Nickel-Coated ceramic hollow fiber cathode for fast enrichment of chemolithoautotrophs and efficient reduction of CO2 in microbial electrosynthesis

• Membrane cathode made via electroless plating showed excellent hydrogen evolution. • High recovery of acetate was feasible via microfiltration through membrane cathode. • Fast enrichment of chemolithoautotrophs was achieved via biomass microfiltration. • Acetate production was enhanced with higher H 2 supply and thicker biocathode. Microbial electrosynthesis (MES) explores the potential of chemolithoautotrophs for the production of value-added products from CO 2 . However, the enrichment of chemolithoautotrophs on a cathode is relatively slow and the separation of the products is energy intensive. In this study, a novel and multifunctional cathode configuration, enabling the simultaneous enrichment of chemolithoautotrophs and separation of acetate from MES, was developed through one-step electroless nickel plating on ceramic hollow fiber (CHF) membrane. A thick layer of chemolithoautotrophs with 5.2 times higher cell density, which was dominated by Sporomusa (68% of the total sequence reads in biocathode), was enriched on the membrane cathode surface through suspended biomass microfiltration compared to MES reactors operated without filtration. Simultaneously, more than 87% of acetate (31 mM) per batch could be harvested after catholyte microfiltration. The Ni content was >80% on the CHF surface after long-term operation in the two-chamber MES system, which exhibited 78% lower charge transfer resistance compared to three-chamber MES system (∼110 vs 510 ohms) for acetate separation/extraction. The ease of product separation in two-chamber MES systems and the fast establishment of chemolithoautotrophs on the cathode is a step forward in realizing MES systems as a promising platform for CO 2 reduction and biochemical production in a circular carbon bioeconomy.