8052
Polyvinylidene fluoride ( PVDF ) ultrafiltration membranes were investigated for the first time in vanadium redox flow battery ( VFB ) applications .
 Polyvinylidene fluoride, PVDF, vanadium
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 Polyvinylidene fluoride, PVDF, vanadium