Room temperature separation of hydrogen isotopes to accelerate fusion

Hydrogen has three isotopes: protium, deuterium, and tritium. These isotopes play crucial roles in the production of hydrogen fuel, nuclear fusion, and the development of advanced pharmaceuticals.

However, it is not easy to isolate these isotopes at room temperature. Indeed, they have almost similar sizes and shapes. In addition, each of them has a proton and an electron, which gives them similar chemical and thermodynamic properties.

Therefore, the methods currently used to extract hydrogen isotopes are resource intensive because they require extreme conditions to operate.

For example, “it has been known for almost 15 years that porous metal-organic frameworks can, in principle, be used to purify and separate hydrogen isotopes,” said Knut Asmis, professor of chemistry at the University of Leipzig.

“However, this was only possible at very low temperatures, around minus 200 degrees Celsius – conditions that are very expensive to implement on an industrial scale,” he added.

Asmis and his colleagues recently published a study that provides valuable insight into how hydrogen isotopes can be isolated at room temperature and at low cost. Here’s what their research reveals:

The secret is the aqueous ligand

When porous metal ions such as Cu+ interact with hydrogen under extreme conditions, they perform selective absorption to isolate an isotope.

“Adsorption is a process by which atoms, ions or molecules of a gas or liquid adhere to a solid, often porous, surface,” the study authors note.

During their study, the researchers found that when water molecules are used as ligands with the copper ion, the metal becomes more efficient at attracting and holding hydrogen molecules.

Moreover, the resulting copper-water complex is better able to distinguish the energy difference in the bonds between H₂ (regular hydrogen) and D₂ (heavy hydrogen) compared to bare copper.

“By combining experimental and computational methods, we demonstrate a high isotopological selectivity in the binding of dihydrogen to Cu+(H2O), which results from a large difference in the zero-point energies of adsorption (2.8 kJ mol−1 between D2 and H2, including an anharmonic contribution of 0.4 kJ mol−1),” note the authors of the study.

Moreover, unlike bare copper ions, the copper-water complex does not require large amounts of energy to isolate hydrogen isotopes. This means that it could lead to more efficient, less resource-intensive and highly cost-effective methods for obtaining hydrogen isotopes.

The study shows that porous metal complexes with aqueous ligands are promising candidates for the isolation of hydrogen isotopes. It also suggests that metal-water complexes could be used to study chemical reactions that occur at particular locations in large systems.

“These systems are ideal model complexes for gas-phase studies of the chemistry of individual active sites as they occur in framework materials,” the study author added.

In addition, Asmis and his team also performed complex spectroscopy and quantum calculations to understand in detail the interaction between hydrogen isotopes. Their findings could reveal more practical ways of selectively absorbing isotopes.

“For the first time, we were able to show the influence of individual atoms of the framework compounds on adsorption,” says Thomas Heine, one of the authors of the study and an expert in theoretical chemistry at the Technical University of Dresden.

“We can now optimize them in a targeted manner to obtain materials with high selectivity at room temperature,” adds Heine.

The study is published in the journal Chemical sciences.