Inside a fuel cell, protons must race through a solid material like commuters through turnstiles at rush hour. If the turnstiles are sparse and narrow, the current is weak. In the past, to find a material with good proton conductivity, chemists had to screen compounds almost blindly, one by one. Now, a computer program has screened more than six million candidates on its own.
The program didn't search by ready-made formulas but by the pattern of atoms: how exactly oxygen and other atoms are arranged in the crystal. This approach helped find 27 compounds that conduct protons excellently. Among them are already known conductors (which confirms the method works) as well as more than ten entirely new substances, including organic materials and compounds not yet synthesized in the lab.
The most intriguing finding is a universal rule: at the moment a proton jumps from one oxygen atom to another, the distance between these atoms is always about 2.5 angstroms (that's five times smaller than a billionth of a meter). Such a distance appears across a wide range of chemical compositions. It turns out that proton conductivity depends not on the specific substance but on how atoms can rotate, how hydrogen bonds are connected, and how likely the proton jump itself is. This understanding will help design new materials for fuel cells that work without water.
A proton is the nucleus of a hydrogen atom, stripped of its electron. In a solid, it doesn't fly freely but hops from one oxygen atom to another, like along a chain.