6935
After deposition of noble metal catalysts , p - WSe ( 2 ) photocathodes exhibited thermodynamically based photoelectrode energy - conversion efficiencies of > 7 % for the hydrogen evolution reaction under mildly acidic conditions , and were stable under cathodic conditions for at least 2 h in acidic as well as in alkaline electrolytes .
 hydrogen
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 hydrogen