Electrophoretic deposition of copper–copper hydroxide/graphene oxide nanocomposite for supercapacitor

Copper–copper hydroxide-electrochemically reduced graphene oxide (Cu–Cu(OH)₂/RGO) nanocomposite is formed successfully on stainless steel (SS) in two steps: (i) electrophoretic deposition of nanocomposite film from CuSO₄ and graphene oxide (GO) colloidal suspension on SS and (ii) electrochemical reduction of prepared electrode in 0.5 M NaNO₃ electrolyte. Cu–Cu(OH)₂/RGO is characterized by X-ray diffraction, atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectrometry. AFM and FESEM images indicate the homogenous distribution of Cu–Cu(OH)₂ nanoparticles on the surface of RGO. The electrochemical properties of Cu–Cu(OH)₂–RGO/SS are investigated by cyclic voltammetery, galvanostatic charge/discharge technique and electrochemical impedance spectroscopy. Cu–Cu(OH)₂–RGO/SS exhibits a high capacitance of 333 F g⁻¹ in 0.5 M Na₂SO₄ electrolyte which is two times higher than that of RGO/SS (192 F g⁻¹) and indicate the positive effect of Cu–Cu(OH)₂ on capacitance of electrode. Also, it is observed that with addition of 0.1 M \({\text{Fe}}({\text{CN}})_{6}^{{3 - /4 - }}\) into aqueous solution of 0.5 M Na₂SO₄, the electrochemical performance of Cu–Cu(OH)₂–RGO/SS increases substantially and shows a high specific capacitance of 492 F g⁻¹ at current density of 5 A g⁻¹, which is higher than that of Cu–Cu(OH)₂–RGO/SS (333 F g⁻¹). A positive effect of the presence of \({\text{Fe}}({\text{CN}})_{6}^{{3 - /4 - }}\) in the electrolyte is due to electron relay of \({\text{Fe}}({\text{CN}})_{6}^{{ - 3}}/{\text{Fe}}({\text{CN}})_{6}^{{ - 4}}\) ion pair at the electrode/electrolyte interface by coupling in the redox transition of Cu(I)/Cu(II). The electrochemical tests indicate that Cu(OH)₂–RGO/SS in 0.5 M Na₂SO₄ electrolyte containing 0.1 M \({\text{Fe}}({\text{CN}})_{6}^{{3 - /4 - }}\) shows an outstanding cyclic stability with specific retention of 97% after 500 cycles.