Study on the Inhibition of Hydrogen Evolution Reaction by Electrocatalytic Reduction of Carbon Dioxide Using Elsholtzia Harchowensis Biochar

Round 1

Reviewer 1 Report

This manuscript is devoted to the preparation of the Cu/C electrocatalyst from the biomass of Elsholtzia Harchowensis and its testing in the CO2RR process. The motivation of the work is interesting and highly promising. But after detailed examination of the work, it is become clear that actually authors greatly overpriced the importance of the utilization of the Elsholtzia Harchowensis for the preparation of electrocatalysts for CO2RR.

As it is stated in the experimental section, to prepare the catalysts the biomass was mixed with Cu salt and then calcined to form a Cu-containing biochar. In this situation it is clear that biomass from any other plant can be successfully utilized because the proposed method do not rely on the Cu accumulation by plant. 

Beside the noted serious inconsistency, the paper is inaccurately written and contain errors and weak points.

1) For example, in the introduction it is stated that " To further enhance the performance of biomass carbon catalysts for copper superaccumulating plants, this study used Cu/C-BN electrode material prepared by modifying sea houttuynia cordata biochar through B and N doping as a basis"  but in the topic and throughout of manuscript it is described that biochar was obtained from  Elsholtzia Harchowensis not sea houttuynia cordata. 

Also, the beginning of this phrase looks quite strange, it is not clear that authors intend to communicate here.

2) The method of the preparation of "copper grass powder " is not provided. Moreover, the composition of this material with respect to dominant elements was not presented, however it seems quite important in this particular study. 

3)  From the manuscript, it is not clear whether the coating with polytetrafluoroethylene (PTFE) to mitigate HER is an original idea proposed by authors for the first time or such approach was used previously? Corresponding references should be given in this case.

See the text of revision.

Author Response

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Reviewer 2 Report

This manuscript studies Cu/C-BN electrode materials using biochar via B and N doping by dripping PTFE onto the electrode materials, improving hydrophobicity. The following should be addressed before acceptance.

 1.     In the Introduction, Elsholtzia Harchowensis and previous studies should be explained in more detail. The significance of HER and CO₂RR should be added.

2.     Abbreviations should be used after spelling out the terms, including the Abstract. XPS results should be well explained, including its figure numbers. The quality of all figures, including numbering, should be reconsidered, as they were prepared unprofessionally in an SCI-level journal, in particular, Figure 1.

3.     Clarification of two different materials, Cu/C-BN-CC and Cu/C-BN-PT, should be added.

4.     What is the significance of adding polytetrafluoroethylene (PTFE) enhancing the hydrophobicity of the material?

5.     It is very curious if the EIS spectra are fitted using the EEC models, which look like simple symbol-line plots without performing non-linear fitting using the EEC models shown in the insects. If EIS analyses are included in this manuscript, the charge transfer mechanisms should be added.

6.     The contact angle-related studies should be explained in more detail. Also, the thin-film preparation should be explained well. 

None.

Author Response

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Reviewer 3 Report

Regarding the work entitled “Study on the inhibition of hydrogen evolution reaction by electrocatalytic reduction of carbon dioxide using Elsholtzia Harchowensis biochar” submitted to Catalysts: The work deals with the use of a biochar rich in copper for the CO2RR. The work is kind a continuation of two previous works. I found some difficulties to read the work due to the information is not clearly presented, and thus, I have several comments regarding this work:

1)      CC and PT are not defined in the manuscript, I never knew what they stand for

2)      Fig. S2: EDS-elemental mapping shows well-defined regions of O element in a sort of hemispherical shapes, analyzing C, N and Cu distribution, these shapes are not based on C, and the Cu content is low, being O the dominant element. So, what are these shapes?

3)      Fig. S6: I consider the authors must revise the deconvolution of O 1s, it seems require extra peak of other oxygenated species found on carbonaceous materials.

4)      Page 4: I think the authors should revise the redaction of XRD. How this technique indicates that materials maintain great catalytic performance?

5)      Figure 4: Authors say that Cu mainly exists as Cu+ and Cu2+ species, while during XRD the authors indicate that Cu (zero valent) is found in the material. Please revise, during XPS did the authors any cleaning step with N2?

6)      Fiig. 5: There are some aspects to revise from this figure a) How the authors normalized the current? B) Why the current of Cu/C-BN-CC in Ar and CO2 is far from zero when any faradic process is occurring? C) why if the surface is hydrophobic, the Cu/C-BN-PT did present near cero capacitive current at low overpotentials? D) Considering the capacitive current, is it valid the EIS experiments at voltages below -0.3 V and the discussing regarding activity?

7)      Fig S8. What about the validity of comparing activity for CO2RR when the materials display differences in capacitive current? I consider it should be subtracted and the abstract, main text and conclusions should be revised.

8)      Figure 7. Why the onset potential for Co2RR is less favorable in the PC electrolytes compared to the aqueous electrolyte, I observe potential differences of at least 400 mV. Additionally, the discussion of the electrochemistry behind this figure is poor.

Author Response

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Round 2

Reviewer 1 Report

The authors have done work on the text of the article, but some comments mentioned in the review remain unanswered.

1) If the authors claim that copper, which is present in the plant is also involved in the catalytic process, it is necessary to provide data on the elemental composition of the powder prepared from the herb, in particular to give the copper content in it. The current comment

"he Elsholtzia Harchowensis was collected from the copper mining area in Tongling City, Anhui Province, China, located at a central latitude of N 30°52'22.05" 270 and a longitude of E 118°01'42.09". Its main elemental composition includes carbon, hydrogen, oxygen, and nitrogen, the surface functional groups were mainly C-O-C, C=O, COOH. "

is completely unacceptable, as it is clear a priori that the plant is mainly composed of carbon, hydrogen, oxygen and nitrogen, specific values are needed.

If the copper content of the original powder is negligible with the introduced artificially, then the text of the paper and the introduction should be revised to eliminate the emphasis on copper hyperaccumulation in the plant. 

2) It is not clear why the XPS spectra of both catalysts CF3 groups are detected in the XRD spectra of both catalysts, because only in the Cu/C-BN-PT catalyst PTFE was introduced.

Author Response

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Reviewer 3 Report

The revised version is suitable for publication in catalysts. I recommend acceptation.

Author Response

Reviewer  recommend acceptation.