Hydrogen isotopes separation at room temperature to boost fusion

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

However, it’s not easy to isolate these isotopes at room temperature. This is because they have almost similar sizes and shapes. Plus, each of them has one proton and one electron, leading to similar chemical and thermodynamic properties. 

Therefore, the methods currently used for extracting hydrogen isotopes are resource-intensive as they require extreme conditions to work. 

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

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

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

The secret is water 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 from 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 better at attracting and holding hydrogen molecules. 

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

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

Moreover, unlike bare copper ions, the copper water complex doesn’t require large amounts of energy to achieve hydrogen isotope isolation. This means that it might lead to more efficient, less resource-intensive, and highly cost-effective ways of obtaining hydrogen isotopes.

The study shows that porous metal complexes with water ligands are promising candidates for hydrogen isotope isolation. It also suggests that metal-water complexes could be used to study chemical reactions that take place at particular sites in large systems. 

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

Moreover, Asmis and his team also performed spectroscopy and complex quantum calculations to understand the interaction between the hydrogen isotopes in detail. Their findings might reveal more practical ways of selective absorption of isotopes.

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

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

The study is published in the journal Chemical Science.