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Solid Oxide Fuel Cells - the SOFC has a solid oxide or ceramic electrolyte
- Nov 15, 2020 10:05 pm GMT
Solid Oxide Fuel Cells - the SOFC has a solid oxide or ceramic electrolyte
A solid oxide fuel cell (or SOFC) is an electrochemical conversion device that produces electricity directly from oxidizing a fuel. Fuel cells are characterized by their electrolyte material; the SOFC has a solid oxide or ceramic electrolyte. Advantages of this class of fuel cells include high combined heat and power efficiency, long-term stability, fuel flexibility, low emissions, and relatively low cost. The largest disadvantage is the high operating temperature which results in longer start-up times and mechanical and chemical compatibility issues.
It is clear that over 100 times more solar photovoltaic energy than necessary is readily accessible and that practically available wind alone may deliver sufficient energy supply to the world. Due to the intermittency of these sources, effective and inexpensive energy-conversion and storage technology is needed. Motivation for the possible electrolysis application of reversible solid-oxide cells (RSOCs), including a comparison of power-to-fuel/fuel-to-power to other energy-conversion and storage technologies is presented.
From hydrogen to renewable energies
When switching to renewable energies, technologies for storing energy are required. Hydrogen can provide valuable services here. Especially in the transport sector, because around a third of the energy generated is currently required for mobility. The nationwide expansion with hydrogen filling stations is particularly worthwhile if a large number of vehicles have to be supplied. For several million vehicles or more, the necessary infrastructure is significantly cheaper than setting up charging stations for a comparable number of electric cars with batteries.
Almost free of platinum: PEM electrolysers for "green" hydrogen
The prerequisite for environmentally friendly hydrogen technology is the generation of "green" hydrogen by converting water with the help of wind and solar power. For this purpose, Jülich researchers are presenting a new generation of electrolysis cells that are a perfect match for fluctuating renewable sources. PEM electrolysers contain a polymer electrolyte membrane inside. They can handle high current densities and adapt to sudden fluctuations in electricity in a matter of seconds, so they can use large amounts of solar and wind energy and generate more hydrogen than conventional electrolysers. So far, the high costs, which are caused in particular by the high content of precious metals, have been considered disadvantageous.
Optimizing the coating process
Researchers at the Jülich Institute for Energy and Climate Research (IEK-3) have now developed a new generation of PEM electrolysis cells that use significantly fewer precious metals than before. By optimizing the coating process, they were able to reduce the platinum content at the cathode to a tenth (0.1 mg / cm2). According to current market prices, only platinum worth 25 euros is required per square meter of cell area. The iridium content at the anode was reduced to a fifth (0.4 mg / cm2). The porous transport layers, which now allow high power densities and long-term stable operation, have also matured.
One for all: reversible fuel cell for the island
Reversible fuel cells that can be operated in two directions are still relatively new. Depending on their needs, they generate electricity or even hydrogen themselves, if electricity that is not otherwise required is fed to them. Such cells could, for example, help to independently supply remote islands or huts and stations in the mountains with energy. With the help of electricity from solar cells or wind turbines, the cells then produce hydrogen, which can be stored well over long periods of time. Also useful: When converting back into electricity, the end product is pure water that can be used for the water supply.
Jülich researchers have set up a 5 kW stack with high-temperature fuel cells for demonstration purposes, which can also be operated in electrolysis mode. The cells work at 600 to 800 degrees Celsius and achieve the highest electrical efficiencies of up to 60 percent in fuel cell mode. The waste heat can be used for heating or cooling by means of combined heat and power, which further improves efficiency. The cell structure is based on extremely durable ceramic solid oxide fuel cells developed in Jülich. In a long-term test, these have been delivering electricity for over 10 years - longer than any other cell of this type before. The reversible version as RSOC (Reversible Solid Oxide Cell) does not last that long, however. The special conditions in the electrolysis mode typically lead to increased aging of the electrodes.
Against nitrogen oxides: clean synthetic fuels for combustion engines
On the way to environmentally friendly vehicles, one can start with the drive - or with the fuel. Scientists at the Institute for Energy and Climate Research (IEK-3) are researching synthetic fuels that burn much cleaner than conventional diesel and gasoline. The aim is to find a designer fuel that hardly releases any nitrogen oxides and at the same time forms few soot particles, i.e. fine dust.
Sophisticated design: contactless measurement in flight
Nothing works in aviation without aerodynamic optimization. This also applies to the measuring instruments with which research aircraft are equipped for atmospheric research. Experts from the Jülich Institute for Engineering and Technology (ZEA-1), together with partners from the Institute for Energy and Climate Research and the German Aerospace Center (DLR), have developed two air inlets that are now being used worldwide in measurement campaigns with the German research aircraft HALO can be used.
Challenges & certifications
Among other things, OH radicals are measured, which contribute significantly to the self-cleaning of the atmosphere. The ingenious design slows down the incoming air and prevents the reactive molecules from coming into contact with the surface. And the pieces made to measure by Jülich engineers master another challenge. They are certified for safe flight operations. This includes testing for collisions with birds in complex simulation calculations and experiments: a problem that many other aircraft also have to struggle with again and again.
Neutrons: perfect probes for energy research
Neutrals have no electrical charge. Therefore, they do not interact with the electron shell, but only with the nuclei of the atoms and penetrate deep into matter. This makes them ideal probes, especially for studies on "light" elements such as hydrogen and lithium. Neutrons are therefore predestined for materials that are currently being researched in the energy sector: for better batteries, fuel cells and solar cells.
At the Institute Laue-Langevin (ILL), which this year will be presented at the joint stand of the state of North Rhine-Westphalia at the Hanover Fair, around 1,400 scientists carry out over 850 experiments on around 40 instruments every year. State-of-the-art equipment enables researchers to research samples at this world's most powerful neutron source at different temperatures, pressures and magnetic fields in order to map real working conditions as precisely as possible. The ILL also works closely and confidentially with research departments of industrial companies. Germany has a 33 percent stake as a shareholder and is represented in this function by research department Jülich.
Tomographs of a fuel cell:
Neutron radiation also makes lighter elements visible, in this case the distribution of water in the cell during operation.
This is important for optimizing the performance and service life of the cells.
Still not good enough
Germany is an international pioneer in renewable energies. But it cannot rest on that. Solar energy and wind power fluctuate strongly. For the increasing expansion in the course of the energy turnaround, technologies are required that enable the energy generated to be temporarily stored and transferred to other sectors. Examples include the generation and storage of hydrogen or methane by electrolysis (power-to-gas) and the conversion into liquid substances such as synthetic fuels for mobility (power-to-liquid) and high-quality basic chemicals for the chemical industry (power- to-Chemicals).
Kopernikus-Projekts "Power to X
This recording was made during the first Kopernikus press morning on July 8th, 2020. Prof. Walter Leitner, spokesman for the Kopernikus project P2X, explains what P2X will research by 2022. Leitner is Director at the Max Planck Institute for Chemical Energy Conversion and Professor at "RWTH Aachen University".
For a climate-neutral Germany by 2050, transport, industry and heating need low-emission solutions. The Kopernikus project P2X examines one of the most promising approaches: Power-to-X technologies. In other words, technologies that convert renewable electricity into other forms of energy. For example in fuels and plastics, in heat and gases or in chemical raw materials.
In order to limit global warming to less than two degrees, Germany wants to become largely climate-neutral by 2050. This can only be achieved with the help of renewable energies. That means: solar energy, wind and water power have to replace fossil raw materials. The aim of the Kopernikus project P2X is to develop technologies and processes that can convert and store renewable energy. Accordingly, the project is researching ways of converting electricity into chemical energy. This can then be used in high-emission sectors such as transport and industry or as a heat source for industrial processes and make them more climate-friendly.
Power-to-X: electricity in, material solutions out
Scientists call the conversion of electricity into other substances Power-to-X, or P2X for short. Translated, electricity (is) converted to X. With power-to-gas (electricity to gas), for example, gaseous substances such as hydrogen or methane are produced. Power-to-Chemicals (electricity to chemicals) produces chemical raw materials that are further processed industrially. The result of power-to-fuel (electricity to fuel) is climate-friendly fuel. Here, carbon dioxide (CO2) obtained from the air or from exhaust gases is used. In this way, a significant overall reduction in emissions is achieved when the fuel is burned.
In the second of three planned funding phases, the Kopernikus project P2X is investigating two raw materials that can be produced with Power-to-X. Firstly hydrogen and secondly a synthesis gas that consists of a mixture of hydrogen and carbon monoxide. Hydrogen is produced by scientists using electrolysis to electrify water. If CO2 is also added during the electrolysis (co-electrolysis), the synthesis gas is produced.
Hydrogen: What P2X is researching
- The hydrogen electrolysers examined in the P2X project currently require larger quantities of the rare and expensive metal iridium. The P2X scientists are looking for ways to use as little iridium as possible in electrolysis - without making the process less efficient.
- Once the hydrogen has been produced, there are a number of uses for it. For example, the P2X researchers are investigating how hydrogen and CO2 can be converted into polymer building blocks that the chemical industry urgently needs.
- Hydrogen can also be used as a fuel for road traffic. The P2X team also develops concepts for the optimal operation of hydrogen filling stations.
- Because hydrogen burns at high temperatures, the P2X partners are also investigating how industrial furnaces can be inexpensively heated with hydrogen. Specifically, they test it at a glass manufacturer.
- One of the problems that needs to be overcome is transportation. Hydrogen only becomes liquid under high pressure and is the only way to transport it. It's complicated and expensive. That is why the P2X team is also researching to temporarily bind hydrogen to liquids, liquid organic hydrogen carriers, so that it can be transported more easily.
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