Solid state electrochemistry of direct carbon/air fuel cells

In direct carbon fuel cells (DCFCs), elemental carbon is electrochemically oxidized 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 biocarbon fuel sources and the opportunity for scale-up. Here we discuss a DCFC which utilizes 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°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 1 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.