Roles of sliding-induced defects and dissociated water molecules on low friction of graphene

Abstract

Sliding contact experiments and first-principles calculations were performed to elucidate the roles of structural defects and water dissociative adsorption process on the tribo-chemical mechanisms responsible for low friction of graphene. Sliding friction tests conducted in ambient air and under a dry N2 atmosphere showed that in both cases a high running-in coefficient of friction (COF) occurred initially but a low steady-state COF was reached only when the sliding was continued in air with moisture. Density functional theory (DFT) calculations indicated that the energy barrier (E b) for dissociative adsorption of H2O was significantly lower in case of reconstructed graphene with a monovacancy compared to pristine graphene. Cross-sectional transmission electron microscopy of graphene transferred to the counterface revealed a partly amorphous structure incorporating damaged graphene layers with d-spacings larger than that of the original layers. DFT calculations on the reconstructed bilayer AB graphene systems revealed an increase of d-spacing due to the chemisorption of H, O, and OH at the vacancy sites and a reduction in the interlayer binding energy (E B) between the bilayer graphene interfaces compared to pristine graphene. Thus, sliding induced defects facilitated dissociative adsorption of water molecules and reduced COF of graphene for sliding tests under ambient and humid environments but not under an inert atmosphere.

Origin of the catalytic activity at graphite electrodes in vanadium flow batteries

“…The major part consists of hydroxyl groups formed at basal planes, whereas carbonyls and carboxylic groups develop at edge sites. 34,81,82 This is consistent with the decrease of the D-parameter (from 19 to 17, Figure 6b), which we ascribe mostly to the formation of oxygen groups at edges or defects of the sp 2 planes, resulting in sp 3 carbon-oxygen bonds. The higher amount of oxygen is also observed in the increased σ(C-O) signal of the O 2s region in the valence band spectra (Figure S13).…”

A review of recent advances in tribology

“…The dependence of frictional behavior on the interfacial atomic architecture and morphological corrugation has been confirmed by independent studies. Yang et al [709] have elucidated the roles of structural defects and water adsorption in the running-in process, showing that the chemisorption of H, O, and OH at the defect sites will reduce the interlayer binding energy of bilayer graphene, which accounts for the coefficient of friction reduction of graphene sliding under humid environments. A recent DFT calculation indicates that the atomic scale topography and corresponding potential corrugation would be affected by chemical modifications, e.g., when a fluorinated h-BN layer slides against fluorinated h-BN/Ni (111) substrate, a smooth potential corrugation is obtained [710].…”

Reduced graphene oxide–coated anode gas diffusion layer for performance enhancement of proton‐exchange membrane fuel cell

“…Graphene as a coating material for GDLs has to owe to its excellent electron conductivity, high mechanical strength, and good chemical stability . However, pure graphene is inert in nature and is highly hydrophobic . Graphene oxide (GO) has numerous oxygen‐containing functional groups and is highly hydrophilic, but it is a strongly insulating material and hence cannot be used to coat GDLs .…”

“…[15][16][17] However, pure graphene is inert in nature and is highly hydrophobic. 18 Graphene oxide (GO) has numerous oxygen-containing functional groups and is highly hydrophilic, but it is a strongly insulating material and hence cannot be used to coat GDLs. 19 Reduced graphene oxide (RGO), produced by the chemical reduction of GO, combines the advantages of both graphene and GO, such as residual oxygen-containing functional groups, good chemical stability, and high surface area.…”