Graphene-Graphene Oxide Interfaces Enable Moisture-Tolerant Solid Lubrication

Protecting sliding surfaces from friction and wear remains a persistent engineering challenge. Graphene oxide (GO) and pristine graphene (PG), the two different carbon-based 2D materials, are attractive solid-lubricant coatings, but both are compromised by moisture. GO readily forms a protective transfer layer at the sliding contact through the reactive, adhesive chemistry of its oxygen-containing functional groups. These same groups, however, make it hydrophilic and humidity-sensitive, resulting in moisture-driven failure. PG is hydrophobic and chemically stable, yet its inert basal plane cannot sustain a persistent transfer layer, so it also loses durability under prolonged sliding in a humid environment. Here, we show that blending GO and PG, exploiting the compositional flexibility of solution-processed 2D coatings, turns this shared moisture vulnerability into a tunable design parameter. Across the full GO:PG composition range, the blended coatings sustain stable, low-friction sliding at humid sliding conditions, where both parent materials fail. In all cases, the improvement comes from keeping the carbonaceous transfer layer intact. GO and PG achieve this through complementary roles. In GO-rich blends, PG mitigates the moisture-induced failure of the GO-driven transfer layer against moisture, while in PG-rich films, GO enables the transfer-layer formation that PG alone cannot achieve. Representative GO-rich and PG-rich blends outperform their parent materials by one to two orders of magnitudes under the same humid conditions. The moisture sensitivity of graphene-derived coatings is therefore not a fixed material property but a compositionally tunable outcome, offering a practical route to moisture-tolerant solid lubrication.