2D hydrogen-carrier liquid fuel: Graphene oxide electrochemically hydrogenated by copper porous catalysts in continuous flow cell conditions and its H2 recovery

Graphene-based materials have attracted considerable attention in the energy storage field due to their unique properties and the possibility of storing hydrogen. Graphene oxide (GO), reduced graphene oxide (rGO), or graphane (GA), among others, are well-studied graphene derivatives where the aromatic structure has been tuned and adapted for long-term energy-dense hydrogen storage. We present the controlled hydrogenation of GO for the first time obtained in continuous flow electrochemical reactor conditions, directly fed with GO flakes in aqueous suspension. The system directly splits water and bonds the hydrogen to the GO flakes, producing an energy-rich, chemically hydrogenated reduced graphene oxide (rGO H) liquid fuel at cell potentials as low as 1.5 V, in a scalable process architecture. The influence of foam-like porous cathodes such as nickel (Ni) or copper (Cu) has identified the unfavorable catalytic surface of Cu to the hydrogen gas evolution to be beneficial for faradaic efficiency towards GO polarization and hydrogenation. The resulting rGO-H has been fully characterized to study the mechanism involved in the oxygenated group's loss, structure reorganization, and H-fixation steps occurring during the electrochemical reduction. rGO-H programmed thermal decomposition at mild temperatures describes the hydrogen recovery as molecular gas (H 2 ) on demand, with binding energies of 0.98 eV/at. • The electrochemical hydrogenation of graphene oxide (GO) is presented as a hydrogen storage cheap, facile and abundant candidate. • Chemically bonded hydrogen enables a long term, dense liquid, safe storage. • Hydrogenation is performed in flow conditions requiring solely 1.5 V cell potential. • Copper foam electrodes enhance the hydrogen storage efficiency, in front of H2 gas generation. • Hydrogen (H 2 ) can be recovered on demand with energies of 0.98 eV/at.