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

•Microwave electrodeposition was utilized to prepare a Co9S8@Ni(OH)2 heterostructure.•Co9S8@Ni(OH)2 exhibits a p-n junction and possesses abundant defect.•Co9S8@Ni(OH)2 delivered specific capacitances of 7.56/6.48 F cm-2 at 1/20 A g-1. 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.