Hydrogen has three isotopes: H (protium), D (deuterium), and T (tritium). Because chemical properties are primarily determined by the type of element, H, D, and T exhibit almost identical chemical properties. However, since their atomic masses differ, their properties are slightly different. In recent years, it has been discovered that by exploiting these subtle differences and replacing H with D (deuteration), it is possible to slow down the degradation of pharmaceuticals and prolong their effectiveness, extend the lifetime of organic light-emitting diode (OLED) displays, and improve the performance of semiconductor devices. As a result, the demand for deuterium is expected to increase further in the future.
However, the source molecules H2 and D2 have very similar properties, making their separation difficult. Currently, they are separated by cryogenic distillation at approximately −250℃, utilizing their slight difference in boiling points. This method requires large-scale facilities and substantial energy input, and therefore the development of simpler and more energy-efficient separation technologies is strongly desired.
One promising alternative is a new method called chemical affinity quantum sieving (CAQS). This technique utilizes the slight difference in metal–hydrogen bond energies when hydrogen molecules adsorb onto metal atom surfaces. Due to the difference in atomic mass between H2 and D2, their zero-point vibrational energies—a quantum mechanical property—are slightly different, leading to a difference in binding strength (adsorption enthalpy). The larger this difference, the more efficient the separation becomes.
In our laboratory, we observed the largest adsorption enthalpy difference reported to date, 5.0 kJ/mol, in a metal complex. Furthermore, we successfully demonstrated the separation of H2 and D2 at room temperature using gas chromatography. This achievement represents an important step toward enabling hydrogen isotope separation at room temperature, which previously required extremely low temperatures. In the future, this approach is expected to contribute to the realization of more energy-efficient and practical isotope separation technologies.
