Facile Synthesis of Polyacrylic Acid/Graphene Oxide Composite Hydrogel Electrolyte for High-Performance Flexible Supercapacitors

Round 1

Reviewer 1 Report

Reviewer’s Comments:

The manuscript “Facile Synthesis of Polyacrylic Acid/Graphene Oxide Composite Hydrogel Electrolyte for High-Performance Flexible Supercapacitors” is very interesting work. This paper investigates the development of hydrogel electrolytes plays a critical role in high-performance flexible supercapacitor devices. Herein a composite hydrogel electrolyte of polyacrylic acid (PAA) and graphene oxide (GO) has been successfully prepared, where the oxygen-containing functional groups of GO may crosslink and form hydrogen bonds with carboxyl on the molecular chain of PAA, therefore significantly enhancing the mechanical properties of PAA-based gel electrolyte. Meanwhile, GO will promote the transportation of electrolyte ions, which are favorable for enhancing the ionic conductivity of PAA hydrogel. As a result, the assembled supercapacitor based on PAA/GO composite hydrogel electrolyte shows enhanced capacitance retention of 65% at a large current density of 20 A g-1 and excellent cycling stability over 10,000 cycles at 5 A g-1.  However, the following issues should be carefully treated before publication.

1. In abstract, the author should add more scientific findings.

2. Keywords: the synthesized system is missing in the keywords. So, modify the keywords.

3. In the introduction part, the introduction part is not well organized and cited references should cite the recently published articles such as 10.1002/slct.202103694 and 10.1016/j.molstruc.2022.134100

4. Introduction part is not impressive and systematic. In the introduction part, the authors should elaborate the scientific issues in the Flexible Supercapacitors research.

5. Results and discussion…, The author should provide reason about this statement “However, when the content of GO increases to 2%, obvious wrinkles appear due to the aggregation of GO layers, which greatly affects the uniformity of gel electrolytes”.

6. The authors should explain regarding the recent literature why “The hydrogel can produce large

elastic deformation and quickly return to its original shape, as shown in Figure 3a.”.

7. The author should explain the latest literature “Due to the abundant oxygen-containing groups in GO, the PAA/GO gel display a relatively higher O content than pristine PAA gel.”.

8. The author should provide reason about this statement, “However, PAA/0.5%GO could still maintain a larger area than PAA, indicating that PAA/0.5% GO's better rate performance and maintained electrochemical double layer capacitance behavior even at high scan rates”.

9. Comparison of the present results with other similar findings in the literature should be discussed in more detail. This is necessary in order to place this work together with other work in the field and to give more credibility to the present results.

10. The conclusion part is very week. Improve by adding the results of your studies.

 

 

 

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

Manuscript ID: coatings-2182748

Title: Facile Synthesis of Polyacrylic Acid/Graphene Oxide Composite Hydrogel Electrolyte for High-Performance Flexible Supercapacitors

Authors: Yue Xin , Zhaoxin Yu , Razium Ali Soomro , Ning Sun*

Comments: The research paper is interesting, but it needs to be improved. Here are some queries and suggestions.

·         The authors nicely presented how PAA-GO composite hydrogel electrolytes are made and investigated. How does COOH functionalization improve its mechanical properties?

·         In the XRD data, little difference is observed (see figure 3(d)) why?

·         The author will compose a uniqueness statement based on the study they conducted. Must convey the overarching scientific conclusion that can be drawn from the investigation.

 

·         Include a comparison table with other works that are in a similar manner as the one you are discussing and have been reported before.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

In the manuscript entitled “Facile Synthesis of Polyacrylic Acid/Graphene Oxide Composite Hydrogel Electrolyte for High-Performance Flexible Supercapacitors” the authors reported the development and electrochemical investigations of flexible supercapacitors developed by PAA/GO electrolyte. The idea of the electrode is exciting but also important for the development of flexible electronics. However, the manuscript contains some inconsistencies, and the results are not explained properly. Hence, the manuscript needs further major revision

 

1.    Author reported in the abstract and introduction that the capacitive retention is about 65%, but in figure 4h it was reported as 103.6%. I wonder how it is possible. Explanation needed for the different graph and writing in the manuscript.

 

Note: Usually the activated carbon-based capacitor shows very low capacitive retention rate compared to metal oxides. It is impossible for the activated carbon-based electrode to show 103.6% of capacitive retention.

 

2.    Usually in CV curve the area of the curve gradually increases with increase in scan rate. But in Figure 4c and 4d it is totally opposite where the curve area decreases with increases in scan rate. Why? I think that author miss interpreted the graph.

 

3.    Moreover author said that it showed EDLC behaviour via CV curve “ The curve shapes of PAA and PAA/0.5%GO are similar to a rectangle, and the pseudocapaci-tance peaks at about 0.4 V can be mainly attributed to the contribution from PAA” but by investigating the CV curves in figure 4 c and d, I could see oxidation and reduction peaks. Why? Explanation needed. Note: For carbon-based supercapacitor, the device exhibits EDLC behaviour.

 

4.    Author should calculate capacitive contribution of the electrode using PAA/GO electrolyte.

 

5.    Author should further provide XRD for in-depth characterization of the electrolyte.

 

6.    Author should explain why this flexible electrolyte is important for the supercapacitor and I doubt that it improves the specific capacitance of the electrode.

 

7.    Author should calculate energy and power density of the device.

Comments for author File: Comments.pdf

Author Response

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Reviewer 4 Report

This manuscript is devoted to the study of hydrogel electrolytes based on polyacrylic acid and graphene oxide for flexible supercapacitors. The subject of the manuscript is of practical importance for developers of electronic technology and may be of interest to the scientific community. The manuscript is executed at a decent level and can be accepted for publication after minor corrections.
1. The selected GO concentrations (0.1, 0.5, 1.0 and 2.0%) need to be justified. Why are these values chosen? There is a typo in concentrations in Figure 2.
2. I recommend adding to Section 2 the characteristics of graphene oxide used, in particular: bulk density or specific surface area, particle size distribution.
3. According to Figure 4a, the electrolyte with 0.5% GO has the best electrical conductivity. What could this be related to?
4. It is necessary to add a paragraph about the possible practical use of the results obtained.
5. Conclusions should be presented point by point, for each completed study.

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

Recommended to accept in present form