In situ synthesis of NiCo2O4/carbon nanocomposites: effect of carbon content and symmetric/asymmetric device configuration on supercapacitor performance

Abstract

Herein, a simple in situ hydrothermal carbonization (HTC) approach has been used to synthesize different ratios of carbon-incorporated nickel cobaltite nanocomposites, denoted as NiCo₂O₄/C (Dx) (where x = 1, 2, 5, and 10, representing the molar ratio of dextrose to nickel precursor). The prepared nanomaterials were further characterized using XRD, SEM, TEM, Raman, FT-IR, BET, and XPS techniques and subsequently subjected to supercapacitor (SC) studies using 3 M KOH as the electrolyte. In the three-electrode SC studies, NiCo₂O₄/C (D2) showed a superior specific capacitance of 736 F g⁻¹ at 1 A g⁻¹ in comparison with pure NiCo₂O₄ (307 F g⁻¹) and carbon nanospheres (CNS, 52 F g⁻¹), with appreciable cycling stability, retaining about 85% of capacity up to 1000 cycles. Furthermore, in the two-electrode SC studies for NiCo₂O₄/C (D2) at 1 A g⁻¹, the asymmetric configuration exhibited twice the energy density (20.3 W h kg⁻¹) and power density (406 W kg⁻¹) compared to the symmetric configuration, due to the hybrid EDLC–pseudocapacitive mechanism. In contrast, the symmetric configuration showed lower energy density (13.5 W h kg⁻¹) and power density (213 W kg⁻¹) owing to pseudocapacitive behavior alone. This noted synergistic enhancement effect on the supercapacitor performance of the NiCo₂O₄/C (D2) nanocomposite can be ascribed to the incorporation of optimal carbon content into NiCo₂O₄ to facilitate more electroactive sites for charge storage compared to pure NiCo₂O₄ and CNS. This kind of tuning of the carbon ratios in the metal oxide/carbon nanocomposites through the in situ HTC approach and tailoring the symmetric/asymmetric SC device configurations will efficiently deliver a promising SC in the near future.