Commercial development of the direct carbon fuel cell for low emission energy generation

The direct carbon fuel cell (DCFC) is promised as the most efficient method of generating electrical energy from carbonaceous fuels, including coal. Efficiencies of over 80% have been suggested along with several other attractive features compared to traditional coal fired power stations, including: generation of a pure carbon dioxide stream and the elimination of particulate, SOx and NOx emissions. Here, learnings from a two year demonstration project for the build and commission of a 1.0 kW DCFC system will be presented. The high temperature fuel cell uses tubular solid oxide ionic conductors (yttria stabilised zirconia) and a molten carbonate secondary electrolyte. In order to deliver the solid fuel to the electrode, a particulate slurry is utilitsed along with mesh current collectors in the first ever semi-continuous prototype of a direct carbon fuel cell. Challenges related to this technology are not trivial and include the corrosive nature of the molten salt utilised (ternary Li/Na/K carbonate eutectic), recovery of coal mineral matter from the anode reaction chamber, engineering issues related to high temperature integration and sealing of materials, and continuous delivery of fuel to the reaction chamber. Mass and energy balance modelling of the system has also suggested that the final efficiency of the system depends heavily on several competing factors within the fuel cell system, including a parasitic side reaction, boudouard gasification (C+CO2⇌2CO, note that CO can also contribute to electrochemical performance), and heat generation through resistive heating. This can result in significant energy penalties along with efficiency losses arising from fuel pre-treatment and method of electrical grid integration. The prospects of this technology moving forward will be discussed including highlights of the most pressing challenges related to materials fabrication, complexity of the design process and unit efficiency.