Gas that's clean yet bursting with energy (9)
I believe the answer is:
acetylene
'gas' is the definition.
(acetylene is a gas)
'clean yet bursting with energy' is the wordplay.
'bursting with' indicates an anagram.
'energy' becomes 'e' (physics symbol as in E=mc2).
'clean'+'yet'='cleanyet'
'cleanyet' with its letters anagrammed with 'e' makes 'ACETYLENE'.
'that's' acts as a link.
(Other definitions for acetylene that I've seen before include "Illuminating stuff also used for joining" , "Gas used chiefly in welding" , "Flammable gas" , "cutting gas emission?" , "powers industrial torch" .)