Macroscopic superlubricity of potassium hydroxide solution achieved by incorporating in-situreleased 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−πstacking 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-situfrom 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-situproduced 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.