Electro-microbial CO2 conversion with C2 intermediates (EMC2): A Systematic approach to solar-driven carbon utilization

Abstract: Natural photosynthesis converts solar energy into chemical bond energy stored as biomass, with efficiencies below 1% in most terrestrial plants. This rate is incompatible with the decarbonization demands of a post-industrial society. To overcome this constraint, we present a fully integrated electro-microbial CO2 conversion (EMC2) platform that bypasses the kinetic limitations of Rubisco-based carbon fixation by coupling electrocatalytic CO2 reduction (CO2RR) with engineered microbial bioconversion. The EMC2 strategy centers on soluble C2 intermediates (i.e., acetate and ethanol) as molecular bridges between the chemical and biological domains. Compared to C1 intermediates (i.e., formate and methanol) or hydrogen, C2 compounds offer faster mass transfer, higher energy and electron density, lower cellular toxicity, and broader compatibility with primary metabolic pathways. To fully exploit these advantages, we pursued a multi-layer design strategy spanning electrocatalysis, the chem-bio interface, and synthetic biology. On the electrochemical side, we systematically engineered electrolyte composition, electrode architecture, electrolyser configuration, and catalyst design to achieve selective electrochemical reduction of carbon dioxide (CO2 RR) to acetate and ethanol under conditions compatible with downstream biological processing. On the biological side, multi-module cellular engineering enhanced substrate utilization efficiency, reductant generation, and metabolic flux toward target products. This integrated design enabled continuous, high-productivity microbial biomass and polyhydroxyalkanoate (PHA) synthesis directly from CO2 . Biomass productivity surpassed C1- and hydrogen-based systems by 6- and 8-fold, respectively. Our synthetic biology modules produced medium-chain-length PHAs, which are biodegradable, bio-based polymers at record productivity and chain lengths unattainable via competing electro-bio platforms. Overall, the EMC2 system achieved 4.5% solar-to-biomass conversion efficiency, representing a multiple-fold improvement over natural photosynthesis (<1%).