# Unique Triboelectric Nanogenerator Using Carbon Nanotube Composite Papers
## 2 Materials and Methods
### Construction of and Experiments on TENG Based on CNT Composite Papers  
In this section, the fabrication of and experimental methods using the proposed TENG are described. As explained in the Introduction, a TENG requires two materials. In this study, the TENG is constructed using the CNT composite paper, as described in Section 2.1, as well as aluminum plates. The proposed TENG generates electricity by periodically creating contact and separation between the aluminum electrode and the CNT composite paper. In order to quantitatively evaluate the output voltage, an apparatus (Figure 3) that can create such contact and separation at a constant speed is used in this study. A schematic of the experimental setup used is shown in Figure 4. In the apparatus, the rotation of a motor placed at the top is converted into linear (up-and-down) motion by a crank. One end of the crank is connected to an aluminum electrode plate, which periodically establishes contact with and separates from the CNT composite paper. By controlling the voltage applied to the motor, the rotational speed of the motor can be controlled, resulting in a change in the speed of contact and separation. To supply a DC voltage to the motor, we use a DC stabilized power supply (Agilent, E3630A, Agilent Technologies, Inc., Santa Clara, CA, USA). In the experiment, resistance of 1 M\(\Omega\) is applied as a load, and the voltage at both ends of the load resistance is measured with a digital oscilloscope (IWATSU, DS-5105B, IWATSU Electric Co., Ltd., Tokyo, Japan). As the CNT composite paper contains many paper fibers, the top surface of the paper is expected to be negatively charged, and the aluminum plate is expected to be positively charged across the triboelectric series of paper and aluminum [2]. On the other hand, one side of the CNT composite paper is fixed to the other aluminum electrode, as shown in Figure 4. In the contact process, the contact interface of aluminum will be biased positively, and the oscilloscope probe side will be  
Figure 4: Schematic of the experimental system. Figure 3: Apparatus for demonstration of the proposed TENG. biased negatively. Also, the contact interface of the CNT composite paper will be biased negatively, and the probe side will be biased positively. Therefore, a negative peak will be seen in the contact process because the negative current will flow to the oscilloscope. In the separation process, the reverse of the contact process will occur, and the positive current will flow to the oscilloscope. As a result, a positive peak will be seen in the separation process. In this experiment, the aluminum electrode on the bottom side is used as a reference, as shown in Figure 4.  
In the experiment, the output data often contain a large amount of noise. To remove the noise from the obtained output data, a Fourier transform is used. Then, the RMS of the waveform without the noise is calculated to obtain the output, and it is evaluated. For the evaluation, the proposed TENG device was constructed. Firstly, four types of CNT composite paper were prepared using the method described in Section 2.1 to clarify the role of CNTs in the proposed TENG. Here, the CNTs SG101-CNT (ZEON CORPORATION, Tokyo, Japan), (6,5)-chirality CNT (CHASM, SG65i), and (7,6)-chirality CNT (CHASM, SG76, CHASM Advanced Materials, Canton, MA, USA), which are single-walled and have semiconducting properties, were prepared. In addition, NC7000 (Nanocyl SA, Sambreville, Belgium), which is multi-walled and has metallic properties, was also used. To prepare the CNT dispersions as described in step 2 of the method presented in Section 2.1, 15 mg each of the chosen CNTs, 100 mg of sodium dodecyl sulfate (SDS, Nacalai Tesque, Inc., Kyoto, Japan) as a dispersant, and 20 mL of pure water were used. In addition, to prepare the pulp dispersion for step 4 of the method given in Section 2.1, 100 mg of pulp material and 100 mL of pure water were used.