The direct carbon fuel cell (DCFC) is a special type of high temperature fuel cell which allows direct conversion of the chemical energy of different carbon materials into electricity. The thermodynamic efficiency of this process is high, and thus the overall conversion efficiency has the potential to exceed these of other fuel cell concepts. Until now the most developed DCFC-systems are based on molten carbonate or hydroxide as electrolyte. In this publication we show that also for a system with a solid electrolyte such as in solid oxide fuel cells (SOFC), which suffers, in principle, from limited contact between the solid fuel and the solid electrolyte, significant conversion rates can be achieved at such interfaces. The principal aspects of the direct electrochemical conversion of carbon powders in an SOFC-system have been investigated in the temperature range of 800 C to 1000 C. It has been shown that using a flat planar anode, carbon conversion rates exceeding 100 mA cm À2 are possible. Different solid fuels have been investigated in order to determine the influence of carbon properties on the electrochemical conversion.

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Direct carbon fuel cells (DCFCs) are high temperature fuel cells which offer the possibility to directly convert the chemical energy of carbon materials (e.g. coal, lignite, char, carbonized biomass) into electricity. In addition to using solid carbon fuels, higher overall efficiencies should be possible because the thermodynamic efficiency is close to 100 %. This means higher than those of conventional fuel cell types for gaseous fuels. DCFC technology can employ three different electrolyte types: Molten carbonate electrolyte (liquid salt), molten hydroxide electrolyte (liquid salt) and solid oxide electrolyte (solid ceramic layer). Recently, also combined technologies have been developed. In this chapter, all the concepts are described and their advantages and difficulties are discussed.