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

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.