ABSTRACT
Zn-ZnO(Nw)-rGO hybrid electrodes for supercapacitor applications were successfully prepared in situ by a one-step microwave-assisted hydrothermal method by deposition of reduced graphene oxide (rGO) on the structure of ZnO nanowires grown on the Zn foil. During the hydrothermal treatment, two processes occur the reduction of graphene oxide (GO) and the deposition of rGO on the Zn-ZnO(Nw) support. The growth of ZnO nanowires was achieved by thermal oxidation below the melting point of the Zn foil in a controlled atmosphere. The as-obtained electrodes were assessed for structural, optical, and morphological properties by X-ray diffraction, Raman spectroscopy, ultraviolet-visible spectroscopy, SEM microscopy, and EDX analysis. The supercapacitor properties of the Zn-ZnO(Nw)-rGO hybrid electrodes were investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge-discharge analysis. The CV curve reveals that the Zn-ZnO(Nw)-rGO hybrid structures work as negative electrodes and exhibit a non-ideal rectangle-like shape, suggesting that the as-synthesized structure behaves as a pseudo-capacitor. A maximum capacitance was determined to be 395.79 mF cm-2 at a scan rate of 5 mV s-1. Based on GCD analysis, the maximum specific capacitance of 145.59 mF cm-2 was achieved at a low power density of 2 mA cm-2. The cycle life assessment of the Zn-ZnO(Nw)-rGO hybrid electrode over a 250-cycle number was performed by CV and GCD analysis. The maximum retention rate of 120.86% was achieved from GCD analysis over 250 cycles for the Zn-ZnO(Nw)-rGO hybrid electrode.
ABSTRACT
A flexible electrode constructed from Fe-based amorphous ribbons decorated with nanostructured iron oxides, representing the novelty of this research, was successfully achieved in one-step via a chemical oxidation method, using a low concentration of NaOH solution. The growth of metal oxides on a conductive substrate, which forms some metal/oxide structure, has been demonstrated to be an efficient method for increasing the charge transfer efficiency. Through the control and variation of synthetic parameters, different structures and morphologies of iron oxide were obtained, including hexagonal structures with a hollow ball shape and rhombohedral structures with rhombus-like shapes. Structural and morphological characterization methods such as X-ray diffraction and SEM morphology were used on the as-synthesized composite materials. The supercapacitor properties of the as-developed amorphous ribbons decorated with Fe2O3 nanoparticles were investigated by cyclic voltammetry, galvanostatic charge discharge, and electrochemical impedance spectroscopy. The flexible supercapacitor negative electrode demonstrates a specific capacitance of 5.96 F g-1 for the 0.2 M NaOH treated sample and 8.94 Fg-1 for the 0.4 M NaOH treated sample. The 0.2 M treated negative electrodes deliver 0.48 Wh/kg at a power density of 20.11 W/kg, and the 0.4 M treated electrode delivers 0.61 Wh/kg at a power density of 20.85 W/kg. The above results show that these flexible electrodes are adequate for integration in supercapacitor devices, for example, as negative electrodes.
ABSTRACT
A self-powered photodetector with the FTO/n-TiO2/p-CuMnO2 configuration, representing the novelty of the work, was successfully achieved for the first time and presumes two steps: deposition of the n-type semiconductor (TiO2) by the doctor blade method and of the p-type semiconductor (CuMnO2) by the spin coating technique, respectively. Investigation techniques of the structural and morphological characteristics of the as-synthesized heterostructures, such as XRD, UV-VIS analysis, and SEM/EDX and AFM morphologies, were used. The I-t measurements of the photodetector showed that the responsivity in the self-powered mode was 2.84 × 107 A W-1 cm2 and in the 1 V bias mode it was 1.82 × 106 A W-1 cm2. Additionally, a self-powered current of 14.2 nA was generated under UV illumination with an intensity of 0.1 mW/cm2. Furthermore, under illumination conditions, the response time (tres) and the recovery time (trec) of the sensor exhibited a good response; thus, tres = 7.30 s and trec = 0.4 s for the self-powered mode, and in the 1 V bias mode, these were tres = 15.16 s and trec = 2.18 s. The above results show that the transparent heterojunction device of n-TiO2/p-CuMnO2 exhibited a self-powered ultraviolet photodetector with high sensitivity.
