Hydrogen is a champion in energy per kilogram, but storing it is a hassle. As a gas, it takes up a huge volume, and if you compress it or cool it to a liquid, you need heavy tanks and lots of energy. There's a third way: some solid materials absorb hydrogen like a sponge soaks up water and hold it within. Heat it up, hydrogen comes out; cool it down, it gets absorbed back. Such materials are called hydrides, and they could make hydrogen fuel safe and compact.
To find the best sponge-like material, you'd have to try thousands of options. Previously, experimental data were scattered across papers, making comparisons difficult. Now researchers have brought it all together: the DigHyd database contains over 30,000 records from 4,000 scientific papers. Each record includes not only how much hydrogen the material absorbs (by mass) but also how easily it releases hydrogen back. These numbers are like the pressure in a pump: if it takes a lot of effort to squeeze water out of a sponge, then extracting hydrogen will be tough too.
After compiling the data, the scientists tested whether a material's composition could predict its properties. It turned out yes: even a simple computer model can guess how much hydrogen a new material will absorb, with accuracy comparable to complex calculations. This means the database is truly useful: instead of running thousands of experiments, you can first screen promising candidates on a computer. This will speed up the search for materials for hydrogen cars, home energy storage, and even storing excess solar energy.
Hydrogen is the lightest element in the universe, but in a solid hydride it can take up less space than in liquid form: hydrogen atoms sit in the crystal lattice more densely than molecules in a liquid.