High-pressure Raman, infrared, x-ray, and neutron studies show that H ₂ and H ₂ O mixtures crystallize into the sII clathrate structure with an approximate H ₂ /H ₂ O molar ratio of 1:2. The clathrate cages are multiply occupied, with a cluster of two H ₂ molecules in the small cage and four in the large cage. Substantial softening and splitting of hydrogen vibrons indicate increased intermolecular interactions. The quenched clathrate is stable up to 145 kelvin at ambient pressure. Retention of hydrogen at such high temperatures could help its condensation in planetary nebulae and may play a key role in the evolution of icy bodies.

This perspective highlights the application of MOFs for solid-state electrolytes, emphasizing their advantages, challenges and future directions.