Fuel cell vehicles with a heart inspired by blood
The battery. Its plus. And its minus.
Emission-free driving – free of nitrogen oxides and greenhouse gases such as carbon dioxide (CO2) – has long been little more than a dream, as cars powered by combustion engines have dominated our roads for the past 100 years. But this is now changing, and electric mobility is on the rise. In 2019, more than 42% of all newly registered cars in Norway were electric, and within five years, the Scandinavians will have moved away from combustion engines entirely. Denmark, Sweden, the Netherlands, Ireland, and Israel intend to ban the sale of vehicles with gasoline and diesel engines beginning in 2030, and the United Kingdom and France are planning to follow suit in 2035 and 2040, respectively. Throughout the EU, a limit of 95 grams of CO2 per kilometer has already taken effect in 2020 for all newly registered passenger vehicles. Manufacturers whose vehicles, on average, fail to meet that standard are subject to substantial financial penalties.
This target can only be achieved by dramatically increasing the percentage of electric cars. To that end, most manufacturers are focusing on vehicles powered by lithium-ion batteries. Such vehicles are in fact emission-free – that is, if their batteries are charged from renewable sources such as wind, solar or hydroelectric power. In 2019, more than 60,000 fully electric passenger vehicles were newly registered in Germany. While that represents only 1.75% of all new registrations, the number of these vehicles on Germany’s roads has increased by more than a factor of ten over the past six years to approximately 140,000 – and automobile companies are currently introducing many new models to the market.
Yet developers are not satisfied, because they recognize that battery-powered electric cars are by no means the solution to every problem. Manufacturing batteries is expensive and requires a lot of energy, which in turn produces a large amount of CO2. Lithium extraction is far from environmentally-friendly, which increases the environmental footprint of electric cars – and what's more, these vehicles have a limited range. Most mid-sized electric cars have to be recharged after no more than 250 kilometers of normal driving, and the car has to remain plugged in for about 45 minutes. According to the German Transport Ministry, 95% of all car trips are shorter than 50 kilometers. While that means regular lithium-ion batteries provide sufficient range for millions of vehicles, batteries are simply not very practical for longer trips.
Did you know?
is the distance a fuel cell vehicle can travel before refueling.
is the time it takes to refuel at a hydrogen fueling station.
of Platinum is in today's fuel cells. Its value: 1.000 euros.
The power station on board: the fuel cell
A so-called fuel cell (FC) which generates power for an electric engine directly on board the vehicle is a much better approach. This technology uses hydrogen and combines it with oxygen, producing water and releasing energy – not explosively, as in the classic oxyhydrogen reaction, but in the form of electric power. These vehicles merely emit water vapor rather than pollutants or greenhouse gases.
The tanks in fuel cell vehicles, which hold hydrogen gas under considerable pressure (700 bar), are sufficient for trips from 500 to 700 kilometers before refueling with hydrogen is required – and refueling takes only three minutes. H2 Mobility, a joint venture of the automobile industry and gas producers, has already built more than 100 hydrogen fueling stations in Germany, and that number is expected to increase to 400 in the next three years.
Hydrogen can be extracted from water in an eco-friendly manner, for example when surplus wind energy provides the electricity required for this so-called electrolysis reaction. Electric cars powered by fuel cells are outstanding from an ecological perspective as well. A study by the Fraunhofer Institute for Solar Energy Systems has shown that the ecological footprint of hydrogen-based fuel cell vehicles, including manufacture and disposal, is better than that of battery-driven electric cars with a battery capacity that allows for longer trips, i.e. exceeding 250 kilometers.
Expensive platinum slows down the fuel cell
Despite these advantages, however, there are still very few hydrogen fuel cell vehicles on the road. Over the past ten years, fewer than 15,000 of these cars, produced by manufacturers such as Hyundai, Honda, Toyota and Daimler, have been registered worldwide. Why is that? In part, it is because many automobile companies continue to focus on battery technology, and the network of hydrogen fueling stations is still relatively sparse. But the main reason is the high price. Only 170 metric tons of platinum are processed in the entire world each year, so this precious metal will continue to be scarce and expensive. “By itself, the value of the 40 grams of platinum required as a catalyst in one of these fuel cell vehicles amounts to €1,000,” explains Ulrike Kramm, an expert on catalysts and assistant professor in the departments of Chemistry and Material and Geosciences at TU Darmstadt.
This platinum serves as an accelerator (catalyst) of chemical reactions in a fuel cell. A unit of the so-called PEM fuel cells commonly used in vehicles consists of an anode and a cathode, with a wafer-thin plastic membrane between them. PEM stands for “proton-exchange membrane”, meaning that the hydrogen gas from the vehicle's tank enters the membrane and splits on the anode side into hydrogen ions (protons) and electrons. The protons move through the membrane at an operating temperature of 80 to 100 degrees Celsius, combining on the cathode side with oxygen to form water. Simultaneously, the electrons flow through an external electrical circuit, where they go to work – for example supplying power to a vehicle’s electric engine.
From the blood cell to the fuel cell
Fuel cells today contain only one-tenth as much platinum as they did in the 1990s, when the first fuel cell vehicles were introduced. However, the target amount of 10 grams per vehicle, which would lower the cost of the car substantially, is still far out of reach. Accordingly, scientists have long been searching for alternatives. On the anode side, says Kramm, finely distributed platinum in a layer of carbon is still the material of choice, since no better alternative is available. “But on the cathode side, where so far we have been using about ten times as much platinum as on the anode side, we can now use catalysts that are free of precious metals.”
Researchers were inspired by nature – specifically by the hemoglobin in our red blood cells – when they came up with the idea for building catalysts free of precious metals. Located at the center of this protein complex is a heme group with an iron atom in the middle, surrounded by four nitrogen-carbon rings. The heme group serves to transport oxygen in the blood, as the iron is able to bind and then release oxygen. “This is precisely the quality we need for our catalysts,” says Ulrike Kramm. Just like in the heme group, the active center of Kramm’s Fe-N-C catalysts is an iron atom (Fe) stabilized by several nitrogen atoms (N) in a sponge-like carbon structure (C).
Scientists first used these elements to build catalysts in the 1970s. But for an efficient use in fuel cells, the catalyst does not only have to be active. “Its environment needs to be porous so that oxygen can move easily to the active centers. There, the oxygen has to combine with the protons that have moved through the membrane and with the electrons from the electrical circuit to form water, which must then be quickly carried away,” Kramm explains.
To ensure that these Fe-N-C catalysts are as active and stable as possible, the iron atoms must be surrounded by precisely the right number of nitrogen atoms – since “only then will water be produced, rather than the aggressive oxidizer hydrogen peroxide that can destroy the catalyst.” In addition, the iron must not separate from the surrounding carbon environment even if there is a dynamic change in the fuel cell’s current load. To meet these requirements, it is important to determine precisely how the atomic centers behave during operation. Ulrike Kramm is examining that question with the help of Mössbauer spectroscopy to collect in situ and operando measurements. Her team is a world leader in this area of precise spectral analysis.
In connection with fuel cell construction, moreover, she and her doctoral students have developed a preparation and cleaning procedure. Their design makes it possible, inexpensively and in only a few steps, to create a fine powder out of simple raw materials – iron, nitrogen and carbon – that can be used to prepare the membrane-electrode unit. Initial analyses have shown that this catalyst is just as active and stable as the material recently introduced by the ElectroCat consortium, a group of universities and major national research institutions in the United States.
“My vision: electric cars powered by batteries for local driving and by hydrogen-based fuel cells for long trips”
Excellent research. Excellent perspectives
Ulrike Kramm has received several awards for these successful efforts. She won the Adolf Messer Foundation Prize in 2018, and in 2019 she received the Curious Mind Research Award in the “Mobility and Energy” category. The latter is awarded by Merck KGaA, Darmstadt, Germany and Manager Magazin to scientists under the age of 40 who are working in the field of electromobility. “Such top-level research will enable us to use our scarce natural resources much more efficiently in the future,” said Stefan Oschmann, Chairman of the Executive Board and CEO of Merck KGaA, Darmstadt, Germany, at the award ceremony in Berlin. As a company that operates sustainably and is committed to the United Nation’s Sustainable Development Goals, we as a company are supporting the project to create environmentally friendly catalysts that will improve the environmental footprint of electric cars. Ulrike Kramm is particularly pleased by the recognition: “This award significantly increases the visibility of our research group and is attracting the attention of potential collaborators,” she points out.
What’s next? “We are in the process of patenting and publicizing our method of producing Fe-N-C catalysts,” says Kramm. “We also intend to launch a startup that will work with the industry and take charge of marketing activities.” The new catalysts have become much more stable over the past few years, but there is still a long way to go to achieve the target of 5,000 hours of operation without any noticeable decline in vehicle performance. However, Ulrike Kramm is confident that this can be done by optimizing the steps in the synthesis process. Hydrogen-based fuel cells might then become much less expensive than they are today, and we would be a substantial step closer to Kramm’s vision of emission-free driving: “My vision for the future is a combination of battery-powered electric cars for city traffic and hydrogen fuel cell vehicles for long trips – and perhaps synthetic fuels, also derived from hydrogen and CO2, for heavy-duty trucks, airplanes and ships.” The national hydrogen strategy announced by the German government in June 2020 points exactly in this direction: Germany wants to invest around nine billion euros in the coming years to build a world-leading hydrogen industry.
“Our catalyst does not require platinum; it functions much like the active center of a blood cell”
- PwC 2020 study, development of electromobility: https://www.pwc.de/de/automobilindustrie/elektromobilitaet-europa-war-2019-vorreiter-mit-weltweit-groesstem-wachstum-von-78-weitere-dynamik-in-2020-abzusehen.html
- Fraunhofer ISE 2019 study, greenhouse gas emissions, fuel cell and battery-powered vehicles: https://www.ise.fraunhofer.de/content/dam/ise/de/documents/news/2019/ISE_Ergebnisse_Studie_Treibhausgasemissionen.pdf
- Timetables for banning vehicles with combustion engines: https://www.auto-motor-und-sport.de/verkehr/verbrenner-aus-immer-mehr-verbote-zukunft-elektroauto/
- Curious Mind Research Award (Press release): https://www.emdgroup.com/en/news/curious-mind-researcher-award-granted-29-10-2019.html
- Ulrike Kramm website, TU Darmstadt: https://www.mawi.tu-darmstadt.de/ekat/ekat/index.de.jsp
 www.mobilitaet-in-deutschland.de › pdf › MiD2017_Ergebnisbericht (S. 72)
 https://www.ise.fraunhofer.de/content/dam/ise/de/documents/news/2019/ ISE_Ergebnisse_Studie_Treibhausgasemissionen.pdf
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