Investigation on the tribological properties and electrification performance of grease-lubricated triboelectric nanogenerators

Compared with lubricating oil, grease can firmly adhere to the lubricated surface without loss even on the vertical surface, which is more conducive to improving the durability of triboelectric nanogenerators (TENGs) in practical engineering applications by reducing material wear. However, the correlation between property parameters of grease and triboelectrification is still unclear. In this paper, rotary freestanding TENG with the most severe wear among the working modes of TENGs is taken as the research subject. First, the tribological properties and electrification performance of TENGs lubricated by different greases are studied, and then the effects of the dielectric constant, shear-thinning behavior and cone penetration on the electrical output as well as durability of TENG are explored to reveal the triboelectrification mechanism of the grease-lubricated interface. The results show that, the electrical output of TENG lubricated by the grease with a low dielectric constant can increase by more than 3.5 times compared to dry friction, where the thickener in the grease participates in triboelectrification at the grease-lubricated interface. With increasing sliding distance, the electrical output increases first and then decreases, and the durability is related to the shear-thinning behavior of grease. For greases with similar relative dielectric constant, with increasing cone penetration, the maximum electrical output of TENG decreases, but its durability is improved. This study provides a new approach to improve the electrical output and durability of TENG simultaneously, which further promotes the practical applications of TENGs.