Fig. 2

Electric characteristics of FR-TENG and discharge, and optical emission spectra of N₂ corona discharge. a Circuit schematic measuring electric characteristics of triboelectric nanogenerator (TENG) and microplasma. The voltage, current and charge waveforms are measured using a high-voltage probe (HVP, Tektronix P6015A) and two electrometers (Keithley 6514, one for current, and the other for charge in different ranges), respectively. GND, electrical ground. Switching position 1, 2, and 3 means measurement of open circuit voltage, short circuit current and charge, and simultaneously electric characteristics with microplasma (as load), respectively. b, c Open circuit voltage and short circuit current of TENG with various rotational speeds. d–f Electric characteristic of dielectric barrier discharge (DBD) capillary plasma. d In five electric cycles voltage, current, and charge waveform. e In one electric cycle voltage, current, and charge waveform. There are three obvious discharges in the cycle. Arrows indicate the sequence of characteristics evolving. The number 1–3 and the blue gray bars correspond to three sequential discharges in (e). f Corresponding to e, Lissajous pattern of current–voltage and charge–voltage describing the circulation of characteristics in one full electric cycle. g–i Electric characteristics of microspark discharge, which are similar to d–f, respectively. However, voltage fluctuation in microspark discharge is more significant than DBD. In microspark discharge, the amplitudes of current and charge transferring through the electrodes gap are several orders higher than those in DBD. j Five-stage voltage multiplier circuit for converting AC to DC with high voltage, which is used in N₂ corona discharge. k, l Optical emission spectra of N₂ corona discharge. k Intensity of three spectral lines, voltage and current simultaneously change with time. The inset shows details of I/V around the time of t = 25.00 s. l Emission spectrum of N₂ 2nd positive system in UV–vis region at the time of t = 4.0 s (Ocean Optics Maya2000 Pro, 200–650 nm, integration time is 100 ms.)