Enzymatic Biofuel Cells: A Review on Flow Designs
Round 1
Reviewer 1 Report
The work deals with some interesting reviewing on enzymatic biofuel cell research and the authors have done a good job in this research topic. Therefore, it is suggested to be published by Energies.
Author Response
Answers to Reviewer 1 are in the enclosed file
Author Response File: 
Author Response.docx
Reviewer 2 Report
Barelli et al. reported a review paper about the enzymatic biofuel cells. The authors focus on the performance assessment of enzymatic biofuel cells based on flow designs, which is interesting for powering biosensors and wearable devices.
The manuscript is of interest concerning materials for catalytic applications. However, the authors should perform major revision in order to make clear the novelty of the review for the readers.
Examples are given below.
-On page 2, line 9-116, the applications for miniaturized portable electronic equipment, sensors to integrated lab-on-chip power devices should be better described. I can not see correlation of the EFC bioanode device and a direct electron transfer-based biocathode . Moreover, the Eq 1 and Eq2 should be better explained and correlated with EFC working principles.
On page 5, line 165, ‘Electron transfer mechanism’, The EFCs operation and design is associated with the efficiency of biocatalysts with the electrodes. However, the correlation with the electron transfer mechanism is not clear to the readers.
On page 11, line 456, How about the 3D-printing MEFCs methodology, Is this new?
On page 13, figure 7, a detailed picture or schema of the Y-shaped microfluidic EFC should be included .
On page 7. the discussion about the effectiveness of the strategies for enzyme immobilization should be improved to make it clear to the readers.
On page 21 although the variation of glucose concentration in the anodic enzymatic half-cell as function of time is well described, I can not understand the association with the temperature and flow rates. This is not justified by the authors.
On page 24, future outlooks regarding the main features regarding enzymatic fuel cell systems, and flow design configurations is not clear.. I did not see the emphasis in the new fabrication methods for electrodes and cells.
Author Response
Answers to reviewer 2 are in the enclosed file
Author Response File: Author Response.docx
Reviewer 3 Report
The Authors present a review paper on the flow design of enzymatic biofuel cells. The topi is interesting and the manuscript well written. Nevertheless, some minor changes are mandatory prior to acceptance from my side.
Check the English form in the Abstract and Introduction sections, which is of lower quality with respect to the rest of the manuscript.
- Line 7: replace “is borning”
- Line 8: “can be considered a promising”. As a promising…
- Line 16 “The focus of this review regards”, please reformulate in correct English.
- Line 25: “is being born”
- Line 28: what do you mean with “according to the fuel and oxidant availability?
- Line 37: “Nowadays” should be placed at the beginning of the sentence.
- Please, when citing bibliographic studies, address to the first Author, and not generally “in [x]”.
- Line 53: why “Nevertheless”? maybe Moreover, Also, In addition…..
- Line 61: “in [14] it is presented a mini review….” Please reformulate.
- Line 66: “performances” maybe?
- Lines 67-76: the description of the numbering of the review sections and their contents is very confusing: “first……. Section 3…….Subsequently……Section 4. Please explain better what can be found in Sections 1-4.
- Please write in correct form the chemical formulas: O2 and H2O2, not O2 and H2O2.
- From line 93: here glucose as most used source of energy it is presented. Nevertheless, from line115, it is stated that sugars in general represent the main fuel for these kind of cells.
- I suggest to merge these two parts in order to avoid confusion.
- Line 206: replace “cited” with other word, maybe “described”, “discussed”, or other ones.
- Figure 4: too bad quality, please improve it.
- Line 450: “(Figure 5Figure 4A).” Something in this text is not correct.
- Include in the discussion some hybrid biofuel cells.
- Can you add some economic consideration at least in the introduction part regarding the industrial applicability of enzymatic biofuel cells?
Author Response
Answers to Reviewer 3 are in the enclosed file
Author Response File: Author Response.docx
Reviewer 4 Report
The review article by Barelli et al. is ideally suited for the Journal energies. Enzymatic biofuel cells are a dawning technology with high ecological and socioecological importance. The authors motivate that there is a lack of reviews that consider the aspect of flow cell design, which I assumed to be accurate. Thus, this comprehensive overview of past and current flow designs is very reasonable and should attract reader from many energy-related sciences. Overall, I am very pleased with the review and the discussion of the various aspects. However, few aspect might need to be revised in order to avoid misunderstandings and to clarify the significance of physicochemical aspects that currently fall short.
As such, I recommend acceptance after minor revisions.
Comments/questions:
- In Eq.1, it might make sense to include the 24 extractable electrons per mole glucose.
- 4 is blurry and lacks resolution.
- If a Figure includes artwork or data from an already published source than the permission needs to be obtained for reproduction. Also, the authors need to state if the contents have been merely reproduced or adapted. This applies for all Figures with already published data
- There is a reference error in line 261.
- The authors might want to put more emphasis of the physicochemical aspects of enzyme immobilization. Give, that many catalysts are noble metals, this has been studied in several works of related fields with a stronger focus on macromolecule-metal interactions. Recently, de Barros and Lopez-Gallego studied reported on the mechanistic details of an enzyme adsorbed onto different nanomaterials (DOI: 10.1021/acscatal.0c04919). Though this was not in the view of energy research, it is most relevant for the preservation of enzymatic activity when adsorbed onto metal surfaces. In fact, it could be shown that enzymatic activity can be increased beyond the natural limits of free enzyme.
- The presentation quality of Fig 15 and 16 and 17 need to be improved. They look like from a technical report.
- Another aspect that falls short is related to section 3.3. The authors should discuss in more detail the adsorption of biomacromolecules onto noble metals and the acting forces in action. How does the enzyme bind to the surface? Which functional groups are involved (e.g. for gold, this would be mainly thiols and amines)? In many cases it could be expected that an immobilization results a decrease of the enzymatic activity. How can this be prevented?
Author Response
Answers to reviewer 4 are in the enclosed file
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
I recccomend acceptation of the manuscript
