Hierarchical self-assembly of microscale leaf-like CuO on graphene sheets for high-performance electrochemical capacitors

In this paper, a leaf-like porous CuO-graphene nanostructure is synthesized by a hydrothermal method. The as-prepared composite is characterized using XRD, Raman, SEM, TEM and nitrogen adsorption-desorption. The growth mechanism is discussed by monitoring the early growth stages. It is shown that the CuO nanoleaves are formed through oriented attachment of tiny Cu(OH)(2) nanowires. Electrochemical characterization demonstrates that the leaf-like CuO-graphene are capable of delivering specific capacitances of 331.9 and 305 F g(-1) at current densities of 0.6 and 2 A g(-1), respectively. A capacity retention of 95.1% can be maintained after 1000 continuous charge-discharge cycles, which may be attributed to the improvement of electrical contact by graphene and mechanical stability by the layer-by-layer structure. The method provides a facile and straightforward approach to synthesize CuO nanosheets on graphene and may be readily extended to the preparation of other classes of hybrids based on graphene sheets for technological applications.