Physics

Central to the work of the Nienhaus research group is the question of how chemical energy is converted directly into electrical energy. In their work, the researchers study simple reactions between gases and metallic surfaces as they occur in the environment and technology on an everyday basis. They are developing and fabricating special silicon-based chemical sensors which deliver an electric current when exposed to reactive gas particles – comparable to when light is shone onto a solar cell. This method permits precise measurement during reactions and energy conversion processes, since the strength of the current is a direct representation of the reaction rate. The most recent studies focus on the oxidisation of magnesium, aluminium and potassium with pure oxygen. While these are everyday reactions, they are still a source of many unanswered questions. It was possible for the first time in this work to examine separately the different conversion processes from chemical to electrical energy on potassium surfaces. The ultrafast motion of the oxygen atoms in the molecule during the reaction was identified as the driving force behind the processes. Surprisingly, it is not necessary for the molecule to break apart, which was previously thought to be essential. A particularly noticeable quantum effect is observed on nanometre-thin magnesium films. On certain thicknesses of film, the metal is oxidised twice as effectively as under normal conditions. In these films, the metal electrons are confined at a characteristic length. The size of this ‘confinement’ massively affects the reactivity of the surface, because during oxidation electrons pass from the metal to the molecule.