One-dimensional (1D) transition metal phosphides (TMPs) with large specific surface areas,high charge transfer efficiency and excellent electrical conductivity have attracted significant attention in hydrogen evolution reaction (HER) as versatile and active catalysts.Herein,the sub-4 nm Mo-Co2P ultrafine nanorods (NRs) anchored on reduced graphene oxide (rGO) were successfully synthesized by a colloidal mesostructured strategy.Electrochemical test results reveal that the Mo-Co2P@rGO electrode exhibits superior activity with overpotentials of 204mV and Tafel slope of 88mV/dec for HER at 10mA/cm2,relative to the Co2P@rGO electrode in 0.5M H2SO4 solution.This improvement could be ascribed to the Mo doping,which results in more active sites,higher electrical conductivity and faster electron-transfer rates.This versatile strategy will provide a promising pathway for transition metal-doped compounds as an efficient catalyst.