Macroscopic superlubricity of potassium hydroxide solution achieved by incorporating in-situ released graphene from friction pairs

Graphene (G), as a typical two-dimensional material, is often used as an additive for liquid lubricants. However, graphene is mostly added to liquid lubricants in a one-time manner in friction; it mainly exists in the form of multilayer agglomerated structures due to the π−π stacking between graphene sheets, making it unable to fully exert the synergistic lubrication function. Herein, we propose a new macroscopic superlubric system of graphene/potassium hydroxide (G/KOH) solution; and the graphene additive involved is exfoliated in-situ from graphene/epoxy (G/EP) friction pair by friction, continuously providing freshly-peeled graphene into KOH solution and minimizing the adverse effects of graphene agglomeration. Moreover, the in-situ produced graphene additive has thinner thickness and better anti-aggregation ability, which provide more graphene to accommodate OH − , form more stacked sandwich structures of OH − /graphene/OH − between friction pairs (i.e., equivalent to a moving pulley block with more wheels), and finally realize superlubricity. This study develops a new liquid superlubric system suitable for alkaline environments, and at the same time proposes a new way to gradually release graphene additives in situ , rather than adding them all at once, deepening the understanding to liquid superlubricity mechanism, and paving the experimental foundation for the practical application of macroscopic superlubricity.