A high-performance battery–supercapacitor hybrid device and electrocatalytic oxygen evolution reaction based on NiCo2−xMnxO4@Ni-MOF ternary metal oxide core–shell structures

Abstract

The electrodes, refined by adjusting the Co and Mn ratios in the precursor solution to NiCo_2−xMn_xO₄ (x = 0, 0.5, 1, 1.5, 2), demonstrate superior electrochemical performance compared to binary metal oxides and other electrodes synthesized by varying the concentration of Co and Mn. Notably, the optimized ternary metal oxide electrode, NiCo_2−xMn_xO₄-1, exhibits particularly significant electrochemical performance. Additionally, a two-step hydrothermal approach has been presented in this study, demonstrating the growth of Ni-MOF arrays on the surface of the NiCo_2−xMn_xO₄-1 optimized electrode. The resultant NiCo_2−xMn_xO₄@Ni-MOF-1 hybrid electrode, which combines the strengths of the NiCo_2−xMn_xO₄ core and the Ni-MOF shell, exhibits enhanced electrochemical properties with a potential window range of −0.2 to 0.5 V (vs. Ag/AgCl). These properties include a significant specific capacitance/capacity of 3543.5 F g⁻¹/2480.4 C g⁻¹ at 6 mA g⁻¹, as well as impressive cycling stability, retaining 93.7% of its performance over 15 000 cycles in a 2 M KOH electrolyte. Additionally, NiCo_2−xMn_xO₄@Ni-MOF-1 demonstrates excellent oxygen evolution reaction (OER) activities with an overpotential of 296 mV and a Tafel slope of 131 mV dec⁻¹ at 10 mA cm⁻², outperforming RuO₂, the conventional benchmark. Furthermore, a battery–supercapacitor hybrid (BSH) device has been introduced, employing the optimized NiCo_2−xMn_xO₄@Ni-MOF-1 and activated carbon as the anode and cathode, respectively. This device is noted for achieving a high energy density of 33.8 W h kg⁻¹ at a power density of 750 W kg⁻¹ and demonstrating remarkable cycling performance of nearly 106% retention over 5000 cycles.