A team of microbiologists from Goethe University has succeeded in storing and releasing hydrogen in a controlled manner with the help of bacteria. This is an important step in the search for CO 2 -neutral energy sources in the interest of climate protection. The corresponding paper has now been published in the renowned journal “Joule”.
The fight against climate change makes the search for CO 2 -neutral energy sources more and more urgent. Green hydrogen, which is obtained from water with the help of renewable energies such as wind power or solar energy, is one of the hopes. However, transporting and storing the highly explosive gas is difficult, and researchers around the world are looking for chemical and biological solutions. A team of microbiologists from Goethe University found an enzyme in bacteria that live in the absence of air that binds hydrogen directly to CO 2 and thus produces formic acid. This process is completely reversible, a prerequisite for hydrogen storage.
These acetogenic bacteria, which are found in the deep sea, for example, feed on carbon dioxide, which they metabolize into formic acid with the help of hydrogen. Normally, however, this formic acid is just an intermediate product of their metabolism, which is further digested into vinegar and ethanol. However, the team around the head of the Department of Molecular Microbiology and Bioenergetics, Prof. Volker Müller, has adapted the bacteria in such a way that this process can not only be stopped at the formic acid level, but also reversed. The basic principle has been patented since 2013.
Model of a possible bacterial hydrogen storage: During the day, electricity is generated with the help of a solar system, which then drives the hydrolysis of water. The hydrogen generated in this way is bound to CO 2 by the bacteria and formic acid is formed as a result. This reaction is freely reversible and the direction of the reaction is controlled only by the concentration of the starting materials and end products. During the night, the hydrogen concentration in the bioreactor drops and the bacteria begin to release the hydrogen from the formic acid. The released hydrogen can then be used as an energy source.
“The measured rates of CO 2 reduction to formic acid and back are the highest ever measured and are many times greater than for other biological or chemical catalysts; Unlike the chemical catalysts, the bacteria do not need rare metals or extreme conditions such as high temperatures and high pressure for the reaction, but do the job at 30 °C and normal pressure,” reports Müller. Now the group is reporting a new success, the development of a biobattery for hydrogen storage with the help of the bacteria mentioned.
For municipal or domestic hydrogen storage, a system in which the bacteria first store hydrogen in one and the same bioreactor and then release it again, as stable as possible over a long period of time, makes sense. Fabian Schwarz, who wrote his doctoral thesis on this topic in Prof. Müller’s laboratory, has succeeded in developing such a bioreactor. He fed the bacteria hydrogen for eight hours and then put them on a hydrogen diet for a 16-hour overnight phase. The bacteria then completely released the hydrogen again. The unwanted formation of acetic acid could be eliminated by genetic engineering. “The system was extremely stable for at least two weeks,” explains Fabian Schwarz, who is pleased that this work was accepted for publication in “Joule”, a respected journal of chemical and physical engineering. “It’s rather unusual for biologists to publish in this top-class journal,” Schwarz says happily.
Volker Müller already dealt with the properties of these special bacteria in his doctoral thesis – and conducted basic research on them for years. “I was interested in how these first organisms organized their life processes and how they manage to grow in the absence of air with simple gases such as hydrogen and carbon dioxide,” he explains. Due to climate change, his research gained a new, application-oriented dimension. Biology offers – surprising for many engineers – quite practicable solutions.
Publication: Fabian M. Schwarz, Florian Oswald, Jimyung Moon, Volker Müller: Biological hydrogen storage and release through multiple cycles of bi-directional hydrogenation of CO2 to formic acid in a single process unit. Joule (2022) https://doi.org/10.1016/j.joule.2022.04.020
Read the most up to date Fuel Cell and Hydrogen Industry news at FuelCellsWorks
