High rate CO2 valorization to organics via CO mediated silica nanoparticle enhanced fermentation

Carbon dioxide (CO2) valorization to high energy density fuels presents an economically sound approach to directly couple waste mitigation with sustainable energy production, yielding tremendous environmental and societal benefits. Here, a new two-stage hybrid system was developed that pairs highly efficient electrochemical CO2 reduction (CO2-R) to carbon monoxide (CO) with acetogenic bacteria for the rapid production of green chemicals. This original design seeks to solve issues in mediator production and utilization evident in related studies. A progressive silver-based gas diffusion electrode with anion exchange membrane sustained current densities of 200 mA/cm2 for over 240 h at a time and produced CO at excellent Faradaic efficiencies of over 80% at a cell voltage ca. 3.2 V. The effluent gas from the CO2 electrolyzer was connected to a bioreactor containing Clostridium ljungdahlii where the blend of CO/CO2 was converted into a mixture of mainly acetate and ethanol. This demonstrates the first time this organism has been tested in a two-stage hybrid CO2-R system. Competitive acetate and ethanol production rates of 17.87 ± 7.1 and 3.23 ± 1.4 mg/L/h were achieved under autotrophic conditions. In addition, mercapto-modified silica nanoparticles were developed to increase gas mass transfer and resulted in 217% and 224% increases in acetate and ethanol production rates, respectively. This system presents a viable approach to produce sustainable fuels and chemicals in a process that exploits commercially scalable C1 electron carries.