Prototype has been running for 1,000 hours
Hydrogen will become increasingly important in future for supplying energy because it enables large, renewably generated energy volumes to be stored for longer periods. Together with partners from science and industry, scientists from Forschungszentrum Jülich are developing methods for producing hydrogen by electrolysing water as part of the Ekolyser project. They have tested more robust and cost-effective materials in a new test facility. The prototype has now reached its intended lifetime of 1,000 hours. It is planned that the developed technology will be ready for operational use on a broad scale by 2020.
Hydrogen is excellent for reliably storing generated energy so that the energy can be called upon again in times of shortage. The universally usable energy carrier can be fed into a gas network or further processed into liquid fuels. Hydrogen can also be used directly as a fuel in vehicles equipped with corresponding fuel cells. Only water is produced as a waste gas during the reaction. However, hydrogen does not occur freely in nature but has to be first of all generated, which requires energy. This is done, for example, by splitting water using electrical energy.
With modern polymer electrolyte membrane (PEM) electrolysis, distilled water is split by an electric current at electrodes into oxygen, free electrons and positively charged hydrogen ions (protons). The ions pass through a membrane and combine with the electrons to form hydrogen. To create an effective system, several of these cells are connected in series in so-called stacks, like batteries in an electric torch. Separator plates, which are usually made of titanium, separate the cells in such stacks.
High performing even without chemicals
In contrast to other types of electrolysis, PEM electrolysis does not require harmful chemicals. It is also more efficient – the cells are smaller and more hydrogen is produced. However, its disadvantage is the high price. The efficiency is currently around 70 percent. Nearly a third of the energy is lost. The hydrogen produced is too expensive; particularly the precious metals used as catalyst material and separators drive up the price.
Within the Ekolyser project, which is being coordinated by the Institute of Energy and Climate Research, the researchers are therefore developing cost-effective sustainable materials for PEM electrolysis. The research is focussing, for example, on more robust types of membranes with increased conductivity that improve the efficiency of the electrolysis. It is also intended to considerably reduce the precious metal content in the catalyst coatings and separator plates or even completely replace it with cheaper materials.
The researchers have studied a variety of different materials and coatings, and subjected them to long-term tests in test electrolysers. The newest prototype works with specially developed catalyst layers and separator plates where the titanium has been replaced with structured stainless steel sheets. The scheduled 1,000-hour practical test has now been successfully completed. A larger test facility is now planned as the next step. The individual cells in the current prototype have an active area 300 square centimetres in size; the planned new cell stack is intended to have 1,000 square centimetres per cell. This will enable more than one megawatt of electrical power to be converted into hydrogen and stored. By way of comparison: The rated power of large wind turbines ranges between approximately two and seven megawatts.