Enhanced electrochemical energy storage of binder-free ternary copper manganese selenide nanocomposite electrodes via polydopamine coating for quasi-solid-state hybrid supercapacitors

Owing to promising reliability, high energy storage capability, good stability, etc., nanostructured bimetallic selenides have attracted widespread interest in establishing supercapacitor devices with auspicious electrochemical properties. Focusing on this, herein, we proposed a novel polydopamine (PDA)-coated nanostructured copper manganese selenide (CuMn₂Se₄) on nickel foam via a hydrothermal method. The chemical composition of the cathode electrode was modified according to the chemical formula of Cu_xMn_2-xSe₄ (x = 0, 0.5, and 1) (CMS), and its effect on electrochemical properties as well as on surface morphology was investigated. The optimized CMS electrode exhibited an evenly spread petal-like lawn structure, offering rapid electron/ion kinetics, which results in improved capacitive properties. Furthermore, PDA as a redox-active neurotransmitter was evenly coated on the optimized CMS (i.e., PDA@CMS) to increase electron availability, thus enhancing energy storage capacity. The PDA@CMS electrode showed a superior specific capacitance of 3140 F g⁻¹ at 3 A g⁻¹ of current density. The quasi-solid-state hybrid supercapacitor was fabricated using PDA@CMS as a positive electrode and radish-derived carbon as a negative electrode with gel-type electrolyte, which delivered the power and energy densities of 7750 W kg⁻¹ and 21.85 Wh kg⁻¹, respectively with superior cycling stability (96.5 % capacitance retention over 10,000 cycles).