Peer review of: Boosting output performance of sliding mode triboelectric nanogenerator by charge space-accum  (2020)

Reviewers' Comments: 
 
Reviewer #1: 
Remarks to the Author: 
1. What does ‘in-plane low frequency mechanical energy harvesting’ mean? Why is it the ‘most 
effective’ method? What is the comparing metrics here? Please provide more detailed discussions. 
 
2. The authors emphasized several times that TENG is the ‘most effective’, ‘most promising’ energy 
harvester in different applications. However, there is no data or chart to support this argument 
directly. Please benchmark using relevant figures of merits to help readers understand it. 
 
3. How good is ‘2.3 times’? How to evaluate this value? It is easy to boost the charge density from a 
tiny number to a relatively large number; however, it is challenging to improve the charge density 
starting from a big number. 
 
4. Is this 1.63 mC/m^2 physically correct? Please justify this number by adding some physical 
explanation. What is the mechanism of keeping these charges on the surface, and most importantly, 
how to effectively measure the value? 
 
5. What is the scientific meaning of the FEA result in Fig. 1c? What is the boundary condition in the 
FEA initial setup? What is the contribution of the FEA result in this paper? 
 
6. In Fig. 1b and also supporting Fig 1, the charge distribution in Nylon and metal is the same (both 
positive). Is it reasonable? If so, it means there is no electrical field drop between these two layers. 
Also, based on Nylon’s chemical structure, the polarization should result in one side positive and the 
other side negative. Thus it is suggested the author double-check their working mechanism. 
 
7. Overall, the capacitor charging curve is impressive. However, since the author mentioned that 
TENG is the ‘most effective’ energy harvester, the author should include the calculation of input 
mechanical energy, calculate an energy conversion ratio, and compared with other energy harvesting 
technology. 
 
8. What is the limitation of such a TENG structure design? 
 
 
 
Reviewer #2: 
Remarks to the Author: 
In the manuscript, the authors suggested a new strategy by designing shielding layer and alternative 
blank-tribo-area enabled charge space-accumulation (CSA) for boosting output performance of sliding 
mode triboelectric nanogenerator (CSA-S-TENG). As a result, the authors successfully demonstrated 
that the charge density of CSA-S-TENG achieves 1.63 mC/m2 by designing grounded electrode to 
overcome the limitation of air breakdown and introducing extra blank-tribo area to accumulate 
charges. They validated working principles of device and demonstrated not only optimized CSA-S-
TENG, but also their rotation type which drives hydro-thermometer by powering capacitor. There are 
several deficiencies to be revised, while I would recommend this manuscript for the possible 
publication in Nature Commun. after minor revision. The drawbacks and deficiencies are listed below. 
 
- According to Equation (2) and Supplementary Note 1, transferred charge Qt is affected by d1, d2, 
the thickness of dielectric film. However, the authors described and demonstrated that different 
thickness of dielectric film has no significant effect on the charges and output in the main text and 
Supplementary Figure 11. Therefore, it is thought that equations do not explain phenomenon suitably 
or there are deficiencies in experimental validation. I recommend the authors to explain the reason 
why theoretical expectation and experimental result show different behavior. 
 
- The authors described that dissipation of charges on the extra blank-tribo area enables maximizing 
charge space-accumulation effect. In Supplementary Figure 3, they demonstrated dissipation of 
charges occurs in tens of minutes and dissipation rate is not fast. However, in Supplementary Figure 
4, the authors illustrated all the charges on the extra blank-tribo area are dissipated during even half 
cycle. Therefore, Supplementary Figure 4 is not exact to explain the role of extra blank-tribo area. It is 
thought that there is partial dissipation of charges on the extra blank-tribo area and it makes 
saturation of charges on the slider. Therefore, I recommend the authors to illustrate additionally the 
process of charge saturation of slider and partial dissipation of charges of extra blank-tribo area. 
 
- Reference selection is basically okay. Addition of very recent comprehensive papers to reference 
section would make this manuscript better, e.g., Hinchet et al., Science, 365, 491, 2019. 
 
 
 
Reviewer #3: 
Remarks to the Author: 

This manuscript reports a new strategy to boost the output performance of sliding mode TENG, by 
utilizing a shielding layer and alternative blank-tribo-area to enable charge space-accumulation. It is 
concluded that the shielding layer can effectively prevent the air breakdown occurring on interfacial 
layers, while the blank-tribo-area with rapid charge dissipation can promote charge accumulation. 
Authors performed a comprehensive study on the charge space-accumulation mechanism theoretically 
and experimentally, showing a 2.3 folds enhancement of normal S-TENG can be achieved. This study 
can be of interest to the broad audience in the community, thus I recommend the publication of this 
manuscript in Nat Comm, and have the following comments for the authors to address. 
1. According to the author’s description, the blank-area is designed for achieving charge space 
accumulation, and enabling the charge dissipation to replenish the charges. As per reviewer’s 
understanding, the sliding speed is then affecting the amount of dissipated charges, and probably the 
charge space accumulation. Can the author comment on it? 
2. In the working mechanism part, the authors stated that “the charges on the blank-tribo-area would 
be quickly dissipated, which ensures continuing charge replenishment on PTFE during each friction”. In 
Figure S3, the graph shows that the charge on the PA layers decreases slowly, and a 50% drop may 
take a few minutes. This duration is much larger than the time interval between each sliding cycle. 
Can the author explain this phenomenon? 
3. A few other strategies in previous literature to boost the output performance of TENG is suggested 
to be included in order to broaden the coverage of the introduction, e.g., Nano Energy, 2020, 73, 
104760; Adv. Sci., 6(24), 1901437; etc. 
4. For the swith OFF state, what is the position of the slider when the switch is turned off? And what is 
the influence of switch-off position on the output performance? 
5. What is the difference in designing a rotary mode CSA-S-TENG and a sliding mode CSA-S-TENG? 
6. From Figure 2, the output charge increases from 200 nC to 700 nC with the increase of gap from 
1.5 to 18.5 mm; while the charge increases from 400 nC to 700 nC when the extra tribo-area is 
extended from 46.5 to 76.5 mm. Apparently, the 17 mm increment of the gap contributes to the extra 
500 nC charge, but the 30 mm increment on the tribo-area contributes to a 300 nC extra charge. Both 
gap and extra sliding range should correspond to the blank tribo-area. Could the author explain the 
different improvement efficiency of these two methods? Or is there an optimized ratio for maximum 
performance? 
7. In Figure 2, the color of the dashed lines separating Figure 2 a-d is too light, especially closed to 
white at the edges, which is hard to differentiate the four graphs. Also please label the outputs of 
different colors shown in Figure 2g and Figure 2h. For Figure 4b, the title of the x axis ‘Time(s)’ has 
been blocked, please check. 
8. Although the charge boosting mechanism is designed for sliding mode TENG, can it also be used for 
other TENG modes to boost the output performance? 
9. Environmental factors, such as humidity, have a great influence on the triboelectric output. Please 
discuss the influence of the humidity on the device’s output.