Valorization of Carbon Dioxide by Electrocatalytic Reduction Coupled to Acetogens via Multiple Electron Carriers (ECat-acetogens)

The spatial decoupling of the electrochemical production of electron carriers from the microbial consumption in a suspension of acetogens in the cathode cell compartment has the potential of increasing the efficiency of the bioelectrochemical systems (BES) by two orders of magnitude compared to CO2 reduction via direct electron transfer to acetogens attached as a biofilm on a cathode. It may be the most promising approach with respect to energetic efficiency and the production of more reduced products by acetogens because of the use of multiple electron carriers (H2, CO and formate) produced electrochemically at a cathode in parallel. Improvements beyond the state-of-the-art are envisaged by the employment of larger electrodes of inexpensive CO2R electrocatalysts, utilized to increase the total reaction rate and by the replacement of the non-productive anode reaction with the formation of value-added hypochlorite solutions by saltwater oxidation. Formate is an intermediate in the reductive acetyl-CoA pathway of acetogens. There are two further advantages expected for such a system. No selective electrochemical CO2 reduction will be required since the bacteria are able to metabolize H2, CO and formate. As a consequence, biocompatible/non-bactericidal electrocatalysts free of precious metals can be used.

One main challenge for MES based on electroautotrophs is the design and operation of the microbial electrochemical reactors that are also known as bioelectrochemical systems (BES). BES can be one-chamber systems with anode and cathode facing the same solution or two-chambers systems, where both electrodes are separated by a membrane. In any case, oxygen evolving at the anode from water splitting that enters the cathode severely harms the obligate anaerobic bacteria. Thus, there is an urgent need to create solutions that allow future scaling and exploitation of electroautotrophic MES.

Project overview