Here we report a series of classical molecular dynamics simulations for icosahedral Au nanoparticles with four different sizes in 1-Butyl-3-methylimidazolium tetrafluoroborate([C4mim][BF4])ionic liquids.Our simulation results reveal that the alkyl chains in thecationsare predominant to aggregate around the smallest Au13 nanoparticle,while theirimidazolium rings begin to dominatethe first solvation shells of larger Au55 and Au147 nanoparticles.However,the anions are found to make the same contribution as the imidazolium rings in the cations to the stabilization of largest Au309 nanoparticle.Above solvation structures of cations and anions around different Au nanoparticles are well consistent with the corresponding multi-shell radial electrostatic charge profiles.Such size-dependent stabilization mechanism of Au nanoparticles in [C4mim][BF4] ionic liquid can be attributed to the enhanced strength of interfacial hydrogen bonds(HBs)between cations and anions.The large Au nanoparticle can provide enough surface space to accommodatemore cations and anions than the small nanoparticle,which is favorable for the formation ofregular HB network in the first solvation shell.Accordingly,the rotational dynamics of cationsand anionsin the first solvation shell are found to be suppressed more significantly with the increase of particle size.The simulationresults in this work can be of great benefit for experimental scientists to understand the unique stabilization mechanismof various metal nanoparticlesin ionic liquids.