Reed biochar is used as fuel of direct carbon fuel cells. KCl is the main impurity in raw reeds, which decreases the graphitization degree of biochar obtained from the pyrolysis of reeds, resulting in a high oxidation activity of the biochar. The reed char exhibits a straight hollow tubular structure, bringing about a high electronic conductivity of the anode. A single cell supported by a 610 mu m-thick Ce0.8Sm0.2O1.9-carbonate composite electrolyte layer with the reed char as fuel achieves a maximum power density of 378 mW cm(-2) at 750 degrees C. The cell with 0.04 g carbon fuel exhibits a discharge current density of 30 mA cm(-2) for 3 h. The producing rates of CO and CO2 in the anode under various discharge currents are examined. (C) 2019 The Electrochemical Society.