Abstract
For electrochemical supercapacitors, nickel cobaltite (NiCo2O4) has emerged as a new energy storage material. The electrocapacitive performance of metal oxides is significantly influenced by their morphology and electrical characteristics. The synthesis route can modulate the morphological structure, while their energy band gaps and defects can vary the electrical properties. In addition to modifying the energy band gap, doping can improve crystal stability and refine grain size, providing much-needed surface area for high specific capacitance. This study evaluates the electrochemical performance of aluminum-doped Ni1−xAlxCo2O4 (0 ≤ x ≤ 0.8) compounds. The Ni1−xAlxCo2O4 samples were synthesized through a hydrothermal method by varying the Al to Ni molar ratio. The physical, morphological, and electrochemical properties of Ni1−xAlxCo2O4 are observed to vary with Al3+ content. A morphological change from urchin-like spheres to nanoplate-like structures with a concomitant increase in the surface area, reaching up to 189 m2/g for x = 0.8, was observed with increasing Al3+ content in Ni1−xAlxCo2O4. The electrochemical performance of Ni1−xAlxCo2O4 as an electrode was assessed in a 3M KOH solution. The high specific capacitance of 512 F/g at a 2 mV/s scan rate, 268 F/g at a current density of 0.5 A/g, and energy density of 12.4 Wh/kg was observed for the x = 0.0 sample, which was reduced upon further Al3+ substitution. The as-synthesized Ni1−xAlxCo2O4 electrode exhibited a maximum energy density of 12.4 W h kg−1 with an outstanding high-power density of approximately 6316.6 W h kg−1 for x = 0.0 and an energy density of 8.7 W h kg−1 with an outstanding high-power density of approximately 6670.9 W h kg−1 for x = 0.6. The capacitance retention of 97% and 108.52% and the Coulombic efficiency of 100% and 99.24% were observed for x = 0.0 and x = 0.8, respectively. First-principles density functional theory (DFT) calculations show that the band-gap energy of Ni1−xAlxCo2O4 remained largely invariant with the Al3+ substitution for low Al3+ content. Although the capacitance performance is reduced upon Al3+ doping, overall, the Al3+ doped Ni1−xAlxCo2O4 displayed good energy, powder density, and retention performance. Thus, Al3+ could be a cost-effective alternative in replacing Ni with the performance trade off.
Highlights
Researchers are actively engineering an efficient, clean, and cost-effective electrode for better electrochemical performance [1]
Conventional capacitors display high power density compared to a battery, but because of their lower energy density, researchers are interested in advanced energy storing devices that mitigate the demerits of both battery and capacitor
The experimental results revealed the dependence of surface area, specific capacitance, and electrochemical performance of NiCo2 O4 on Al3+ content
Summary
Researchers are actively engineering an efficient, clean, and cost-effective electrode for better electrochemical performance [1]. Various kinds of transition metal oxides having higher theoretical specific capacitance, such as RuO2 [11], MnO2 [12], NiO [13], Ni(OH)2 [14], CuO [15], Co3 O4 [16], and Co(OH)2 [17], have been investigated as an active electrode material Their poor electronic conductivity [18,19], lower cyclic performance [20,21], and substantial volume change during the charge/discharge process [22] demand the development of nanostructured materials to meet the increasing and urgent demands for energy storing devices. Nickel cobaltite (NiCo2 O4 ) is one of the most valuable electrode materials studied because of its high theoretical specific capacitance, lower cost, low toxic nature, good redox activity, higher electrical conductivity, and environmentally benign nature [24]. First-principles density functional theory (DFT) calculations were employed to assess the energy band-gap of the doped Ni1−x Alx Co2 O4
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