Enhanced Supercapacitive Performance of Chemically Grown Cobalt–Nickel Hydroxides on Three-Dimensional Graphene Foam Electrodes

Abstract

Chemical growth of mixed cobalt-nickel hydroxides (CoxNi1-x(OH)2), decorated on graphene foam (GF) with desirable three-dimensional (3D) interconnected porous structure as electrode and its potential energy storage application is discussed. The nanostructured CoxNi1-x(OH)2 films with different Ni:Co (x) compositions on GF are prepared by using the chemical bath deposition (CBD) method. The structural studies (X-ray diffraction and X-ray photoelectron spectroscopy) of electrodes confirm crystalline nature of CoxNi1-x(OH)2/GF and crystal structure consists of Ni(OH)2 and Co(OH)2. The morphological properties reveal that nanorods of Co(OH)2 reduce in size with increases in nickel content and are converted into Ni(OH)2 nanoparticles. The electrochemical performance reveals that the Co0.66Ni0.33(OH)2/GF electrode has maximum specific capacitance of ∼1847 F g(-1) in 1 M KOH within a potential window 0 to 0.5 V vs Ag/AgCl at a discharge current density of 5 A g(-1). The superior pseudoelectrochemical properties of cobalt and nickel are combined and synergistically reinforced with high surface area offered by a conducting, porous 3D graphene framework, which stimulates effective utilization of redox characteristics and communally improves electrochemical performance with charge transport and storage.

A Simple Electrochemical Route to Access Amorphous Mixed‐Metal Hydroxides for Supercapacitor Electrode Materials

“…[ 5,23 ] The spectrum that was fi t for Co 2p, as shown in Figure 2 b, consisted of strong spin-orbit doublet peaks at 781.6 and 797.7 eV and shakeup satellite peaks at 787.5 and 804 eV, which are generally associated with Co 2+ . [ 5,23,25 ] The XPS spectra of Ni and Fe were obtained using a similar fi tting analysis. The results reveal that the peaks at binding energies of 856.7 and 874.3 eV can be assigned to Ni 2+ [ 5,24 ] and the peaks at 712.1 and 725.9 eV can be assigned to Fe 3+ .…”

“…[ 5,23,25 ] The XPS spectra of Ni and Fe were obtained using a similar fi tting analysis. The results reveal that the peaks at binding energies of 856.7 and 874.3 eV can be assigned to Ni 2+ [ 5,24 ] and the peaks at 712.1 and 725.9 eV can be assigned to Fe 3+ . [ 5,23 ] The XPS studies thus confi rm the formation of a Ni-Co-Fe mixedmetal hydroxide.…”

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mixed-metal hydroxide compounds such as Ni-Al, [ 3 ] Co-Ni, [4][5][6][7][8][9][10] Mn-Co, [ 11 ] Co-Ru, [ 12 ] Ni-Co-Cu, [ 13 ] and Ni-Co-Zn [ 14 ] have advantages over single-composition compounds as positive electrode materials for supercapacitors because mixed-metal compounds greatly promote the integrated electrochemical performance. [15][16][17][18] Almost all efforts in this fi eld have been directed towards crystalline mixed-metal hydroxide materials because these compounds have superior electrochemical performance with high specifi c capacitance, excellent rate capability, high energy density, and high power density.

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“…[15][16][17][18] Almost all efforts in this fi eld have been directed towards crystalline mixed-metal hydroxide materials because these compounds have superior electrochemical performance with high specifi c capacitance, excellent rate capability, high energy density, and high power density. [4][5][6][7][8][9][10]19,20 ] However, supercapacitors made from crystalline compounds usually exhibit a very poor or short cycle life, [4][5][6][7][8][9][10] which makes their practical use limited. Typically, the cycling stability of a Ni(OH) 2 -Co(OH) 2 -graphene asymmetric supercapacitor shows a 70% retention after 1000 cycles.…”

Solvothermal synthesis of NiAl double hydroxide microspheres on a nickel foam-graphene as an electrode material for pseudo-capacitors

“…[25][26][27][28] In recent studies, Khamlich et al 26 27 adopted an innovative strategy of in situ growth of cobalt oxide (Co 3 O 4 ) nanowires on 3D graphene foam grown by CVD. The graphene/Co 3 O 4 composite was used as a monolithic free-standing supercapacitor electrode and exhibited a high specific capacitance of ∼1100 F g −1 at a current density of 10 A g −1 with excellent cycling stability after 1000 cycles.…”