Bio-Electrocatalytic Application of Microorganisms for Carbon Dioxide Reduction to Methane.

We present a study on a microbial electrolysis cell with methanogenic microorganisms adapted to reduce CO to CH with the direct injection of electrons and without the artificial addition of H or an additional carbon source except gaseous CO . This is a new approach in comparison to previous work in which both bicarbonate and gaseous CO served as the carbon source. The methanogens used are known to perform well in anaerobic reactors and metabolize H and CO to CH and water. This study shows the biofilm formation of those microorganisms on a carbon felt electrode and the long-term performance for CO reduction to CH using direct electrochemical reduction. CO reduction is performed simply by electron uptake with gaseous CO as the sole carbon source in a defined medium. This "electrometabolism" in such microbial electrolysis cells depends strongly on the potential applied as well as on the environmental conditions. We investigated the performance using different adaption mechanisms and a constant potential of -700 mV vs. Ag/AgCl for CH generation at 30-35 °C. The experiments were performed by using two-compartment electrochemical cells. Production rates with Faradaic efficiencies of around 22 % were observed.