Review Reports - Anchoring Monodispersed NiSe@Ni Particles on Graphene for Energy Storage in Supercapacitors

Round 1

Reviewer 1 Report

In the current manuscript “Anchoring monodispersed NiSe@Ni particles on graphene for energy storage in supercapacitors” the authors studied processing-morphology-electrochemical properties relationship of single electrodes as well as full device with different electrodes.

The authors mentioned in Abstract that “NiSe@Ni particles were successfully anchored on graphene sheets by electroless nickel plating combined with a chemical vapor reaction process, in which the nickel particles were deposited firstly onto graphene sheets and transformed subsequently in-situ into the NiSe@Ni at the elevated temperature.”

However, described process is not clear:

1. In 2.2. “pre-treated graphene” was described. However, the role of SnCl and PbCl2 in the process was not explained. What happens with Sn, Cl, Pb?

2. In 2.3 “Ni/G” was described. However, there are three reagents with Na (NaH2PO2, C6H5Na3O7, C12H25SO3Na): what are their roles? Why these mentioned values of the weights of the reagents were used (add Refs).

3. What ratio between Ni and G was the expected in Ni/G?

4. In 2.4. NiSe@Ni/G preparation was described as the simple mix Se powder with Ni/G powder and heat up to 700oC in Ar. However, there are no SEM images of Ni/G only for comparison. Please, add it.

5. Why exactly 400 mg Se and only 100 mg Ni/G? Is it means that Se is in 4 times more than Ni+G must be in SEM mapping? Or only Se, SeNi and Ni/G? Check it, please.

6. Check: “NiSe particles with an average diameter of 180-210 nm” but “NiSe particles (30-60 nm)”. Why?

7. Check “The working electrodes ...the mixture of the active materials (2.0 mg), conductive agent (super P, 80 wt%) and polyvinylidene fluoride (PVDF, 10 wt%)”. Is the active material 10wt% only in the electrode?

8. Is mass loading “active materials (2.0 mg)” onto “1 x 1.5 cm2” could be as 2/1.5=1.33 mg/cm2 for all samples?

9. Is Ni/G strong battery-type material? Or with capacitive impact? What is “selenedization” impact? To be sure, “parameter b” must be calculated: b=1 means EDLC, b=0.5 means battery-type (easy to find in many papers or see i.e. https://doi.org/10.1021/acsnano.8b01914 or https://doi.org/10.3390/nano11051240).

10. What is the value of the specific capacitance of AC here?

11. Check “specific CAPACITY” inside in Fig. 6d.

12. Explanation for the strange behavior of Coulomb efficiency?

13. Big Table for the comparison: obtained results of analyzed single electrodes and full device and already reported similar electrodes prepared by other methods, with different electrolytes, etc. is missing. More details could be mentioned such as working area, mass load, capacitance, window, electrolyte, components of composite, their ratio, etc

14. Add Eqs. for the calculations the specific CAPACITANCE and energy/power densities with Refs.

15. Add more discussion and explanations.

Author Response

Point 1: In 2.2. “pre-treated graphene” was described. However, the role of SnCl and PbCl₂ in the process was not explained. What happens with Sn, Cl, Pb?

Response 1: Thank you for your comment. In section "2.2 Surface treatment of graphene", we have clarified the purpose of using SnCl and PbCl₂. Specifically, during the sensitization step, SnCl was utilized to absorb Sn²⁺ ions onto the surface of graphene oxide. Meanwhile, in the activation step, PbCl₂ was utilized to create catalytic nuclei composed of lead on the sensitized graphene surface.

Point 2: In 2.3 “Ni/G” was described. However, there are three reagents with Na (NaH₂PO₂, C₆H₅Na₃O₇, C₁₂H₂₅SO₃Na): what are their roles? Why these mentioned values of the weights of the reagents were used (add Refs).

Response 2: Thank you for your comment. We have explained the function of the three reagents mentioned in the material preparation and incorporated your suggestion into the article. In summary: NaH₂PO₂, with its strong reducing properties, undergoes redox reactions to reduce Ni²⁺ to metallic nickel anchored on pretreated graphene. At the same time, H₂PO^2- is oxidized to PO₄^3- and deposited on the metal nickel layer to form a phosphate protective layer, improving the corrosion resistance. C₆H₅Na₃O₇ acts as a complexing agent to reduce the concentration of Ni²⁺ during electroless nickel plating. This helps to improve the dispersion ability and coverage degree of the pretreated graphene coating. C₁₂H₂₅SO₃Na (SDS) is an anionic surfactant that improves the adsorption of metal nickel on the pretreated graphene surface. SDS also suppresses the generation of H₂ and prevents pinholes from forming on the surface of metal nickel, leading to a higher quality and better performance of the metal nickel layer. Based on our previous research on electroless nickel plating, we will determine the specific parameters for the reagents used.

Point 3: What ratio between Ni and G was the expected in Ni/G?

Response 3: Thank you for your comments. During the preparation of the Ni/graphene composite, we mixed a solution containing 0.4 g of graphene and 3 g of NiSO₄ 6H₂O to serve as the source of nickel. Since both the pretreated graphene and metallic nickel are insoluble during the process, we did not take experimental errors into account. As a result, the composite material consists of 0.4 g of graphene and 0.6 g of metallic nickel. The expected ratio of graphene to metallic nickel in the composite can be determined by the following calculation： M_graphene: M_{metal nickel} = 0.4 g : 0.6 g = 2 : 3

Point 4: In 2.4. NiSe@Ni/G preparation was described as the simple mix Se powder with Ni/G powder and heat up to 700oC in Ar. However, there are no SEM images of Ni/G only for comparison. Please, add it.

Response 4: Thank you for your comments. We have added the SEM images of Ni/graphene in Fig. 2(a, b). Compared and analyzed the difference between Ni/graphene and NiSe@Ni/graphene.

Point 5: Why exactly 400 mg Se and only 100 mg Ni/G? Is it means that Se is in 4 times more than Ni+G must be in SEM mapping? Or only Se, SeNi and Ni/G? Check it, please.

Response 5: Thank you for your comments. Based on theoretical calculations, the synthesis of NiSe required 100 mg of selenium powder. However, during the nickel selenide experiments, the research group found that at 700 °C, selenium powder exists in a gaseous state, leading to a significant loss of gaseous selenium powder in the vacuum tube with high flow rate, which did not participate in the reaction [Journal of Power Sources, 2021, 514: 230587]. As a result, chemical vapor deposition required 400 mg of selenium powder, but only 80 mg of selenium powder was utilized in synthesizing NiSe. Due to the need for excess selenium powder to participate in the reaction, the Se content is not four times that of Ni/graphene in SEM mapping. Instead, the actual ratio is more akin to M_graphene : M_Ni: M_Se = 2 : 3 : 3, based on the aforementioned explanation.

Point 6: Check: “NiSe particles with an average diameter of 180-210 nm” but “NiSe particles (30-60 nm)”. Why?

Response 6: Thank you for your comments. It was our mistake not to check the multiple problem marked in the picture. We have revised Fig. 2(g) in revision. We are sorry for our carelessness. We will avoid similar problems in our future work.

Point 7: Check “The working electrodes ...the mixture of the active materials (2.0 mg), conductive agent (super P, 80 wt%) and polyvinylidene fluoride (PVDF, 10 wt%)”. Is the active material 10wt% only in the electrode?

Response 7: Thank you for your comments. We are sorry for our carelessness. We have made modifications to the electrochemical test.

Point 8: Is mass loading “active materials (2.0 mg)” onto “1 x 1.5 cm²” could be as 2/1.5=1.33 mg/cm² for all samples?

Response 8: Thank you for your comments. According to the description of electrochemical measurement, we follow the ratio of super P: PVDF: active material = 1:1:8. Then fully mixing the three materials and evenly spreading on the nickel foam (1 × 1.5 cm²). Therefore, in order to compare the electrochemical performance between different samples, the surface density of the electrodes were 1.33 mg cm⁻².

Point 9: Is Ni/G strong battery-type material? Or with capacitive impact? What is “selenedization” impact? To be sure, “parameter b” must be calculated: b=1 means EDLC, b=0.5 means battery-type (easy to find in many papers or see i.e. https://doi.org/10.1021/acsnano.8b01914 or https://doi.org/10.3390/nano11051240).

Response 9: Thank you for your comments. The composite material we prepared belongs to strong battery-type material. Due to space limitation, we have added your questions to the main text and the articles you recommended as references [38, 37]. Thanks for your question, we will enrich this kind of questions into our future work.

Point 10: What is the value of the specific capacitance of AC here?

Response 10: Thank you for your comments. We have added data of AC electrodes to the supporting literature (fig. S1). We will pay attention to this issue in future work.

Point 11: Check “specific CAPACITY” inside in Fig. 6d.

Response 11: Thank you for your comments. For your question about "specific CAPACITY" in Fig. 6d, we have changed the unit of specific capacity to mAh g⁻¹. We will avoid similar problems in our future work.

Point 12: Explanation for the strange behavior of Coulomb efficiency?

Response 12: Thank you for your comments. The anomalous behavior observed in the Coulombic efficiency could be explained as follows: during 10,000 charge-discharge cycles at a current density of 10 A g⁻¹, the Coulombic efficiency of the NiSe@Ni/graphene∥AC device consistently remained above 98%, as indicated in Fig. 6(e). However, in the early cycles, the capacitance decreased significantly due to electrolyte decomposition and the formation of an irreversible SEI layer, resulting in the loss of electrode capacity. Nevertheless, after 2000 cycles, the specific capacity of the NiSe@Ni/graphene electrode gradually increased, indicating excellent long-term cycle stability, with a capacitance retention of 72.53% even after 10,000 cycles. This increase in specific capacity was primarily due to the reversible formation of a gel-like protective layer by the nanoparticles on the surface of the NiSe@Ni/graphene electrode, exhibiting a common "pseudocapacitive behavior" characteristic of graphene/transition metal compound electrodes. The results of these tests demonstrate that the NiSe@Ni/graphene∥AC supercapacitor exhibits excellent charge-discharge and cycle performance and is an exceptional energy storage device.

Point 13: Big Table for the comparison: obtained results of analyzed single electrodes andfull device and already reported similar electrodes prepared by other methods,with different electrolytes, etc. is missing. More details could be mentioned suchas working area, mass load, capacitance, window, electrolyte, components ofcomposite, their ratio, etc.

Response 13: Thank you for your comments. We have added to the supporting literature (Table S1).

Point 14: Add Eqs. for the calculations the specific CAPACITANCE and energy/power densities with Refs.

Response 14: Thank you for your comments. We have made modifications to the “2.6 Electrochemical measurements”. and related references.

Point 15: Add more discussion and explanations.

Response 15: Thank you for your comments. We have added more discussion and explanations. Similar problems will be avoided in our future writing.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments for author File: Comments.docx

Author Response

Point 1: English grammar and writing are not upto the mark and needs thorough revision. Some sentences ae difficult to comprehend. For example, the line “Ceren et al controlled and improved the surface morphologic and surface nitrogen content thus effectively enhanced capacitive performance of GO can be achieved [12].” in introduction. There are many such sentences throughout the manuscript. Try to conform to a singular form of writing style; rewrite experimental section.

Response 1: Thank you for your comments. We have substantially revised the article for grammatical issues and added discussion and explanations at your request.

Point 2: The introduction does not provide enough background or motive for the present work. Highlight the objective as well as novelty of the proposed material. If enough work is already reported for Nickel selenide nanomaterials for supercapacitor applications, how does your material/method stand out?

Response 2: Thank you for your comments. Based on your suggestions, we have substantially revised the “Introduction”. In future writing, we will pay attention to similar issues.

Point 3: Why have the authors chosen commercial grade graphene and pre-treated it for surface functionalization? What advantage does it have over chemically synthesized reduced graphene oxide at lab scale?

Response 3: Thank you for your comments. Graphene nanoplates used in this work were fabricated from expanded graphite by liquid-phase exfoliation method. Unlike graphene oxide, the used graphene has high chemical inertness, which limits the direct functionalization of graphene surfaces. Therefore, the graphene was treated with the acid solutions to introduce abundant oxygen-containing functional groups on the graphene. This process will facilitate the following deposition of nickel. The sensitization and activation treatments are the common and necessary process for electroless nickel plating on non-metal solid surfaces. This was reported by a large number of literatures.

Point 4: Electroless Ni plating is an excellent method to get homogeneous coating but widely known to contain Nickel Phosphorous alloy in the deposit, rather than just Ni. Is there any trace of P present in the material? If so, how do you explain the surface reactivity coming only from Ni, without any contribution from P?.

Response 4: Thank you for your comments. NaH₂PO₂ has a strong reducing property and can undergo redox reactions. Ni²⁺in solution was reduced to metallic nickel anchored on pretreated graphene. Meanwhile, H₂PO²⁻ was oxidized to PO₄³⁻ and deposited on the metal nickel layer together to form a phosphate protective layer, which can improve the corrosion resistance. We have briefly outlined the role of the P.

Point 5: In the final step of preparation of Ni/graphene, the powder was dried at 60˚C after washing with deionised water. Water evaporates at 100˚C.

Response 5: Thank you for your comments. As we know, deionized water has a volatile property at room temperature. We place the samples to be dried in a constant temperature vacuum oven at 60°C for the following two reasons:

(1) Increase the ambient temperature around the sample to be dried to accelerate the evaporation rate of deionized water.

(2) Avoided contamination of samples caused by air mixing.

Point 6: From CVD experiment, Se:Ni ratio is 4:1 (w/w). What exactly is the structure of the composite NiSe@Ni/graphene? Provide sufficient characterization in support of the structure.

Response 6: Thank you for your comments. Based on theoretical calculations, 100 mg of selenium powder was required for the synthesis of NiSe. However, the research group's extensive experiments on nickel selenide showed that at 700°C, selenium powder existed in a gaseous state and caused a significant amount of loss in the vacuum tube with high flow rate, resulting in insufficient participation in the reaction. As a result, 400 mg of selenium powder was needed for chemical vapor deposition, but only 80 mg of selenium powder actually participated in the synthesis of NiSe. The use of excess selenium powder in the reaction explains why the content of Se is not four times that of Ni/graphene in SEM mapping. Instead, the actual ratio is closer to M_graphene: M_Ni: M_Se= 2: 3: 3, which was determined based on the amount of selenium powder that actually participated in the reaction.

Point 7: The Raman spectra of the composite is inconclusive and noisy. Kindly provide a better data in support of your claim.

Response 7: Thank you for your comments. Despite the small peak of the D peak in the Raman image, the low ratio of the D peak to the G peak indicates that the graphene in the composite material has few edge lattice defects, similar to the structure of the composite sample. Additionally, the broad peak at 2D is consistent with the few-layer graphene utilized, as reported in [Applied Surface Science, 2018, 460: 17-24; Journal of Colloid and Interface Science, 2018, 527: 40-48.]. As a result, the inconspicuous peaks and high noise levels will not hinder the subsequent characterization of the composite materials. We have included specific Raman image characterizations in the text.

Point 8: The claim, “It can be seen that augment of active sites after selenization and the load of graphene enhances the electroconductibility” is confusing and merely supported by any physical characterization. Se can’t possibly enhance electroconductivity. Please explain the role of Se.

Response 8: Thank you for your comments. First, selenization reduced the agglomeration of metallic nickel on the graphene surface, resulting in uniform dispersion of metallic nickel and NiSe particles with a core-shell structure. It created more interfaces and pathways for ion diffusion and provides enough space for structural changes during ion intercalation/extraction, while increasing the electrode-electrolyte contact [Chemical Engineering Journal, 2019, 375: 122090 ; Synthetic Metals, 2021, 275: 116751]. Second, the introduction of NiSe particles with a core-shell structure makes the electrode surface rough, increasing the effective surface area and capacitance. Inhibiting the chemical reaction between the core material and the shell material in the core-shell structure can prolong the service life of the supercapacitor. Therefore, the specific capacity and Nyquist curve of the current density function indicate that NiSe@Ni/graphene has better conductivity and higher charge transfer efficiency indirectly due to selenization [ACS Applied Energy Materials, 2021, 4(4): 3288-3296].

Point 9: What finding support the line, “This transformation is mainly due to the lower internal resistance of the NiSe@Ni/graphene hybrid electrode compared to the pristine NiSe electrode, which results in a better reversible redox reaction”? There is hardly any shift in the selenised electrode, both in terms of anodic/cathodic peak current or potential as well as solution/charge transfer resistance values from the Nyquist plot. Even the redox changes are coming from the Ni species. It seriously raises the question, what is the purpose of selenization?

Response 9: Thank you for your comments. We examined the performance of composite samples in Fig. (a, b) and Fig. (e, f) before and after selenization. The selenized sample displayed a significant increase in the integral area of the CV curve while maintaining a distinct pair of redox peaks. Additionally, the capacitance performance of the composite sample improved significantly before and after selenization, at different current densities. The Nyquist curve showed that the impedance of NiSe@Ni/graphene was reduced. The enhancement of the sample's electrochemical performance was attributed to the combined effects of electroless nickel plating and selenization treatment.

Point 10: The authors have used Ni foam as working electrode, which ironically can interfere in the redox process. Please provide the capacitive contribution of a blank Ni foam for comparison as a control experiment (show comparative CV/GCD curve).

Response 10: Thank you for your comments. We have added data on AC electrodes to the supporting literature (fig. S2). We will pay attention to this issue in future work.

Point 11: What is the purpose of using so high amount (80%) of conductive agent (super P)? How did you annul the capacitive contribution of this material?

Response 11: Thank you for your comments. We are sorry for our carelessness. We have made modifications to the electrochemical test. And we will avoid similar problems in future work.

Point 12: In Fig. 5f, coulombic efficiency is mentioned in the text of the figure but the graph showing coulombic efficiency is missing.

Response 12: Thank you for your comments. We are sorry for our mistake, we have reworked the labeling of the pictures. We will avoid similar problems in future work.

Point 13: Fig. 6e is misleading as coulombic efficiency and capacitance retention got mixed up.

Response 13: Thank you for your comments. We have revised the annotations on the images and reorganized the descriptions of the images. We are very sorry for our mistake. In future work, we will consolidate our grasp of the theoretical basis and avoid similar problems from happening.

Author Response File: Author Response.docx

Reviewer 3 Report

In this paper, the work done to synthesis a new material by combining graphene sheets and monodispersed particles, NiSe@Ni achieved by depositing nickel particles onto the graphene sheets and then transforming them into NiSe@Ni at a high temperature. This resulting unique structure of NiSe@Ni particles, attached to the graphene sheets, with potential application of the material in storing electrical energy. The resulting material was used to make a supercapacitor that can store a high energy capacity, while maintaining its performance for thousands of cycles.

The abstract is well written to summarize the work done. The introduction stated the problem statement clearly. However, in normal practice, result from the current work normally not discussed as shown at the last paragraph of the introduction section.

Section 2.2 and 2.3 need a rewrite as it merely stated the instruction rather than scientific report.

The other preparation method was properly defined. The equipment involved were clearly described/presents. The results, analysis, and discussion are well explained.

The conclusion require minor revision as it should be very concise, highlighting only the important aspect of the work in this manuscript.

Author Response

Point 1: In this paper, the work done to synthesis a new material by combining graphene sheets and monodispersed particles, NiSe@Ni achieved by depositing nickel particles onto the graphene sheets and then transforming them into NiSe@Ni at a high temperature. This resulting unique structure of NiSe@Ni particles, attached to the graphene sheets, with potential application of the material in storing electrical energy. The resulting material was used to make a supercapacitor that can store a high energy capacity, while maintaining its performance for thousands of cycles.

Section 2.2 and 2.3 need a rewrite as it merely stated the instruction rather than scientific report.

The other preparation method was properly defined. The equipment involved were clearly described/presents. The results, analysis, and discussion are well explained.

The conclusion require minor revision as it should be very concise, highlighting only the important aspect of the work in this manuscript.

Response 1: Thank you for your comments. We have made substantial changes to the experimental and conclusions based on your suggestions. In our future work, we will avoid similar problems.

Author Response File: Author Response.docx

Reviewer 4 Report

Ms. No.: Coatings-2307738

Title: Anchoring monodispersed NiSe@Ni particles on graphene for energy storage in supercapacitors

The introduction was well described the developments in supercapacitors area. In reviewing the published papers both advantages and disadvantages of the electrode modifiers were mentioned.

The developed nanomaterial of NiSe@Ni/graphene was previously used for solar cell application, its uses for supercapacitor electrode construction is valuable and novel.

It seems that a comprehensive attention was paid to electrochemical supercapacitance performance of the NiSe@Ni/graphene and the all criteria were discussed. The conclusion part was well written based of research funding.

The investigation and the results obtained were well correlated. Meanwhile, there are some issues that should be corrected before further consideration regarding following comments:

1. In section 2.2, what is the role of Sn and Pb role? Why were these ions adsorbed on the graphene surface?

2. Section 3.2, “The crystallite sizes of Ni/graphene and NiSe@Ni/graphene were calculated using the Debye-Scherrer formula [28, 29], and found to be 11.8 nm and 75.0 nm respectively [30]”, what is the relation of mentioned references to this part?

3. In EIS study, please add the equivalent circuit. And please provide the open circuit potential.

4. Does the deposition quantity of NiSe@Ni impact on the electrochemical performance? How was the optimal value determined? This should be discussed.

5. In case of Fig. 6B, why did the contribution of diffusion current decrease by scan rate increment?

6. It was mentioned that the he specific capacity enhanced after 2000 cycles, so why was capacitance retention decreased to 72.53% after 10,000 cycles.

7. The language of the manuscript is very pitiful, due to which several times it is hard to understand what the authors exactly want to tell. Hence, the language must be improved by a professional service.

For example, in the section 2.2, “Poured 0.4 g graphene to be treated into a mixed acid solution of nitric acid and sulfuric acid at a ratio of 3:1.”

“For adsorbing Sn2+ ions on the surface of oxidized graphene, added the oxidized graphene and 10 g SnCl2 to 0.12 M HCl.

“After ultrasonic stirring for 20 min, washed repeatedly with deionized water until the pH = 7. Mixed the sensitized graphene and 0.05 g PbCl2 to 0.24 M HCl. After ultrasonic stirring for 20 min to form lead catalytic nuclei on the sensitized graphene surface, washed with deionized water until the pH = 7”.

8. In introduction, “transition metal oxides [5], hydroxides [6]” should corrected as “transition metal oxides [5] and hydroxides [6]”

9. Page 1, at the end of first paragraph of introduction in case of Ref [11], the family of the author should be mentioned. Correct as “Ceren et al.” as “Karaman et al.”

10. Page 2, First paragraph, “It is a well-recognized idea to increase the specific surface area of the electrode by enhancing the nanostructure of the electrode, utilizing large-area materials, or enlarging its surface area to improve the electrochemical performance [12].” It can be rewritten with short but meaningful statements.

11. Section 2.2, Omit “Due to” at the beginning of second sentence.

12. In figure 5a, check the unit of horizontal line, is the A^-1 correct?

Author Response

Response to Reviewer 4 Comments

Point 1: In section 2.2, what is the role of Sn and Pb role? Why were these ions adsorbed on the graphene surface?

Response 1: Thank you for your comments. When sensitizing graphene, stannous chloride is commonly utilized as both a reducing agent and surface modifier. This compound is capable of reducing oxygen functional groups present in graphene oxide to organic functional groups, such as hydroxyl and carbonyl, while simultaneously removing impurities from the graphene surface to enhance its quality. Additionally, stannous chloride can chemically react with functional groups, including hydroxyl and carbonyl, on the graphene surface, resulting in improved properties such as enhanced conductivity, stability, and dispersibility. When activating graphene, lead chloride can be introduced as an activator. Lead chloride has the ability to form chemical bonds with surface oxygen atoms on the graphene, altering its lattice structure, and subsequently increasing its conductivity.

Point 2: Section 3.2, “The crystallite sizes of Ni/graphene and NiSe@Ni/graphene were calculated using the Debye-Scherrer formula [28, 29], and found to be 11.8 nm and 75.0 nm respectively [30]”, what is the relation of mentioned references to this part?

Response 2: Thank you for your comments. We sincerely apologize for the typographical error that occurred. The issue arose due to a problem with the revision mode in Word, which resulted in the original references not being deleted, causing them to be irrelevant to the revised content. We will take steps to prevent similar issues from occurring in our future work.

Point 3: In EIS study, please add the equivalent circuit. And please provide the open circuit potential.

Response 3: Based on your suggestion, we have included an equivalent circuit (fig 7(e)) in the revised manuscript and provided a description of the open circuit potential in the text.

Point 4: Does the deposition quantity of NiSe@Ni impact on the electrochemical performance? How was the optimal value determined? This should be discussed.

Response 4: Thank you for your comments. This is an important inquiry that merits consideration. Our next area of focus will be investigating the impact of varying amounts of metallic nickel deposition on electrochemical properties. We plan to delve deeper into this topic in our future research.

Point 5: In case of Fig. 6B, why did the contribution of diffusion current decrease by scan rate increment?

Response 5: Thank you for your comments. If the surface capacitance contribution increases, this indicates an increase in electrode surface area, which results in more effective reaction areas on the electrode surface to accommodate additional ions. As a result, the distance for ion diffusion between the electrode and electrolyte is reduced, leading to a decrease in the contribution of the diffusion current. Moreover, when the surface capacitance contribution increases, the total capacitance of the electrode also increases, which slows down the rate of voltage drop over time. This results in more uniform ion diffusion between the electrode and electrolyte, further reducing the contribution of the diffusion current [Journal of Alloys and Compounds, 2022, 898: 162861].

Point 6: It was mentioned that the he specific capacity enhanced after 2000 cycles, so why was capacitance retention decreased to 72.53% after 10,000 cycles.

Response 6: Thank you for your comments. In the early cycles, the capacitance experiences a significant decrease due to the loss of electrode capacity caused by electrolyte decomposition and the formation of an irreversible solid-electrolyte interphase (SEI) layer. The active material serves as the main contributor to the electrode capacity. As the number of cycles increases, the capacity of the electrode may decrease due to particle detachment or structural damage of the active material. Additionally, the electrochemical performance may be affected by the degradation, volatilization, or aggregation of the solvent in the electrolyte over time.

Point 7: The language of the manuscript is very pitiful, due to which several times it is hard to understand what the authors exactly want to tell. Hence, the language must be improved by a professional service. For example, in the section 2.2, “Poured 0.4 g graphene to be treated into a mixed acid solution of nitric acid and sulfuric acid at a ratio of 3:1.” Or “For adsorbing Sn2+ ions on the surface of oxidized graphene, added the oxidized graphene and 10 g SnCl2 to 0.12 M HCl.

Response 7: Thank you for your comments. We have revised the grammar of the article according to your suggestion, and in future work, we will improve our English. The specific changes are as follows:

“An electroless plating method was utilized to produce nickel-coated graphene sheets (Ni/graphene). The graphene sheets obtained by the liquid phase exfoliation method are highly chemically inert. The graphene sheets underwent a three-step treatment process consisting of acid oxidation, sensitization, and activation prior to the nickel deposition [18]. Mixed 0.4 g of graphene with a solution of 30 mL nitric acid and 10 mL sulfuric acid. After 1 h of sonication, heated the mixture for 5 h at 80 °C in a water bath. Adjusted the pH of the samples to 7, wash them with deionized water. To reduce the oxygen functional groups on graphene oxide to organic functional groups such as hydroxyl and carbonyl groups, combine graphene oxide and 10 g SnCl2 in 0.12 M hydrochloric acid. After ultra-sonic stirring for 20 minutes, repeatedly wash the sample with deionized water until the pH value is 7 to obtain sensitized graphene. Finally, mixed sensitized graphene and 0.05 g PbCl2 in 0.24 M hydrochloric acid, and stir with ultrasound for 20 minutes to form lead catalyst core on the surface of graphene. Washed the samples with deionized water to pH 7 and dry them at 60 °C for 12 h to obtain pretreated graphene.”

Point 8: In introduction, “transition metal oxides [5], hydroxides [6]” should corrected as “transition metal oxides [5] and hydroxides [6]”

Response 8: Thank you for your comments. We have modified the article based on your suggestions.

Point 9: Page 1, at the end of first paragraph of introduction in case of Ref [11], the family of the author should be mentioned. Correct as “Ceren et al.” as “Karaman et al.”

Response 9: Thank you for your comments. We have incorporated the revisions you suggested into the updated manuscript and will take steps to prevent similar issues in future projects.

Point 10: Page 2, First paragraph, “It is a well-recognized idea to increase the specific surface area of the electrode by enhancing the nanostructure of the electrode, utilizing large-area materials, or enlarging its surface area to improve the electrochemical performance [12].” It can be rewritten with short but meaningful statements.

Response 10: Thank you for your comments. We have changed in the revised manuscript to:” A commonly accepted notion is that improve electrode's electrochemical perfor-mance by utilizing large-area materials, or enlarging its surface area.”

Point 11: Section 2.2, Omit “Due to” at the beginning of second sentence.

Response 11: Thank you for your comments. We have removed "Due to" in section 2.2 based on your suggestion.

Point 12: In figure 5a, check the unit of horizontal line, is the A-1 correct?

Response 12: Thank you for your comments. That's a good question. When performing electrochemical tests, we measure the total area under the curve within a specified voltage range, which is expressed in volts (V).

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The manuscript was well edited.

Just few comments:

1. Include “Response 5” to the text.

2. Check Ref 44: authors, pages, doi.

3. Check “Figure 3. (a) XRD of NiSe@Ni/graphene and Ni/graphene. (b) Raman spectra of the NiSe@Ni/graphene. 3.3 XPS analysis”

4. Please, include to the text the value of the specific capacitance for full hybrid device together with capacity.

Author Response

Point 1: Include “Response 5” to the text.

Response 1: Thank you for your comments. We have added the answer to "Response 5" to the revised manuscript. We will avoid similar problems from happening.

Point 2: Check Ref 44: authors, pages, doi.

Response 2: Thank you for your comments. We have revised "Ref.44" and checked all references. We will pay attention to the occurrence of similar issues in future work.

[Tkach, A. Graphene/Reduced Graphene Oxide-Carbon Nanotubes Composite Electrodes: From Capacitive to Battery-Type Behaviour. Nanomaterials. 2021. 11. https://doi.org/10.3390/nano.11051240.]

Point 3: Check “Figure 3. (a) XRD of NiSe@Ni/graphene and Ni/graphene. (b) Raman spectra of the NiSe@Ni/graphene. 3.3 XPS analysis”.

Response 3: Thank you for your comments. We have revised the image question and added more analysis. The analysis that we have changed is as follows:

The surface elemental compositions and chemical states of the NiSe@Ni/graphene composite were analyzed using XPS, as depicted in Figure 4. Based on the survey spec-trum of XPS (Fig. 4 (a)), the primary components of the NiSe@Ni/graphene composites were found to be C, Se, and Ni elements. The O 1s peak observed in the spectrum was attributed to contamination resulting from exposure of the sample to ambient air [32,33]. Fig. 4 (b) displays the C 1s spectra that were separated into three distinct peaks with binding energy of 284.8, 285.5, and 286.7 eV, which correspond to C-C, C-O-C, and O=C-O bonds, respectively [34]. The XPS spectrum of Ni 2p in Fig. 4(c) indicates the presence of Ni 2p_3/2 and Ni 2p_1/2 as well as their associated satellite peaks [35]. The observed weak peaks at 856.4 and 873.7 eV were identified as Ni³⁺ in Ni₃Se₄, while the sharp peaks at 855.3 and 872.6 eV were identified as Ni²⁺ in NiSe. Furthermore, the intense peaks at 861.1 and 878.8 eV were observed as shakeup satellites for the Ni 2p_3/2 and Ni 2p_1/2 levels (represented as "Sat." in the spectrum) [36]. Notably, the characteristic peaks observed at 852.5 and 869.8 eV originate from metallic nickel, which provides solid evidence for the presence of metallic nickel as an effective medium for ion transport between graphene and NiSe. The peaks deconvoluted at energy of binding of 53.61 and 54.47 eV can be attributed to the Se 3d_5/2 and Se 3d_3/2 spin-orbit levels of the Se-Ni in NiSe, respectively. This suggests that there is chemical bonding between the NiSe particles and the graphene sheets with large surface areas [37]. The peaks centered at 58.4 eV represents the related oxides of Se[38].

Point 4: Please, include to the text the value of the specific capacitance for full hybrid device together with capacity.

Response 4: Thank you for your comments. we have added value of the specific capacitance for full hybrid device together with capacity.We will avoid similar issues in future work.

Author Response File: Author Response.docx

Reviewer 2 Report

Although the modified manuscript comes with a lot of red markings (indicative of 'apparent' changes made), it barely improved the quality of the manuscript. The authors are either deliberately trying to avoid the obvious questions raised by the referee or don't know how to scientifically explain their own findings. Despite mentioning several new citations, they fail to highlight correlation between their findings and the works they referred. It is important to mention that there are a few good improvements from previous manuscript, for example better grammar, less typographical error and most importantly, a good discussion about the battery type and capacitive type behavior. Still there are many unanswered questions which needs serious thinking and additional experiments to perform.

Author Response

Point 1: Although the modified manuscript comes with a lot of red markings (indicative of 'apparent' changes made), it barely improved the quality of the manuscript. The authors are either deliberately trying to avoid the obvious questions raised by the referee or don't know how to scientifically explain their own findings. Despite mentioning several new citations, they fail to highlight correlation between their findings and the works they referred. It is important to mention that there are a few good improvements from previous manuscript, for example better grammar, less typographical error and most importantly, a good discussion about the battery type and capacitive type behavior. Still there are many unanswered questions which needs serious thinking and additional experiments to perform.

Response 1: Dear Reviewer, we appreciate your feedback on our revised manuscript. Based on your comments, we have extensively revised the Introduction and Conclusions sections to better highlight the innovative aspects of our work. Additionally, we have provided detailed analysis of the data in each chapter, including information on sample preparation, structural characterization (Raman spectroscopy, Mapping, and XPS), and electrochemical analysis (factors influencing performance improvement and the effects of selenization). We possess the necessary theoretical understanding as evidenced by the literature we have referenced, and we have cited articles recommended by three reviewers to enrich our work. The responses to the questions raised by the reviewers have been incorporated into the second revised manuscript. We acknowledge that our English writing skills and theoretical knowledge could still be improved in order to better explain the experimental phenomena. This is a problem that cannot be ignored. Appreciating your constructive criticism and affirmation of the strengths of our work. In future research, we will work to address these deficiencies. Thank you again for your valuable feedback.

Author Response File: Author Response.docx

Reviewer 4 Report

The revised manuscript sounds well and can be accepted for publication.

Round 3

Reviewer 2 Report

Despite mentioning several new citations, they fail to highlight correlation between their findings and the works they referred. For example-

(1) To the query no. 3, they answered why they pretreated liquid-phase exfoliated few-layer graphene and mentioned several other literatures also reported so. But they fail to answer the question how is it better than lab scale reduced graphene oxide? Discuss, if your goal is to utilise the defect sites in graphene for your subsequent steps, which one is a more sustainable synthesis technique energetically?

(2) To the query no. 4, as claimed by the authors, there's a protective P layer to be corrosion resistent, why there is no evidence of the element either in EDS or XPS? Please also mention the role of P in the reply to the referee or atleast mention where the due changes are in the modified manuscript.

(3) The referee is confused about how the authors reached this conclusion in the answer the query no. 6, "As a result, 400 mg of selenium powder was needed for chemical vapor deposition, but only 80 mg of selenium powder actually participated in the synthesis of NiSe. The use of excess selenium powder in the reaction explains why the content of Se is not four times that of Ni/graphene in SEM mapping." There is no physical evidence presented that supported this claim.

(4) The authors cite the articles [Applied Surface Science, 2018, 460: 17-24; Journal of Colloid and Interface Science, 2018, 527: 40-48.], but the Raman peaks there are strikingly different from what they have found in their own sample. The 2D peaks are found to be far sharper here than either D or G peaks, even if it is counted as a reproducible/denoised data of the composite sample (as the authors claimed) which is an odd trend for few layer graphene.

(5) While the authors can agree on the explanations for the advantage of selenization, it is a pretty bold claim if it is not supported by physical evidence of physicochemical or electrochemical characterizations. Show atleast one microscopic surface image of the as-claimed core-shell structure and how the structure changes after cycling the material for 10000 cycles.

(6) Similarly for electrochemical evidence, the authors just provided a control data for AC electrode, instead of a blank Ni foam electrode, as asked. How is this going to prove the data is from your composite electrode instead of the contribution from Ni foam? The referee has pointed this out in the previous query, but the authors just repeated their claim without any justifications.T

There are a few good improvements from previous manuscript, for example better grammar, less typographical error and most importantly, a good discussion about the battery type and capacitive type behavior. Still there are many unanswered questions which needs serious thinking and additional experiments to perform.

Author Response

Response to Reviewer 2 Comments

Point 1: To the query no. 3, they answered why they pretreated liquid-phase exfoliated few-layer graphene and mentioned several other literatures also reported so. But they fail to answer the question how is it better than lab scale reduced graphene oxide? Discuss, if your goal is to utilise the defect sites in graphene for your subsequent steps, which one is a more sustainable synthesis technique energetically?

Response 1: Thank you for your comments. Few-layer graphene produced via liquid-phase exfoliation has a greater specific surface area compared to reduced graphene oxide synthesized in the laboratory. This translates to a larger electrode surface area, which can enhance the energy storage density of capacitors. The lower number of layers in few-layer graphene allows for greater ease of electron transfer across its surface, resulting in improved electrical conductivity of the capacitor. Consequently, we have chosen to deposit metallic nickel on the graphene surface that provides a larger specific surface area, making liquid-phase exfoliated few-layer graphene a more suitable material for our purposes.

Point 2: To the query no. 4, as claimed by the authors, there's a protective P layer to be corrosion resistent, why there is no evidence of the element either in EDS or XPS? Please also mention the role of P in the reply to the referee or atleast mention where the due changes are in the modified manuscript.

Response 2: Thank you for your comments. We have updated the revised manuscript to include the revised role of NaH₂PO₂, which is now highlighted in red font. For this study, we employed the conventional electroless nickel plating technique, in which NaH₂PO₂ plays a crucial role in reducing Ni²⁺ to metallic nickel. Following selenization by vapor deposition, the P content is minimal, and as a result, we did not detect the P element in XPS and EDS. Nevertheless, it is probable that a small quantity of P element remains on the surface of the graphene. We apologize for not providing a clear explanation of the main function of the phosphorus-based compounds, and we will strive to address similar issues in future research. The main reactions in electroless plating bathe are as follows:

Ni²⁺+2H₂PO₂^-+2H₂O→Ni+2HPO₃^2-+H₂+2H⁺

Point 3: The referee is confused about how the authors reached this conclusion in the answer the query no. 6, "As a result, 400 mg of selenium powder was needed for chemical vapor deposition, but only 80 mg of selenium powder actually participated in the synthesis of NiSe. The use of excess selenium powder in the reaction explains why the content of Se is not four times that of Ni/graphene in SEM mapping." There is no physical evidence presented that supported this claim.

Response 3: Thank you for your comments. In our previous work, we reported on the use of vapor deposition for the selenization process [Journal of Power Sources, 2021, 514: 230587]. Through numerous experiments, we have found that using excess selenium powder is necessary for optimal results. Our XRD, EDS, and Mapping images indicate that there is not a significant difference in the peak or distribution of Se compared to the characteristic peak phase of Ni, suggesting that the Se content is not four times that of Ni. However, it remains uncertain whether the selenium powder is in complete contact with the metal nickel during the selenization reaction when carried out under high flow rates of inert gas. After the reaction is complete, most of the gasified black selenium powder remains on the cotton at the gas outlet, which is why excess selenium powder is needed. We acknowledge that this approach may lead to unnecessary waste and will work towards improving our experimental plan in future studies. Thank you for your question. We have made changes to the original text in the revised manuscript based on your suggestions.

Point 4: The authors cite the articles [Applied Surface Science, 2018, 460: 17-24; Journal of Colloid and Interface Science, 2018, 527: 40-48.], but the Raman peaks there are strikingly different from what they have found in their own sample. The 2D peaks are found to be far sharper here than either D or G peaks, even if it is counted as a reproducible/denoised data of the composite sample (as the authors claimed) which is an odd trend for few layer graphene.

Response 4: Thank you for your comments. As the D band is derived from the vibration of sp3 hybridized carbon atoms present in disordered domains and defect regions, the intensity ratio of the D band to the G band at a high temperature of 700°C, being 0.1, indicates the presence of a higher number of defects in the composite sample. This can be advantageous in terms of exposing more active sites and accelerating mass transport during the electrochemical process. In contrast to single-layer graphene, where the 2D peak has a single peak form as it is formed by the direct intersection of two equal energy band electrons, the 2D peak in multilayer graphene is a result of the interaction between the layers. As the number of layers increases, the interaction between the layers weakens, resulting in a decrease in the intensity of the 2D peak. Based on these findings, the 2D peak in single-layer graphene in this study is expected to be more pronounced.

Point 5: While the authors can agree on the explanations for the advantage of selenization, it is a pretty bold claim if it is not supported by physical evidence of physicochemical or electrochemical characterizations. Show atleast one microscopic surface image of the as-claimed core-shell structure and how the structure changes after cycling the material for 10000 cycles.

Response 5: Thank you for sharing your thoughts. Your question is quite challenging. Regrettably, we are unable to obtain a new SEM to confirm the core-shell structure conjecture due to equipment maintenance issues. Therefore, we have opted for a uniform distribution of nickel and nickel selenide on the surface of graphene, as reflected in the revised manuscript. Whether NiSe@Ni can form a core-shell structure, we will conduct experiments to verify it in future work. We appreciate your question and apologize for any errors. We will take steps to avoid similar issues in our future research.

Point 6: Similarly for electrochemical evidence, the authors just provided a control data for AC electrode, instead of a blank Ni foam electrode, as asked. How is this going to prove the data is from your composite electrode instead of the contribution from Ni foam? The referee has pointed this out in the previous query, but the authors just repeated their claim without any justifications.T

Response 6: Thank you for your comments. That's an excellent question. Nickel foam itself does not possess any capacitance since it is not a capacitor. The primary function of the nickel foam is to act as a support for the active material. The high specific surface area, porous structure, and excellent electrical conductivity of nickel foam maximize the electrochemical reaction efficiency of the active material. Furthermore, nickel foam can maintain stable operation in different environments, and it is resistant to corrosion and oxidation reactions, which can improve the electrode's reliability and service life. Since activated carbon can impact the electrochemical performance of the active material, we have provided the GCD and CV curves of the electrode coated solely with activated carbon.

Author Response File: Author Response.docx

Round 4

Reviewer 2 Report

The answers to the questions are unsatisfactory. The attempts to answer is dodgy at best. For example- "We apologize for not providing a clear explanation of the main function of the phosphorus-based compounds, and we will strive to address similar issues in future research." or "Regrettably, we are unable to obtain a new SEM to confirm the core-shell structure conjecture due to equipment maintenance issues. Therefore, we have opted for a uniform distribution of nickel and nickel selenide on the surface of graphene, as reflected in the revised manuscript. Whether NiSe@Ni can form a core-shell structure, we will conduct experiments to verify it in future work. We appreciate your question and apologize for any errors. We will take steps to avoid similar issues in our future research." are not suitable replies for convincing the reviewer. If the current work doesn't have enough supporting proofs for the claims the authors are making, it is impossible to let it publish for the sake of science. What the authors plan to do in their future work, is not the concern here.