and if so is it the highest temperature superconductor known?
No one has -as far as I know- ever even demonstrated that metallic hydrogen is a superconductor (all known phases are insulating). It is most definitely not a superconductor at 273K
(which is a bit of a "silly" temperature anyway, it happens to be equal to 0 degrees Celsius which is also the freezing temperature of water; it would if nothing else be a HUGE coincidence if metallic H had a Tc of that temperature).
Yes, metallic hydrogen has been predicted to be superconducting at very high temperatures. But no one has actually shown that this prediction is correct.
Also, the pressure needed to keep the hydrogen metallic at 290K would be truly enormous.
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