Activated carbons (AC) pretreated with HNO3 and NaOH are investigated as the fuel of direct carbon fuel cells. HNO3 and NaOH treatments both increase the oxygen content and decrease the graphitization degree of AC. The amount of hydroxyl groups on the surface of AC increases after the treatments with HNO3 and NaOH, and then decreases during the subsequent heating process in an inert atmosphere. On the contrary, the carbonyl and quinone groups on the surface of the activated carbon remain stable during the heating process. The activated carbon treated with HNO3 shows the highest reactivity towards oxidation and reverse Boudouard reactions due to its lowest graphitization degree and highest oxygen content. The single cell with a 380 mu m-thick yttria stabilized zirconia layer as the electrolyte and the activated carbon treated with HNO3 as the fuel exhibits the lowest polarization and the highest maximum power density of 128 mW cm(-2) at 800 degrees C. (C) 2018 Elsevier Ltd. All rights reserved.