Hexagonal boron nitride nanosheets (h-BNNs) show great potential in the field of tribology due to their typical two-dimensional layered structure and are essential for replacing conventional sulfur/phosphate-containing additives. However, the large particle size and poor dispersion of h-BNs seriously restrict their green lubrication application. In this paper, MnO2@h-BNNs nanocomposites were successfully prepared by ultrasonically exfoliating a hydrothermal method. The tribological properties of MnO2@h-BNNs nanocomposites as lubricant additives in poly- alpha-olefin oil (PAO) were investigated. The results show the oil dispersed with 0.25 wt% MnO2@h-BNNs had the best friction reduction and antiwear effect with 42% and 11.2% reduction, respectively, compared with the plain oil. Through further wear surface analyzing, we verified the antiwear mechanism of additives in filling the micropits and grooves on the wear surface and forming a friction protection film including Fe2O3, MnO2, and BN on the wear surface, avoiding direct contact between the friction subsets. This can provide ideas for other lubricating oil additives.
The slow kinetics of the oxygen evolution reaction (OER) is one of the significant reasons limiting the development of electrochemical hydrolysis. Doping metallic elements and building layered structures have been considered effective strategies for improving the electrocatalytic performance of the materials. Herein, we report flower-like nanosheet arrays of Mn-doped-NiMoO4/NF (where NF is nickel foam) on nickel foam by a two-step hydrothermal method and a one-step calcination method. The doping manganese metal ion not only modulated the morphologies of the nickel nanosheet but also altered the electronic structure of the nickel center, which could be the result of superior electrocatalytic performance. The Mn-doped-NiMoO4/NF electrocatalysts obtained at the optimum reaction time and the optimum Mn doping showed excellent OER activity, requiring overpotentials of 236 mV and 309 mV to drive 10 mA cm−2 (62 mV lower than the pure NiMoO4/NF) and 50 mA cm−2 current densities, respectively. Furthermore, the high catalytic activity was maintained after continuous operation at a current density of 10 mA cm−2 of 76 h in 1 M KOH. This work provides a new method to construct a high-efficiency, low-cost, stable transition metal electrocatalyst for OER electrocatalysts by using a heteroatom doping strategy.
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