Biological hydrogen storage and release through multiple cycles of bi-directional hydrogenation of CO2 to formic acid in a single process unit

Hydrogen is a promising fuel in a carbon-neutral economy, and many efforts are currently undertaken to produce hydrogen. One of the challenges is to store and transport the highly explosive gas in a safe and easy way. One option that is intensively analyzed by chemists and biologists is the conversion of hydrogen and CO2 to formic acid, the liquid organic hydrogen carrier. Here, we demonstrate for the first time that a bio-based system, using Acetobacterium woodii as the biocatalyst, allows multiple cycles of bi-directional hydrogenation of CO2 to formic acid in one bioreactor. The process was kept running over 2 weeks producing and oxidizing 330 mM formic acid in total. Unwanted side-product formation of acetic acid was prevented through metabolic engineering of the organism. The demonstrated process design can be considered as a future biobattery for the reversible storage of electrons in the form of H-2 in formic acid, a versatile compound.

Automated summary

Hydrogen is a promising fuel for a carbon-neutral economy, but the challenge lies in storing and transporting the highly explosive gas safely. Researchers have discovered a bio-based system using a specific biocatalyst that can convert hydrogen and CO2 into formic acid, a versatile compound. The process has been successfully demonstrated in a bioreactor, with the ability to continually produce and oxidize formic acid over a period of two weeks. Unwanted side-products have been eliminated through metabolic engineering. This system shows potential as a future biobattery for reversible electron storage.