Indigo-Mediated Semi-Microbial Biofuel Cell Using an Indigo-Dye Fermenting Suspension
, Kasumi Nakagawa 2, Momoka Matsunaga 2, Akinori Ando 1, Kenji Kano 3, Michiki Takeuchi 4,* and Eiji Sakuradani 2,5,*Round 1
Reviewer 1 Report
I read this article with interest. The use of japanese indigo dyieng for microbial biofuel cells is an attractive idea and the study nice.
- what future suggestions for improving the cathode stability issue linked to evaporation? this can be fixed with clever cell design or integration of more appropriate gas diffusion layer? Such discussion should be included in the article
- chemical structures and at least basic mechanisms needed to show conversions fromindican to indigo to leuco-indigo (H2O soluble), accompanying the text
- I may have missed this but why pH 11 and not something more neutral and biofriendly? (and also compatible with enzymatic biocathodes to avoid Pt). the alkaline conditions seems to be a big drawback of the system. Please provide comments in the text.
- Experimantal seemed to lack details about the anode. How was it assembled and connected? What are the details for the carbon felt - source, properties, purities, SEM characteriation of porous structure.
- Have the authors considered using carbon nanotube buckypaper as an alternative to the carbon felt (higher surface area, increased mesopores, higher conductivity, tunability). This can be obtained commercially but lab made can provide some interesting advantages. The following ref includes a section dedicated to literature reporting buckypapers for microbial anodes and cathodes: Buckypapers for bioelectrochemical applications. Bioelectrochemistry, De Gruyter, pp.1-22, 2019. It will depend on the specifics of the materials but lab made BP could improve bioanode performance further? High performance lab made buckypaper e.g. ACS Catal. 2017, 7, 7, 4408–4416
Author Response
Response to Reviewer 1 Comments
I read this article with interest. The use of japanese indigo dyieng for microbial biofuel cells is an attractive idea and the study nice.
Thank you very much for reading our article and giving valuable comments.
Point 1: what future suggestions for improving the cathode stability issue linked to evaporation? this can be fixed with clever cell design or integration of more appropriate gas diffusion layer? Such discussion should be included in the article
Response 1: Thank you very much for valuable comments.
One way to avoid the effects of evaporation is to place the electrodes on the side of the tank or float the electrodes above the dye-suspension. In order to achieve this concept, constructing a membrane electrode assembly (MEA) with water-repellent material will be necessary. We added some explanations about this concept in red on pages 9 and 12.
Point 2:chemical structures and at least basic mechanisms needed to show conversions fromindican to indigo to leuco-indigo (H2O soluble), accompanying the text
Response 2: Thank you very much for important suggestion. We added chemical structure and proposal mechanisms in Figure 1. Figure S1 was added for explaining conversion from indican to indigo and leuco-indigo.
Point 3: I may have missed this but why pH 11 and not something more neutral and biofriendly? (and also compatible with enzymatic biocathodes to avoid Pt). the alkaline conditions seems to be a big drawback of the system. Please provide comments in the text.
Response 3: As shown in line26 of p. 2, acetaldehyde is a strong reductant, and its reducing power increases with the pH. In addition, leuco-indigo is soluble under alkalin condition. From above reasons, pH 11 is necessary for use of indigo-dye fermenting suspension. In future work, we want to obtain multi-copper oxidase-like enzymes which have activity at pH 11. After use of indigo-dye fermenting suspension, the alkaline solution is sowed in the field to grow indigo plants. That’s why the alkaline condition of this system is not a big drawback.
Point 4: Experimantal seemed to lack details about the anode. How was it assembled and connected? What are the details for the carbon felt - source, properties, purities, SEM characteriation of porous structure.
Response 4: Thank you very much for important remarks. We added the details of the fabrication method of the anode. Also. we added the additional information on the materials as much as we could. These contents are written in red on page 9.
Point 5: Have the authors considered using carbon nanotube buckypaper as an alternative to the carbon felt (higher surface area, increased mesopores, higher conductivity, tunability). This can be obtained commercially but lab made can provide some interesting advantages. The following ref includes a section dedicated to literature reporting buckypapers for microbial anodes and cathodes: Buckypapers for bioelectrochemical applications. Bioelectrochemistry, De Gruyter, pp.1-22, 2019. It will depend on the specifics of the materials but lab made BP could improve bioanode performance further? High performance lab made buckypaper e.g. ACS Catal. 2017, 7, 7, 4408–4416
Response 5: Thank you for providing this information. We think that buckypaper using CNT is one of the most promising electrode materials. Therefore, we added it as a solution to improve the output power. These contents are written in red on pages 9 and 12.
Reviewer 2 Report
The paper entitled "Indigo-mediated semi-microbial biofuel cell using an indigo-dye fermenting suspension" is a suitable research article for the publication in this journal. The research article is representing the construction of a semi-microbial bofuel cell enabling the indigo-dye fermentation for the first time, which is quite impressive. The paper is quite well composed for publication in its original format but few changes needed to be addressed before final publication. Some of the comments are given below.
- Add reaction schemes for indigo and leuco-indico oxido-reduction reactions (including the chemical structures) into figure 1.
- Lines 251-255: Rewrite the sentences.
- Lines 255-257: Give the references or the data that explains the superior indigo-dyeing process using the indigo-dyeing fermenting suspension over that using a single microorganism.
Author Response
Response to Reviewer 2 Comments
The paper entitled "Indigo-mediated semi-microbial biofuel cell using an indigo-dye fermenting suspension" is a suitable research article for the publication in this journal. The research article is representing the construction of a semi-microbial bofuel cell enabling the indigo-dye fermentation for the first time, which is quite impressive. The paper is quite well composed for publication in its original format but few changes needed to be addressed before final publication. Some of the comments are given below.
Thank you very much for reading our article and giving valuable comments.
Point 1: Add reaction schemes for indigo and leuco-indico oxido-reduction reactions (including the chemical structures) into figure 1.
Response 1: Thank you very much for important suggestion. We added reaction schemes of the reactions to Figure 1.
Point 2: Lines 251-255: Rewrite the sentences.
Response 2: I rewrote the sentences to make it clear.
Point 3: Lines 255-257: Give the references or the data that explains the superior indigo-dyeing process using the indigo-dyeing fermenting suspension over that using a single microorganism.
Response 3: I modified the sentence.
If the sentences (lines251-257) are not suitable for this journal, we delete the sentences.
