Dual Metal Active Sites and an Enhanced Electric Field Boosting CO2 Reduction to CH4 in an Electromethanogenesis System

An electromethanogenesis system incorporating CO2-reducing microorganisms and a cathode material offers a promising approach for CO2 fixation with improved thermodynamic efficiencies. However, low electron transfer rates at microorganism-cathode interfaces can limit CO2 conversion efficiency. A nanoarrays/bacteria hybrid system was proposed for bioelectrochemical reduction of CO2 to CH4. The hierarchical nanoarrays derived from metal-organic frameworks enhanced the CO2 conversion rate with the optimization of both a local electric field and Ni/Co dual metal active sites. Optimizing the electric field intensity (similar to 1.25-fold compared to bare CF) and introducing a heterojunction on the cathode material boosted the electron transfer and achieved a higher current density (maximum 10 A/m(2)) at -0.9 V (vs Ag/AgCl) for 9.6-fold CH4 production (697.9 mmol.day(-1).m(-2)) compared to the control. The dual metal active sites provided extra electron shuttles from a cathode to a microorganism to boost the electron transfer for methane production with a thicker (similar to 1.3-fold) and enhanced conductive EPS production (similar to 1.68-fold). A decreased internal resistance, a reconstituted microbial community, and an enhanced methane production rate indicated an increase in the microbial electron transfer between Methanobacterium and Clostridia, resulting in a selective bioelectroreduction (84%) of CO2 to CH4. This study suggests that nanointerface engineering in electromethanogenesis systems can effectively regulate selective CO2 reduction for new generation biogas projects.