No abstract

The fluctuation and decentralization of renewable energy have triggered the search for respective energy storage and utilization. At the same time, a sustainable bioeconomy calls for the exploitation of CO as feedstock. Secondary microbial electrochemical technologies (METs) allow both challenges to be tackled because the electrochemical reduction of CO can be coupled with microbial synthesis. Because this combination creates special challenges, the electrochemical reduction of CO was investigated under conditions allowing microbial conversions, that is, for their future use in secondary METs. A reproducible electrodeposition procedure of In on a graphite backbone allowed a systematic study of formate production from CO with a high number of replicates. Coulomb efficiencies and formate production rates of up to 64.6±6.8 % and 0.013±0.002 mmol h cm , respectively, were achieved. Electrode redeposition, reusability, and long-term performance were investigated. Furthermore, the effect of components used in microbial media, that is, yeast extract, trace elements, and phosphate salts, on the electrode performance was addressed. The results demonstrate that the integration of electrochemical reduction of CO in secondary METs can become technologically relevant.

Power-to-X technologies have the potential to pave the way towards a future resource-secure bioeconomy as they enable the exploitation of renewable resources and CO 2. Herein, the coupled electrocatalytic and microbial catalysis of the C 5polymer precursors mesaconate and 2S-methylsuccinate from CO 2 and electric energy by in situ coupling electrochemical and microbial catalysis at 1 L-scale was developed. In the first phase, 6.1 � 2.5 mm formate was produced by electrochemical CO 2 reduction. In the second phase, formate served as the substrate for microbial catalysis by an engineered strain of Methylobacterium extorquens AM-1 producing 7 � 2 μm and 10 � 5 μm of mesaconate and 2S-methylsuccinate, respectively. The proof of concept showed an overall conversion efficiency of 0.2 % being 0.4 % of the theoretical maximum.

The coupling of electrochemical CO 2 reduction to formate with the microbial biosynthesis of valuable products is promising for exploiting CO 2 as well as to store excess renewable electricity. Here, electrochemical CO 2 reduction to formate at bioprocesscompatible conditions was transferred from the scale of 50 mL electrochemical cells to 1 L electrobioreactors. In the 1 L electrobioreactor, a reproducible coulombic efficiency of 74.9 � 5.5 % and formate production rate of 0.038 � 0.005 mmol h À 1 cm À 2 could be achieved. Autoclaving by standard steam sterilization was shown to negatively affect the reliability of the process performance and, therefore, needs further investigation. However, mass transfer is not limiting for the process performance. Thus, the coupling of electrochemical CO 2 reduction to formate with microbial biosynthesis in sterile conditions at technical scale can be targeted in the future.[a] Dr.

We propose a cheap, time and resource efficient screening and upscaling strategy for microbiome-based production of bio-based fuels and chemicals.