Fabrication of High-Performance Asymmetric Supercapacitor Consists of Nickel Oxide and Activated Carbon (NiO//AC)
, Rajendran Suresh Babu 2,*, Raji Atchudan 3,†, Hee-Je Kim 4, Moonsuk Yi 1,*, Leandro Marques Samyn 2 and Ana Lucia Ferreira de Barros 2Round 1
Reviewer 1 Report
The manuscript reports interesting capacitance values obtained with NiO supercapacitor electrodes in aqueous electrolyte. However experimental conditions are not sufficiently described and some claims appear unsubstantiated. Therefore I consider that the article requires major revisions.
- Experimental details are missing (Where were the reagents purchased from? the cellulose filter paper? There is no indication on the origin and nature of the Ni foam substrates and tissue paper used for the preparation of porous NiO. How was the NiO paste coated on Ni foam? EIS experiments: recorded at which potential?...)
- XRD data: there are obvious differences from one sample to another that are not discussed (impurities? multiple phases?)
- It is claimed that NiO-300 is more porous. However there is no quantification. BET experiments could be performed to substantiate this claim.
- high coulombic efficiency is claimed, but values are not given. Actually, it seems rather low. Contrary to what is stated, the GCD features are not quasi-symmetrical
- Fig 6: current densities indicated in Fig 6e do not match those indicated in Fig 6b-d. Fig. 6a current density is not specified.The data should be checked carefully.
- It is not obvious that the conductivity of NiO is "exraordinary". It should be quantified and compared with other reported materials.
- GCD curves after electrochemical cycling should be shown
Author Response
Journal: Catalysts
Manuscript ID: catalysts-1646230
We thank the editors and reviewers for their valuable comments in respect of this manuscript. As per their comments and suggestions, the manuscript is thoroughly checked, appropriately modified, corrected the mistakes and new experimental results are added and discussed. The answers to the comments of the reviewers, point by point, are given as follows, and some of the answers are incorporated in the revised manuscript as well.
Reviewer#1
The manuscript reports interesting capacitance values obtained with NiO supercapacitor electrodes in aqueous electrolyte. However experimental conditions are not sufficiently described and some claims appear unsubstantiated. Therefore I consider that the article requires major revisions.
Comment: Experimental details are missing (Where were the reagents purchased from? the cellulose filter paper? There is no indication on the origin and nature of the Ni foam substrates and tissue paper used for the preparation of porous NiO. How was the NiO paste coated on Ni foam? EIS experiments: recorded at which potential?...).
Answer: The given comment is valid and accepted. As per the reviewer suggestion, the experimental details such as procurement of reagents and other materials used for the present investigation, fabrication of NiO electrodes and EIS characterization details has been incorporated in the experimental section of the revised manuscript.
Comment: XRD data: there are obvious differences from one sample to another that are not discussed (impurities? multiple phases?).
Answer: We appreciate and comply with the referre’s comment. The adequate discussion has been included in the revised manuscript.
Comment: It is claimed that NiO-300 is more porous. However there is no quantification. BET experiments could be performed to substantiate this claim?
Answer: As suggested by the reviewer, BET characherization has been carried out and included in the revised manuscript (Fig. 2(b)) along with the following discussion.
The N2 sorption measurements for all the prepared materials were carried out to characterize their BET surface area and porosity. Based on the adsorption/desorption curves shown in Fig. 2(b), all NiO materials possesses type-II isotherms. At initial relative pressures (p/p0=0.1), all three materials exhibited a sharp and small increase in the volume of nitrogen adsorption indicates the existence of micropores, and mesopores respectively. Whereas steep enhancement was observed at high relative pressure of p/p0=1 demonstrates the presence of macropores. The existence of hierarchical pores (i.e., micro, meso and macropores) is one of the beneficial parameters for supercapacitor applications. Because it will allow the passage of electron at electrode/electrolyte interfaces.The maximum surface area was found to be 48 m2 g-1 for NiO-300, where as 32 and 27 m2 g-1 for NiO-500 and NiO-700, respectively.
Comment: high columbic efficiency is claimed, but values are not given. Actually, it seems rather low. Contrary to what is stated, the GCD features are not quasi-symmetrical?
Answer: We appreciate and comply with the reviewers comment. We presented the GCD curves of NiO electrodes in first cycle. The NiO-300 electrode shows 68% of the columbic efficiency in the first cycle, whereas the NiO-500 and NiO-700 electrodes display 52% and 48%, respectively. The electrode materials signify moderate columbic efficiencies owing to the reversible electrochemical reactions and excellent electric conductivity.
Comment: Fig 6: current densities indicated in Fig 6e do not match those indicated in Fig 6b-d. Fig. 6a current density is not specified. The data should be checked carefully.
Answer: We apologize for this error, now we have corrected in the revised Figure 6. Thank you.
Comment: It is not obvious that the conductivity of NiO is "extraordinary". It should be quantified and compared with other reported materials.
Answer: Thank you for your suggestion, now we have included the Table 1 for comparing the results of previous NiO materials. Please refer Table 1 in the revised manuscript.
Comment: GCD curves after electrochemical cycling should be shown.
Answer: As suggested by the reviewer, we have included the GCD curves before and after the electrochemical cycling in the revised manuscript. Please see Fig. 9(c).
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Reviewer’s comments
Manuscript Number: catalysts-1641068
Title: Fabrication of High Performance Asymmetric Supercapacitor Consists of Nickel Oxide and Activated Carbon (NiO//AC)
Journal: Catalysts
The manuscript reports preparation and electrochemical investigation of nickel oxide and activated carbon asymmetric supercapacitor. The manuscript needs some revision according to the following comments:
- Equations 1-2 need to be supported with relevant references.
- BET surface area and pore size distribution should be provided where the electrochemical behavior is highly dependent on surface area and porosity.
- EIS data (Fig. 7) should be fitted with an equivalent circuit, and the electrochemical parameters should be obtained and discussed.
- The axes titles of the Ragone plot (Fig. 9a) are missing.
- The main findings (specific capacitance, stability, energy, power densities, …) should be compared with related materials. A comparison table should be provided listing the main findings of this work compared with other related materials.
- The correlation between structural and morphological findings and electrochemical performance should be discussed. Chemical Engineering Journal, 409 (2021) 128216
Author Response
Journal: Catalysts
Manuscript ID: catalysts-1646230
We thank the editors and reviewers for their valuable comments in respect of this manuscript. As per their comments and suggestions, the manuscript is thoroughly checked, appropriately modified, corrected the mistakes, and new experimental results are added and discussed. The answers to the comments of the reviewers, point by point, are given as follows, and some of the answers are incorporated in the revised manuscript as well.
Reviewer#2
The manuscript reports preparation and electrochemical investigation of nickel oxide and activated carbon asymmetric supercapacitor. The manuscript needs some revision according to the following comments.
Comment: Equations 1-2 need to be supported with relevant references.
Answer: We appreciate and comply with the reviewers comment. We have included the appropriate references in the revised manuscript as suggested by reviewer.
Comment: BET surface area and pore size distribution should be provided where the electrochemical behavior is highly dependent on surface area and porosity.
Answer: As suggested by the reviewer, BET characherization has been carried out and included in the revised manuscript (Fig. 2(b)) along with the following discussion.
The N2 sorption measurements for all the prepared materials were carried out to characterize their BET surface area and porosity. Based on the adsorption/desorption curves shown in Fig. 2(b), all NiO materials possesses type-II isotherms. At initial relative pressures (p/p0=0.1), all three materials exhibited a sharp and small increase in the volume of nitrogen adsorption indicates the existence of micropores, and mesopores respectively. Whereas steep enhancement was observed at high relative pressure of p/p0=1 demonstrates the presence of macropores. The existence of hierarchical pores (i.e., micro, meso and macropores) is one of the beneficial parameters for supercapacitor applications. Because it will allow the passage of electron at electrode/electrolyte interfaces.Themaximum surface area was found to be 48 m2 g-1 for NiO-300, where as 32 and 27 m2 g-1 for NiO-500 and NiO-700, respectively.
Comment: EIS data (Fig. 7) should be fitted with an equivalent circuit, and the electrochemical parameters should be obtained and discussed.
Answer: We appreciate and comply with the reviewers comment. We have included the equivalent circuit and the electrochemical parameters in the revised manuscript.
Comment: The axes titles of the Ragone plot (Fig. 9a) are missing.
Answer: Thanks to the reviewer to identified the mistake. We apologies for this error and it
has been rectified in the revised manuscript. Please see Fig. in the revised manuscript.
Comment: The main findings (specific capacitance, stability, energy, power densities,) should be compared with related materials. A comparison table should be provided listing the main findings of this work compared with other related materials.
Answer: We appreciate and comply with the reviewers comment. We have included the comparative table of NiO electrodes with related materials in the revised manuscript. Please refer Table 1.
Comment: The correlation between structural and morphological findings and electrochemical performance should be discussed. Chemical Engineering Journal, 409 (2021) 128216.
Answer: We appreciate and comply with the reviewers comment. Giving due respect to reviewer comment, the present manuscript dealt with synthesis, characterization, and suitability of the porous NiO nanoparticles with three different calcination temperatures using laboratory tissue paper as the template for supercapacitor applications. The SEM and TEM analyses were carried out to study the surface morphology. Furthermore, the prepared NiO samples were studied by nitrogen sorption isotherm to explore the porous nature and its specific surface area. As per the reviewer suggestion, the revised manuscript clearly discussed their electrochemical performance of the synthesiszed NiO materials with respect to the structure and morphology. The mentioned reference has been cited in the revised manuscript[Chemical Engineering Journal, 409 (2021) 128216]. Please see [22] in the revised manuscript.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Most concerns have been addressed. However, I do not agree completely with the interpretation of the BET experiments that have been added, as it rather looks like type III isotherms. This points toward low porosity (in agreement with the relatively low estimated surface area). Yet, it is true that NiO-300 is closer to a type II isotherm and may exhibit some microporosity. Also, there is still no convincing evidence that the conductivity of NiO is extraordinary. This should not be claimed. Finally, the frequency factor indicated in EIS discussion is not defined. Thus, I consider that these revisions are required previous to publication.
Author Response
Journal: Catalysts
Manuscript ID: catalysts-1646230
We thank the editors and reviewers for their valuable comments in respect of this manuscript. As per their comments and suggestions, the manuscript is thoroughly checked, appropriately modified, corrected the mistakes and new experimental results are added and discussed. The answers to the comments of the reviewers, point by point, are given as follows, and some of the answers are incorporated in the revised manuscript as well.
Reviewer#1
Comment: Most concerns have been addressed. However, I do not agree completely with the interpretation of BETexperiments that have been added, as it rather looks like type III isotherms. This points toward low porosity (in agreement with the relatively low estimated surface area). Yet, it is true that NiO-300 is closer to a type II isotherm and may exhibit some microporosity.
Answer: We appreciate and comply with the referee’s comment. As per the reviewer's suggestion, we have mentioned NiO-300 exhibits Type II isotherm whereas NiO-500 and NiO-700 exhibit Type-III isotherm in the revised manuscript.
Comment: Also, there is still no convinicing evidence that the conductivity of NiO is extraordinary. This should not be claimed.
Answer: We appreciate and comply with the referee’s comment. Now we have excluded the above mentioned sentence in the revised manuscript.
Comment: Finally, the frequency factor indicated in EIS discussion is not defined.
Answer: We appreciate and comply with the reviewers comment. Giving due respect to reviewer comment, we have given the explanation of the freguency factor (n) already in the revised manuscript. Now, we have highlighted the frequency factor content in the revised manuscript. Fuerthermore, ee have provided the n value of all three electrode materials in the revised manuscript. Please find the following statement in the revised manuscript. “The major parameter for a supercapacitor is the frequency factor (n), which can give details the ideality of an electrode toward supercapacitive behavior. The values of n differ between 0 and 1: n = 0 indicate the resistor; n = 1 indicates the ideal capacitor. The NiO-300 electrodes showed moderate supercapacitor behavior and achieved the highest n value of 0.90 compared to NiO-500 and NiO-700 electrodes shows 0.76 and 0.71 respectively.”
Author Response File: Author Response.pdf
Reviewer 2 Report
The authors have addressed most of the comments in the revised version. The current version could be accepted for publication.
Author Response
Journal: Catalysts
Manuscript ID: catalysts-1646230
We thank the editors and reviewers for their valuable comments in respect of this manuscript. As per their comments and suggestions, the manuscript is thoroughly checked, appropriately modified, corrected the mistakes, and new experimental results are added and discussed. The answers to the comments of the reviewers, point by point, are given as follows, and some of the answers are incorporated in the revised manuscript as well.
Reviewer#2
Comment: The authors have addressed most of the comments in the revised version. The current version could be accepted for publication.
Answer: We thankful to the reviewer to accept our research manuscript in the esteemed journal of catalysts.
Author Response File: Author Response.pdf
