Carbon and Nitrogen‐Co‐Doped Se/NiSe₂/CoSe₂ Nanocomposite as Superior Performance Electrode Material in Hybrid Supercapacitors

Abstract Metal selenides are essential electrode materials for promising electrochemical energy storage with comparable or improved electrochemical performance than metal oxides. Herein, Se/NiSe₂/CoSe₂ (S/NS/CS) is fabricated using a solvothermal approach with the assistance of polyethyleneimine, followed by annealing at different temperatures (300, 400, 500, and 600 °C) for one hour under an argon atmosphere. After annealing, all electrodes’ physical and electrochemical properties were examined, which determined that the best electrode is NiCo₂O₄/NiO (NCO/NO) formed at 500 °C. Additional hydrothermal method uses NCO/NO with SeO₂ as a selenium source to prepare S/NS/CS nanocomposite, with a specific surface architecture that enables easy ion movement and robust conductivity, giving it exceptional electrochemical energy storage properties. It exhibited a remarkable capacitance of 468 F g⁻¹ at a current density of 0.5 A g⁻¹. For practical applications, the hybrid S/NS/CS//AC device was designed using S/NS/CS as a positive electrode and commercial activated carbon (AC) as a negative electrode. The asymmetric device demonstrated an excellent capacitance of 142 F g⁻¹ (189 C g⁻¹) and a superb specific energy of 44 Wh kg⁻¹ at a specific power of 840 W kg⁻¹ at a current density of 1 A g⁻¹, providing 80 % capacity retention and 100 % coulombic efficiency after 5000 cycles.