Plants where the central component, the electrolyte, is an alkaline liquid can be bought off the shelf, so to speak. Alkaline electrolysis plants make do with inexpensive materials. A major disadvantage is their low power density: they produce comparatively little hydrogen per square centimetre of surface area. Large space requirement and high material consumption are the result. “Alkaline electrolysers are generally considered to be technically mature, but we are pursuing new approaches to increase their power density,” says Müller. One of these approaches is based on new partitions which are installed in the liquid electrolyte to electrically isolate the negative pole (cathode) and the positive pole (anode) from each other.
Higher power densities than alkaline electrolysers are achieved in systems in which the electrolyte does not consist of a liquid but of an extremely thin layer, a so-called polymer electrolyte membrane (PEM). However, the high costs of PEM plants stand in the way of wider dissemination. “Jülich researchers have their sights set on various parts of the facility to change this,” says Dr. Marcelo Carmo, electrochemist at IEK-14.
While alkaline and PEM electrolysis systems are usually operated at around 80 °C, the third electrolysis process requires more than 650 °C. In these so-called SOE systems (Solid Oxide Electrolysis), the high operating temperature must be maintained even when no current is available. This is because starting and stopping the system would cost even more energy – and this would also tire out the material more quickly. The technology is economically interesting nevertheless: “The SOE systems are very well suited to use the heat generated by many industrial processes. Then, they convert the electricity very efficiently into the chemical energy of hydrogen,” explains Prof. Ludger Blum of IEK-14. In recent years, Jülich researchers have made SOE electrolysers more reliable and durable through various improvements.