(Munich) - Both fuel cells, which convert hydrogen into electricity, and electrolysers, which produce hydrogen by splitting water using electricity, need the precious metal platinum as a catalyst. It is rare and expensive. However, enzymes called hydrogenases also catalyze the conversion of hydrogen “very quickly and with almost no loss of energy,” explain scientists at the Technical University of Munich (TUM). However, these biocatalysts were previously considered “unsuitable for industrial use because they are highly sensitive to oxygen.”
According to TUM, a research team has managed to “incorporate the sensitive enzymes into a protective polymer in such a way that they can also be used for technical hydrogen conversion.” The TU Munich, the Ruhr University Bochum, the CNRS Marseille and the Max Planck Institute for Chemical Energy Conversion in Mülheim an der Ruhr (CEC) are involved.
Little damage from oxygen
“If you embed the sensitive hydrogenases in suitable polymers, they work for several weeks even in the presence of oxygen,” says Nicolas Plumeré, Professor of Electrobiotechnology at the TUM Campus Straubing for Biotechnology and Sustainability. “Without this protection, they lose activity within minutes.”
According to the researchers, embedding them in so-called redox polymers, plastics whose side groups can transfer electrons, had a decisive disadvantage so far: “They present a high resistance to the flow of electrons.” To overcome this, one had to “invest energy.” must. Due to the heat generated, the hydrogenases would have lost the ability to produce hydrogen. By fine-tuning the polymer matrix, the scientists achieved that the hydrogenase catalyzes the reaction in both directions without any loss of energy.
Efficiency close to 100 percent
The research team used this system to build a fuel cell. A bacterium (Myrothecium verrucaria) reduces the oxygen, and another bacterium (Desulfovibrio desulfuricans) oxidizes the hydrogen and generates electricity. The system can also be used for the reverse reaction, hydrogen production by absorbing electrons: “Its energy conversion efficiency is close to 100 percent, even at current densities of over four milliamperes per square centimeter,” say the scientists.
Reducing energy loss has two advantages, says Nicolas Plumeré: “It not only makes the system much more efficient. At high outputs, the heat generated in a fuel cell stack would be a problem for the biological systems." The team's further research now aims to improve the stability of the hydrogenases at higher current densities in order to compete with systems with platinum-based catalysts to be able to.
The research was funded by the European Research Councils (ERC), the French Center Nationale de la Recherche Scientifique (CNRS) and the Aix-Marseille Université, the German Research Foundation (DFG) as part of joint funding together with the Agence Nationale de la Recherche, the Max Planck Society and the Federal Ministry of Education and Research (BMBF).
deep link
https://idw-online.de/de/news768692
Publication
“Reversible H2 oxidation and evolution by hydrogenase embedded in a redox polymer film”. Steffen Hardt, Stefanie Stapf, Dawit T. Filmon, James A. Birrell, Olaf Rüdiger, Vincent Fourmond, Christophe Léger, Nicolas Plumeré. Nature Catalysis Vol. 4, 251–258 (2021) – DOI: 10.1038/s41929-021-00586-1
Artwork
An iron-sulfur cluster inside the hydrogenase catalyzes the oxidation of hydrogen to protons or the reduction of protons to hydrogen. Additional iron-sulfur clusters enable the electrons to be passed on. / © James Birrell / MPI CEC
