Picture: DLR / Thomas Ernsting
Development of Components for Alkaline Water Electrolysis and Polymer Electrolyte Electrolysis
Especially for intermittent operation the electrodes of alkaline water electrolysis should be highly efficient, cost effective and very durable. DLR has developed anode and cathode coatings based on Raney-Nickel that fulfill these requirements. The coating is applied by vacuum plasma spraying on nickel sheets or nickel-plated steel sheets. With cathode coatings of NiAlMo and anode coatings of NiAl/Co3O4 a voltage of 1.56 V at 300 mA/cm2 and 80°C is obtained (3.7- 4 kWh/Nm3 H2 specific energy consumption), that represent an reduction of overvoltage of 0.4 – 0.5 V und implies a superior efficiency. For these electrodes also long term stability in intermittent operation with photovoltaic profiles and without protective voltage was demonstrated for several years.
Similarly, we study novel electrode electrocatalysts and electrode structures for the promising polymer electrolyte electrolysis that exhibits superior dynamics and power density, with the special focus on reducing noble metal loading. Furthermore, we develop corrosion resistant coatings (e.g. titania on stainless steel) for the expensive bipolar plates to achieve a significant cost reduction. Innovations are tested in industrial stacks and systems to validate their technical and economical relevance. We study long-term stability of components and systems and the ageing phenomena are described by models with lifetime prediction capabilities.
Systemic Integration of Advanced Electrolysis as Storage Option of Future Energy Supply Structures
In the context of a significant increase of installed power of fluctuating renewable energies it is expected that electrical storage will become a necessary component in the future energy supply chain. A promising possibility is chemical storage, e.g. hydrogen production from water electrolysis with renewable energies during temporal surplus conditions. The main advantage is the large energy capacity and the numerous uses of hydrogen. DLR works on the efficient integration of electrolysis into an overall system with different paths for hydrogen use (fueling station, gas injection into grid, electrical reconversion …) and the evaluation as well as optimization of the system versus efficiency, reliability, availability and durability.
Development of High Temperature Electrolysis as Future Hydrogen Generation Option with highest Efficiency, Synthesis of Hydrocarbon Fuels and Electrochemical Storage
The high temperature electrolysis (SOEC, solid oxide electrolysis cell) operated in the temperature range between 700 and 1000 °C promises the highest efficiencies if heat for steam generation is provided. This technology is especially interesting, yielding efficiencies over 90 %, if process heat from industry or from solar thermal power plants can be integrated. Another promising possibility is the co-reduction (or co-electrolysis) of CO2 to CO, which requires a highly concentrated carbon dioxide source. In this way synthesis gas for the production of synthetic hydrocarbons such as alcohols, methane or other synthetic fuels can be generated by SOEC. When biomass and renewable electricity is used this conversion is completely sustainable and environmentally benign. DLR works on the development of functional, efficient and durable SOEC cells with new electrode formulations and structures. New cells are integrated and tested in short stacks and stacks. Electrodes need to be optimized for the different functions and applications. Further priorities are the demonstration of superior efficiencies on stack level and the demonstration of long-term stability with high current densities, high steam ratio, and co-electrolysis of carbon dioxide.