Enhanced carbon dioxide reduction in microbial electrosynthesis using amine-functionalized metal-organic framework catalyst

Microbial electrosynthesis (MES) is a promising technology that can reduce carbon dioxide (CO₂) into valuable platform chemicals using microbial biocatalytic action. However, inefficient microbe-electrode interactions greatly reduce the current uptake by microbes, ultimately hampering the CO₂ reduction reaction. Therefore, this study aimed to enhance microbe-electrode interaction using amine-functionalized metal-organic framework (MOF) catalysts such as NH₂-UiO-66(Zr) and NH₂-UiO-66(Zr/Ni) on the cathode. Both abiotic and biotic cyclic voltammetry (CV) revealed the highest reduction current response from the NH₂-UiO-66(Zr/Ni)-modified cathode among the tested cathodes, such as NH₂-UiO-66, Pt-C, and unmodified cathode (control). Thus, the MES using the NH₂-UiO-66(Zr/Ni) cathode could achieve an acetic acid production rate of 1166 ± 31 mg/L·d at a coulombic efficiency of 76 ± 2 %, which was higher than the MES operations with NH₂-UiO-66(Zr) and without catalyst with corresponding values of 912 ± 12 mg/L·d and 67 ± 3 %, and 428 ± 13 mg/L·d and 56 ± 4 %, respectively. Biofilm analyses using scanning electron microscopy and confocal microscopy showed thick biofilm development on the NH₂-UiO-66(Zr/Ni) cathode with abundant live bacteria. The results suggest that the amine-functionalized MOF can enhance the interaction of microbes with the cathode, resulting in efficient and high-rate bioelectrochemical CO₂ reduction to valuable organic chemicals.