One-Pot Microwave-Assisted Synthesis of Graphene-Supported PtCoM (M = Mn, Ru, Mo) Catalysts for Low-Temperature Fuel Cells
, Teofilius Kilmonis, Virginija Kepenienė, Aldona Balčiūnaitė, Raminta Stagniūnaitė, Daina Upskuvienė, Jolita Jablonskienė, Jūratė Vaičiūnienė, Martynas Skapas, Loreta Tamašauskaitė-Tamašiūnaitė * and Eugenijus NorkusRound 1
Reviewer 1 Report
Manuscript ID: catalysts-1432993
Title: One-pot microwave-assisted synthesis of graphene supported PtCoM (M = Mn, Ru, Mo) catalysts for low-temperature fuel cells
The manuscript with title: One-pot microwave-assisted synthesis of graphene supported PtCoM (M =Mn, Ru, Mo) catalysts for low-temperature fuel cells, matches a good study and contribution in the field of carbon based with alloy transition metals catalysts for the methanol oxidation in low temperature fuel cells. I find the manuscript generally convincing and suitable for publication in Catalysts Journal. Therefore, an addition of some characterizations along results or supplementary information can significantly improve the scientific impact of the paper and must be performed for the publication.
The following areas should be addressed:
Suggestion: Characterizations about morphologies and surface chemistry need to be implemented in the manuscript to clarify the composition and morphology of the catalysts. For example, X-ray diffraction (XRD) and/or X-ray photoelectron spectroscopy (XPS), where the authors can demonstrate the interactions between the elements in the developed catalysts and its degree of crystallinity, as well as the elemental composition and atomic percentage of each components in the catalysts.
Electrochemical characterizations: The catalysts were well characterized here, the authors have demonstrated the catalytic activity of the catalysts towards methanol oxidation reaction studies via cyclic voltammetry, chronoamperometry. However, an addition of kinetics study need to be implemented in the electrochemistry section of the manuscript. Usually, on the study of methanol oxidation Tafel Slope is essential to determine the rate-determining step, kinetics and reaction mechanism.
Author Response
Response for Reviewer 1
We are most thankful for the valuable Reviewer comments, which we tried to take into account.
Reviewer: The manuscript with title: One-pot microwave-assisted synthesis of graphene supported PtCoM (M = Mn, Ru, Mo) catalysts for low-temperature fuel cells, matches a good study and contribution in the field of carbon based with alloy transition metals catalysts for the methanol oxidation in low temperature fuel cells. I find the manuscript generally convincing and suitable for publication in Catalysts Journal. Therefore, an addition of some characterizations along results or supplementary information can significantly improve the scientific impact of the paper and must be performed for the publication. The following areas should be addressed:
Suggestion: Characterizations about morphologies and surface chemistry need to be implemented in the manuscript to clarify the composition and morphology of the catalysts. For example, X-ray diffraction (XRD) and/or X-ray photoelectron spectroscopy (XPS), where the authors can demonstrate the interactions between the elements in the developed catalysts and its degree of crystallinity, as well as the elemental composition and atomic percentage of each components in the catalysts.
Authors: Many thanks for the valuable comments. Without a doubt, the methods proposed would give additional data for the characterization of our catalysts. We apologize, but at the moment, the XPS facility is closed in our institution due to the COVID-19 restrictions. Therefore, the realization of such experiments is not possible. Concerning the XRD measurements, we have performed additional experiments. A sharp peak at 26.5o observed for investigated catalysts can be attributed to the graphite structure (002) plane of the supports. For PtCoMn/GR, PtCoRu/GR, and PtCoMo/GR catalysts, the peaks corresponding to polycrystalline Pt and other metals cannot be clearly discerned because the catalysts are amorphous and PtCoMn, PtCoRu, and PtCoMo nanoparticles are too small, which results in the broadening of the small peaks.
Figure 1. XRD patterns of PtCoMn/GR, PtCoRu/GR and PtCoMo/GR catalysts.
Reviewer: Electrochemical characterizations: The catalysts were well characterized here, the authors have demonstrated the catalytic activity of the catalysts towards methanol oxidation reaction studies via cyclic voltammetry, chronoamperometry. However, an addition of kinetics study need to be implemented in the electrochemistry section of the manuscript. Usually, on the study of methanol oxidation Tafel Slope is essential to determine the rate-determining step, kinetics and reaction mechanism.
Authors: The new data – Tafel plots for methanol oxidation on the investigated catalysts (new Figure under number 1) were added and discussed in the revised version of the manuscript.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Catalysts (ISSN 2073-4344)
Manuscript ID: catalysts-1432993
Title: One-pot microwave-assisted synthesis of graphene supported PtCoM (M = Mn, Ru, Mo) catalysts for low-temperature fuel cells
In this manuscript, the authors used the preparation method of one-pot microwave-assisted, and synthesized graphene supported PtCoM (M = Mn, Ru, Mo) catalysts for low-temperature fuel cells.
The molar ratios of metals Pt:Co:Mn, Pt:Co:Ru, and Pt:Co:Mo was equal to 1:3:1, 1:2:2, and 7:2:1, respectively. The catalysts tested herein characterized using a variety of techniques i.e., such as Transmission Electron Microscopy (TEM), X-ray Energy Dispersive Analysis (EDX) and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The electrocatalytic activity of the graphene-supported PtCoM catalysts towards the oxidation of methanol in an alkaline medium was investigated using cyclic voltammetry and chrono-techniques. Finally, the authors reported that the highest current density, activity, and stability toward methanol oxidation demonstrated the PtCoMn(1:3:1)/GR catalyst.
This is a very interesting work, well organized and presented. I recommend publication to Catalysts after the following major revisions are addresses.
Comment #1
The authors need to improve on their reference list in terms of the preparation method. Please include the following references in order to make their introduction section more up to date.
- Cui, W. Li, X. Song, Z. Zhang, H. Yu, W. Shan, Y. Xiong, Microwave-assisted one-pot rapid synthesis of mesoporous silica-chitosan composites for efficient recovery of rhenium(Ⅶ). Sep. Purif. Technol. 277 (2021) 119497.
- I. Siakavelas, N.D. Charisiou, S. AlKhoori, A.A. AlKhoori, V. Sebastian, S.J. Hinder, M.A. Baker, I.V. Yentekakis, K. Polychronopoulou, M.A. Goula, Highly selective and stable nickel catalysts for the CO2 methanation reaction based over supported on ceria promoted with Sm2O3, Pr2O3 and MgO for the CO2 methanation, Appl. Catal. B-Environ. 282 (2021) 119562.
- A. AlKhoori, K. Polychronopoulou, A. Belabbes, M.A. Jaoude, L.F. Vega, V. Sebastian, S. Hinder, M.A. Baker, A.F. Zedan, Cu, Sm co-doping effect on the CO oxidation activity of CeO2. A combined experimental and density functional study, Appl. Surf. Sci. 521 (2020) 146305.
- I. Siakavelas, N.D. Charisiou, A. AlKhoori, S. AlKhoori, V. Sebastian, S.J. Hinder, M.A. Baker, I.V. Yentekakis, K. Polychronopoulou, M.A.Goula, Highly selective and stable Ni/La-M (M=Sm, Pr, and Mg)-CeO2 catalysts for CO2 methanation. J. CO2 Util. 51 (2021) 101618.
Comment #2
The authors need to be more clear on the motivation behind their work. Which is the innovation and what are the new aspects being introduced on this research topic?
Comment #3
Is it possible for the authors to calculate the Pt metal particle size for spent catalysts using TEM analysis?
Comments for author File: Comments.pdf
Author Response
Response for Reviewer 2
We are most thankful for the valuable Reviewer comments, which we tried to take into account.
Reviewer: In this manuscript, the authors used the preparation method of one-pot microwave-assisted, and synthesized graphene supported PtCoM (M = Mn, Ru, Mo) catalysts for low-temperature fuel cells.
The molar ratios of metals Pt:Co:Mn, Pt:Co:Ru, and Pt:Co:Mo was equal to 1:3:1, 1:2:2, and 7:2:1, respectively. The catalysts tested herein characterized using a variety of techniques i.e., such as Transmission Electron Microscopy (TEM), X-ray Energy Dispersive Analysis (EDX) and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). The electrocatalytic activity of the graphene-supported PtCoM catalysts towards the oxidation of methanol in an alkaline medium was investigated using cyclic voltammetry and chrono-techniques. Finally, the authors reported that the highest current density, activity, and stability toward methanol oxidation demonstrated the PtCoMn(1:3:1)/GR catalyst.
This is a very interesting work, well organized and presented. I recommend publication to Catalysts after the following major revisions are addresses.
Comment #1
The authors need to improve on their reference list in terms of the preparation method. Please include the following references in order to make their introduction section more up to date.
- Cui, J.; Li, W.; Song, X.; Zhang, Z.; Yu, H.; Shan, W.; Xiong, Y. Microwave-assisted one-pot rapid synthesis of mesoporous silica-chitosan composites for efficient recovery of rhenium(Ⅶ). Sep. Purif. Technol. 2021, 277, 119497. https://doi.org/10.1016/j.seppur.2021.119497
- Siakavelas, I.; Charisiou, N.D.; AlKhoori, S.; AlKhoori, A.A.; Sebastian, V.; Hinder, S.J.; Baker, M.A.; Yentekakis, I.V.; Polychronopoulou, K.; Goula, M.A. Highly selective and stable nickel catalysts for the CO2 methanation reaction based over supported on ceria promoted with Sm2O3, Pr2O3 and MgO for the CO2 Appl. Catal. B-Environ. 2021, 282, 119562. https://doi.org/10.1016/j.apcatb.2020.119562
- AlKhoori, A.; Polychronopoulou, K.; Belabbes, A.; Jaoude, M.A.; Vega, L.F.; Sebastian, V.; Hinder, S.; Baker, M.A.; Zedan, A.F. Cu, Sm co-doping effect on the CO oxidation activity of CeO2. A combined experimental and density functional study. Appl. Surf. Sci. 2020, 521, 146305. https://doi.org/10.1016/j.apsusc.2020.146305
- Siakavelas, I.; Charisiou, N.D.; AlKhoori, A.; AlKhoori, S.; Sebastian, V.; Hinder, S.J.; Baker, M.A.; Yentekakis, I.V.; Polychronopoulou, K.; Goula, M.A. Highly selective and stable Ni/La-M (M=Sm, Pr, and Mg)-CeO2 catalysts for CO2 J. CO2 Util. 2021, 51, 101618. https://doi.org/10.1016/j.jcou.2021.101618
Authors: The reference list was improved by adding new references in the revised version of the manuscript.
Reviewer: Comment #2
The authors need to be more clear on the motivation behind their work. Which is the innovation and what are the new aspects being introduced on this research topic?
Authors: Short motivation was added to the Introduction part.
Reviewer: Comment #3
Is it possible for the authors to calculate the Pt metal particle size for spent catalysts using TEM analysis?
Authors: We apologize, but at this moment, it is not possible.
Author Response File: Author Response.pdf
Reviewer 3 Report
The article "One-pot microwave-assisted synthesis of graphene supported PtCoM (M = Mn, Ru, Mo) catalysts for low-temperature fuel cells " is devoted to the important problem of obtaining effective catalysts of methanol oxidation.
Nevertheless, there are a number of serious remarks to the article, presented below.
It is necessary to present the results оf XRD for all studied materials, determine the phase composition, parameter of crystal lattice and average size of metal nanoparticles using the Scherrer equation.
Need to build a histogram of the size distribution and determine the average particle size according to TEM results for all materials and compared this date with value of ESA.
The synthesis technique needs to be described in more detail, microwave-assisted characteristics, what graphene was used, its characteristics.
The value of ESA for PtCoMn/C materials is huge (160.0 m2 g-1), TEM results (fig 1a) inconsistent with this result. With such a surface area, the size of metal nanoparticles should be extremely small.
What is the reason for the choice of such a high loading of platinum on the electrode, usually it is about 20 μg cm-2?
What is the reason for choosing just such compositions of trimetallic nanoparticles? If we study the influence of the nature of the alloying metal on the activity of the catalyst, it is logical to do it with a constant composition. This work changes both the composition and the nature of the alloying component.
It has not been proven in the work that it is trimetallic nanoparticles that are formed, EDX measurements in this case do not show sufficient resolution, and XRD data are not presented.
The conclusions do not explain why the PtCoMn (1: 3: 1)/GR material was the most active.
We believe that publication is impossible without substantial revision of the article.
Author Response
Response for Reviewer 3
We are most thankful for the valuable Reviewer comments, which we tried to take into account.
Reviewer: The article "One-pot microwave-assisted synthesis of graphene supported PtCoM (M = Mn, Ru, Mo) catalysts for low-temperature fuel cells " is devoted to the important problem of obtaining effective catalysts of methanol oxidation. Nevertheless, there are a number of serious remarks to the article, presented below. It is necessary to present the results оf XRD for all studied materials, determine the phase composition, parameter of crystal lattice and average size of metal nanoparticles using the Scherrer equation.
Authors: Many thanks for the valuable comments. Without a doubt, the methods proposed would give additional data for the characterization of our catalysts. We apologize, but at the moment, the XPS facility is closed in our institution due to the COVID-19 restrictions. Therefore, the realization of such experiments is not possible. Concerning the XRD measurements, we have performed additional experiments. A sharp peak at 26.5o observed for investigated catalysts can be attributed to the graphite structure (002) plane of the supports. For PtCoMn/GR, PtCoRu/GR, and PtCoMo/GR catalysts, the peaks corresponding to polycrystalline Pt and other metals cannot be clearly discerned because the catalysts are amorphous and PtCoMn, PtCoRu, and PtCoMo nanoparticles are too small, which results in the broadening of the small peaks.
Figure 1. XRD patterns of PtCoMn/GR, PtCoRu/GR and PtCoMo/GR catalysts.
Reviewer: Need to build a histogram of the size distribution and determine the average particle size according to TEM results for all materials and compared this date with value of ESA.
Authors: We apologize, but at this moment, it is not possible.
Reviewer: The synthesis technique needs to be described in more detail, microwave-assisted characteristics, what graphene was used, its characteristics.
Authors: The description of microwave synthesis was improved in the Materials and Methods part.
Reviewer: The value of ESA for PtCoMn/C materials is huge (160.0 m2 g-1), TEM results (fig 1a) inconsistent with this result. With such a surface area, the size of metal nanoparticles should be extremely small.
Authors: The real results are presented.
Reviewer: What is the reason for the choice of such a high loading of platinum on the electrode, usually it is about 20 μg cm-2?
Authors: The reason was to get better catalytic activity of the catalysts.
Reviewer: What is the reason for choosing just such compositions of trimetallic nanoparticles? If we study the influence of the nature of the alloying metal on the activity of the catalyst, it is logical to do it with a constant composition. This work changes both the composition and the nature of the alloying component.
Authors: For the synthesis of catalysts, the concentrations of H2PtCl6 and CoCl2 were kept constant for all catalysts and RuCl3, Na2MoO4, and MnCl2 were added in concentrations enough for the formation of ternary catalysts.
Reviewer: It has not been proven in the work that it is trimetallic nanoparticles that are formed, EDX measurements in this case do not show sufficient resolution, and XRD data are not presented.
Authors: The practical composition of metallic catalysts was measured by ICP-OES.
Reviewer: The conclusions do not explain why the PtCoMn (1: 3: 1)/GR material was the most active.
Authors: At the moment, we have no proper explanation for this phenomenon.
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
The authors responded to some of the comments and made corrections, however, some points remain unclear
Table 2 provides a comparison of the activity (currents) for the materials obtained in the article and analogs from the literature. At the same time, such a comparison does not take into account the loading of platinum on the electrode, which makes the comparison of activity incorrect.
Reviewer: Need to build a histogram of the size distribution and determine the average particle size according to TEM results for all materials and compared this date with value of ESA.
Authors: We apologize, but at this moment, it is not possible.
- Why, to obtain this result, no equipment is needed, all the necessary TEM photographs should be with the authors. This result is important because the structure of the material can explain its activity.
Reviewer: The value of ESA for PtCoMn/C materials is huge (160.0 m2 g-1), TEM results (fig 1a) inconsistent with this result. With such a surface area, the size of metal nanoparticles should be extremely small.
Authors: The real results are presented.
= Of course, but if there is some unexpected result that stands out and contradicts other data, you need to pay attention to this. At the very least, it is necessary to make an assumption about the possible reasons for this fact.
Reviewer: What is the reason for choosing just such compositions of trimetallic nanoparticles? If we study the influence of the nature of the alloying metal on the activity of the catalyst, it is logical to do it with a constant composition. This work changes both the composition and the nature of the alloying component.
Authors: For the synthesis of catalysts, the concentrations of H2PtCl6 and CoCl2 were kept constant for all catalysts and RuCl3, Na2MoO4, and MnCl2 were added in concentrations enough for the formation of ternary catalysts.
- in the methodology specified (p.13)
- a) PtCoRu/GR: 1.2 mM H2PtCl6, 12 mM CoCl2, 6 mM RuCl3, 0.1 g graphene powder, ethylene glycol;
- b) PtCoMo/GR: 1.2 mM H2PtCl6, 12 mM CoCl2, 6 mM Na2MoO4, 0.1 g graphene powder, ethylene glycol;
- c) PtCoMn/GR: 1.2 mM H2PtCl6, 12 mM CoCl2, 3.1 mM MnCl2, 0.1 g graphene powder, ethylene glycol.
Why is it used 6 mM RuCl3, 6 mM Na2MoO4 but only 3.1 mM MnCl2
According to these data, with the complete recovery of precursors, the materials should have the following composition: PtCo10Ru5, PtCo10Mo5, PtCo10Mn2.58. The actual compositions of the materials differ significantly, therefore, the restoration was not complete. The article does not mention this.
Author Response
Response for Reviewer
We are most thankful for the valuable Reviewer comments, which we tried to take into account.
Reviewer: Table 2 provides a comparison of the activity (currents) for the materials obtained in the article and analogs from the literature. At the same time, such a comparison does not take into account the loading of platinum on the electrode, which makes the comparison of activity incorrect.
Authors: The data of the mass activity for the materials obtained in the article and analogs from the literature are given in Table 2.
Reviewer: Need to build a histogram of the size distribution and determine the average particle size according to TEM results for all materials and compared this date with value of ESA.
- Why, to obtain this result, no equipment is needed, all the necessary TEM photographs should be with the authors. This result is important because the structure of the material can explain its activity.
Authors: The particle size distribution for all catalysts are given in Figure 2.
Reviewer: The value of ESA for PtCoMn/C materials is huge (160.0 m2 g-1), TEM results (fig 1a) inconsistent with this result. With such a surface area, the size of metal nanoparticles should be extremely small.
= Of course, but if there is some unexpected result that stands out and contradicts other data, you need to pay attention to this. At the very least, it is necessary to make an assumption about the possible reasons for this fact.
Authors: The data for ESA in m2 g-1 is not being reported.
Reviewer: What is the reason for choosing just such compositions of trimetallic nanoparticles? If we study the influence of the nature of the alloying metal on the activity of the catalyst, it is logical to do it with a constant composition. This work changes both the composition and the nature of the alloying component.
- in the methodology specified (p.13)
- a) PtCoRu/GR: 1.2 mM H2PtCl6, 12 mM CoCl2, 6 mM RuCl3, 0.1 g graphene powder, ethylene glycol;
- b) PtCoMo/GR: 1.2 mM H2PtCl6, 12 mM CoCl2, 6 mM Na2MoO4, 0.1 g graphene powder, ethylene glycol;
- c) PtCoMn/GR: 1.2 mM H2PtCl6, 12 mM CoCl2, 3.1 mM MnCl2, 0.1 g graphene powder, ethylene glycol.
Why is it used 6 mM RuCl3, 6 mM Na2MoO4 but only 3.1 mM MnCl2
According to these data, with the complete recovery of precursors, the materials should have the following composition: PtCo10Ru5, PtCo10Mo5, PtCo10Mn2.58. The actual compositions of the materials differ significantly, therefore, the restoration was not complete. The article does not mention this.
Authors: The initial composition was taking with the aim to get like composition of final catalysts, i.e. PtCoMn(1:3:1), PtCoRu (1:2:2), PtCoMo(7:2:1). It can be noted that our result show experimentally obtained composition, but not theoretical like the reviewer’s calculation because the reduction of metal ions was not complete.
Author Response File: Author Response.pdf
Round 3
Reviewer 3 Report
The authors have mostly corrected the remarks and the article can be published.
