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 H2, that deliver reducing equivalents from the electrodes to the microbes. Here we report that the introduction of a biocompatible perfluorocarbon nanoemulsion as a H2 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 H2 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. H2 is a promising mediator of electrons from electrodes to microbes for chemicals production from CO2—but its low solubility limits the productivity. This work reports nanoemulsions as H2 carriers that improve the solubility and transfer kinetics of H2, increasing the productivity of the system.