Fabrication of FeO@CuCo₂S₄ multifunctional electrode for ultrahigh-capacity supercapacitors and efficient oxygen evolution reaction

The outstanding multifunctional electrochemical properties of chalcogenide-based FeO@CuCo₂S₄, such as electrochemical energy storage (EES) and electrocatalytic oxygen evolution reaction are demonstrated. The FeO@CuCo₂S₄ film is fabricated using a two-step synthesis procedure. First, CuCo₂S₄ was grown on 3D porous nickel foam substrate using a mild hydrothermal growth technique, onto which FeO was then deposited via a magnetron sputtering. The FeO@CuCo₂S₄ film shows a cordillera-like morphology with a uniformly distributed island-like nanospheres on its surface. The optimized FeO@CuCo₂S₄ electrode delivers an ultrahigh specific capacitance of 3213 F g⁻¹ at 1 A g⁻¹. This FeO@CuCo₂S₄ electrode shows superior capacity retention and coulombic efficiency of ~116% and ~99%, respectively, after 10 000 charge/discharge stability cycles. Moreover, this superior electrode is also serves as an OER electrocatalyst in alkaline solution (1 M aqueous KOH), demonstrating better catalytic activity by attaining a low overpotential of ~240 mV at 10 mA cm⁻² and a small Tafel slope of 51 mV dec⁻¹. This FeO@CuCo₂S₄ catalyst has excellent current rate performance and endurance properties at a high current density rate of up to 100 mA cm⁻² even after 25 hours. The post-measurement HR-TEM, EDS-STEM mapping, and Raman analysis reveal the phase transformation of FeO@CuCo₂S₄ upon electro-oxidation.