Enhancing Microbial Electrosynthesis of Acetate and Butyrate from CO₂ Reduction Involving Engineered Clostridium ljungdahlii with a Nickel-Phosphide-Modified Electrode

Microbial electrosynthesis (MES) is an emerging technology through which autotrophic microorganisms can directly uptake electrons or indirectly uptake electrons through H₂ in the cathode for reducing CO₂ to chemicals. In this study, the performance of MES with engineered Clostridium ljungdahlii was improved by electrochemically depositing a nickel phosphide (Ni–P) catalyst on the cathode. The acetate production rate of MES with 15 cycles was 0.17 g L^–1 day^–1, which was 1.7 times higher than that of MES without the catalyst. The corresponding butyrate production rate was remarkably enhanced at 0.1 g L^–1 day^–1, which was 2.5 times higher than that of MES without the catalyst. Electrochemical studies, scanning electron microscopy, and confocal scanning laser microscopy showed that Ni–P could accelerate the release of hydrogen and promote biofilm formation. These results also implied that more H₂ evolution could provide more reducing power for butyrate production in the presence of Ni–P. This study attempted to provide effective strategies for the accumulation of C₄ products in MES.