Synergistic integration of 2D NiMn hydroxides and Ni MOF via reverse engineering method for high-performance hybrid supercapacitors

Transition metal-based electroactive materials such as nickel manganese (NiMn) hydroxides and Ni metal-organic frameworks (MOFs) embrace enormous potential as electrodes for hybrid supercapacitors (HSCs) because of their good conductivity and multiple valence states. Nevertheless, traditional techniques often encounter restrictions stemming from single-phase structures and a restriction of synergetic active sites. Herein, we report a novel strategy to overcome these limitations by designing hybrid electrodes consisting of two-dimensional (2D) NiMn hydroxides and Ni MOF on 3D Ni foam (NF). Through systematic optimization, the composition of Ni MOF is modulated to achieve enhanced electrochemical performance. Specifically, adjusting the Ni metal precursor concentration in Ni MOF effectively enhances the synergistic interaction between NiMn hydroxides and Ni MOF, thereby improving the overall electrochemical performance. The resultant hybrid electrode, denoted as Ni MOF_0.09@NiMn/NF, delivers superior electrochemical properties, exhibiting areal/specific capacities of 638 μAh cm⁻²/79.7 mAh g⁻¹ at 5 mA cm⁻² in a 2 M KOH electrolyte. Furthermore, the assembled HSC device, comprising Ni MOF_0.09@NiMn/NF as a positive electrode and activated carbon as a negative electrode, demonstrates ultrahigh energy density (0.46 mWh cm⁻²) and good cycling stability (∼90 % capacity retention over 10,000 cycles in a 2 M KOH electrolyte). This work highlights the potential of synergistic multiphase systems in advancing the performance of HSCs and provides valuable insights for the development of high-efficiency energy storage devices.