Fabrication of nanoporous nickel oxide by de-zincification of Zn–Ni/(TiO2-nanotubes) for use in electrochemical supercapacitors

• NiO–ZnO/TiO2NTs electrodes were synthesized by de-zincification of Zn–Ni/TiO2-nanotubes.
• The nanoporous/cracked structures of the NiO–ZnO/TiO2NTs obtained at the electroplating time of 20 min.
• The effect of electroplating time on the supercapacitive behavior of new electrode was investigated by EIS.
• Extra porosity in electrodes improved the parameters effectively influencing the capacitive behavior.
• The specific capacitance of new electrode was 130 mF cm−2 at 0.45 mA cm−2.

NiO–ZnO/TiO2NTs electrodes were synthesized by the electrodeposition of Zn–Ni onto TiO2 nanotubes, dealloying in a concentrated alkaline solution and finally calcination of the resulting Zn(OH)2–Ni(OH)2/TiO2NTs at 300 °C. Morphology of the electrodeposited nanostructures was studied using scanning electron microscopy (SEM) while their electrochemical characterizations were carried out using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge procedures. The SEM analysis revealed the nanoporous/cracked structures of the NiO–ZnO/TiO2NTs obtained at the electroplating time of 20 min. The EIS studies showed that nanoporous/cracked structures of prepared electrodes can significantly improve the parameters effectively influencing the capacitive behavior such as ohmic resistance (Rs), charge transfer resistance (Rct) and constant phase element (CPE). The electrochemical investigations showed that the specific capacitance of these electrodes were around 130 mF cm−2 (325 F g−1) in 1.0 M NaOH electrolyte as measured at a current density of 0.45 mA cm−2 (1.1 A g−1). The modified electrodes also showed high stability and maintained 92% of initial capacity in 1.0 M NaOH electrolyte after ten days of being used in electrochemical experiments.

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