Perfluorocarbon nanoemulsion promotes the delivery of reducing equivalents for electricity-driven microbial CO2 reduction

Combining inorganic catalysts with CO2-fixing microorganisms has displayed a high efficiency for electricity-driven CO2 reduction. However, the maximum throughput can be limited by the low solubility of mediators, such as H-2, that deliver reducing equivalents from the electrodes to the microbes. Here we report that the introduction of a biocompatible perfluorocarbon nanoemulsion as a H-2 carrier increases the throughput of CO2 reduction into acetic acid by 190%. With the acetogen Sporomusa ovata as a model system, an average acetate titre of 6.4 +/- 1.1 g l(-1) (107 mM) was achieved in four days with close to 100% Faradaic efficiency. This is equivalent to a productivity of 1.1 mM h(-1), among the highest in bioelectrochemical systems. A mechanistic investigation shows that the non-specific binding of perfluorocarbon nanoemulsions promotes the kinetics of H-2 transfer and subsequent oxidation by more than threefold. Introducing nanoscale gas carriers is viable to alleviate throughput bottlenecks in the electricity-driven microbial CO2 reduction into commodity chemicals.