The Effect of Slurry Wet Mixing Time, Thermal Treatment, and Method of Electrode Preparation on Membrane Capacitive Deionisation Performance
Round 1
Reviewer 1 Report
This manuscript uses three methods including Slurry Infiltration by Calendaring (SIC), Ink Infiltration Dropwise (IID), and Ink Deposition by Spray Coating (SC) to synthesize the electrode, which is later used in an MCDI cell, and explores the effects of electrode synthesis method, slurry wet-mixing time and thermal treatment temperature on the cell performance such as maximum salt adsorption capacity (mSAC).
This study does provide the detailed mixing and deposition procedures in the electrode synthesis, however, the design of experiments such as the uneven distribution of the temperatures chosen for the thermal treatment is not well-supported, making the conclusions less convincing. In addition, the manuscript is neither concise nor well-organized with a lot of repeating and unnecessary explanations about the experimental procedures even in ‘Results and Discussions’ section, and the key discoveries are not thoroughly discussed and highlighted. Also, English grammar needs huge improvement since singular and plural of some sentences are misused and some sentences are incomplete.
Specific comments are listed as follows:
The abstract should be improved. The effects of slurry wet-mixing time, thermal treatment and electrode preparation method on MCDI performance should be clearly described.
Introduction should be more specific and informative. It should include the frontiers and current challenges in synthesizing CDI and MCDI electrodes with a great performance. The last paragraph should emphasize the objectives, novelty and significance of this work.
Materials and methods are a bit tedious. Some unnecessary descriptions about experimental details (e.g. the details of preparing NaCl solutions, L274: ‘An appropriate amount of 3 g NaCl was weighed and transferred to an Erlenmeyer flask with 3 L of mill-Q ultrapure water’) can be omitted. 2.5, 2.6, and 2.7 should be the sub-sections under 2.4 as 2.4.1, 2.4.2, and 2.4.3 since they are the three methods used to produce the electrode. ‘2.8.7 Salt Adsorption Capacity’ should be independent of the ‘2.8 Electrode Characterization’, and 2.9, 2.10 and 2.11 should be the sub-sections of 2.87. There’s a gap between 2.11 and 2.16, any paragraphs missing, or just the wrong numbers of subtitles? Besides, the materials in 2.16 overlaps a bit with that in 2.10.
Results and discussions section needs more discussions of the results. Necessary analyses about the characterization results are omitted. Results should be compared with some reported theory and experimental observations. Graphs are not presented appropriately. The scales of SEM figures in Figure 2 and Figure 3 are not clear. No Y-coordinate of EDS figures in Figure 4 and Figure A.1. The deviations of EDS figures between the mixture and pure PVDF (Figure 4 and Figure A.1.) are not discussed. Figure 6 is a bit busy. The pre-conditioning results are unnecessary. In Table 3, the thermal treatment temperature points should include some values close to the optimal point, 130 °C, to make the conclusion that 130 °C is the optimal temperature point more convincing. The Y-coordinate in Figure A.4 should be ‘Weight (%)’ instead of ‘mass loss (%)’. TGA figures (Figure A.5. and Figure 7) lack Y-coordinate. Figure A.X should be changed to Figure S.X.
Conclusions section should also be improved. The authors should clearly summarize the actions taken and the main discoveries. Research limitations and future work are totally missing. The authors should correlate the advances in current research and their results
L13: ‘Ink Deposition by Spray Coating’ should be (IDSC)
L13: No comma
L18: At what temperate did you get the optimized electrode?
L22: Give the full name of ‘TGA-MS’, ‘DSC’, ‘SEM’, ‘EDS’.
L48: Prepare some references to support that electrode stability is important in achieving a good performance.
L55: What kind of active material is used?
L57: Give some examples of the tools and techniques.
L67-69: The performance characteristics of the electrodes in Li-ion battery are very different from that in CDI and MCDI batteries. The analogy is inappropriate.
L262: Bad quality of the equation;
L267: ‘dt’ is the changes of ‘t’, so it should be ‘t is the time …’
L273: Bad quality of concentration unit, ‘·’ should be in the middle, and ‘-1’ should be subscripted.
L293-295: Which type of microscale structures contribute most to the electrically conductive network of the electrode?
L511: What is the upper limit of mSAC of pure CDI? References should be provided here.
Author Response
Please see attachment
Author Response File: 
Author Response.docx
Reviewer 2 Report
In this paper, porous electrodes, which are one of the core materials of the CDI process, were manufactured by various methods and their desalination characteristics were compared. This paper is believed to be able to provide useful information to the researchers dealing with CDI, and therefore it could be published in the "Processes" journal. However, the final decision on the publication could be made after making several changes.
1) minutes -> min, seconds -> sec, hours -> h
2) Grammatical errors have been found in many sentences, so they need to be corrected.
3) An expression such as "see Figure X" in the sentences is not appropriate and therefore should be corrected accordingly.
4) In some sentences, unnecessary commas should be deleted. e.g.) "Figure 3C, shows ..."
5) In Figure 7, the Y-axis should be displayed.
6) It would be better if the salt removal efficiency is presented.
7) If possible, include the results of measuring the long-term stability of the electrodes.
Author Response
Please see attachment
Author Response File: Author Response.docx
Reviewer 3 Report
Please be consistent in presenting decimal separators. Choose either period or comma.
Line 22, please spell out the characterization techniques used. Do not just abbreviate when they first appear in the manuscript.
Introduction, please provide a detailed description of the CDI process. Do not assume that potential readers already know what CDI is. What are the research gaps in existing techniques for electrode preparation? Do not just report/regurgitate on what others have done.
Please provide detailed figures of characterization instruments and setups that were assembled in-house (i.e., contact angle, electrode conductivity, desalination setup).
Is there a reason why 1000 ppm was selected as the feed concentration? It would be interesting to see the effects of feed concentration on the performance of the electrodes.
How many replicate experiments were performed? What is the standard deviation or error?
EDS provided in the manuscript does not help distinguish between PVDF and carbon black in Figure 3B. Please provide EDX mappings instead (see: https://doi.org/10.1021/acsami.9b05967)
Figure 5, is it possible to include SEM images of lower magnification so that the authors can categorically state that the calendared electrode indeed has fewer cavities and not just at a few particular spots? Please also provide data on porosity and pore size distribution.
Figure 6, is mSA a typo? Is it possible to use colored axes and/or lines to represent the different variables (i.e., conductivity and current) so that it’s less confusing to readers?
Please provide the conductivity and electric current data for the control electrode and other electrodes of significance.
Tables 1 and 2, BET specific ‘surface’ area instead of ‘surfaces’.
Line 448, include melting point of PVDF (i.e., 177 degree C).
How does the best electrode developed in this manuscript compare to other electrodes in the literature? A comparison table would be helpful.
Line 511, please include the upper limit values of pure capacitive desalination and provide a citation.
Please improve the ending of the Conclusions Section (e.g., what is the potential of this newly developed electrode) as it falls kind of flat.
Author Response
Please see attachment
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The authors have addressed adequately all the comments I left in the first round. The revised version of the manuscript has better organized content, highlighting the discoveries of this work. The figures are improved with better quality. Hence, it is now recommended for publication in Processes.
Reviewer 3 Report
No further comments.
