Ordered Co/Ni oxide nanostructures from MOFs: enhancing efficiency in hybrid asymmetric energy devices†

Abstract

MOF-derived metal oxides are promising electrode materials for energy storage due to their tunable porosity, large surface area, and versatile structures, which enhance electrochemical performance. However, their practical use is currently limited by poor conductivity and structural instability, requiring advanced modifications to circumvent this issue. This research investigates the synthesis of Co₃O₄/NiO nanostructures (MD-Co/Ni) derived from bimetallic metal–organic frameworks (Co/Ni-MOFs) with varying Co : Ni ratios (0.25 : 1, 0.5 : 1, 0.75 : 1, and 1 : 1) through thermal decomposition. The primary objective is to enhance energy storage efficiency. The study also examines how different Co : Ni ratios influence the electrochemical performance of the resulting nanostructures. The Co/Ni-MOF precursor was synthesized via a straightforward solvothermal method using trimesic acid (TA) as the ligand and polyvinylpyrrolidone (PVP) as a stabilizer. XRD analysis confirmed the high crystallinity of MD-Co/Ni nanostructures, while FE-SEM revealed its nanorod-/nanosheet-like morphology featuring rod-shaped nanoparticles. Electrochemical evaluations demonstrated that MD-Co/Ni achieved a superior specific capacitance (C_sp) of 2836 F g⁻¹ at 1 A g⁻¹, surpassing its pure bimetallic MOF counterparts. This improvement is credited to the synergistic effects of its bimetallic oxide composition, increased surface area from the meso-porous structure, and enhanced electron/ion transport pathways. Furthermore, a hybrid asymmetric supercapacitor (HS) was fabricated using MD-Co/Ni as the positive electrode. The device exhibited an exceptional energy density (E_d) of 27.28 W h kg⁻¹ at a power density (P_d) of 380 W kg⁻¹ and an outstanding working stability, retaining 80% capacitance and achieving a coulombic efficiency of 99.53% after 9500 cycles. These findings highlight the significant potential of thermally derived MOF-based nanostructures for futuristic energy storage systems.