# Reducing Oxygen Stress and Improving Hydrogen Availability Boosts Microbial Electrosynthesis by Clostridium ljungdahlii

## TL;DR

Scientists improved a process that uses microbes to convert carbon dioxide into useful chemicals by reducing oxygen stress and boosting hydrogen availability.

## Contribution

A combinatorial approach using specific cathode and anode materials with controlled current regimes significantly enhances microbial electrosynthesis performance.

## Key findings

- Using a carbon fiber fabric cathode and nitrogen-flushed anodes achieved the highest acetate concentration of 12.44 g L−1.
- The maximum acetate production rate reached 0.6 g L−1 d−1, the highest reported for pure culture MES from CO2.
- The study shows that strict anaerobic MES has significant room for improvement at larger scales.

## Abstract

Microbial electrosynthesis (MES) holds great promise for converting carbon dioxide (CO2) into building blocks of the (bio)chemical industry. Its advancement is hindered by limited process control and an incomplete understanding of the oxygen (O2) stress response of biocatalysts or key engineering parameters like the availability of hydrogen (H2). With Clostridium ljungdahlii as a model acetogen for strict anaerobic MES from CO2, the effect of O2 stress and H2 availability using 1‐L electrobioreactors is showcased, providing high process control and relevance for follow‐up engineering and scaling. Using a combinatorial approach of two cathode materials, three anode types, and various current regimes ranging from −5 to −80 mA, MES performance is boosted by overcoming O2 stress and insufficient H2 distribution at high current. It is demonstrated that a large‐surface‐area carbon fiber fabric cathode combined with O2 evolution anodes flushed with nitrogen (N2) allows the highest reproducible acetate concentration of 12.44 ± 1.56 g L−1 and maximum acetate production rate of 0.6 ± 0.1 g L−1 d−1 reported for MES from CO2 using a pure culture. There is certainly room for improved process control at this and even larger scales, showing that the ceiling of strict anaerobic MES is far from being reached.

Microbial electrosynthesis (MES) from CO2 by acetogens enables the production of value‐added chemicals. However, its current limitations include O2 stress and insufficient H2 availability. Using Clostridium ljungdahlii as a model in 1‐L electrobioreactors providing high process control, MES is boosted to unprecedent acetate concentrations and rates through a combinatorial approach involving different electrode materials and current regimes.© 2025 WILEY‐VCH GmbH