Nickel hydroxide nanosphere decorated reduced-TiO2 nanotubes as supercapacitor electrodes

•Fabrication of a binder-free R-TiO2 NTs/Ni(OH)2 supercapacitor electrode.•Introducing oxygen vacancies via electrochemical reduction of TiO2 NTs.•Improved electrical conductivity and Ni(OH)2 deposition with oxygen vacancies.•Enhanced areal specific capacitance and capacitive retention of R-TiO2 NTs/Ni(OH)2. A straightforward electrochemical method was developed to modify titanium dioxide nanotubes (TiO2 NTs), creating oxygen vacancies via electrochemical reduction (ER) and depositing nickel hydroxide nanospheres (Ni(OH)2 NSs). This was done to discover the electrochemical properties of a TiO2 NTs based binder-free supercapacitor electrode. The improved conductivity of the reduced TiO2 NTs (R-TiO2 NTs) electrode provided a 90-fold increase in the specific capacitance compared to that of pristine TiO2 NTs. R-TiO2 NTs were further decorated with Ni(OH)2 NSs by an electrodeposition method to further improve the supercapacitive performance. Fabricated R-TiO2 NTs/Ni(OH)2 electrodes exhibited a high areal specific capacitance value of 305.91 mF/cm2 at a current density of 0.75 mA/cm2. The modified electrode shows an improved charge-storage capacity compared to the TiO2 NTs/Ni(OH)2 electrodes, and to previously reported 1D-TiO2/Ni(OH)2 nanocomposite structures. Furthermore, the proposed electrode showed good cyclic stability by retaining 71% of its initial capacitance after 1500 cycles and a promising rate capability with a capacitive retention of 86% while increasing the current density from 0.75 to 5 mA/cm2. Overall, the ER step proved to improve the conductivity of the R-TiO2 NTs, which favors the deposition of the Ni(OH)2 NSs and promotes the Faradaic reactions at the electrode-electrolyte interface demonstrating a promising supercapacitor electrode material.