Exploration of new liquid organic hydrogen carrier materials for safer and transportable energy sources

To reduce CO2 emissions, an energy transition from carbon-based energy systems to more sustainable systems based on hydrogen energy is urgently needed. However, the properties of hydrogen (low volume density, flammability, embrittlement, etc.) make it very difficult to use it as a widespread energy source. Therefore, the key to building a hydrogen society is to use hydrogen safely and efficiently.

One way to achieve this is through liquid organic hydrogen carrier (LOHC) technology, which can safely store and transport large amounts of hydrogen through chemical bonding.

LOHC technology offers a solution by allowing hydrogen to be stored in a liquid organic compound that remains stable at ambient temperature and pressure, similar to gasoline or diesel fuel. The technology also leverages existing fossil fuel infrastructure to streamline hydrogen transportation and reduce costs associated with hydrogen distribution compared to other hydrogen storage methods.

Significant efforts have been directed toward developing catalysts and new reactor designs to enhance the dehydrogenation and hydrogenation efficiency of LOHC-based systems. However, the most effective approach lies in addressing the inherent limitations of the LOHC materials themselves.

The key to LOHC technology lies in the development of suitable organic compounds for hydrogen storage. The properties of LOHC materials are of great importance in determining important factors such as hydrogen storage capacity, reaction kinetics, energy consumption during the dehydrogenation/hydrogenation process, and reversibility.

Previous studies focused on meeting the hydrogen storage capacity (>6 wt%) and physicochemical properties (wide liquid range from subzero to 300 °C) of aromatic LOHC supports, resulting in a lack of material diversity. This limited the potential for performance improvement. .

A research team led by Dr. Jihoon Park from the Korea Research Institute of Chemical Technology (KRICT) is actively exploring new LOHC compounds to develop advanced LOHC materials and increase the diversity of LOHC materials for improved performance. I went.

The research results are published in the Chemical Engineering Journal.

The team focused on optimizing the LOHC material through a molecular engineering approach and redesigning its molecular structure to overcome its limitations. In 2018, the research team developed a new LOHC material (MBP, 2-(n-methylbenzyl)pyridine) with enhanced dehydrogenation performance by adding an N atom to the benzene ring of benzyltoluene.

However, by combining experimental and theoretical research, the research team made a breakthrough discovery. The methyl group (-CH3), which was previously thought to have little effect, now plays an important role in improving the performance of LOHC materials. Unlike previous LOHC materials (MBPs), which existed as mixtures of isomers, the research team developed a new version of pure LOHC materials (2-benzyl-6-methylpyridine, BMP) with precise control over the position of the methyl groups. We proposed a synthesis method.

The new LOHC material (BMP) increased the hydrogen storage and release rates by 206% and 49.4%, respectively, compared to MBP.

Additionally, the research team created new LOHC candidates by rearranging the methyl groups of dibenzyltoluene, one of the most promising commercially available LOHC materials, to overcome the limitations of slow reaction rates due to its chemical structure. We have developed benzyl-methylbenzyl-benzene (BMB). .

BMB exhibits a 150% faster hydrogenation rate than DBT at 150 °C and releases 170% more hydrogen compared to DBT at 270 °C. Additionally, the research team uncovered a dehydrogenation mechanism in which the N-heterocyclic LOHC material interacts with various active metals in the catalyst to promote hydrogen extraction.

Dr. Jihoon Park said, “Our research focuses on optimizing the LOHC structure, allowing us to precisely control the placement of methyl groups as functional groups within LOHC materials, and opening new possibilities for LOHC systems. “These findings are also expected to influence future designs.” We will develop next-generation hydrogen storage materials and pave the way to a safer and more efficient hydrogen energy society. ”