Electrochemical performance of ceria-gadolinia electrolyte based direct carbon fuel cells

A direct carbon fuel cell offers a high efficiency alternative to traditional coal fired electrical power plants. In this paper, the electrochemical performance of electrolyte supported button cells with Gd2O3-doped CeO2 (CGO) electrolyte is reported over the temperature range 600 to 800 °C with solid carbon as a fuel and He/CO2 as the purge gases in the fuel chamber. The electrochemical characterisation of the cells was carried out by the Galvanostatic Current Interruption (GCI) technique and measuring V-I and P-I curves. Power densities over 50 mWcm-2 have been demonstrated using carbon black as the fuel. Results indicate that at low temperatures around 600 °C, the direct electrochemical oxidation of carbon takes place. However, at higher temperatures (800 °C) both direct electrochemical oxidation and the reverse Boudouard reaction take place leading to some loss in fuel cell thermodynamic efficiency and reduced fuel utilisation due to the in-situ production of CO. In order to avoid reverse Boudouard reaction whilst maximising performance, an operating temperature of around 700 °C appears optimal. Further, the electrochemical performance of fuel cells has been compared for graphite and carbon black fuels. It was found that graphitic carbon fuel is electrochemically less reactive than relatively amorphous carbon black fuel in the DCFC when tested under similar conditions.