Component development for alkaline water electrolysis and polymer electrolysis
Electrodes for alkaline water electrolysis should be efficient, cost-effective and stable over long periods of intermittent operation. DLR has developed Raney nickel-based coatings for anodes and cathodes that meet these requirements. The coating is applied by the vacuum plasma spraying (VPS) process to nickel sheets or nickel-plated steel sheets. For a coating with NiAlMo on the cathode and NiAl/Co3O4 on the anode, a cell voltage of 1.56 V for water decomposition was achieved at 300mA/cm2 and 80°C (3.7- 4 kWh/Nm3 H2 spec. energy consumption), which represents a reduction of 0.4-0.5 V in overvoltage compared to uncoated electrodes, and thus a substantial increase in efficiency. Excellent long-term stability in intermittent operation with a solar current density profile without support voltage for several years has also been demonstrated for these electrodes.
New electrode catalysts and electrode structures are also being researched for the promising polymer electrolyte electrolysis, which combines high dynamics with high power density, in order to significantly reduce the precious metal content. In addition, corrosion-stable coatings for the bipolar plates are being developed (e.g. titanium coatings on stainless steel), which enable significant cost reductions. The innovations will be integrated into stack and system configurations of industrial partners and thus validated with respect to technical and economic relevance. The long-term stability of the components and the system will be investigated and aging phenomena will be described with different models.
System integration of advanced electrolysis as storage in future energy supply structures
In connection with the increasing installed capacity of fluctuating, renewable energies, storage technologies for electrical energy are increasingly becoming the focus of industrial and political interest. One promising option here is chemical storage technologies, such as hydrogen storage, combined with the production of hydrogen from (preferably renewable) electricity using water electrolysis. These can store an excess supply of electrical energy, e.g. from wind turbines, as hydrogen. Large amounts of energy can be stored in the process. DLR is working on the efficient integration of electrolysis into an overall system, in which different types of use (filling station, feeding into gas grids, reverse power generation, ...) are being investigated and the electrolysis system is being optimized in terms of efficiency, availability, reliability and durability.
Development of high-temperature electrolysis as a future option for hydrogen production with highest efficiency, synthesis of hydrocarbons and electrochemical energy storage
Significantly higher efficiencies are promised by high-temperature water electrolysis (SOEC, solid oxide electrolysis cell) in the temperature range between 700 and 1000°C, where water vapor is decomposed into hydrogen and oxygen. Particularly if it is possible to couple process heat from industrial or solar thermal processes into the electrolysis process, which takes place at high temperatures, efficiencies of 90% and higher can be achieved. Another interesting option is the simultaneous reduction of CO2 to CO if a concentrated carbon dioxide source is available. Thus, a SOEC can be used to provide syngas for the production of hydrocarbons, such as alcohols or synthetic fuels. When biomass and electricity from renewables are used, this pathway can be made completely sustainable. DLR is working on the development of functional, efficient and long-term stable SOEC cells and their assembly into short stacks and stacks. In the process, the electrodes must be optimized for the various applications. Further focal points are the demonstration of high efficiency at stack level and the proof of long-term stable operation at high current density, high steam content and co-electrolysis of carbon dioxide.