The Fraunhofer Institute for Microtechnology and Microsystems IMM in Mainz is working on a decentralized, space-saving and energy-efficient ammonia cracking technology as part of several research projects.

"Ammonia has great potential for a sustainable transformation of our energy system," explains Dr. Gunther Kolb, Head of Energy and Deputy Director of the Fraunhofer IMM. "The challenge of the energy transition is not just to produce sufficient emission-free energy. As green electricity can be generated in large quantities, particularly in very windy or sunny locations such as Chile or Australia, low-loss transportation to locations with lower energy consumption also plays a relevant role." This is where the use of ammonia can bring revolutionary advantages.

Storing and transporting hydrogen with ammonia

Green hydrogen (_H₂), which serves as a storage medium for renewable electricity, can be converted into ammonia (NH_₃) in a ratio of 3:1 in combination with nitrogen (_N₂).

In this form, it can be stored and transported with significantly lower losses. This is because ammonia liquefies at normal pressure from around -33 °C or at a pressure of just 7.5 bar - in contrast to hydrogen, which has to be fed into a vacuum and cooled down to -253 °C for liquefaction.

In addition, ammonia has a higher volumetric energy density than liquid hydrogen, i.e. it transports more energy per unit volume.

"Only around five percent more energy is needed to produce ammonia from hydrogen and nitrogen than to produce hydrogen from green electricity," explains Kolb. "And both the production and splitting of ammonia are completely CO₂-free."

Although ammonia is toxic and flammable and is therefore considered dangerous goods, its transportation is well established: Around 25 million tons of ammonia are transported safely by ship and rail worldwide every year, mainly for fertilizer production.

Cracking as a key technology - also decentralized

In order for ammonia to be used in the chemical industry or as an energy source, it must be split back into hydrogen and nitrogen on site. The so-called cracking process takes place in a reactor at around 600 °C on a nickel-based, inorganic catalyst with a large surface area.

Fraunhofer IMM pilot plant for ammonia cracking with a capacity of 20 kg/h of ammonia © Fraunhofer IMM

"The first large-scale electrolysis plants to produce ammonia are currently being built in green energy-rich locations such as Australia and Chile. In Europe, for example, one of the first large cracker plants is being built in Rotterdam at the same time," says the chemical engineer.

The recovered hydrogen is then to be distributed via pipelines. However, smaller companies often do not yet have access to this infrastructure. The German hydrogen supply is currently being developed: A hydrogen core network around 9000 kilometers long is planned by 2032 - mainly by converting existing natural gas pipelines. But even after that, many regions will not be connected.

"Our decentralized cracking technology can close this supply gap efficiently and without emissions for demand quantities of between 100 kilograms and 10 tons of hydrogen per day," explains Kolb.

Fraunhofer IMM has already developed a compact ammonia cracker together with the Fraunhofer Institute for Industrial Mathematics ITWM in the "AMMONPAKTOR" project funded by the state of Rhineland-Palatinate.

Thanks to innovative plate heat exchanger technology and integrated waste gas incineration of the pressure swing adsorption used for cleaning, an efficiency of 90 percent is achieved. Conventional technologies are around 70 percent.

Cracking process: Efficient and compact

The heat required for the cracking process is generated directly in the cracking reactor using the exhaust gas flows. No additional fuel or electricity is required. The reactor is around 90 percent smaller than conventional systems, making it ideal for mobile or space-limited applications. Thanks to the use of exhaust gas, the CO₂ _footprint is also lower than with electrically heated reactors.

"In addition to the system-internal exhaust gas utilization, the innovative Fraunhofer IMM plate heat exchanger coated directly with a catalyst is the decisive difference," explains Kolb. "Instead of the usual heat being generated in a high-energy pipe system heated from the outside to around 900 degrees Celsius, our technology generates the heat required for fission directly where it is needed. Our system therefore has a significantly better heat transfer. This means enormous energy savings."

A prototype at the Mainz site is already producing around 75 kilograms of hydrogen per day - enough to operate a small hydrogen filling station, for example.

"You could supply a small hydrogen filling station with this amount, for example," says Kolb.

Next step: Upscaling

The next development goal is to scale up production to 10 tons of hydrogen per day. This is being worked on as part of the five-year EU project "GAMMA" and the Fraunhofer lighthouse project "AmmonVektor", among others. The latter aims to map the entire value chain for green ammonia in order to make hydrogen available decentrally and as cost-effectively as possible. The project has been running since the beginning of 2024 under the leadership of the Fraunhofer Institute for Environmental, Safety and Energy Technology UMSICHT.

Source: Fraunhofer IMM