Cleaner energy protects oxygen (4)
I believe the answer is:
soap
'cleaner' is the definition.
(soap is a kind of cleaner)
'energy protects oxygen' is the wordplay.
'energy' becomes 'sap' (I've seen this before).
'protects' indicates putting letters inside.
'oxygen' becomes 'o' (atomic symbol for oxygen).
'sap' going around 'o' is 'SOAP'.
(Other definitions for soap that I've seen before include "TV programme - sudsy bar" , "Cleaner - long-running TV show" , "Cleaner - TV programme" , "TV entertainment" , "Bath tablet" .)