Can hydrogen be used for superconductors? I learned that heaver isotopes of a substance have a lower superconductivity transition temperature. Does this mean that things like hydrogen which are lighter can be used for high temperature superconductors?
 A: In fact hydrogen is an old idea to get a high temperature superconductor, based exactly on the idea of its light mass.
The problem is that one has to start from metallic hydrogen, which is a problem on itself. It has not yet been fully experimentally confirmed in the lab. You need pressures of several hundreds of GPa to achieve that (100 GPa is about 1 million times the atmospheric pressure).
However, very recently a group in Germany suceeded in producing a hydrogen based superconductor at 200 K. The largest ever measured critical temperature for a superconductor. The report is here and it was published in nature this month. They got superconductivity in H$_2$S, a substance that smell like rotten eggs. The caveat is that they had to go to 200 GPa to observe it. 
In short, the lightness of hydrogen makes is a very good candidate to achieve high temperature superconductivity. The experimental conditions to obtain it are quite complicated, though. It is unlikely (not impossible) that this will lead to a practical application.
