Investigating sulfur precursor effects on wet-chemically synthesized CuCo bimetallic sulfides for supercapacitor applications via electrochemical measurement and thermodynamic and DFT calculations

In this research, an in-situ two-step solvothermal technique was used for the direct growth of thiospinel CuCo₂S₄ material and CoS₂/CuS composite material on Ni foam substrate. The type of electroactive materials was adjusted using two distinct sulfur sources: sodium thiosulfate pentahydrate (Na₂S₂O₃.5H₂O) and sodium sulfide nonahydrate (Na₂S.9H₂O) at an equal concentration of sulfur. The phase and microstructure were characterized by X-ray diffractometry, X-ray photoelectron spectroscopy, and scanning electron microscopy techniques. The electrochemical behavior was studied using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy techniques in a 3 M KOH aqueous electrolyte. The Na₂S.9H₂O source resulted in the synthesis of single-phase CuCo₂S₄ material, while the composite CoS₂/CuS material was obtained by the sulfur precursor of Na₂S₂O₃.5H₂O. In comparison with CuCo₂S₄ material, the CoS₂/CuS electrode showed a higher electrochemical performance with a specific capacitance of 2195 F g⁻¹ at 1 Ag⁻¹ due to its finer morphology. The assembled asymmetric supercapacitor with CoS₂/CuS as positive electrode and active carbon as negative electrode harvested an energy density of 46.6 Wh kg⁻¹ at a power density of 750 W kg⁻¹ in a voltage window of 1.5 V. Computational simulations based on density functional theory (DFT) validated the experimental findings, revealing that the CuS/CoS₂ material exhibited significant potential for electrochemical applications in the renewable energy field.