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

Reviewers' Comments: 
 
Reviewer #1: 
Remarks to the Author: 
The manuscript appears technical sound, and is an interesting read. The concept of using bricks to 
store electrical energy is certainly novel. However, I do have concerns: 
1. Could enough energy be stored by bricks to be of any possible use? Perhaps the authors could 
present a calculation as to the energy stored per unit area of a brick wall? Or simply admit the energy 
stored will be very small, and most suitable for powering some sort of embedded microdevice. 
2. It was hard to determine what was the significant advance in the flexible supercapacitor. While the 
work appeared technically sound, it seemed rather similar to a number of other reports. 
 
Given the interest likely by the general public in "storing energy in bricks", I suppose this is an 
worthwhile paper to publish. In the long run however, I suspect this paper will not add considerably to 
the field. 
 
 
 
Reviewer #2: 
Remarks to the Author: 
I am afraid I’ve got a mitigated feeling about this manuscript. On one hand, the novelty seems to be 
very high and the presented results are quite impressive and innovative as well. On the other hand, 
after careful reading of the paper and of the supplementary materials I cannot determine if the 
authors are intentionally hiding the main parameters in a forest of data or if they are simply not aware 
of good practices in the field of electrochemical capacitors (same for batteries). What is most puzzling 
me is the choice they made to report all their data as areal values (F/cm2, Wh/cm2, etc.) while this 
only applies for microdevices or wearable electronics (see good practice in the field from ("A Guideline 
for Reporting Performance Metrics with Electrochemical Capacitors: From Electrode Materials to Full 
Devices", A. Balducci et al., J. Electrochem. Soc. 2017 volume 164, issue 7, A1487-A1488). In their 
case, the right metrics to be used are F/cm3 and F/g and so on. Moreover, I will say that if such 
values were provided instead of unrealistic surface values, I would not ask me the question whether 
this paper deserves to be published in Nature Comm. Or not and my answer would have been yes. 
The authors must be aware that the readers must have th correct information about electrode 
geometry at the right place which means in the manuscript together with the related electrochemical 
tests. In this version of the paper it seems geometries, shapes and electrochemical data are randomly 
split between the manuscript and the SI so that the reader cannot make adequate calculations for 
single electrodes, single device and series devices. It is mandatory to give the right information at the 
right place and not drown the pertinent data in a bunch of minor information. But the way it is 
presented opens up many questions that should probably prevent publication. In-depth revisions of 
the paper are required before it can be considered again for publication in Nature Comm. 
My second main concern is about the changes occurring to the bricks: what happened to Al2O3 or 
SiO2? There seems to be no evidence of how these minerals further behave inside the brick. The data 
are required. 

Additional comments (related or not to the two main comments are: 
1) Line 73 & 74: concentrations values seem to come out of nowhere. What is the driving forces and 
limitatiosn behind that? 
2) Same question for 14h line 82? 
3) Line 91: no news from other minerals from the brick? 
4) Line 103: problems begin. Which surface are we talking about. What is the electrode volume? What 
is the electrode mass? 
5) Line 104: the poser density seems to be very low. A cycling rate of 2 mV/s is quite unusual in ECs 
field. This point needs to be addressed in the manuscript. 
6) Line 107: what is “Faradic pseudocapacitance”. I know “pseudocapacitance” and “Faradic 
electrodes” but both terms combined together looks weird. Reading of ("To Be or Not To Be 
Pseudocapacitive?", D. Bélanger et al., J. Electrochem. Soc. 2015 volume 162, issue 5, A5185-A5189 
can be of help. 
7) Line 120: 3 Ohm is quite a huge value which will hinder power capability. 
8) Line 124: problems continue. Which surface are we talking about. What is the device volume? What 
is the device mass? Is the value calculated for a single device electrode or is it the capacitance of the 
full device? 
9) Line 132: it works up to 1.2V at the expense of ohmic drop and probably long term cycling ability. 
10) Line 139: what are the device geometry and dimensions? A scheme inside the main text is 
required. 
11) Line 159: what such temperature range? Any reason for not going higher? 
12) Line 163: the waterproof module is still a mystery to me due to lack of clear explanations about 
its design. 
13) Line 181: the abusive numbers of minerals tested is probably a source of misunderstanding of the 
scientific message. Most of the SI data are definitely not useful for the readers but deserves to be 
gathered in another paper and submitted elsewhere. It is clear for the reviewer that a lot of work has 
bene done on bricks and this is largely enough to be considered for publication in Nature Comm. 
14) Line 182: 6,194 mF/cm2 (cm2 of what?) together with 205 F/g of PEDOT (and not per g of fabric 
+ PEDOT) do not inform the reader about gravimetric and volumetric performance for the real life 
device made out of PEDOT and carbon cloth. 
15) Line 285 and whole paragraph: give these values in the related figure captions together with 
gravimetric and volumetric capacitances. 
 
Finally, I would like to add that I tried hard to made some calculations according to the manuscript, 
the SI and Fig. 1 and 4. Sometimes interesting values came out of these calculations and sometimes I 
ended up with capacitance poor capacitance value (and a headache. I strongly doubt that the authors 
are not aware that they are not providing values with the right metric. They already did so in one of 
their previous paper in the field (Self-woven nanofibrillar PEDOT mats for impact-resistant 
supercapacitors, Sustainable Energy & Fuels, 2019). In this paper they provide gravimetric values 
without providing the mass loading of each electrode neither for the device (mass loading which is 
suspected to be very low). 
Once again, the science and technology behind the current paper seem nice but they are not 
highlighted as they should be. 
 
 
 
Reviewer #3: 
Remarks to the Author: 
In this manuscript, the authors developed a chemical synthesis to control oxidative radical 
polymerization and deposition of a nanofibrillar coating of the conducting polymer poly(3,4-
ethylenedioxythiophene) (PEDOT) on fired brick and evaluated its capacitance performance based on 
this synthesis. The results are interesting, but some key issues still need to be addressed. The 
manuscript is recommended to be published after major modification. Here are my comments: 

1. One of the highlights of this manuscript is using the iron oxide in bricks to induce polymerization 
reaction. But bricks are building materials after all. What is the purity of iron oxide in bricks? What's 
the size of the α-Fe2O3? Is it evenly distributed? Can different bricks guarantee the stability of 
quality? Does the conditions mentioned above affect the polymerization of PEDOT and the 
performance of capacitor? This is very important and needs to be characterized and evaluated in 
detail. 2. In this manuscript, bricks, natural minerals and rocks, and α-Fe2O3-impregnated carbon cloth are 
used as substrates to produce flexible nanofibrillar PEDOT. Is there any difference between PEDOT 
nanofibrillar made on bricks, other minerals and carbon cloth carrying iron oxide? Like size, 
polymerization degree, conductivity and so on? And their influences on capacitor performance needs 
to be analyzed. 
3. As stated in the article, water evaporation from the gel’s hydrated ionic percolation network effects 
the performance of quasi-solid-state nanofibrillar PEDOT-coated brick supercapacitor. How to ensure 
that the water content of the gel electrolyte is consistent for each device assembling? 
4. What is the difference of areal capacitance of bricks with different volume? Does it increase linearly 
or remain unchanged? 
5. Iron oxide itself has pseudo-capacitance properties. Since α-Fe2O3 nanoparticles are widely 
disputed in bricks or α-Fe2O3-impregnated carbon cloth, does the capacitance performance of iron 
oxide reflect in this device? Meanwhile, is there any other metal oxide in the bricks? Does it affect 
capacitance performance? This is very important and directly affects the interpretation of capacitor 
performance. 
6. How to expalin the Nyquist plot in low-frequency range of symmetric nanofibrillar PEDOT-coated 
brick supercapacitor? (Supplementary Fig. 5e)