Template-free approach to synthesize hierarchical porous nickel cobalt oxides for supercapacitors

Abstract

Nickel cobalt oxides with various Ni/Co ratios were synthesized using a facile template-free approach for electrochemical supercapacitors. The texture and morphology of the nanocomposites were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller analysis (BET). The results show that a hierarchical porous structure assembled from nanoflakes with a thickness of ∼10 nm was obtained, and the ratio of nickel to cobalt in the nanocomposites was very close to the precursors. Cyclic voltammetry (CV) and galvanostatic charge and discharge tests were carried out to study the electrochemical performance. Both nickel cobalt oxides (Ni-Co-O-1 with Ni : Co = 1, Ni-Co-O-2 with Ni : Co = 2) outperform pure NiO and Co(3)O(4). The Ni-Co-O-1 and Ni-Co-O-2 possess high specific capacities of 778.2 and 867.3 F g(-1) at 1 A g(-1) and capacitance retentions of 84.1% and 92.3% at 10 A g(-1), respectively. After full activation, the Ni-Co-O-1 and Ni-Co-O-2 could achieve a maximum value of 971 and 1550 F g(-1) and remain at ∼907 and ∼1450 F g(-1) at 4 A g(-1), respectively. Also, the nickel cobalt oxides show high capacity retention when fast charging.

Hybrids of NiCo 2 O 4 nanorods and nanobundles with graphene as promising electrode materials for supercapacitors

“…Distinct pairs of redox peaks can be observed in the anodic and cathodic curves within 0.05-0.45 V (vs Ag/AgCl) in all CV curves. Such peaks can be ascribed to the redox couples of Co 3 O 4 /CoOOH and NiO/NiOOH [31]. As the increasing of the scan rate, the peak current increases, while the shapes of these CV curves do not significantly change as the scan rate increases from 2 to 100 mV S À1 , revealing the fast redox reactions for electrochemical energy storage.…”

Direct syngas hydrogenation over a Co–Ni bimetallic catalyst: Process parameter optimization

“…In the Co-Ni bimetallic catalyst, nickel oxides and cobalt oxides are potentially present. Due to the similarity in structural feature and the close position of diffraction peaks between NiCo 2 O 4 , Co 3 O 4 , and NiO, distinguishing between these three phases is very difficult (Chang et al, 2012;Li et al, 2012). Based on the XRD data, the particle size of metal oxides can be estimated by using Scherrer's equation.…”

Electrospun Porous NiCo2O4 Nanotubes as Advanced Electrodes for Electrochemical Capacitors

“…Therefore, synthesizing NiCo 2 O 4 with a rationally designed morphology, size, and nanoscale structure provides one of the most feasible ways to create high-performance ECs. Currently, some research has been carried out to prepare different NiCo 2 O 4 nanostructures with good electrochemical performances, including nanoparticles, [20,21] nanoflakes, [22][23][24][25] nanoneedles, [26,27] nanowires, [28][29][30][31] and nanoflowers. [32,33] Various wet-chemical techniques have been used, such as hydrothermal, solvothermal, or sol-gel methods.…”