Synthesis of CuO-Cu ₂ O@graphene nanosheet arrays with accurate hybrid nanostructures and tunable electrochemical properties

Herein, we describe the fabrication of CuO-Cu ₂ O@graphene nanosheet composites by one-step in situ anodic oxidation, showing that graphene nanosheets vertically oriented on the Cu foam skeleton can be easily grown by microwave plasma-enhanced chemical vapor deposition. Microstructural characterization revealed that the formation of CuO-Cu ₂ O nanoparticles in the bottom gaps of graphene nanosheet arrays (i.e., at locations featuring active sites and having access to the Cu source) results in the generation of accurate hybrid nanostructures. Additionally, the spread of the electrolyte could be effectively adjusted to control the transition of the charge storage mechanism from electrical double-layer capacitor to pseudo-capacitor-type. Thus, at high scan rates, the composite electrode acted as an electrical double-layer capacitor, acting as a pseudo-capacitor at low scan rates. A specific capacitance of 243 mF cm ⁻² was determined at a scan rate of 10 mV s ⁻¹ in 6 M aqueous KOH, increasing by almost 20% after 5000 charge-discharge cycles. The fabricated electrode exhibited a maximum energy density of 5.06 mWh cm ⁻³ at a power density of 0.18 W cm ⁻³ and a maximum power density of 5.64 W cm ⁻³ at an energy density of 2.27 mWh cm ⁻³ , thus showing superior performance in terms of electrochemical property tunability and cyclability.