Abstract
Microbial electrosynthesis (MES) converts CO(2) into value-added products such as volatile fatty acids (VFAs) with minimal energy use, but low production titer has limited scale-up and commercialization. Mediated electron transfer via H(2) on the MES cathode has shown a higher conversion rate than the direct biofilm-based approach, as it is tunable via cathode potential control and accelerates electrosynthesis from CO(2). Here we report high acetate titers can be achieved via improved in situ H(2) supply by nickel foam decorated carbon felt cathode in mixed community MES systems. Acetate concentration of 12.5 g L(-1) was observed in 14 days with nickel-carbon cathode at a poised potential of -0.89 V (vs. standard hydrogen electrode, SHE), which was much higher than cathodes using stainless steel (5.2 g L(-1)) or carbon felt alone (1.7 g L(-1)) with the same projected surface area. A higher acetate concentration of 16.0 g L(-1) in the cathode was achieved over long-term operation for 32 days, but crossover was observed in batch operation, as additional acetate (5.8 g L(-1)) was also found in the abiotic anode chamber. We observed the low Faradaic efficiencies in acetate production, attributed to partial H(2) utilization for electrosynthesis. The selective acetate production with high titer demonstrated in this study shows the H(2)-mediated electron transfer with common cathode materials carries good promise in MES development.