The electron transfer mechanism between metal and amorphous polymers in humidity environment for triboelectric nanogenerator

Humidity tends to deteriorate the output performance and the stability of triboelectric nanogenerator (TENG). However, the microscopic mechanism of how water molecules adsorbed on the surface affect electron transfer in the metal-amorphous polymer contact electrification of TENG remains elusive. Here in order to investigate the effect of humidity on the electron transfer process between metal-amorphous polymer in TENG, we employ first-principles calculations to study the typical material pair Al- polyethylene (PE). We find that water molecules adsorbed between the interfaces replace the original electron donor Al in the electron transfer between Al/PE pair, providing the electron to the LUMO (lowest unoccupied molecular orbital) of PE and the surface atoms of Al and reducing the amount of charge transfer for Al/PE pair. Most importantly, we demonstrate that the existence of hydrogen bonds makes water molecules the electron donor (positively charged) in metal/polymer interface, in which only the non-hydrogen bond H atom is the main electron donor. In addition, it is also found that the number of transferred charge is closely related to the number of electron donors, which can explain the declining trend of the amount of charge transfer. The gained insights provide a theoretical basis for the regulation of the contact electrification process and the design of TENG in humidity environment.