In this study, Cu₂O microcubes and microspheres were synthesized using facile hydrothermal methods by manipulating the synthesis parameters. The Cu₂O microcubes (∼2 μm in diameter) were formed in presence of formic acid, whereas hierarchical Cu₂O microspheres (∼5 μm in diameter) were formed in acetic acid. Transmission electron microscopy (TEM) confirmed the formation of single crystalline microcubes and polycrystalline microspheres. The possible growth mechanism suggested that microcubes were formed due to the cubic crystal structure of Cu₂O and the formation kinetics, whereas microspheres were formed due to the orientational attachment of nuclei with similar aggregation velocities along every direction. The electrochemical properties of the Cu₂O microcubes and microspheres were investigated to understand the role of the morphology on the supercapacitor properties. The Cu₂O microcubes exhibited a higher specific capacitance, better rate capability and cycling stability as compared to microspheres, although the particle size and pore size were larger and surface area was lower. The specific capacitance of the Cu₂O microcubes and microspheres were 660 and 516 F g⁻¹, respectively, at a 1 A g⁻¹ current density. The Cu₂O microcubes showed 80% specific capacitance retention at a 5 A g⁻¹ current density after 1000 cycles. The single crystalline nature and the presence of a smaller number of grain boundaries in the microcubes compared to the microspheres resulted in an increase in conductivity and an increase in capacitance. The results showed that the Cu₂O microcubes can be a promising electrode material for high performance supercapacitors.

We show for the first time, a composite of carbon and binary transition metal oxide, in the form of reduced graphene oxide and nickel tungstate (RGO/NiWO₄) nanocomposite, is an effective material for electrochemical detection of heavy metal ions.