Developing efficient carbon-based metal-free electrocatalysts can bridge the gap between laboratory studies and practical applications of CO2 reduction.However,along with the ambiguous understanding of the active sites in carbon-based electrocatalysts,carbon-based electrocatalysts with high selectivity and satisfactory stability for electroreduction of CO2 remain rare.Hera,using the nitrogen rich silk cocoon as a precursor,carbon-based electrocatalysts with intrinsic defects can be prepared for efficient and long-term electroreduction of CO2 by a simple two-step carbonization.The obtained electrocatalyst can catalyze CO2 reduction to CO with a Faradaic efficiency of ～ 89％ and maintain good selectivity for about 10 days.Particularly,our experimental studies suggest that in-plane defects are the main active sites on which the rate-determining step for CO2 reduction should be the direct electron transfer to CO2 but not the proton-coupled electron transfer.Further theoretical calculations consistently demonstrate that the intrinsic defects in carbon matrix,particularly the pentagon-containing defects,act as main active sites to accelerate the direct electron transfer for CO2 reduction.In addition,our synthetic approach can convert egg white into efficient catalysts for CO2 electroreduction.These findings,providing new insights into the biomass-derived catalysts,should pave the way for fabricating efficient and stable carbon-based electrocatalysts with catalytically active defects by using naturally abundant precursors.