Abstract A graphene quantum dots (GQDs)-reinforced nickel-based composite coating was electrodeposited on the surface of a copper plate with a supercritical carbon dioxide fluid (SC-CO 2)-assisted DC power supply. The effect of the current density on surface morphology, microstructure, average grain size, hardness, and corrosion resistance of the resulting coatings was investigated in detail. It was found that the GQDs composite coating showed a more compact surface, a smaller grain size, higher microhardness, and stronger corrosion resistance than the pure Ni coating produced in SC-CO 2 and a texture coefficient indicative of a (111) preferred orientation. When the current density was 8 A/dm 2, the surface morphology of the GQDs composite coating showed a high density, and the grain size was about 23 nm. In addition, the micro-hardness and corrosion resistance of the GQDs composite coating was greatly improved compared with those of the pure nickel coating; at the same time, its wear rate, friction coefficient, and self-corrosion current density were decreased by 73.2%, 17.5%, and 9.2%, respectively. Keywords: supercritical electrodeposition; GQDs; current density; microstructure; performance