Designing trimetallic Ni-Mg-Mn selenide and bio-derived carbon electrodes for wearable semi-solid-state hybrid capacitor applications

Trimetallic selenides have emerged as a promising electrode for wearable supercapacitors applications, due to their high electrical conductivity, rich redox activity, structural robustness, and porosity. In this report, a trimetallic nickel–magnesium-manganese selenide (NMMSe) electrode with a well-defined nanosphere morphology was prepared using a low-cost and rapid electrodeposition technique. The electrochemical performance of the NMMSe electrodes was systematically investigated as a positive electrode. The NMMSe electrode prepared with a deposition time of 200 s (denoted as NMMSe-200) revealed a high areal/specific capacity of 439.4 µAh cm⁻²/225.6 mA h g⁻¹ at 4 mA cm^–2, along with excellent cycling stability. To further investigate the effect of deposition time on the nanostructure evaluation and electrochemical behavior, additional NMMSe electrodes were synthesized at the growth times of 100 and 300 s. For the negative electrode, activated carbon derived from pistachio shell waste (i.e., porous activated carbon (PAC)) was employed, demonstrating a high areal capacitance of 913.4 mF cm⁻² and an excellent surface area of 320.6 m²/g. Finally, a semi-solid-state hybrid capacitor (HC) cell was assembled using NMMSe-200 as the positive (+) electrode and PAC as the negative (-) electrode. The resulting NMMSe//PAC/nickel foam HC cell delivered an impressive areal capacitance of 928.8 mF cm⁻² at 2 mA cm^–2, a high energy density of 338.5 µWh cm^–2 (56.4 Wh kg⁻¹), and exceptional cycling stability. These results highlight the strong potential of NMMSe-200 electrodes for high-performance, wearable energy storage systems.