Rational design of NiMoO4/carbon nanocomposites for high-performance supercapacitors: an in situ carbon incorporation approach†

Abstract

Understanding the impact of different compositions of nanocomposites synthesized via in situ incorporation of different ratios of carbon with metal oxides is an important factor for designing efficient electrode materials for high-performance supercapacitors. Here, a series of nanomaterials, NiMoO₄, carbonaceous nanospheres (CNSs), and NiMoO₄/C nanocomposites (NiMoO₄/C (Dx), where, x = 10, 25, 50, and 75 represents the molar ratio of dextrose (D) to Ni²⁺), have been synthesized via an in situ hydrothermal method. The structural and surface analysis revealed the efficient integration of NiMoO₄ and carbon in the NiMoO₄/C (D50) nanocomposite, consisting of 71.1% NiMoO₄ and 28.9% carbon components. The nanocomposite features a graphitic carbon sheet-like structure embedded with NiMoO₄ nanorods, showing increased defects with higher carbon content and enhanced surface area with larger mesoporosity. In three-electrode supercapacitor studies for these electrode materials using 3 M KOH as the electrolyte, the NiMoO₄/C (D50)-based electrode delivered superior specific capacitance (940 F g⁻¹) at a current density of 1 A g⁻¹ compared to bare NiMoO₄ (520 F g⁻¹), CNS (75 F g⁻¹) and NiMoO₄/C (D10, D25 and D75) nanocomposites (436–583 F g⁻¹), with 71% capacity retention up to 5000 cycles. Furthermore, for the fabricated NiMoO₄/C (D50)-based two-electrode supercapacitors at 1 A g⁻¹ using 3 M KOH, the symmetric configuration delivered a doubled specific capacitance (83 F g⁻¹), while the asymmetric configuration led to a doubled performance in both energy density (14.2 W h kg⁻¹) and power density (444 W kg⁻¹), in comparison to each other. The enhanced supercapacitor performance of NiMoO₄/C (D50) can be attributed to the synergistic effect between carbon and NiMoO₄ in the optimized nanocomposites, which improves the electrolyte-philicity by altering the surface composition and properties, leading to more electroactive sites and increased charge storage capacity. Thus, designing new electrode materials via in situ hydrothermal synthesis of different metal oxide/C nanocomposites with optimal composition and choosing different carbon source materials will deliver high-performance supercapacitors in the near future.