Two-step cathodic microwave electrodeposition for construction of Co9S3(OH)5@Ni(OH)2 hetero-structure as supercapacitor electrode materials

The preparation of two-phase electrode materials of Co₉S₈@Ni(OH)₂ typically involves a laborious three-step process. In this study, a two-step cathode microwave electrochemical method was proposed for the fabrication of Co₉S₈@Ni(OH)₂ electrode materials for supercapacitors, eliminating the need for precursor synthesis. This approach not only simplified the preparation process and saved time but also successfully produced a p-n heterostructure electrode material consisting of Co₉S₈@Ni(OH)₂ phases, where the Co₉S₈ phase has a chemical formula of Co₉S₃(OH)_5. This unique structure is capable of inducing an internal electrical field by facilitating the transfer of charge carriers from Co₉S₃(OH)₅ to Ni(OH)₂, thereby enhancing charge transfer kinetics. As a result, the electrode exhibited remarkable supercapacitive performance, achieving a high specific capacitance of 255.4 mAh g^-1 (7.56 F cm^-2) at 1 A g^-1. Even at a 20-fold increase in charge/discharge current density, the specific capacitance remained high at 218.9 mAh g^-1 (6.48 F cm^-1), retaining 85.8 % of the initial capacity. Furthermore, the Co₉S₃(OH)₆@Ni(OH)₂ electrode materials demonstrated excellent durability, enduring 10000 cycles with a capacitance retention of 92.9 % of the initial value. An asymmetric supercapacitor constructed with Co₉S₃(OH)₅@Ni(OH)₂ as the anode and a commercial active carbon film as the cathode was able to power a red light diode continuously emitting light for up to 42 min.