Abstract: Carbon dots (CDs) have attracted increasing attention due to their high specific surface area, good dispersion, abundant surface functional groups, low biotoxicity and photoluminescence. However, their preparation on a large-scale is still a great challenge because of the high cost and environmental problems, and this seriously limits their practical applications. Herein, carbonized corncobs were used as the starting material for the preparation of the CDs by electrochemical oxidation. Their natural porous structures with well-developed channels allow the electrode to be filled with electrolyte, and the electrochemical oxidation takes place both on the inside and outside surfaces of the carbonized corncob, achieving a CD output of 79.8 mg h⁻¹ per gram of electrode material at 1 A. The CDs were combined with graphene oxide (GO) to produce CD/rGO composite aerogels by a hydrothermal method. After heat treatment at 600 °C, the materials obtained were used as the anode in a sodium ion battery, which had a capacity of 263.3 mAh g⁻¹ after 1 000 cycles at 1 A g⁻¹. This work suggests a new way to prepare CDs and possibly expand their range of application.