synthesis of NiCoO/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 NiCo 2 O 4 /C (D x ) (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, NiCo 2 O 4 /C (D2) showed a superior specific capacitance of 736 F g −1 at 1 A g −1 in comparison with pure NiCo 2 O 4 (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 NiCo 2 O 4 /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 NiCo 2 O 4 /C (D2) nanocomposite can be ascribed to the incorporation of optimal carbon content into NiCo 2 O 4 to facilitate more electroactive sites for charge storage compared to pure NiCo 2 O 4 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. In situ synthesized NiCo 2 O 4 /C (D2) nanocomposite with optimal carbon content surpassingly boosts supercapacitor performance via synergistic effect, while tailoring their symmetric/asymmetric configurations enables tunable energy and power densities.