Accelerating CO₂ conversion to volatile fatty acids using metal-organic framework–biocathode interfaces in microbial electrosynthesis

This study presents the development of an innovative biocathode using amine-functionalized bimetallic metal-organic framework (NH₂-UiO-66 Zr/Fe) coated on polypyrrole‑carbon cloth (PPy-MOF/CC) for enhanced microbial electrosynthesis (MES). The engineered electrode exhibited improved electrochemical performance under both abiotic and biotic conditions. When used in MES, the PPy-MOF/CC cathode achieved the highest average current density of 2.17 A/m² among all tested systems, supporting efficient conversion of carbon dioxide (CO₂) into acetate and isobutyrate with an equivalent chemical oxygen demand (COD) yield of 0.72 gCOD/L·d. This yield is higher compared to MES using PPy/CC and bare CC, which had average COD yields of 0.33 and 0.11 gCOD/L·d, respectively. The MES also achieved notable Coulombic efficiency (87 %) and carbon conversion efficiency (81 %). Cyclic voltammetry confirmed the superior bioelectrochemical activity of the PPy-MOF/CC cathode relative to the control biocathodes. These findings demonstrate the effectiveness of PPy-MOF/CC as a biocathode material for improving CO₂-to-VFA conversion in MES.