Described here is a metal-carbon composite, comprising (a) a porous three-dimensional scaffold comprising one or more of carbon nanotubes, graphene and graphene oxide, and (b) metal nanoparticles disposed on said porous scaffold, wherein the metal-carbon composite has a density of 1 g/cm.sup.3 or less, and wherein the metal nanoparticles account for 1 wt. % or more of the metal-carbon composite. Also described are methods for making the metal-carbon composite.
FEDERAL FUNDING STATEMENT
 This invention was made with government support under Contract No. DE-AC52-07NA27344 awarded by the U.S. Department of Energy. The government has certain rights in this invention.