# Unique Triboelectric Nanogenerator Using Carbon Nanotube Composite Papers
## 4 Discussion
### Future Issues  
In this study, the feasibility of triboelectricity generation using the CNT composite paper was confirmed. In addition, the optimal amount of CNTs required to create a CNT composite paper and the conditions of the pulp material were examined. Although an effective method to improve the output could not be found, it may be possible to improve the output by optimizing the amount of CNTs and compositing pulp. According to the results obtained in this study, the challenge is to establish a more direct and efficient method of improving the output. The core materials involved in triboelectric power generation in this study were considered to be the paper (pulp) and aluminum, which are relatively close in the triboelectric series of the paper. Therefore, the specific optimization conditions regarding the amount of CNTs, the pulp material, and the mixing ratio of pulp material required to improve the output will be studied. In addition, although it was confirmed that the triboelectricity performance of the CNT composite paper did not decline for approximately 30 min, it is necessary to evaluate how TENGs operate over longer timescales and with repeated use in the next stage of our research. In this study, the measured voltages as outputs were also discussed. We should extend the discussion to the output power for the TENGs with the CNT composite paper. Actually, the power estimates can be derived by the equation \(P=V^{2}/R\) or by the integral formula corresponding to the time variation of the voltage. For example, using the RMS value of the voltage obtained from Sample 5 above, 36.21 nW can be derived with 1 M\(\Omega\) of the load resistance. If we also use the RMS value obtained from Sample 3, which is the largest voltage obtained, we can derive 83.39 nW (the power estimations based on the other measured values are given in the Supplementary Materials (Tables S1-S3)). As we have already explained, the CNT composite paper is a non-uniform material, including locally large variations in resistance (on a fine scale, they have a mixture of surfaces that are advantageous for triboelectric power generation (pulp area) and surfaces that can easily collect the generated charge (CNT network area), etc.). Since we considered it necessary to examine whether it is acceptable to estimate power in the same way as other TENGs using plain materials, we discussed the results of the actual measured voltages in this study. In addition to them, there were several samples that did not show clear triboelectric signals in this study. That is, not only pulse-like outputs but also outputs with some width were observed (e.g., samples 1 and 5 in Figure 9). To consider the cause of this, we prepared new CNT composite papers with higher resistivity values by reducing the amount of CNTs and measuring them. Specifically, two types of the CNT composite papers were prepared with 3 mg of SG101-CNT and 100 mg and 200 mg of pulp. These are samples with 1/5 the amount of contained CNTs of samples 1 and 5 in the paper, respectively. The measured outputs and data are given in the Supplementary Materials (Figures S3 and S4 and Table S4). As a result, a noise signal with an amplitude of approximately \(\pm\)50 mV was observed. In the measurement, the signal was observed with the CNT composite paper set in the apparatus in contact with the electrode and kept stationary without tapping. The amplitude of the observed noise was approximately the same as the small amplitude signal seen between the peaks, as shown in Figures 5, 7 and 9. Therefore, the periodic peaks with large amplitude shown in the figures can be considered to originate from triboelectric generation. Then, focusing on these large positive and negative peaks that approximately matched the tap period, we believe that a clear triboelectric peak was observed. In addition, a comparison of Figure S4a,b shows that the peaks appear in roughly the same positions, and from this point of view, it can be concluded that the peaks originate from the tapping apparatus.