Technical photosynthesis involving CO2 electrolysis and fermentation

Solar-powered electrochemical reduction of CO2 and H2O to syngas, followed by fermentation, could lead to sustainable production of useful chemicals. However, due to insufficient electric current densities and instabilities of current CO2-to-CO electrolysers, a practical, scalable artificial photosynthesis remains a major challenge. Here, we address these problems using a commercially available silver-based gas diffusion electrode (used in industrial-scale chlorine–alkaline electrolysis) as the cathode in the CO2 electrolyser. Electric current densities up to 300 mA cm–2 were demonstrated for more than 1,200 hours with continuous operation. This CO2 electrolyser was coupled to a fermentation module, where the out-coming syngas from the CO2 electrolyser was converted to butanol and hexanol with high carbon selectivity. Conversion of photovoltaic electricity, CO2 and H2O to the desired alcohols achieved close to 100% Faradaic efficiency. Industrial production of useful and high-value chemicals via artificial photosynthesis is closer than expected with the proposed scalable hybrid system. The generation of useful chemicals from CO2 and renewable energy is an attractive—but challenging—endeavour. This work reports on the long-term operation of commercial electrodes for efficient CO2 reduction, with subsequent fermentation of the syngas product completing the technical photosynthesis of alcohols.