Optimizing the Charge Transfer Process by Synthesizing NiO Microspheres on Ni Foam through Microwave-assisted Method

doi:10.15541/jim20150607

Abstract

Abstract:

The porous nickel oxide microsphere on Ni foam was adopted to optimize the charge transfer process to improve electrochemical performance by a microwave-assisted method. Microstructure and morphologies of the resulting materials were investigated by X-ray diffraction, scanning electron microscope, transmission electron microscope. Results showed that the as-prepared NiO microspheres with nickel sulfate had average diameter of ~2 µm. The ultrathin secondary nanoflakes composed of nanowire building blocks were interconnected with each other forming a highly open net-structure. Because of enhanced electron transfer capability, charge transfer resistances of the porous microsphere were reduced and the electrochemical performances were improved, the charge-discharge measurements tested at a discharge current of 0.5 A/g showed higher rate specific capacitance (455 F/g). The impedance characterization illustrated lower electronic and ionic resistance of porous NiO due to its superior surface properties for enhanced electrode electrolyte contact during the faradaic redox reactions.

Key words: microwave-assisted synthesis, hierarchical nickel oxide, porous Nanoflake, electrochemical performance

CLC Number:

O646

HAN Dan-Dan, JING Xiao-Yan, XU Peng-Cheng, TAN Ao, CHENG Zhen-Yu. Optimizing the Charge Transfer Process by Synthesizing NiO Microspheres on Ni Foam through Microwave-assisted Method[J]. Journal of Inorganic Materials, 2016, 31(6): 667-672.

Figures/Tables 7

Fig. 1 XRD patterns of NW-NiO microspheres scratched down from Ni foam and NiO/Ni sample

Fig. 2 Schematics of fabrication processes of NW-NiO microspheres

Fig. 3 SEM images of (a, b) NW-NiO microspheres (fine structure in inset), TEM images of (c) NW-NiO microspheres, HRTEM image and SAED pattern (d)

Fig. 4 Electrochemical properties of NW-NiO electrode. (a) CVs of hierachical NW-NiO electrode at the scan rates of 5, 10, 20, 30, 40, 50 mV/s, respectively; (b) Specific capacitance as a function of scan rate, the inset of (b) Shows the linearity of anodic current density with scan rate; (c) Charge and discharge curves of samples at different current density; (d) Specific capacitances and coulombic efficiency as function of discharge current densities of NW-NiO electrode

Fig. 5 Nyquist plots of experimental impedence data for NW-NiO electrode before and after 1000 charge-discharge cycles

Table 1 Compared Rct for different structured NiO electrodes reported in previous literature

Electrode structure	Electrolyte	R_ct /Ω	Reference
Hierarchical NiO sphere/Ni	KOH (2mol·L^-1)	0.53	This work
Porous NiO sheet/Ni	KOH (6 mol·L^-1)	≈10	[23]
Co-doped NiO film/FTO	KOH (1 mol·L^-1)	12.03	[24]
NiO/CuO nanoflower/ Ni	KOH (6 mol·L^-1)	≈15	[25]
NiO/MWCNT thin film/stainless steel	KOH (2 mol·L^-1)	1.72	[26]

Fig. 6 Long cycle performance of NiO spheres measured at the current density of 2 A/g

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