  Transition metal dichalcogenide (TMD) coatings have attracted enormous
scientific and industrial interest due to their outstanding tribological
behavior. The paradigmatic example is MoS2, even though selenides and
tellurides have demonstrated superior tribological properties. Here, we
describe an innovative in-operando conversion of Se nano-powders into
lubricious 2D selenides by sprinkling them onto sliding metallic surfaces
coated with Mo and W thin films. Advanced material characterization confirms
the tribochemical formation of a thin tribofilm containing selenides, reducing
the coefficient of friction down to below 0.1 in ambient air, levels typically
reached using fully formulated oils. Ab initio molecular dynamics simulations
under tribological conditions reveal the atomistic mechanisms that result in
shear-induced synthesis of selenide monolayers from nano-powders. The use of Se
nano-powder provides thermal stability and prevents outgassing in vacuum
environments. Additionally, the high reactivity of the Se nano-powder with the
transition metal coating in the conditions prevailing in the contact interface
yields highly reproducible results, making it particularly suitable for the
replenishment of sliding components with solid lubricants, avoiding the
long-lasting problem of TMD-lubricity degradation caused by environmental
molecules. The suggested straightforward approach demonstrates an
unconventional and smart way to synthesize TMDs in-operando and exploit their
friction- and wear reducing impact.
