 Thus in Step 1, S1 was turned on and S2 was turn off to measure QSC,max; if QSC,max is lower than the expected value, additional triboelectrification process is conducted to approach that.And then in Step 2, x was set into a certain value, and the short-circuit charge transfer QSC(x) at a certain x was measured by coulometer Q1.In step 3, S1 was turned off, S2 was turn on, and then the TENG2 was triggered to supply high-voltage output for TENG1.