Microbial Electrosynthesis for Sustainable Polyhydroxybutyrate Production from CO₂ Using Bismuth Nanoparticles

Microbial electrochemical technologies (MET) are a promising approach that integrates electrochemical and microbial processes to convert CO 2 into value‐added chemicals. Herein, Cupriavidus necator is utilized to produce polyhydroxybutyrate (PHB) using electrochemically synthesized formate as the sole carbon source. Formate is generated via CO 2 reduction using a Bi‐based electrode in a physiological electrolyte, achieving concentrations of ≈40 mM with a production rate of 0.05 mmol h −1 cm −2 and the highest faradaic efficiency achieved up to 50.81%. Two MET configurations are evaluated: an integrated system, where CO 2 reduction and fermentation occur in a single reactor, and a drop‐in system, where electrochemically produced formate is collected and later is used for fermentation. The drop‐in system achieves the highest PHB production, reaching ≈340 mg L −1 within 24 h. By directly utilizing the formate‐containing electrolyte as a fermentation medium, this approach simplifies process integration, reduces purification steps, and improves compatibility between electrochemical and microbial systems. These findings highlight the potential of MET as a scalable platform for sustainable biopolymer production from CO 2 .