Fluidized Bed Cathodes Enable High-Rate CO2 to Formate Production and In Situ Microbial Growth

Electrochemical CO2 Reduction Reaction (eCO2RR) to formate offers a sustainable and promising route for storing renewable electricity in a microbial energy substrate. Conventional CO2 electrolyzers rely on flat electrodes with limited catalytic surface area, mass-transfer constraints, and electrolytes that are incompatible with microbial growth, preventing direct coupling of electrochemical formate production with biological conversion. Here, we developed a biocompatible CO2 electrolysis configuration that uses fluidized particles of Sn, Bi, and In as electrocatalysts to enhance CO2 to formate conversion while supporting microbial utilization in the same chamber. The fluidized configuration enabled high formate production rates up to 0.24 mmol cm2 with Faradaic efficiencies of 86 to 92%, representing a two fold improvement over static electrodes. The system also achieved a carbon conversion efficiency of 42%, approaching the theoretical limit for co-generation of formate and bicarbonate. Importantly, electrolysis was performed in a biocompatible medium that supported direct in situ cultivation of Cupriavidus necator within the cathode chamber using only electricity and CO2/O2 as fed substrates. C. necator continuously consumed electro-generated formate for 5 to 6 days under aerobic conditions, demonstrating integrated CO2 to biomass conversion. This work establishes a fluidized electrocatalytic platform for simultaneous electrosynthesis and microbial upgrading in a single reactor, providing a scalable strategy for renewable carbon fixation and sustainable biomanufacturing.