Synthesis of Honeycomb-Like Co₃O₄ Nanosheets with Excellent Supercapacitive Performance by Morphological Controlling Derived from the Alkaline Source Ratio.

Wanli Jia,Jun Li,Yunqiang Jiang,Yongfei Juan,Zhongjie Lu

doi:10.3390/ma11091560

Abstract

Honeycomb-like Co3O4 nanosheets with high specific surface area were successfully synthesized on porous nickel foam by the facile hydrothermal method followed by an annealing treatment (300 °C), which were used as high-performance supercapacitor electrodes. The effects of the mole ratio of hexamethylenetetramine (HMT) and Co(NO3)2 (1:1, 2:1, 3:1, 4:1, 5:1 and 6:1) as the reactants on the morphological evolution and electrochemical performance of the electrodes were investigated in detail. X-ray diffractometry (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were applied to characterize the structure and morphology of the products. The electrochemical performance was measured by cyclic voltammetry (CV) and galvanostatic charge/discharge. The mole ratio of HMT and Co(NO3)2 produced a significant effect on the morphological evolution of Co3O4. The morphological evolution of Co3O4 with the increase in the mole ratio was followed: the nanosheets accompanied with a large number of spherical nanoparticles → the formation of some strip-like particles due to the agglomeration of spherical nanoparticles → the formation of new nanosheets resulting from the growth of strip-like particles → the formation of coarse flower-like particles owing to the connection among the nanosheets → the nanosheets gradually covered with flower-like particles. Accompanied with the change, the specific surface area was increased firstly, and then decreased. A maximum was obtained at a HMT and Co(NO3)2 mole ratio of 4:1. The evolution in morphology of Co3O4 was responsible for the change in electrochemical performance of the electrode. The specific capacitance value of the electrode prepared at a HMT and Co(NO3)2 mole ratio of 4:1 was highest (743.00 F·g−1 at 1 A·g−1 in the galvanostatic charge/discharge test). The similar result was also observed in the CV test with a scanning rate of 5 mV·s−1. Moreover, the electrode also demonstrated an excellent cyclic performance, in which about 97% of the initial specific capacitance remained at 1 A·g−1 for 500 cycles in the galvanostatic charge/discharge test. This excellent electrochemical performance was ascribed to high specific surface area of Co3O4 nanosheets that provide added channels and space for the ions transportation.

Highlights

In today's world, with the rapid economic development and the growth of the global population, conventional energy is gradually depleted and pollution is worsening, new energy has become an urgent need for social development [1]
Co3O4 nanosheets with a high specific surface area were prepared on nickel foam by hydrothermal synthesis method followed by the annealing treatment (300 C)
With the increase in their mole ratio from 1:1 to 4:1, the nucleation and growth of nanosheets were predominant, which contributed to the enhancement in specific surface area of Co3O4

Summary

Introduction

In today's world, with the rapid economic development and the growth of the global population, conventional energy is gradually depleted and pollution is worsening, new energy has become an urgent need for social development [1]. Speaking, hydrothermal method is especially widely used in the preparation domain of Co3O4 electrode materials considering its low cost, good crystal shape, high purity, easy operation, high production and uneasy reunion [18]. The optimum hydrothermal temperature was confirmed as 100 °C, at which the specific capacitance of prepared Co3O4 microspheres was 850, 780, 700, 630 F g-1 at current densities of 1, 2, 4, 8 A·g-1, respectively. The modified Co3O4 electrode exhibited the specific capacitance of 655 F g−1 at a current density of 0.5 A g−1. Mesoporous Co3O4 bundles were synthesized by a hydrothermal method (180 °C for 24 h) followed by an annealed treatment (350 °C for 3 h) [23]. The average specific capacitance calculated from the CV curve was approximately 360 F g-1 at a scanning rate of 10 mV s-1 and the value of 454 F g-1 was retained at 2 A g-1 after 2500 cycles

Methods

Results

Conclusion