As the demand for green and sustainable energy increases, the advantages of high power density, instantaneous charge and discharge capabilities as well as long life span have made supercapacitor as ...one of the important device for energy storage and power supply management. Nevertheless, one of the main issues is their low energy density which has limit the employment of supercapacitors in broader applications. To address this issue, developing electrode materials that are efficient, cost-effective, tunable and have high surface area is an appealing alternative to boost the performance of supercapacitor (i.e. capable to store high charge and yet undergo minimal decayed during prolong life cycle). Herein, this work is reported on the synthesis of electrode materials and their relationships with supercapacitor performance. In this study, different nanostructures and morphologies of nickel phosphate Ni3(PO4)2 have been prepared by sonochemical method followed by calcination (with different calcination temperatures). The crystallinity, purity, morphology and surface area of Ni3(PO4)2 were authenticated by Xray diffraction (XRD), fourier transform infrared (FTIR), field emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS) analysis. The electrochemical performances such as specific capacity, rate capability and electrical conductivity of the synthesized materials were studied through cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) techniques. It was observed that the amorphous structure of Ni3(PO4)2 renders in high specific capacity (539 C/g at the current density of 1 A/g)) mainly because of its highly porous structure that augmented the electroactive sites for redox reaction. Nevertheless, it exhibited low rate capability due to its poor electrical conductivity which motivated the incorporation of Ni3(PO4)2 with silver (Ag) ions to form binary composite of nickel phosphate-silver phosphate nanocomposite (Ni3(PO4)2-Ag3PO4). Ni3(PO4)2- Ag3PO4 was prepared by fixing the amount of Ag precursor with various mass of Ni3(PO4)2. Crystalline structure of Ag3PO4 nanoparticles were found to be intimately decorated on the surface of Ni3(PO4)2 and had significantly improved the rate capability of the host Ni3(PO4)2 from 29 to 78 % of capacity retention. Unfortunately at low current rate, the specific capacity achieved by Ni3(PO4)2-Ag3PO4 was lower than that of Ni3(PO4)2 with the specific capacity of 478 C/g at 1 A/g. Ni3(PO4)2-Ag3PO4 was further blended with polyaniline (PANI) (synthesized by chemical oxidative polymerization of aniline monomer) without any binder to form tertiary composite of polyaniline-nickel phosphate-silver phosphate (PANI-Ni3(PO4)2-Ag3PO4). The specific capacity shown by PANI-Ni3(PO4)2-Ag3PO4 was increased to 677 C/g at 1 A/g with the rate capability of 76 % capacity retention. Overall, the improved performance displayed by PANI-Ni3(PO4)2- Ag3PO4 electrode is attributed to (i) the utilization of the surface area from each material for the effective redox reaction, (ii) the presence of Ag3PO4 nanoparticles which increased the electrical conductivity and (iii) tubular shape of conductive PANI that support Ni3(PO4)2-Ag3PO4, providing the interconnected paths for quick electron transfer rate and preventing closely packed of Ni3(PO4)2-Ag3PO4 particles. For real application, PANINi3(PO4)2-Ag3PO4 was fabricated into hybrid supercapacitor (PANI-Ni3(PO4)2- Ag3PO4//activated carbon) and obtained energy density of 38.9 Wh/kg at 400 W/kg with 88 % capacity retention after 5000 cycles.
Hierarchical Si/ZnO trunk-branch nanostructures (NSs) have been synthesized by hot wire assisted chemical vapor deposition method for trunk Si nanowires (NWs) on indium tin oxide (ITO) substrate and ...followed by the vapor transport condensation (VTC) method for zinc oxide (ZnO) nanorods (NRs) which was laterally grown from each Si nanowires (NWs). A spin coating method has been used for zinc oxide (ZnO) seeding. This method is better compared with other group where they used sputtering method for the same process. The sputtering method only results in the growth of ZnO NRs on top of the Si trunk. Our method shows improvement by having the growth evenly distributed on the lateral sides and caps of the Si trunks, resulting in pine-leave-like NSs. Field emission scanning electron microscope image shows the hierarchical nanostructures resembling the shape of the leaves of pine trees. Single crystalline structure for the ZnO branch grown laterally from the crystalline Si trunk has been identified by using a lattice-resolved transmission electron microscope. A preliminary photoelectrochemical (PEC) cell testing has been setup to characterize the photocurrent of sole array of ZnO NR growth by both hydrothermal-grown (HTG) method and VTC method on ITO substrates. VTC-grown ZnO NRs showed greater photocurrent effect due to its better structural properties. The measured photocurrent was also compared with the array of hierarchical Si/ZnO trunk-branch NSs. The cell with the array of Si/ZnO trunk-branch NSs revealed four-fold magnitude enhancement in photocurrent density compared with the sole array of ZnO NRs obtain from VTC processes.
Zinc oxide/reduced graphene oxide (ZnO/rGO) nanocomposites were successfully synthesized in the presence of diethylenetriamine (DETA) via a facile microwave assisted method. The x-ray diffraction ...(XRD) patterns of the ZnO/rGO nanocomposites reveal that obtained nanocomposite materials containing ZnO in hexagonal phase with wurtzite structure. The high-resolution transmission electron microscopy (HRTEM) images indicates that the prepared nanocomposites having ZnO nanorods, with an average length:diameter ratio of 10 and which is found to be deposited onto the rGO sheets. Under the irradiation of sunlight, the ZnO/rGO nanocomposites showed two-fold improved photocatalytic performance than that of unmodified ZnO towards the photodegradation of methylene blue. This may due to the high adsorbtivity of ZnO/rGO nanocomposite and synergistic effect raised between smaller ZnO nanorods and rGO matrix led to the improved photocatalytic activity. Further, the ZnO/rGO nanocomposites showed six-fold enhanced photocurrent response than that of bare ZnO nanorods. The excellent photocatalytic performance of the newly prepared ZnO/rGO nanocomposites could be a potential candidate for the photocatalysis and photoelectrochemical applications.
We investigated different molar concentrations of cobalt precursor intercalated reduced graphene oxide (rGO) as possible electrode materials for supercapacitors. Cobalt oxide (Co
3
O
4
) nanocubes ...intercalated reduced graphene oxides (rGO) were synthesized
via
a facile hydrothermal method. It has been found that the Co
3
O
4
particles with a cubical shape are decorated on rGO matrix with an average size of ∼45 nm. The structural crystallinity of rGO-Co
3
O
4
composites was examined by X-ray diffraction (XRD). Raman spectroscopy confirmed the successful reduction of GO to rGO and effective interaction between Co
3
O
4
and the rGO matrix. The electrochemical performances of rGO-Co
3
O
4
electrodes were examined using cyclic voltammetry and charge-discharge techniques. The maximum specific capacitance (278 F g
−1
) is observed at current density of 200 mA g
−1
in the C2 electrode resulting from effective ion transfer and less particle aggregation of Co
3
O
4
on the rGO matrix than in the other electrodes. C2 exhibits good rate capability and excellent long-term cyclic stability of 91.6% for 2000 cycles. The enhanced electrochemical performance may result from uniform intercalation of cobalt oxide over the rGO. These results suggest that the Co
3
O
4
intercalated rGO matrix could play a role in improved energy storage capability.
We investigated different molar concentrations of cobalt precursor intercalated reduced graphene oxide (rGO) as possible electrode materials for supercapacitors.
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