“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 Technical University of Munich, formerly at the Ruhr University in Bochum. “Without this protection, they lose their activity within minutes.” However, embedding in so-called redox polymers, plastics, whose side groups can transfer electrons, has a decisive disadvantage: They offer high resistance to the flow of electrons. In order to overcome it, one has to invest energy, and this is lost in the form of heat. The embedded hydrogenases completely lost their ability to generate hydrogen.