Ball-milled sulfur-doped graphene materials contain metallic impurities originating from ball-milling apparatus: their influence on the catalytic properties

Ball-milling apparatus is a source of metallic impurities in graphene materials. Sulfur-doped graphene obtained from zirconium dioxide-based ball-milling apparatus contains drastically lower amount of metallic impurities than that obtained from stainless-steel based ball-milling apparatus. The metallic impurities exhibit catalytic effects toward the electrochemical catalysis of hydrazine and cumene hydroperoxide.