Graphene growth

Graphene film was synthesized with the CVD method on copper foil. First, a piece of copper foil with a thickness of 30 μm was electrochemically polished in 85wt.% H₃PO₄ solution for ~1 min. The counter electrode is also copper foil with twenty times larger area. The applied voltage is 5 V. The as-prepared copper foil was then put in tube furnace for graphene growth. The tandem graphene growth system is composed of three functional parts (Supplementary Fig. ²²)—gas purification part, CO activation part and graphene growth part. The gas purification part contains three purification tubes filled with NaOH/asbestos, dried silica gel and MnO, respectively, in order to remove unfavored CO₂, water and O₂. The CO activation part is 6 g of commercial Ni/Al₂O₃ catalyst (Sichuan Shutai Co. Ltd.), which can transform CO into hydrocarbon intermediates. The graphene growth part is a conventional CVD tube furnace. Before graphene growth, the copper foil was annealing in air atmosphere (25 mttor) at 1060 °C for 10 s, then H₂ (50 sccm, ~8000 Pa) as the reductant was flowed into quartz tube. Subsequently, 300 mL of CO product was pumped into the tandem system. With adjusting the flow rate of CO product, the total pressure was controlled at ~8400 Pa for at least 5 min. Graphene fragment using pure CO₂ was synthesized in the similar way, but NaOH/asbestos and MnO was removed for they can adsorb CO₂.