Hydrothermal synthesis and electrochemical properties of hierarchical vanadyl hydroxide spheres with hollow core and mesoporous shell

- Hierarchical porous VOOH hollow spheres were successfully prepared.
- Hierarchical VOOH hollow spheres possessed macropores in their hollow interior and mesopores in shell.
- Hierarchical VOOH hollow spheres exhibited the capacitive behavior based on the pseudocapacitance.
- Hierarchical VOOH hollow spheres exhibited specific capacitance of 93 F g−1 at 0.2 A g−1.

Hierarchical porous vanadyl hydroxide (VOOH) hollow spheres were successfully prepared using ammonium metavanadate as starting vanadium source materials through a facile hydrothermal method. Their morphology, structure and composition were characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, energy-dispersive X-ray spectrometry, elemental mapping, elemental analysis, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and nitrogen adsorption-desorption isotherms. Brunauer-Emmett-Teller specific surface area of hierarchical VOOH hollow spheres measured 32 m2 g−1, and their most probable distribution pore size reached 3.6 nm. Results demonstrated that hierarchical VOOH hollow spheres possessed macropores in their hollow interior and mesopores in shell. Electrochemical properties of hierarchical VOOH hollow spheres as supercapacitor (SC) electrodes were explored and investigated by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. Results showed that hierarchical VOOH hollow spheres featured capacitive behavior based on pseudocapacitance, and exhibited specific capacitance of 93 F g−1 at current density of 0.2 A g−1. Cycling stability was discussed in detail and indicated good rate capability of studied materials. VOOH hollow spheres are ideal material for SC electrodes in the present study.

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