In direct carbon fuel cells (DCFCs), elemental carbon is electrochemically oxidised 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 fully renewable solid bio-carbon fuel sources 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 small cells working as semi-fuel cells has been successfully demonstrated over an extended temperature range (525-900 degrees C) using a range of carbons derived from fossil, renewable and waste sources. Preliminary mechanistic studies demonstrate open circuit voltages (OCVs) well in excess of I V and indicate that direct oxidation and Boudouard conversion both contribute to the conversion process, with the dominant process changing with both temperature and extent of molten electrode/electrolyte component. (C) 2008 Elsevier B.V. All rights reserved.