Effect of Humidity on the Wear Behavior of Graphene Under Current Carrying Conditions

Wear problem has become an important issue limiting the functionality and lifetime of sliding electrical contact components. Adding conductive solid lubricants is a potential means of improving the tribological performance of these devices. Graphene, a two-dimensional material with excellent electrical conductivity and lubrication property, has been proposed to be a promising candidate for such applications. However, the tribological performance graphene has been demonstrated to be very susceptible to humidity even under non-current-carrying conditions. In this work, we study the effect of humidity on the wear behavior of graphene in the sliding electrical contact interfaces. The tribological behaviors of graphene under 10%, 30%, 60%, and 90% relative humidity conditions and 1 A current are investigated. The results show that the humidity can effectively slow down the wear of graphene in the sliding electrical contact interface by two key mechanisms. Firstly, as revealed by the infrared temperature measurements, higher humidity can significantly reduce the Joule heating. Secondly, X-ray photoelectron spectroscopy shows that with the existence of the electric current, at high humidity water molecules can passivate the graphene carbon dangling bonds more readily thereby reducing oxidation and slowing down the wear process. At low humidity, Joule heating not only caused graphene to oxidize but also accelerated the evaporation of water molecules, which was not conducive to its passivation, resulting in severe wear of the graphene.