Peer review of: Quantifying contact status and the air-breakdown model of charge-excitation triboelectric nanoge (2020)

Reviewers' Comments: 
 
Reviewer #1: 
Remarks to the Author: 

This manuscript reports an advanced approach to enhance and evaluate the surface charge density of 
triboelectric nanogenerator (TENG), which is vitally important in TENG related energy harvesting and 
sensing. The authors demonstrated the highest record of average charge density up to 2.38 mC m-2 
using a 4 μm PEI film and homemade carbon/silicone gel electrodes with an ambient atmosphere of 
5% relative humidity. The prospective technic approach provided in this manuscript for surface charge 
density enhancement, will greatly push the output performance of TENG to a new horizon. The 
outcome of this work is impressive and is also important in the TENG field. Thus, I recommend that 
this manuscript can be accepted with a minor revision. 
 
1: Several works have been reported for boosting the surface charge in TENG. What is the major 
difference between this work and the existing work about the surface charges? You can explain them 
in the introduction component. 
2: The green color in Figure 1b is not explained in the manuscript. Please note the meaning of the 
colors in the figures or somewhere. If not, it might confuse the readers. 
3: Please note the specific information about COMSOL simulation in Supporting information (Figure 
1d). For example, the parameters and the model of the simulation. 
4: Why the relative humidity (Figure 2g) is important to the output of TENG? Please explain in the 
manuscript. 
5: Please provide more details about how to measure the open circuit voltage, short circuit current 
and transferred charge (e.g. connection of electrodes). 
6: What is the difference between Figures 3c and 3e? Please explain the purpose of them. 
7: The voltage curves in Figure 3a and Figure 4b look different. Were you using different equipment 
for the measurement? 
8: Please double check the conclusion component. Several “space” need to be deleted in this 
component. For example, line 263 and line 267. 
 
 
 
Reviewer #2: 
Remarks to the Author: 
This review relates to the Manuscript Number NCOMMS-19-195864 submitted to “Nature 
Communications” journal entitled, “Quantification of surface contact efficiency and air breakdown 
model on charge excitation TENG for maximum charge density.” 
 
The manuscript reports on an interesting strategy to achieve high charge density based on Paschen’s 
law, which is intended to improve the output performance of TENGs. While premise is certainly 
interesting, there are major questions that are not fully addressed, and publications at this stage 
seems a bit premature. 
 
1. Given that the optimized thickness of PEI, 4 μm, it is not clear how this is achieved and/or 
controlled. Authors highlighted the contact efficiency, but there is a lack of academic/scientific 
description or understandable mechanism that how this thickness is associated. It would be interesting 
to show thickness (<4 μm) dependence with comments about this. 
 
2. Authors particularly stated that “In the experiments, 
through our contact optimization, the contact efficiency of 4 μm dielectric can be improved…”, but it is 
not at all clear why authors characterized the whole system taking advantage of the external 
capacitance 25 nF, and the explanation provided is far from adequate. 
 
3. It is not particularly useful to compare (in Fig. 2e) charge density as a function of bias voltage (DC) 
and derived charge output values generated by charge excitation TENG (AC or pulsated AC), which is 
not fully accurate. 
 
4. What accounts for the varied charge density as a function of relative humidity in Fig. 2g? Has there 
been any charge density drop in optimized PEI? This seems like far more important parameter that 
has not been discussed at all. One of the weakest parts of the manuscript is in the characterization of 
the device at 5% relative humidity (RH). I would suggest a few more experimental test to be 
performed at different RH (moderate level). 
 
5. Authors studied the performance of the CE-TENG at 3 Hz of applied mechanical load, yet 
demonstration presenting its high output performance was measured at 5 Hz. How working frequency 
would be expected to function at their capacitance of the whole device? 
 
On a more general note, the manuscript seems fall short of the standards expected from a journal like 
Nature Communications. Unfortunately, based on the above comment, I am unable to recommend 
publication. 
 
 
 
Reviewer #3: 
Remarks to the Author: 
The charge density is one of the key indicators to evaluate triboelectric nanogenerator’s performance. 
It has been improved from 460 µC/m2 (Nat. Communication, 2018, DOI: 10.1038/s41467-018-
06045-z) to 1000 µC/m2 (Nano Energy, 49, 625-633 (2018)) to 1250 µC/m2 (Nat. Communication, 
10, 1426 (2019)). This paper presents an interesting experimental and theoretical investigation on 
further improving charge density in a charge excitation triboelectric nanogenerator (TENG). By using a 
4 μm thick PEI film and a homemade carbon/silicon gel electrode, the authors managed to push the 
charge density to 2.38 mC/m2, setting a new record for TENGs. Theoretical modeling predicts an even 
higher value. This research is of substantial interest to the scientific communities in energy harvesting 
devices, material science and device physics. All figures are well prepared and the experimental data 
are carefully analyzed. I recommend to publish this paper. 
A few more comments/questions: 
1. How to set the optimum Zener diode in advance, as the offset in Zener value might deviate the 
optimum power? 
2. Can the authors comment on the device performance (charge accumulation, device stability) at 
frequencies higher than 5 Hz? 
3. Has the energy conversion efficiency of the reported CE-TENG been measured? If yes, what is it? Is 
it following the same trend as that of the charge density? 
4. In supporting Figure 6, the authors report a maximum charge density of 2.55 mC/m2 that was 
achieved when using an external storage capacitor of 110 nF. This value is better than the one 
reported in the abstract. Shall this 2.55 mC/m2 be mentioned in the abstract or in the conclusion? 
5. Can the authors provide more information about the electric properties of their homemade 
carbon/silicon gel electrode? 
6. Two typos: 
a. Line 45: “concatct” 
b. Line 55: “(CE-ENG)”