Peer review of: Energy storing bricks for stationary PEDOT supercapacitors (2020)



RR2
 Reviewers' Comments:
 Reviewer #1:
 Remarks to the Author:
 I'm satisfied with the revised manuscript, and find it much more suitable for Nature Communications
 (keeping the story simple be removing the flexible capacitor discussion certainly helped!). I suggest
 Fig. 5d be revised to plot the CE from 80-100% or 90-100%. The way it is plotted now makes it
 impossible to actually determine the CE.
 Reviewer #2:
 Remarks to the Author:
 The reviewer acknowledges the impressive work the authors made for making their paper clearer and
 focused on the innovation using bricks. It is really a giant improvement to provide the geometric
 details of all the electrodes and devices tested in the manuscript. Most of my previous questions have
 been pertinently addressed and the corresponding changes in the manuscript are quite satisfying. I
 have some remaining comments that may help the authors to further improve their manuscript.
 Main remarks:
 1) I am a little bit puzzled by the answer provided by the authors to one of my question. Line 144:
 “The Fe3+/Fe2+ redox pair at 0.37 V and 0.49 V (versus Ag/AgCl) arise due to iron species in brick
 and disappears as scan rate increases to 25 mV/s because double-layer capacitance outcompetes
 Faradaic processes at faster rates”. Am I just wondering if the authors mean PEDOT stores charges by
 a capacitive proves. If so, this is not correct: Electronically Conducting Polymers such as PEDOT store
 charges by doping/dedoping (faradic), rather than adsorption/desorption (non-faradic). So at least the
 sentence must be corrected but the authors must also check all their assumption in the manuscript
 and in the SI about this fact. Figure 4c simply evidences that Faradaic processes in PEDOT are faster
 than those occurring from solid Fe2O3.
 2) The authors state that: “Our stationary supercapacitor is not conventional by any stretch of the
 imagination and not designed for portable electronics or electric vehicles. The weight of our final
 device i.e., a brick wall, is less important than area and volume.” This is clear now but wasn’t in the
 original version, with too many data and too many devices. I am still convinced that volumetric energy
 and power densities must be implemented in Supplementary Table 2, and must appear somewhere
 when the use of brick walls is mentioned together with surface values. It seems that the authors are
 also convinced that volume matters as well when talking of a building, so why being reluctant to
 provide such values to the attention of the readers. SI is one option, but few word about this fact in
 the manuscript will also give this information to “fast readers” and probably provide more citations to
 the future paper.
 Minor remarks:
 1) The reported values, especially for capacitance, etc..., contain too many significant figures. See for
 example: “maximum device capacitance of 11,523 F/m2 and an energy density of 1.606 Wh/m2”. It is
 quite difficult to provide such accuracy and if the authors think their values are correct they must
 provide the error bars; I strongly doubt that they will give such accuracy and shortening the figures
 will give some additional credibility to the study.
 2) The authors answered to my previous question about pseudocapacitance: “Thank you for pointing
 this out. The phrase “Faradaic pseudocapacitance” refers to pseudocapacitance contributed by
 Faradaic processes instead of ion intercalation. We adopted it from “Gogotsi Y, Penner RM. Energy
 Storage in Nanomaterials - Capacitive, Pseudocapacitive, or Battery-like? ACS Nano 12, 2081-2083
 (2018).” After a more thorough literature search, we discovered that this terminology is used with low
 frequency and we therefore have changed it to “Faradaic processes” on Page 7, line 143 to avoid any

 confusion.” They must be aware that ion intercalation is a Faradaic process also. The term
 pseudocapacitance designates a Faradaic process that provides a capacitive-like signature to the
 electrode which is quite uncommon in electrochemical energy storage devices.
 Reviewer #3:
 Remarks to the Author:
 The authors have revised the manuscript carefully and the questions have been well addressed.
 Therefore, the manucsript is recommended to be published.