▎ 摘　　要

Willow leaf-like Mn3O4 nanoplates@graphene nanocomposites were synthesized using graphene instead of graphene oxide as initial materials with the assistance of supercritical CO2. The near-zero surface tension and the gas-like viscosity of supercritical CO2 favored the intercalation and dispersion of precursors among the graphene nanosheets. In addition, MnCl2 center dot 4H(2)O ultra-small nanoparticles with diameter of 1-3 nm were supported on graphene using MnCl2 center dot 4H(2)O as precursor, supercritical CO2 as solvent and methanol as co-solvent under very moderate conditions. It was also found that the specific capacitance of the MnCl2 center dot 4H(2)O ultra-small nanoparticles@graphene with a metal loading of only 12.4% was twice that of pure graphene. In addition, the capacitance retention ratio of the MnCl2 center dot 4H(2)O ultra-small nanoparticles@graphene composite decreased by only 5.4% when the cycle number increased from 200 to 1000.