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The use of bioelectrodes helps diminishing the overpotential in both, anode and cathode. The reduction of CO₂ to CH₄ and acetic acid follows metabolic pathways that depend on the cathode potential. Jiang et al. [171] reported that exclusive formation of methane and hydrogen was obtained in the range from −850 to −950 mV, whereas the simultaneous formation of CH₄, H₂ and acetate occurred in potentials more negatives than −950 mV.

Cathode potentials have been compared by Blanchet et al. [79]. The authors tested −0.36 and −0.66 V/SHE, finding that the former potential was appropriate for CO₂ reduction whereas the second potential resulted in hydrogen production in addition to CH₄. Thus, acetate was produced in an amount of 244 mg L⁻¹. In the same way, Siegert et al. [172] observed that methane production increased with more negative cathode potential in the order −650 mV > −600 mV > −550 mV. The products recovered were CH₄, acetate and some cases formate.

Co-products are expected in MECs, which represent another advantage if they are high value-added metabolites. For instance, acetate has been produced in a membrane-less system at potentials lower than −1.0 V/SHE, but by varying the potential to −0.4 V, the production increased to 600 mg L⁻¹ in 9 days [173]. Similarly, Nie et al. [174] obtained 540 mg L⁻¹ after 8 days, and Marshall et al. [175], using graphite granules at −0.59 V/SHE, produced up to 10,500 mg L⁻¹ over 20 days.