Potentials and kinetics in electron uptake by Sporomusa ovata in microbial electrosynthesis

CO 2 conversion into fuels and chemicals with a Power to X like microbial electrosynthesis reactor (MES) is promising. The overpotential or energy loss in the electron uptake in experimental works with Sporomusa ovata appears high and modelling was attempted to determine theoretical overpotential and kinetics. A key parameter to deduce upfront was the unknown redox potential of the electron uptake system. Both parameters were determined in Nernstian-Tafel inspired modelling. The analysis started with recording an experimental reductive j-E curve incorporating potential loss transforming CO 2 into acetate with Sporomusa ovata by voltammetry. It was combined with an ideal Nernstian j-E curve (free of potential losses). The estimated redox potential of the electron uptake system was developed and found to be E RSys = 0.12 V Ag/AgCl (3 M KCl) indicating a cytochrome b or c (or another compound). The new fitting method was validated by Shewanella oneidenis parametrisation. The difference between the j-E curves led to a theoretical overpotential of η ′ = −0.29 V for acetogenesis with Sporomusa ovata . Tafel parameters were derived with a slope b = 0.186 V/decade ( R = 0.996) indicating a complex reaction, an exchange current j o = 0.065 μA/cm 2 , and a symmetry factor of α = 0.68. Applied CO 2 to acetate transformations were performed in a 50 mL MES reactor for kinetic verification by overpotential switches between η ′ = −0.76 to −0.96 V vs Ag/AgCl (3 M KCl). Global Coulombic efficiencies suffered from non-faradaic losses but peaked up to 84%. The study showed the utility of potential loss modelling when working with an unknown electron uptake system to enhance the kinetic understanding in performance optimisation for microbial electrosynthesis. • Theoretical overpotential determination in microbial electrosynthesis • Redox potential estimation of unknown electron uptake system • Tafel parameters of the kinetics in microbial electrosynthesis • Verification of theoretical kinetic parameters in processing