Do you ever wonder how hydrogen can be liquefied? Hydrogen is the first element in the Periodic Table, but it has the second lowest boiling point temperature of -423 F. Do you ever wonder who has the lowest boiling point temperature? The answer is Helium, the 2nd element in the Periodic Table. How about the third and the fourth lowest boiling point? They are Neon and Nitrogen. Because of the low boiling temperature, so Helium, Neon and Nitrogen are commonly used to liquefy hydrogen. In today's video, a helium Brayton cycle and liquid nitrogen are used to liquefy hydrogen.