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Solid Oxide Fuel Cells - the SOFC has a solid oxide or ceramic electrolyte

image credit: iridium catalyst and solid oxide fuel cell
Hatvani Robert's picture

Raw materials are crucial to the economy. They form a strong industrial base in which a wide range of goods and applications of daily life as well as modern technologies are produced. Reliable...

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  • Nov 16, 2020

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.


fuel cells


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".

Power-to-X technologies


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.


Matt Chester's picture
Matt Chester on Nov 16, 2020

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.

Aren't there pilots out there that are mixing hydrogen direction into natural gas so they can be safely transported via existing gas infrastructure? 

Hatvani Robert's picture
Hatvani Robert on Dec 3, 2020

For transportation, the overarching technical challenge for hydrogen storage is how to store the amount of hydrogen required for a conventional driving range (>300 miles) within the vehicular constraints of weight, volume, efficiency, safety, and cost. Durability over the performance lifetime of these systems must also be verified and validated, and acceptable refueling times must be achieved. Requirements for off-board bulk storage are generally less restrictive than on-board requirements; for example, there may be no or less-restrictive weight requirements, but there may be volume or "footprint" requirements. The key challenges include:

  • Weight and Volume. The weight and volume of hydrogen storage systems are presently too high, resulting in inadequate vehicle range compared to conventional petroleum fueled vehicles. Materials and components are needed that allow compact, lightweight, hydrogen storage systems while enabling mile range greater than 300 miles in all light-duty vehicle platforms.
  • Efficiency. Energy efficiency is a challenge for all hydrogen storage approaches. The energy required to get hydrogen in and out is an issue for reversible solid-state materials. Life-cycle energy efficiency is a challenge for chemical hydride storage in which the byproduct is regenerated off-board. In addition, the energy associated with compression and liquefaction must be considered for compressed and liquid hydrogen technologies.

  • Durability. Durability of hydrogen storage systems is inadequate. Materials and components are needed that allow hydrogen storage systems with a lifetime of 1500 cycles.

  • Life-Cycle and Efficiency Analyses. There is a lack of analyses of the full life-cycle cost and efficiency for hydrogen storage systems.

  • Refueling Time. Refueling times are too long. There is a need to develop hydrogen storage systems with refueling times of less than three minutes over the lifetime of the system.

  • Cost. The cost of on-board hydrogen storage systems is too high, particularly in comparison with conventional storage systems for petroleum fuels. Low-cost materials and components for hydrogen storage systems are needed, as well as low-cost, high-volume manufacturing methods.

  • Codes and Standards. Applicable codes and standards for hydrogen storage systems and interface technologies, which will facilitate implementation/commercialization and ensure safety and public acceptance, have not been established. Standardized hardware and operating procedures, and applicable codes and standards, are required.

The Hydrogen and Fuel Cell Technologies Office Multi-Year Research, Development, and Demonstration (MYRD&D) Plan describes the goals, objectives, technical targets, tasks, and schedules for all activities within the Hydrogen and Fuel Cell Technologies Office (HFTO) (formerly the Fuel Cell Technologies Office [FCTO]), which is part of the U.S. Department of Energy's (DOE's) Office of Energy Efficiency and Renewable Energy (EERE). The MYRD&D Plan is a living document, which is revised periodically to reflect progress in the technologies, revisions to developmental timelines and targets, updates based on external reviews, and changes in the scope of the HFT Office. The document was first published in 2003, and revised in 2005. The document was significantly revised in 2012 to reflect scientific advancements and the changing technological landscape. Any revisions made to the MYRD&D Plan are conducted through a rigorous Change Control process as documented in the Systems Integration section of this report. The hydrogen and fuel cell activities within DOE continue to receive extensive review by stakeholders in the hydrogen and fuel cell community, including panels of the National Research Council and the National Academy of Engineering.

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