A facile hydrothermal synthesis of graphene porous NiO nanocomposite and its application in electrochemical capacitors

A new porous graphene/NiO has been prepared successfully by hydrothermal method with graphene oxide solution, Ni(NO3)2·6H2O and urea as raw materials. The as-prepared composite is characterized by X-ray diffraction, Raman, FT-IR, SEM, TEM and nitrogen adsorption/desorption. It is shown that graphene sheets are well decorated by the NiO nanoparticles to form a hierarchical nanostructures with rich porosity (ca. 2–5 nm) and large specific surface area (174.1 m2 g−1). Electrochemical characterization demonstrates that the mesoporous graphene/NiO are capable of delivering a specific capacitance of 429.7 F g−1 at the current density of 200 mA g−1 and offer good capacitance retention of 86.1% at 1 A g−1 after 2000 continuous charge–discharge cycles. These rich and evenly distributed porosity could reduce the transportation distance and offer a robust sustentation of OH− ions due to its “ion-buffering reservoirs”, ensuring that sufficient Faradaic reactions can take place at the surfaces of electroactive NiO nanoparticles. It suggests that the hierarchical nanostructure is helpful in improving the electrochemical performance of the oxide.

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► Graphene porous NiO nanocomposite is prepared by hydrothermal method.
► The hierarchical nanostructures possess rich porosity and large specific surface area.
► The rich and evenly distributed porosity offers a robust sustentation of OH− ions and reduce transportation distance during charge/discharge process.
► The composite delivers a capacitance of 342.9 F g−1 at 1 A g−1 with capacity retention of 86.1% after 2000 cycles.