One‐Pot Fabrication of Layered α‐Phase Nickel–Cobalt Hydroxides as Advanced Electrode Materials for Pseudocapacitors

Abstract

A novel and facile one‐step method for growing α‐phase nickel–cobalt hydroxides is developed. The use of 1‐methyl‐2‐pyrrolidone (NMP) in the mixed solvent plays the decisive role in the precipitation of metal ions and the formation of α‐phase hydroxides. The synthetic method is robust enough to synthesize Ni–Co hydroxides with different stoichiometric ratios of Ni and Co, and can be extended to the fabrication of Ni0.67Zn0.33 hydroxide in the α phase. More encouragingly, the method employed can be further used to grow layered nickel‐cobalt hydroxides on Ni foam. As the electroactive materials for pseudocapacitors, the Ni–Co hydroxides deliver an ultrahigh specific capacitance (1337.4 F g−1 at 1 A g−1 for Ni0.67Co0.33 hydroxide) with improved rate capability and cycling stability. Moreover, a greatly increased specific capacitance (2248.9 and 2286.7 F g−1 at 1 A g−1 for Ni0.5Co0.5 and Ni0.67Co0.33 hydroxides, respectively) with superior cycling stability is obtained after growth on Ni foam.

Flexible Asymmetric Threadlike Supercapacitors Based on NiCo2Se4 Nanosheet and NiCo2O4/Polypyrrole Electrodes

“…[24,25] In addition, the signal from Se can be definitely observed, as shown in Figure 3d.T he peaks situated at 59.5 and 54.8 eV can be ascribed to Se 3d 3/2 and Se 3d 5/2 ,w hich are typical of metal selenium bonds. The cyclic voltammetry (CV) analysis of the NiCo 2 Se 4 nanosheets is shown in Figure 4a.T he CV curveso fN iCo 2 Se 4 are very similart ot hose of various Ni-Co based electroactive materials, such as Ni-Co oxide, [27][28][29] hydroxides, [30][31][32] and sulfides. The cyclic voltammetry (CV) analysis of the NiCo 2 Se 4 nanosheets is shown in Figure 4a.T he CV curveso fN iCo 2 Se 4 are very similart ot hose of various Ni-Co based electroactive materials, such as Ni-Co oxide, [27][28][29] hydroxides, [30][31][32] and sulfides.…”

Diaphragm‐Regulated Growth of Nanosheet Arrays of α‐Phase Ni–Co Layered Double Hydroxides on Arbitrary Substrates for Wettability Control and Rechargeable Alkaline Batteries

“…From the galvanostatic charge–discharge profiles, plateaus were observed (Figure b). Previously, Ni–Co LDHs were typically treated as electrodes for supercapacitors . However, based on our understanding, the observed CV and charge–discharge profiles clearly suggested a battery behavior instead of capacitor behavior.…”

“…The good electrochemical performance could be attributed to unique structures of nanosheet arrays on 3D Ni foam where large surface area, abundant active sites, easy ion and electron transfer, and interconnected and interlocked arrangements were presented. The synergetic effect of bimetallic components may also play a certain role in improving electrochemical performance . The electrode after 3000 cycles was examined by SEM (Figure S7 in Supporting Information).…”

A Facile One-Step Electrophoretic Deposition of Co−Ni-Layered Double Hydroxide Nanosheets for a High Performance Supercapacitor

“…The redox couple can be attributed to the redox reaction shown in Eq. 7 ,. The CoOOH will undergo further electron transfer to form CoO 2 as shown in Eq.…”