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As an energy source and chemical raw material, green hydrogen will make a decisive contribution to achieving climate targets. However, this can only succeed if the systems for generating, storing, transporting and using H2 become more energy-efficient, robust, safe and economical. Fraunhofer has the expertise to make a decisive contribution in this field.
To produce green hydrogen, water is broken down into H2 and O2 using an electric current. Each type of electrolysis has specific advantages, so the choice of technology can vary depending on the application scenario. Fraunhofer researchers have significant expertise in all types of electrolysis, and can contribute a great deal to its further development. While aqueous alkaline electrolysis (AEL) and, to a large extent, acidic membrane electrolysis (known as PEM electrolysis) are technically quite mature, in the case of alkaline membrane electrolysis and high-temperature electrolysis some technological issues remain to be clarified.
The robust electrolyzers for AEL were previously used in power plants and chemical plants with a stationary and static load. However, a paradigm shift is now imminent: renewable energies cause significant load fluctuations, meaning that new concepts are required. Fraunhofer IFAM is investigating these dynamics on a pilot plant scale, in a system with an output of 30 kilowatts. The institute offers its partners services for analyzing the real behavior of AEL electrolyzers. In addition, Fraunhofer IFAM and Fraunhofer IMWS are optimizing the long-term stability of the electrodes. Fraunhofer IKTS is researching new materials and stack systems for the next generation of alkaline electrolyzers operating at elevated temperatures and pressures, in the AWEC++ and HHoch 2 projects with funding from the TAB and the Federal Ministry for Economic Affairs and Climate Action (BMWK). This enables an increase in power density and stable operation.
PEM electrolysis is a more recent development than AEL. While the latter has a technology readiness level of eight to nine, PEM electrolysis has a TRL of seven to eight. It also offers various advantages: the current densities used can be very high, the design very compact, and the process can be operated dynamically. However, due to the acidic medium, the materials used must be very robust. Researchers at Fraunhofer ISE are developing new membrane materials, extending the durability of the cells with an anti-corrosion coating, carrying out service life tests, and aiming to transfer the process to a larger scale. All these measures can help to reduce costs. In the BMWK-funded project H2GO, Fraunhofer IKTS is also working on the recycling of PEM stacks and their electrochemical characterization.
High-temperature electrolysis takes place at over 800 °C. It has particular advantages if waste heat is available: no precious metals are required to catalyze the reactions; moreover, the same systems can be used in both electrolysis and fuel cell mode. It also enables co-electrolysis, in which water is split into H2, O2 and CO2 in oxygen and carbon monoxide (CO). Together with H2, CO forms a »synthesis gas« which is the precursor for the production of numerous chemical products. Fraunhofer IKTS focuses on the long-term stability of electrolyzers as well as their efficiency and costs.
The IKTS teams optimize materials, manufacture cells and assemble them into stacks. In material tests within the BMBF-funded projects ElKoHEL and SOC Degradation 2.0, they are investigating the degradation mechanisms in stack components, including those resulting from various contaminants and concentrations. This forms a basis for reliable energy systems, for example for coupling high-temperature electrolysis and Fischer-Tropsch synthesis. In the globally unique recycling plant in Thallwitz, biological waste can be converted back into useful materials such as synthetic fuels and biowaxes (see chapter »Climate-neutral industrial processes «). Fraunhofer IKTS worked on planar cells and stacks for combined heat(/cooling) and power with hydrogen – for example for off-grid supply – and developed the technology to market maturity with the Dresden-based company Sunfire.
Fuel and electrolysis cells can only be operated smoothly if the gas atmospheres are completely separated from each other. This requires solders that can be used stably up to approx. 850 °C. As part of various industrial partnerships, Fraunhofer ISC has developed crystallizing glass solders that meet all thermal, chemical and mechanical requirements. These can even be used in a fully automated manufacturing process.
Fraunhofer IWU is working with Chemnitz University of Technology and industrial partners to ensure that the stack remains tight during operation: smart seals detect changes to the preload of the stack during operation. Using shape-memory alloys, the optimum preload is then restored.
At present, hydrogen is usually not produced via water electrolysis, but rather via reforming of organic compounds – in the simplest case methane or methanol. This type of H2 or synthesis gas production can also contribute to a sustainable industry if, for example, the organic compounds come from biomass, and if the resulting CO2 is removed from the global cycle. Several Fraunhofer institutes are working on optimizing the underlying reformer systems: Fraunhofer IMM develops complete solutions for fuel processing and synthesis from laboratory through to pilot scale and series production.
Work at Fraunhofer IKTS centers on the afterburner required in a fuel cell system, or rather its core component, the foam ceramic. To ensure a long service life, this must be extremely resistant to high temperatures and thermal shock. Opencell foam ceramics made of silicon carbide are particularly suitable for this purpose. The researchers adjust these cellular ceramics specifically to the burner or reformer type and further develop them. Fraunhofer IKTS’ specialized foam ceramics have a particularly high strength in the temperature range up to 1300 °C.
High-capacity and inexpensive catalysts are essential for efficient electrolyzers or fuel cells. Several Fraunhofer institutes have built up considerable expertise in this area, aiming to reduce the use of precious metals and to increase efficiency. In the electrolyzer, completely different requirements apply for the hydrogen electrode than for the oxygen electrode. For example, in the project HyCOn (funded by the German Federal Ministry of Education and Research (BMBF)) researchers at Fraunhofer ICT have developed supported catalysts based on iridium oxide, to produce oxygen. They are also investigating the increase in activity resulting from the formation of mixed oxide or defects due to doping with halides. Based on this preliminary work, bifunctional oxygen catalysts for unitary reversible PEM fuel cells can ultimately be developed.
Fraunhofer ICT is also developing electrocatalysts for different types of electrochemical cells in the low and medium temperature range (up to around 200 °C). For example, the researchers are working to improve electrodes for high-temperature PEM fuel cells. On behalf of the Federal Ministry of Defence, research is also being conducted into materials and systems that can be operated with logistical fuels in this type of fuel cell.
PEM fuel cells can play an important role in the field of heavy-duty transportation, as they offer a high power density and very high dynamics. The energy density of hydrogen gives them additional advantages for this application compared to purely battery-electric drive systems. The coatings of a membrane serve as electrodes. This is referred to as a »membrane electrode assembly«, or MEA. In the HyFab project, which is funded by the state of Baden-Württemberg, Fraunhofer ISE is investigating the functional relationships in the catalyst layer, and optimizing process technologies for the mass-production of MEAs. Our colleagues at Fraunhofer UMSICHT are also developing new catalysts for water and CO2 electrolysis.
Fraunhofer ISC specializes in the upscaling of catalyst materials, and in catalysts for the use of hydrogen, for example to produce solar chemicals. Such catalytic reactions show sufficient performance and yield on a laboratory scale, but in order to upscale them for industrial application, promising catalyst materials such as the photocatalysts titanium dioxide and graphitic carbon nitride must be widely accessible. In the EU-funded project SPOTLIGHT, catalysts developed by project partners1, are being upscaled at Fraunhofer ISC. The synthesis of various catalyst materials, which are used for example to produce methane and carbon monoxide from green hydrogen and carbon dioxide, was transferred from the 100 mg scale to the 100 g scale. The performance of these catalysts in the conversion processes is comparable to or better than the systems produced on a small scale.
Different applications for hydrogen require different concepts for storing and transporting the valuable gas. For distances of less than 100 kilometers, Fraunhofer IFF is developing a portable, modular H2 storage system that weighs less than 750 kilograms and can be loaded onto »green« vans. Hydrogen can also be stored in liquid organic hydrogen carrier (LOHC) systems. To this end, H2 is chemically bound to a carrier oil: there is no need for complex pressure accumulators or cooling systems. Researchers at Fraunhofer IAO have built Europe's first next-generation LOHC storage system, with a storage capacity of 2000 kilowatt hours. As an alternative, Fraunhofer IFAM in Dresden is developing an easy-to-handle »POWERPASTE« in which hydrogen can be chemically stored at room temperature and ambient pressure, and can be released as required by adding water.
The use of hydrogen to reduce the CO2 footprint of thermal processes will play an important role in achieving climate targets. This applies in particular to processes that cannot be electrified. Depending on the settings of the burners, and on the combustion conditions, the combustion of hydrogen leads to significantly higher temperatures and gas volume flows as well as increased water content in the gas atmosphere. This increased water content can affect both the product in the furnace and the furnace components. In addition to the burners, the refractory lining and furnace furniture are particularly affected. Fraunhofer ISC has special furnaces in which the influence of increased water vapor content (up to 100%) on the furnace feed and components can be investigated in-situ. In addition, a broad spectrum of analytical methods is available, including at the Center for Applied Analytics (ZAA) for the subsequent investigation of the reactions taking place within the materials. Based on these results, customized furnace programs, furnace materials and coatings can be proposed and developed using simulation tools developed in-house. Beside the influence of the water content, the influence of hydrogen or other gases can also be investigated at temperatures of up to 1800 °C.
The materials used to encapsulate sensitive components, separate gas flows or transport gases, must be gas-tight. Plastic components or films are often used for such applications, as they can be produced easily, flexibly and cost-effectively in various geometries. However, plastics are a very limited migration barrier to non-polar gases (e.g. oxygen or nitrogen). They must consequently be modified. One option that offers significant material savings and therefore increased sustainability is the use of functional layers that serve as a gas barrier. Such layers are a central component of many packaging applications, and an important subject of research, for example in the Fraunhofer POLO Alliance.
In addition to vapor deposition, sputtering and plasma coatings, functional hybrid polymer coating systems (such as ORMOCER®materials from Fraunhofer ISC) create an especially effective barrier against oxygen due to their inorganic and organic cross-linking within a single matrix. With a high network density and a suitable polarity, ORMOCER® functional layers can reduce the migration levels of plastic films from over 1300 to less than 15 cm3/m2dbar. As the layers are very flexible and only a few micrometers thick, they can also be applied to very thin films. The coating materials are produced by simple synthesis (e.g. in the synthesis reactor shown in Figure 7) and can be applied to 2D and 3D surfaces using conventional methods such as spraying. A further improvement of their properties with regard to the barrier effect can be achieved by the addition of particles. In future, hydrogen barrier layers will be developed according to similar functional principles and, for example, through the use of (layered) silicates. The use of crystalline, inorganic nanofillers significantly reduces the permeability of the polymer matrix by extending the diffusion path of the permeates. The use of hydrogen barrier layers can therefore play an important role in reducing losses during hydrogen transport, and can significantly improve the barrier properties under high pressure.
Fraunhofer MATERIALS research covers the entire value chain, from new material development and improvement of existing materials through manufacturing technology on a quasi-industrial scale, to the characterization of properties and assessment of service behavior. The Group covers the full spectrum of metallic, inorganic non-metallic, polymeric, and renewable raw material-based substances, as well as semiconductor materials. In recent years, hybrid materials and composites have gained significant importance. Material innovations are crucial in addressing the challenge of creating a robust, resilient, and efficient future energy system. Consequently, the group has recognized the energy sector as a key business area, with a particular focus on hydrogen. Research in materials for hydrogen technology is crucial, as hydrogen can reduce the strength and toughness of materials, leading to either immediate or delayed failure of components. This issue is particularly pertinent given the increasing importance of repurposing existing natural gas pipelines and storage facilities for hydrogen distribution and storage. At Fraunhofer MATERIALS, comprehensive evaluations, monitoring, simulations, and characterizations are conducted to develop materials that are as resistant as possible to hydrogen embrittlement.
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