From NiCo-glycerate to tri-metallic selenide: engineering yolk–shell MnNiCoSe spheres with nanosheet arrays for hybrid supercapacitors†

The progress of the supercapacitor industry heavily depends on the development and synthesis of novel electrode materials with specific architectures. Transition metal selenides have recently gained recognition as promising materials for energy storage devices due to their high theoretical capacitance and excellent electronic conductivity. This has spurred extensive research on mono- and di-selenide active materials. However, reports on tri-metallic selenides are scarce, and their charge storage mechanisms remain unclear. In this study, uniform NiCo-glycerate precursors were employed as sacrificial templates in combination with a selenization process to synthesize tri-metallic MnNiCoSe yolk–shell spheres encased in nanosheets through a straightforward self-templating method. The resulting MnNiCoSe electrode material demonstrates exceptional electrochemical performance, attributed to its numerous redox-active sites, large surface area with mesoporous pathways, high electrical conductivity, and the synergistic interaction of manganese, nickel, and cobalt elements. The MnNiCoSe electrode material exhibits a high specific capacity of 263.67 mA h g⁻¹ at 1 A g⁻¹, retains 76.63% of its capacity at 20 A g⁻¹, and maintains 84.28% of its capacity after 10 000 GCD cycles. Moreover, the hybrid supercapacitor device, assembled using NiF@MnNiCoSe as the positive electrode and NiF@AC as the negative electrode, achieves an impressive energy density of 53.32 W h kg⁻¹ at a power density of 1031.39 W kg⁻¹.