; Nian, Q.; Shao, J.Y.; Hu, Y.W.; Saeib, M.; Jin, S.Y.; Cheng, G.J.. Laser sintered graphene nickel nanocomposites. J. Mater. Process. Tech. 2016, 231, 143-150. http://dx.doi.org/10.1016/j.jmatprotec.2015.12.022

[37] Houshi, M.N.; Aakyiir, M.; Ma, J.. Low-temperature, rapid preparation of functionalized graphene platelets. Compos. Commun. 2020, 22, 100500. https://doi.org/10.1016/j.coco.2020.100500

[38] Chen, G.J.; Ng, K.Y.S.; Lin, C.C.. Effects of nitrogen-doping or alumina films on graphene as anode materials of lithium-ion batteries verified by in situ XRD. J. Nanomater. 2022, 2022, 1758789. https://doi.org/10.1155/2022/1758789

[39] Liu, J.C.; Su, Z.J.; Xu, J.M.; Zhang, Y.B.. Thermal storage performance of NaNO₃/cordierite-mullite ceramic (CMC) composites deriving from metallurgical slag. Ceram. Int. 2023, 49, 38094-38102. https://doi.org/10.1016/j.ceramint.2023.09.139

[40] Yang, W.T.; Zheng, G.P.. The enhanced energy storage properties of (1-x)(0.94BNT-0.06BT)-x(Bi_0.2Na_0.2K_0.2La_0.2Sr_0.2)TiO₃ solid solutions. Ceram. Int. 2024, 50, 7834-7842. https://doi.org/10.1016/j.ceramint.2023.12.111

[41] Chen, Y.H.; Sun, J.X.; Chai, Z.H.; Zhang, B.Q.; Cao, Y.; Zhang, Y.H.. High thermal conductivity and high energy density compatible latent heat thermal energy storage enabled by porous Al₂O₃@Graphite ceramics composites. Ceram. Int. 2024, 50, 19864-19872. https://doi.org/10.1016/j.ceramint.2024.03.111

[42] Dou, Z.M.; Yang, Yi.; Zhou, L.; Luo, G.G.; Li, Y.H.; Hu, J.; Wang, S.X.; Wang, W.; Ruan, S.J.; Zhang, G.Z.; Jiang, S.L.; Li, K.H.. Enhancing energy storage performance in multilayer ceramic capacitors with (Pb,La)(Zr,Sn,Ti)O₃-based antiferroelectric solid solutions. Appl. Mater. Today. 2024, 41, 102488. https://doi.org/10.1016/j.apmt.2024.102488

[43] Shen, Y.Q.; Xu, X.H.; Wu, J.F.; Yu, J.Q.; Qiu, S.X.; Zhang, D.. Effect of ZrO₂-MoO₃ on the properties of in situ synthesized corundum-mullite composite thermal storage ceramics. Ceram. Int. 2025, 51, 6110-6124. https://doi.org/10.1016/j.ceramint.2024.12.056

[44] Chen, W.L.; Meng, X.N.; Wu, D.Q.; Yao, D.C.; Zhang, D.D.. The effect of vacuum annealing on microstructure, adhesion strength and electrochemical behaviors of multilayered AlCrTiSiN coatings. Appl. Surf. Sci.. 2019, 467-468, 391-401. https://doi.org/10.1016/j.apsusc.2018.10.171

[45] Warcaba, M.; Kowalski, K.; Kopia, A.; Moskalewicz, T.. Impact of surface topography, chemistry and properties on the adhesion of sodium alginate coatings electrophoretically deposited on titanium biomaterials. Metall. Mater. Trans. A. 2021, 52, 4454-4467. https://doi.org/10.1007/s11661-021-06397-0

[46] Wan, H.X.; Min, W.L.; Song, D.D.; Chen, C.F.. Research progress of hydrogen blocking coatings. Mater. Chem. Phys.. 2024, 328, 130028. https://doi.org/10.1016/j.matchemphys.2024.130028

[47] Lv, J.; Zhu, C.X.; Qiu, H.N.; Zhang, J.; Gu, C.D.; Feng, J.. Robust icephobic epoxy coating using maleic anhydride as a crosslinking agent. Prog. Org. Coat.. 2020, 142, 105561. https://doi.org/10.1016/j.porgcoat.2020.105561

[48] Binbin Li; Shenghui Qian; Cong Sun; Min Wang; Xiaohong Zhan. Mechanical properties and wear resistance of Cf/epoxy resin composites with in-situ grown SiC nanowires on carbon fibers. Compos. Interface. 2023, 30, 923-939. https://doi.org/10.1080/09276440.2023.2179250

[49] Nakamura, H.; Isobe K.; Nakamichi M.; Yamanishi T.. Evaluation of deuterium permeation reduction factor of various coatings deposited on ferritic/martensitic steels for development of tritium permeation barrier. Fusion Eng. Des. 2010, 85, 1531-1536. https://doi.org/10.1016/j.fusengdes.2010.04.028

[50] Wu, Y.Y.; Wang, S.M.; Li S.; He D.; Liu X.P.; Jiang L.J.; Huang, H.T.. Deuterium permeation properties of Er₂O₃/Cr₂O₃ composite coating prepared by MOCVD on 316L stainless steel. Fusion Eng. Des. 2016, 113, 205-210. https://doi.org/10.1016/j.fusengdes.2016.09.007

[51] Yang, H.; Shao, Z.M.; Wang, W.; Ji, X.; Li, C.J.. A composite coating of GO-Al₂O₃ for tritium permeation barrier. Fusion Eng. Des. 2020, 156, 111689. https://doi.org/10.1016/j.fusengdes.2020.111689

[52] Hu, L.L.; Wei, G.; Yin, R.; Hong, M.Q.; Cheng, T.; Zhang, D.X.; Zhao, S.Q.; Yang, B.; Zhang, G.K.; Cai, G.X.; Shi, Y.; Jiang C.Z.; Ren F.. Significant hydrogen isotopes permeation resistance via nitride nano-multilayer coating. Int. J. Hydrogen. Energ. 2020, 45, 19583-19589. https://doi.org/10.1016/j.ijhydene.2020.05.123

[53] Mukai, K.; Kenjo, S.; Iwamatsu, N.; Mahmoud, B.; Chikada, T.; Yagi J.; Konishi, S.. Hydrogen permeation from F82H wall of ceramic breeder pebble bed: The effect of surface corrosion. Int. J. Hydrogen. Energ. 2022, 47, 6154-6163. https://doi.org/10.1016/j.ijhydene.2021.11.225

[54] Wang, Z.G.; Chen, W.D.; Yan, S.F.; Zhong, X.K.; Ma, W.; Song, X.W.; Wang, Y.M.; Ouyang, J.H.. Direct fabrication and characterization of zirconia thick coatings on zirconium hydride as a hydrogen permeation barrier. Coatings, 2023, 13, 884. https://doi.org/10.3390/coatings13050884

[55] Raia, S.; Rayjada, P.A.; Dhorajiya, P.B.; Patel, R.B.; Sharma, S.K.; Sircar, A.; Bhattacharyay, R.. Deuterium permeation studies through bare and Er₂O₃ coated SS 316L. Fusion Eng. Des. 2024, 206, 114587. https://doi.org/10.1016/j.fusengdes.2024.114587”

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

It is an interesting work with specific characterization techniques. Some points need clarification, and the authors should add some references. Overall, it is a good work and a nice addition to the journal. Please refer to the pdf attached with all comments.

Comments for author File: Comments.pdf

Author Response

Point-by-point response to the comments made by the reviewer(s)

 

REVIEWER REPORT(S):

Reviewer #2:

Comments and Suggestions for Authors

It is an interesting work with specific characterization techniques. Some points need clarification, and the authors should add some references. Overall, it is a good work and a nice addition to the journal. Please refer to the pdf attached with all comments.

Response to the reviewer #1:

Thanks for your helpful comments on our paper. We have revised our paper according to your comments. We also responded point by point to your comments as listed below, along with clear indications of the locations of the revisions, which are shown in red.

 

Comment 1. Lines 43-44: Please add references.

Response: Thank you for your great suggestion. We agree with this suggestion. According to your suggestion, we have added references on the page 2 line 55.

 

Comment 2. 2.1 Materials: I think the authors should provide more information about the graphene. For example, the elemental analysis of GN and possible sizes of the platelets.

Response: Thank you for your great suggestion. According to your suggestion, we have added the more information about the grapheme in the experiments on the page 3 line 115 to 117, such as the elemental analysis of GN and possible sizes of the platelets, which is as follow:

“The graphene (GN, the total oxygen content is from 3% to 5%) with the thickness of 0.55 nm~3.74 nm and the diameter of 0.5 μm~3 μm is purchased from the Disney's Aladdin.”

 

Comment 3. 2.1 Materials: Also, for the polyvinylpyrrolidone (PVP) and polyamide curing agent, the authors should give the molecular weights.

Response: Thank you for your great suggestion. According to your suggestion, we have added the molecular weights of the polyvinylpyrrolidone (PVP) and polyamide curing agent in the experiments on the page 3 line 113 and 114, which are as follow:

“The n-butanol (C₄H₁₀O, 99.5%), xylene (C₈H₁₀, 99%), epoxy resin (C₁₁H₁₂O₃)_n, 95%), polyvinylpyrrolidone (PVP, K30, molecular weight 40000~58000), polyamide curing agent (molecular weight 600~1100), are all analytical grade and purchased from the Tianjin Damao Reagent Company.”

 

Comment 4. Line 109: At which temperature did the authors perform the drying and for how much time?

Response: Thank you for your great suggestion. According to your suggestion, we have added the drying temperature and time in the experiments on the page 3 line 124 and 125, which are as follow:

“After that, we rinsed with acetone and dry in an oven at 105 ℃ for 30 min as the later use.”

 

Comment 5. 2.2 Preparation: If the authors used a specific protocol they should add it here.

Response: Thank you for your great suggestion. According to your suggestion, we have added the descriptions in the experiments on the page 3 line 128 to 131, and the page 4 line 154 and 155, which are as follow:

“(a) GN-ER precursors: We mixed the n-butanol with 120 mL and the xylene with 80 mL to prepare the diluent. We placed the GN with 10 g and the PVP with 1 g in the three necked flask with the diluent and stir at 500 r/min for 10 min in the water bath at 60 ℃, maintaining the condensation reflux with tap water, in order to obtain the uniform system. The PVP, as a dispersant, plays the role in dispersing the GN and SiC, enabling them to be fully dispersed in the ER. Then we added the epoxy resin with 100 g to the system and kept stirring for 20 min to obtain the homogeneous system. Next, we added the polyamide curing agent with 5 g to the system and kept stirring for 2 h to obtain the GN-ER precursors. The function of the polyamide curing agent is to promote cross-linking reaction and accelerate the curing process.

(3) Preparation of the coatings

The coatings were prepared by using the spin coating method, and the coating num-bers are shown in Table 1. The S-1 to S-5 are the comparative samples to the S-6, which are used to research and discuss the influence of coating composite ways on the hydrogen barrier performances. We took the preparation of S-6 as the example in order to introduce the preparation process. We applied the GN-ER precursor onto the treated 316L surface with the fine brush, let it stand in the air for 10 min until the surface was dry, and then cured it in the 60 ℃ drying oven for 12 h. Afterwards, the SiC-ER precursor was coated on the surface of GN-ER and allowed to stand in air for 10 minutes until the surface dried. It was then cured in the 60 ℃ drying oven for 12 h. Then, the GN-ER precursor was coated on the surface of SiC-ER and allowed to stand in air for 10 min until the surface dried. In order to avoid the peeling of the outermost coatings of GN-ER, the amount of the outer-most coatings of GN-ER is half of that of the innermost GN-ER layer. Finally, the compo-site coating S-6 can be achieved by curing in the 60 ℃ drying oven for 24 h. The preparation process of other coatings are similar to that of the S-6.”

 

Comment 6. 2.2 Preparation: Why do the authors use PVP in their mixtures?

Response: Thank you for your kind suggestion. The PVP serves as the dispersant, specifically to disperse the grapheme (GN) and silicon carbide (SiC), enabling them to be fully dispersed in the epoxy resins (ER), reducing the agglomeration phenomenon, thereby enhancing the uniformity of coating components.

 

Comment 7. Figure 2: The authors should add references for these peaks.

Response: Thank you for your great suggestion. According to your suggestion, we have added the references for the XRD peaks in the results and discussion on the page 5 line 195, 198, 200, 205, 207 and 208.

 

Comment 8. Lines 181-183: Please add references.

Response: Thank you for your great suggestion. According to your suggestion, we have added the references on the page 5 line 210. Meanwhile, we have added the corresponding descriptions on the page 5 line 210 to 217, which is as follow:

“The XRD diffraction peaks of the S-2 to S-6 display the diffraction peaks at 34°, 36°, 38°, 60°, 72°, and 74° (Figure 2), which are the same as the S-1, corresponding to the PDF card numbered 29-1130, indicating that they all contain the SiC phase. For the S-2 to S-6, the XRD diffraction peaks appeared at the diffraction angles of 26°, 43°, 51° and 75° (Figure 2), which corresponded to the XRD characteristic peaks of the GN [30, 35-38]. The XRD characteristic peaks at diffraction angles of 26° and 43° correspond to the (002) and (101) crystal planes of GN, respectively, indicating that the S-2 to S-6 contain the GN [30, 35-38]. From the diffraction angular displacements of the S-2 to S-6, no angular shift was observed, displaying that the samples are the composite structures rather than the solid solution [39-43]. This is because if the material is the composite structure, each component maintains the independent crystal structure, and its XRD pattern shows the superposition of different phase characteristic peaks, with each peak position consistent with the pure phase standard card, without systematic shift [39-43]. When the material forms the displacement or interstitial solid solution, solute atoms can cause the change in the lattice constant of the main crystal phase, resulting in an overall shift of XRD diffraction peaks towards higher angles (lattice contraction) or lower angles (lattice expansion) [39-43]. Therefore, the XRD characterization results indicate that the S-2 to S-6 are composite phases of the SiC, GN, and GN-SiC with the ER matrix, respectively.”

 

Comment 9. Lines 201-203: Please add references.

Response: Thank you for your great suggestion. According to your suggestion, we have added the references on the page 6 line 237.

 

Comment 10. Figure 4: I think an extra image with zoom in the interface could be useful.

Response: Thank you for your constructive suggestion. We agree with this suggestion. According to your suggestion, we have added the extra image with zoom in the interface in the figure 4, which is named the figure 4b on the page 7 line 258 to 260. The supplementary figure is as follows:

“

Figure 4. (a) SEM of the S-6 cross-section (b) partial enlarged SEM of the S-6 cross-section (the red rectangle).”

 

Comment 11. Figure 4: Why the 1st and 3rd layers have different thickness?

Response: Thank you for your great suggestion. The reason why the thickness of the first-layer is greater than that of the third layer is to improve the adhesive strength between the composite coatings with the sandwich structures and the substrate. At the same time, as the hydrogen barrier coatings, the first-layer plays the role in both improving the bonding strength and hydrogen barrier. In order to avoid the peeling of the outermost coatings of GN-ER, the amount of the outermost coatings of GN-ER is half of that of the innermost GN-ER layer.

 

Comment 12. Lines 218-219: Please add references.

Response: Thank you for your great suggestion. According to your suggestion, we have added the references on the page 6 line 253, 254.

 

Comment 13. Have the authors performed EDX to map the Si and C and other elements on the different layers. I think it could be a good addition.

Response: Thank you for your great suggestion. We strongly agree with the importance of EDS analysis for material characterization, and your feedback provides important directions for the improvement of this article. Due to the current maintenance cycle of the EDS equipment in the laboratory, we are temporarily unable to conduct the additional EDS experiments. We have characterized the S-1 to S-6 through the XRD and provided the relatively detailed description. At the same time, the references on the XRD analysis have been added. The XRD results indicate that the S-1 to S-6 samples are all composite coatings with compositions of the SiC-ER, GN-ER, (SiC-ER)/(GN-ER), (GN-ER)/(SiC-ER), (SiC-ER)/(GN-ER)/(SiC-ER) and (GN-ER)/(SiC-ER)/(GN-ER), respectively. These results are consistent with the results reported in the added references [28-38] in the revised manuscript. The core objective of this research is to improve the PRF through the sandwich structured composite coatings. We will combine the EDS and other analytical methods in the subsequent researches to further explore the influence of composite structure sequences on the PRF, and the relevant results will be discussed in detail in future work. The references [28-38] are as follow:

“[28] Longhi, M.; Zini, L.P.; Kunst, S.R.; Zattera, A.J.. Influence of the type of epoxy resin and concentration of glycidylisobutyl-poss in the properties of nanocomposites. Polym. Polym. Compos. 2017, 25, 593-602. https://doi.org/10.1177/096739111702500804

[29] Joseph, E.J.; Panneerselvam, K.. Manufacturing and characterization of tungsten particulate-reinforced aw106 epoxy resin composites. Transactions of the Indian Institute of Metals 2021, 74, 817-825. https://doi.org/10.1007/s12666-021-02202-z

[30] Sujith, R.; Chauhan, P.K.; Gangadhar, J.; Maheshwari, A.. Graphene nanoplatelets as nanofillers in mesoporous silicon oxycarbide polymer derived ceramics. Sci. Rep-UK. 2018, 8, 17633. https://doi.org/10.1038/s41598-018-36080-1

[31] Wei, S.N.; Guan, L.; Song, B.Z.; Fan, B.B.; Zhao, B.; Zhang, R.. Seeds-induced synthesis of SiC by microwave heating. Ceram. Int. 2019, 45, 9771-9775. https://doi.org/10.1016/j.ceramint.2019.02.012

[32] Yang, H.Y.; Li, M.Y.; Zhou, X.G.; Wang, H.L.; Yu, J.S.. Flexural modulus of SiC/SiC composites sintered by microwave and conventional heating. Ceram. Int. 2019, 45, 10142-10148. https://doi.org/10.1016/j.ceramint.2019.02.062

[33] Li, B.B.; Mao, B.X.; Wang, X.B.; He, T.. Fabrication and frictional wear property of bamboo-like SiC nanowires reinforced SiC coating. Surf. Coat. Tech. 2019, 45, 10142-10148. https://doi.org/10.1016/j.surfcoat.2020.125647

[34] Lü, X.X.; Li, L.B.; Sun, J.J.; Yang, J.H.; Jiao, J.. Microstructure and tensile behavior of (BN/SiC)_n coated SiC fibers and SiC/SiC minicomposites. J. Eur. Ceram. Soc. 2023, 43, 1828-1842. https://doi.org/10.1016/j.jeurceramsoc.2022.12.032

[35] Stobinski, L.; Lesiak, B.; Malolepszy, A.; Mazurkiewicz, M.; Mierzwa, B.; Zemek, J.; Jiricek, P.; Bieloshapka, I.. Graphene oxide and reduced graphene oxide studied by the XRD, TEM and electron spectroscopy methods. J. Electron. Spectrosc. 2014, 195, 145-154. http://dx.doi.org/10.1016/j.elspec.2014.07.003

[36] Hu, Z.R.; Tong, G.Q.; Lin, D.; Nian, Q.; Shao, J.Y.; Hu, Y.W.; Saeib, M.; Jin, S.Y.; Cheng, G.J.. Laser sintered graphene nickel nanocomposites. J. Mater. Process. Tech. 2016, 231, 143-150. http://dx.doi.org/10.1016/j.jmatprotec.2015.12.022

[37] Houshi, M.N.; Aakyiir, M.; Ma, J.. Low-temperature, rapid preparation of functionalized graphene platelets. Compos. Commun. 2020, 22, 100500. https://doi.org/10.1016/j.coco.2020.100500

[38] Chen, G.J.; Ng, K.Y.S.; Lin, C.C.. Effects of nitrogen-doping or alumina films on graphene as anode materials of lithium-ion batteries verified by in situ XRD. J. Nanomater. 2022, 2022, 1758789. https://doi.org/10.1155/2022/1758789”

 

Comment 14. How brittle are these layered materials? Have the authors conducted any mechanical tests compared to the 316L.

Response: Thank you for your constructive and kind suggestion. The brittleness of the 316L stainless steel is mainly manifested as the stress corrosion cracking, high-temperature tempering brittleness, and alkali induced brittle peeling. Due to the limitations in experimental equipments and instruments, we were unable to achieve the brittle characterization of the composite coatings and the 316L stainless steel. Because of the focus of this research on improving the PRF, it has been verified through research that the composite coatings have the ability to reduce the hydrogen embrittlement (HE) and have the promising application prospects. In the next step of researches, we will collaborate with the relevant research institutions to conduct the in-depth comparative studies on the brittleness and their impact of the composite coatings and the 316L stainless steel. Through further research, the application scope and scenarios of the composite coatings will be further elucidated.

 

Comment 15. Lines 252-253: Please add references.

Response: Thank you for your great suggestion. According to your suggestion, we have added the references on the page 8 line 291.

 

Comment 16. Lines 295-296: Please add references.

Response: Thank you for your great suggestion. According to your suggestion, we have added the references on the page 9 line 334.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript is now fully ready for acceptance. Just a small remark: check the manufacturer again. Lines 165-166: “…using an electrochemical workstation (PGSTAT302N, Metrohm, China)…” or ”Autolab PGSTAT 302N galvanostat/potentiostat (Metrohm, Switzerland)"? For the rest, I recommend it: Accept in present form.

Author Response

Point-by-point response to the comments made by the reviewer(s)

 

REVIEWER REPORT(S):

Reviewer #1:

Comments and Suggestions for Authors

The manuscript is now fully ready for acceptance. Just a small remark: check the manufacturer again. Lines 165-166: “…using an electrochemical workstation (PGSTAT302N, Metrohm, China)…” or ”Autolab PGSTAT 302N galvanostat/potentiostat (Metrohm, Switzerland)"? For the rest, I recommend it: Accept in present form.

Response to the reviewer #1:

Thanks for your helpful comments on our paper. We have revised our paper according to your comments, which are shown in red. In the revised manuscript, the changes can be found in the abstract on the page 4 line 165, which is as follow:

“The phase structures of the coatings were characterized by the X-ray diffraction (XRD, Advance, Bruker, Germany), which uses a Cu target with a test angle range of 10º~90º and a scanning speed of 1º/min. The microstructures of the coatings were characterized by the scanning electron microscopy (SEM, Quanta-600, FEI, USA). The electrochemical hydrogen permeation curves of the substrate and the coatings were characterized by the electrochemical workstation (PGSTAT302N, Metrohm, China). The electrochemical hydrogen permeation tests were conducted via a Devanathan-Stachurski double-cell setup, an electrochemical workstation, and a direct current power supply.”

Author Response File: Author Response.pdf