Effects of surface modification on the reactivity of activated carbon in direct carbon fuel cells

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 μm-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 °C.