Bioelectrochemical Power-to-Gas: State of the Art and Future Perspectives  Florian Geppert, Dandan Liu, Mieke van Eerten-Jansen, Eckhard Weidner, Cees Buisman, Annemiek ter Heijne  Trends in Biotechnology  Volume 34, Issue 11, Pages 879-894 (November 2016) DOI: 10.1016/j.tibtech.2016.08.010 Copyright © 2016 Elsevier Ltd Terms and Conditions

Figure 1 Schematic representation of a two-chamber methane-producing bioelectrochemical system (adapted from [23]). Typically, the anodic oxidation of water is coupled to the production of methane at the cathode. Trends in Biotechnology 2016 34, 879-894DOI: (10.1016/j.tibtech.2016.08.010) Copyright © 2016 Elsevier Ltd Terms and Conditions

Figure I (A) Overview of oxidation and reduction reactions for methane-producing bioelectrochemical systems (BESs). The standard electrode potential for each reaction was calculated from the Gibb's free energy [38] at standard conditions (1M or 1bar for all chemicals involved in the reaction, pH 7 and 298K). (B) Mechanisms of methane-producing BESs: 1, direct electron transfer for methane production by electrochemical reduction or catalyzed by methanogens (green ellipses); 2, mediated electron transfer for methane production via hydrogen generated by hydrogen-producing microorganism (orange ellipse); 3. mediated electron transfer for methane production via acetate (or formic acid) generated by acetate- (or formic acid-) producing microorganisms (violet ellipse). Trends in Biotechnology 2016 34, 879-894DOI: (10.1016/j.tibtech.2016.08.010) Copyright © 2016 Elsevier Ltd Terms and Conditions