Abstract
Increasing the specific electrical capacitance of supercapacitors has been received great attention from both researchers and industry. Herein, how to achieve this by coating the surface of reduced graphene oxide (rGO) with copper(II) oxide (CuO) and zinc oxide (ZnO) is reported. The CuO/rGO and ZnO/rGO hybrid layers were prepared via chemical reactions between graphene oxide (GO) and salts of copper and zinc, respectively. The crystallographic structures and surface morphologies of composite materials were studied by using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. Cyclic voltammetry (CV) and electrical capacitance measurements were used to analyze the electrochemical properties of the composites. The results show that CuO and ZnO increased the specific electrical capacitance of rGO, while the composite CuO/rGO and ZnO/rGO materials have good chemical stability with a higher specific electrical capacity (465.73 F×g−1) than CuO/rGO (167.52 F×g−1), ZnO/rGO (185.48 F×g−1), rGO (113.50 F×g−1), and annealed graphite (53.12 F×g−1). The mechanism of increasing the specific capacitance depending on whether the composite CuO/rGO and ZnO/rGO materials act as a pseudocapacitor and/or an electrical double-layer capacitor is elucidated.
 HIGHLIGHTS
 
 One challenging problem for supercapacitor improvement is increasing its specific electrical capacitance
 CuO/rGO and ZnO/rGO hybrid layers were prepared using graphene oxide and copper and zinc salts
 The composite CuO/rGO and ZnO/rGO materials have better chemical stability with a higher specific electrical capacity than CuO/rGO, ZnO/rGO, rGO, and annealed graphite
 
 GRAPHICAL ABSTRACT
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