Entwicklung von Membran-Elektroden-Einheiten für die Anionenaustauschmembran-Wasserelektrolyse
Aachen (2016) [Dissertation / PhD Thesis]
Page(s): 1 Online-Ressource (II, 136 Seiten) : Illustrationen, Diagramme
The use of an anion exchange membrane as an electrolyte allows to combine the benefits of the alkaline- and the polymer electrolyte membrane water electrolysis and simultaneously eliminates their limitations. The ionomers used in this so called anion exchange membrane water electrolysis usually contain quaternary amines as functional groups. These kind of ionomers provide a sufficiently high ionic conductivity for the elctrolysis operation. Hydroxide anions that are formed at the cathode however destroy those functional groups causing a subsequent loss in ionic conductivity and thus reduce the hydrogen production rate of the electrolyser. The aim of this work is a material screening of commercial and pre-commercial anion exchange membranes, ionomers and electro catalysts. The most suitable materials are chosen for the development of membrane electrode assemblies and characterised during water electrolysis operation. By selecting the membranes and ionomers and by optimizing the operational parameters, the chemical degradation of the functional groups of the ionomers is to be reduced. During water electrolysis operation, the membrane electrode assemblies should show the highest possible current densities. Furthermore, the electrode layers are designed without the use of precious metal catalysts. Based on anion exchange membranes, ionomers and electro catalysts that are available on the market to date, it is possible to build membrane electrode assemblies that reach a current density of 1.4 A/cm2 at 2.1 V and 50 °C during electrolysis operation. The membrane electrode assemblies developed in this study only contained nickel-based electro catalysts and reached an operational lifetime of 300 h at a performance degradation of 0.7 mV/h. By observing the ion-exchange-capacity, it was demonstrated that particularly the ionomer used in the electrode layer is responsible for this severely limited lifetime.