8053
Surprisingly , PVDF ultrafiltration membranes with hydrophobic pore walls and relatively large pore sizes of several tens of nanometers proved able to separate vanadium ions and protons efficiently , thus being suitable as a VFB separator .
 PVDF, vanadium
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 PVDF, vanadium