[1] Polyhydrides are important because they can form substances with a very high density of hydrogen.
These are formed at 30 GPa and 2,100 K.[2] Heating and compressing a metal with ammonia borane avoids using bulky hydrogen, and produces boron nitride as a decomposition product in addition to the polyhydride.
There should also be electron-phonon coupling which happens when the electric properties are tied to the mechanical position of the hydrogen atoms.
[35][50][51] The highest superconduction critical temperatures are predicted to be in groups 3 and 3 of the periodic table.
Late transitions elements, heavy lanthanides or actinides have extra d- or f-electrons that interfere with superconductivity.
[52] For example, lithium hexahydride is predicted to lose all electrical resistance below 38 K at a pressure of 150 GPa.
PH3 doped H3S is also predicted to have a transition temperature above the 203 K measured for H3S (contaminated with solid sulfur).
[56] H3Se actually is a van der Waals solid with formula 2H2Se·H2 with a measured Tc of 105 K under a pressure of 135 GPa.