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Microbial electrosynthesis (MES) is a promising technology platform for the production of chemicals and fuels from CO₂ and external conducting materials (i.e., electrodes). In this system, electroactive microorganisms, called electrotrophs, serve as biocatalysts for cathodic reaction. While several CO₂-fixing microorganisms can reduce CO₂ to a variety of organic compounds by utilizing electricity as reducing energy, direct extracellular electron uptake is indispensable to achieve highly energy-efficient reaction. In the work reported here, <i>Rhodobacter sphaeroides</i>, a CO₂-fixing chemoautotroph and a potential electroactive bacterium, was adopted to perform a cathodic CO₂ reduction reaction via MES. To promote direct electron uptake, the graphite felt cathode was modified with a combination of chitosan and carbodiimide compound. Robust biofilm formation promoted by amide functionality between <i>R. sphaeroides</i> and a graphite felt cathode showed significantly higher faradaic efficiency (98.0%) for coulomb to biomass and succinic acid production than those of the bare (34%) and chitosan-modified graphite cathode (77.8%), respectively. The results suggest that cathode modification using a chitosan/carbodiimide composite may facilitate electron utilization by improving direct contact between an electrode and <i>R. sphaeroides</i>.