Advances of Biowaste-Derived Porous Carbon and Carbon–Manganese Dioxide Composite in Supercapacitors: A Review
, Wanlu Li 5, Akmaral Kalybayeva 6, Guldarikha Zhumanova 7 and Olga Zubova 7
Round 1
Reviewer 1 Report
The review paper discusses the preparation of porous carbon and carbon-manganese dioxide composite from biowaste, as well as their utilization as supercapacitor electrode materials. This paper is a collection of basics rather than a review that critically examines the state-of-the-art in the area with a quantitative performance evaluation of reported supercapacitor electrodes based on porous carbon and carbon-manganese dioxide composite, their limitations, and critical outlooks in the field. This review paper can be accepted in the journal Inorganics after properly addressing the following points:
1. Numerous studies on biowaste-derived carbon and their nanocomposites have previously been published in this field as reviews. How does the current review improve upon or differ from earlier review studies? It should be made very clear in the introduction of the manuscript. The authors should clearly indicate the significance of this review study and how it might benefit future research in this area.
2. Page 3 Line 96, sucrose is not a fossil fuel.
3. Lignin, an important biomass waste from the pulping industry, is widely used to produce activated carbons. Lignin-derived carbon and carbon-MnO2 composites must be included in the article.
4. To increase the quality of the manuscript, the authors could add the performance evaluation of the supercapacitor electrodes based on porous carbon and carbon-manganese dioxide composite from biowaste as well as more references to pertinent literature on the subject.
5. Include a section to highlight the performance of the state-of-the-art in supercapacitors, corresponding drawbacks, and future perspectives/ challenges for the use of this material in supercapacitor devices.
Author Response
- Numerous studies on biowaste-derived carbon and their nanocomposites have previously been published in this field as reviews. How does the current review improve upon or differ from earlier review studies? It should be made very clear in the introduction of the manuscript. The authors should clearly indicate the significance of this review study and how it might benefit future research in this area.
Author’s response:
This article reviewed the types, obtaining methods of biowaste derived-activated carbon and its composite based on MnO2, and considered the influence of different crystal structures of MnO2 on the structure of activated carbon, which affects the supercapacitor performance and briefly described the characteristics of commercial supercapacitors. This article is a brief review about and we hope to help students and scientists who are well versed in this topic.
- Page 3 Line 96, sucrose is not a fossil fuel.
Author’s response:
thank you, I deleted it
- Lignin, an important biomass waste from the pulping industry, is widely used to produce activated carbons. Lignin-derived carbon and carbon-MnO2composites must be included in the article.
Author’s response:
I included in table 2 and 5
In [54] to obtain the composite material, the ratio of lignin and surfactant (Pluronic F-127) was 120 wt.%, and the Mn(NO3)2·4H2O content was varied to obtain 5, 10, and 20 wt.% Mn in porous carbon. The material and lignin with a Pluronic of 120% and manganese oxide of 20% were surface oxidized using 15% v/v of H2O2.
- To increase the quality of the manuscript, the authors could add the performance evaluation of the supercapacitor electrodes based on porous carbon and carbon-manganese dioxide composite from biowaste as well as more references to pertinent literature on the subject.
Author’s response:
I included part 4.
- The performance of supercapacitors
- Include a section to highlight the performance of the state-of-the-art in supercapacitors, corresponding drawbacks, and future perspectives/ challenges for partthe use of this material in supercapacitor devices.
Author’s response:
In part 4. The performance of supercapacitors
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The article (review) submitted for review is devoted to the description of methods for obtaining activated carbon from various natural fossils and biological objects, including biowaste, subsequent physical and chemical activation, the formation of composites with manganese dioxide, for the subsequent manufacture of supercapacitor electrodes. Some information on the specific characteristics of such supercapacitors is also given. The topic of the review is relevant and corresponds to the profile of the journal, however, the material presented needs serious revision.
The given information on the capacitance of supercapacitors with electrodes made of activated carbon obtained from various biomaterials needs to specify the types of devices (flat, radial, etc.; with symmetrical or asymmetric electrodes; which electrolyte was used).
As is known, and this is noted by the authors (line 113), the surface functional groups of carbon electrodes play a decisive role in the capacitance of a supercapacitor. However, this review does not analyze the effect of the feedstock and the activation method on the quantitative and qualitative composition of the surface compounds of activated carbons. Also, information on the influence of the method of obtaining activated carbon and its activation on the specific surface area and porosity is not systematized (tables 1-4).
Description of anodic electrodeposition of manganese dioxide (lines 373-382) contains incorrect information. How does the Mn 2+ cation migrate towards the anode under the action of an electric field? This information quoted not from original source , and from review by Wang JG, Kang F., Wei B. Engineering of MnO2 based nanocomposites for high-performance supercapacitors // Prog. mater. 641 Sci., 2015. V. 74. P . 51–124 which in turn refers to the work of Wen S , Lee J - W , Yeo I - H , Park J , Mho S - I . The role of cations of the electrolytes for the pseudocapacitive behavior of metal oxide electrodes, MnO2 and RuO2. Electrochim Acta 2004;50:849–55. In this work, there is no information about the anodic electrodeposition of manganese dioxide. When writing a review article, I recommend authors to refer to primary sources, and not to broadcast information from other previously written reviews.
The review does not present a single chemical and electrochemical reaction confirming the occurrence of the discussed processes of synthesis, functionalization and electrode processes.
Author Response
- The given information on the capacitance of supercapacitors with electrodes made of activated carbon obtained from various biomaterials needs to specify the types of devices (flat, radial, etc.; with symmetrical or asymmetric electrodes; which electrolyte was used).
Author’s response:
Since the non-commercial supercapacitors were considered in this article, cell configurations should be considered, so I included «Types of test cells» in Tables 1,2,5.
- As is known, and this is noted by the authors (line 113), the surface functional groups of carbon electrodes play a decisive role in the capacitance of a supercapacitor. However, this review does not analyze the effect of the feedstock and the activation method on the quantitative and qualitative composition of the surface compounds of activated carbons.
Author’s response:
(3.1.2. Chemical activation)
It should be mentioned that the surface functional groups of activated carbon can also affect the performance of the supercapacitor, which may depend on the method of obtaining of AC and the electrolyte used etc. For example scientists in [91] work modified the AC by (NH4)2S2O8 oxidation and their results indicate that the oxygen functional groups, especially carboxyl and carbonyl groups improved the wettability of the pore surfaces, increased the electrolyte diffusion rate into the electrode and increased the specific capacitance by an additional pseudo-capacitance in a 6 mol/L KOH aqueous electrolyte, an excess oxygen content blocked the pores, leading to poor electrochemical performance, but annealing at 300 °C in an inert atmosphere increased the specific capacitance and improved the rate performance in a 6 mol/L KOH aqueous electrolyte. However, in organic electrolyte oxygen functional groups reduced the specific capacitance. In [92] work scientists obtained the activated carbon from argan seed shells by KOH activation. AC induced oxygen and nitrogen groups on the surface and the experimental findings show that nitrogen-enriched activated carbons exhibited the highest capacitance and retention of 355 F/g at 125 mA/g and 93% at 1 A/g, respectively, compared to oxygen-doped activated carbons. Results show that surface carboxyl functionalities in oxygen-enriched activated carbons prevent electrolyte diffusion into the porous network, while the existence of nitrogen groups can produce micro-mesoporosity and excellent pseudo capacitance properties [93]. Functional groups are claimed as main responsible for performance degradation and ageing of activated carbon in organic electrolytes. These functionalities (mainly carboxylic, lactone or phenolic groups) are thought to be harmful in organic electrolytes but beneficial in aqueous-based electrolytes, where they can provide an extra capacitance through a pseudocapacitive mechanism, however scientists proved that the functionalities on the surface of activated carbon contribute to the capacitance through pseudo-redox reactions in the organic electrolytes and can also be beneficial for inhibiting the potential shift of AC [94]. Based on the above, we can conclude that activation methods, types of electrolyte can affect the performance and efficiency of the supercapacitor, since one sample can show different characteristics in organic and aqueous based electrolyte due to the functional groups.
- Also, information on the influence of the method of obtaining activated carbon and its activation on the specific surface area and porosity is not systematized (tables 1-4).
Author’s response:
I also already had brief conclusions at the end of Tables 3 and 4, but I included this:
(3.1.2. Chemical activation)
Based on Table 3 and 4 it can be concluded that the activation method affects the porosity and specific surface area and according to the authors chemical activation and activators mixture are better suited to obtain AC, since large specific surface area and micropore volume are reached by activation.
- Description of anodic electrodeposition of manganese dioxide (lines 373-382) contains incorrect information. How does the Mn 2+ cation migrate towards the anode under the action of an electric field? This information quoted not from original source , and from review by Wang JG, Kang F., Wei B. Engineering of MnO2 based nanocomposites for high-performance supercapacitors // Prog. mater. 641 Sci., 2015. V. 74. P . 51–124 which in turn refers to the work of Wen S , Lee J - W , Yeo I - H , Park J , Mho S - I . The role of cations of the electrolytes for the pseudocapacitive behavior of metal oxide electrodes, MnO2 and RuO2. ElectrochimActa 2004;50:849–55. In this work, there is no information about the anodic electrodeposition of manganese dioxide. When writing a review article, I recommend authors to refer to primary sources, and not to broadcast information from other previously written reviews.
Author’s response:
I cited this from another source, but I decided to delete it and included an article where an electrodeposition composite was obtained and also included it in the table 5.
(3.2. Methods of obtaining AC-MnO2 composites)
In [109] work, the composite was prepared by anodic electrodeposition. It was achieved by using a Pt plate as a counter electrode and Ag/AgCl electrode as a reference electrode. Before electrodeposition, AC electrode was soaked in the electrolyte containing 0.1 M of Mn(CH3COO)2 and 0.1 M of Na2SO4 for one night. A constant current (1 mA/cm2) was applied to ensure the growth of MnO2 nanosheets on the AC membrane. After the as-prepared samples were rinsed gently by the water and vacuum dried at 60 °C to obtain the electrodes.
5. The review does not present a single chemical and electrochemical reaction confirming the occurrence of the discussed processes of synthesis, functionalization and electrode processes.
Author’s response:
It is difficult to describe the processes of obtaining, but included the following equations
In the initial stage, a negative potential induces the electrolysis of water at the cathode surface, resulting in the formation of hydrogen gas and hydroxyl ions (Eq. (1)), simultaneously, the electrochemical reduction of oxygen contributes to the formation of hydroxyl ions (Eq. (2)). The hydroxyl ions increases the pH value in the vicinity of cathode, which then leads to the precipitation of Mn hydroxide (Mn(OH)2) (Eq. (3)). The final formation of MnO2 can be obtained through three routes as follows: (1) the metastable Mn(OH)2 is readily oxidized to MnO2 in the presence of oxygen (Eq. (4)); (2) Mn(OH)2 can be electrochemically oxidized into MnO2 or Mn3O4 solids (Eq. 5); and (3) thermal annealing of Mn(OH)2 in air at an elevated temperature results in the conversion of MnO2 via dehydration and oxidation (Eq. (4)).
2H2O + 2e- → H2 + 2OH- (1)
O2 + 2H2O + 4e- → 4OH- (2)
Mn2+ + 2OH- → Mn(OH)2 (3)
2Mn(OH)2 + O2 → MnO2 + H2O (4)
Mn(OH)2 + 2OH- → MnO2/Mn3O4 + 2H2O + 2e- (5)
Another cathodic electrodeposition path is based on reducing Mn7+ species from (MnO4)- ions in solution on the cathode surface according to reaction (Eq. (6)) [110].
(MnO4)- + 2H2O + 3e- → MnO2 + 4OH- (6)
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
All of the reviewer's concerns have been properly addressed by the authors. So the manuscript can be accepted for publication.
Reviewer 2 Report
The article has been improved with the changes made.
