Microbial electrosynthesis for acetate production from carbon dioxide: innovative biocatalysts leading to enhanced performance

Production of chemicals has significant influence on the emission of greenhouse gases (GHG) in particular carbon dioxide (CO2), thereby contributing to the climate changes of our planet. There is a general acceptance that we need to reduce the emission of GHG on a global level to cope with these changes.

Production of chemicals utilization of CO2 as feedstock represents a sustainable alternative to many fossil derived products, which are non-renewable and have a strong negative impact on the environment. Microbial electrosynthesis (MES) is an emerging technique utilizing electrical energy for reduction of CO2.

In a MES reactor, microbial catalysts are acquiring electrons from an externally powered cathode to transform CO2 into multi-carbon chemical commodities. The direct acquisition of electrons enables the use of multiple renewable electricity-sources including solar, wind, biochemical oxidation processes, or surpluses electricity from the power grid.

Although MES is a promising approach, it is restricted by a low electron transfer rate from the cathode to a microbe as well as the CO2 reduction rate is insufficient for scaling up. The main objective of the present study was to increase the overall productivity of MES by identifying more efficient electroautotrophicmicrobial catalysts and developing better cathode materials.

The genus Sporomusa is known for its abilities to convert CO2 into acetate by MES. This study investigated the performance in MES of selected species of the Sporomusa genus including; Sporomusa ovata DSM-2662, Sporomusa ovata DSM-2663, Sporomusa ovata DSM-3300, Sporomusa acidovorans, Sporomusa malonica, and Sporomusa aerivorans.

In which, S. ovata DSM-2663 was identified the most productive MES microbial catalyst among the tested group. Furthermore, the study developed and tested novel cathode materials for application in MES including three-dimensional graphene functionalized carbon felt, freestanding and flexible graphene paper, and copper-reduced graphene oxide composite.

When the copper-reduced graphene oxide composite electrode was used as the cathode for S. ovata-driven MES, acetate production rates as well as current densitywere significantly increased to1708.3 ± 333.3 mmol d-1 m-2 and -20.4 ± 1.0 A m-2 which is almost 21.5 fold higher acetate production compared to unmodified copper foam electrode.

By identifying a better MES microbial catalyst and developing novel composite cathodes the electron transfer during MES as well as CO2 reduction into acetate was significant improved.