Design of multicore–shell structured Co3O4–NiO nanocomposites as high-performance cathodes for zinc-ion hybrid supercapacitors

Abstract

Mixed-metal oxides (MMOs) hold great promise as cathodes for zinc-ion hybrid supercapacitors (Zn-HSCs); however, the lack of comprehensive insight into how their compositional tuning affects the electrochemical performance hinders the systematic design of MMO-based high-performance materials. To examine the impact of MMOs’ composition on the performance of Zn-HSCs, a series of cathode materials were selected, including carbon (acetylene black), Co₃O₄, NiO, and Co₃O₄–NiO nanocomposites with different Co²⁺ : Ni²⁺ molar ratios (Co–Ni(x : y), where x : y = 1 : 0.1, 1 : 0.2, 1 : 0.3, 1 : 0.5, and 1 : 1). Notably, the Co–Ni(1 : 0.2) nanocomposite exhibited a multicore–shell structure with well-integrated Co₃O₄ and NiO nanoparticles, combined with a large surface area and an optimized pore architecture. The as-fabricated Zn-HSCs, assembled with a Zn anode, an active material-coated stainless steel cathode, a Whatman filter paper separator, and a 2 M ZnSO₄ electrolyte, offered specific capacitance values at 0.2 A g⁻¹ in the following order: carbon (23 F g⁻¹) < Co–Ni(1 : 1) (83 F g⁻¹) < Co–Ni(1 : 0.5) (134 F g⁻¹) < Co₃O₄ (139 F g⁻¹) < NiO (180 F g⁻¹) < Co–Ni(1 : 0.1) (253 F g⁻¹) < Co–Ni(1 : 0.3) (309 F g⁻¹) < Co–Ni(1 : 0.2) (355 F g⁻¹), emphasizing the superior energy storage capability of the optimized MMO composition over monometallic oxides. Remarkably, the Co–Ni(1 : 0.2) cathode exhibited an impressive energy density of 217 Wh kg⁻¹ and a power density of 525 W kg⁻¹ at 0.2 A g⁻¹, with 90% of initial capacity maintenance over 5000 cycles at 2 A g⁻¹. Thus, the observed superior cathodic performance of the Co–Ni(1 : 0.2) nanocomposite could be attributed to its optimized Co₃O₄–NiO composition, enabling synergistic improvements in the cathode's structural and electrical properties alongside efficient electrode–electrolyte wettability. These results underscore the necessity for compositional engineering of mixed-metal oxides as a strategic direction for developing durable, high-performance cathodes for Zn-HSC applications.