One-pot interfacial charge programming of α‑Ni(OH)2 nanosheets via cation engineering: Intercalation-ionization dual effects enabling superior lubrication

One‑pot cation intercalation and interfacial charge programming for α‑Ni(OH)₂ nanosheets. • Unique intercalation‑ionization dual effects expand interlayer spacing and reverse surface charge polarity. • Central heteroatoms (N vs. P) dictate heterolytic vs. homolytic tribochemical pathways. • Ni‑P additive achieves 64.4% friction reduction, 95.1% anti‑wear and 500 N load‑carrying capacity. Layered metastable α-Ni(OH) 2 is a promising lubricant additive due to its tunable interlayer chemistry, yet its intrinsic thermodynamic instability and weak positive surface charge severely hinder interfacial adhesion, oil dispersion and tribological performance. Herein, we develop a facile one-pot interfacial charge programming strategy via cation engineering to modify α-Ni(OH) 2 nanosheets, using tetrabutylammonium hydroxide (TBAOH) and tetrabutylphosphonium hydroxide (TBPOH) as trifunctional alternatives versus NaOH to accomplish Ni 2 ⁺ precipitation, organic cation intercalation and surface charge polarity transition, simultaneously. Compared to traditionally fabricated Ni-Na, the intercalated Ni-N (TBA + ) and Ni-P (TBP + ) exhibit expanded interlayer spacings, exfoliated thin flexible nanosheets, increased specific surface areas and negative surface potentials. Utilized as additives in PAO 10, the intercalation-ionization dual effects leverage molecular rollers, electrostatic anchoring and tribochemical film formation. Combined with multiple characterizations and theoretical calculation, this work reveals that the distinct chemical and electronic properties of the central N/P atoms in TBA + and TBP + leads to preferential heterolytic cleavage for Ni-N and homolytic cleavage for Ni-P under nanoconfinement, friction, and possible Ni-catalyzed conditions, which governs the evolution pathway and final composition of the interfacial tribofilm. As a result, Ni-P delivers the optimal friction-reducing (64.4%), anti-wear (95.1%), load-carrying capacity (500 N), and long-term durability. This work clarifies the structure-tribology relationship governed by intercalation-ionization dual effects, and provides a novel strategy for designing high-efficiency layered lubricant additives. Download: Download high-res image (327KB) Download: Download full-size image