In direct carbon fuel cells (DCFCs), elemental carbon is directly oxidised electrochemically to generate electrical power. Carbon is readily available, easily transported and stored and, therefore, affordable to the global energy economy. Further operational advantages include the use of a fully renewable solid bio-carbon fuel source and the opportunity for scale-up. Herein we discuss a DCFC which utilises a molten mixed alkali metal carbonate eutectic as a secondary electrolyte, contained within a solid oxide fuel cell. The operation of the cells over an extended temperature range (525-700 degrees C) was examined using standard electrochemical methods. We will present the electrochemical performance of Super S, a high surface area carbon black.