Microbial Electrosynthesis (MES) is emerging as a promising technology for the decarbonization of the economy. The use of CO₂ as a feedstock, i.e. through carbon capture and utilization, can create attractive business opportunities for the production of 3rd generation biofuels. Achieving highly efficient electron transfer from the cathode to microbes is one of the main challenges hindering the development of MES reactors. It is, therefore, essential to improve biofilm growth for enhanced electron-transfer during bioconversion.

In this study we show the first use of 3D bio-printing for microbial electrosynthesis systems, creating a “synthetic biofilm”, containing Sporomusa ovata. The synthetic biofilm greatly improves the acetate production rate while drastically decreasing start-up time. Using H-cell reactors, poised at -0.8 V vs Ag/AgCl, with a synthetic biofilm printed on a carbon cloth electrode, an average acetate productivity of 47±5.1 g⋅day^-1⋅m^-2 (0.31 ±0.55 g⋅L^-1⋅day^-1) with a maximum productivity of 104 g⋅day¹⋅m^-2 (0.68 g⋅L^-1⋅day^-1) was achieved. This is an order of magnitude higher than typical S. ovata production rates, and 2-3 fold higher than reactors using specialized cathodes. Start-up of MES reactors typically require days, whereas a high production rate was achieved almost directly after the start-up (±40 hours) using the synthetic biofilm. Cyclic voltammetry data showed H2 formation occurred at much higher potentials than in the control reactors, (approx. -550 mV vs. -950 mV for controls). Imaging showed that the synthetic biofilm allowed for dense growth of S. ovata cells at the cathode, increasing electron transfer efficiency and potentially improving the bio-catalyzation of H₂.