Advanced symmetric supercapacitor of spinel NiCo2O4-incorporated 2D g-C3N4 electrodes in a PVA–KOH gel-electrolyte-based pouch cell

Abstract

Carbon-based materials and metal oxides show great potential in the field of supercapacitors. This study examines the charge storage properties of a NiCo₂O₄-incorporated 2D g-C₃N₄ hybrid in a redox-active PVA–KOH gel-electrolyte-based pouch cell. In this study, the synthesis of exfoliated graphitic carbon nitride (CN)-nickel cobalt oxide (NiCo₂O₄) nanocomposites was achieved through the ultrasonication method by employing varying weight ratios (1 : 0.01, 1 : 0.05, and 1 : 0.1), and the samples were designated as NCOCN1, NCOCN2, and NCOCN3, respectively. The analysis of structural and morphological characteristics was conducted through X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM). The specific capacitance of the NCOCN2 nanocomposite was found to be 1206 F g⁻¹ at 1 A g⁻¹, approximately eight times that of CN. The increased specific capacitance of the nanocomposite arises from the synergistic interaction between the nitrogen in carbon nitride and the nickel and cobalt present at various oxidation states (Ni²⁺, Ni³⁺, Co²⁺, and Co³⁺) in NiCo₂O₄. In the current density range of 1 to 10 A g⁻¹, the NCOCN2 nanocomposite demonstrated a capacitance retention of 98%. The NCOCN2 demonstrated an impressive energy density of 41.88 W h kg⁻¹ while maintaining a power density of 833.33 W kg⁻¹ in a 1.0 M KOH electrolyte. NCOCN2 stood out among the nanocomposites, exhibiting the highest electrochemical performance. A symmetric supercapacitor was thus constructed using the NCOCN2 nanocomposite in a Swagelok cell and a gel electrolyte-based pouch cell. The NCOCN2/W/NCOCN2 SSCD demonstrated a significant operating voltage window of 1.8 V, coupled with a specific capacitance of 300 F g⁻¹ at 1.0 A g⁻¹ and an energy density of 192 W h kg⁻¹ at a power density of 1800 W kg⁻¹. This NCOCN2/W/NCOCN2 pouch cell activated a red LED, which showcases its functionality. Furthermore, the NCOCN2/GE/NCOCN2 pouch cell exhibited a high operating voltage window of 2.0 V, along with a specific capacitance of 177 F g⁻¹ at 1.0 A g⁻¹ and an energy density of 77 W h kg⁻¹ at a power density of 1200 W kg⁻¹. This NCOCN2/GE/NCOCN2 pouch cell illuminated a red LED, demonstrating practicality. Therefore, this study suggests that NCOCN nanocomposites have the potential to be utilized in energy storage applications.