Hydrogen fuel is one potential solution in the nationwide effort to decrease reliance on fossil fuels. According to the DOE, improving hydrogen storage is key to advancing hydrogen fuel cell technologies. At Ames Laboratory, scientists Long Qi and Wenyu Huang research the extraction of hydrogen from a class of materials called liquid organic hydrogen carriers, or LOHCs.

One of the ways to store hydrogen is chemically. Chemical storage relies on materials that react with hydrogen molecules and store them as hydrogen atoms, such as in LOHCs. This type of storage allows large amounts of hydrogen to be stored in small volumes at ambient temperatures. However, for the hydrogen to be useful, catalysts are needed to activate LOHCs and release the hydrogen. This process is called dehydrogenation.

Qi explained that currently there are other dehydrogenation methods, but they raise some challenges. Some methods rely on metal-based catalysts, which involve critical platinum group metals. Supplies of these metals are limited and expensive. Other methods require additives to release the hydrogen. The additives are not reusable and result in a higher overall cost because they need to be added in each cycle.

The catalyst Qi and Huang developed does not require metals or additives. “It’s fairly simple,” Qi said. “Basically, just add the metal-free catalyst into the LOHC, and then the hydrogen gas is just popping out, even at room temperature.”

The catalyst is composed of nitrogen and carbon. The key to its efficiency is the structure of the nitrogen. Catalytic activity can take place at room temperature because of the unique closely spaced graphitic nitrogens as nitrogen assembly which were formed during the carbonization process. The nitrogen assembly catalyzes the cleavage of carbon-hydrogen (C-H) bonds in LOHCs and facilitates the desorption of hydrogen molecules. This process is what makes the catalyst more efficient than other catalysts in use.

Qi and Huang explained that based on DOE goals for vehicle technologies, the hydrogen storage capacity needs to be close to 6.5% by weight. They are optimistic about the future of their research to meet the goal with molecules that have a larger capacity.

“This research will positively impact the target of reducing carbon dioxide emission,” Huang said, “and we will need to develop more efficient catalytic systems.”

In 2019, the transportation industry accounted for 29% of the overall carbon dioxide emissions in the U.S. Qi said that the ease and efficiency of this process could benefit the transportation industry in the future. The benefits come from a combination of using LOHCs and a catalyst like this one. The combination can extract usable hydrogen from storage at a lower cost and under milder conditions than current technologies. A greater hydrogen density can provide a greater charge for hydrogen fuel cells which could provide power to vehicles over greater distances.

Both Qi and Huang emphasized that this research is an important step to support the national mission to become carbon-neutral by 2050 by providing an easy and efficient way to dehydrogenate LOHCs.

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Materials provided by DOE/Ames Laboratory. Note: Content may be edited for style and length.

Following the example of the sun, fusion power plants aim to fuse the hydrogen isotopes deuterium and tritium and release large amounts of energy in the process. The only plant in the world currently capable of operating with such fuel is the European joint project JET, the Joint European Torus in Culham near Oxford, UK. However, the last experiments with the fuel for future fusion power plants were conducted there in 1997. Because tritium is a very rare raw material that also poses special handling challenges, research teams usually use hydrogen or deuterium for plasma experiments. In future power plants, tritium will be formed from lithium during energy production.

Experiments with deuterium-tritium mixtures in preparation for ITER

“We can explore the physics in fusion plasmas very well by working with hydrogen or deuterium, so this is the standard worldwide,” explains IPP’s Dr. Athina Kappatou, who with her IPP colleagues Dr. Philip Schneider and Dr. Jörg Hobirk led significant parts of the European collaborative experiments at JET.” However, for the transition to the international, large-scale, fusion experiment ITER, it is important that we prepare for the conditions prevailing there.” ITER is currently under construction in Cadarache, in southern France, and is expected to be able to release ten times as much energy as is fed into the plasma in terms of heating energy, using deuterium-tritium fuel.

To bring the JET experiment as close as possible to future ITER conditions, the previous carbon lining of the plasma vessel was replaced by a mixture of beryllium and tungsten, as is also planned for ITER, between 2009 and 2011. The metal tungsten is more resistant than carbon, which, moreover, stores too much hydrogen. However, the now metallic wall places new demands on the quality of the plasma control. The current experiments demonstrate the successes of the researchers: At temperatures ten times higher than those at the center of the sun, record levels of generated fusion energy have been achieved.

World record under ITER-like conditions

Prior to the change of the wall material, JET had set the world energy record in 1997 with a plasma that produced 22 megajoules of energy. This record stood until now. “In the latest experiments, we wanted to prove that we could create significantly more energy even under ITER-like conditions,” explains IPP physicist Dr. Kappatou. Several hundred scientists and researchers were involved in years of preparation for the experiments. They used theoretical methods to calculate in advance the parameters they needed to obtain to generate the plasma in order to achieve their goals. The experiments confirmed the predictions in late 2021 and delivered a new world record: JET produced stable plasmas with deuterium-tritium fuel that released 59 megajoules of energy.

To produce net energy — that is, to release more energy than the heatering systems provide — the experimental facility is too small. This will not be possible until the larger-scale ITER experiment in southern France comes online. “The latest experiments at JET are an important step toward ITER,” concludes Prof. Sibylle Günter, Scientific Director of the Max Planck Institute for Plasma Physics. “What we have learned in the past months will make it easier for us to plan experiments with fusion plasmas that generate much more energy than is needed to heat them.”

Background information: Megawatts vs. Megajoules

In the recent record-breaking experiment, the fusion reactions in JET released a total of 59 megajoules of energy in the form of neutrons during a five-second phase of a plasma discharge. Expressed in units of power (energy per time), JET achieved a power output of just over 11 megawatts averaged over five seconds. The previous energy record, set in 1997, was just under 22 megajoules of total energy and 4.4 megawatts of power averaged over five seconds.

About JET

JET was jointly designed and built by the members of the European fusion program EUROfusion and has been jointly operated since 1983. The English fusion center “Culham Centre for Fusion Energy” in Culham near Oxford is responsible for the technical operations, while temporarily seconded researchers and technicians from the EUROfusion laboratories work on the facility on a campaign basis. With numerous secondments, IPP is an important participant in the JET program.

About Max Planck Institute for Plasma Physics

The research conducted at the Max Planck Institute for Plasma Physics (IPP) in Germany (locations: Garching near Munich and Greifswald) is concerned with investigating the physical basis of a fusion power plant. Like the sun, such a plant aims to generate energy from fusion of atomic nuclei. IPP’s research is part of the European fusion program. With its workforce of approximately 1,100 IPP is one of the largest fusion research centers in Europe.

“The discovery shows that our closest stellar neighbour seems to be packed with interesting new worlds, within reach of further study and future exploration,” explains João Faria, a researcher at the Instituto de Astrofísica e Ciências do Espaço, Portugal and lead author of the study published today in Astronomy & Astrophysics. Proxima Centauri is the closest star to the Sun, lying just over four light-years away.

The newly discovered planet, named Proxima d, orbits Proxima Centauri at a distance of about four million kilometres, less than a tenth of Mercury’s distance from the Sun. It orbits between the star and the habitable zone — the area around a star where liquid water can exist at the surface of a planet — and takes just five days to complete one orbit around Proxima Centauri.

The star is already known to host two other planets: Proxima b, a planet with a mass comparable to that of Earth that orbits the star every 11 days and is within the habitable zone, and candidate Proxima c, which is on a longer five-year orbit around the star.

Proxima b was discovered a few years ago using the HARPS instrument on ESO’s 3.6-metre telescope. The discovery was confirmed in 2020 when scientists observed the Proxima system with a new instrument on ESO’s VLT that had greater precision, the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO). It was during these more recent VLT observations that astronomers spotted the first hints of a signal corresponding to an object with a five-day orbit. As the signal was so weak, the team had to conduct follow-up observations with ESPRESSO to confirm that it was due to a planet, and not simply a result of changes in the star itself.

“After obtaining new observations, we were able to confirm this signal as a new planet candidate,” Faria says. “I was excited by the challenge of detecting such a small signal and, by doing so, discovering an exoplanet so close to Earth.”

At just a quarter of the mass of Earth, Proxima d is the lightest exoplanet ever measured using the radial velocity technique, surpassing a planet recently discovered in the L 98-59 planetary system. The technique works by picking up tiny wobbles in the motion of a star created by an orbiting planet’s gravitational pull. The effect of Proxima d’s gravity is so small that it only causes Proxima Centauri to move back and forth at around 40 centimetres per second (1.44 kilometres per hour).

“This achievement is extremely important,” says Pedro Figueira, ESPRESSO instrument scientist at ESO in Chile. “It shows that the radial velocity technique has the potential to unveil a population of light planets, like our own, that are expected to be the most abundant in our galaxy and that can potentially host life as we know it.”

“This result clearly shows what ESPRESSO is capable of and makes me wonder about what it will be able to find in the future,” Faria adds.

ESPRESSO’s search for other worlds will be complemented by ESO’s Extremely Large Telescope (ELT), currently under construction in the Atacama Desert, which will be crucial to discovering and studying many more planets around nearby stars.

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