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Our results indicate that graphene - graphane systems could be used for hydrogen storage with high speed of charge - discharge of hydrogen .
 Chemical: graphene; Chemical: graphane; Chemical: hydrogen; Chemical: hydrogen
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: graphene; Chemical: graphane; Chemical: hydrogen; Chemical: hydrogen