You might be thinking of supercapacitors, which store energy. <a href="http:&#x2F;&#x2F;physicsworld.com&#x2F;cws&#x2F;article&#x2F;news&#x2F;2010&#x2F;nov&#x2F;26&#x2F;graphene-supercapacitor-breaks-storage-record" rel="nofollow">http:&#x2F;&#x2F;physicsworld.com&#x2F;cws&#x2F;article&#x2F;news&#x2F;2010&#x2F;nov&#x2F;26&#x2F;graphen...</a>